全文获取类型
收费全文 | 34579篇 |
免费 | 323篇 |
国内免费 | 313篇 |
专业分类
安全科学 | 875篇 |
废物处理 | 1401篇 |
环保管理 | 4199篇 |
综合类 | 7067篇 |
基础理论 | 8459篇 |
环境理论 | 12篇 |
污染及防治 | 8867篇 |
评价与监测 | 2298篇 |
社会与环境 | 1840篇 |
灾害及防治 | 197篇 |
出版年
2022年 | 305篇 |
2021年 | 306篇 |
2019年 | 260篇 |
2018年 | 482篇 |
2017年 | 469篇 |
2016年 | 744篇 |
2015年 | 539篇 |
2014年 | 811篇 |
2013年 | 2694篇 |
2012年 | 1012篇 |
2011年 | 1297篇 |
2010年 | 1146篇 |
2009年 | 1207篇 |
2008年 | 1366篇 |
2007年 | 1487篇 |
2006年 | 1307篇 |
2005年 | 1049篇 |
2004年 | 1066篇 |
2003年 | 1098篇 |
2002年 | 991篇 |
2001年 | 1317篇 |
2000年 | 931篇 |
1999年 | 623篇 |
1998年 | 450篇 |
1997年 | 421篇 |
1996年 | 467篇 |
1995年 | 461篇 |
1994年 | 453篇 |
1993年 | 403篇 |
1992年 | 408篇 |
1991年 | 390篇 |
1990年 | 416篇 |
1989年 | 396篇 |
1988年 | 360篇 |
1987年 | 303篇 |
1986年 | 270篇 |
1985年 | 311篇 |
1984年 | 311篇 |
1983年 | 302篇 |
1982年 | 350篇 |
1981年 | 287篇 |
1980年 | 271篇 |
1979年 | 298篇 |
1978年 | 265篇 |
1977年 | 230篇 |
1976年 | 225篇 |
1975年 | 196篇 |
1974年 | 220篇 |
1973年 | 211篇 |
1967年 | 201篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
601.
602.
603.
604.
605.
606.
Self-diffusion coefficients were studied for the highly polar liquid N-methylformamide at pressures up to 200 MPa between the melting pressure curves and 420 K by the spin-echo method. N-Methylformamide exists as a mixture of two conformers in the neat liquid. These conformers have large differences at lower
temperatures in their dynamic and structural properties. The self-diffusion coefficient of the cis-conformer being 17% lower than that of the trans-conformer at the same T and p. This is the first observation of such an effect. The experimental study is supported by Monte Carlo (MC) calculations which
show that the first neighbors around a cis conformer are arranged differently than in an all trans liquid. The difference leads in the simulations to a much lower dielectric constant for the trans-cis mixture and might also explain the retardation of diffusion for the cis conformer.
Received: 15 November 1999 / Accepted in revised form: 28 February 2000 相似文献
607.
Maternal serum CA 125 levels were determined at 9–11 menstrual weeks for 26 cases of trisomy 13 (n = 4), trisomy 18 (n = 7), trisomy 21 (n = 15), and appropriate controls. There were no statistically significant differences between groups. 相似文献
608.
H. Brandenburg MD W. De Koning M. G. J. Jahoda Th. Stijnen M. A. J. De Ridder E. S. Sachs J. W. Wladimiroff 《黑龙江环境通报》1992,12(12):1031-1035
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
609.
610.