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   28142篇
  免费   319篇
  国内免费   171篇
安全科学   728篇
废物处理   1204篇
环保管理   3622篇
综合类   4608篇
基础理论   7660篇
环境理论   23篇
污染及防治   7529篇
评价与监测   1813篇
社会与环境   1250篇
灾害及防治   195篇
  2022年   257篇
  2021年   304篇
  2020年   183篇
  2019年   230篇
  2018年   465篇
  2017年   495篇
  2016年   710篇
  2015年   539篇
  2014年   789篇
  2013年   2170篇
  2012年   981篇
  2011年   1297篇
  2010年   1007篇
  2009年   979篇
  2008年   1254篇
  2007年   1294篇
  2006年   1146篇
  2005年   963篇
  2004年   895篇
  2003年   849篇
  2002年   829篇
  2001年   891篇
  2000年   663篇
  1999年   411篇
  1998年   327篇
  1997年   351篇
  1996年   336篇
  1995年   412篇
  1994年   376篇
  1993年   317篇
  1992年   323篇
  1991年   318篇
  1990年   332篇
  1989年   299篇
  1988年   275篇
  1987年   260篇
  1986年   259篇
  1985年   228篇
  1984年   281篇
  1983年   242篇
  1982年   299篇
  1981年   243篇
  1980年   207篇
  1979年   223篇
  1978年   204篇
  1977年   165篇
  1975年   153篇
  1974年   168篇
  1973年   170篇
  1972年   162篇
排序方式: 共有10000条查询结果,搜索用时 257 毫秒
351.
352.
353.
A very dry climate which prevailed during the last glacial maximum of the Pleistocene from India to the Sahara, was replaced by variable weather conditions with alternating more or less humid phases, starting from the Pleistocene-Holocene transition period and lasting up to about 3000 years ago, when present arid conditions set in. A particularly wet phase is recognized throughout the region some 5000 years ago. Phase shifts within the region and in particular changes in rain distribution patterns, are interpreted as due to shifting spheres of influence of the monsoonal circulation, of Atlantic depressions and moisture originating from the Mediterranean Sea. The condition of the Mediterranean Sea itself, which is influenced by runoff and melt waters from the European Continent and by the Nile floods, as well as by the eustatic sea-level changes, is not a good indicator of local climate conditions.  相似文献   
354.

Neither the “Green Revolution” in the developing countries nor “yield explosion” in the agricultural production of the industrialized nations have reached the genetic and physiologic limits of crop growth. Breeding of better varieties is still the most promising defense against hunger. The ambiguity of modern agroindustry throughout the world resides in its high dependence on the existence of functional technological, economical, and political systems.

  相似文献   
355.
Amniocentesis and subsequent tests are reported on a fetus conceived of a rare mating type: its mother has an intermediate level of β hexosaminidase A (HEX A), characteristic of carriers of Tay-Sachs disease (TSD), while the father suffers from an adult-onset GM2 ganglio-sidosis (AOG) with severe HEX A deficiency. Activity of HEX A in the cultured fetal cells was very low when measured by the heat-inactivation method, thus showing the typical biochemical phenotype of TSD fetuses. However, upon separation of HEX isozymes by ion exchange chromatography, residual HEX A (17 per cent of total HEX) was demonstrated. Also in contrast to TSD fetuses, this fetus' fibroblasts were able to synthesize the precursor of a chains of HEX, and ultrastructural examination of its brain revealed few atypical lamellar bodies, unlike those found in TSD fetuses of the same gestational age. It is therefore concluded that the fetus was not affected with TSD, but rather with AOG.  相似文献   
356.
357.
Peptide chemistry has reached a plateau on which more work is devoted to the improvement of known basic principles than to the development of really new methods. As a consequence, routine syntheses of peptides concentrate on few protecting groups and coupling procedures only. The recent progress in purification of peptides by liquid chromatography helped to promote this trend. Meanwhile, recombinant technology permits the synthesis of proteins and possibly of some lower peptides, too. It cannot compete, however, with chemical solid-phase synthesis of a newly discovered peptide with up to about 40 amino acids in speed but may take over the synthesis for large-scale production. Peptides containing modified or non-natural structures, which are often superior to the natural compounds as drugs, will remain subject of chemical synthesis, too. Present research focuses on the role of peptide and protein factors in the immune response and on structure and biological activities of neuropeptides.  相似文献   
358.
359.
360.
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