全文获取类型
收费全文 | 24575篇 |
免费 | 179篇 |
国内免费 | 921篇 |
专业分类
测绘学 | 1411篇 |
大气科学 | 1987篇 |
地球物理 | 4567篇 |
地质学 | 11658篇 |
海洋学 | 1005篇 |
天文学 | 1653篇 |
综合类 | 2161篇 |
自然地理 | 1233篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 4767篇 |
2017年 | 4044篇 |
2016年 | 2583篇 |
2015年 | 242篇 |
2014年 | 86篇 |
2013年 | 37篇 |
2012年 | 996篇 |
2011年 | 2740篇 |
2010年 | 2029篇 |
2009年 | 2316篇 |
2008年 | 1896篇 |
2007年 | 2368篇 |
2006年 | 60篇 |
2005年 | 195篇 |
2004年 | 411篇 |
2003年 | 412篇 |
2002年 | 255篇 |
2001年 | 54篇 |
2000年 | 53篇 |
1999年 | 14篇 |
1998年 | 26篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1940年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Few assessments of species vulnerability to climate change used to inform conservation management consider the intrinsic traits that shape species’ capacity to respond to climate change. This omission is problematic as it may result in management actions that are not optimised for the long-term persistence of species as climates shift. We present a tool for explicitly linking data on plant species’ life history traits and range characteristics to appropriate management actions that maximise their capacity to respond to climate change. We deliberately target data on easily measured and widely available traits (e.g. dispersal syndrome, height, longevity) and range characteristics (e.g. range size, climatic/soil niche breadth), to allow for rapid comparison across many species. We test this framework on 1237 plants, categorising species on the basis of their potential climate change risk as related to four factors affecting their response capacity: reproduction, movement capability, abiotic niche specialisation and spatial coverage. Based on these four factors, species were allocated risk scores, and these were used to test the hypothesis that the current protection status under national legislation and related management actions capture species response capacity to climate change. Our results indicate that 20% of the plant species analysed (242 species) are likely to have a low capacity to respond to climate change based on the traits assessed, and are therefore at high risk. Of the 242 high risk species, only 10% (24 species) are currently listed for protection under conservation legislation. Importantly, many management plans for these listed species fail to address the capacity of species to respond to climate change with appropriate actions: 70% of approved management plans do not include crucial actions which may improve species’ ability to adapt to climate change. We illustrate how the use of easily attainable traits associated with ecological and evolutionary responses to changing environmental conditions can inform conservation actions for plant species globally. 相似文献
992.
Jan-Ludolf Merkens Daniel Lincke Jochen Hinkel Sally Brown Athanasios Thomas Vafeidis 《Climatic change》2018,151(3-4):413-426
Large-area coastal exposure and impact analysis has focussed on using sea-level rise (SLR) scenarios and has placed little emphasis on socioeconomic scenarios, while neglecting spatial variations of population dynamics. We use the Dynamic Interactive Vulnerability Assessment (DIVA) Framework to assess the population exposed to 1 in 100-year coastal flood events under different population scenarios, that are consistent with the shared socioeconomic pathways (SSPs); and different SLR scenarios, derived from the representative concentration pathways (RCPs); and analyse the effect of accounting for regionalised population dynamics on population exposure until 2100. In a reference approach, we use homogeneous population growth on national level. In the regionalisation approaches, we test existing spatially explicit projections that also account for urbanisation, coastal migration and urban sprawl. Our results show that projected global exposure in 2100 ranges from 100 million to 260 million, depending on the combination of SLR and population scenarios and method used for regionalising the population projections. The assessed exposure based on the regionalised approaches is higher than that derived from the reference approach by up to 60 million people (39%). Accounting for urbanisation and coastal migration leads to an increase in exposure, whereas considering urban sprawl leads to lower exposure. Differences between the reference and the regionalised approaches increase with higher SLR. The regionalised approaches show highest exposure under SSP5 over most of the twenty-first century, although total population in SSP5 is the second lowest overall. All methods project the largest absolute growth in exposure for Asia and relative growth for Africa. 相似文献
993.
