全文获取类型
收费全文 | 99277篇 |
免费 | 6080篇 |
国内免费 | 44篇 |
专业分类
林业 | 4230篇 |
农学 | 3137篇 |
基础科学 | 577篇 |
12572篇 | |
综合类 | 17248篇 |
农作物 | 4196篇 |
水产渔业 | 5196篇 |
畜牧兽医 | 50177篇 |
园艺 | 1420篇 |
植物保护 | 6648篇 |
出版年
2021年 | 804篇 |
2020年 | 899篇 |
2019年 | 1052篇 |
2018年 | 1749篇 |
2017年 | 1862篇 |
2016年 | 1781篇 |
2015年 | 1527篇 |
2014年 | 1816篇 |
2013年 | 4147篇 |
2012年 | 3479篇 |
2011年 | 3941篇 |
2010年 | 2470篇 |
2009年 | 2345篇 |
2008年 | 3710篇 |
2007年 | 3578篇 |
2006年 | 3269篇 |
2005年 | 3145篇 |
2004年 | 2961篇 |
2003年 | 2944篇 |
2002年 | 2697篇 |
2001年 | 3130篇 |
2000年 | 2954篇 |
1999年 | 2443篇 |
1998年 | 1048篇 |
1997年 | 945篇 |
1996年 | 840篇 |
1995年 | 1016篇 |
1994年 | 906篇 |
1993年 | 890篇 |
1992年 | 1879篇 |
1991年 | 1872篇 |
1990年 | 1806篇 |
1989年 | 1862篇 |
1988年 | 1618篇 |
1987年 | 1721篇 |
1986年 | 1787篇 |
1985年 | 1709篇 |
1984年 | 1354篇 |
1983年 | 1196篇 |
1982年 | 863篇 |
1979年 | 1141篇 |
1978年 | 920篇 |
1977年 | 794篇 |
1975年 | 823篇 |
1974年 | 1026篇 |
1973年 | 1059篇 |
1972年 | 1017篇 |
1971年 | 970篇 |
1970年 | 914篇 |
1969年 | 834篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Margaret C. McEntee DVM Donald E. Thrall DVM PhD 《Veterinary radiology & ultrasound》2001,42(3):221-225
Twenty two dogs with an infiltrative lipoma had computed tomographic (CT) images acquired to evaluate the extent of local disease. Ten dogs had undergone at least one cytoreductive surgical procedure (range = 1-3; median = 2) prior to imaging. Twenty dogs had measurable disease on CT images; 2 dogs had diffuse disease at a previous surgical site that could not be measured. Tumor volume (n = 20) ranged from 20 to 5,632 cm3 (median = 345 cm3; mean = 996 cm3). None of the dogs had evidence of bone involvement on the CT images; 2 of the 22 dogs had tumors that did not come into direct contact with osseous structures. All dogs with measurable disease had evidence of a fat opacity mass with variable degrees of muscle infiltration. Eleven of 22 dogs were given intravenous contrast medium prior to image acquisition and there was not evidence of enhancement of the infiltrative lipoma in any dog. Based on CT images, tumors were classified as well-defined in 9 dogs, moderately well-defined in 4, not well-defined in 3 and a mix of well-defined and not well-defined in 6 dogs. Tumors tended to be less well-defined in regions where the infiltrative lipoma interdigitated with normal body fat. It appears CT imaging allows adequate discrimination of tumor with the caveat that differentiation of normal fat from infiltrative lipoma can be problematic. 相似文献
42.
43.
44.
Praveen C. Verma Debasis Chakrabarty Satya Narayan Jena Devesh K. Mishra Pradhyumna K. Singh Samir V. Sawant Rakesh Tuli 《Industrial Crops and Products》2009,29(2-3):581-589
Vanilla is a large genus of about 110 species in the orchid family (Orchidaceae), including the species Vanilla planifolia from which commercial vanilla flavoring is derived. Since most species of vanilla are considered rare and endangered there is an urgent need to conserve them through genetic analysis and propagation/conservation studies on this crop.The present study investigated the genetic diversity among nine leafy- and leaf-less Vanilla species employing 30 decamer RAPD primers and 10 ISSR primers. The species under study were diverse and displayed a range of variability (0–66% and 0–81% for RAPD and ISSR, respectively). A total of 154 RAPD polymorphic markers (83.24%, h = 0.378) and 93 ISSR polymorphic markers (86.11%, h = 0.363) were used to generate a genetic similarity matrix followed by the cluster analysis. Specific groupings were revealed by each cluster analysis with slight variation between two different markers. Among the nine species studied, V. planifolia, Vanilla aphylla and Vanilla tahitensis revealed very low level of variation within their collections, thus indicating a narrow genetic base. The large genetic distance of Vanilla andamanica from other species suggests its different origin. A close genetic affinity was observed between the pairs V. planifolia, V. tahitensis and Vanilla albida, V. aphylla. These are the first comparative results for RAPD and ISSR reporting inter-relationship among nine cultivated, wild and hybrid Vanilla species. 相似文献
45.
46.
47.
48.
49.
50.