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   14090篇
  免费   1942篇
  国内免费   7篇
  2021年   129篇
  2019年   136篇
  2018年   150篇
  2017年   143篇
  2016年   251篇
  2015年   308篇
  2014年   414篇
  2013年   543篇
  2012年   648篇
  2011年   592篇
  2010年   438篇
  2009年   368篇
  2008年   562篇
  2007年   569篇
  2006年   485篇
  2005年   546篇
  2004年   487篇
  2003年   486篇
  2002年   447篇
  2001年   458篇
  2000年   448篇
  1999年   397篇
  1998年   176篇
  1997年   167篇
  1996年   168篇
  1995年   153篇
  1994年   185篇
  1993年   150篇
  1992年   317篇
  1991年   304篇
  1990年   298篇
  1989年   287篇
  1988年   308篇
  1987年   281篇
  1986年   246篇
  1985年   259篇
  1984年   235篇
  1983年   195篇
  1982年   150篇
  1981年   148篇
  1980年   147篇
  1979年   197篇
  1978年   200篇
  1977年   147篇
  1976年   164篇
  1975年   176篇
  1974年   210篇
  1973年   193篇
  1972年   153篇
  1970年   146篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
Casein: a milk protein with diverse biologic consequences   总被引:1,自引:0,他引:1  
The consequences of bovine milk consumption are diverse, some of which are potentially deleterious. Although certain cultures shun cow's milk or milk-based products, Western societies consume large quantities of cow's milk. Although there are stronger similarities between bovine whey proteins and human whey proteins, the quantity and nature of casein in cow's milk differ markedly from human milk. We propose that the consequences of diets based on bovine casein should be more closely evaluated and certainly expanded beyond the simplistic approach of growth. What is good for the goose may be good for the gander, but what is good for the cow could be harmful to the human.  相似文献   
4.
The efficient aquisition of nutrients from leaves by insect herbivores increases their nutrient assimilation rates and overall fitness. Caterpillars of the gypsy moth (Lymantria dispar L.) have high protein assimilation efficiencies (PAE) from the immature leaves of trees such as red oak (Quercus rubra) and sugar maple (Acer saccharum) (71–81%) but significantly lower PAE from their mature leaves (45–52%). By contrast to this pattern, both PAE and carbohydrate assimilation efficiencies (CAE) remain high for L. dispar larvae on the mature leaves of poplar (Populus alba × Populus tremula) grown in greenhouse conditions. The present study tests two alternative hypotheses: (i) outdoor environmental stresses cause decreased nutrient assimilation efficiencies from mature poplar leaves and (ii) nutrients in the mature leaves of trees in the poplar family (Salicaceae) remain readily available for L. dispar larvae. When poplar trees are grown in ambient outdoor conditions, PAE and CAE remain high (approximately 75% and 78%, respectively) in L. dispar larvae, in contrast to the first hypothesis. When larvae feed on the mature leaves of species in the Salicaceae [aspen (Populus tremuloides), cottonwood (Populus deltoides), willow (Salix nigra) and poplar], PAE and CAE also remain high (68–76% and 72–92%, respectively), consistent with the second hypothesis. Larval growth rates are strongly associated with protein assimilation rates, and more strongly associated with protein assimilation rates than with carbohydrate assimilation rates. It is concluded that tree species in the Salicaceae are relatively high‐quality host plants for L. dispar larvae, in part, because nutrients in their mature leaves remain readily available.  相似文献   
5.
6.
The hinge in IgA1 and the linker in endoglucanase A (CenA) are quite similar. The IgA1 hinge is 18 amino acids long and contains only proline, threonine and serine. The linker in CenA is 27 amino acids long and contains only proline, threonine and a single serine. IgA proteases from Neisseria gonorrhoeae cleave Pro-Ser and Pro-Thr bonds within the IgA1 hinge sequence, but they do not attack CenA. When the linker sequence of CenA is replaced with the hinge sequence of IgA1, the hybrid polypeptide is susceptible to the N. gonorrhoeae proteases. It is cleaved within the hinge sequence at the same sites as IgA1.  相似文献   
7.
8.
9.
A field study was carried out for 6 wks to assess, from both an efficiency and economic perspective, the effect of individual and integrated success of feeding and topical applications of two formulations of Bacillus thuringiensis var. israelensis (Bti) in controlling house fly (Musca domestica L.) larvae and adults in poultry houses. There was no significant difference between the 1 g and 2 g L?1 spray applications of Bti. In the absence of spray applications, no significant differences in larval mortalities were observed between the 250 mg and 500 mg kg?1 feed applications. The percentage mortality of larvae accomplished as a result of using a combination of 250 mg kg?1Bti feed and 2 g L?1 spray applications was equivalent to that obtained as a result of combining 500 mg kg?1Bti and 1g L?1 spray applications. Treatment with Bti caused significant reductions in the emergence (up to 74%) of house fly adults compared to the control. The fact that the emergence of adult house flies was affected by Bti treatments implies that Bti has sublethal effects on house fly larvae. The cost–benefit analysis (expressed in terms of mortality of larvae growing) indicated that the most effective combination for house fly larvae and adult house fly emergence control was the 500 mg kg?1 of feed and 2 g L?1 spray application combination that resulted in 67% larval mortality and a 74% decrease in adult house fly emergence. This study presents commercial users with various alternatives for possible combinations of the two Bti formulations.  相似文献   
10.
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