全文获取类型
| 收费全文 | 327595篇 |
| 免费 | 19187篇 |
| 国内免费 | 893篇 |
专业分类
| 林业 | 25084篇 |
| 农学 | 14764篇 |
| 基础科学 | 3172篇 |
| 48352篇 | |
| 综合类 | 43455篇 |
| 农作物 | 17752篇 |
| 水产渔业 | 19811篇 |
| 畜牧兽医 | 141770篇 |
| 园艺 | 6618篇 |
| 植物保护 | 26897篇 |
出版年
| 2020年 | 3339篇 |
| 2019年 | 4364篇 |
| 2018年 | 4876篇 |
| 2017年 | 5362篇 |
| 2016年 | 5587篇 |
| 2015年 | 4946篇 |
| 2014年 | 6284篇 |
| 2013年 | 17007篇 |
| 2012年 | 8595篇 |
| 2011年 | 11063篇 |
| 2010年 | 8562篇 |
| 2009年 | 8781篇 |
| 2008年 | 10215篇 |
| 2007年 | 9291篇 |
| 2006年 | 9710篇 |
| 2005年 | 8767篇 |
| 2004年 | 8562篇 |
| 2003年 | 8368篇 |
| 2002年 | 7779篇 |
| 2001年 | 9049篇 |
| 2000年 | 8646篇 |
| 1999年 | 7493篇 |
| 1998年 | 4471篇 |
| 1997年 | 4522篇 |
| 1996年 | 4229篇 |
| 1995年 | 4861篇 |
| 1994年 | 4328篇 |
| 1993年 | 3987篇 |
| 1992年 | 6074篇 |
| 1991年 | 6304篇 |
| 1990年 | 6127篇 |
| 1989年 | 6060篇 |
| 1988年 | 5439篇 |
| 1987年 | 5520篇 |
| 1986年 | 5513篇 |
| 1985年 | 5637篇 |
| 1984年 | 4975篇 |
| 1983年 | 4538篇 |
| 1982年 | 3545篇 |
| 1981年 | 3350篇 |
| 1980年 | 3282篇 |
| 1979年 | 4443篇 |
| 1978年 | 3857篇 |
| 1977年 | 3426篇 |
| 1975年 | 3195篇 |
| 1974年 | 3775篇 |
| 1973年 | 3765篇 |
| 1972年 | 3492篇 |
| 1971年 | 3330篇 |
| 1970年 | 3192篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
991.
Guidi A. Iannone G. Castigliego L. Gianfaldoni D. 《Veterinary research communications》2004,28(1):193-196
Veterinary Research Communications - 相似文献
992.
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
993.
A porcine in vitro fertilization (IVF) system and seminal quality parameters of frozen–thawed boar semen were used to assess the effectiveness of two different thawing rates of frozen boar semen, and to address the question of whether differences between fertility of ejaculates could be predicted in a limited field trial. In the first experiment, two thawing procedures were analysed (37°C, 30 s; 50°C, 12 s) and no differences in sperm quality were found. However, when the procedure was 50°C, 12 s the IVF results showed a higher number of sperm per penetrated oocyte and a near 10 points higher rate of pronuclear formation. In the second experiment, the fertility results obtained in the limited field trial show to be efficient enough for application in a commercial use, especially for three of the employed boars (fertility ≥80%). In this limited study, the conventional seminal parameters are not accurate enough to discriminate good and bad boars in relation to fertility. On the contrary, parameters of in vitro penetrability are more precise to predict subsequent fertilities. As conclusion, the IVF fertilization system seems to be a good tool to evaluate the quality of frozen–thawed boar semen previous to its commercial way, to verify the bank semen storage quality and a good way to assay new sperm freezing procedures, as it is the more precise evaluating method in estimating the potential fertilizing ability. 相似文献
994.
995.
Über die Winterfestigkeit des BlutlausparasitenAphelinus mali Hald. im niederelbischen Obstbaugebiet
W. Speyer 《Journal of pest science》1942,18(2):19-21
Ohne Zusammenfassung 相似文献
996.
997.
998.
999.
1000.