全文获取类型
收费全文 | 11905篇 |
免费 | 113篇 |
国内免费 | 89篇 |
专业分类
安全科学 | 338篇 |
废物处理 | 444篇 |
环保管理 | 1641篇 |
综合类 | 2119篇 |
基础理论 | 3144篇 |
环境理论 | 7篇 |
污染及防治 | 2969篇 |
评价与监测 | 735篇 |
社会与环境 | 625篇 |
灾害及防治 | 85篇 |
出版年
2023年 | 66篇 |
2022年 | 103篇 |
2021年 | 99篇 |
2020年 | 81篇 |
2019年 | 93篇 |
2018年 | 164篇 |
2017年 | 144篇 |
2016年 | 223篇 |
2015年 | 195篇 |
2014年 | 269篇 |
2013年 | 880篇 |
2012年 | 356篇 |
2011年 | 497篇 |
2010年 | 410篇 |
2009年 | 479篇 |
2008年 | 523篇 |
2007年 | 519篇 |
2006年 | 456篇 |
2005年 | 420篇 |
2004年 | 352篇 |
2003年 | 368篇 |
2002年 | 351篇 |
2001年 | 472篇 |
2000年 | 346篇 |
1999年 | 210篇 |
1998年 | 132篇 |
1997年 | 157篇 |
1996年 | 163篇 |
1995年 | 191篇 |
1994年 | 194篇 |
1993年 | 159篇 |
1992年 | 132篇 |
1991年 | 169篇 |
1990年 | 163篇 |
1989年 | 157篇 |
1988年 | 115篇 |
1987年 | 114篇 |
1986年 | 118篇 |
1985年 | 91篇 |
1984年 | 108篇 |
1983年 | 111篇 |
1982年 | 118篇 |
1981年 | 108篇 |
1980年 | 96篇 |
1979年 | 112篇 |
1978年 | 73篇 |
1977年 | 76篇 |
1975年 | 76篇 |
1973年 | 72篇 |
1967年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Peter R. Brown Neil I. Huth Peter B. Banks Grant R. Singleton 《Agriculture, ecosystems & environment》2007,120(2-4):405-415
Developing a relationship between pest abundance and damage to crops is essential for the calculation of economic injury levels (EIL) leading to informed management decisions. The crop modelling framework, APSIM, was used to simulate the impact of mouse damage on yield loss on wheat where a long-term dataset on the density of mice was available (1983–2003). The model was calibrated using results from field trials where wheat plants were hand clipped to imitate mouse damage. The grazing effect of mice was estimated using the population density, daily intake per mouse and the proportion of wheat grain and plant tissue in the diet to determine yield loss. The mean yield loss caused by mice was 12.4% (±5.4S.E.; range −0.5 to 96%). There were 7/21 years when yield loss was >5%. A damage/abundance relationship was constructed and a sigmoidal curve explained 97% of variation when accounting for different trajectories of mouse densities from sowing to harvest. The majority of damage occurred around emergence of the crop when mouse densities were >100 mice ha−1. This is the first time that field data on mouse density and a crop simulation model have been combined to estimate yield loss. The model examines the efficacy of baiting and how to estimate EILs. Because the broadscale application of zinc phosphide is cheap and effective, the EIL is very low (<1% yield loss). The APSIM model is highly flexible and could be used for other vertebrate pests in a range of crops or pastures to develop density/damage relationships and to assist with management. 相似文献
143.
In angiosperms, archesporial cells in the anther primordium undergo meiosis to form haploid pollen, the sole occupants of anther sacs. Anther sacs are held together by a matrix of parenchyma cells, the connective tissue. Cells of the connective tissue are not known to differentiate. We report the differentiation of parenchyma cells in the connective tissue of two Gordonia species into pollen-like structures (described as pseudopollen), which migrate into the anther sacs before dehiscence. Pollen and pseudopollen were distinguishable by morphology and staining. Pollen were tricolpate to spherical while pseudopollen were less rigid and transparent with a ribbed surface. Both types were different in size, shape, staining and surface architecture. The ratio of the number of pseudopollen to pollen was 1:3. During ontogeny in the connective tissue, neither cell division nor tetrad formation was observed and hence pseudopollen were presumed to be diploid. Only normal pollen germinated on a germination medium. Fixed preparations in time seemed to indicate that pseudopollen migrate from the connective tissue into the anther sac. 相似文献
144.
145.
Mechanics and Morphology of Silk Drawn from Anesthetized Spiders 总被引:1,自引:0,他引:1
CO2 and N2 anesthetized Nephila spiders produced dragline silk with mechanical properties that differed from control silk as a function of time under anesthesia.
Silk from CO2 spiders had a significantly lower breaking strain and breaking energy, significantly higher initial modulus, and marginally
lower breaking stress. At the onset of anesthesia the silk diameter became highly variable. During deep anesthesia silk either
became thinner or retained cross-section but fibrillated.
Received: 26 August 1999 / Accepted in revised form: 22 December 1999 相似文献
146.
147.
148.
149.
150.