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   71468篇
  免费   6881篇
  国内免费   30篇
  78379篇
  2023年   280篇
  2022年   593篇
  2021年   1162篇
  2020年   723篇
  2019年   933篇
  2018年   1147篇
  2017年   1008篇
  2016年   1717篇
  2015年   2897篇
  2014年   3190篇
  2013年   3777篇
  2012年   4955篇
  2011年   4843篇
  2010年   3100篇
  2009年   2795篇
  2008年   4013篇
  2007年   4101篇
  2006年   3900篇
  2005年   3736篇
  2004年   3646篇
  2003年   3376篇
  2002年   3350篇
  2001年   997篇
  2000年   808篇
  1999年   961篇
  1998年   1029篇
  1997年   726篇
  1996年   637篇
  1995年   587篇
  1994年   605篇
  1993年   604篇
  1992年   718篇
  1991年   593篇
  1990年   599篇
  1989年   593篇
  1988年   538篇
  1987年   509篇
  1986年   487篇
  1985年   470篇
  1984年   542篇
  1983年   515篇
  1982年   550篇
  1981年   495篇
  1980年   486篇
  1979年   374篇
  1978年   383篇
  1977年   338篇
  1976年   320篇
  1974年   298篇
  1973年   261篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A method for the immobilization of lipoxygenase (LOX) in an alginate-silicate gel matrix was developed. In this method, a mixture of calcium alginate beads and LOX in borate buffer are dispersed into a hexane solution of tetramethoxy-ortho-silicate (TMOS). Hydrolysis of the TMOS gives products that permeate and co-polymerize with the alginate gel to form a colloid within the beads that entraps the LOX. Optimum reaction conditions for sol-gel entrapment of LOX are at pH 9.0 in 0.2M borate buffer. The composite gel, after isolation and vacuum drying, had excellent protein retention that has good enzyme activity and stability at room temperature. The activity of the entrapped LOX was less than the activity of the free enzyme. However, the activity of the immobilized LOX can be restored by the addition of borate buffer and glycerol, or borate buffer saturated with an organic solvent. In contrast to the free enzyme in solution, which loses its activity in less than one day, sol-gel entrapped LOX retains its activity at ambient temperature for at least 25 days and can be recycled. This report demonstrates that the sol-gel entrapment method for immobilizing LOX can be useful in developing a process for the oxidation of polyunsaturated fatty acids.  相似文献   
72.
73.
Thomas MacDonald 《CMAJ》1967,96(10):615-616
  相似文献   
74.
75.
Techniques are described for capturing and marking redtail monkeys (Cercopithecus ascanius). An air-powered darting rifle and syringe darts loaded with a Ketamine-Rompun mixture were used for capture. Ketamine was used for maintaining anesthesia. Monkeys were darted 48 times and captured 27 times. In 24 of the 27 captures, the monkeys were released unharmed. Adult males were marked with radiotransmitters attached to collars of nylon webbing. Females received nylon webbing collars with colorcoded plastic washers for identification.  相似文献   
76.
77.
78.
Summary This contribution deals with problems associated with the culture of a thermotolerant methylotrophic Bacillus sp. The results reported clearly demonstrate why conventional enrichment/isolation procedures have, in the past, failed to allow such microbes to assert themselves. The catastrophic effect of carbon substrate (methanol) exhaustion on such cultures is clearly evidenced, but the effects of other nutrient exhaustion or limitations are demonstrated to be markedly less stringent. The failure of such cultures to complete the sporulation process when growing on methanol has important consequences with respect to their survival characteristics.  相似文献   
79.
This study examined the effect of light on relaxation associated with flotation restricted environmental stimulation therapy (REST), as measured by plasma cortisol, mean arterial pressure, and psychometric parameters. Twenty-one subjects were paired by baseline cortisol levels into two groups: one experiencing flotation REST in the presence of light (REST-L) and one experiencing flotation REST in the absence of light (REST-D). Subjects were 15 male and 6 female students aged 22–28 in normal health who had not experienced REST. Repeated flotation REST (8 sessions) either with light or without light was associated with a decrease in plasma cortisol and a decrease in mean arterial pressure, with no differences in effectiveness between groups. The psychometric assessment of mood, using the POMS scale, before and after sessions 1 and 8 revealed mood state improvement in both REST-L and REST-D groups. These data suggest that the presence of light did not compromise the flotation REST experience, as evidenced by the lack of difference between REST-L and REST-D groups.  相似文献   
80.
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