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   16214篇
  免费   969篇
  国内免费   81篇
耳鼻咽喉   144篇
儿科学   340篇
妇产科学   247篇
基础医学   2277篇
口腔科学   356篇
临床医学   1655篇
内科学   3433篇
皮肤病学   201篇
神经病学   1746篇
特种医学   637篇
外科学   2468篇
综合类   77篇
一般理论   36篇
预防医学   1108篇
眼科学   195篇
药学   1270篇
中国医学   19篇
肿瘤学   1055篇
  2023年   103篇
  2022年   175篇
  2021年   404篇
  2020年   289篇
  2019年   435篇
  2018年   454篇
  2017年   335篇
  2016年   445篇
  2015年   431篇
  2014年   634篇
  2013年   851篇
  2012年   1221篇
  2011年   1254篇
  2010年   683篇
  2009年   632篇
  2008年   1041篇
  2007年   1111篇
  2006年   1020篇
  2005年   982篇
  2004年   875篇
  2003年   756篇
  2002年   795篇
  2001年   123篇
  2000年   79篇
  1999年   109篇
  1998年   144篇
  1997年   147篇
  1996年   128篇
  1995年   101篇
  1994年   105篇
  1993年   106篇
  1992年   79篇
  1991年   64篇
  1990年   66篇
  1989年   51篇
  1988年   45篇
  1987年   43篇
  1986年   53篇
  1985年   58篇
  1984年   50篇
  1983年   61篇
  1982年   66篇
  1981年   69篇
  1980年   65篇
  1979年   32篇
  1978年   40篇
  1977年   45篇
  1976年   33篇
  1975年   28篇
  1974年   34篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
AIMS: To study the relation between maximum urethral closure pressure at rest and urethral hypermobility in female patients. PATIENTS AND METHODS: We selected 255 patients aged 20 years and older, with a stable bladder on multichannel urodynamics, without known neurological pathology, and without a history of pelvic or anti-incontinence surgery. A resting urethral pressure profile and the degree of urethral hypermobility were registered. Two-tailed analyses of variance (ANOVA) with Fisher's post-hoc tests were used to detect any statistically significant difference (P < 0.05) in urethral closure pressure between groups with varying degrees of urethral hypermobility. RESULTS: Mean age was 45.6 +/- 12.7 (range 20-77) years. Mean maximum urethral closure pressure for the entire group was 62.7 +/- 29 (range 10-150) cm of water. A statistically significant inverse relationship was found between age and maximum urethral closure pressure (r = 0.489, P < 0.0001) when both analyzed as continuous variables, and with age categorized in 10-year increments (P < 0.0001). When comparing mean urethral closure pressure in each group examined for urethral hypermobility, a statistically significant difference was noted when grades I, II, and III were compared to grade 0 hypermobility. No significant difference was observed when grades I, II, and III were compared to each other. Even if statistically non-significant, there exists an inverse relationship between the degree of urethral hypermobility and the maximum urethral closure pressure: a higher hypermobility is associated with a lesser urethral closure pressure. CONCLUSIONS: Urethral closure pressure falls significantly when urethral hypermobility is present. This decrease is not related to patient's age or parity. Our observations demonstrate an inverse relation between urethral closure pressure and the degree of cysto-urethrocele. As hypermobility increases, closure pressure decreases, even if this decrease does not reach the level of statistical significance.  相似文献   
993.
SUMMARY: Cytochromes P450 (CYP) 2C8 and 2C9 are polymorphic enzymes responsible for the biosynthesis of vasoactive substances from arachidonic acid including endothelium-derived hyperpolarizing factor. Inter-individual differences in the action of these substances might be important in the pathogenesis of cardiovascular diseases such as acute myocardial infarction (AMI) and hypertension. This study describes the relationship between genetic variants of CYP2C8 and CYP2C9, and morbidity in myocardial infarction in a large Swedish patient material. The study included 1172 AMI patients and 1503 control subjects (matched by age, sex and residential area) who participated in the Stockholm Heart Epidemiology Program (SHEEP). Genotyping was performed by allelic discrimination using a 5'-nuclease assay for the CYP2C8 and CYP2C9 variants. To estimate associations to AMI risks, odds ratios (OR) with 95% confidence intervals (CI) were calculated. The frequencies of CYP2C8*1, 2C8*3, 2C9*1, 2C9*2 and 2C9*3 variants in the control group were 0.91, 0.095, 0.83, 0.11 and 0.065, respectively. The risk of AMI in the female individuals carrying the *2 or *3 variant alleles of CYP2C9 and that of all individuals carrying the *3 variant of CYP2C8 was higher [OR (95% CI): 1.3 (1.0-1.9), P = 0.09; 1.5 (1.0-2.2), P = 0.06 and 1.2 (1.0-1.5), P = 0.07, respectively] compared to the groups with CYP2C8*1 and CYP2C9*1. Possession of rare genetic variants of the CYP2C8 and CYP2C9 genes in females is associated with a modest increase in risk of AMI. This might be related to genetic differences in the formation of endogenous vasoregulating eicosanoids.  相似文献   
994.
995.
996.
