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   20010篇
  免费   199篇
  国内免费   228篇
安全科学   522篇
废物处理   920篇
环保管理   2763篇
综合类   4029篇
基础理论   4417篇
环境理论   8篇
污染及防治   5214篇
评价与监测   1332篇
社会与环境   1154篇
灾害及防治   78篇
  2022年   164篇
  2021年   176篇
  2019年   165篇
  2018年   294篇
  2017年   275篇
  2016年   427篇
  2015年   320篇
  2014年   463篇
  2013年   1526篇
  2012年   582篇
  2011年   824篇
  2010年   642篇
  2009年   730篇
  2008年   853篇
  2007年   899篇
  2006年   817篇
  2005年   689篇
  2004年   683篇
  2003年   685篇
  2002年   639篇
  2001年   698篇
  2000年   450篇
  1999年   336篇
  1998年   240篇
  1997年   248篇
  1996年   263篇
  1995年   274篇
  1994年   270篇
  1993年   251篇
  1992年   229篇
  1991年   244篇
  1990年   231篇
  1989年   198篇
  1988年   199篇
  1987年   173篇
  1986年   177篇
  1985年   174篇
  1984年   213篇
  1983年   201篇
  1982年   212篇
  1981年   189篇
  1980年   164篇
  1979年   166篇
  1978年   163篇
  1977年   139篇
  1976年   126篇
  1975年   112篇
  1974年   130篇
  1973年   104篇
  1971年   112篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Collections made in the course of long-term field studies on ecology of the northern mole vole Ellobius talpinus Pall. in the Ural Region and neighboring areas (more than 2000 individuals from 24 points of the species range) were used to analyze geographic variation in its coat color (color morphs). On the basis of long-term observations (1985–1999) on marked animals from a polymorphic population (Kurtamyshskii raion, Kurgan oblast), the life spans of males and females and the dependence of life span on population density and structure were estimated in animals of different color morphs. Each color morph of E. talpinus was shown to have specific features of the seasonal dynamics of age structure and migrations.  相似文献   
22.
The importance of eating habits and the number of fish sampled in the estimation of mercury environmental contamination through biological indicators was studied. The species used were one with piscivorous habits (Anguilla anguilla) and another with omnivorous habits (Ciprinus carpio). From one original sample for each species, randomized samples were generated using the subroutine GGSRS from the mathematics library IMSL, and later the statistical significance of Pearson's correlation coefficient for the relationship between fish weight and mercury concentrations in muscle was obtained for each random sample. The results show that the use of omnivorous species such as Ciprinus carpio as a biological indicator of contamination enables us to carry out estimations with a greater degree of confidence than when piscivorous species such as Anguilla anguilla are used.  相似文献   
23.
A prenatal diagnosis of partial monosomy 18p(18p11.2→pter) and trisomy 21q(21q22.3→qter) in a fetus with alobar holoprosencephaly (HPE) and premaxillary agenesis (PMA) but without the classical Down syndrome phenotype is reported. A 27-year-old primigravida woman was referred for genetic counselling at 21 weeks' gestation due to sonographic findings of craniofacial abnormalities. Level II ultrasonograms manifested alobar HPE and median orofacial cleft. Cytogenetic analysis and fluorescence in situ hybridization (FISH) on cells obtained from amniocentesis revealed partial monosomy 18p and a cryptic duplication of 21q,46,XY,der(18)t(18;21)(p11.2;q22.3), resulting from a maternal t(18;21) reciprocal translocation. The breakpoints were ascertained by molecular genetic analysis. The pregnancy was terminated. Autopsy showed alobar HPE with PMA, pituitary dysplasia, clinodactyly and classical 18p deletion phenotype but without the presence of major typical phenotypic features of Down syndrome. The phenotype of this antenatally diagnosed case is compared with those observed in six previously reported cases with monosomy 18p due to 18;21 translocation. The present study is the first report of concomitant deletion of HPE critical region of chromosome 18p11.3 and cryptic duplication of a small segment of distal chromosome 21q22.3 outside Down syndrome critical region. The present study shows that cytogenetic analyses are important in detecting chromosomal aberrations in pregnancies with prenatally detected craniofacial abnormalities, and adjunctive molecular investigations are useful in elucidating the genetic pathogenesis of dysmorphism. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
24.
25.
26.
27.
28.
Progress in Restoration of the Mauritius Kestrel   总被引:1,自引:0,他引:1  
In the 1970s, the Mauritius Kestrel ( Falco punctatus ) was the most endangered bird of prey in the world, at one time with only two known pairs surviving in the remnant native forest of the Black River Gorges (ca. 4,000 ha). At the end of the 1991–1992 breeding season, a minimum of 30 nesting pairs and more than 170 individuals were distributed in four separate forested areas, thanks mainly to manipulation of the reproductive potential of the wild pairs, to captive propagation, and to reintroduction (restocking). Since 1984, 139 young have been reared from 618 eggs laid by captive kestrels, and 147 from 265 wild eggs incubated and hatched in the laboratory; 235 young kestrels have been released on Mauritius by hacking and fostering. Adjustments in feeding and nesting habits of kestrels hacked and released outside the Black River Gorges in areas dominated by exotic vegetation and agriculture have allowed these kestrels to survive and reproduce in an array of previously unused habitats. Now that the kestrels have been released from dependence on the remnant and dying native forest, a viable population of more than 100 nesting pairs should be achievable in a few more years.  相似文献   
29.
30.
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