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   7321篇
  免费   738篇
  国内免费   49篇
耳鼻咽喉   48篇
儿科学   186篇
妇产科学   171篇
基础医学   1034篇
口腔科学   364篇
临床医学   919篇
内科学   1422篇
皮肤病学   122篇
神经病学   473篇
特种医学   401篇
外科学   1015篇
综合类   130篇
一般理论   5篇
预防医学   696篇
眼科学   74篇
药学   617篇
中国医学   7篇
肿瘤学   424篇
  2022年   53篇
  2021年   97篇
  2020年   77篇
  2019年   95篇
  2018年   120篇
  2017年   77篇
  2016年   93篇
  2015年   108篇
  2014年   159篇
  2013年   226篇
  2012年   263篇
  2011年   308篇
  2010年   185篇
  2009年   154篇
  2008年   256篇
  2007年   316篇
  2006年   310篇
  2005年   308篇
  2004年   250篇
  2003年   239篇
  2002年   256篇
  2001年   229篇
  2000年   232篇
  1999年   263篇
  1998年   123篇
  1997年   119篇
  1996年   108篇
  1995年   88篇
  1994年   91篇
  1993年   87篇
  1992年   198篇
  1991年   175篇
  1990年   159篇
  1989年   155篇
  1988年   181篇
  1987年   154篇
  1986年   150篇
  1985年   161篇
  1984年   118篇
  1983年   94篇
  1982年   75篇
  1981年   79篇
  1979年   74篇
  1978年   59篇
  1977年   59篇
  1974年   78篇
  1973年   74篇
  1971年   62篇
  1970年   52篇
  1968年   56篇
排序方式: 共有8108条查询结果,搜索用时 18 毫秒
31.
32.
OBJECTIVES: To examine factors influencing the rate of transmitted drug resistance (TDR) among seroconverters, with particular emphasis on 3 widely used genotypic drug resistance algorithms. METHODS: The study used data from CASCADE (Concerted Action on Seroconversion to AIDS and Death in Europe), a collaboration of seroconverter cohorts in Europe and Canada. Genotypic resistance data were derived within 18 months of the last seronegative test or date of laboratory evidence of acute infection and before the initiation of antiretroviral therapy. The Stanford algorithm was used to analyze each individual's nucleotide sequence. A multivariate logistic model was used to assess independent relationships between the presence of TDR and exposure category, sex, age at seroconversion, and year of seroconversion. The paper also describes 3 alternative definitions of resistance: the Stanford algorithm, the key resistance mutations defined by the International AIDS Society, and the Agence Nationale de Recherches sur le Sida (ANRS) algorithm. RESULTS: Forty-five of 438 patients (10.3%) seroconverting between 1987 and 2003 were infected with a drug-resistant HIV-1 variant. Forty patients (9.1%) showed resistance mutations to only 1 class of antiretroviral drugs, 2 (0.5%) to 2 classes, and 3 (0.7%) to 3 classes of antiretroviral therapy. It was suggested that individuals seroconverting later in calendar time were more likely to have TDR (relative risk 3.89 and 95% CI: 0.84 to 18.02, and relative risk 4.69 and 95% CI: 1.03 to 21.31, for 1996-1999 and 2000-2003, respectively, compared with pre-1996; P trend = 0.08). This trend was apparent regardless of the definition of TDR used. The total estimated proportion of individuals with TDR varied between 10.3% and 15.5% according to which definition was used. CONCLUSIONS: Evidence was found for the rise of TDR over time. A specific definition of what constitutes TDR rather than a simple list of mutations is needed.  相似文献   
33.
The T-cell receptor β locus (TCRB) on chromosome 7q35 was studied as a candidate region for genetic susceptibility to type 1 insulin-dependent diabetes (IDDM). A highly polymorphic microsatellite marker mapping to the TCRBV6.7 gene and a TCRB C-region RFLP were used to genotype the members of a total of 21 multiplex IDDM families from two different geographical areas. There was no evidence to support linkage to either of these markers with IDDM, and conventional two-point analysis excluded linkage to the telomeric end of the TCRB complex, in the region of the highly informative TCRBV6.7 marker. There was significant linkage of IDDM to the class II HLA-D locus with significant lod scores >3.0 obtained for the HLA-DRB1 and HLA-DQB1 genes. Affected sib-pair (ASP) and transmission disequilibrium (TDT) association tests confirmed these findings.  相似文献   
34.
