全文获取类型
收费全文 | 39948篇 |
免费 | 2591篇 |
国内免费 | 3238篇 |
专业分类
林业 | 2611篇 |
农学 | 2091篇 |
基础科学 | 1711篇 |
4705篇 | |
综合类 | 15572篇 |
农作物 | 2536篇 |
水产渔业 | 1885篇 |
畜牧兽医 | 9841篇 |
园艺 | 2334篇 |
植物保护 | 2491篇 |
出版年
2024年 | 252篇 |
2023年 | 909篇 |
2022年 | 1951篇 |
2021年 | 1853篇 |
2020年 | 1636篇 |
2019年 | 1713篇 |
2018年 | 1311篇 |
2017年 | 1772篇 |
2016年 | 1375篇 |
2015年 | 1780篇 |
2014年 | 1950篇 |
2013年 | 2448篇 |
2012年 | 3076篇 |
2011年 | 3214篇 |
2010年 | 2805篇 |
2009年 | 2677篇 |
2008年 | 2709篇 |
2007年 | 2487篇 |
2006年 | 2020篇 |
2005年 | 1743篇 |
2004年 | 1107篇 |
2003年 | 785篇 |
2002年 | 824篇 |
2001年 | 678篇 |
2000年 | 674篇 |
1999年 | 364篇 |
1998年 | 93篇 |
1997年 | 81篇 |
1996年 | 75篇 |
1995年 | 67篇 |
1994年 | 55篇 |
1993年 | 49篇 |
1992年 | 95篇 |
1991年 | 63篇 |
1990年 | 75篇 |
1989年 | 79篇 |
1988年 | 70篇 |
1987年 | 60篇 |
1986年 | 53篇 |
1985年 | 62篇 |
1984年 | 40篇 |
1983年 | 43篇 |
1982年 | 30篇 |
1980年 | 25篇 |
1979年 | 42篇 |
1977年 | 26篇 |
1974年 | 25篇 |
1973年 | 25篇 |
1972年 | 24篇 |
1970年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 881 毫秒
31.
32.
A de la Concha-Bermejillo C E Schore C A Dangler C C de Mattos C A de Mattos B I Osburn 《American journal of veterinary research》1992,53(12):2245-2250
A slot blot hybridization technique was applied for detection of bluetongue virus (BTV) in blood mononuclear cells (BMNC) obtained from cattle with experimentally induced infection. This technique lacked sensitivity to detect the viral nucleic acid directly in clinical specimens. When aliquots of mononuclear cells from these cattle were cultivated in vitro for 10 days to amplify virus titer, only 33.3% of the samples collected during viremia gave a positive signal in the slot blot hybridization format. By contrast, results for 34.3% of noncultured and 63.3% of cultured mononuclear cell samples collected during viremia were positive by immunofluorescence. The average number of infected cells, as detected by immunofluorescence in the noncultured mononuclear cell samples, was 1 to 5/300,000, and was usually > 10/300,000 in the cultured cell samples. Virus was isolated from all postinoculation blood samples obtained from 4 heifers that were seronegative at the time of inoculation, but was not isolated from any of the preinoculation samples, or from any of the postinoculation samples obtained from 2 heifers that were seropositive at the time of inoculation. When virus isolation was attempted from separated mononuclear cells in 2 heifers, 43.7% of the noncultured and 87.5% of the cultured samples had positive results. 相似文献
33.
Maria J. Perestrello de Vasconcelos Bernard P. Zeigler Lee A. Graham 《Landscape Ecology》1993,8(4):273-286
A multi-scale spatial ecological model of a wet sclerophyllous forest subject to recurrent fires is presented. The model is specified in a Discrete Event Systems framework (DEVS) (Zeigler, 1990) interfaced with a Geographic Information System (GIS), and includes the ability to simulate landscape dynamics at several levels of resolution simultaneously. This is achieved by encoding a modular hierarchical representation of the forest landscape components into a set of nested, interconnected, and spatially referenced dynamic models. The results of the landscape dynamics simulations are displayed as sequences of maps through time, illustrating the potential of this modeling methodology for dealing with complex hierarchical structures that operate at several spatial and temporal resolutions.Research work supported by Junta Nacional de Investigaçäo Científica e Tecnológica, Portugal, and the Advanced Resource Technology Program, University of Arizona, USA. 相似文献
34.
邓恩桉组培中影响继代增殖条件的研究 总被引:7,自引:1,他引:6
探讨抗寒树种邓恩桉组培快繁中影响其继代培养的因素。实验表明,继代培养以改良MS为基本培养基,随继代次数的增加逐渐减少细胞分裂素BA和生长素NAA的浓度。最初几次继代,BA的浓度为0.5 mg/L,NAA的浓度为0.2 mg/L。然后BA的浓度逐渐降低到0.1~0.3 mg/L,NAA的浓度逐渐降至0.05~0.1 mg/L,继代5~6次后,BA的浓度保持在0.1~0.3 mg/L,NAA的浓度保持在0.05~0.1 mg/L。继代周期随季节而不同,夏季为15~25 d,春秋季为20~35 d,冬季为40~50 d,芽的月增殖系数为3~5倍,满足工厂化育苗的要求。组培苗的玻璃化和遗传变异等异常现象很少,节间长度适中,有利于生根。 相似文献
35.
36.
野生青狗尾草与中国栽培谷子进行杂交,并用浸有氟特力溶液的小培养皿进行发芽试验,快速鉴别F2代的抗除草剂性能。抗性被隐性基因控制,但更确切的结果有待进一步试验。氟特力不同用药量的选择试验表明,对氟特力抗性与敏感不同的谷子品种在 0~2.4 L/hm2 的处理表现不同,抗型品种的抗性大约是敏感型抗性的5倍。为我们选育谷子抗性新品种提供了依据。 相似文献
38.
39.
40.
Techniques for in vitro production of embryos have been developed world-wide in different species, with promising results in human and ruminants. Thousands of human IVF-babies have been born during the last 20 years and thousands of in vitro -produced calves have been born since the late 1980s. With current methods for bovine in vitro fertilization, about 30–40% of in vitro -fertilized bovine oocytes develop further to the blastocyst stage and can be used for transfer. A proper evaluation of blastocyst quality remains however, an important challenge for every researcher involved in embryology and for every clinician who wants to select the best embryos for transfer. This review attempts to summarize the different methods available for estimation of blastocyst quality with a special emphasis upon differential staining. 相似文献