Lithological and geochemical record of anthropogenic changes in recent sediments of a small and shallow lake (Lake Pusty Staw,northern Poland) 总被引:4,自引:0,他引:4
Wojciech Tylmann 《Journal of Paleolimnology》2005,33(3):313-325
The article presents the results of lithological and geochemical investigations of recent sediments of Lake Pusty Staw. The analysed sediments document about 300 years of the history of this lake. Historical materials indicate that significant changes in the catchment of the lake took place from the beginning of the 18th century (deforestation and afforestation) followed by 19th century tourist development, and 20th century industrialisation. The sediments were dated using the 210Pb and 137Cs method and core lithology. These made it possible to establish a reliable chronology to the year 1730. The calculated sedimentation rates ranged between 0.17 and 0.83 cm year–1. There was a period of intensified erosion caused by land clearance between 1734 and 1810, which resulted in an acceleration in sedimentation rate (0.36 cm year–1) and a change of lithological type of sediment from detritus gyttja to clayey gyttja. On the basis of Cu, Zn, Cd and Pb content in the sediments, it was determined that the beginning of pollution of the lake dates back to the 19th century and was caused probably by the existence of a health resort. A systematic increase in pollution occurred in the 20th century as a result of industrial plants. Normalised with respect to Al, the content of heavy metals in polluted sediments was from several to twenty times higher than in sediments of the preindustrial period, and a comparison of historical materials with changes of sediments in most cases made it possible to identify the direct causes of the increase in pollution. 相似文献
994.
Although the logistics industry provides critical services to all sectors of the economy, few studies exist in economic geography that examine and explain the organizational dynamics of this industry. This article highlights the significance of the logistics industry in contemporary industrialization and argues that an enriched understanding of the interaction between technology and space can be achieved by examining the evolution of an industry that plays a central role in the contemporary economy. We focus on dimensions that are identified as particularly important: organizational, geographic, and risk and security. 相似文献
995.
生态服务价值与方法研究 总被引:6,自引:0,他引:6
1Ecosystemservicesandtheirvalueoftheworld1.1EcosystemservicesHuman societies derive many essential goods from natural ecosystems, including seafood, game animals, fodder, fuelwood, timber, and pharmaceutical products (Constanza, 1997). These goods represent important and familiar parts of the economy. What has been less appreciated until recently is that natural ecosystems also perform fundamental life-support services without which human civilizations would cease to thrive. These include the… 相似文献
996.
Min Kyung Lee Yong Il Lee Hyoun Soo Lim Jae Il Lee Jeong Heon Choi Ho Il Yoon 《Journal of Paleolimnology》2011,45(2):127-135
Both radiocarbon and optically stimulated luminescence (OSL) dating methods were applied to test their suitability for establishing
a chronology of arid-zone lacustrine sediments using a 5.88-m-long core drilled from Lake Ulaan, southern Mongolia. Although
the radiocarbon and OSL ages agree in some samples, the radiocarbon ages are older than the corresponding OSL ages at the
550-cm depth horizon (late Pleistocene) and in the 100–300-cm interval (early to late Holocene). In the early to late Holocene,
radiocarbon ages are consistently older than OSL ages by 4,100–5,800 years, and in the late Pleistocene by 2,700–3,000 years.
Grain-size analysis of early to late Holocene sediments and one late Pleistocene sediment sample (550-cm depth) indicates
that eolian processes were the dominant sediment-transport mechanism. Also, two late Pleistocene sediments samples (from 400-
to 500-cm depths) are interpreted to have been deposited by both eolian and glaciofluvial processes. Accordingly, the radiocarbon
ages that were older than the corresponding OSL ages during the Holocene seem to have been a consequence of the influx of
14C-deficient carbon delivered from adjacent soils and Paleozoic carbonate rocks by the westerly winds, a process that is also
active today. In addition to the input of old reworked carbon by eolian processes, the late Pleistocene sediments were also
influenced by old carbon delivered by deglacial meltwater. The results of this study suggest that when eolian sediment transport
is suspected, especially in lakes of arid environments, the OSL dating method is superior to the radiocarbon dating method,
as it eliminates a common ‘old-carbon’ error problem. 相似文献
997.
Devleena Mani T. Satish Kumar M. A. Rasheed D. J. Patil A. M. Dayal T. Gnaneshwar Rao V. Balaram 《Natural Resources Research》2011,20(1):75-88
The association of iodine with organic matter in sedimentary basins is well documented. High iodine concentration in soils
overlying oil and gas fields and areas with hydrocarbon microseepage has been observed and used as a geochemical exploratory
tool for hydrocarbons in a few studies. In this study, we measure iodine concentration in soil samples collected from parts
of Deccan Syneclise in the west central India to investigate its potential application as a geochemical indicator for hydrocarbons.
