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   16964篇
  免费   181篇
  国内免费   141篇
安全科学   488篇
废物处理   657篇
环保管理   2503篇
综合类   2604篇
基础理论   4589篇
环境理论   4篇
污染及防治   4400篇
评价与监测   1057篇
社会与环境   875篇
灾害及防治   109篇
  2022年   113篇
  2021年   131篇
  2020年   108篇
  2019年   153篇
  2018年   233篇
  2017年   234篇
  2016年   366篇
  2015年   258篇
  2014年   371篇
  2013年   1302篇
  2012年   457篇
  2011年   661篇
  2010年   559篇
  2009年   538篇
  2008年   729篇
  2007年   714篇
  2006年   699篇
  2005年   532篇
  2004年   618篇
  2003年   547篇
  2002年   495篇
  2001年   720篇
  2000年   491篇
  1999年   292篇
  1998年   245篇
  1997年   229篇
  1996年   235篇
  1995年   256篇
  1994年   282篇
  1993年   230篇
  1992年   256篇
  1991年   229篇
  1990年   261篇
  1989年   243篇
  1988年   198篇
  1987年   179篇
  1986年   166篇
  1985年   175篇
  1984年   201篇
  1983年   189篇
  1982年   196篇
  1981年   186篇
  1980年   143篇
  1979年   154篇
  1978年   138篇
  1977年   126篇
  1975年   122篇
  1974年   115篇
  1973年   110篇
  1972年   136篇
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
171.
This paper reports results of an exploratory study of prenatal diagnosis patients who experienced voluntary terminations of pregnancy following the detection of an abnormality or spontaneous miscarriages. The 121 participants were part of the national collaborative Chorionic Villus Sampling and Amniocentesis Study. They completed semi-structured telephone interviews and mailed questionnaires at 1 month and 6 months after the pregnancy losses. Scores on the Profile of Mood States showed that mood levels improved significantly over time. However, there were some declines in loss-related support from partners and others. The persisting distress and difficulties of a minority highlight the variability in women's responses to pregnancy losses. Women who lost pregnancies later in gestation, showed the greatest mood disturbances at initial assessments, used professional mental health assistance after the loss, or reported less satisfactory loss-related support from significant others showed the greatest levels of mood disturbance at the six-month assessment. Follow-up contacts with patients who lose pregnancies should be used to inform women about the variation in possible grief reactions, to assess the extent of support the women are receiving from their partners and significant others, and to provide additional follow-up or referral of those experiencing the greatest distress.  相似文献   
172.
173.
Prenatal real-time ultrasonographic diagnosis of microphthalmia is presented. Diagnosis was made at 18 weeks' gestation in a fetus of a patient with a previous infant affected with the syndrome of cryptophthalmia with absence of septum nasi and ambiguous genitalia (Fraser syndrome). Recognition of microphthalmia as a part of Fraser syndrome and the easy visualization of fetal facial bones and orbits in the second trimester made the diagnosis possible.  相似文献   
174.
175.
176.
177.
We have investigated the ability of high-resolution proton NMR spectroscopy to provide a biochemical constituent screening of human amniotic fluid (AF). Proton NMR spectra were obtained at 300 MHz on AF from patients undergoing amniocentesis in the mid-trimester. Only AF from normal pregnancies (normal fetal karyotype, normal a-fetoprotein levels, normal birth outcome) was used in this study. The AF supernatant was lyophilized and resuspended in deuterated water containing 0.1 mm phosphate buffer and 6.02 mm disodium maleate. Identification of low molecular weight compounds was confirmed by two-dimensional NMR spectra (primarily correlated spectroscopy, or COSY) and standard addition techniques. A broad profile of compounds were ‘NMR visible’ in a single proton spectrum, including creatinine, glucose, organic acids (acetate, citrate, and lactate) and several amino acids (alanine, histidine, leucine, phenylalanine, tyrosine and valine). The proton spectrum was unaffected by prior freezing/thawing of AF samples. We were able to quantify compounds by comparison with an added concentration standard (maleate) at concentrations as low as 30 μm. Good agreement with literature values based on other analytical techniques was obtained.  相似文献   
178.
179.
180.
The radiation budget of planets substantially determines their climates. For the terrestrial planets having their own imperceptible heat source compared to the solar radiation, the radiation budget supplies energy that can be transformed and used in their atmospheres and at their surfaces. The crucial role of the radiation budget for the Earth's climate is manifested in current international programs like the World Climate and Global Change Programs. The intercomparison and analysis of the radiation budget of the terrestrial planets, due to quite different atmospheric compositions and external conditions, provide a deeper insight into the relations of the different components of the radiation budget.  相似文献   
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