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   29711篇
  免费   277篇
  国内免费   274篇
安全科学   819篇
废物处理   1333篇
环保管理   3813篇
综合类   4462篇
基础理论   7809篇
环境理论   11篇
污染及防治   7779篇
评价与监测   2175篇
社会与环境   1864篇
灾害及防治   197篇
  2022年   297篇
  2021年   288篇
  2020年   201篇
  2019年   251篇
  2018年   457篇
  2017年   435篇
  2016年   707篇
  2015年   518篇
  2014年   766篇
  2013年   2437篇
  2012年   944篇
  2011年   1244篇
  2010年   1104篇
  2009年   1147篇
  2008年   1292篇
  2007年   1358篇
  2006年   1207篇
  2005年   1031篇
  2004年   965篇
  2003年   991篇
  2002年   929篇
  2001年   1262篇
  2000年   885篇
  1999年   557篇
  1998年   382篇
  1997年   379篇
  1996年   423篇
  1995年   429篇
  1994年   409篇
  1993年   368篇
  1992年   346篇
  1991年   346篇
  1990年   341篇
  1989年   353篇
  1988年   292篇
  1987年   258篇
  1986年   228篇
  1985年   213篇
  1984年   261篇
  1983年   242篇
  1982年   287篇
  1981年   228篇
  1980年   201篇
  1979年   249篇
  1978年   179篇
  1977年   168篇
  1976年   152篇
  1975年   152篇
  1974年   139篇
  1973年   139篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
431.
432.
First trimester prenatal cytogenetic diagnosis was attempted in 350 pregnancies after trans-abdominal chorionic villus sampling. The cytogenetic investigation was performed using both a short-term method (24 h incubation) and cell culture. Adequate samples were obtained in 99·1 per cent and in all these cases the fetal karyotype was established. A chromosome abnormality was found in 2·0 per cent of cases. A discrepancy between the karyotype obtained after 24 h incubation and the karyotype in cell culture was observed in 2·3 per cent. Maternal cell contamination in the cultures was confirmed in 13 of 181 cases where the 24 h incubation revealed a male karyotype. Studies of culture morphology showed that colonies of convoluted cells may serve as a marker for contamination with maternal cells in culture. For the present, we recommend using a short-term method as well as cell culture for cytogenetic investigation until the problems with karyotype discrepancy and maternal cell contamination have been further clarified.  相似文献   
433.
434.
We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/ 47.XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study.  相似文献   
435.
Maternal serum CA 125 levels were determined at 9–11 menstrual weeks for 26 cases of trisomy 13 (n = 4), trisomy 18 (n = 7), trisomy 21 (n = 15), and appropriate controls. There were no statistically significant differences between groups.  相似文献   
436.
One hundred and fifty-one women of advanced maternal age who underwent genetic termination of pregnancy (TOP) were studied for their reproductive behaviour and the type of procedure for prenatal diagnosis in a subsequent pregnancy. A total of 59 women (39 per cent) had a further pregnancy. In all continuing pregnancies prenatal diagnosis was performed, of which 75 per cent consisted of chorionic villus sampling (CVS). Reproductive behaviour following a genetic termination was negatively correlated with maternal age and parity. Both reproductive behaviour and the choice to undergo a diagnostic procedure in the next pregnancy were independent of the type of diagnostic procedure in the previous affected pregnancy.  相似文献   
437.
438.
439.
The sinusoidal fetal heart rate pattern has been described in association with severe fetal anaemia, with fetal hypoxaemia, and with the administration of parenteral narcotics. Here, we report a case of decreased fetal movement in which a sinusoidal tracing was recorded. The sonographic diagnosis of a massive fetal intracranial haemorrhage was made. A non-interventive approach was taken and the fetus died soon after in utero. We review 28 previous cases in which the prenatal sonographic diagnosis of fetal intracranial haemorrhage was made, including the underlying maternal and fetal factors and neonatal outcomes. We propose that the sinusoidal tracing in this case was due to the intracranial bleed and suggest that fetal intracranial haemorrhage be considered in the sonographic evaluation of the fetus with a sinusoidal pattern.  相似文献   
440.
We report two cases of apparently balanced complex de novo chromosomal rearrangements (BCCR) detected prenatally at 17 weeks and 10 weeks of gestation, respectively. Chromosomes were studied using GTG-banding and fluorescent in situ hybridization (FISH). In one case four chromosomes and in the other case three chromosomes were involved in the rearrangements. One of the pregnancies was terminated and no external or internal abnormalities were detected at autopsy. The other pregnancy continued to term. Level III ultrasound examination showed no abnormalities. The child is now 3 years old and has neither congenital anomalies nor evidence of delayed psychomotor development.  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