全文获取类型
收费全文 | 21643篇 |
免费 | 223篇 |
国内免费 | 207篇 |
专业分类
安全科学 | 636篇 |
废物处理 | 980篇 |
环保管理 | 2862篇 |
综合类 | 2880篇 |
基础理论 | 5498篇 |
环境理论 | 8篇 |
污染及防治 | 6451篇 |
评价与监测 | 1524篇 |
社会与环境 | 1089篇 |
灾害及防治 | 145篇 |
出版年
2023年 | 125篇 |
2022年 | 271篇 |
2021年 | 287篇 |
2020年 | 166篇 |
2019年 | 199篇 |
2018年 | 384篇 |
2017年 | 371篇 |
2016年 | 589篇 |
2015年 | 460篇 |
2014年 | 711篇 |
2013年 | 1880篇 |
2012年 | 834篇 |
2011年 | 1032篇 |
2010年 | 776篇 |
2009年 | 876篇 |
2008年 | 1038篇 |
2007年 | 1060篇 |
2006年 | 942篇 |
2005年 | 779篇 |
2004年 | 772篇 |
2003年 | 703篇 |
2002年 | 705篇 |
2001年 | 801篇 |
2000年 | 578篇 |
1999年 | 329篇 |
1998年 | 252篇 |
1997年 | 233篇 |
1996年 | 284篇 |
1995年 | 282篇 |
1994年 | 272篇 |
1993年 | 235篇 |
1992年 | 210篇 |
1991年 | 193篇 |
1990年 | 214篇 |
1989年 | 192篇 |
1988年 | 185篇 |
1987年 | 172篇 |
1986年 | 152篇 |
1985年 | 151篇 |
1984年 | 179篇 |
1983年 | 180篇 |
1982年 | 168篇 |
1981年 | 171篇 |
1980年 | 137篇 |
1979年 | 161篇 |
1978年 | 111篇 |
1977年 | 102篇 |
1975年 | 96篇 |
1973年 | 94篇 |
1972年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
331.
Observations have been made on the locomotory behaviour and swimming performances of the Norway lobster, Nephrops norvegicus (L.), fitted with an acoustic transmitter ventrally under the cephalothorax. The walking behaviour of adult males (44 mm carapace length) appeared to be unaffected, but the tag caused significant reductions in certain measures of tail-flip swimming performance such as swimming speed and endurance. Flume-tank experiments in low water currents suggested that the transmitter would increase hydrodynamic drag during swimming by 9 to 32%, depending on lobster size. Given the weight and dimensions of the acoustic transmitters currently available, it is considered advisable to confine acoustic tracking studies to relatively large N. norvegicus.Correspondence to: C. J. Chapman 相似文献
332.
Summary We tested the proposition that among humans (1) differences in lactational duration result in differences in costs of reproduction even under rich nutritional conditions; and (2) elimination of factors postulated to favor male-biased parental care will be reflected in elimination or reversal of sex-biased care. To do so, we examined the relationship between lactational duration and fertility among Hutterites, a communal-living human population in which the levels of nutritional resources and fertility are high, breast-feeding is the norm, contraceptive use is limited and the collective social and economic system results in low resource variance among individuals. We demonstrate that even under good nutritional conditions, duration of nursing was a significant predictor of the length of time to next pregnancy and that nursing continued to suppress fertility after the resumption of menses. Moreover, we find that daughters were nursed longer than sons, leading to a longer interval to next pregnancy. We examine this uncommon, but not unique, finding of female-biased human parental care in the light of Hutterite social structure, and we explore the consistency of this finding with the most applicable models of parental investment.
Correspondence to: S.W. Margulis 相似文献
333.
334.
335.
Duffy JC 《Disasters》1978,2(2-3):159-162
336.
337.
338.
A dynamic programming code was formulated for the purpose of assigning sampling frequencies throughout a regulatory water quality monitoring network in order to optimize the statistical performance of the network while operating within a fixed budgetary constraint. The statistical objective is to achieve the greatest possible station to station uniformity in confidence interval widths about annual geometric means of the measured water quality variables and to keep the average confidence width reasonably small. The objective function is the sum (over several selected variables and all stations) of the normalized positive deviations of the predicted confidence interval widths from preselected design confidence interval widths. The code was designed to account for the effects of deterministic seasonal variation and serial correlation of the water quality observations by incorporating the results of the time series analysis of historical quality data. The economic constraint ensures that the annual operating cost of the system, including direct costs of travel and laboratory analysis, will not exceed the allowable budget. As an example situation, the dynamic programming code was used to assign sampling frequencies to the nine stations in Illinois from which historical quality data had been obtained and analyzed. Using five design quality constituents and representative travel and laboratory costs, an “optimal” design was produced. The optimal design achieved a 10% improvement in uniformity (standard deviation) of confidence interval widths when compared to a more traditional design based on the same budget and using identical sampling frequencies at every station. 相似文献
339.
Various suggested definitions of the term “traceability” are discussed from the standpoint of proposed adoption and use of the concept by the International Organization of Legal Metrology. 相似文献
340.