首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   80088篇
  免费   3921篇
  国内免费   55篇
林业   3800篇
农学   2428篇
基础科学   417篇
  8536篇
综合类   16097篇
农作物   3242篇
水产渔业   3684篇
畜牧兽医   40059篇
园艺   1012篇
植物保护   4789篇
  2018年   926篇
  2017年   1009篇
  2016年   941篇
  2015年   831篇
  2014年   1037篇
  2013年   2745篇
  2012年   1827篇
  2011年   2316篇
  2010年   1471篇
  2009年   1388篇
  2008年   2216篇
  2007年   2288篇
  2006年   2098篇
  2005年   2030篇
  2004年   1958篇
  2003年   1977篇
  2002年   1860篇
  2001年   2266篇
  2000年   2268篇
  1999年   1898篇
  1998年   752篇
  1997年   742篇
  1995年   846篇
  1993年   723篇
  1992年   1532篇
  1991年   1591篇
  1990年   1702篇
  1989年   1682篇
  1988年   1557篇
  1987年   1496篇
  1986年   1551篇
  1985年   1550篇
  1984年   1275篇
  1983年   1168篇
  1982年   796篇
  1981年   745篇
  1979年   1260篇
  1978年   999篇
  1977年   862篇
  1976年   812篇
  1975年   932篇
  1974年   1224篇
  1973年   1257篇
  1972年   1274篇
  1971年   1197篇
  1970年   1114篇
  1969年   1011篇
  1968年   874篇
  1967年   917篇
  1966年   842篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
95.
96.
97.
Adipose tissue in various stages of fish oil-induced yellow fat disease in the rat had the same acid phosphatase and 5-nucleotidase activity pattern as similar stages of the disorder in mink and pig. A weak acid phosphatase and 5-nucleotidase activity was seen in interstitial lipofuscin-laden macrophages in "stage M" yellow fat disease without fat cell degeneration. Activity of these macrophagic enzymes increased when there was fat cell degeneration ("stage S" and "stage E" yellow fat disease). This different phosphatase activity in the same cell type may result from phagocytosis of substrates with variable digestibility. Macrophages directly surrounding affected fat cells in steatitis areas ("stage S" and "stage E") had strong acid phosphatase and 5-nucleotidase activity. As in the pig, increased 5-nucleotidase activity was found in affected fat cells, which probably indicates plasma membrane damage. Increased nonspecific esterase activity occurred around affected fat cells. Only a small part of this esterase activity originated from inflammatory cells. This indicates that an increase of esterase activity in degenerating adipose tissue may be an endogeneous process in this tissue.  相似文献   
98.
99.
Based on the time that symptoms of blackleg become evident in the field and the various ways of inoculation, it is concluded that the spread of symptom expression is due to the depth at which the bacteria penetrate into the interior of the tubers. Moreover, it is demonstrated that it is not the closed lenticels which prevent penetration, but the absence of a waterfilm in the intercellular spaces of the tuber tissue.  相似文献   
100.
Marine sponge-derived endozoic fungi have been gaining increasing importance as promising sources of numerous and unique bioactive compounds. This study investigates the phytochemical profile and biological activities of the ethyl acetate extract of Penicillium chrysogenum derived from Cliona sp. sponge. Thirty-six compounds were tentatively identified from P. chrysogenum ethyl acetate extract along with the kojic acid (KA) isolation. The UPLC-ESI-MS/MS positive ionization mode was used to analyze and identify the extract constituents while 1D and 2D NMR spectroscopy were used for kojic acid (KA) structure confirmation. The antimicrobial, antioxidant, and cytotoxic activities were assessed in vitro. Both the extract and kojic acid showed potent antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa with MIC 250 ± 0.82 µg/mL. Interestingly, the extract showed strong antifungal activity against Candida albicans and Cryptococcus neoformans with MIC 93.75 ± 0.55 and 19.53 ± 0.48 µg/mL, respectively. Furthermore, KA showed the same potency against Fusarium oxysporum and Cryptococcus neoformans with MIC 39.06 ± 0.85 and 39.06 ± 0.98 µg/mL, respectively. Ultimately, KA showed strong antioxidant activity with IC50 33.7 ± 0.8 µg/mL. Moreover, the extract and KA showed strong cytotoxic activity against colon carcinoma (with IC50 22.6 ± 0.8 and 23.4 ± 1.4 µg/mL, respectively) and human larynx carcinoma (with equal IC50 30.8 ± 1.3 and ± 2.1 µg/mL, respectively), respectively. The current study represents the first insights into the phytochemical profile and biological properties of P. chrysoenum ethyl acetate extract, which could be a promising source of valuable secondary metabolites with potent biological potentials.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号