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   15539篇
  免费   923篇
  国内免费   95篇
耳鼻咽喉   91篇
儿科学   430篇
妇产科学   360篇
基础医学   2538篇
口腔科学   287篇
临床医学   1363篇
内科学   3824篇
皮肤病学   213篇
神经病学   1957篇
特种医学   348篇
外科学   1330篇
综合类   35篇
一般理论   4篇
预防医学   808篇
眼科学   130篇
药学   1208篇
中国医学   30篇
肿瘤学   1601篇
  2024年   11篇
  2023年   116篇
  2022年   288篇
  2021年   465篇
  2020年   286篇
  2019年   379篇
  2018年   426篇
  2017年   369篇
  2016年   399篇
  2015年   506篇
  2014年   615篇
  2013年   741篇
  2012年   1235篇
  2011年   1237篇
  2010年   714篇
  2009年   632篇
  2008年   1071篇
  2007年   1061篇
  2006年   1028篇
  2005年   956篇
  2004年   901篇
  2003年   880篇
  2002年   768篇
  2001年   104篇
  2000年   93篇
  1999年   137篇
  1998年   152篇
  1997年   116篇
  1996年   108篇
  1995年   101篇
  1994年   75篇
  1993年   73篇
  1992年   59篇
  1991年   51篇
  1990年   45篇
  1989年   55篇
  1988年   30篇
  1987年   24篇
  1986年   40篇
  1985年   27篇
  1984年   35篇
  1983年   25篇
  1982年   18篇
  1981年   18篇
  1980年   17篇
  1979年   12篇
  1977年   8篇
  1976年   7篇
  1974年   6篇
  1965年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Over the past decade extracorporeal shock-wave therapy (ESWT) has been increasingly applied to orthopaedic and musculoskeletal pathologies, the aim of this study was to assess how the energy density of the shock waves and the number of impulses affect viability, differentiation and synthetic activity of osteoblasts. Primary sheep osteoblasts cultures were treated with ESWT with an electro-hydraulic shock wave generator by selecting three different energy levels (14-21-28 kV corresponding at 0.15-0.31-0.40 mJ/mm2) and two different total numbers of impulses (500, 1000) for each level. At the end of treatment, cell counts and viability were recorded. Cells were then cultivated for 48 hours starting from a concentration of 1 x 10(4) cells/ml. The biological activity and viability were evaluated at 24 and 48 hours after treatment. No cytodestructive effects were observed in Group A, while a cytodestructive effect of ESWT was seen in cultures receiving the highest energy treatments. The different shock wave treatment induced differences in MTT assays after 24 and 48 hours, in particular the highest level showed a detrimental effect on cell respiration at both experimental times as compared to the Control Group and the protein metabolism was generally depressed by ESWT with impulses at the highest energy level. After 24 hours such effect further increased with the growing number of impulses. The lowest energy level appeared to significantly improve the metabolic parameter in primary cell cultures as compared to controls when 500 impulses were selected. The current study has demonstrated that one of the most important aspects to be considered is not the total number of impulses used but the energy level of the shock waves, thus confirming that ESWT has a dose-dependent effect on cells.  相似文献   
32.
Natural killer (NK) cell function is largely modulated by growth factors and cytokines. In particular, interleukin (IL)-2, IL-12, and IL-15 have major effects on the proliferative and cytotoxic activities of NK cells against tumor and virus-infected cells. It is thought that the members of the protein kinase C (PKC) family of serine/threonine kinases play an important role in mediating the pleiotropic effects of cytokines on their target cells. We have investigated the downstream effects generated in purified human NK cells by IL-2, IL-12, and IL-15 on PKCalpha and PKCepsilon--a canonical and a novel isoform of PKC, respectively. By means of Western blotting, PKC activity assays, and immunofluorescence performed on highly purified preparations of primary human NK cells, we demonstrate that: 1) the three cytokines have similar effects on PKCalpha and PKCepsilon activities; 2) whereas PKCepsilon activity is induced by cytokine stimulation, PKCalpha activity is inhibited; and 3) both the induction of PKCepsilon and the inhibition of PKCalpha functional activity are relatively early events in NK cells, while longer cytokine stimulations do not generate significant variations in enzyme activity, suggesting that the activation of both the canonical and novel isoforms of PKC are events required in the early phases of cytokine-induced NK cell stimulation.  相似文献   
33.
We describe a large inbred Sicilian family that includes four 46, XX (SRY-) brothers. Palmoplantar hyperkeratosis (PPK) and an associated predisposition to squamous cell carcinoma (SCC) of the skin, segregates as a recessive trait within the family. Interestingly, all the PPK-affected members of the family are phenotypic males (46,XY or 46,XX) while seven XX sibs are healthy phenotypic females with no signs of PPK. We propose that homozygosity for a single mutational event, possibly including contiguous genes, may cause PPK/SCC in both XY or XX individuals and sex reversal in XX individuals. The family is informative for linkage analysis for the PPK trait and allows linkage exclusion for the sex reversal trait. Here we show that 15 loci involved in PPK etiology, skin differentiation, function or malignancy, and nine loci involved in sex determination/differentiation are not implicated in the phenotype of this family.  相似文献   
34.