PURPOSE: It has been hypothesized that the biosynthesis of O-linked glycans on proteins, particularly on the highly O-glycosylated mucins, by the corneal and conjunctival epithelium is necessary for the protection and maintenance of a healthy ocular surface. The initial step in O-glycosylation is the enzymatic addition of N-acetyl galactosamine (GalNAc) to serine and threonine residues by a large family of polypeptide GalNAc-transferases (GalNAc-Ts). The purpose of this study was to determine the cellular distribution of GalNAc-Ts in the normal ocular surface epithelia and to compare their distribution with that in pathologically keratinized conjunctival epithelia. METHODS: Five conjunctival biopsy specimens and 5 corneas from normal individuals, and 14 conjunctival specimens from patients with ocular cicatricial pemphigoid (OCP) were used. Based on the histologic characteristics of their epithelia, OCP specimens were divided into two groups: less advanced, nonkeratinized (n = 6), and late-stage, keratinized (n = 8). Five monoclonal antibodies raised against the GalNAc-T1, -T2, -T3, -T4, and -T6 isoenzymes, were used for immunofluorescence microscopic localization according to standard protocols. RESULTS: Immunohistochemical studies revealed the presence of GalNAc-T2, -T3, and -T4 isoforms within the stratified epithelium of the cornea and the conjunctiva. The GalNAc-T4 isoenzyme was found in the apical cell layers, whereas GalNAc-T2 was found in the supranuclear region of the basal cell layers of both cornea and conjunctiva. GalNAc-T3 was distributed throughout the entire ocular surface epithelium, whereas GalNAc-T1 was found in scattered cells in conjunctiva only. Binding of antibody to GalNAc-T6 was restricted exclusively to conjunctival goblet cells. There were distinct alterations in expression patterns of GalNAc-T2, -T6, and -T1 in nonkeratinized OCP epithelia compared with normal epithelia. Both GalNAc-T2 and -T6 were expressed in the apical stratified epithelia, and T1 was detected in all cell layers in five of six biopsy specimens. By comparison with nonkeratinized OCP epithelia, a marked reduction in the binding of GalNAc-T antibody was observed in the late-stage keratinized conjunctival epithelia of patients with OCP. In all samples, apical GalNAc-T2 was absent, and GalNAc-T6 was entirely absent. Only one of eight samples was positive for GalNAc-T1. CONCLUSIONS: The presence of GalNAc-T isoenzymes in the human corneal and conjunctival epithelia is cell-layer and cell-type specific. The increased distribution of GalNAc-Ts observed in early stages of the keratinization process in patients with OCP suggests a compensatory attempt of the ocular surface epithelium to synthesize mucin-type O-glycans to maintain a wet-surface phenotype. This early increase in isoenzymes in nonkeratinized OCP epithelia is reduced as keratinization proceeds in the disease.  相似文献   
997.
9-Benzyl-3-methylene-1,5-di-p-toluenesulfonyl-1,5,9-triazacyclododecane (CADA) has been identified as a novel antiviral lead compound with significant anti-human immunodeficiency virus and anti-human herpesvirus 7 activity. Surprisingly, this compound selectively decreased the expression of the CD4 glycoprotein, the primary receptor needed for the entry of both viruses. Herein, we describe the CD4 down-modulating and antiviral potencies of more than 25 CADA derivatives. Flow cytometric evaluation of cellular CD4 receptor expression in T cells demonstrated the specific CD4 down-modulating capacity of the CADA derivatives, with IC(50) values similar to those obtained in the antiviral assays. The close correlation observed between the CD4 down-regulating and anti-HIV potencies of the CADA derivatives further points to CD4 receptor down-modulation as the primary mode of antiviral action for this group of compounds.  相似文献   
998.
We describe a pregnant patient with a long history of inhalant abuse who came to our hospital twice during her pregnancy. In both admissions, she was treated with fomepizol (4-MP), a newly available alcohol dehydrogenase antagonist for treatment of ethylene glycol poisoning.  相似文献   
999.
Congress has required CMS to expand the Medicare outpatient prospective payment system (PPS) for dialysis services to include as many drugs and diagnostic procedures provided to end stage renal disease (ESRD) patients as possible. One important implementation question is whether dialysis facility case mix should be reflected in payment. We use fiscal year (FY) 2000 cost report and patient billing and clinical data to determine the relationship between costs and case mix, as represented by several patient demographic, diagnostic, and clinical characteristics. Results indicate considerable variability in costs and case mix across facilities and a significant and substantial relationship between case mix and facility cost, suggesting case mix payment adjustment may be important.  相似文献   
1000.
Soil artificially contaminated with fluorene, phenanthrene, pyrene, and benz[a]anthracene was inoculated with the wood-rotting fungi Plrurotus ostreatus and Antrodia vaillantii. During 12 weeks of incubation, polycyclic aromatic hydrocarbon (PAH) degradation and the formation of persistent degradation products were monitored by chemical analysis. In addition, the effect on the indigenous soil bacteria was studied by plate count techniques and by measuring the concentration of bacteria-specific phospholipid fatty acids (PLFAs). In both soils inoculated with fungi, the PAH degradation was enhanced compared to the control soil without fungi. The white-rot fungus P. ostreatus accelerated the degradation rate radically the first weeks, while the effect of the brown-rot fungus was more pronounced at later stages during the 12-week study. In a soil with no amendments, the final degradation result was similar to that in the soil with added fungi, although the degradation pattern for the individual PAHs was different. Furthermore, the degradation by P. ostreatus was accompanied by an accumulation of PAH metabolites, that is, 9-fluorenone, benz[a]anthracene-7,12-dione, and two compounds identified as 4-hydroxy-9-fluorenone and 4-oxapyrene-5-one, that was not seen in the other soils. The inoculation with the white-rot fungus also had a large negative effect on the indigenous soil bacteria. This could be an important drawback of using the white-rot fungus P. ostreatus in soil bioremediation since a sequential fungal-bacterial degradation probably is needed for a complete degradation of PAHs in soil. In the soil inoculated with A. vaillantii, on the other hand, no metabolites accumulated, and no negative effects were observed on the indigenous microorganisms.  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