全文获取类型
收费全文 | 531篇 |
免费 | 63篇 |
专业分类
林业 | 21篇 |
农学 | 5篇 |
基础科学 | 3篇 |
40篇 | |
综合类 | 169篇 |
农作物 | 9篇 |
水产渔业 | 45篇 |
畜牧兽医 | 255篇 |
园艺 | 13篇 |
植物保护 | 34篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 13篇 |
2013年 | 13篇 |
2012年 | 62篇 |
2011年 | 64篇 |
2010年 | 24篇 |
2009年 | 16篇 |
2008年 | 41篇 |
2007年 | 42篇 |
2006年 | 50篇 |
2005年 | 46篇 |
2004年 | 29篇 |
2003年 | 37篇 |
2002年 | 41篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有594条查询结果,搜索用时 15 毫秒
61.
62.
Miller G 《Science (New York, N.Y.)》2005,308(5730):1853-1855
63.
Miller G 《Science (New York, N.Y.)》2007,318(5858):1856-1858
64.
Miller G 《Science (New York, N.Y.)》2003,300(5628):2020-2022
65.
66.
Murphy WJ Larkin DM Everts-van der Wind A Bourque G Tesler G Auvil L Beever JE Chowdhary BP Galibert F Gatzke L Hitte C Meyers SN Milan D Ostrander EA Pape G Parker HG Raudsepp T Rogatcheva MB Schook LB Skow LC Welge M Womack JE O'brien SJ Pevzner PA Lewin HA 《Science (New York, N.Y.)》2005,309(5734):613-617
The genome organizations of eight phylogenetically distinct species from five mammalian orders were compared in order to address fundamental questions relating to mammalian chromosomal evolution. Rates of chromosome evolution within mammalian orders were found to increase since the Cretaceous-Tertiary boundary. Nearly 20% of chromosome breakpoint regions were reused during mammalian evolution; these reuse sites are also enriched for centromeres. Analysis of gene content in and around evolutionary breakpoint regions revealed increased gene density relative to the genome-wide average. We found that segmental duplications populate the majority of primate-specific breakpoints and often flank inverted chromosome segments, implicating their role in chromosomal rearrangement. 相似文献
67.
Many volcanic arcs display fast seismic shear-wave velocities parallel to the strike of the trench. This pattern of anisotropy is inconsistent with simple models of corner flow in the mantle wedge. Although several models, including slab rollback, oblique subduction, and deformation of water-rich olivine, have been proposed to explain trench-parallel anisotropy, none of these mechanisms are consistent with all observations. Instead, small-scale convection driven by the foundering of dense arc lower crust provides an explanation for the trench-parallel anisotropy, even in settings with orthogonal convergence and no slab rollback. 相似文献
68.
Herd CD Blinova A Simkus DN Huang Y Tarozo R Alexander CM Gyngard F Nittler LR Cody GD Fogel ML Kebukawa Y Kilcoyne AL Hilts RW Slater GF Glavin DP Dworkin JP Callahan MP Elsila JE De Gregorio BT Stroud RM 《Science (New York, N.Y.)》2011,332(6035):1304-1307
The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration. At least some molecules of prebiotic importance formed during the alteration. 相似文献
69.
Ruiz-Matute AI Brokl M Sanz ML Soria AC Côté GL Collins ME Rastall RA 《Journal of agricultural and food chemistry》2011,59(8):3693-3700
The selective fermentation by human gut bacteria of gluco-oligosaccharides obtained from the reaction between the glucosyl group of sucrose and cellobiose, catalyzed by dextransucrases (DSR) from Leuconostoc mesenteroides , has been evaluated. Oligosaccharides were fractionated according to their molecular weight, and their effect on the growth of different bacterial groups was studied. To determine the structure (position and configuration of glycosidic linkages)-function relationship, their properties were compared to those of DSR maltose acceptor products (DSRMal) and of recognized prebiotic carbohydrates (fructo-oligosaccharides, FOS). Cellobiose acceptor products (DSRCel) showed bifidogenic properties similar to those of FOS. However, no significant differences related to molecular weight or isomeric configurations were found for DSRCel and DSRMal products. 相似文献
70.
Evaluating simultaneous impacts of three anthropogenic effects on a floodplain-dwelling marsupial Antechinus flavipes 总被引:1,自引:0,他引:1
Regulation of river flows has altered floodplain ecosystems around the world. Floods are less frequent, which leads to reduction of favourable environmental conditions for many terrestrial and aquatic organisms adapted to natural flooding regimes. In Australia, the Murray River floodplains have been subjected to decline in inundations, to extensive logging and to removal of fallen timber. The yellow-footed antechinus (Antechinus flavipes) is the only small, native, ground-dwelling/semi-arboreal mammal on most floodplains of south-eastern Australia, yet the effects of floods on its population dynamics largely are unknown. Here, we found positive effects of proximity to flooding, higher woodloads and of abundance of large, hollow-bearing trees on antechinus numbers. Mean trapping rates of antechinuses were lowest in 2003 following a 3-year period with no inundation, higher in 2004 following the first breeding season during a small, controlled flood in 2003, and higher again in 2005, following a small, controlled flood in 2004. In 2004 and 2005, trapping rates declined with distance from floodwaters. This study provides evidence for the benefits of using management flows to inundate floodplains, conserving large trees and ensuring high woodloads in floodplains for sustaining populations of the yellow-footed antechinus. 相似文献