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   3484篇
  免费   332篇
  国内免费   6篇
  2023年   12篇
  2021年   51篇
  2020年   33篇
  2019年   46篇
  2018年   64篇
  2017年   46篇
  2016年   96篇
  2015年   167篇
  2014年   176篇
  2013年   198篇
  2012年   273篇
  2011年   275篇
  2010年   176篇
  2009年   147篇
  2008年   194篇
  2007年   198篇
  2006年   197篇
  2005年   156篇
  2004年   182篇
  2003年   133篇
  2002年   123篇
  2001年   75篇
  2000年   60篇
  1999年   91篇
  1998年   40篇
  1997年   36篇
  1996年   26篇
  1995年   25篇
  1994年   25篇
  1993年   22篇
  1992年   52篇
  1991年   40篇
  1990年   41篇
  1989年   32篇
  1988年   40篇
  1987年   29篇
  1986年   29篇
  1985年   19篇
  1984年   16篇
  1983年   14篇
  1982年   15篇
  1981年   10篇
  1980年   13篇
  1979年   13篇
  1977年   15篇
  1976年   12篇
  1975年   10篇
  1974年   10篇
  1973年   11篇
  1972年   10篇
排序方式: 共有3822条查询结果,搜索用时 281 毫秒
1.
2.
3.
4.
5.
Tryptophan loading enhances sleep quality by increasing the ratio of plasma tryptophan to large neutral amino acids (TRP:LNAA) and consequently synthesis and availability of serotonin in the brain. Alpha-lactalbulmin (A-LAC) is rich in tryptophan and has the highest TRP:LNAA of all protein sources. This pilot study investigated the effect of an evening intake of A-LAC on objective and subjective sleep measures in male subjects without sleep complaints. Ten healthy male university students (aged: 26.9 ± 5.3 years; BMI: 21.7 ± 1.9 kg.m?2) participated in a double-blind, randomized, and placebo-controlled crossover counter-balanced study. Objective (actigraphy) and subjective (sleep log) sleep measures were recorded for two nights after a standardized evening meal supplemented with either A-LAC (20 g) or a placebo of sodium caseinate (20 g) one hour before bedtime. Evening A-LAC intake resulted in increased objective and subjective total sleep time by 12.8% (p = 0.037) and 10.8% (p = 0.013), respectively, compared to placebo. Objective sleep efficiency increased by 7.0% (p = 0.028) following A-LAC with no significant effects for other sleep indices. This pilot study demonstrates the efficacy of evening A-LAC intake on sleep quality in young healthy adults, however further large-scale studies are warranted to confirm the benefit.  相似文献   
6.

Background  

Pathogen detection using DNA microarrays has the potential to become a fast and comprehensive diagnostics tool. However, since pathogen detection chips currently utilize random primers rather than specific primers for the RT-PCR step, bias inherent in random PCR amplification becomes a serious problem that causes large inaccuracies in hybridization signals.  相似文献   
7.
8.
Yu  Zheng-Chao  Lin  Wei  Zheng  Xiao-Ting  Chow  Wah Soon  Luo  Yan-Na  Cai  Min-Ling  Peng  Chang-Lian 《Photosynthesis research》2021,149(1-2):41-55
Photosynthesis Research - Increasing amounts of experimental evidence show that anthocyanins provide physiological protection to plants under stress. However, the difference in photoprotection...  相似文献   
9.
Y C Wong  W G Breed  P H Chow 《Acta anatomica》1985,121(3):163-169
The large ventral prostate of the hopping mouse has abundant secretory units whose epithelial cells vary in height and which often have nuclei in the apical region of the cell. TEM observations indicated two epithelial cell types in which some unusual features occurred. Type A cells had granular endoplasmetic reticulum (GER) whose membranes often formed intracytoplasmic confronting cisternae. Type B cells had more fragmented and vesiculated GER with sparse ribosomes and less frequently also intracytoplasmic confronting confronting cisternae. In the latter cells, two types of granules were found, one of which was derived from the Golgi and the other possibly directly from the GER. Type A cells only had one type of granule present. A highly convoluted membrane was also found at the basal region in many of the cells. The significance of these unusual ultrastructural features has yet to be ascertained.  相似文献   
10.
The Simple View of Reading (SVR) in Chinese was examined in a genetically sensitive design. A total of 270 pairs of Chinese twins (190 pairs of monozygotic twins and 80 pairs of same-sex dizygotic twins) were tested on Chinese vocabulary and word reading at the mean age 7.8 years and reading comprehension of sentences and passages one year later. Results of behavior-genetic analyses showed that both vocabulary and word reading had significant independent genetic influences on reading comprehension, and the two factors together accounted for most but not all of the genetic influences on reading comprehension. In addition, sentence comprehension had a stronger genetic correlation with word reading while passage comprehension showed a trend of stronger genetic overlap with vocabulary. These findings suggest that the genetic foundation of the SVR in Chinese is largely supported in that language comprehension and decoding are two core skills for reading comprehension in nonalphabetic as well as alphabetic written languages.  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