全文获取类型
收费全文 | 1144篇 |
免费 | 8篇 |
国内免费 | 5篇 |
专业分类
安全科学 | 18篇 |
废物处理 | 45篇 |
环保管理 | 70篇 |
综合类 | 667篇 |
基础理论 | 138篇 |
污染及防治 | 167篇 |
评价与监测 | 32篇 |
社会与环境 | 18篇 |
灾害及防治 | 2篇 |
出版年
2017年 | 14篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 39篇 |
2012年 | 33篇 |
2011年 | 30篇 |
2010年 | 22篇 |
2009年 | 28篇 |
2008年 | 23篇 |
2007年 | 26篇 |
2006年 | 29篇 |
2005年 | 32篇 |
2004年 | 37篇 |
2003年 | 33篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1998年 | 11篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1989年 | 9篇 |
1978年 | 10篇 |
1966年 | 10篇 |
1965年 | 15篇 |
1964年 | 15篇 |
1963年 | 25篇 |
1962年 | 17篇 |
1961年 | 14篇 |
1960年 | 23篇 |
1959年 | 24篇 |
1958年 | 15篇 |
1957年 | 17篇 |
1956年 | 15篇 |
1955年 | 27篇 |
1954年 | 33篇 |
1953年 | 19篇 |
1952年 | 14篇 |
1951年 | 24篇 |
1948年 | 9篇 |
1947年 | 11篇 |
1941年 | 9篇 |
1939年 | 9篇 |
1938年 | 12篇 |
1935年 | 8篇 |
1933年 | 9篇 |
1931年 | 11篇 |
1930年 | 12篇 |
1929年 | 13篇 |
1921年 | 8篇 |
排序方式: 共有1157条查询结果,搜索用时 31 毫秒
981.
Pregnancy outcome after transcervical cvs with a flexible biopsy forceps: Evaluation of risk factors
The pregnancy outcome of 1936 women who had transcervical chorionic villus sampling (CVS) with a flexible biopsy forceps was evaluated. Follow-up until 4 weeks after delivery was 99.4 per cent. Various patient- and procedure-related risk factors for spontaneous loss (fetal or neonatal death) were analysed using stepwise logistic regression analysis. The overall spontaneous loss rate was 4.5 per cent. Factors found to be significantly associated with spontaneous loss were quantity of villi ≤ 15 mg (relative risk (RR) 2.13), a history of first-trimester miscarriage (RR 1.87) or delivery between 16 and 27 weeks (RR 3.87), cervical culture positive for anaerobes (RR 4.52) or group B streptococcus (RR 3.62), post-procedural bleeding >3 days (RR 1.99), and multiple insertions (RR 2.64). Significant differences in loss rates between individual operators were found. A learning effect was not present. There were no infants born with terminal transversal limb anomalies in our series. 相似文献
982.
983.
984.
Hans Kuhn 《Die Naturwissenschaften》1976,63(2):68-80
In an attempt to understand the origin of living systems we encounter the following problems: How can we conceive the origin of the first self-reproducing forms, and by means of what stimuli could a constant increase in the complexity of such forms commence? How can a translation apparatus for genetic information develop? One cannot that such an apparatus for the synthesis of enzymes can function alone without the interference of enzymes themselves, which, however, could only become available after the construction of the apparatus itself. What stimulus mechanism is conceivable that leads to the division of the genetic apparatus into a replication system, and an enzyme-synthesis system?The main problem therefore, is not the search for basic theoretical concepts. It is not a question which can be answered by means of specific experiments. One should rather explore the principal possibilities of how molecules combine to produce more and more complicated functional units. We look for the fundamental structural changes in the organizational systems and the driving forces initiating these developments. Questions concerning the detailed chemical realization are of secondary importance. In trying to solve the puzzle of how the genetic apparatus is gradually built up as complex aggregates of molecules, we consider a consistent causal chain of simple and transparent physicochemical model steps. 相似文献
985.
986.
987.
988.
989.
990.