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   33636篇
  免费   2306篇
  国内免费   526篇
耳鼻咽喉   604篇
儿科学   583篇
妇产科学   492篇
基础医学   5581篇
口腔科学   422篇
临床医学   2808篇
内科学   7003篇
皮肤病学   1543篇
神经病学   2334篇
特种医学   2046篇
外科学   4023篇
综合类   338篇
一般理论   6篇
预防医学   1364篇
眼科学   1023篇
药学   3082篇
  2篇
中国医学   496篇
肿瘤学   2718篇
  2024年   21篇
  2023年   223篇
  2022年   763篇
  2021年   1135篇
  2020年   656篇
  2019年   898篇
  2018年   1051篇
  2017年   883篇
  2016年   1307篇
  2015年   1821篇
  2014年   2056篇
  2013年   2241篇
  2012年   3250篇
  2011年   3014篇
  2010年   2040篇
  2009年   1585篇
  2008年   2101篇
  2007年   1943篇
  2006年   1699篇
  2005年   1572篇
  2004年   1237篇
  2003年   1071篇
  2002年   975篇
  2001年   445篇
  2000年   421篇
  1999年   331篇
  1998年   164篇
  1997年   153篇
  1996年   107篇
  1995年   76篇
  1994年   64篇
  1993年   56篇
  1992年   100篇
  1991年   117篇
  1990年   84篇
  1989年   93篇
  1988年   109篇
  1987年   85篇
  1986年   58篇
  1985年   48篇
  1984年   36篇
  1983年   42篇
  1982年   18篇
  1981年   23篇
  1980年   26篇
  1979年   37篇
  1978年   30篇
  1977年   28篇
  1973年   19篇
  1971年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Angiogenesis is an essential process in the development, growth, and metastasis of malignant tumors including lung cancer. DNA sequence variations in the vascular endothelial growth factor (VEGF) gene may lead to altered VEGF production and/or activity, thereby causing interindividual differences in the susceptibility to lung cancer via their actions on the pathways of tumor angiogenesis. To test this hypothesis, we investigated the potential association between three VEGF polymorphisms (-460T > C, +405C > G, and 936C > T)/haplotypes and the risk of lung cancer in a Korean population. VEGF genotypes were determined in 432 lung cancer patients and 432 healthy controls that were frequency matched for age and sex. VEGF haplotypes were predicted using Bayesian algorithm in the phase program. Compared with the combined +405 CC and CG genotype, the +405 GG genotype found associated with a significantly decreased risk of small cell carcinoma [SCC; adjusted odds ratio (OR), 0.36; 95% confidence interval (95% CI), 0.17-0.78]. The 936 CT genotype and the combined 936 CT and TT genotype were also associated with a significantly decreased risk of SCC compared with the 936 CC genotype (adjusted OR, 0.47; 95% CI, 0.26-0.85 and adjusted OR, 0.44; 95% CI, 0.24-0.80, respectively). Haplotype CGT was associated with a significantly decreased risk of SCC (adjusted OR, 0.39; 95% CI, 0.18-0.87), whereas haplotype TCC conferred a significantly increased risk of SCC (adjusted OR, 1.63; 95% CI, 1.14-2.33). None of the VEGF polymorphisms studied significantly influenced the susceptibility to lung cancer except SCC. However, haplotypes TCT and TGT were significantly associated with the risk of overall lung cancer, respectively (adjusted OR, 0.38; 95% CI, 0.25-0.60 and adjusted OR, 3.94; 95% CI, 2.00-7.76, respectively). These effects of haplotypes TCT and TGT on lung cancer risk were observed in three major histologic types of lung cancer. These results suggest that the VEGF gene may be contribute to an inherited predisposition to lung cancer.  相似文献   
82.
83.
