全文获取类型
收费全文 | 3257篇 |
免费 | 313篇 |
出版年
2022年 | 27篇 |
2021年 | 39篇 |
2020年 | 26篇 |
2019年 | 37篇 |
2018年 | 34篇 |
2017年 | 47篇 |
2016年 | 53篇 |
2015年 | 94篇 |
2014年 | 115篇 |
2013年 | 133篇 |
2012年 | 150篇 |
2011年 | 188篇 |
2010年 | 109篇 |
2009年 | 115篇 |
2008年 | 136篇 |
2007年 | 118篇 |
2006年 | 113篇 |
2005年 | 122篇 |
2004年 | 119篇 |
2003年 | 121篇 |
2002年 | 102篇 |
2001年 | 87篇 |
2000年 | 84篇 |
1999年 | 55篇 |
1998年 | 31篇 |
1997年 | 27篇 |
1996年 | 31篇 |
1995年 | 36篇 |
1993年 | 25篇 |
1992年 | 52篇 |
1991年 | 47篇 |
1990年 | 57篇 |
1989年 | 55篇 |
1988年 | 49篇 |
1987年 | 43篇 |
1986年 | 31篇 |
1985年 | 44篇 |
1984年 | 37篇 |
1983年 | 34篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 27篇 |
1977年 | 34篇 |
1975年 | 34篇 |
1974年 | 38篇 |
1973年 | 33篇 |
1972年 | 27篇 |
1971年 | 40篇 |
1970年 | 36篇 |
1969年 | 32篇 |
排序方式: 共有3570条查询结果,搜索用时 15 毫秒
1.
2.
Barry Barnes 《New genetics and society》2013,32(3):292-302
The concern of this paper is with how the accounts of human beings and their behaviour now emerging from genetics, genomics and the new human biotechnology should be related to traditional accounts in which we identify ourselves as responsible agents, capable of choice, who normally act freely and voluntarily. The paper addresses these apparently competing accounts in terms of their functions and modes of use, and thereby arrives at a general solution to this current version of the ancient problem of free will and determinism. The causal scientific discourse of genetics and the everyday discourse of responsibility and choice do different things for us, it suggests, and should not be regarded as articulating conflicting theories. Whilst the former is oriented to the task of naturalistic explanation, the latter is predominantly, if not entirely, a medium of communication through which we affect each other and thereby mutually regulate our conduct. If this is indeed the case, then interesting implications follow concerning the proper relationship of the two kinds of account, which need no longer be regarded as incompatible with each other. And insights emerge into both the limitations and the profound importance of the contribution that genetics and genomics seem destined to make to the understanding of human behaviour. 相似文献
3.
4.
How reliable are dung counts for estimating elephant numbers? 总被引:4,自引:0,他引:4
R. F. W. Barnes 《African Journal of Ecology》2001,39(1):1-9
Dung counts are the most commonly used techniques for estimating elephant numbers in forests, yet there is considerable scepticism concerning their accuracy. Published accounts of dung counts show that they give estimates similar to those from other methods for vertebrates ranging in size from lizards to elephants. For ungulates, macropods and elephants there are strong correlations between estimates from dung counts and other methods. Thus, dung counts are as accurate or inaccurate as other methods for estimating vertebrate numbers, including elephants. Dung counts for elephants give estimates that are as precise as, and sometimes more precise than, those from aerial surveys of elephants. This is because the variance in dung density is usually low and results in a lower than expected variance for the final elephant estimate when combined with the variances of defecation and decay rates. Dung counts may be more appropriate than aerial surveys for monitoring small or declining elephant populations. 相似文献
5.
Benzene, an accepted leukemogen, has been suggested to cause other hemato- and lymphopoietic cancers. Here we review the published literature for non-Hodgkin lymphoma (NHL) and occupational exposure to benzene. Six cohorts, sixteen case–control studies and two studies of other designs were identified through keyword searches of bibliographic databases. Twenty-two of twenty-four studies found no association between NHL and ever exposed to benzene compared to never; a random-effects meta-analysis gave a pooled risk estimate of 1.11 (95% confidence interval 0.94–1.30). Our finding of no effect agrees with one of two previous meta-analyses. The other meta-analysis examined if high benzene exposure increased NHL risk but a lack of consistent exposure categories within the same metric should have precluded pooling risks by exposure level. Instead, we reviewed whether dose–response relationships existed. The best available data came from six studies where exposure was estimated from historical measurements and on the whole, no trends in risks of NHL with rising cumulative, average, peak, or duration of benzene exposure were found. NHL is a heterogeneous group of malignancies and although less well-studied, benzene was not associated with any NHL subtype. In conclusion, benzene at either low or high doses does not increase the risk of NHL. 相似文献
6.
One hundred and forty five women who had undergone hemiarthroplasty for a subcapital fracture of the femoral neck but who were otherwise fit were studied to determine whether undue delay between injury and operation influenced their social circumstances three months after surgery. The median delay for those patients who showed good rehabilitation at three months was 29 hours, but for those who showed poor rehabilitation it was 57 hours. This difference was significant. It is suggested that a subcapital fracture in an otherwise fit elderly patient should therefore be regarded as a surgical emergency. 相似文献
7.
8.
9.
10.