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   560795篇
  免费   57216篇
  国内免费   1084篇
  619095篇
  2018年   16092篇
  2017年   14749篇
  2016年   13630篇
  2015年   10125篇
  2014年   10881篇
  2013年   15331篇
  2012年   20876篇
  2011年   28570篇
  2010年   22080篇
  2009年   17376篇
  2008年   23302篇
  2007年   25007篇
  2006年   13901篇
  2005年   13346篇
  2004年   13348篇
  2003年   13126篇
  2002年   12319篇
  2001年   21135篇
  2000年   21229篇
  1999年   16630篇
  1998年   5934篇
  1997年   6403篇
  1996年   6083篇
  1995年   5656篇
  1994年   5514篇
  1993年   5632篇
  1992年   13822篇
  1991年   13618篇
  1990年   12929篇
  1989年   12733篇
  1988年   11650篇
  1987年   11242篇
  1986年   10518篇
  1985年   10471篇
  1984年   8831篇
  1983年   7591篇
  1982年   5872篇
  1981年   5197篇
  1980年   5021篇
  1979年   8196篇
  1978年   6588篇
  1977年   5970篇
  1976年   5598篇
  1975年   6228篇
  1974年   6418篇
  1973年   6367篇
  1972年   5949篇
  1971年   5507篇
  1970年   4426篇
  1969年   4263篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Total creatine kinase (CK) and CK MB activities were determined in gastrocnemius muscle and serum obtained from 14 female marathon runners. The level of CK MB in muscle increased significantly (p less than 0.05) after chronic exercise training from 5.3% to 10.5% of the total CK activity, but not after acute exercise (post-marathon 8.9%). No significant differences in total CK activities were detected. However, the total CK activity in the muscles were significantly (p less than 0.05) less than those previously reported from the muscle of men runners (1800 U/g, 3000 U/g respectively). No significant correlation existed between fiber type and muscle CK MB activity. Additionally, trace amounts of mitochondrial CK and CK BB were present in muscle homogenates. A significant correlation was observed in the increase in mean serum total CK (597 UL-1) and CK MB (23 UL-1) activities 24 h after the race (r = 0.97, p less than 0.05). These results suggest that gastrocnemius muscle in women adapts to training with increased CK MB activities and imply that skeletal muscle is the major source of elevated serum CK MB activities in women marathon runners.  相似文献   
995.
Tree size, survival, and coppicing of micropropagated plantlets, macropropagated cuttings, and seedlings of Eucalyptus grandis Hill ex Maiden were monitored through 57 months in a study in southern Florida to assess propagation options. Two plantlet lines developed by direct micropropagation and orchard open-pollinated seedlings from three ortets were compared in the main study. Rooted cuttings from up to four ramets of each of the three ortets and another ortet were examined in an adjacent supplemental study. Freezes at six and 16 months killed most initial and first-coppice stems to the ground. Most developmental differences in the main study were consistent from ages 2 to 57 months. Propagation by ortet interactions were observed beginning at 21 months, due to the poor performance of seedlings of one ortet after the second freeze. At 57 months, no differences in tree height, DBH, volume, or survival were detected between plantlet lines and between rooted cuttings and plantlets, but seedlings were inferior to plantlets and cuttings. Vegetative propagules had more uniform tree size at every age, with typically less than one-half the variability observed among seedlings. Even though plantlets and cuttings may be more expensive to produce, they have numerous advantages over seedlings for E. grandis plantation establishment in Florida.  相似文献   
996.
The acarological+ study of dust samples from the homes of allergic patients and normal persons in Moscow mite antigens were detected, respectively, in 66.7% and 38.1% of homes. The indirect mast cell degranulation test and the brain gliacyte volume change test in white rats gave similar results. The occurrence of Dermatophagoides pteronyssinus was approximately twice as great of D. farinae, and the numerical prevalence of the former species over the latter one was 1.3-fold. Dermatophagoides mites occurred in the homes of allergic patients 1.8-2.3 times as frequently as in the homes of normal persons.  相似文献   
997.
998.
Ischemia of the rat small intestine lasting 40 min leads to pronounced structural disorders in lipid transport across the enterocytes, reduction in enzymatic activity of the cells and in absorption function, and to the loss of fat with feces. The normalization of the indicated parameters occurs at varying times and ends after 1 month. Fat transport abnormality is marked by an increase in lipid drops in the cavities of the smooth endoplasmic network, appearance of large and numerous matrix lipids, by a greater reduction, as compared to normal, in the membranes of the rough endoplasmic network and lamellar complex in the epithelium of the villi. Accumulation of lipids and retardation of their release from the cytoplasm are determined by incomplete differentiation of the epithelium, which is also combined with a decreased enzymatic activity.  相似文献   
999.
1000.
We have analysed the lineage of olfactory receptor neurons usinga replication-incompetent retrovirus injected beneath the olfactoryepithelium of young rats. There are two major types of clustersof infected cells seen at 5–40 days after infection: (i)horizontal basal cells (HBCs); (ii) variable numbers of globosebasal cells (GBCs), and immature and mature sensory neurons.Olfactory nerve lesion increased the frequency of the globose/sensoryneuron clusters, as well as the number of cells/cluster, butdid not change the number of HBC clusters or cells/cluster.No clusters contained sustentacular cells. These data indicatethat, at least in young rats: (i) HBCs are not precursors ofolfactory neurons; (ii) there is a lineage path from GBCs tomature neurons; and (iii) sustentacular cells arise from a separatelineage.  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