全文获取类型
收费全文 | 84139篇 |
免费 | 4640篇 |
国内免费 | 317篇 |
专业分类
林业 | 4005篇 |
农学 | 2822篇 |
基础科学 | 520篇 |
10710篇 | |
综合类 | 15023篇 |
农作物 | 3284篇 |
水产渔业 | 3882篇 |
畜牧兽医 | 42405篇 |
园艺 | 970篇 |
植物保护 | 5475篇 |
出版年
2019年 | 857篇 |
2018年 | 1408篇 |
2017年 | 1499篇 |
2016年 | 1343篇 |
2015年 | 1169篇 |
2014年 | 1444篇 |
2013年 | 3371篇 |
2012年 | 2584篇 |
2011年 | 2972篇 |
2010年 | 1994篇 |
2009年 | 2097篇 |
2008年 | 2906篇 |
2007年 | 2780篇 |
2006年 | 2604篇 |
2005年 | 2357篇 |
2004年 | 2257篇 |
2003年 | 2233篇 |
2002年 | 2050篇 |
2001年 | 2584篇 |
2000年 | 2530篇 |
1999年 | 2012篇 |
1998年 | 800篇 |
1997年 | 844篇 |
1996年 | 778篇 |
1995年 | 860篇 |
1994年 | 776篇 |
1993年 | 735篇 |
1992年 | 1490篇 |
1991年 | 1620篇 |
1990年 | 1503篇 |
1989年 | 1542篇 |
1988年 | 1439篇 |
1987年 | 1434篇 |
1986年 | 1462篇 |
1985年 | 1409篇 |
1984年 | 1123篇 |
1983年 | 1012篇 |
1979年 | 1145篇 |
1978年 | 920篇 |
1977年 | 789篇 |
1976年 | 785篇 |
1975年 | 857篇 |
1974年 | 1099篇 |
1973年 | 1032篇 |
1972年 | 1065篇 |
1971年 | 961篇 |
1970年 | 931篇 |
1969年 | 942篇 |
1968年 | 773篇 |
1967年 | 828篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
2 groups of 20 cocks each were selected at random from non-dwarf White Leghorn (28 weeks post-hatch) and dwarf Krishna-J (38 weeks post-hatch) genotypes. The treated groups comprised 10 White Leghorn and 10 Krishna-J cocks. The remaining birds served as controls. 8 weeks prior to furazolidone treatment, semen was collected from both control groups at regular 4-day intervals, for 4 weeks. Cocks of the treated groups of both genotypes were administered furazolidone (0.14 g/bird/day) for 7 consecutive days. Semen was collected from all cocks at regular 4-day intervals for 4 weeks. Semen from the cocks of the same group was pooled. The pooled ejaculate volume and sperm density did not differ significantly in the 2 genotypes. The semen output as well as sperm density increased along with progressive attainment of sexual maturity. Furazolidone treatment caused significant reduction in semen volume as well as sperm concentration in either genotype. 相似文献
53.
54.
Abstract. Experiments were started in 1967 to investigate the effects of soil mixing on fen peat soil. Peaty topsoil was mixed with mineral subsoil to a maximum depth of 80 cm at two sites, one with a clay subsoil, the other sand. Mixing was done on a commercial scale with a range of implements. After initial increases, yields of arable crops on both mixed soils were subsequently similar to those on unmixed soil. Residual herbicide activity was enhanced on mixed soils, and evidence of peat conservation was obtained at one site. The practice has not been taken up commercially because of the high capital cost of mixing and lack of serious problems which had been predicted following peat wastage. 相似文献
55.
56.
57.
Jewett FB 《Science (New York, N.Y.)》1940,92(2393):412-415
58.
59.
E Hinsch JG Boehm S Groeger F Mueller-Schloesser K-D Hinsch 《Reproduction in domestic animals》2003,38(2):155-160
Outer dense fibres (ODF) are important substructures of mammalian sperm tails that are involved in the regulation of sperm motility. In this study, we investigated the identity of several sodium dodecyl sulphate (SDS)‐insoluble ODF proteins. Bovine ODF were purified by separating sperm heads and tails using ultrasound and Percoll® density gradient centrifugation. Sperm flagella were treated with the detergent cetyltrimethylammonium bromide (CTAB). CTAB‐insoluble material, which reportedly represents the ODF fraction, was collected, and electron microscopy confirmed a highly purified ODF fraction. We found after solubilization of this fraction with SDS that high amounts of insoluble material were retained after centrifugation. SDS‐insoluble material was collected and quantitatively dissolved in 8 M urea. SDS‐gel electrophoresis in the presence of urea revealed polypeptides with apparent molecular masses of approximately 25, 43, and 50 kDa. Subsequent immunoblotting with anti‐cytokeratin antibodies detected two urea‐soluble, SDS‐insoluble proteins with apparent molecular masses of 45 and 66 kDa. The 45‐kDa protein was identified as cytokeratin 19. An antibody reacting with a palette of cytokeratins (CK 1–18 and CK 20), KL1, was the only antibody that reacted with the 66‐kDa polypeptide. We conclude that sperm ODF fractions contain at least one each of type I and type II intermediate filaments. As keratins and intermediate filaments are described as rope‐like structures, we suggest that these intermediate filaments play an important structural or tension‐bearing role in sperm flagella. 相似文献
60.