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   6893篇
  免费   847篇
  国内免费   656篇
测绘学   1110篇
大气科学   383篇
地球物理   984篇
地质学   3021篇
海洋学   1235篇
天文学   14篇
综合类   590篇
自然地理   1059篇
  2024年   14篇
  2023年   32篇
  2022年   118篇
  2021年   197篇
  2020年   206篇
  2019年   243篇
  2018年   183篇
  2017年   309篇
  2016年   275篇
  2015年   318篇
  2014年   392篇
  2013年   470篇
  2012年   436篇
  2011年   458篇
  2010年   426篇
  2009年   459篇
  2008年   439篇
  2007年   494篇
  2006年   462篇
  2005年   381篇
  2004年   341篇
  2003年   281篇
  2002年   244篇
  2001年   217篇
  2000年   180篇
  1999年   195篇
  1998年   134篇
  1997年   113篇
  1996年   73篇
  1995年   78篇
  1994年   44篇
  1993年   42篇
  1992年   28篇
  1991年   17篇
  1990年   19篇
  1989年   16篇
  1988年   19篇
  1987年   9篇
  1986年   6篇
  1985年   7篇
  1984年   9篇
  1983年   3篇
  1982年   3篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1971年   1篇
排序方式: 共有8396条查询结果,搜索用时 15 毫秒
71.
给出一种适合各种DOS版本和各种机型的微机硬盘安全管理方法。不仅可以预防已知或未知的计算机病毒,而且可对上机人员的权限进行统一分级管理,以防止硬盘重要系统信息的损坏,从而提高公用微机系统的可靠性。  相似文献   
72.
73.
Chemical fluxes of Asian rivers into oceans bear different regional variations. Three zones are characteristic of distinct dissolved sediment loads and yields and ionic concentration.Rivers into oceans in China play an important role in Asia because of their different chemical fluxes, among which those draining the Loess Plateau have high ionic concentration, low water discharges and dissolved sediment loads and yields.Climate, vegetation, soil and strata lithology, chemical weathering intensity and tectonic activity dominate chemical fluxes of Asian rivers into oceans, and different factors have different effects on the chemical fluxes of separate regional rivers. Rising of the Tibet Plateau also exerts an important influence on chemical compositions of rivers originating from it.  相似文献   
74.
75.
Considering the small land, dense population and poor natural resources, the oceans are important to Korea, but the recognition of oceans has been weak in Korean society. So ocean governance was fragmented in both institution and policies, which resulted in serious problems in the coastal waters and oceans. However, a series of maritime accidents and failures of policies increased the recognition of the coastal waters and resources and led to the establishment of one single ocean-related governmental agency in 1996. Over the last decade, the ocean governance in Korea has been successful and strong.  相似文献   
76.
77.
78.
Vietnam is in the process of introducing adaptive management based on indicators and time-series to manage its marine fisheries. The development of indicator-based frameworks for fisheries management has accelerated in recent years. This article describes the suite of indicators being suggested or used in Vietnam including the data-collection system. The Vietnamese approach is supported by an institutional structure consisting of a multi-disciplinary advisory system to facilitate the process of using indicators and to introduce knowledge-based management. The article concludes by identifying current problems and weaknesses and by providing suggestions for future improvement of the system.  相似文献   
79.
80.
The Continuous Plankton Recorder (CPR) survey was conceived from the outset as a programme of applied research designed to assist the fishing industry. Its survival and continuing vigour after 70 years is a testament to its utility, which has been achieved in spite of great changes in our understanding of the marine environment and in our concerns over how to manage it. The CPR has been superseded in several respects by other technologies, such as acoustics and remote sensing, but it continues to provide unrivalled seasonal and geographic information about a wide range of zooplankton and phytoplankton taxa. The value of this coverage increases with time and provides the basis for placing recent observations into the context of long-term, large-scale variability and thus suggesting what the causes are likely to be. Information from the CPR is used extensively in judging environmental impacts and producing quality status reports (QSR); it has shown the distributions of fish stocks, which had not previously been exploited; it has pointed to the extent of ungrazed phytoplankton production in the North Atlantic, which was a vital element in establishing the importance of carbon sequestration by phytoplankton.The CPR continues to be the principal source of large-scale, long-term information about the plankton ecosystem of the North Atlantic. It has recently provided extensive information about the biodiversity of the plankton and about the distribution of introduced species. It serves as a valuable example for the design of future monitoring of the marine environment and it has been essential to the design and implementation of most North Atlantic plankton research.  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