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   854篇
  免费   130篇
  国内免费   1篇
  2020年   6篇
  2019年   10篇
  2018年   10篇
  2017年   5篇
  2016年   13篇
  2015年   17篇
  2014年   35篇
  2013年   43篇
  2012年   41篇
  2011年   42篇
  2010年   32篇
  2009年   20篇
  2008年   43篇
  2007年   46篇
  2006年   31篇
  2005年   38篇
  2004年   29篇
  2003年   26篇
  2002年   23篇
  2001年   18篇
  2000年   31篇
  1999年   19篇
  1998年   11篇
  1997年   9篇
  1996年   9篇
  1995年   5篇
  1994年   9篇
  1993年   10篇
  1992年   22篇
  1991年   29篇
  1990年   32篇
  1989年   22篇
  1988年   22篇
  1987年   23篇
  1986年   9篇
  1985年   11篇
  1984年   9篇
  1983年   7篇
  1982年   6篇
  1981年   10篇
  1980年   8篇
  1979年   10篇
  1978年   6篇
  1977年   14篇
  1976年   14篇
  1975年   12篇
  1974年   10篇
  1973年   5篇
  1972年   6篇
  1965年   5篇
排序方式: 共有985条查询结果,搜索用时 31 毫秒
31.
32.
33.
Direct intratumoral injection of interleukin-2 (IL-2) was evaluated in a murine model. Balb/c mice received 5 × 104 Line 1 alveolar carcinoma cells (L1C2) by subcutaneous injection. On the third day following tumor implantation, mice received injections of IL-2 (5 × 103–5 × 104 units) or diluent twice daily, either by i. p. or intratumoral injection, 5 days/week for 3 weeks. Intratumoral injection of 5 × 104 units IL-2 significantly reduced tumor volume (P <0.05 versus control), increased median survival time (P = 0.0001), and resulted in a 23.5% cure rate (P = 0.008). There were no long-term survivors in the other treatment groups. Both tumor-infiltrating lymphocytes (TIL) and splenic lymphocytes isolated directly from IL-2-treated mice demonstrated enhanced cytolytic activity compared to diluent-treated controls. To determine whether non-T-cell-mediated antitumor responses were active in our model, intratumoral immunotherapy was evaluated in athymic Balb/cnu/nu mice. In order to decrease the recruitment of lymphocyte precursors, nude mice were splenectomized and received cyclophosphamide prior to tumor injection and IL-2 therapy. Intratumoral IL-2 immunotherapy also significantly decreased tumor volume in these immunodeficient mice (P <0.02), but did not lead to long-term survival. We conclude that both TIL and splenic lymphocytes are activated in vivo in response to intratumoral IL-2 immunotherapy, suggesting that intratumoral therapy with IL-2 activates both local and systemic antitumor responses.Supported by the Tobacco-Related Disease Research Program of the University of California, the Cancer Research Coordinating Committee, the Jonsson Cancer Center Foundation, and Veterans Administration Medical Research Funds  相似文献   
34.
Macroconidiation in Neurospora crassa is influenced by a number of environmental cues, including the nutritional status of the growing organism. Conidia formation is normally observed when the fungus is exposed to air. However, carbon limitation can induce conidiation in mycelia submerged in an aerated liquid medium. A mutant was previously isolated that could conidiate in submerged culture without imposing nutrient limitation and the gene responsible for this phenotype (rco-3) has now been cloned. RCO3 exhibits sequence similarity to members of the sugar transporter gene superfamily, with greatest similarity to glucose transporters of yeast. Consistent with this structural similarity, we find that glucose transport activity is altered in the mutant. However, growth of the mutant in media containing alternate carbon sources does not suppress conidiation in submerged culture. The properties of the mutant suggest that RCO3 is required for expression of glucose transport activity, glucose regulation of gene expression, and general carbon repression of development.  相似文献   
35.
Using a probe isolated from a human liver cDNA library, polymorphisms were observed in the human ceruloplasmin gene with the enzymes PstI and MspI. The PstI polymorphism was frequent (allele frequencies, 0.46 and 0.54) whereas the polymorphisms found with MspI were rare.  相似文献   
36.
The human calcitonin gene is located on the short arm of chromosome 11   总被引:6,自引:0,他引:6  
By molecular hybridization of human calcitonin cDNA probes to DNA from human-rodent hybrid cells containing identified human chromosomes, we have mapped the human calcitonin gene to the short arm of chromosome 11. This location has been confirmed by in situ hybridization, which further localized the calcitonin gene to region 11p13-15. The significance of this region regarding gene linkage and possible markers for inherited cancers is discussed.  相似文献   
37.