The electrophoretic mobility of peripheral blood lymphocytes from human subjects with positive Mantoux tests was measured before and after treatment with purified protein derivative. Lymphocytes from subjects with negative Mantoux reactions were used as controls. A large number of the first group lymphocytes showed a reduction of electrophoretic mobility and hence of the surface electrical charge. The mobility of the control cells submitted to the same treatment was unchanged. The possible presence of cytophilic antibodies or of cellular specific receptors on the lymphocyte surface is discussed.  相似文献   
35.
Buschini A  Poli P  Rossi C 《Mutagenesis》2003,18(1):25-36
The toxicity of most drugs is associated with their enzymatic conversion to toxic metabolites. Bioactivation reactions occur in a range of cellular organs and organelles, including mitochondria. We have investigated different effects (i.e. growth inhibition, mortality and genotoxicity) of doxorubicin, epirubicin and mitoxantrone on the D7 strain of Saccharomyces cerevisiae and on its petite (rho degrees ) respiratory-deficient mutant at various cellular concentrations of cytochrome P450 and glutathione (GSH). The data confirmed the importance of oxygen production for doxorubicin toxicity. The complete absence, or a very low level, of cytochrome oxidase subunit IV conferred some resistance to doxorubicin. Low GSH levels decreased resistance to doxorubicin in both strains, suggesting that thiol depletion could potentiate membrane lipid peroxidation. Doxorubicin induction of petite colonies suggests that the drug is able to select rather than induce respiratory-deficient mutants. Epirubicin induced levels of cytotoxicity similar to those of doxorubicin. The effects did not appear to be significantly dependent on mitochondrial function or GSH levels, whereas cells were strongly protected by cytochrome P450. GSH did not induce an evident alteration. Neither were genotoxic effects induced. Mitoxantrone had reduced levels of both growth inhibition and cytotoxicity in comparison to anthracyclines and induced convertants, revertants and aberrants. All the effects considered were amplified at high cytochrome P450 cellular concentrations, although the drug was also shown to act without previous metabolism via cytochrome P450. Anthracenedione effectiveness was increased by metabolism via cytochrome P450 and partially reduced by GSH. However, further mechanisms were suggested, which might implicate mitochondrial function and/or production of electrophilic cytotoxic and/or genotoxic intermediates by means of GSH conjugation. The biological effectiveness of doxorubicin, epirubicin and mitoxantrone on S.cerevisiae was shown to be strictly dependent on cell-specific physiological/biochemical conditions, such as a functional respiratory chain and levels of cytochrome P450 and GSH.  相似文献   
36.
We evaluated the BDProbeTec ET system (Becton Dickinson, Sparks, Md.), a strand displacement amplification-based technique, for direct detection of Mycobacterium tuberculosis in 867 clinical samples. Of 294 extrapulmonary specimens, 52 had positive results by both BDProbeTec ET and culture and 209 had negative results by both methods; sensitivity and specificity were 76.5 and 95.9%, respectively. After resolution of discrepancies, the sensitivity rose to 77.8%.  相似文献   
37.
Sclerosteosis: report of a case in a black African man   总被引:3,自引:0,他引:3  
Sclerosteosis is a rare genetic disorder of bone modelling, similar to, but distinct from, van Buchem disease; it has been described almost exclusively in Afrikaners of South Africa, a white population of Dutch ancestry. Isolated cases have been reported in a girl in Japan, a boy in Spain, and in multiracial families in Brazil and USA.
Here we report a case of sclerosteosis in a black man born in Senegal. He presented with the full features of the disease: tall stature; syndactyly; nail dysplasia; massive sclerosis of the long tubular bones, the ribs, the pelvis and the skull; multiple cranial nerve involvement: optic atrophy, facial palsy and trigeminal neuralgia. Radiologic examination, visual and brainstem auditory evoked potentials, computerized tomography and magnetic resonance imaging of the skull were performed. This seems to be the first case of the disease in a black African individual, with no known relationship with Dutch ancestry.  相似文献   
38.
In the original version of this article, the title was incorrect. Please find the correct title given here. The publisher deeply regrets this error. The original article to which this Erratum refers was published in Human Mutation 22:179–180 Human Mutation(2003) 22(2) 179–180  相似文献   
39.
Malignant granular cell tumors (MGCTs) are rare neoplasms of uncertain histogenesis. We report a case of MGCT involving a peripheral nerve with peritoneal and omental dissemination in which cytogenetic findings are available. Our results show that MGCTs share some cytogenetic abnormalities with malignant peripheral nerve sheath tumors (MPNSTs), supporting the hypothesis that they may represent histogenetically related lesions.  相似文献   
40.
We combined conventional cytogenetic analysis and fluorescence in situ hybridization of short-term cultures of 28 samples from benign prostatic hyperplasia. Lou of the Y chromosome was the most common chromosome change, followed by trisomy 7. Trisomy 7, however, may be unrelated to the origin of benign prostate hyperplasia, in which the only and not very specific change seems to be the loss of the Y chromosome. Genes Chrom Cancer 9:227-233 (1594). © 1994 Wiley-Liss, Inc.  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