Adhesive force of chondrocytes to cartilage. Effects of chondroitinase ABC   总被引:5,自引:0,他引:5  
Chondrocyte transplantation is a clinical procedure for cartilage repair. Transplanted cells may have difficulty attaching to the surface of chondral lesions because of the anti-adhesive properties of the proteoglycan rich matrix. This study used micromanipulation methods to determine if pretreatment of cartilage with chondroitinase ABC affects chondrocyte adhesion to cartilage and if chondrocytes adhere preferentially to the superficial, middle, or deep layers of cartilage. Bovine chondrocytes were transplanted in vitro on articular cartilage sections cut perpendicular to the articular surface. At various times between 15 and 75 minutes after seeding, a micropipette micromanipulation system was used to measure the adhesion force of individual chondrocytes to cartilage. The chondrocyte adhesion force increased with chondroitinase ABC treatment and seeding time but generally was similar for the different regions of articular cartilage (superficial, middle, deep layer) to which the cells were attached. For normal cartilage, the adhesion force increased from 1.29 +/- 0.24 mdyne after 15 to 30 minutes seeding to 5.29 +/- 0.25 mdyne after 60 to 75 minutes. Treatment with chondroitinase ABC at certain concentrations and durations (1.0 U/mL for 5 minutes or 0.5 or 1 U/mL for 15 minutes) led to an increase in adhesion force, whereas relatively low concentration or treatment time (0.25 U/mL for 15 minutes or 0.5 U/mL for 5 minutes) had little or no detectable effect. The increase in adhesion attributable to chondroitinase ABC treatment appeared most marked (+144% to +292%) for short (15 to 30 minutes) seeding durations but was still significant (+46%) for the longest seeding period (60 to 75 minutes) studied after the 1 U/mL for 15 minute treatment condition. These results provide direct biomechanical evidence that enzymatic treatment of a cartilage surface can enhance chondrocyte adhesion.  相似文献   
84.
85.
Background: Redistribution hypothermia caused by vasodilation during anesthesia is the primary cause of perioperative hypothermia. Propofol exerts a dose-dependent vasodilatory effect, whereas dexmedetomidine induces peripheral vasoconstriction at high plasma concentrations. This study compared the effects of dexmedetomidine and propofol on core temperature in patients undergoing surgery under spinal anesthesia.Methods: This prospective study included 40 patients (aged 19-70 years) with American Society of Anesthesiologists Physical Status class I-III who underwent elective orthopedic lower-limb surgery under spinal anesthesia. Patients were randomly allocated to a dexmedetomidine or propofol group (n = 20 per group). After induction of spinal anesthesia, patients received dexmedetomidine (loading dose: 1 μg/kg over 10 min; maintenance dose: 0.2-0.7 μg/kg/h) or propofol (loading dose: 75 μg/kg over 10 min; maintenance dose: 12.5-75 μg/kg/min). The doses of sedatives were titrated to maintain moderate sedation. During the perioperative period, tympanic temperatures, thermal comfort score, and shivering grade were recorded.Results: Core temperature at the end of surgery did not differ significantly between the groups (36.4 ± 0.4 and 36.1 ± 0.7°C in the dexmedetomidine and propofol groups, respectively; P = 0.118). The lowest perioperative temperature, incidence and severity of perioperative hypothermia, thermal comfort score, and shivering grade did not differ significantly between the groups (all P > 0.05).Conclusions: In patients undergoing spinal anesthesia with moderate sedation, the effect of dexmedetomidine on patients'' core temperature was similar to that of propofol.  相似文献   
86.
