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   17947篇
  免费   215篇
  国内免费   157篇
安全科学   568篇
废物处理   702篇
环保管理   2666篇
综合类   2731篇
基础理论   4869篇
环境理论   6篇
污染及防治   4626篇
评价与监测   1108篇
社会与环境   912篇
灾害及防治   131篇
  2022年   129篇
  2021年   145篇
  2020年   127篇
  2019年   166篇
  2018年   265篇
  2017年   277篇
  2016年   409篇
  2015年   293篇
  2014年   408篇
  2013年   1381篇
  2012年   513篇
  2011年   762篇
  2010年   628篇
  2009年   596篇
  2008年   783篇
  2007年   802篇
  2006年   758篇
  2005年   564篇
  2004年   650篇
  2003年   582篇
  2002年   530篇
  2001年   737篇
  2000年   497篇
  1999年   303篇
  1998年   268篇
  1997年   231篇
  1996年   249篇
  1995年   261篇
  1994年   285篇
  1993年   234篇
  1992年   262篇
  1991年   228篇
  1990年   263篇
  1989年   241篇
  1988年   203篇
  1987年   187篇
  1986年   166篇
  1985年   172篇
  1984年   201篇
  1983年   185篇
  1982年   192篇
  1981年   183篇
  1980年   141篇
  1979年   159篇
  1978年   131篇
  1977年   117篇
  1975年   119篇
  1974年   117篇
  1973年   110篇
  1972年   133篇
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
171.
Chorionic villus sampling (CVS) with either transcervical catheters or transabdominal needles is a widely-accepted method for prenatal diagnosis. However, there exists a small subset of patients in whom sampling is difficult or impossible with either route because of individual anatomic variations. A new method of chorionic villus biopsy has been developed to circumvent these problems, utilizing transvaginal chorionic needle aspiration guided by an intravaginal ultrasound probe. This technique was performed successfully in 15 patients in whom villi could not be obtained by either of the conventional methods. This method now makes CVS possible in essentially all women regardless of their uterine anatomy or placental placement; it may also prove useful for very early chorionic sampling.  相似文献   
172.
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   
173.
174.
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   
175.
176.
177.
178.
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   
179.
180.
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