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   5274篇
  免费   328篇
  2022年   8篇
  2021年   24篇
  2020年   15篇
  2019年   30篇
  2018年   60篇
  2017年   36篇
  2016年   72篇
  2015年   127篇
  2014年   143篇
  2013年   285篇
  2012年   284篇
  2011年   272篇
  2010年   187篇
  2009年   175篇
  2008年   287篇
  2007年   260篇
  2006年   284篇
  2005年   298篇
  2004年   277篇
  2003年   263篇
  2002年   300篇
  2001年   165篇
  2000年   165篇
  1999年   138篇
  1998年   78篇
  1997年   83篇
  1996年   54篇
  1995年   51篇
  1994年   42篇
  1993年   48篇
  1992年   89篇
  1991年   101篇
  1990年   83篇
  1989年   93篇
  1988年   74篇
  1987年   69篇
  1986年   77篇
  1985年   58篇
  1984年   59篇
  1983年   49篇
  1982年   46篇
  1981年   44篇
  1980年   41篇
  1979年   41篇
  1978年   24篇
  1977年   26篇
  1976年   29篇
  1975年   19篇
  1973年   11篇
  1968年   10篇
排序方式: 共有5602条查询结果,搜索用时 15 毫秒
1.
2.
 On the basis of a temporal model of animal behavior we conducted temporal analysis of eye movements in schizophrenic subjects (n=10) and normal controls (n=10). We found a fractal property in schizophrenic subjects, the fixation time of eye movement during reading ambiguous and difficult sentences showing a clear inverse power law distribution. An exponential distribution of a nonfractal nature was found in normal controls. Received: 21 July 1995/Accepted in revised form: 30 April 1996  相似文献   
3.
Motorcyclists who work in some offices sometimes complained of coldness, pain and numbness of upper limbs. We studied how to discriminate between vibration syndrome and local fatigue of the motorcyclists. Subjects are 42 motorcyclists of an office in Aichi prefecture. 25 of them held several letters in their left hand when they delivered the letters. They complained of coldness, pain and numbness in the left upper limbs more than in the right limbs (p less than 0.01). We think that it is the local fatigue rather than the disorder of vibration syndrome that causes such symptoms. So it is very important to recognize the existence of local fatigue in order to know how to discriminate between vibration syndrome and local fatigue of the motorcyclists.  相似文献   
4.
Separations of nucleic acids and the related compounds were investigated by HPLC on a new fluorinated bonded silica gel column. Polyadenylate (Poly (A)) enzymatic partial hydrolysate sample and the mixture of various polynucleotide samples were sufficiently separated by the reversed-phase mode using a gradient elution with aqueous ammonium acetate/acetonitrile system. Mixed-mode separation on the fluorinated bonded phase coated with a tert-alkylammonium salt was also examined for the separation of the various polynucleotides including tRNAs.  相似文献   
5.
We investigated the basic technology of cell culture conditions for production of useful substances such as cytokines, and related proteins produced by Namalwa cells. Namalwa cells (Klein, 1972), human B lymphoblastoid cells, were used for large scale production of alpha-interferon (Klein, 1979). Namalwa KJM-1, a subline of Namalwa cells, adapted to serum- and albumin-free medium, can grow at a high density above 1 × 107 cells/ml in suspension mode by the use of a perfusion culture system, Biofermenter?, containing a cone-type cell-sedimentation column as cell separator (Sato, 1983).Several kinds of cytokine cDNA can be introduced and expressed in Namalwa KJM-1 cells (Miyaji, 1990a,b,c). Some of these were produced in large quantities by use of a gene amplification method with dhfr (Miyaji, 1990c), even though the Namalwa KJM-1 cells contained endogenous dhfr genes. For stable production of the target protein, Namalwa KJM-1 cells are very useful host cells, because they have no effective endogenous protease activity in the conditioned medium.Using Biofermenter with micro-silicone fibers and a dialysis system, the specific productivity of the target proteins was not depressed at a high cell density.  相似文献   
6.
Received 20 September 2001/ Accepted in revised form 10 October 2001  相似文献   
7.
Summary A novel procedure is described for fluorescence staining of microbodies, which can be applied quickly and easily. We developed this technique of microbody staining with the unicellular red algaCyanidioschyzon merolae. Cyanidioschyzon merolae only contains a single chloroplast, mitochondrion, and microbody per cell, and the mitotic cycle and the organelle division cycle are easily synchronized. Knowing that the concentration of H2O2 in the microbody is higher than it is in the cytosol and other cell components, we attempted to visualize the microbody by using fluorescence microscopy to detect H2O2. Brilliant sulfoflavin (BSF), used for detecting Fe2+ in analytical chemistry, fluoresces when it reacts with Fe2+ and H2C2. We were able to specifically stain microbodies with BSF, under acidic conditions (pH 3.0 or pH 2.5) with blue-light excitation. Using this procedure, we observed division of the microbody and the effect of aphidicolin on the microbody. We also discovered that microbody division is regulated by the cell nucleus and follows division of the cell nucleus.  相似文献   
8.
9.
T Itoh  T Tamura  T Matsumoto 《Steroids》1976,27(2):275-285
The proton magnetic resonance spectra were measured for four series of tetracyclic triterpen-3beta-ols, i.e. 5alpha-lanostane, 5alpha-euphane, 5alpha-tirucallane, and 5alpha-dammarane series, in the presence of a molar equivalent of tris (dipivalomethanato) europium, a lanthanide shift reagent. The spectral pattern measured in the presence of the shift reagent was found useful for distinguishing each series and also for characterizing each skeletal isomer of tetracyclic triterpene alcohols.  相似文献   
10.
It is suggested that migration of airway smooth muscle (ASM) cells plays an important role in the pathogenesis of airway remodeling in asthma. Increases in intracellular Ca2+ concentrations ([Ca2+]i) regulate most ASM cell functions related to asthma, such as contraction and proliferation. Recently, STIM1 was identified as a sarcoplasmic reticulum (SR) Ca2+ sensor that activates Orai1, the Ca2+ channel responsible for store-operated Ca2+ entry (SOCE). We investigated the role of STIM1 in [Ca2+]i and cell migration induced by platelet-derived growth factor (PDGF)-BB in human ASM cells. Cell migration was assessed by a chemotaxis chamber assay. Human ASM cells express STIM1, STIM2, and Orai1 mRNAs. SOCE activated by thapsigargin, an inhibitor of SR Ca2+-ATPase, was significantly blocked by STIM1 siRNA and Orai1 siRNA but not by STIM2 siRNA. PDGF-BB induced a transient increase in [Ca2+]i followed by sustained [Ca2+]i elevation. Sustained increases in [Ca2+]i due to PDGF-BB were significantly inhibited by a Ca2+ chelating agent EGTA or by siRNA for STIM1 or Orai1. The numbers of migrating cells were significantly increased by PDGF-BB treatment for 6 h. Knockdown of STIM1 and Orai1 by siRNA transfection inhibited PDGF-induced cell migration. Similarly, EGTA significantly inhibited PDGF-induced cell migration. In contrast, transfection with siRNA for STIM2 did not inhibit the sustained elevation of [Ca2+]i or cell migration induced by PDGF-BB. These results demonstrate that STIM1 and Orai1 are essential for PDGF-induced cell migration and Ca2+ influx in human ASM cells. STIM1 could be an important molecule responsible for airway remodeling.  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