全文获取类型
收费全文 | 4074篇 |
免费 | 756篇 |
国内免费 | 673篇 |
专业分类
测绘学 | 237篇 |
大气科学 | 641篇 |
地球物理 | 1369篇 |
地质学 | 1642篇 |
海洋学 | 438篇 |
天文学 | 85篇 |
综合类 | 241篇 |
自然地理 | 850篇 |
出版年
2024年 | 41篇 |
2023年 | 108篇 |
2022年 | 204篇 |
2021年 | 231篇 |
2020年 | 216篇 |
2019年 | 248篇 |
2018年 | 214篇 |
2017年 | 179篇 |
2016年 | 227篇 |
2015年 | 193篇 |
2014年 | 292篇 |
2013年 | 326篇 |
2012年 | 234篇 |
2011年 | 239篇 |
2010年 | 225篇 |
2009年 | 225篇 |
2008年 | 251篇 |
2007年 | 206篇 |
2006年 | 238篇 |
2005年 | 162篇 |
2004年 | 168篇 |
2003年 | 144篇 |
2002年 | 135篇 |
2001年 | 107篇 |
2000年 | 79篇 |
1999年 | 89篇 |
1998年 | 89篇 |
1997年 | 65篇 |
1996年 | 74篇 |
1995年 | 74篇 |
1994年 | 59篇 |
1993年 | 35篇 |
1992年 | 40篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有5503条查询结果,搜索用时 31 毫秒
81.
我国部分市郊农田的重金属污染与防治途径 总被引:12,自引:2,他引:12
分析了我国部分主要城市农田土壤及农作物重金属污染状况,以了解土壤中与农作物中重金属污染物间的相互关系、变化趋势及造成污染的影响因素。结果表明,我国各大城市的农田土壤及农作物都存在不同程度的重金属污染,北方地区的土壤及农作物受重金属污染程度普遍高于南方。重金属在农作物与土壤中的含量一般呈正相关关系,受多种因素影响。对于已污染的土壤,可采用农业工程措施、生物修复法和施用改良剂等予以治理。 相似文献
82.
建立了一个数学模型来预测多氯联苯湿地生物降解过程。该模型全面考虑了多氯联苯湿地生物降解的各子过程,包括:吸附/解吸、土壤屏蔽、扩散和生物降解,利用模型,预测了多氯联苯湿地生物降解的规律性及处理时间、处理终点;利用Monte-Carlo法,进行了多氯联苯湿地生物降解污染风险分析,结果表明,在采用基地现有处理方式的情况下,经过8年处理,土壤中4-Cl-PCBs不低于69.4%被降解的可能性为75%,此时土壤中能够继续污染外部环境的4-Cl-PCBs部分不超过10.9%的可能性为75%;土壤中4-Cl-PCBs全部生物降解完毕所需处理时间不超过16.20年的可能性为75%,最后被土壤不可逆屏蔽的残余物不超过20.9%的可能性为75%。 相似文献
83.
S. E. Beaubien G. Ciotoli S. Lombardi 《Journal of Volcanology and Geothermal Research》2003,123(1-2):63
The sudden and catastrophic, or slow and continuous, release at surface of naturally occurring toxic gases like CO2, H2S and Rn poses a serious health risk to people living in geologically active regions. In general this problem receives little attention from local governments, although public concern is raised periodically when anomalous toxic-gas concentrations suddenly kill humans or livestock. For example, elevated CO2 concentrations have been linked to the death of at least 10 people in the central Italian region of Lazio over the last 20 years, while it was the CO2 asphyxiation of 30 cows in a heavily populated area near Rome in 1999 which prompted the present soil-gas study into the distribution of the local health risk. A detailed geochemical survey was carried out in an area of about 4 km2 in the Ciampino and Marino districts, whereby a total of 274 soil-gas samples were collected and analysed for more than 10 major and trace gas species. Data were then processed using both statistical and geostatistical methods, and the resulting maps were examined in order to highlight areas of elevated risk. General trends of elevated CO2 and Rn concentrations imply the presence of preferential pathways (i.e. faults and fractures) along which deep gases are able to migrate towards the surface. The CO2 and Rn anomalous trends often correspond to and are usually elongated parallel to the Apennine mountain range, the controlling structural feature in central Italy. Because of this fundamental anisotropy in the factors controlling the soil-gas distribution, it was found that a geostatistical approach using variogram analysis allowed for a better interpretation of the data. With regard to the health risk to local inhabitants, it was found that although some high risk areas had been zoned as parkland, others had been heavily developed for residential purposes. For example, many new houses were found to have been built on ground which has soil-gas CO2 concentrations of more than 70% and radon values of more than 250 kBq m−3. It is recommended that land-use planners incorporate soil-gas and/or gas flux measurements in environmental assessments in areas of possible risk (i.e. volcanic or structurally active areas). 相似文献
84.
This paper illustrates the seismic risk preliminary estimates of two different groups of structures located on the territory of the Friuli–Venezia Giulia region (NE Italy) : the first group includes some special industrial plants, and the second group includes bridges and tunnels belonging to the regional highway network. The part of the study on special industrial plants tries to evaluate the degree of expected damage, taking into account their structural typology and ground shaking expressed in terms of macroseismic intensity. The second part of the study is an application of the HAZUS methodology to the tunnels and bridges of a highway network: the combination of expected ground shaking and the construction characteristics lead to very different risk levels, especially when considering the bridges. The resulting damage levels to bridges and tunnels are still only indicative because of the fragility curves used in the evaluations: they were developed for existing bridge and tunnel structural typologies in the U.S.A. Moreover, both examples show the power of GIS technology in storing, elaborating, and mapping spatial data. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
85.
