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   16230篇
  免费   1632篇
  国内免费   2篇
  2023年   45篇
  2022年   40篇
  2021年   270篇
  2020年   157篇
  2019年   238篇
  2018年   294篇
  2017年   248篇
  2016年   521篇
  2015年   814篇
  2014年   856篇
  2013年   1040篇
  2012年   1345篇
  2011年   1196篇
  2010年   771篇
  2009年   752篇
  2008年   945篇
  2007年   981篇
  2006年   903篇
  2005年   884篇
  2004年   832篇
  2003年   830篇
  2002年   796篇
  2001年   196篇
  2000年   134篇
  1999年   191篇
  1998年   200篇
  1997年   141篇
  1996年   116篇
  1995年   138篇
  1994年   127篇
  1993年   120篇
  1992年   129篇
  1991年   106篇
  1990年   112篇
  1989年   106篇
  1988年   82篇
  1987年   70篇
  1986年   81篇
  1985年   86篇
  1984年   105篇
  1983年   64篇
  1982年   87篇
  1981年   69篇
  1980年   82篇
  1979年   52篇
  1977年   46篇
  1976年   34篇
  1975年   39篇
  1974年   50篇
  1973年   39篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
AimThe aim of our paper was to explore expressions of life choices and life chances (aspects of agency within structures) related to power and experiences of health among early unemployed adolescent young men during the transition period to adulthood. These expressions of agency within structure were interpreted in the light of Cockerham’s Health Lifestyles Theory. Furthermore, social constructions of masculinities were addressed in our analysis.MethodsRepeated interviews with ten young men in a cohort of school leavers were analyzed with qualitative content analysis.ConclusionsQualitative research could contribute to develop the understanding of the agency within structure relationships. Future studies need to pay attention to experiences of health among young people at the margin of the labor market in various milieus – and to analyze these in relation to gender constructions and within the frame-work of agency within structure.  相似文献   
2.
3.
4.
The Hoechst dye staining method has been successfully applied to the central nervous system in mammals and its use has been demonstrated in intracerebral transplantation. The technique is rapid, simple and based on intrinsic nuclear properties. It was found to be permanent and valid whatever the animal strains or ages, allowing the distinction of rat cells from those of mouse, studied either separately or in a cross-transplantation model. It permitted the detection of grafted cells in the area of transplantation and the observation of early dispersion around the implantation site. Moreover, it can be combined with immunohistochemistry as demonstrated by a myelin marker in a relevant model. Immunodetection can thus help to directly observe grafted cells, at distance from the locus of transplantation, confirming their presence in the graft-type myelin patches.

Because of its rapid performance, this technique can be used systematically after transplantation to check for the presence of grafted cells in the host.  相似文献   
5.
Imberty  Anne; Perez  Serge 《Glycobiology》1994,4(3):351-366
By means of a series of new molecular modelling tools, the conformationalbehaviour of mannose-containing di- and trisaccharides boundto either concanavalin A or Lathyrus ochrus isolectin I (LOLI)has been assessed. Tools for estimating and analysing eitherthe ‘rigid’ or the ‘relaxed’ potentialenergy surfaces, representing the conformational space availablefor carbohydrates once interacting with lectins, are reportedfor the first time. Restrictions of conformational space arepredicted to occur with different magnitudes, depending on thenature of the glycosidic linkages, as well as the size of thecarbohydrates. Results from these molecular modelling studiesare compared to existing structural data. Not only could theobserved conformations and orientations of carbohydrates incrystalline lectin–oligosaccharides complexes be reproduced,but several other likely situations were also predicted to occur.Entropy calculations have been performed for comparison withexperimental thermodynamics data. The results of the simulationcan also help giving an explanation of some observed affinityconstants at the molecular level. concanavalin A Lathyrus ochrus lectin-oligosaccharide molecular modelling  相似文献   
6.
Immunohistochemical and physiological studies on various insect photoreceptors have demonstrated that the Na,K-ATPase (sodium pump) is restricted to the nonreceptive nonmicrovillar area of the plasma membrane. Here, we examined the distribution of the Na,K-ATPase in photoreceptor cells of the superposition-type compound eye in the moth Manduca sexta. Using immunofluorescent and immunogold cytochemistry, we show that the Na,K-ATPase is localized to both the nonmicrovillar and the microvillar parts of the plasma membrane. Manduca photoreceptors thus deviate from the common concept that the sodium pump and the molecular components of the photoreceptive machinery reside on different domains of the plasma membrane.  相似文献   
7.
We measured the rate of cell biomass growth, the consumption of organic substrate, and the heat developed during growth. The relationship between thermodynamic efficiency and the rate of microbial growth was considered.  相似文献   
8.
9.
Cochrane  Anne 《Plant Ecology》2019,220(2):241-253

This multi-year study examined temperature requirements for dormancy release in physically dormant seeds of the threatened legume Acacia awestoniana (Fabaceae) from Western Australia. Seeds were collected from a single site in three consecutive years and exposed to multiple laboratory-based ‘fire’-related temperature treatments (intensity × duration). Experiments were conducted on seeds freshly collected and after 12 months storage under dry laboratory conditions in order to separate the influence of the maternal environment from post-harvest storage conditions on thresholds for dormancy release. Initial seed viability and non-dormant seed fraction did not differ between seed cohorts but there was a clear effect of storage on seed response: fresh seeds from 2016 demonstrated greater thermal resilience than stored seeds collected in the same year. Equally, there was a strong inter-annual response to treatments from fresh seeds collected in 2016 and 2017 attributed to the influence of the maternal environment during seed development. Seeds collected in 2015 and 2016 and stored for 12 months also demonstrated significant differences in their response to treatments, with 2015 seeds responding more favourably to treatment conditions than those from 2016. Plastic responses to external stimuli provide seeds with a strong bet-hedging capacity and the potential to cope with high levels of environmental heterogeneity, especially a mosaic of fire conditions. Such data provide insight for the management, conservation and restoration of this and similar threatened plant species in fire-prone ecosystems in the face of a rapidly changing climate and expected associated changes in the fire regime.

  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