首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4298篇
  免费   146篇
  国内免费   92篇
测绘学   157篇
大气科学   295篇
地球物理   1115篇
地质学   1516篇
海洋学   376篇
天文学   696篇
综合类   21篇
自然地理   360篇
  2022年   30篇
  2021年   48篇
  2020年   47篇
  2019年   63篇
  2018年   85篇
  2017年   104篇
  2016年   119篇
  2015年   110篇
  2014年   136篇
  2013年   258篇
  2012年   130篇
  2011年   231篇
  2010年   164篇
  2009年   225篇
  2008年   237篇
  2007年   208篇
  2006年   191篇
  2005年   171篇
  2004年   136篇
  2003年   162篇
  2002年   136篇
  2001年   84篇
  2000年   87篇
  1999年   61篇
  1998年   69篇
  1997年   56篇
  1996年   65篇
  1995年   52篇
  1994年   55篇
  1993年   42篇
  1992年   48篇
  1991年   42篇
  1990年   35篇
  1989年   37篇
  1988年   37篇
  1987年   40篇
  1986年   44篇
  1985年   57篇
  1984年   47篇
  1983年   50篇
  1982年   52篇
  1981年   57篇
  1980年   48篇
  1979年   39篇
  1978年   47篇
  1977年   28篇
  1976年   29篇
  1975年   24篇
  1974年   32篇
  1973年   29篇
排序方式: 共有4536条查询结果,搜索用时 0 毫秒
91.
In this article, we use parcel-based land-use data to analyze 50 years of residential development in the Toronto region. We test two hypotheses: (1) Toronto’s form does not conform to conventional definitions of suburban sprawl and (2) Toronto’s suburban development shows high levels of continuity over time with relatively high densities and mixed housing types. Contrary to recent research suggesting a convergence of urban forms among North American metropolitan regions, Ontario’s robust planning system has created a distinctive, highly consistent pattern of residential development that has, for half a century, achieved many of the core goals of smart growth including relatively compact, contiguous, and concurrent development. This form continues to be automobile dependent, however, and is not producing many of the benefits ascribed to smart growth. Rather than continuing to adopt United States-inspired smart growth policies, a more ambitious set of initiatives will be required to address current regional challenges.  相似文献   
92.
93.
94.
This study examined the impacts of reservoir properties on carbon dioxide (CO2) migration after subsurface injection and evaluated the possibility of characterizing reservoir properties using CO2 monitoring data such as spatial–temporal distributions of gas pressure, which can be reasonably monitored in practice. The injection reservoir was assumed to be located 1,400–1,500 m below the ground surface such that CO2 remained in the supercritical state. The reservoir was assumed to contain layers with alternating conductive and resistive properties, which is analogous to actual geological formations such as the Mount Simon Sandstone unit. The CO2 injection simulation used a cylindrical grid setting in which the injection well was situated at the center of the domain, which extended out 8,000 m from the injection well. The CO2 migration was simulated using the latest version of the simulator, subsurface transport over multiple phases (the water–salt–CO2–energy module), developed by Pacific Northwest National Laboratory. A nonlinear parameter estimation and optimization modeling software package, Parameter ESTimation (PEST), is adopted for automated reservoir parameter estimation. The effects of data quality, data worth, and data redundancy were explored regarding the detectability of reservoir parameters using gas pressure monitoring data, by comparing PEST inversion results using data with different levels of noises, various numbers of monitoring wells and locations, and different data collection spacing and temporal sampling intervals. This study yielded insight into the use of CO2 monitoring data for reservoir characterization and how to design the monitoring system to optimize data worth and reduce data redundancy. The feasibility of using CO2 saturation data for improving reservoir characterization was also discussed.  相似文献   
95.
The Colville basin drains the North Slope of Alaska and is one of several large Arctic river systems located within permafrost. The timing and style of fluvial processes in the earth's permafrost regions differ from those occurring in midlatitude settings. Moreover, in comparison to temperate-zone systems, rivers located entirely within permafrost perform most of their work during relatively short periods of time. This paper examines river ice hydrology and the resulting geomorphic processes that occur within the Colville delta, Alaska. Fluvial processes and landform development within the Colville delta occur after the flood-pulse is initiated by the breakup of river ice. During this 4-month period, the geomorphic processes are largely influenced by the movement of ice. The flood-pulse and accompanying river ice influences erosional and depositional processes and results in unique styles of sediment transport, deposition, and riverbank erosion.  相似文献   
96.
The composition and metallogeny of igneous rocks and relevant weathering crusts of Jurassic–Cretaceous provenances of the Russian Platform are considered. It is shown that the association of metals that accumulated in the process of weathering and erosion of ancient substratum includes P, Fe, Ti, V, and Cr. This process is reflected in the formation of nodular phosphorites, Ti and Zr placers, and iron ore deposits in the Jurassic–Cretaceous seas of the platform.  相似文献   
97.
98.
99.
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号