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   32276篇
  免费   379篇
  国内免费   483篇
安全科学   1030篇
废物处理   1512篇
环保管理   4292篇
综合类   5185篇
基础理论   8355篇
环境理论   19篇
污染及防治   8507篇
评价与监测   2205篇
社会与环境   1838篇
灾害及防治   195篇
  2023年   146篇
  2022年   339篇
  2021年   332篇
  2020年   261篇
  2019年   307篇
  2018年   496篇
  2017年   505篇
  2016年   783篇
  2015年   599篇
  2014年   907篇
  2013年   2670篇
  2012年   1119篇
  2011年   1509篇
  2010年   1242篇
  2009年   1244篇
  2008年   1526篇
  2007年   1574篇
  2006年   1359篇
  2005年   1167篇
  2004年   1036篇
  2003年   1151篇
  2002年   1020篇
  2001年   1260篇
  2000年   893篇
  1999年   543篇
  1998年   383篇
  1997年   381篇
  1996年   386篇
  1995年   447篇
  1994年   469篇
  1993年   369篇
  1992年   395篇
  1991年   373篇
  1990年   407篇
  1989年   359篇
  1988年   318篇
  1987年   295篇
  1986年   240篇
  1985年   269篇
  1984年   306篇
  1983年   285篇
  1982年   271篇
  1981年   257篇
  1980年   200篇
  1979年   232篇
  1978年   201篇
  1977年   136篇
  1975年   143篇
  1972年   134篇
  1971年   140篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
621.
622.
623.
624.
625.
626.
627.
A case of body stalk anomaly diagnosed prenatally by ultrasound during the 24th week of pregnancy in a cocaine abusing mother is presented. Accurate visualization of the fetal organs was difficult due to the severe oligohydramnios caused by premature rupture of membranes, probably related to the cocaine use. The sonographic findings were an omphalocoele, fetal attachment to the placenta, kyphoscoliosis, and absence of a floating umbilical cord. The prenatal diagnosis of the syndrome and the possible relationship with cocaine abuse are discussed.  相似文献   
628.
629.
Early arnniocentesis between 11 and 14 weeks' gestation was offered to 110 women at risk of a chromosomally abnormal fetus due to maternal age. Four were found to be unsuitable for the procedure, and 106 early amniocenteses were performed. In 102 cases, clear amniotic fluid was obtained with a single tap. There were two dry taps and two bloodstained tapis; sampling was repeated in three of these cases before 15 weeks. In the fourth case, placental biopsy was performed at 16 weeks. Thus, we were able to obtain a satisfactory sample in all but three cases(2.8 percent). Karyotyping of cells harvested from the early amniotic fluid samples was successful in all the 105 cases. Cell culture from the initial samples revealed a normal karyotype in 99 cases, two balanced translocations, two tetraploid karyotypes, and two cases of pseudomosaicism. Of the 105 pregnancies successfully sampled, there have been two losses to date (1–8 per cent). Two further patients presented with premature rupture of membranes, both pregnancies having successful outcomes. Sixty-two babies have delivered to date, with four congenital anomalies. There were no respiratory problems. Twenty-nine pregnancies are continuing without known complications, and details are not yet available on the remaining 12. The results indicate that early arnniocentesis may replace the traditional test at 15–17 weeks.  相似文献   
630.
A new dimension in the prevention of birth defects will be achieved when genetic diseases can be routinely diagnosed in embryos prior to implantation. The impressions and attitudes towards preimplantation diagnosis were studied in prospective patients, women at high reproductive risk for a genetic disease. Their perspective highlighted not only the advantages and disadvantages of this new approach, but also those changes necessary in order for preimplantation diagnosis to become a useful and practical technique. The data presented are based on information obtained by a mailed questionnaire answered by 58 women. The main benefit of preimplantation diagnosis for these high-risk women would be the ability to undertake a pregnancy without having to be subjected to the physical and/or emotional trauma of elective termination. Their major concerns related to possible damage to the embryo following biopsy, the cost of the procedure, and the low success rate of completed pregnancies. Other issues to be addressed before preimplantation diagnosis could begin to compare favourably with existing forms of prenatal testing were that the methods of obtaining oocytes or embryos should be simple, well tolerated, highly efficient, and low in maternal risk, and that the genetic analysis of embryonic or extraembryonic cells should be unequivocally accurate.  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