86.
Tsunamis have occurred in Canada due to earthquakes, landslides, and a large chemical explosion. The Pacific coast is at greatest risk from tsunamis because of the high incidence of earthquakes and landslides in that region. The most destructive historical tsunamis, however, have been in Atlantic Canada – one in 1917 in Halifax Harbour, which was triggered by a catastrophic explosion on a munitions ship, and another in 1929 in Newfoundland, caused by an earthquake-triggered landslide at the edge of the Grand Banks. The tsunami risk along Canada's Arctic coast and along the shores of the Great Lakes is low in comparison to that of the Pacific and Atlantic coasts. Public awareness of tsunami hazard and risk in Canada is low because destructive tsunamis are rare events. 相似文献
87.
Ken Durham 《Natural Hazards》2003,30(2):251-261
Cairns is exposed to the well-known natural hazards oftropical cyclone, flood, stormsurge and thunderstorm, but is also exposed to thelesser-known hazards of landslip, earthquake and dam break flooding. Recommendations fortreating the risks associated with these hazards have been made that will involve amulti-disciplinary approach to treatment strategies, require the cooperation of allthree levels of government, involve public utility authorities and private enterprise andinvolve the community as a whole.This paper summarises the suggested mitigation treatmentoptions, presented to the Cairns City Council and identified in the LocalGovernment Disaster Mitigation Project conducted in Cairns in 1999/2000 by theQueensland Department of Emergency Services. 相似文献
88.
Quantifying Storm Tide Risk in Cairns 总被引:6,自引:5,他引:6
Ken Granger 《Natural Hazards》2003,30(2):165-185
The United Nations International Decade for Natural Disaster Reduction (IDNDR)gave rise to an increasing level of attention to the risks posed by a range of naturalhazards and the development of strategies by which to reduce those risks. It waswidely recognised that in order to evaluate risk treatment strategies it was necessaryto `measure' the level of risk that already existed and the level of risk that would beencountered with the treatment strategy(s) in place.This paper outlines the methodology developed under the AGSO (now GeoscienceAustralia) Cities Project to quantify the risk associated with storm tide inundation. It includes the methodology for `measuring' the level of community exposure to storm tide hazards and the methodology for `measuring' community vulnerability. The Far North Queensland city of Cairns is used as the case study to demonstrate the application of these methods. 相似文献
89.
Linda J. Anderson-Berry 《Natural Hazards》2003,30(2):209-232
This paper is a partial discussion of a four-year study that investigated the vulnerability of the people living in the Cairns region to the tropical cyclone hazard. The longitudinal case study, focussing on the Cairns Northern Beaches area, was unique in that it included a social and societal `pre-cyclone impact' evaluation of various resident communities within the region, and then two consecutive `post-cyclone impact' studies. The primary research method supported an inductive qualitative approach to the collection and analysis of survey data. Some quantitative methods were invoked to support qualitative research findings. Survey data was collected in five separate questionnaire-based social surveys that were administered between 1996 and 2000. During the study, residents experiencedthe direct impact of two land-falling tropical cyclones. In addition to this, targeted andfocussed tropical cyclone awareness education was made increasingly available withinthe community. The social and demographic attributes that influence the individual'sperception of risk and contribute to our understanding of community vulnerability were examined and evaluated. Changes in the residents' attitudes, cyclone preparednessbehaviours and willingness to respond to cyclone warnings were monitored and measured. Analysis of early survey data indicated that community residents generally had some knowledge of cyclones but a limited understanding of cyclone processes and very little direct personal experience of the cyclone hazard. Individually and collectively, residents frequently demonstrated a biased perception of the risks associated with cyclones. The resident community was shown to be fragmented, with limited support being available to individual households. Initially, residents were found to be poorly prepared for cyclones and unlikely to respond to warnings appropriately. It appeared that, in the event of a land-falling tropical cyclone impacting the area, the community was highly vulnerable to unnecessary loss of property, livelihood and – in extreme circumstances – life. By 2000, Cairns community residents were somewhat better informed about cyclones and certainly more experienced. This paper provides some insight into how cyclone experience and education may synergisticly have contributed to a change in risk perceptions and a reduction in the vulnerability of Cairns residents to the tropical cyclone and storm surge hazards. 相似文献
90.
Adnan A. Basma Samer A. Barakat Maher T. Omar 《Geotechnical and Geological Engineering》2003,21(3):225-242
The design methods currently used for earth reinforcement are mostly based on deterministic properties of both the soil and
the construction materials used. Nowadays, however, the general trend is designing at a specific degree of reliability. This
is even more true where the raw data such as soil properties exhibit significant variation. Deterministic solutions, in this
case, may not suffice. Therefore, this paper will attempt to use probabilistic formulations thereby modifying the existing
design procedure of reinforced earth retaining walls to account for uncertainties and variabilities. Through a first order
Taylor's series expansion about the mean, the mean and variance of the strip reinforcing components, namely width and length,
are derived in terms of the variations in the soil properties. Design charts that enable estimation of both mean and variance
are developed to avoid extensive partial differentiation involved in the computations. Using appropriate probability distributions
along with the mean and variance, the final design outputs are determined for a selected failure probability by introducing
what is refered to as 'risk index'. The results indicate that the risk index increases with an increase in the coefficient
of variations and a decrease in failure probability. Furthermore, it is shown that in some cases, depending on the variabilities
of the soil properties, the classical design technique produced a relatively high failure probability.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献