Mouse mammary epithelial cells (HC-11) and mammary tissues were analyzed for developmental changes in circadian clock, cellular proliferation, and differentiation marker genes. Expression of the clock genes Per1 and Bmal1 were elevated in differentiated HC-11 cells, whereas Per2 mRNA levels were higher in undifferentiated cells. This differentiation-dependent profile of clock gene expression was consistent with that observed in mouse mammary glands, as Per1 and Bmal1 mRNA levels were elevated in late pregnant and lactating mammary tissues, whereas Per2 expression was higher in proliferating virgin and early pregnant glands. In both HC-11 cells and mammary glands, elevated Per2 expression was positively correlated with c-Myc and Cyclin D1 mRNA levels, whereas Per1 and Bmal1 expression changed in conjunction with beta-casein mRNA levels. Interestingly, developmental stage had differential effects on rhythms of clock gene expression in the mammary gland. These data suggest that circadian clock genes may play a role in mouse mammary gland development and differentiation.  相似文献   
35.
36.
Puri  Beena  Nelson  William  Porter  Kevin R.  Henchal  Erik A.  Hayes  Curtis G. 《Virus genes》1998,17(1):85-88
We have determined the complete nucleotide sequence and the deduced amino acid polypeptide sequence of the genome of a dengue-1 (DEN-1) virus strain isolated from a patient on Nauru in the Western Pacific in 1974 (West Pac 74). The complete genome is 10,735 nucleotides in length and contains a single long open reading frame of 10,176 nucleotides encoding a polyprotein of 3392 amino acids. When compared to DEN-1 Singapore S275/90, the nucleotide and amino acid sequence homology are 94% and 97.8%, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
37.
38.
Coeliac disease is an important cause of malabsorption, particularly of folic acid, in adults. We investigated the possibility that it might be a maternal risk factor for neural tube defect (NTD)-associated pregnancy by screening affected mothers using serum endomysial antibody (EmA) which has high sensitivity and specificity for coeliac disease. One (1.6%) of 60 patients was EmA positive and had a diagnosis of coeliac disease confirmed by the finding of villous atrophy on jejunal biopsy. In conclusion, the majority of NTD-associated pregnancies are not associated with maternal coeliac disease and our study is additional evidence that abnormalities of folic acid metabolism rather than absorption are the most important risk factors for NTD. Further studies are needed to determine whether the coeliac disease prevalence among women with NTD-affected pregnancy is higher than that of the general population.  相似文献   
39.
This exploratory study was designed to begin analysis on the "Faculty Work Plan" and its potential for faculty role development in a university setting. The specific goals were: (1) to identify the degree of congruence between faculty work plans and the school goals; and (2) to determine the relationship between faculty work plan/school goal congruence, faculty productivity, potency, and job satisfaction. The sample was composed of 26 respondents, 26 to 50 years old, from a pool of 48 full-time faculty members affiliated with a school of nursing in a university setting. Likert-type rating scores were used to measure Faculty Work Plan-School Goal Congruence (FWP-SG), job satisfaction, productivity, and potency. Data analyses were focused on frequency distribution, group means, and Pearson Correlation Coefficients on selected pairs of variables. Interesting findings were revealed. A strong relationship was found between FWP-SG congruence and faculty productivity (r = .85; p = .000) and potency (r = .84; p = .000). Several recommendations were suggested.  相似文献   
40.
The initial results from a diagnostic breast clinic in which clinical examination, x-ray mammography and ultrasound are used to establish a diagnosis during a single patient-visit are described. In 3461 patient-visits, 82 histologically-proven breast cancers were detected. Fifty-two per cent of these cancers were 2 cm or less in diameter and 61% had no axillary lymph-node metastases. Fifteen cancers were impalpable lesions which were detected by mammography alone. The over-all malignant-to-benign biopsy ratio was 1:2.7; for impalpable tumours, this ratio was 1:3.9. The role of such a diagnostic breast clinic is discussed, and attention is drawn to a relatively low attendance of women in the "high-risk" age group of over 50 years of age.  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