全文获取类型
收费全文 | 29407篇 |
免费 | 2827篇 |
国内免费 | 2992篇 |
出版年
2024年 | 27篇 |
2023年 | 401篇 |
2022年 | 523篇 |
2021年 | 1432篇 |
2020年 | 1047篇 |
2019年 | 1335篇 |
2018年 | 1218篇 |
2017年 | 896篇 |
2016年 | 1194篇 |
2015年 | 1901篇 |
2014年 | 2149篇 |
2013年 | 2318篇 |
2012年 | 2826篇 |
2011年 | 2555篇 |
2010年 | 1721篇 |
2009年 | 1539篇 |
2008年 | 1734篇 |
2007年 | 1564篇 |
2006年 | 1365篇 |
2005年 | 1147篇 |
2004年 | 1005篇 |
2003年 | 890篇 |
2002年 | 765篇 |
2001年 | 511篇 |
2000年 | 441篇 |
1999年 | 394篇 |
1998年 | 286篇 |
1997年 | 227篇 |
1996年 | 220篇 |
1995年 | 166篇 |
1994年 | 188篇 |
1993年 | 118篇 |
1992年 | 176篇 |
1991年 | 127篇 |
1990年 | 97篇 |
1989年 | 94篇 |
1988年 | 71篇 |
1987年 | 95篇 |
1986年 | 74篇 |
1985年 | 61篇 |
1984年 | 56篇 |
1983年 | 50篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 24篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1973年 | 13篇 |
1972年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Plant and Soil - To investigate the effects of polystyrene microplastics (PS-beads) on the soil properties, photosynthesis of Flowering Chinese cabbage, the rhizosphere microbial community and... 相似文献
22.
Wanwisa Dejnirattisai Daming Zhou Helen M. Ginn Helen M.E. Duyvesteyn Piyada Supasa James Brett Case Yuguang Zhao Thomas S. Walter Alexander J. Mentzer Chang Liu Beibei Wang Guido C. Paesen Jose Slon-Campos César López-Camacho Natasha M. Kafai Adam L. Bailey Rita E. Chen Baoling Ying Gavin R. Screaton 《Cell》2021,184(8):2183-2200.e22
23.
24.
25.
Industrial aquaculture wastewater contains large quantities of suspended particles that can be easily broken down physically. Introduction of macro-bio-filters, such as bivalve filter feeders, may offer the potential for treatment of fine suspended matter in industrial aquaculture wastewater. In this study, we employed two kinds of bivalve filter feeders, the Pacific oyster Crassostrea gigas and the blue mussel Mytilus galloprovincialis, to deposit suspended solids from marine fish aquaculture wastewater in flow-through systems. Results showed that the biodeposition rate of suspended particles by C. gigas (shell height: 8.67±0.99 cm) and M. galloprovincialis (shell height: 4.43±0.98 cm) was 77.84±7.77 and 6.37±0.67 mg ind−1•d−1, respectively. The total solid suspension (TSS) deposition rates of oyster and mussel treatments were 3.73±0.27 and 2.76±0.20 times higher than that of the control treatment without bivalves, respectively. The TSS deposition rates of bivalve treatments were significantly higher than the natural sedimentation rate of the control treatment (P<0.001). Furthermore, organic matter and C, N in the sediments of bivalve treatments were significantly lower than those in the sediments of the control (P<0.05). It was suggested that the filter feeders C. gigas and M. galloprovincialis had considerable potential to filter and accelerate the deposition of suspended particles from industrial aquaculture wastewater, and simultaneously yield value-added biological products. 相似文献
26.
The functioning of the vertebrate eye depends on its absolute size, which is presumably adapted to specific needs. Eye size variation in lidless and spectacled colubrid snakes was investigated, including 839 specimens belonging to 49 genera, 66 species and subspecies. Variations of adult eye diameters (EDs) in both absolute and relative terms between species were correlated with parameters reflecting behavioral ecology. In absolute terms, eye of arboreal species was larger than in terrestrial and semiaquatic species. For diurnal species, EDs of terrestrial species do not differ from semiaquatic species; for nocturnal species the ED of terrestrial species is larger than fossorial species but not different from semiaquatic species. In relative terms, ED did not differ significantly by habitat for diurnal species. Although the ED of terrestrial species is larger than fossorial species there were no differences for nocturnal species between semiaquatic and fossorial snakes. In contrast to other vertebrates studied to date, colubrid EDs in absolute and relative terms are larger in diurnal than in nocturnal species. These observations suggest that among colubrid snakes, eye size variation reflects adaptation to specific habitats, foraging strategies and daily activities, independently of phylogeny. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc. 相似文献
27.
拟似然非线性模型中的置信域:几何法 总被引:2,自引:0,他引:2
对拟似然非线性模型在欧氏内积实间建立了修改的Bates&Watts几何结构,基于此几何结构,导出了参数和子集系数的与统计曲率有关的三种近似置信域,进一步推广和发展了Hamilton et al.(1982)。Hamilton(1986)和Wei(1994,1998)等人的相应结果。 相似文献
28.
29.
30.
Homeobox gene database (HomeoDB), a manually curated database of homeobox genes and their classification, has been well received since its release in 2008. Here, we report HomeoDB2, an expansion and improvement of the original database that provides greater functionality for the user. HomeoDB2 includes all homeobox loci from 10 animal genomes (human, mouse, chicken, frog, zebrafish, amphioxus, nematode, fruitfly, beetle, honeybee) plus tools for downloading sequences, comparing between species and BLAST searching. HomeoDB2 provides a resource for studying the dynamics of homeobox gene evolution, and is freely accessible at http://homeodb.zoo.ox.ac.uk 相似文献