Microbial flora of in-use soap products.   总被引:2,自引:0,他引:2       下载免费PDF全文
A comparison has been made of the in-use bacterial load of two bar soaps with and without antibacterials and two liquid soaps in five different locations over a 1-week period. Of the 25 samples taken from each soap, 92 to 96% of samples from bar soaps were culture positive as compared to 8% of those from liquid soaps. Bacterial populations ranged from 0 to 3.8 log CFU per sample for bar soaps and from 0 to 2.0 log CFU per sample for liquid soaps. The mean bacterial populations per sample were 1.96 and 2.47 log CFU for the two bar soaps, and 0.08 and 0.12 log CFU for the two liquid soaps. The difference in bacterial population between bar soaps and liquid soaps was statistically significant (P = 0.005). Staphylococcus aureus was isolated on three occasions from bar soaps but not from liquid soaps. S. aureus was isolated twice from the exterior of the plastic dispensers of liquid soap but not from the soap itself. Gram-negative bacteria were cultured only from soaps containing antibacterials. Bacterial populations on bar soaps were not high compared with bacterial populations on hands, and the flora was continually changing without evidence of a carrier state.  相似文献   
38.
Abstract— Crude synaptosomal (P2) preparations were obtained from the cerebella of rats in which the granule cell population had been selectively reduced by X-irradiation treatment and from the cerebella of control animals. In the P2 fraction from control cerebella, the level of glutamate was greater than any other of the 5 amino acids measured and was 2-fold higher than taurine, which was present at the next highest level. The content of taurine was slightly higher than that found for aspartate and was 3-fold greater than that observed for GABA. Alanine and glycine were present in the lowest amounts. The levels of glutamate and aspartate were significantly (P < 0.05) lower by 25 and 15%, respectively, in the P2 fraction isolated from the X-irradiated cerebella in comparison to control values. The content of taurine, GABA, glycine, and alanine were not changed by the X-irradiation treatment. The uptake of 1.0 μm -l -[3H]glutamate and l -[3H]aspartate was reduced approx 20% by X-irradiation treatment, whereas the uptake of 1.0 μm -[3H]GABA and [3H]taurine was unchanged. A more detailed kinetic analysis of l -[3H]glutamate uptake revealed there was a 20% decrease in the Vmax value with X-irradiation treatment and no change in the apparent Km value. In a second study, the uptake of l -[3H]glutamate, l -[3H]aspartate and [3H]GABA was measured using P2 fractions obtained from the cerebella of rats in which the population of granule, stellate and basket cells had been reduced by X-irradiation treatment. The uptake of 1.0μm -l -[3H]glutamate, l -[3H]aspartate and [3H]GABA was significantly (P < 0.05) reduced to 57, 68, and 59%, respectively, of control values. A more detailed kinetic analysis of [3H]GABA uptake revealed no significant change in the apparent Km and a 35% decrease in the Vmax value. The data are discussed in terms of glutamate being the excitatory neurotransmitter released from granule cells and GABA being the inhibitory neurotransmitter released from basket cells.  相似文献   
39.
M.A. Rea  W.J. McBride 《Life sciences》1978,23(24):2355-2359
The effect of the x-irradiation-induced loss of cerebellar granule and stellate cells on the levels of glutamate, aspartate and GABA in regions of the rat cerebellum was determined. The level of glutamate was significantly lower in the neuron-depleted cerebellar cortex while GABA levels were higher than control values in the cerebellar cortex and white matter of the x-irradiated rats. Aspartate levels were not changed by x-irradiation in any cerebellar region. The data is discussed in terms of the proposed role of glutamate as the excitatory neurotransmitter released from granule cells.  相似文献   
40.
The metabolic response to L-lysine of Escherichia coli ATCC 13002, a lysine-histidine double auxotroph, has been examined in a synthetic medium containing sucrose. In shaken cultures largest amounts of extracellular DAP were produced with an initial lysine concentration of 7·5 mg/1 and in static cultures of 2·5 mg/1. Considerably smaller amounts of DAP accumulated under stationary conditions. In cultures shaken for 20 and 43 h there was an overall decrease in the yields of DAP, expressed in terms of cell biomass and of sucrose consumed, as the initial concentration of lysine was increased from 0·75 mg/1 in steps up to 25 mg/1. The regulatory effect of lysine on DAP production was also observed when lysine was supplied to cultures at a constant rate employing diffusion capsules.  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