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   282篇
  免费   16篇
林业   8篇
农学   1篇
  28篇
综合类   53篇
农作物   2篇
水产渔业   9篇
畜牧兽医   191篇
园艺   2篇
植物保护   4篇
  2021年   4篇
  2020年   5篇
  2019年   8篇
  2018年   5篇
  2017年   4篇
  2016年   4篇
  2015年   5篇
  2014年   3篇
  2013年   21篇
  2012年   9篇
  2011年   13篇
  2010年   9篇
  2009年   8篇
  2008年   15篇
  2007年   7篇
  2006年   10篇
  2005年   19篇
  2004年   18篇
  2003年   17篇
  2002年   14篇
  2001年   10篇
  2000年   6篇
  1999年   5篇
  1997年   2篇
  1996年   3篇
  1995年   4篇
  1993年   5篇
  1992年   8篇
  1990年   3篇
  1985年   5篇
  1984年   4篇
  1980年   3篇
  1979年   2篇
  1972年   2篇
  1971年   4篇
  1969年   4篇
  1968年   3篇
  1967年   2篇
  1966年   1篇
  1954年   1篇
  1938年   1篇
  1934年   1篇
  1926年   1篇
  1919年   1篇
  1917年   3篇
  1915年   1篇
  1900年   1篇
  1896年   1篇
  1893年   1篇
  1880年   1篇
排序方式: 共有298条查询结果,搜索用时 15 毫秒
31.
Azima tetracantha L. (needle bush; bee sting bush; Salvadoraceae) is used as a food and for various herbal medicines in Africa, India, and Madagascar, but there is very little information on the secondary metabolites in this species. High concentrations of N-methoxy-3-indolylmethyl-glucosinolate, a common glucosinolate of Brassica crops such as Brussels sprouts and broccoli, were found in the roots and seeds of A. tetracantha. Lower concentrations were detected in the stems and young leaves. The roots also contained another indole glucosinolate that was provisionally identified, from MS data and comparison with indole glucosinolate standards, as N-hydroxy-3-indolymethyl-glucosinolate. The roots, stems, and leaves contained neoascorbigen (the condensation product of N-methoxy-indole-3-carbinol and ascorbic acid). The seeds of A. tetracantha contained a complex mixture of 26 flavonoids predominantly as glycosides and acyl-glycosides, with traces of aglycones. The core aglycones of these flavonoids were identified as quercetin, isorhamnetin (3'-O-methylquercetin), rhamnetin (7-O-methylquercetin), and rhamnazin (7, 3'-di-O-methylquercetin). No flavonoids or anthocyanins were detected in other tissues, and procyanidins were undetectable. The dimeric piperidine alkaloids azimine, azcarpine, and carpaine were found in all tissues of A. tetracantha.  相似文献   
32.
33.
A pseudohermaphrodite possesses gonads of one sex, but with external genitalia of the opposite sex. Although cases of male pseudohermaphroditism have been published, there is no report of a monorchid male pseudohermaphrodite. This Case Report documents a 12-year-old monorchid male pseudohermaphrodite displaying stallion-like behaviour, with an elevated serum oestrone sulphate concentration confirming the presence of functional testicular tissue. A complete resolution of all behavioural signs occurred after laparoscopic-assisted castration under general anaesthesia, along with a drop in serum oestrone sulphate concentrations to <0.01 ng/ml and no response in serum testosterone concentration following administration of hCG.  相似文献   
34.
35.
A semi-portable flow-through cloud water monitoring system was developed for measurements of cloud water conductivity and pH in remote sites lacking AC line power. This system was tested from May to September on Camels Hump mountain, Vermont. High temporal resolution data from seven cloud events were collected during the 1991 growing season. Mean cloud water conductivity and pH for all events was 467 μmhos cm?1 and 3.2, respectively. The highest conductivity was 997 (μmhos cm?1 recorded on 19 September 1991 and the lowest pH of 2.9 was recorded during several events over the summer. Data from this system may be used to achieve a better understanding of the chemical environment in areas experiencing forest decline.  相似文献   
36.
The (7)Be, (22)Na, (26)Al, (44)Ti, (46)SC, (48)V (51)Cr, (54)Mn, (56)Co, (57)Co, (57)CO, (40)K, (238)U, and (232)Th were measured in lunar fines and portions of three rocks. Major production of cosmogenic radionuclides is due to solar protons, thus their concentrations are far different than those in meteorites. Surface exposures of the rocks and fines are long compared with the 0.74 million year half-life of (26)Al. Lunar fines show substantially higher concentrations of low energy reaction products. The ratios of thorium to uranium are extremely constant at 3.8, which indicates very little geochemical differentiation and are in good agreement with a common nucleosynthesis for lunar and earth materials.  相似文献   
37.
The regulated activation of numerous sets of genes in multiple chromosomal locations is a hallmark of cellular differentiation in both eukaryotes and prokaryotes. Certain species of bacteria that experience complex developmental cycles are especially attractive as systems in which to study the mechanisms of this kind of gene regulation because they are highly amenable to both biochemical and genetic approaches. Bacillus subtilis, which undergoes extensive cellular differentiation when it sporulates, is one such system. Many new methods are now available in this Gram-positive species for identifying, manipulating, and studying the regulation of genes involved in spore formation, including the use of transposable genetic elements that create gene fusions in vivo as an automatic consequence of insertions into genes.  相似文献   
38.
The depletion of hypolimnetic DO and the upper depth boundary of anoxia for four different years (1978, 1979, 1980 and 1981), and the accumulation of sulfide for a single year (1981), are documented for ionically enriched hypereutrophic Onondaga Lake, NY, USA. The depletion rate, represented as the areal hypolimnetic oxygen deficit (AHOD, g m?2 day?1), was extremely high (1.2–2.7 g m?2 day?1), The large differences in the rate within individual years and from year to year were largely a result of differences in attendant vertical mixing (parameterized as the hypolimnetic heating rate). The entire hypolimnion (depth interval from 11 to 20 m) was without O2 by late June of all 4 yr; anoxia was observed above the hypolimnion on some occasions when secondary stratification occurred. Sulfide accumulated progressively in the hypolimnion in 1981 following the onset of anoxia to a volume weighted concentration of I1 mg L?1. The ionic discharge from an adjoining alkali manufacturer exacerbated the problem of limited O2 resources of the hypolimnion by: (1) decreasing vertical mixing, (2) prolonging the duration of stratification, (3) causing abbreviated turnovers, and (4) encouraging increased rates of phytoplankton settling.  相似文献   
39.
女人三国     
4.0、3.0和2.0,她们之间本不应该有交点,但因为对网球的痴迷程度都是7.0,于是这三个在各自圈子里红得发烫的人,走到了一起。  相似文献   
40.
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