全文获取类型
收费全文 | 167219篇 |
免费 | 9523篇 |
国内免费 | 99篇 |
专业分类
林业 | 6883篇 |
农学 | 5708篇 |
基础科学 | 1064篇 |
21627篇 | |
综合类 | 24851篇 |
农作物 | 6127篇 |
水产渔业 | 8809篇 |
畜牧兽医 | 88472篇 |
园艺 | 2279篇 |
植物保护 | 11021篇 |
出版年
2020年 | 1363篇 |
2019年 | 1650篇 |
2018年 | 2707篇 |
2017年 | 2959篇 |
2016年 | 2761篇 |
2015年 | 2334篇 |
2014年 | 2881篇 |
2013年 | 6801篇 |
2012年 | 5117篇 |
2011年 | 6161篇 |
2010年 | 4180篇 |
2009年 | 4174篇 |
2008年 | 6058篇 |
2007年 | 5866篇 |
2006年 | 5462篇 |
2005年 | 5324篇 |
2004年 | 5085篇 |
2003年 | 5085篇 |
2002年 | 4541篇 |
2001年 | 5808篇 |
2000年 | 5723篇 |
1999年 | 4574篇 |
1998年 | 1830篇 |
1997年 | 1775篇 |
1996年 | 1645篇 |
1995年 | 1983篇 |
1994年 | 1659篇 |
1993年 | 1668篇 |
1992年 | 3466篇 |
1991年 | 3617篇 |
1990年 | 3605篇 |
1989年 | 3576篇 |
1988年 | 3268篇 |
1987年 | 3295篇 |
1986年 | 3228篇 |
1985年 | 3045篇 |
1984年 | 2501篇 |
1983年 | 2190篇 |
1982年 | 1461篇 |
1979年 | 2090篇 |
1978年 | 1667篇 |
1977年 | 1462篇 |
1976年 | 1403篇 |
1975年 | 1497篇 |
1974年 | 1755篇 |
1973年 | 1819篇 |
1972年 | 1792篇 |
1971年 | 1550篇 |
1970年 | 1581篇 |
1969年 | 1505篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
A biostratigraphic survey of 57 Late Ordovician marine shelly invertebrates from the Climacograptus manitoulinensis zone of eastern Canada supports suggestions that throughout the Early Phanerozoic benthic marine speciations occurred preferentially in marginal marine environments. The species subsequently spread onto the craton. There is no obvious positive correlation between the times of first appearance of new associations or novel communities along the continental margin and the first appearance on the craton of the species making up these communities. Taxonomic similarities between marine communities that occupied both marginal and cratonic regimes may reflect a more static local ecology than the evolutionary dynamics of a piecemeal species-by-species reassembly. 相似文献
952.
953.
Tanzer ML 《Science (New York, N.Y.)》1985,227(4684):289-290
954.
955.
956.
957.
958.
D T Cappucci D C Johnson M Brugh T M Smith C F Jackson J E Pearson D A Senne 《Avian diseases》1985,29(4):1195-1200
Avian influenza virus (A/Chicken/Pennsylvania/83; H5N2) was recovered from the yolk, albumen, and shell surface of eggs obtained from naturally infected chicken flocks in Pennsylvania and Virginia. These findings represent the first reported isolation of avian influenza virus from the internal contents of eggs from naturally infected flocks. The need for adequate safeguards to prevent spread of the virus during commercial movement of table and hatching eggs, cracked and "checked" eggs, and egg flats and other materials is emphasized. 相似文献
959.
Bussanich MN Rootman J Kumi C Gudauskas G 《The Canadian veterinary journal. La revue veterinaire canadienne》1985,26(9):263-266
The ocular absorption, elimination and toxicity of 12.5 mg of methotrexate in 0.5 cc administered subconjunctivally was studied in the dog. The purpose of this study was to establish ocular pharmacokinetics for treatment of intraocular tumours in dogs. Drug levels were measured in ocular compartments, and serum at 1,2,4,6,8 and 12 hours respectively. Tumoricidal concentrations of the drug were attained in the anterior chambers of the injected eyes up to and including six hours postinjection. Consistent signs of toxicity were anorexia, vomiting, weight loss and leukopenia. Local ocular toxicity following subconjunctival injection was minimal conjunctival hyperemia lasting up to 48 hours. 相似文献
960.
Smith DL Palmer SJ Hulland TJ McSherry BJ Blackwell TE 《The Canadian veterinary journal. La revue veterinaire canadienne》1985,26(12):385-386,387-390
Steers and bulls under feedlot conditions and on an apparently adequate ration developed transitory signs of diarrhea and unthriftiness. One animal became recumbent. Sick and clinically normal animals in the group had elevated serum creatine kinase and aspartate aminotransferase enzyme values and degenerative changes in muscle fibers on biopsy. Feed analysis was carried out and the animals were monitored over several weeks by means of muscle biopsy and serum enzyme analysis as well as by postmortem examination at slaughter. Subclinical myopathy was found in several animals and was thought to be related to low vitamin E content in the high moisture corn ration. 相似文献