The Deccan Syneclise consists of rifted depositional sites with Gondwana–Mesozoic sediments up to 3.5 km concealed under the
Deccan Traps and is considered prospective for hydrocarbons. The concentration of iodine in soil samples is determined using
ICP-MS and the values range between 1.1 and 19.3 ppm. High iodine values are characteristic of the northern part of the sampled
region. The total organic carbon (TOC) content of the soil samples range between 0.1 and 1.3%. The TOC correlates poorly with
the soil iodine (r
2 < 1), indicating a lack of association of iodine with the surficial organic matter and the possibility of interaction between
the seeping hydrocarbons and soil iodine. Further, the distribution pattern of iodine compares well with two surface geochemical
indicators: the adsorbed light gaseous hydrocarbons (methane through butane) and the propane-oxidizing bacterial populations
in the soil. The integration of geochemical observations show the occurrence of elevated values in the northern part of the
study area, which is also coincident with the presence of exposed dyke swarms that probably serve as conduits for hydrocarbon
microseepage. The corroboration of iodine with existing geological, geophysical, and geochemical data suggests its efficacy
as one of the potential tool in surface geochemical exploration of hydrocarbons. Our study supports Deccan Syneclise to be
promising in terms of its hydrocarbon prospects. 相似文献
998.
The geomorphological environment is one of the most fundamental variables af-fecting the development of human society.The mission of geomorphological environment research is to explore the most basic environment and features of our Earth’s surface mor-phology.The results can be applied to resource evaluation,environmental protection and reducing and preventing geological disasters.Thus,it can serve to help achieve sustainable development.This paper examines the Shenzhen east coastal zone as a case strongly in-fluenced by urban expansion.We use modern geomorphological theory and methods,along with GIS and RS techniques,to reveal key characteristics of the geomorphological environ-ment and landform classification.Furthermore,coastal ecosystem evaluation and regional resources sustainable utilization should be considered relative to the corresponding geo-morphological environment.Based on this study,we conclude that modern geomorphological theory and methods,supported by "3S" techniques including GIS,RS and GPS,can play an important role in resolving the environment,resources and population problems as well as sustainable development challenges facing humankind at present. 相似文献
999.
改革开放以来中国农业政策效果的时空计量分析 总被引:1,自引:0,他引:1
Since reform and opening up, how much contribution has China’s implementation of new agricultural policy made to agricultural output? This paper is trying to establish an agricultural policy output econometric model for doing a quantitative analysis of China’s new agricultural policy. The results show that China’s agricultural policies on agricultural output have an average contribution rate of about 7% since 1978, which is consistent with the OECD’s basic forecast. There are obvious temporal and spatial differences. Generally speaking, we can divide the contribution of agricultural policy into three periods, which are the start-up phase from 1978 to 1991 (14 years), the stationary phase from 1992 to 2002 (11 years) and the rising phase from 2003 to 2008 (6 years). In space, the contribution of agricultural policy underwent a process from the all-low in the start-up phase, the gradual increase in the stationary phase to the all-high in the rising phase. Northern and western regions are more sensitive to policies. There are three major factors that can affect the contribution of regional agricultural policies, which are the process of national industrialization strategy, terrain and the level of local finance. 相似文献
1000.
In the last decade, there has been increasing interest in climate change, pasture degradation and its driving forces, and innovations in nomadic pastoralism on the Tibetan Plateau. However, little is known of indigenous strategies of adaptation to pasture degradation, which limits the effectiveness of adaptation strategies planned by local government. This paper analyzes nomads’ strategies of adaptation to pasture degradation on the basis of a field survey of three townships of Dalag County in the source regions of the Yangtze and Yellow rivers. Pastures there have evidently degraded, with pastures in Wasai mainly in a state of slight or medium degradation and those in Manzhang and Jianshe in a state of medium or severe degradation. With the degradation of pasture, the grazing time is reduced, which affects the livelihoods of nomads. Although the Four-Package Project has commenced in this region, there is still severe fodder shortage in winter and spring. The traditional hay storage strategy does not work because of pasture degradation, and few nomads establish fenced and artificial pastures. Therefore, nomads have employed other strategies, such as renting pasture, providing supplementary feed, and diversifying their livelihoods. Local strategies taken by nomads can provide valuable insights into ecological restoration and livelihood improvement in the region and suggest changes to means promoted by local government. It is necessary to seek new means that combine the best aspects of nomadic pastoralism with modern stockbreeding technologies to help nomads adapt to pasture degeneration and improve their livelihoods. 相似文献