全文获取类型
收费全文 | 34502篇 |
免费 | 284篇 |
国内免费 | 361篇 |
专业分类
安全科学 | 858篇 |
废物处理 | 1550篇 |
环保管理 | 3750篇 |
综合类 | 6913篇 |
基础理论 | 8429篇 |
环境理论 | 11篇 |
污染及防治 | 8830篇 |
评价与监测 | 2543篇 |
社会与环境 | 2068篇 |
灾害及防治 | 195篇 |
出版年
2022年 | 351篇 |
2021年 | 326篇 |
2020年 | 216篇 |
2019年 | 286篇 |
2018年 | 526篇 |
2017年 | 527篇 |
2016年 | 813篇 |
2015年 | 578篇 |
2014年 | 940篇 |
2013年 | 2625篇 |
2012年 | 1107篇 |
2011年 | 1369篇 |
2010年 | 1230篇 |
2009年 | 1272篇 |
2008年 | 1418篇 |
2007年 | 1523篇 |
2006年 | 1329篇 |
2005年 | 1155篇 |
2004年 | 1100篇 |
2003年 | 1114篇 |
2002年 | 1027篇 |
2001年 | 1383篇 |
2000年 | 962篇 |
1999年 | 647篇 |
1998年 | 431篇 |
1997年 | 409篇 |
1996年 | 437篇 |
1995年 | 460篇 |
1994年 | 430篇 |
1993年 | 357篇 |
1992年 | 382篇 |
1991年 | 370篇 |
1990年 | 378篇 |
1989年 | 353篇 |
1988年 | 340篇 |
1987年 | 256篇 |
1986年 | 246篇 |
1985年 | 272篇 |
1984年 | 288篇 |
1983年 | 262篇 |
1982年 | 307篇 |
1981年 | 247篇 |
1980年 | 213篇 |
1979年 | 252篇 |
1978年 | 225篇 |
1977年 | 200篇 |
1976年 | 195篇 |
1975年 | 177篇 |
1974年 | 186篇 |
1967年 | 181篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
601.
602.
Mitigation and Adaptation Strategies for Global Change - 相似文献
603.
Prenatal cytogenetic diagnosis after transabdominal chorionic villus sampling in the first trimester
First trimester prenatal cytogenetic diagnosis was attempted in 350 pregnancies after trans-abdominal chorionic villus sampling. The cytogenetic investigation was performed using both a short-term method (24 h incubation) and cell culture. Adequate samples were obtained in 99·1 per cent and in all these cases the fetal karyotype was established. A chromosome abnormality was found in 2·0 per cent of cases. A discrepancy between the karyotype obtained after 24 h incubation and the karyotype in cell culture was observed in 2·3 per cent. Maternal cell contamination in the cultures was confirmed in 13 of 181 cases where the 24 h incubation revealed a male karyotype. Studies of culture morphology showed that colonies of convoluted cells may serve as a marker for contamination with maternal cells in culture. For the present, we recommend using a short-term method as well as cell culture for cytogenetic investigation until the problems with karyotype discrepancy and maternal cell contamination have been further clarified. 相似文献
604.
605.
We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/ 47.XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study. 相似文献
606.
607.
608.
609.
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
610.