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   16271篇
  免费   1884篇
  国内免费   4篇
  2021年   189篇
  2020年   136篇
  2019年   168篇
  2018年   195篇
  2017年   188篇
  2016年   335篇
  2015年   501篇
  2014年   589篇
  2013年   734篇
  2012年   809篇
  2011年   842篇
  2010年   524篇
  2009年   521篇
  2008年   743篇
  2007年   724篇
  2006年   681篇
  2005年   658篇
  2004年   640篇
  2003年   592篇
  2002年   605篇
  2001年   438篇
  2000年   417篇
  1999年   370篇
  1998年   232篇
  1997年   200篇
  1996年   185篇
  1995年   180篇
  1994年   163篇
  1993年   194篇
  1992年   299篇
  1991年   305篇
  1990年   281篇
  1989年   239篇
  1988年   242篇
  1987年   232篇
  1986年   195篇
  1985年   221篇
  1984年   202篇
  1983年   177篇
  1982年   158篇
  1981年   163篇
  1980年   136篇
  1979年   193篇
  1978年   175篇
  1977年   140篇
  1976年   143篇
  1975年   119篇
  1974年   124篇
  1973年   138篇
  1972年   112篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
The World Society for Virology (WSV) was founded and incorporated as a nonprofit organization in the United States in 2017. WSV seeks to strengthen and support both virological research and virologists who conduct research of viruses that affect humans, other animals, plants, and other organisms. One of the objectives of WSV is to connect virologists worldwide and support collaboration. Fulfilling this objective, virologists from fourteen countries in North America, Europe, Africa, Asia, and the Middle East met on 25–27th August 2019 in Stockholm, Sweden at the Karolinska University Hospital for the first Committee Meeting of WSV. This meeting included compelling keynote and honorary speeches and a series of 18 scientific talks were given encompassing a diverse array of subjects within virology. Followed by the scientific session, a business session was held where multiple aspects and next steps of the society were discussed and charted out.  相似文献   
63.
64.
65.
This study tested whether children's eating behavior and parental feeding prompts during a laboratory test meal differ among children born at high risk (HR) or low risk (LR) for obesity and are associated with excess child weight gain. At 4 years of age, 32 HR children (mean maternal prepregnancy BMI = 30.4 kg/m2) and 29 LR children (maternal BMI = 19.6 kg/m2) consumed a test meal in which their eating behavior was assessed, including rate of caloric consumption, mouthfuls/min, and requests for food. Parental prompts for the child to eat also were measured at year 4, and child body composition was measured at ages 4 and 6 years. T‐tests, and logistic and multiple regression analyses tested study aims. Results indicated that HR and LR children did not differ in eating rate or parental feeding prompts. Greater maternal BMI, child mouthfuls of food/min, and total caloric intake/min during the test meal predicted an increased risk of being overweight or obese at age 6, whereas greater active mealtime was associated with a reduced risk of being overweight or obese. Regression analyses indicated that only mouthfuls of food/min predicted changes in BMI from 4 to 6 years, and mouthfuls of food/min and gender predicted 2‐year changes in sum of skinfolds and total body fat. Thus, a rapid eating style, characterized by increased mouthfuls of food/min, may be a behavioral marker for the development of childhood obesity.  相似文献   
66.
The progression of Swiss 3T3 fibroblasts from the quiescent state (G0) through G1 to DNA synthesis in S phase generally requires the synergistic action of two mitogens. The main aim of this study was to compare systematically the early Ca2+ and pH responses in quiescent cells to all of the pair combinations of eight mitogens (bombesin, platelet-derived growth factor, vasopressin, prostaglandin F2 alpha, epidermal growth factor, 12-O-tetradecanoyl phorbol-13-acetate, insulin, 8-bromo-cAMP) with their subsequent effects on DNA synthesis. Each of the mitogens which caused inositol phosphate accumulation (bombesin, platelet-derived growth factor, vasopressin, prostaglandin F2 alpha) also activated Ca2+- and phospholipid-dependent protein kinase (protein kinase C) and generated both the Ca2+ and pH responses, although epidermal growth factor also generated the ionic responses without causing release of inositol phosphates or activation of protein kinase C. For sequential mitogen additions the ionic signals were measured in single cells as well as in cell populations to avoid ambiguities due to heterogeneity in the responses of the cells to the various mitogens. The modulating effects of the mitogens on the [Ca2+]i responses to subsequent mitogen additions varied widely, but detailed comparisons showed that the pattern of blocking effects could not be attributed solely to the effect of the first mitogen causing either maximal breakdown of phosphatidylinositol 4,5-bisphosphate or complete depletion of the intracellular Ca2+ pool or activation of protein kinase C. From these analyses it was concluded that the requirement for two mitogens for effective DNA synthesis could not be attributed to the summation to a critical threshold of either the ionic signals or phosphatidylinositol 4,5-bisphosphate breakdown, and that these responses are insufficient by themselves to cause the cells to progress to DNA synthesis in S phase.  相似文献   
67.
Isozyme analysis of young leaf tissue was performed on progeny produced from cultured ovules resulting from crosses of seedless × seedless grapes. Two polymorphic loci, Idh and Gpi-c, were found to segregate in a simple Mendelian fashion in the populations examined. Analyses of 70 seedlings indicated that most seedlings produced by this method were zygotic. Isozyme data of 11 plants from 5 polyembryonic ovules, along with data previously reported, suggest that several mechanisms may be operative in grape that give rise to polyembryony: 1) fertilization and development of more than one cell in the embryo sac, 2) adventive embryogenesis from the zygote, or 3) embryogenic development of gametic cells in addition to the zygote in the embryo sac.Fl. Agri. Exp. Sta. Journal Series No. 9112.  相似文献   
68.
69.
70.
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