全文获取类型
收费全文 | 21162篇 |
免费 | 183篇 |
国内免费 | 385篇 |
专业分类
安全科学 | 490篇 |
废物处理 | 918篇 |
环保管理 | 2370篇 |
综合类 | 4402篇 |
基础理论 | 5043篇 |
环境理论 | 6篇 |
污染及防治 | 5218篇 |
评价与监测 | 1574篇 |
社会与环境 | 1593篇 |
灾害及防治 | 116篇 |
出版年
2022年 | 246篇 |
2021年 | 198篇 |
2020年 | 135篇 |
2019年 | 187篇 |
2018年 | 324篇 |
2017年 | 344篇 |
2016年 | 481篇 |
2015年 | 366篇 |
2014年 | 611篇 |
2013年 | 1615篇 |
2012年 | 680篇 |
2011年 | 903篇 |
2010年 | 731篇 |
2009年 | 807篇 |
2008年 | 905篇 |
2007年 | 909篇 |
2006年 | 796篇 |
2005年 | 723篇 |
2004年 | 692篇 |
2003年 | 681篇 |
2002年 | 655篇 |
2001年 | 868篇 |
2000年 | 552篇 |
1999年 | 354篇 |
1998年 | 217篇 |
1997年 | 232篇 |
1996年 | 264篇 |
1995年 | 297篇 |
1994年 | 257篇 |
1993年 | 209篇 |
1992年 | 230篇 |
1991年 | 245篇 |
1990年 | 233篇 |
1989年 | 207篇 |
1988年 | 218篇 |
1987年 | 163篇 |
1986年 | 174篇 |
1985年 | 187篇 |
1984年 | 180篇 |
1983年 | 166篇 |
1982年 | 171篇 |
1981年 | 179篇 |
1980年 | 126篇 |
1979年 | 136篇 |
1978年 | 130篇 |
1976年 | 123篇 |
1974年 | 134篇 |
1973年 | 119篇 |
1972年 | 135篇 |
1967年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
401.
Cooperative prey retrieval in the monomorphic ant Formica schaufussi is carried out by workers that perform functionally distinct roles which persist only for the duration of a single retrieval event. A forager (scout) that locates prey too large to retrieve individually organizes cooperative prey transport by recruiting nestmates (recruits) to assist in retrieval. The scout and recruit roles appear to be determined by whether a worker activates recruitment or is recruited from the nest. Scouts organize recruitment and play a key role in maintaining the cohesion of the retrieval group. If a scout that has initiated group transport is experimentally removed, the recruited workers composing the retrieval group typically abandon the prey and cooperative foraging is terminated. In this context, recruits are unable to function as scouts and reorganize group transport. Individuals marked as recruits in one prey retrieval, however, can switch and act as scouts in subsequent retrievals. Because the roles of individuals persist within but not between retrieval events, the specialization involved in cooperative prey retrieval cannot easily be explained as a response associated with age-related or genetic predispositions. This transient division-of-labor, in which individual roles may persist only for the duration of a single group action, represents a novel type of short-term individual specialization. 相似文献
402.
R.H. Field S. Benke K. Bdonyi R.B. Bradbury 《Agriculture, ecosystems & environment》2007,120(2-4):399-404
Bird use of conservation tillage-established (CT—seedbed preparation without soil inversion) crops was assessed at two adjacent sites in western Hungary, in comparison with conventionally established (mouldboard ploughed—P) fields. Bird abundance was assessed in a typical rotation of spring-sown maize and winter wheat in three consecutive winters. In the first winter, several species and the guild of seed-eating passerines were significantly more abundant on CT established plots, in both crop types. In the second winter, only starlings were more abundant on CT plots. In the third winter, only skylarks favoured CT over P plots. In combination with agri-environment scheme measures designed to provide resources for biodiversity, conservation tillage could play a role in softening the impact of agriculture on farmland birds in Hungary and elsewhere in Eastern Europe, in addition to its potential for reducing soil erosion and diffuse pollution. 相似文献
403.
404.
Flavonoid wing pigments increase attractiveness of female common blue (Polyommatus icarus) butterflies to mate-searching males 总被引:1,自引:0,他引:1
Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval host plants and allocate these UV-absorbing pigments to the wings. In field experiments
using dummies constructed from female butterflies, mate-searching males inspected flavonoid-rich dummies more intensively
than those with little or no flavonoids. Flavonoid content as signalled by UV-wing pattern may indicate ontogenetically determined
female quality or enhance detectability to males.
Received: 21 March 2000 / Accepted in revised form: 17 May 2000 相似文献
405.
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
406.
407.
408.
409.
410.