全文获取类型
收费全文 | 9033篇 |
免费 | 1914篇 |
国内免费 | 2012篇 |
专业分类
测绘学 | 188篇 |
大气科学 | 1775篇 |
地球物理 | 2393篇 |
地质学 | 5917篇 |
海洋学 | 1068篇 |
天文学 | 81篇 |
综合类 | 495篇 |
自然地理 | 1042篇 |
出版年
2024年 | 26篇 |
2023年 | 111篇 |
2022年 | 271篇 |
2021年 | 356篇 |
2020年 | 360篇 |
2019年 | 436篇 |
2018年 | 362篇 |
2017年 | 431篇 |
2016年 | 438篇 |
2015年 | 434篇 |
2014年 | 557篇 |
2013年 | 642篇 |
2012年 | 476篇 |
2011年 | 582篇 |
2010年 | 473篇 |
2009年 | 604篇 |
2008年 | 628篇 |
2007年 | 625篇 |
2006年 | 547篇 |
2005年 | 509篇 |
2004年 | 488篇 |
2003年 | 436篇 |
2002年 | 382篇 |
2001年 | 325篇 |
2000年 | 319篇 |
1999年 | 294篇 |
1998年 | 280篇 |
1997年 | 236篇 |
1996年 | 242篇 |
1995年 | 219篇 |
1994年 | 182篇 |
1993年 | 164篇 |
1992年 | 120篇 |
1991年 | 97篇 |
1990年 | 76篇 |
1989年 | 75篇 |
1988年 | 48篇 |
1987年 | 37篇 |
1986年 | 23篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Paul F. Hudak 《Environmental Geology》2008,55(6):1311-1317
This modeling study evaluated the capability of alternative funnel-and-gate structures with three gates for capturing contaminated
groundwater in a hypothetical unconfined aquifer. Simulated interceptor structures were linear and 45 m wide, consisting of
three gates and two funnels (walls). One gate occupied the center and two gates occupied the ends of the interceptor structures.
The structures, positioned perpendicular to regional groundwater flow, traversed the entire thickness of the aquifer. A total
of four structures were evaluated (numbers designate widths of end, center, and end gates, respectively, in meters): 3-3-3,
2-5-2, 1-7-1, and 4-1-4. Particle tracking and zonal water budgets identified shapes of capture zones and discharge patterns
for each interceptor structure. A mass transport model, accounting for advection and hydrodynamic dispersion, tested the capability
of each structure for capturing a contaminant plume. Results suggest that: time-dependent capture zones underestimate the
amount of time to capture a contaminant plume, wide center gates facilitate plume capture, and wide end gates facilitate lateral
containment of contaminants. Of the structures simulated, the 2-5-2 configuration was relatively efficient at processing and
containing the simulated contaminant plume. 相似文献
32.
Qiang Wang Derek A. Wyman Jifeng Xu Yusheng Wan Chaofeng Li Feng Zi Ziqi Jiang Huaning Qiu Zhuyin Chu Zhenhua Zhao Yanhui Dong 《Contributions to Mineralogy and Petrology》2008,155(4):473-490
New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched
basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized
by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and εND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments
of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive εND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle
normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids.
A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite.
The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series”
recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and
southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates
that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane. 相似文献
33.
The questions of how land use change affects climate, and how climate change affects land use, require examination of societal and environmental systems across space at multiple scales, from the global climate to regional vegetative dynamics to local decision making by farmers and herders. It also requires an analysis of causal linkages and feedback loops between systems. These questions and the conceptual approach of the research design of the Climate-Land Interaction Project (CLIP) are rooted in the classical human-environment research tradition in Geography.This paper discusses a methodological framework to quantify the two-way interactions between land use and regional climate systems, using ongoing work by a team of multi-disciplinary scientists examining climate-land dynamics at multiple scales in East Africa. East Africa is a region that is undergoing rapid land use change, where changes in climate would have serious consequences for people’s livelihoods, and requiring new coping and land use strategies. The research involves exploration of linkages between two important foci of global change research, namely, land use/land cover (LULC) and climate change. These linkages are examined through modeling agricultural systems, land use driving forces and patterns, the physical properties of land cover, and the regional climate. Both qualitative and quantitative methods are being used to illustrate a diverse pluralism in scientific discovery. 相似文献
34.
The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to
the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic
crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed
sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges
are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this
study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern
part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on
the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain,
the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary
Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into
the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks
the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran
region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and
some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such
data should be of value to the developing Indian Ocean Tsunami Warning System. 相似文献
35.
在分析综合辽宁省海岸带调查和沿海经济贝类污染监测资料基础上,根据辽宁海岸带水质,沉积物和生物污染现状及发展趋势。针对所存在的问题,讨论了辽宁省海洋污染特别是赤潮对海洋资源的破坏,并在组织机构,地方立法,海岸带环境保护规划,污染源控制与整体环境改进,监测方案等方面提出了建设海上辽宁、加强辽宁省海洋环境保护与海岸可持续开发利用的建议。 相似文献
36.
37.
象山港、三门湾软相潮间带底栖动物数量的水平分布与港湾的屏蔽性程度有一定的关系,生物量是三门湾(180.95g/m2)高于象山港(94.47g/m2),生物密度是象山港(816个/m2)高于三门湾(347个/m2)。决定所面生物数量变化的主要底栖动物种类数随着港湾屏蔽性程度的提高而相应地减少。生物数量的垂直分布主要受潮汐作用的影响,以中潮区为最高。生物量以6月份最大,密度是4月份最大。 相似文献
38.
Gu Jialong Shen Xianrong
Professor Hohai University Nanjing
Engineer The Investigation Design Institute Bureau of Communications of Zhejiang Province Hangzhou 《中国海洋工程》1991,(2)
In accordance with the similarity between breaking waves and hydraulic jumps, the expressions for estimating wave decay and wave energy dissipation in the surf zone are derived based on the fundamental equations of fluid mechanics. Using the numerical solution of cnoidal wave theory, the various kinematic properties of waves in the surf zone, including the relative wave crest height, wave energy, and radiation stress are discussed. The values calculated with the method proposed in this paper are in good agreement with the experimental data gained by other researchers. The present expressions can be used in the studies of sediment transport on gently sloping beaches, especially on muddy beaches. 相似文献
39.
G.T. Ruggerone J.L. Nielsen J. Bumgarner 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2776
We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976–1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976–1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean. 相似文献
40.
Modelling and forecasting long-term dynamics of Western Baltic macrobenthic fauna in relation to climate signals and environmental change 总被引:1,自引:0,他引:1
Long-term macrobenthos data from Kiel Bight in the Western Baltic collected between 1968 and 2000 have been correlated with the winter NAO index (North Atlantic Oscillation Index) and other environmental data such as temperature, salinity and oxygen content in the bottom water in order to detect systematic patterns related to so far unexplained abiotic signals in the dynamics of zoobenthic species assemblages. The benthos data come from a cluster of five stations (Süderfahrt/ Millionenviertel) in Kiel Bay. Our investigations concentrated on the macrobenthic dynamics with a focus on the number of species m− 2 (species richness). Using logarithms and the time series analysis approach of Box/Jenkins (ARIMA modelling, transfer function modelling) it was shown that species richness was strongly influenced by the winter NAO (adjusted for a linear time trend within the 1968-2000 period) and salinity (with a shift/lag of four years). Bootstrapping experiments (i.e. sampling from the error process) and analysis of prediction power (by means of the one- or more-years leaving-out method) showed that the parameter estimates behaved in a stable way, leading to a relatively robust model. 相似文献