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   4094篇
  免费   484篇
  国内免费   5篇
  4583篇
  2021年   34篇
  2019年   32篇
  2018年   37篇
  2017年   44篇
  2016年   49篇
  2015年   133篇
  2014年   99篇
  2013年   162篇
  2012年   234篇
  2011年   225篇
  2010年   135篇
  2009年   125篇
  2008年   148篇
  2007年   169篇
  2006年   214篇
  2005年   160篇
  2004年   197篇
  2003年   166篇
  2002年   156篇
  2001年   48篇
  2000年   41篇
  1999年   38篇
  1998年   62篇
  1997年   51篇
  1996年   43篇
  1995年   38篇
  1994年   44篇
  1993年   25篇
  1992年   40篇
  1991年   43篇
  1990年   47篇
  1989年   37篇
  1988年   41篇
  1987年   30篇
  1986年   36篇
  1985年   36篇
  1984年   50篇
  1983年   36篇
  1982年   66篇
  1981年   52篇
  1980年   50篇
  1979年   41篇
  1978年   25篇
  1977年   51篇
  1976年   47篇
  1975年   42篇
  1974年   44篇
  1973年   29篇
  1970年   29篇
  1962年   25篇
排序方式: 共有4583条查询结果,搜索用时 15 毫秒
91.
92.
93.
From February 1972 to August 1974 ten immatureCebus albifrons monkeys were weighed and vaginal swabbing performed at monthly or shorter intervals to determine age and weight at the onset of puberty. The average weight (±S.E.M.) at birth and at puberty was 226±5.8 g and 1,617±32.45 g, respectively. The average age at puberty was 3.59±0.17 years. The average weight velocity for all ten monkeys shows the maximum rate of weight gain to occur shortly after birth and decrease rapidly to its smallest prepubertal increment at nine months of age (weaning). From nine months there is a post-weaning weight spurt which reaches its greatest velocity at an average age of 15 months. Thereafter, the weight velocity decreases to its lowest level. Individual weight velocity curves of each of the ten animals show a slight prepubertal weight spurt which is not obvious in the average growth curve.  相似文献   
94.
95.
Methionine sulfoxide is transported into purified intestinal and renal brush border membrane vesicles from rabbit by an Na+-dependent mechanism and is accumulated inside the vesicles against the concentration gradient. Both in intestine and kidney, the rate of transport is enhanced with increasing concentrations of Na+ in the external medium. Increasing the Na+ gradient reduces the apparent Kt for methionine sulfoxide without causing any change in Vmax. With an outward K+ gradient (vesicle > medium), valinomycin stimulates the Na+-gradient-dependent transport of methionine sulfoxide in the kidney, showing the electrogenicity of the transport process. A number of amino acids inhibit methionine sulfoxide transport in both the intestine and kidney. An enzymatic activity capable of reducing methionine sulfoxide to methionine is present in the intestinal mucosa, renal cortex and liver. The activity is highest in renal cortex and lowest in intestine. The methionine sulfoxide-reducing activity is stimulated by NADH, NADPH, glutathione and dithiothreitol and the potency of the stimulation is in the order: dithiothreitol > NADPH > glutathione > NADH.  相似文献   
96.
The activation of uterine smooth muscle adenylate cyclase was studied by pretreating the particulate form of the enzyme with the GTP analog guanyl-5′-yl imidodiphosphate (Gpp(NH)p). Pretreatment with Gpp(NH)p left the enzyme in an irreversibly activated state which survived subsequent washing in guanyl nucleotide-free buffer. Activation under these conditions was multiphasic with rapid and slow components. At 23 °C slow activation proceeded at about 110th the rate of rapid activation. The onset of the slow phase took longer at lower temperatures. Routine adenylate cyclase assay conditions (conversion of [32P]ATP to cyclic [32P]AMP) carried out without pretreatment probably characterized the rapidly activated component. The simplest kinetic model suggests not only the generally accepted two-step association reaction, but also implies the existence of more than one enzyme form, each of which is characterized by a separate activation rate. The complex kinetics of activation might be explained by a heterogeneous mixture of unassociated and preassociated nucleotide binding and catalytic subunits.  相似文献   
97.
