全文获取类型
收费全文 | 63572篇 |
免费 | 697篇 |
国内免费 | 717篇 |
专业分类
安全科学 | 1922篇 |
废物处理 | 2652篇 |
环保管理 | 8296篇 |
综合类 | 11311篇 |
基础理论 | 17262篇 |
环境理论 | 46篇 |
污染及防治 | 16008篇 |
评价与监测 | 4012篇 |
社会与环境 | 3025篇 |
灾害及防治 | 452篇 |
出版年
2022年 | 553篇 |
2021年 | 546篇 |
2020年 | 409篇 |
2019年 | 535篇 |
2018年 | 916篇 |
2017年 | 908篇 |
2016年 | 1385篇 |
2015年 | 1077篇 |
2014年 | 1573篇 |
2013年 | 4902篇 |
2012年 | 1964篇 |
2011年 | 2715篇 |
2010年 | 2233篇 |
2009年 | 2264篇 |
2008年 | 2714篇 |
2007年 | 2820篇 |
2006年 | 2483篇 |
2005年 | 2077篇 |
2004年 | 1993篇 |
2003年 | 2070篇 |
2002年 | 1897篇 |
2001年 | 2371篇 |
2000年 | 1682篇 |
1999年 | 1087篇 |
1998年 | 806篇 |
1997年 | 833篇 |
1996年 | 834篇 |
1995年 | 937篇 |
1994年 | 909篇 |
1993年 | 779篇 |
1992年 | 801篇 |
1991年 | 764篇 |
1990年 | 808篇 |
1989年 | 787篇 |
1988年 | 690篇 |
1987年 | 618篇 |
1986年 | 551篇 |
1985年 | 603篇 |
1984年 | 643篇 |
1983年 | 625篇 |
1982年 | 637篇 |
1981年 | 578篇 |
1980年 | 490篇 |
1979年 | 531篇 |
1978年 | 468篇 |
1977年 | 383篇 |
1976年 | 368篇 |
1975年 | 375篇 |
1973年 | 358篇 |
1972年 | 378篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
881.
As part of the Medical Research Council randomized trial of vitamin supplementation in the prevention of neural tube defects (NTDs), maternal serum alpha-fetoprotein (AFP) was available for 19 NTD pregnancies. Each of these was matched with four unaffected controls, by maternal age, participating centre, and duration of sample storage. The samples came from women whose gestational age ranged from 6 to 14 completed weeks. The median AFP level in the affected pregnancies was 1·2 multiples of the median value in unaffected pregnancies of the same gestational age (95 per cent confidence interval (CI) 0·83–1·59). This confirmed the view that serum AFP measurement is of no practical value in the detection of NTDs in the first trimester of pregnancy. The study also showed that folic acid supplementation, used as a method of preventing NTDs, had no effect on the concentrations of maternal serum AFP up to 14 weeks of pregnancy. 相似文献
882.
E.F. Brünig 《Agriculture, ecosystems & environment》1984,11(2):191
883.
884.
Prenatal diagnosis of trisomy 20 mosaicism was made in two pregnancies by chromosome analysis of cultured amniotic fluid cells. In both cases, the pregnancy continued to term and a healthy male infant was delivered. Regular assessments up to the age of 6-5 years revealed normal physical and intellectual development in both children. 相似文献
885.
In the case-control study of 118 women with autosomal trisomy identified at prenatal diagnosis and their 442 karyotypically normal matched controls, we found that there was no overall association between risk of trisomy and the presence of vaginal bleeding during pregnancy. However, a lengthy duration of bleeding appears to predict increased risk of trisorny. 相似文献
886.
Citrullinaemia was presumed to be excluded in a fetus at risk by the direct assay of argininosuccinate synthetase in chorionic villi. The diagnosis was confirmed after amniocentesis by normal argininosuccinate synthetase activity in the cultured amniotic fluid cells and by a normal citrulline concentration in the amniotic fluid. The prediction of a normal fetus was confirmed at term by the birth of a non-citrullinaemic boy. 相似文献
887.
888.
We report in detail two series of chorionic villus cultivation for prenatal chromosomal diagnosis. Chorionic villi were sampled from both first- and second-trimester pregnancies. One hundred cultures were treated with trypsin–EDTA for 2 h and collagenase overnight, (method A) and 100 were treated with trypsin–EDTA for 1 h and collagenase for 2 h (method B). Using short-term enzymatic digestion, the cultivation time was reduced from 14 days to 6 days. Sufficient amounts of metaphases of good quality were present in 93 per cent of primary cultures harvested in situ, whereas enough metaphases of sufficiently good quality were in most cases present only after subcultivation of the cultures using method A. The decrease in cultivation time obtained is probably due to a higher yield of viable cells in monocellular suspension, an increased attachment efficiency, and a more rapid attachment of single cells (within 24 h). 相似文献
889.
890.
Masera Omar R. Cerón Alma Delia Ordóñez Antonio 《Mitigation and Adaptation Strategies for Global Change》2001,6(3-4):291-312
We examine carbon (C) reference and mitigation scenarios for the Mexicanforest sector between the year 2000 and 2030. Estimates are presentedseparately for the period 2008–2012.Future C emissions and capture are estimated using a simulation modelthat: a) allocates the country land use/land cover classes among differentfuture uses and categories using demand-based scenarios for forestryproducts; b) estimates the total C densities associated to each land usecategory, and c) determines the net carbon implications of the process ofland use/cover change according to the different scenarios.The options analyzed include both afforestation/reforestation, such ascommercial, bionenergy and restoration plantations, and agroforestrysystems, and forest conservation, through the sustainable management ofnative forests and forest protection.The total mitigation potential, estimated as the difference between the totallong-term carbon stock in the reference and the mitigation scenario reaches300 × 106 Mg C in the year 2012 and increases to 1,382 × 106 Mg C in 2030. The average net sequestration in the 30 year period is 46 × 106 Mg C yr-1, or 12.5 × 106 Mg C yr-1 within the period 2008 to 2012. The costs of selected mitigation options range from 0.7–3.5 Mg C-1 to 35 Mg C-1. Some options are cost effective. 相似文献