全文获取类型
收费全文 | 460篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
安全科学 | 2篇 |
废物处理 | 5篇 |
环保管理 | 16篇 |
综合类 | 226篇 |
基础理论 | 87篇 |
污染及防治 | 96篇 |
评价与监测 | 16篇 |
社会与环境 | 15篇 |
出版年
2018年 | 4篇 |
2016年 | 7篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 12篇 |
2011年 | 9篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 14篇 |
2007年 | 23篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 15篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1978年 | 4篇 |
1967年 | 4篇 |
1966年 | 4篇 |
1965年 | 6篇 |
1964年 | 8篇 |
1963年 | 16篇 |
1962年 | 4篇 |
1961年 | 10篇 |
1960年 | 5篇 |
1959年 | 7篇 |
1958年 | 12篇 |
1957年 | 8篇 |
1956年 | 7篇 |
1955年 | 12篇 |
1954年 | 7篇 |
1952年 | 4篇 |
1951年 | 3篇 |
1950年 | 6篇 |
1947年 | 5篇 |
1943年 | 6篇 |
1939年 | 4篇 |
1924年 | 3篇 |
排序方式: 共有463条查询结果,搜索用时 984 毫秒
211.
212.
213.
214.
215.
216.
217.
218.
A specimen of the horned dinosaur Psittacosaurus from the early Cretaceous of China is described in which the integument is extraordinarily well-preserved. Most unusual is the presence of long bristle-like structures on the proximal part of tail. We interpret these structures as cylindrical and possibly tubular epidermal structures that were anchored deeply in the skin. They might have been used in display behavior and especially if one assumes that they were colored, they may have had a signal function. At present, there is no convincing evidence which shows these structures to be homologous to the structurally different integumentary filaments of theropod dinosaurs. Independent of their homology, however, the discovery of bristle-like structures in Psittacosaurus is of great evolutionary significance since it shows that the integumentary covering of at least some dinosaurs was much more complex than has ever been previously imagined. 相似文献
219.
The advantages of a routine screening or indication-based ultrasound investigation during pregnancy are still under debate. This is the first study where both methods are compared in two different time periods. More malformations were diagnosed before the 24th week of gestation by means of screening-based than indication-based investigation (18 per cent vs. 5 per cent, P<0·005), and before 28 weeks in 26 per cent compared with 15 per cent respectively (P<0·01). Twenty-six per cent of all malformations were detected by means of screening-based investigations as opposed to 15 per cent by means of indication-based scans. Primary fetal malformations were also diagnosed much earlier (25 weeks vs. 30 weeks). Except for the fetal head, the detection rate of malformations was higher in nearly all other body regions of the fetus in the screening-based investigation. The most important advantage of a screening-based ultrasound investigation during pregnancy is to detect the malformations early enough in pregnancy for possible intrauterine treatment or to offer safe termination of pregnancy for the woman, at least for those anomalies that are lethal or significantly handicapping. 相似文献
220.