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   30073篇
  免费   339篇
  国内免费   252篇
安全科学   1020篇
废物处理   1461篇
环保管理   3991篇
综合类   4528篇
基础理论   7835篇
环境理论   8篇
污染及防治   7429篇
评价与监测   2159篇
社会与环境   2050篇
灾害及防治   183篇
  2023年   143篇
  2022年   271篇
  2021年   331篇
  2020年   207篇
  2019年   255篇
  2018年   448篇
  2017年   474篇
  2016年   733篇
  2015年   539篇
  2014年   872篇
  2013年   2496篇
  2012年   1030篇
  2011年   1370篇
  2010年   1117篇
  2009年   1162篇
  2008年   1436篇
  2007年   1345篇
  2006年   1218篇
  2005年   1092篇
  2004年   1047篇
  2003年   997篇
  2002年   938篇
  2001年   1100篇
  2000年   768篇
  1999年   485篇
  1998年   365篇
  1997年   386篇
  1996年   397篇
  1995年   467篇
  1994年   397篇
  1993年   343篇
  1992年   377篇
  1991年   357篇
  1990年   327篇
  1989年   325篇
  1988年   295篇
  1987年   241篇
  1986年   248篇
  1985年   247篇
  1984年   268篇
  1983年   256篇
  1982年   269篇
  1981年   222篇
  1980年   165篇
  1979年   182篇
  1978年   162篇
  1977年   133篇
  1975年   137篇
  1973年   168篇
  1972年   142篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
997.
An amniocentesis was performed at 13.3 weeks' gestation for advanced maternal age. A mosaic sex chromosome pattern was found: of 50 cells examined, 34 had a 45,X karyotype. In 14 cells with a modal number of 46, a recognizable Y was substituted by a small non-fluorescent marker. C-banding identified the marker as an isodicentric in 12 cells. In two cells, the non-fluorescent marker appeared to be monocentric and looked like a non-fluorescent del (Yq), but could have been an isodicentric Y with inactivation of one of the centromeres. Two cells with a modal number of 47 showed two copies of the monocentric marker. Fluorescent in situ hybridization with an alpha satellite Y-specific centromeric probe confirmed the Y-chromosome origin of the markers and allowed for more accurate prenatal diagnostic information.  相似文献   
998.
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   
999.

Introduction

Wastewater derived from leather production may contain phenols, which are highly toxic, and their degradation could be possible through bioremediation technologies.

Materials, methods and results

In the present work, microbial degradation of phenol was studied using a tolerant bacterial strain, named CS1, isolated from tannery sediments. This strain was able to survive in the presence of phenol at concentrations of up to 1,000?mg/L. On the basis of morphological and biochemical properties, 16S rRNA gene sequencing, and phylogenetic analysis, the isolated strain was identified as Rhodococcus sp. Phenol removal was evaluated at a lab-scale in Erlenmeyer flasks and at a bioreactor scale in a stirred tank reactor. Rhodococcus sp. CS1 was able to completely remove phenol in a range of 200 to 1,000?mg/L in mineral medium at 30 ± 2?°C and pH 7 as optimal conditions. In the stirred tank bioreactor, we studied the effect of some parameters, such as agitation (200?C600 rpm) and aeration (1?C3?vvm), on growth and phenol removal efficiency. Faster phenol biodegradation was obtained in the bioreactor than in Erlenmeyer flasks, and maximum phenol removal was achieved at 400?rpm and 1 vvm in only 12?h. Furthermore, Rhodococcus sp. CS1 strain was able to grow and completely degrade phenols from tannery effluents after 9?h of incubation.

Conclusion

Based on these results, Rhodococcus sp. CS1 could be an appropriate microorganism for bioremediation of tannery effluents or other phenol-containing wastewaters.  相似文献   
1000.
New fossil spiders (Arachnida: Araneae) from Middle Jurassic (ca. 165 Ma) strata of Daohugou, Inner Mongolia, China are described as Eoplectreurys gertschi gen. et sp. nov. and referred to the modern haplogyne family Plectreuridae. This small family is restricted to southwestern USA, Mexico, and the adjacent Caribbean area today and hitherto has only a sparse Cenozoic fossil record. The morphology of Eoplectreurys is remarkably similar to modern forms and thus demonstrates great evolutionary conservatism. This new discovery not only extends the fossil record of the family by at least 120 Ma to the Middle Jurassic but also supports the hypothesis of a different distribution of the family in the past than today and subsequent extinction over much of its former range.  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