BackgroundPerimetry is important in the management of children with glaucoma, but there is limited evidence-based guidance on its use. We report an expert consensus-based study to update guidance and identify areas requiring further research.MethodsExperts were invited to participate in a modified Delphi consensus process. Panel selection was based on clinical experience of managing children with glaucoma and UK-based training to minimise diversity of view due to healthcare setting. Questionnaires were delivered electronically, and analysed to establish ‘agreement’. Divergence of opinions was investigated and resolved where possible through further iterations.Results7/9 experts invited agreed to participate. Consensus (≥5/7 (71%) in agreement) was achieved for 21/26 (80.8%) items in 2 rounds, generating recommendations to start perimetry from approximately 7 years of age (IQR: 6.75–7.25), and use qualitative methods in conjunction with automated reliability indices to assess test quality. There was a lack of agreement about defining progressive visual field (VF) loss and methods for implementing perimetry longitudinally.Panel members highlighted the importance of informing decisions based upon individual circumstances—from gauging maturity/capability when selecting tests and interpreting outcomes, to accounting for specific clinical features (e.g. poor IOP control and/or suspected progressive VF loss) when making decisions about frequency of testing.ConclusionsThere is commonality of expert views in relation to implementing perimetry and interpreting test quality in the management of children with glaucoma. However, there remains a lack of agreement about defining progressive VF loss, and utilising perimetry over an individuals’ lifetime, highlighting the need for further research.Subject terms: Paediatrics, Glaucoma  相似文献   
87.
88.
博落回中生物碱质谱裂解规律研究进展   总被引:5,自引:1,他引:5  
卿志星  程辟  曾建国 《中草药》2013,44(20):2929-2939
博落回中生物碱的代谢途径可简化为:氨基酸→苄基异喹啉类生物碱→四氢原小檗碱型生物碱(或者转化成阿朴芬类生物碱)→N-甲基-四氢原小檗碱型生物碱(或者转化成原小檗碱型生物碱)→普罗托品类生物碱→二氢苯并菲啶类生物碱→苯并菲啶类生物碱→苯并菲啶类生物碱二聚体。对博落回代谢途径中9类生物碱质谱裂解规律的总结,为利用质谱裂解方式初步确定生物碱的结构类型;利用LC-MS鉴定不同产地、不同时期、不同部位博落回中标识性生物碱;以博落回中生物碱为原料而开发的中兽药药动学以及药物残留的研究;解析博落回中微量生物碱的结构式以及对其他天然药物中同类生物碱的质谱研究提供参考。  相似文献   
89.
90.
PURPOSE: To determine the epidemiology of refractive errors in an adult Chinese population in Singapore. METHODS: A disproportionate, stratified, clustered, random-sampling procedure was used to select names of 2000 Chinese people aged 40 to 79 years from the 1996 Singapore electoral register in the Tanjong Pagar district in Singapore. These people were invited to a centralized clinic for a comprehensive eye examination, including refraction. Refraction was also performed on nonrespondents in their homes. Myopia, high myopia, and hyperopia were defined as a spherical equivalent (SE) in the right eye of less than -0.5 D, less than -5.0 D, and more than +0.5 D, respectively. Astigmatism was defined as less than -0.5 D of cylinder. Anisometropia was defined as a difference in SE of more than 1.0 D between the two eyes. Only phakic eyes were analyzed. RESULTS: From 1717 eligible people, 1232 (71.8%) were examined. Adjusted to the 1997 Singapore population, the overall prevalence of myopia, hyperopia, astigmatism, and anisometropia was 38.7% (95% confidence interval [CI]: 35.5, 42.1), 28.4% (95% CI: 25.3, 31.3), 37.8% (95% CI: 34.6, 41.1), and 15.9% (95% CI: 13.5, 18.4), respectively. The prevalence of high myopia was 9.1% (95% CI: 7.2, 11.2), with women having significantly higher rates than men. The age pattern of myopia was bimodal, with higher prevalence in the 40 to 49 and 70 to 81 age groups and lower prevalence between those age ranges. Prevalence was reversed in hyperopia, with a higher prevalence in subjects aged 50 to 69. There was a monotonic increase in prevalence with age for both astigmatism and anisometropia. Increasing educational levels, higher individual income, professional or office-related occupations, better housing, and greater severity of nuclear opacity were all significantly associated with higher rates of myopia, after adjustment for age and sex. CONCLUSIONS: The results indicate that whereas myopia is 1.5 to 2.5 times more prevalent in adult Chinese residing in Singapore than in similarly aged European-derived populations in the United States and Australia, the sociodemographic associations are similar.  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