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   37632篇
  免费   490篇
  国内免费   426篇
安全科学   1137篇
废物处理   1601篇
环保管理   5030篇
综合类   6879篇
基础理论   10036篇
环境理论   22篇
污染及防治   9579篇
评价与监测   2191篇
社会与环境   1830篇
灾害及防治   243篇
  2022年   289篇
  2021年   295篇
  2020年   284篇
  2019年   278篇
  2018年   531篇
  2017年   520篇
  2016年   794篇
  2015年   639篇
  2014年   919篇
  2013年   2897篇
  2012年   1155篇
  2011年   1678篇
  2010年   1310篇
  2009年   1381篇
  2008年   1668篇
  2007年   1699篇
  2006年   1458篇
  2005年   1233篇
  2004年   1218篇
  2003年   1142篇
  2002年   1134篇
  2001年   1304篇
  2000年   1022篇
  1999年   618篇
  1998年   465篇
  1997年   484篇
  1996年   476篇
  1995年   567篇
  1994年   507篇
  1993年   467篇
  1992年   447篇
  1991年   447篇
  1990年   467篇
  1989年   423篇
  1988年   376篇
  1987年   364篇
  1986年   355篇
  1985年   333篇
  1984年   408篇
  1983年   339篇
  1982年   411篇
  1981年   367篇
  1980年   306篇
  1979年   326篇
  1978年   268篇
  1977年   248篇
  1975年   219篇
  1974年   244篇
  1973年   242篇
  1972年   228篇
排序方式: 共有10000条查询结果,搜索用时 425 毫秒
611.
This paper investigates the current treatment of environmental issues by two companies within the large made-to-order sector. Fifty questionnaires were issued to the design team of each company to assess current practice in the integration of environmental issues with design activities, awareness of environmental issues, awareness of existing environmental design tools and the preferred format for a potential clean design tool.  相似文献   
612.
Single zircons from two orthogneiss complexes, the Grey Gneiss and Red Gneiss, the lowermost tectonic units in the Erzgebirge, were dated. The grey Freiberg Gneiss is of igneous origin and has a 207Pb/206Pb emplacement age of 550±7 Ma. A quartz monzonite from Lauenstein contains idiomorphic zircons with a mean 207Pb/206Pb age of 555±7 Ma as well as xenocrysts ranging in age between 850 and 1910 Ma. Red gneisses from the central Erzgebirge contain complex zircon populations, including numerous xenocrysts up to 2464 Ma in age. The youngest, idiomorphic, zircons in all samples yielded uniform 207Pb/206Pb ages between 550±9 and 554±10 Ma. Nd isotopic data support the interpretation of crustal anatexis for the origin of both units. Nd(t) values for the grey gneisses are –7.5 and –6.0 respectively, (mean crustal residence ages of 1.7–1.8 Ga). The red gneisses have a wider range in Nd(t) values from –7.7 to –2.8 (T DM ages of 1.4–1.8 Ga). The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism ( 8 kbar/600–650° C) are identical in both gneiss units and distinguish these rocks from the Lusatian granitoids. The grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. Zircon xenocryst and Nd model ages in the range 1000–1700 Ma are similar to those in granitoid rocks of Lusatia and the West-Sudetes, and document a pre-Cadomian basement in parts of east-central Europe that, chronologically, has similarities with the Sveconorwegian domain in the Baltic Shield.  相似文献   
613.
614.
615.
Maternal serum alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (βhCG) measurements taken prior to chorionic villus sampling (CVS) in 21 patients who subsequently miscarried were compared with measurements in a control group of 113 patients with uneventful pregnancies. Patients with AFP levels of 10 iu/ml or more prior to the CVS had a 4·3 times greater risk of miscarriage (95 per cent confidence interval 1·3–13·6). AFP levels obtained 1 week after the CVS in the 13 patients with late miscarriages were higher than in the control group (P = 0·06). Patients miscarrying had a greater rise in AFP (P = 0·06) and a greater fall in βhCG levels (P = 0·04) following the CVS procedure, compared with the control subjects. Each 10-unit change in the difference between AFP or βhCG levels prior to and 1 week following the CVS was associated with a significantly increased risk for late miscarriage. Elevated maternal serum AFP levels early in pregnancy and changes in AFP and βhCG levels following CVS may predict an increased risk for subsequent miscarriage.  相似文献   
616.
617.
618.
619.
620.
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