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   13798篇
  免费   153篇
  国内免费   103篇
安全科学   400篇
废物处理   598篇
环保管理   2202篇
综合类   2698篇
基础理论   3128篇
环境理论   6篇
污染及防治   3461篇
评价与监测   833篇
社会与环境   638篇
灾害及防治   90篇
  2022年   107篇
  2021年   119篇
  2019年   98篇
  2018年   198篇
  2017年   171篇
  2016年   282篇
  2015年   222篇
  2014年   293篇
  2013年   1090篇
  2012年   405篇
  2011年   549篇
  2010年   443篇
  2009年   509篇
  2008年   565篇
  2007年   620篇
  2006年   548篇
  2005年   442篇
  2004年   437篇
  2003年   462篇
  2002年   412篇
  2001年   478篇
  2000年   354篇
  1999年   227篇
  1998年   155篇
  1997年   147篇
  1996年   143篇
  1995年   196篇
  1994年   178篇
  1993年   166篇
  1992年   163篇
  1991年   161篇
  1990年   141篇
  1989年   144篇
  1988年   155篇
  1987年   128篇
  1986年   100篇
  1985年   127篇
  1984年   143篇
  1983年   149篇
  1982年   155篇
  1981年   126篇
  1980年   125篇
  1979年   126篇
  1978年   111篇
  1977年   95篇
  1976年   86篇
  1975年   94篇
  1974年   108篇
  1972年   77篇
  1965年   75篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Jørgensen  C. K.  Reisfeld  R.  Berg  W. F.  Jaenicke  L. 《Die Naturwissenschaften》1977,64(9):490-492
The Science of Nature -  相似文献   
172.
173.
A case is presented in which percutaneous umbilical sampling (PUBS) was utilized in the second and third trimesters for the diagnosis and management of a pregnancy at risk for neonatal alloimmune thrombocytopenia (NAIT).  相似文献   
174.
175.
176.
177.
Mechanics and Morphology of Silk Drawn from Anesthetized Spiders   总被引:1,自引:0,他引:1  
 CO2 and N2 anesthetized Nephila spiders produced dragline silk with mechanical properties that differed from control silk as a function of time under anesthesia. Silk from CO2 spiders had a significantly lower breaking strain and breaking energy, significantly higher initial modulus, and marginally lower breaking stress. At the onset of anesthesia the silk diameter became highly variable. During deep anesthesia silk either became thinner or retained cross-section but fibrillated. Received: 26 August 1999 / Accepted in revised form: 22 December 1999  相似文献   
178.
The restoration of surface mining landscapes requires the (re)creation of ecosystems. In Lusatia (eastern Germany), large-scale open-cast lignite mining operations generated spoil dumps widely consisting of acidified, phytotoxic substrates. Amelioration and rehabilitation measures have been developed and applied to these substrates since the 1950s. However, it is still not clear whether these approaches are sustainable. This paper reports on collaborative research work into the ecological potential of forest ecosystem development on typical minesites in the Lusatian lignite district. At first sight, pine stands on minesites along a chronosequence comprising about 35 years did not show differences when compared with stands on non-mined sites of the general region. Furthermore, with some modification, conceptual models for flora and fauna succession in forest stands on non-mined sites seem to be applicable, at least for the early stages of forest ecosystem development. For example, soil organism abundance and activity at minesites had already reached levels typical of non-mined sites after about 20-30 years. In contrast, mine soils are very different from non-mined soils of the test region. Chemically, mine soil development is dominated by processes originating from pyrite oxidation. Geogenic, i.e. lignitic, soil organic carbon was shown to substitute for some functions of pedogenic soil organic matter. Rooting was hampered but not completely impeded in strongly acidified soil compartments. Roots and mycorrhizae are apparently able to make use of the characteristic heterogeneity of young mine soils. Considering these recent results and the knowledge accumulated during more than 30 years of research on minesite rehabilitation internationally, it can be stated that minesite restoration might be used as an ideal case study for forest ecosystem development starting at "point zero" on "terra nova".  相似文献   
179.
We have determined the activity of alkaline phosphatase in chorionic villous tissue obtained in the first trimester of pregnancy, in order to obtain the normal range of values as a prerequisite for application to the prenatal diagnosis of the rare bone disease hypophosphatasia. The activities found were a combination of intestinal and liver/bone/kidney types; traces of placental type were present in only one sample.  相似文献   
180.
Prenatal counselling for fetal agenesis of the corpus callosum is difficult as the prognosis until now has been so uncertain. We have reviewed the current world English literature to provide the best probabilistic information for prospective parents. In total, there are 70 cases where the diagnosis was made prenatally. The diagnosis of apparently isolated agenesis of the corpus callosum (in the absence of other sonographically detectable anomalies) appears to carry an excellent prognosis, with an 85 per cent chance of a normal developmental outcome and a 15 per cent risk of handicap. Fetal karyotyping is recommended as there is a 1 in 10 risk of aneuploidy. If other anomalies are detected prenatally, the outcome is very poor. Termination of pregnancy is advised in these circumstances.  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