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   6739篇
  免费   54篇
  国内免费   34篇
安全科学   141篇
废物处理   351篇
环保管理   521篇
综合类   1015篇
基础理论   1645篇
环境理论   7篇
污染及防治   2191篇
评价与监测   539篇
社会与环境   395篇
灾害及防治   22篇
  2023年   70篇
  2022年   173篇
  2021年   178篇
  2020年   90篇
  2019年   104篇
  2018年   226篇
  2017年   239篇
  2016年   330篇
  2015年   220篇
  2014年   356篇
  2013年   555篇
  2012年   376篇
  2011年   468篇
  2010年   316篇
  2009年   273篇
  2008年   400篇
  2007年   378篇
  2006年   314篇
  2005年   245篇
  2004年   210篇
  2003年   191篇
  2002年   161篇
  2001年   118篇
  2000年   71篇
  1999年   60篇
  1998年   35篇
  1997年   30篇
  1996年   25篇
  1995年   43篇
  1994年   41篇
  1993年   15篇
  1992年   31篇
  1991年   27篇
  1990年   25篇
  1989年   20篇
  1988年   17篇
  1987年   12篇
  1986年   26篇
  1985年   13篇
  1984年   13篇
  1983年   16篇
  1982年   21篇
  1981年   10篇
  1980年   13篇
  1966年   17篇
  1965年   13篇
  1964年   10篇
  1958年   13篇
  1957年   11篇
  1956年   13篇
排序方式: 共有6827条查询结果,搜索用时 265 毫秒
761.
762.
Small terrestrial non-eusuchian mesoeucrocodylians are common components of Cretaceous assemblages of Gondwanan provinces with notosuchians and araripesuchids as flagship taxa in South America, Africa and Madagascar, well into the Late Cretaceous. On the other hand, these are exceedingly rare in Laurasian landmasses during the Late Cretaceous. Small terrestrial mesoeucrocodylians from Europe were often referred to the genus Theriosuchus, a taxon with stratigraphic range extending from the Late Jurassic to the late Early Cretaceous. Theriosuchus is abundantly reported from various European localities, although Asiatic and possibly North American members are also known. It has often been closely associated with the first modern crocodilians, members of the Eusuchia, because of the presence of procoelous vertebrae, a widespread key character diagnosing the Eusuchia. Nevertheless, the relationships of Theriosuchus have not been explored in detail although one species, Theriosuchus pusillus, has been extensively described and referred in numerous works. Here, we describe a new basal mesoeucrocodylian, Theriosuchus sympiestodon sp. nov. from the Maastrichtian of the Haţeg Basin, Romania, suggesting a large temporal gap (about 58 myr) in the fossil record of the genus. Inclusion of the new taxon, along with Theriosuchus guimarotae, in a phylogenetic analysis confirms its referral to the genus Theriosuchus, within a monophyletic atoposaurid clade. Although phylogenetic resolution within this clade is still poor, the new taxon appears, on morphological grounds, to be most closely related to T. pusillus. The relationships of Atoposauridae within Mesoeucrocodylia and especially to Neosuchia are discussed in light of the results of the present contribution as well as from recent work. Our results raise the possibility that Atoposauridae might not be regarded as a derived neosuchian clade anymore, although further investigation of the neosuchian interrelationships is needed. Reports of isolated teeth referable to a closely related taxon from the Upper Cretaceous of Romania and France, together with the presence of Doratodon and Ischyrochampsa, indicate a previously unsuspected diverse assemblage of non-eusuchian mesoeucrocodylians in the Late Cretaceous European archipelago.  相似文献   
763.
764.
765.
766.

Background  

The impact of shipping emissions on urban agglomerations close to major ports and vessel routes is probably one of the lesser understood aspects of anthropogenic air pollution. Little research has been done providing a satisfactory comprehension of the relationship between primary pollutant emissions, secondary aerosols formation and resulting air quality.  相似文献   
767.
This is the first report showing that using honeybee (Apis mellifera) and wild pollinators complementary pollination can enhance soybean productivity (Glycine max). Current industrial production of soybean involves autopollination and high loads of pesticides. Therefore, growers have neglected possible biotic pollination despite suggestions that soybean benefit from insect pollinators. Reports advocating possible biotic pollination are based on experiments where bees are caged with flowering plants and the absence of pesticides, thus not in field conditions. Therefore, here we compared in field conditions soybean yield produced (1) independently of biotic pollinators, (2) with wild pollinators and (3) with honeybee colonies. Results showed an increase of +6.34 % of soybean yield in areas where wild pollinators had free access to flowers. The introduction of honeybee colonies further raised the yield of +18.09 %. Our findings therefore show that, though soybean is autogamous, allowing pollination by wild pollinators leads to higher yields. Moreover, adding honeybee mitigates pollination deficits and improves yield compared to current practices.  相似文献   
768.
769.
770.
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