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   693篇
  免费   23篇
  国内免费   12篇
测绘学   29篇
大气科学   27篇
地球物理   164篇
地质学   354篇
海洋学   35篇
天文学   66篇
综合类   20篇
自然地理   33篇
  2023年   2篇
  2022年   3篇
  2021年   21篇
  2020年   28篇
  2019年   23篇
  2018年   70篇
  2017年   53篇
  2016年   71篇
  2015年   36篇
  2014年   56篇
  2013年   73篇
  2012年   29篇
  2011年   39篇
  2010年   35篇
  2009年   28篇
  2008年   20篇
  2007年   22篇
  2006年   12篇
  2005年   11篇
  2004年   14篇
  2003年   5篇
  2002年   4篇
  2001年   7篇
  2000年   5篇
  1999年   4篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1995年   6篇
  1994年   2篇
  1993年   5篇
  1992年   2篇
  1991年   2篇
  1989年   1篇
  1988年   5篇
  1987年   1篇
  1986年   2篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   4篇
  1981年   4篇
  1980年   2篇
  1978年   1篇
  1977年   4篇
  1974年   2篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
排序方式: 共有728条查询结果,搜索用时 15 毫秒
91.
Dera Ismail Khan (DIK) is situated in the Lower Indus Basin of Pakistan. The land use has been changed in the canal command area due to irrigation activities near the Indus River. To check the current status and predict the groundwater levels in the area, the unconfined aquifer has been simulated in Visual MODFLOW for a period of 35 years, i.e., from 1985 to 2020. The 2900-km2 area has been modeled with a grid of 500 by 500 m and the depth set to 100 m. The aquifer in the study area has been divided vertically and laterally into three and ten zones, respectively, for the characterization. Water wells and streams were used as the sinks and hydrologic boundaries, respectively. The model was successfully calibrated in steady and the non-steady state. The simulation revealed that the whole simulation can be divided into two phases, i.e., before and after the construction of the Chashma Right Bank Canal (CRBC), whereas the results were summarized in the form of water table depth maps and groundwater budget calculations. To determine the groundwater sustainability, a conjunctive use scenario has been employed to simulate the aquifer dynamics till 2020. The simulation revealed incremental drawdowns till the end.  相似文献   
92.
We propose that bubbles of matter ejected from magnetic reconnection sites in polar plumes drive the solar wind in coronal holes.  相似文献   
93.
The correlation function theory on the basis of prescribed boundary conditions provides a deeper understanding in studying the dynamical parameters of galaxy clusters. The approach approximates that the moderate dense systems discussed by a two point correlation function is helpful for describing the dynamical nature of galaxy clusters. The projected theory of two point correlation function for point mass and extended mass structures can be used an alternative tool in measuring the average peculiar motion and temperature profile of galaxy clusters.  相似文献   
94.
This study was conducted to assess the existing concentration of 17β-estradiol(E2)in the surface water samples collected from rivers and lakes around Klang Valley,Malaysia.E2,which is a natural feminizing chemical produced in female organisms,regularly used to compare with other environmental estrogens because they behave similarly and react effectively as a hormone at a very low concentration.It was found that the average concentration of E2 in the aquatic environment of Klang Valley was(14.08 ±3.67)pg/mL,which was 14 times higher than those in the Japanese aquatic environment in this study.The river system had the average concentration of(20.02±5.26)pg/mL while the lake had an average concentration of(5.91±3.39)pg/mL.The E2 concentration was presumed high if the sources occurred nearby the area.Current levels of E2 in the aquatic environment may possess threats to existing aquatic organisms.Since high level of E2 has been discovered in the aquatic environment around Klang Valley,further studies and monitoring of E2 and other EDCs concentrations are needed to determine their levels in Malaysian aquatic environment and help to control these chemicals pollution in the aquatic environment.  相似文献   
95.
Finding a coupling model between a hydraulic parameter such as permeability and a mechanical parameter such as damage is the key element for several recent engineering problems. A review of the technical literature reveals that several mechanical constitutive laws exist which allow determining a damage tensor for a damageable porous material under loading. But the present work develops a method to deduce the permeability change due to the damage propagation.  相似文献   
96.
97.
Ahmad  Dilshad  Afzal  Muhammad 《Natural Hazards》2019,99(1):337-354
Natural Hazards - An environmental variation has caused Pakistan an alarming portrait of vulnerability in flood disasters. The government has focused on a number of realistic actions, heartening...  相似文献   
98.
Journal of Geographical Sciences - Pastoralism is a viable socio-economic system-shaped by landless and agro-pastoral communities in many pastoral regions of the world. This system is mainly based...  相似文献   
99.
Utility Efficient Frontier: An Application in the Oil and Gas Industry   总被引:1,自引:0,他引:1  
Current practice shows that the use of portfolio and utility theory is very low among petroleum companies. This article advocates the use of both portfolio theory and utility theory as decision-making tools to improve performance of oil and gas companies. We introduce a model that can be practically used and applied in the oil and gas industry. This model generates an optimized, efficient portfolio and, at the same time, enables the decision maker to incorporate his risk attitude and policy. This can only be done by combining both the portfolio theory and utility theory through an approach called the utility mean-variance model. A typical oil portfolio optimization problem is investigated by applying both portfolio and utility theories. Through the utility mean-variance model, an efficient frontier that captures decision maker risk attitude is achieved.  相似文献   
100.
Natural Resources Research - Machine learning (ML) schemes can enhance success in geochemical prospectivity mapping. This study has examined the effectiveness of several feature extraction or...  相似文献   
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