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   49801篇
  免费   541篇
  国内免费   436篇
安全科学   1601篇
废物处理   2047篇
环保管理   6883篇
综合类   8699篇
基础理论   12978篇
环境理论   17篇
污染及防治   12330篇
评价与监测   3132篇
社会与环境   2770篇
灾害及防治   321篇
  2022年   379篇
  2021年   453篇
  2020年   288篇
  2019年   393篇
  2018年   678篇
  2017年   691篇
  2016年   1093篇
  2015年   807篇
  2014年   1198篇
  2013年   3982篇
  2012年   1506篇
  2011年   2042篇
  2010年   1660篇
  2009年   1755篇
  2008年   2127篇
  2007年   2117篇
  2006年   1926篇
  2005年   1602篇
  2004年   1644篇
  2003年   1591篇
  2002年   1473篇
  2001年   1827篇
  2000年   1269篇
  1999年   813篇
  1998年   621篇
  1997年   611篇
  1996年   666篇
  1995年   745篇
  1994年   710篇
  1993年   621篇
  1992年   654篇
  1991年   633篇
  1990年   631篇
  1989年   625篇
  1988年   533篇
  1987年   479篇
  1986年   450篇
  1985年   478篇
  1984年   506篇
  1983年   493篇
  1982年   507篇
  1981年   460篇
  1980年   379篇
  1979年   409篇
  1978年   362篇
  1977年   317篇
  1975年   305篇
  1974年   327篇
  1973年   333篇
  1972年   326篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
481.
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   
482.
483.
The prenatal diagnosis of cystinosis is currently based on the increased amount of free-cystine present in amniotic fluid cells. Amniocyte cultures must be grown for at least 2 weeks to obtain sufficient cells for such measurements. Thus, the diagnosis cannot be made until close to 20 weeks gestational age by this method. We report a case in which chorionic villi were used for direct cystine measurement resulting in the in utero diagnosis of cystinosis at 9 weeks gestational age. The diagnosis was confirmed by the study of cultured chorionic villus cells, and of the 10-week abortus.  相似文献   
484.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling.  相似文献   
485.
Plasticity of honeybee castes   总被引:1,自引:0,他引:1  
  相似文献   
486.
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   
487.
A 70,XXX, +18 karyotype was found by chorionic villus sampling, while the fetal fibroblast culture of the affected fetus revealed a 47,XX,+ 18 karyotype. From several possible mechanisms, we assume that a second gamete fusion occurred after the first cell division of the zygote. According to this interpretation, the mosaicism arose in very early pregnancy (at the two-cell stage). This discrepancy can therefore be explained by selection pressure, due to the differentiation processes in the embryonic tissues.  相似文献   
488.
The nature and origin of two de novo small marker chromosomes found at prenatal diagnosis were determined by fluorescence in situ hybridization using chromosome centromere-specific probes and chromosome-specific plasmid libraries. One marker was found in a mosaic state and was shown to be an i(18p). The second marker was characterized as an inv dup(22). We conclude that molecular cytogenetic analysis contributes to the identification of marker chromosomes and therefore facilitates genetic counselling and decision-making for the parents.  相似文献   
489.
490.
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