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   5498篇
  免费   536篇
  国内免费   307篇
测绘学   1047篇
大气科学   298篇
地球物理   802篇
地质学   1393篇
海洋学   1423篇
天文学   12篇
综合类   483篇
自然地理   883篇
  2024年   11篇
  2023年   20篇
  2022年   77篇
  2021年   132篇
  2020年   161篇
  2019年   163篇
  2018年   136篇
  2017年   293篇
  2016年   206篇
  2015年   255篇
  2014年   317篇
  2013年   402篇
  2012年   317篇
  2011年   351篇
  2010年   330篇
  2009年   316篇
  2008年   366篇
  2007年   364篇
  2006年   351篇
  2005年   288篇
  2004年   248篇
  2003年   178篇
  2002年   196篇
  2001年   157篇
  2000年   123篇
  1999年   138篇
  1998年   79篇
  1997年   79篇
  1996年   48篇
  1995年   48篇
  1994年   36篇
  1993年   31篇
  1992年   18篇
  1991年   13篇
  1990年   15篇
  1989年   11篇
  1988年   16篇
  1987年   10篇
  1986年   5篇
  1985年   12篇
  1984年   12篇
  1983年   6篇
  1982年   4篇
  1981年   1篇
  1971年   1篇
排序方式: 共有6341条查询结果,搜索用时 468 毫秒
51.
Identification of Danish North Sea trawl fisheries   总被引:1,自引:3,他引:1  
  相似文献   
52.
本文结合莱西市水资源管理的基本特性,采用人机交互管理方式,成功地运用地理信息系统(GIS),实现了界面良好的莱西市水资源信息系统的各种功能,为规范水资源业务管理的程序、开展地区水资源管理信息系统化建设,提供了有力的技术支持。  相似文献   
53.
54.
55.
56.
ABSTRACT

Environmental sustainability and the long-term wellbeing of Māori (the indigenous people of New Zealand) are interdependent and degradation of landscapes risks the progressive degradation of Māori wellbeing. The present study developed an analysis framework based on Ki Uta Ki Tai (holistic-mountains to the sea- management philosophy advocated by Ngāi Tahu) for exploring relationships between landcover and Māori values to enable predictions of cultural values through space and time. We used this framework to predict how two Māori values (Overall Health and Cultural Land Use) have been altered as a result of landcover change between 2001–2012 in three Canterbury catchments. The area of native vegetation declined while exotic pasture increased between 2001–2012, and there were corresponding declines in both cultural health scores. These results suggest that the change in landcover has reduced the ability of the landscape to support Māori values. This framework for assessing changes in Māori values with respect to changing environmental conditions may identify opportunities for Māori to better engage in land use management decisions.  相似文献   
57.
The production and distribution of biological material in wind-driven coastal upwelling systems are of global importance, yet they remain poorly understood. Production is frequently presumed to be proportional to upwelling rate, yet high winds can lead to advective losses from continental shelves, where many species at higher trophic levels reside. An idealized mixed-layer conveyor (MLC) model of biological production from constant upwelling winds demonstrated previously that the amount of new production available to shelf species increased with upwelling at low winds, but declined at high winds [Botsford, L.W., Lawrence, C.A., Dever, E.P., Hastings, A., Largier, J., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259]. Here we analyze the response of this model to time-varying winds for parameter values and observed winds from the Wind Events and Shelf Transport (WEST) study region. We compare this response to the conventional view that the results of upwelling are proportional to upwelled volume. Most new production per volume upwelled available to shelf species occurs following rapid increases in shelf transit time due to decreases in wind (i.e. relaxations). However, on synoptic, event time-scales shelf production is positively correlated with upwelling rate. This is primarily due to the effect of synchronous periods of low values in these time series, paradoxically due to wind relaxations. On inter-annual time-scales, computing model production from wind forcing from 20 previous years shows that these synchronous periods of low values have little effect on correlations between upwelling and production. Comparison of model production from 20 years of wind data over a range of shelf widths shows that upwelling rate will predict biological production well only in locations where cross-shelf transit times are greater than the time required for phytoplankton or zooplankton production. For stronger mean winds (narrower shelves), annual production falls below the peak of constant wind prediction [Botsford et al., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259], then as winds increase further (shelves become narrower) production does not decline as steeply as the constant wind prediction.  相似文献   
58.
59.
60.
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