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   2781篇
  免费   302篇
  2022年   19篇
  2021年   34篇
  2020年   20篇
  2019年   21篇
  2018年   31篇
  2017年   39篇
  2016年   64篇
  2015年   89篇
  2014年   104篇
  2013年   136篇
  2012年   145篇
  2011年   165篇
  2010年   109篇
  2009年   98篇
  2008年   133篇
  2007年   143篇
  2006年   111篇
  2005年   108篇
  2004年   112篇
  2003年   121篇
  2002年   101篇
  2001年   83篇
  2000年   108篇
  1999年   91篇
  1998年   31篇
  1997年   46篇
  1996年   35篇
  1995年   38篇
  1994年   39篇
  1993年   39篇
  1992年   59篇
  1991年   57篇
  1990年   60篇
  1989年   47篇
  1988年   32篇
  1987年   36篇
  1986年   48篇
  1985年   34篇
  1984年   17篇
  1983年   19篇
  1982年   22篇
  1981年   19篇
  1979年   21篇
  1978年   17篇
  1976年   18篇
  1975年   14篇
  1974年   13篇
  1973年   16篇
  1972年   21篇
  1970年   15篇
排序方式: 共有3083条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Human Vγ9Vδ2 T cells are a unique T-cell type, and data from recent studies of Vγ9Vδ2 T cells emphasize their potential relevance to cancer immunotherapy. Vγ9Vδ2 T cells exhibit dual properties since they are both antigen-presenting cells and cytotoxic toward cancer cells. The majority of Vγ9Vδ2 T cells are double-negative for the co-receptors CD4 and CD8, and only 20–30% express CD8. Even though they are mostly neglected, a small fraction of Vγ9Vδ2 T cells also express the co-receptor CD4. Here the authors show that CD4+ Vγ9Vδ2 T cells comprise 0.1–7% of peripheral blood Vγ9Vδ2 T cells. These cells can be expanded in vitro using zoledronic acid, pamidronic acid or CD3 antibodies combined with IL-2 and feeder cells. Unlike most conventional CD4+ αβ T cells, CD4+ Vγ9Vδ2 T cells are potently cytotoxic and can kill cancer cells, which is here shown by the killing of cancer cell lines of different histological origins, including breast cancer, prostate cancer and melanoma cell lines, upon treatment with zoledronic acid. Notably, the killing capacity of CD4+ Vγ9Vδ2 T cells correlates with co-expression of CD56.  相似文献   
995.
996.
Randell, AD, Cronin, JB, Keogh, JWL, Gill, ND, and Pedersen, MC. Reliability of performance velocity for jump squats under feedback and nonfeedback conditions. J Strength Cond Res 25(12): 3514-3518, 2011-Advancements in the monitoring of kinematic and kinetic variables during resistance training have resulted in the ability to continuously monitor performance and provide feedback during training. If equipment and software can provide reliable instantaneous feedback related to the variable of interest during training, it is thought that this may result in goal-oriented movement tasks that increase the likelihood of transference to on-field performance or at the very least improve the mechanical variable of interest. The purpose of this study was to determine the reliability of performance velocity for jump squats under feedback and nonfeedback conditions over 3 consecutive training sessions. Twenty subjects were randomly allocated to a feedback or nonfeedback group, and each group performed a total of 3 "jump squat" training sessions with the velocity of each repetition measured using a linear position transducer. There was less change in mean velocities between sessions 1-2 and sessions 2-3 (0.07 and 0.02 vs. 0.13 and -0.04 m·s), less random variation (TE = 0.06 and 0.06 vs. 0.10 and 0.07 m·s) and greater consistency (intraclass correlation coefficient = 0.83 and 0.87 vs. 0.53 and 0.74) between sessions for the feedback condition as compared to the nonfeedback condition. It was concluded that there is approximately a 50-50 probability that the provision of feedback was beneficial to the performance in the squat jump over multiple sessions. It is suggested that this has the potential for increasing transference to on-field performance or at the very least improving the mechanical variable of interest.  相似文献   
997.
Plasma membrane ATPases are primary active transporters of cations that maintain steep concentration gradients. The ion gradients and membrane potentials derived from them form the basis for a range of essential cellular processes, in particular Na(+)-dependent and proton-dependent secondary transport systems that are responsible for uptake and extrusion of metabolites and other ions. The ion gradients are also both directly and indirectly used to control pH homeostasis and to regulate cell volume. The plasma membrane H(+)-ATPase maintains a proton gradient in plants and fungi and the Na(+),K(+)-ATPase maintains a Na(+) and K(+) gradient in animal cells. Structural information provides insight into the function of these two distinct but related P-type pumps.  相似文献   
998.
Grouse and vole numbers may peak after peaks in the seed crop of bilberry (Vaccinium myrtillus) because of reduced levels of feeding deterrents in bilberry plants. We predicted that grouse reproduction depends also on summer (June–September) temperatures in the 2 previous years, because bilberry plants will be less exhausted after a high seed crop in or after warm summers, and thus rebuild their chemical defence more quickly. After berry peak years, population indices of capercaillie (Tetrao urogallus) and bank vole (Myodes glareolus) in southern Norway were negatively related to summer temperatures in the previous year or previous 2 years. Willow grouse (Lagopus lagopus) chick production in five areas in Norway was negatively related to summer temperatures in the 2 previous years when controlling for vole density. A similar pattern was found for the bilberry-feeding moth (Eulithis populata), an important prey for grouse chicks. In eastern Norway, autumn densities of capercaillie and black grouse (Tetrao tetrix) were more likely to peak in vole peak years at high altitudes, where summer temperatures are low. We conclude that high summer temperatures may limit grouse reproduction through the effect on bilberry plants and that a warm climate thus adversely affects population levels of grouse.  相似文献   
999.

Background  

Chronic fatigue syndrome is an idiopathic syndrome widely suspected of having an infectious or immune etiology. We applied an unbiased metagenomic approach to try to identify known or novel infectious agents in the serum of 45 cases with chronic fatigue syndrome or idiopathic chronic fatigue. Controls were the unaffected monozygotic co-twins of cases, and serum samples were obtained at the same place and time.  相似文献   
1000.
We have synthesized a carbon linker analogue of INA (oligonucleotides containing insertions of 1-O-(1-pyrenylmethyl)glycerol). Thermal stability studies showed an increase in melting temperature in favor of the carbon linker analogue. We also synthesized a carbon linker analogue with two pyrenes geminally attached. Fluorescence studies of this intercalating nucleic acid with the pyrene moieties inserted as a bulge showed formation of an excimer band. When a mismatch was introduced at the site of the intercalator, an excimer band was formed for the destabilized duplexes whereas an exciplex band was observed when the stability of the duplex was retained.  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