A radiometric viability assay based upon the conversion of [14C]glucose into 14CO2 by the viable cells on the dermal side of whole skin has been developed. The assay proved to be sensitive, reproducible, and practical, and was based upon the use of a microbiological growth detection system commonly used in many hospitals and laboratories. Relatively small samples of skin (0.25–1.00 g) were used in the test, and it was found that microbiological contamination did not interfere with the assay under normal conditions. The linear proportionality of the assay with both time and amount of skin assayed precluded the difficulties of nonlinear proportionality in other systems, allowing direct comparisons to be made between skin samples of different sizes and different incubation times. The assay could also detect 14CO2 released from many radiolabeled substrates, including glucose, aspartate, glutamate, ornithine, orotic acid, and glycerol. Thus, the method could be used to test a number of cellular functions necessary for viability, including glycolysis, the functioning of the citric acid cycle and the pentose phosphate pathway, sugar and amino acid metabolism, pyrimidine biosynthesis, and cryopreservative agent metabolism. Since any of these tests could be performed in 4 hr, a viability assay based upon glycolysis alone, or in combination with any of the other tested substrates, could be carried out after allograft skin procurement before a decision needed to be made on skin cryopreservation.  相似文献   
98.
We have produced a panel of mAb to the endothelial activation Ag endothelial leucocyte adhesion molecule-1 (ELAM-1), using both a conventional immunization protocol and one involving immunosuppression. By constructing ELAM-1 mutants we have demonstrated that seven of these antibodies recognize epitopes within the lectin domain of ELAM-1 and that one binds within the complement regulatory protein domains. These studies also suggest that the EGF-like domain is important in maintaining the conformation of the neighbouring lectin domain. In functional studies, U937 cells bound to Cos cells expressing either ELAM-1 or ELAM-1 with the complement regulatory protein domains deleted. No adhesion was observed to Cos cells expressing ELAM-1 mutants lacking either the lectin or EGF-like domains. The fact that antibodies directed against the lectin domain can inhibit adhesion suggest that this domain is directly involved in cell binding.  相似文献   
99.
The Escherichia coli trp repressor binds to the trp operator in the presence of tryptophan, thereby inhibiting tryptophan biosynthesis. Tryptophan analogues lacking the alpha-amino group act as inducers of trp operon expression. We have used one- and two-dimensional 1H-NMR spectroscopy to compare the binding to the repressor of the corepressors L-tryptophan, D-tryptophan and 5-methyl-DL-tryptophan with that of the inducer indole-3-propionic acid. We have determined the chemical shifts of the indole ring protons of the ligands when bound to the protein, principally by magnetization-transfer experiments. The chemical shifts of the indole NH and C4 protons differ between corepressors and inducer. At the same time, the pattern of intermolecular NOE between protons of the protein and those of the ligand also differ between the two classes of ligand. These two lines of evidence indicate that corepressors and inducers bind differently in the binding site, and the evidence suggests that the orientation of the indole ring in the binding site differs by approximately 180 degrees between the two kinds of ligand. This is in contrast to a previous solution study [Lane, A.N. (1986) Eur. J. Biochem. 157, 405-413], but consistent with recent X-ray crystallographic work [Lawson, C.L. & Sigler, P.B. (1988) Nature 333, 869-871]. D-Tryptophan and 5-methyltryptophan, which are more effective corepressors than L-tryptophan, bind similarly to L-tryptophan. The indole ring of D-tryptophan appears to bind in essentially the same orientation as that of the L isomer. There are, however, some differences in chemical shifts and NOE for 5-methyltryptophan, which indicate that there are significant differences between the two corepressors L-tryptophan and 5-methyltryptophan in the orientation of the indole ring within the binding site.  相似文献   
100.
Altered processing of integrin receptors during keratinocyte activation   总被引:8,自引:0,他引:8  
We used monoclonal antibodies against specific integrin subunits to examine the role of integrin receptors in keratinocyte activation. We found that before activation, beta 1 subunits in keratinocytes showed a diffuse distribution, whereas after activation, keratinocytes organized beta 1 receptors into marginal adhesion plaques. In immunoprecipitation experiments with antibodies against beta 1 integrin subunits, we found mostly immature subunits synthesized in keratinocytes freshly harvested from skin. Moreover, integrin receptor complexes immunoprecipitated from these cells by monoclonal antibodies against alpha 2, alpha 3, or alpha 5 subunits contained only immature beta 1 subunits. With keratinocytes cultured 4-7 days, anti-beta 1 antibodies immunoprecipitated mostly mature beta 1 subunits, and integrin complexes immunoprecipitated from cultured cells by anti-alpha subunit antibodies contained mostly mature beta 1 subunits. Antibodies directed against beta 1 subunits also inhibited keratinocyte migration. Based on these results, we suggest that up-regulation of migration by activated keratinocytes depends on changes in processing of pre-beta 1 subunits to mature beta 1 subunits. We also studied the distribution of integrin subunits in skin and on keratinocytes migrating out of skin explants. Whereas beta 1, alpha 2, and alpha 3 subunits were detected in keratinocytes in skin and migrating out of explants, alpha 5 subunits were observed only in migrating cells.  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