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   91635篇
  免费   1227篇
  国内免费   1121篇
安全科学   3717篇
废物处理   3349篇
环保管理   13986篇
综合类   21135篇
基础理论   26460篇
环境理论   74篇
污染及防治   15278篇
评价与监测   5531篇
社会与环境   3901篇
灾害及防治   552篇
  2022年   810篇
  2021年   819篇
  2020年   657篇
  2019年   867篇
  2018年   1191篇
  2017年   1207篇
  2016年   2211篇
  2015年   1840篇
  2014年   2587篇
  2013年   9260篇
  2012年   2227篇
  2011年   2515篇
  2010年   3316篇
  2009年   3413篇
  2008年   2058篇
  2007年   1950篇
  2006年   2344篇
  2005年   2310篇
  2004年   2617篇
  2003年   2467篇
  2002年   2037篇
  2001年   2414篇
  2000年   2067篇
  1999年   1539篇
  1998年   1384篇
  1997年   1363篇
  1996年   1496篇
  1995年   1580篇
  1994年   1481篇
  1993年   1334篇
  1992年   1335篇
  1991年   1298篇
  1990年   1248篇
  1989年   1218篇
  1988年   1057篇
  1987年   992篇
  1986年   995篇
  1985年   1060篇
  1984年   1159篇
  1983年   1169篇
  1982年   1177篇
  1981年   1095篇
  1980年   944篇
  1979年   928篇
  1978年   823篇
  1977年   720篇
  1976年   638篇
  1974年   605篇
  1973年   634篇
  1972年   632篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
781.
782.
Infections in pregnancy with Ureaplasma urealyticum have been associated with a wide range of adverse outcomes, such as early abortion, stillbirth, prematurity, and neonatal morbidity and mortality. Causality has been difficult to demonstrate secondary to the high prevalence of asymptomatic lower genital tract (LGT) colonization and culture data from inaccessible or potentially contaminated sites. Between 1985 and 1989, 2461 second-trimester genetic amniocenteses were evaluated at the cytogenetics section of the Children's Hospital Medical Center of Akron. All were cultured for the genital mycoplasmas: Mycoplasma hominis and Ureaplasma urealyticum. A total of nine patients were positive, all for Ureaplasma urealyticum, with one patient excluded because of subsequent therapeutic abortion. In addition, complete follow-up data, such as indication for amniocentesis, serum alpha-fetoprotein levels, gestational age at parturition, and out- come of pregnancy, were available on 86 Ureaplasma-negative (U –) patients during an approximate 2-year span within the time-frame of the study. This was in part due to physician response to a questionnaire sent after amniocentesis. Of the eight positive cultures, 100 per cent were associated with an adverse outcome, defined as fetal loss or premature delivery. This was significant compared with the U–group (p<0.001) with a more than eight times greater risk of adverse outcome. Six (75 per cent) resulted in spontaneous miscarriage within 4 weeks of amniocentesis and at less than 21 weeks' gestation. Two (25 per cent) delivered prematurely, with one (12.5 per cent) neonatal death at 24+ weeks. Histological examination of all eight placentae and the seven fetuses revealed a 100 per cent incidence of chorioamnionitis and pneumonia, respectively. In addition, in four of the five cases (80 per cent), cultures were positive for Ureaplasma urealyticum in pure culture from either placenta, fetal lung, or both tissues. The remaining case (20 per cent) was negative for aerobes, anaerobes, and mycoplasmas. The study demonstrates a significant association and supports a causal relationship between isolation of Ureaplasma from mid-trimester amniotic fluid with fetal wastage and premature birth.  相似文献   
783.
The most common mutation in alpha-1-antitrypsin deficiency, conversion of a G to an A at base 9989 (PI-Z), was detected with the chemical cleavage of mismatch method, demonstrating the power of the method for prenatal diagnosis. Exon V of the gene was amplified using the polymerase chain reaction and heteroduplexes were formed to test for the presence of the mutation. The predicted C mismatch was readily detectable with hydroxylamine, and by making the probe from the chorionic villus sample it was possible to determine that the fetus was heterozygous, not homozygous, for the mutation.  相似文献   
784.
785.
786.
787.
788.
789.
The nature of the cosmic redshift is one of the most fundamental questions in modern science. Hubble's discovery of the apparent Expansion of the Universe is derived from observations on a small number of galaxies at very low redshifts. Today, quasar redshifts have a range more than 1000 times greater than those in Hubble's sample, and represent more than 100 times as many objects. A recent comprehensive compilation of published measurements provides the basis for a study indicating that quasar observations are not in good agreement with the original predictions of the Expanding Universe theory, but are well fit by the predictions of an alternative theory having fewer adjustable parameters.  相似文献   
790.
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