全文获取类型
收费全文 | 19236篇 |
免费 | 118篇 |
国内免费 | 93篇 |
专业分类
安全科学 | 283篇 |
废物处理 | 1216篇 |
环保管理 | 2417篇 |
综合类 | 2116篇 |
基础理论 | 5688篇 |
环境理论 | 2篇 |
污染及防治 | 4464篇 |
评价与监测 | 1682篇 |
社会与环境 | 1531篇 |
灾害及防治 | 48篇 |
出版年
2022年 | 100篇 |
2021年 | 76篇 |
2020年 | 65篇 |
2019年 | 75篇 |
2018年 | 1584篇 |
2017年 | 1479篇 |
2016年 | 1392篇 |
2015年 | 287篇 |
2014年 | 253篇 |
2013年 | 752篇 |
2012年 | 740篇 |
2011年 | 1745篇 |
2010年 | 1037篇 |
2009年 | 961篇 |
2008年 | 1319篇 |
2007年 | 1664篇 |
2006年 | 425篇 |
2005年 | 387篇 |
2004年 | 355篇 |
2003年 | 435篇 |
2002年 | 422篇 |
2001年 | 516篇 |
2000年 | 342篇 |
1999年 | 195篇 |
1998年 | 147篇 |
1997年 | 134篇 |
1996年 | 138篇 |
1995年 | 162篇 |
1994年 | 125篇 |
1993年 | 102篇 |
1992年 | 123篇 |
1991年 | 119篇 |
1990年 | 131篇 |
1989年 | 133篇 |
1988年 | 96篇 |
1987年 | 87篇 |
1986年 | 65篇 |
1985年 | 90篇 |
1984年 | 100篇 |
1983年 | 94篇 |
1982年 | 82篇 |
1981年 | 73篇 |
1980年 | 61篇 |
1979年 | 68篇 |
1977年 | 53篇 |
1976年 | 48篇 |
1975年 | 53篇 |
1974年 | 51篇 |
1973年 | 53篇 |
1970年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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
132.
133.
134.
The Mormon cricket, Anabrus simplex, is one of just a few species of katydids (or bushcrickets, Orthoptera: Tettigoniidae) that, like migratory locusts, appear
to have solitary and migratory morphs. Using radio telemetry we studied movements of individuals of two morphs of this flightless
species. Individuals within each migratory band had similar rates of movements along similar directional headings whereas
solitary individuals moved little and showed little evidence of directionality in movement. Our results also add to other
recent radio-telemetry studies showing that flightless insects of 1–2 g in mass can be tracked successfully using these methods.
Received: 28 February 2000 / Accepted in revised form: 19 June 2000 相似文献
135.
Salomao O. Bandeira Rui Paula e Silva Jose Paula Adriano Macia Lars Hernroth Almeida T. Guissamulo Domingos Z.Bergman 《Ambio-人类环境杂志》2002,31(7):606-609
本文概述了莫桑比克包括渔业在内的海洋生物学研究的发展情况.莫桑比克的海岸线约为3000km,海洋的生物资源在莫桑比克的社会中起着重要的作用,主要是作为人们的蛋白质来源以及收入和出口创汇的来源. 相似文献
136.
137.
138.
139.
140.
Bosch J 《Die Naturwissenschaften》2002,89(12):575-578
Female midwife toads (genus Alytes) emit highly variable reciprocal calls of unclear function prior to and during courtship. In some species, female-female competition, expressed as physical fighting, has been reported. Males of Majorcan midwife toads (Alytes muletensis) show phonotactic response to female calls, and females of Iberian midwife toads (Alytes cisternasii) respond differently according to the male call characteristics. In this study, I test the hypothesis of female-female acoustic competition as an additional function of female reciprocal calls. Playback tests indicate that female calls are not clearly involved in female acoustic competition in the Iberian midwife toad, therefore female calls could be directed at males rather than towards competitive females. 相似文献