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   263355篇
  免费   24774篇
  国内免费   262篇
  2018年   2872篇
  2017年   2801篇
  2016年   3810篇
  2015年   4286篇
  2014年   5281篇
  2013年   7353篇
  2012年   8198篇
  2011年   8895篇
  2010年   6023篇
  2009年   5406篇
  2008年   7699篇
  2007年   7851篇
  2006年   7400篇
  2005年   7143篇
  2004年   7043篇
  2003年   6832篇
  2002年   6641篇
  2001年   12474篇
  2000年   12488篇
  1999年   9576篇
  1998年   2899篇
  1997年   2961篇
  1996年   2879篇
  1995年   2679篇
  1994年   2621篇
  1993年   2503篇
  1992年   7544篇
  1991年   7339篇
  1990年   7416篇
  1989年   7157篇
  1988年   6659篇
  1987年   6289篇
  1986年   5580篇
  1985年   5912篇
  1984年   4689篇
  1983年   4068篇
  1982年   2830篇
  1981年   2671篇
  1980年   2453篇
  1979年   4342篇
  1978年   3330篇
  1977年   3070篇
  1976年   2997篇
  1975年   3434篇
  1974年   3660篇
  1973年   3708篇
  1972年   3220篇
  1971年   3001篇
  1970年   2658篇
  1969年   2419篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Fedorov  D. A.  Frolova  M. Yu.  Krasovskaya  I. E.  Kuleva  N. V. 《Biophysics》2019,64(5):808-811
Biophysics - Abstract—The goal of the present study was to investigate the molecular mechanisms that underlie heart and skeletal muscle damage in male Wistar rats weighing 200–250 g in...  相似文献   
992.
993.
Interventions are needed to protect the health of children who live with smokers. We pilot-tested a real-time intervention for promoting behavior change in homes that reduces second hand tobacco smoke (SHS) levels. The intervention uses a monitor and feedback system to provide immediate auditory and visual signals triggered at defined thresholds of fine particle concentration. Dynamic graphs of real-time particle levels are also shown on a computer screen. We experimentally evaluated the system, field-tested it in homes with smokers, and conducted focus groups to obtain general opinions. Laboratory tests of the monitor demonstrated SHS sensitivity, stability, precision equivalent to at least 1 µg/m3, and low noise. A linear relationship (R2 = 0.98) was observed between the monitor and average SHS mass concentrations up to 150 µg/m3. Focus groups and interviews with intervention participants showed in-home use to be acceptable and feasible. The intervention was evaluated in 3 homes with combined baseline and intervention periods lasting 9 to 15 full days. Two families modified their behavior by opening windows or doors, smoking outdoors, or smoking less. We observed evidence of lower SHS levels in these homes. The remaining household voiced reluctance to changing their smoking activity and did not exhibit lower SHS levels in main smoking areas or clear behavior change; however, family members expressed receptivity to smoking outdoors. This study established the feasibility of the real-time intervention, laying the groundwork for controlled trials with larger sample sizes. Visual and auditory cues may prompt family members to take immediate action to reduce SHS levels. Dynamic graphs of SHS levels may help families make decisions about specific mitigation approaches.  相似文献   
994.
The amino acid composition of cell walls and surface proteins, isolated from virulent (M+) and avirulent (M-) streptococcal strains (group A, type 29) has been determined by the method of E. H. Beachey et al. The kinetics of the lysis and proteolysis of streptococcal cell walls with muramidase and protease obtained from Actinomyces levoris and streptolysin has been studied. The constants describing the progress rates of these processes has been determined; their values in case of both lysis and proteolysis are higher in virulent strains than in avirulent ones.  相似文献   
995.
Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low-level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature.  相似文献   
996.
997.
Custom prefabrication of free flaps provides an unlimited variety of applications, since flaps can be created with expendable tissues and without restriction to naturally occurring vascular territories. These principles also can be used to customize flaps that could not be completed by conventional means. We report a case of scalp reconstruction using a random-pattern abdominal flap in which a radial artery fascial flap was induced to serve as the vascular carrier. In addition to providing durable scalp coverage, the prefabricated free flap enabled salvage of an abdominal flap that would otherwise have been aborted after intermediate transfer to the forearm.  相似文献   
998.
999.
1000.
Journal of Ichthyology - The paper considers the effect of the Sea of Azov salinization on the food supply to anchovy Engraulis encrasicolus maeoticus as the level of salinity was rising from 12.7...  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