全文获取类型
收费全文 | 42634篇 |
免费 | 465篇 |
国内免费 | 588篇 |
专业分类
安全科学 | 1366篇 |
废物处理 | 1913篇 |
环保管理 | 5550篇 |
综合类 | 6677篇 |
基础理论 | 11328篇 |
环境理论 | 21篇 |
污染及防治 | 11425篇 |
评价与监测 | 2833篇 |
社会与环境 | 2294篇 |
灾害及防治 | 280篇 |
出版年
2023年 | 183篇 |
2022年 | 408篇 |
2021年 | 415篇 |
2020年 | 311篇 |
2019年 | 384篇 |
2018年 | 645篇 |
2017年 | 637篇 |
2016年 | 1000篇 |
2015年 | 791篇 |
2014年 | 1204篇 |
2013年 | 3513篇 |
2012年 | 1451篇 |
2011年 | 1920篇 |
2010年 | 1574篇 |
2009年 | 1661篇 |
2008年 | 1957篇 |
2007年 | 2032篇 |
2006年 | 1760篇 |
2005年 | 1473篇 |
2004年 | 1407篇 |
2003年 | 1496篇 |
2002年 | 1353篇 |
2001年 | 1708篇 |
2000年 | 1216篇 |
1999年 | 729篇 |
1998年 | 523篇 |
1997年 | 515篇 |
1996年 | 551篇 |
1995年 | 614篇 |
1994年 | 610篇 |
1993年 | 520篇 |
1992年 | 519篇 |
1991年 | 480篇 |
1990年 | 533篇 |
1989年 | 462篇 |
1988年 | 419篇 |
1987年 | 394篇 |
1986年 | 335篇 |
1985年 | 356篇 |
1984年 | 394篇 |
1983年 | 383篇 |
1982年 | 370篇 |
1981年 | 352篇 |
1980年 | 285篇 |
1979年 | 321篇 |
1978年 | 269篇 |
1977年 | 202篇 |
1975年 | 215篇 |
1972年 | 213篇 |
1971年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
651.
This paper investigates the current treatment of environmental issues by two companies within the large made-to-order sector. Fifty questionnaires were issued to the design team of each company to assess current practice in the integration of environmental issues with design activities, awareness of environmental issues, awareness of existing environmental design tools and the preferred format for a potential clean design tool. 相似文献
652.
Vanessa M. Barnabei MD PhD David A. Krantz James N. Macri John W. Larsen Jr 《黑龙江环境通报》1995,15(12):1131-1134
We have applied our multimarker approach of maternal serum alpha-fetoprotein (AFP) and free-beta human chorionic gonadotropin (hCG) for Down syndrome screening to multiple gestations to assess its efficacy for improved detection of twin and triplet pregnancies. This study matched 225 cases of twin pregnancy and 39 cases of triplet pregnancy each with ten singleton pregnancies based on gestational week, race, time to receive sample, time of year of sample, and geographical area. The ratios of the MOM for each group at the tenth, 50th, and 90th percentiles were compared by the Wilcoxon test. Risks for twins were calculated using Bayes' rule, the age-related incidence of twins, and the levels of AFP and free-beta hCG. The tenth, 50th, and 90th percentiles of free-beta hCG MOMs in twin and triplet cases were 0.85, 1.99, and 4.51, and 1.38, 2.78, and 4.07, respectively. For AFP, the MOMs at these percentiles were 1.26, 1.91, and 2.99, and 2.02, 2.68, and 5.30, respectively. The twin and triplet distributions for each marker were statistically significantly different from the singleton distributions (P<0.0001) and from each other (P=0.0012). At a twin risk cut-off of 1 in 50, 77.4 per cent of all twin gestations can be detected in a second-trimester AFP and free-beta hCG screening protocol with 5.1 per cent of singleton pregnancies falsely identified as at risk for twins. Our dual marker protocol for mid-trimester pregnancy screening combining AFP and free-beta hCG can identify over 77 per cent of twin pregnancies in women less than 35 years of age. This benefit may contribute to an improved outcome of pregnancy by early detection of multiple gestation. 相似文献
653.
654.
655.
656.
长江,嘉陵江重庆城区段二维水质对流扩散数学模型 总被引:6,自引:0,他引:6
对二水质对流扩散数学模型的有限差分解作了较详细的叙述,同时对距离步长,时间步长计算,网络内水深,流速,横向扩散系数的求取也作了简要介绍。 相似文献
657.
658.
659.
660.