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   6178篇
  免费   705篇
  国内免费   22篇
耳鼻咽喉   31篇
儿科学   219篇
妇产科学   124篇
基础医学   943篇
口腔科学   256篇
临床医学   694篇
内科学   1644篇
皮肤病学   163篇
神经病学   399篇
特种医学   423篇
外科学   684篇
综合类   102篇
一般理论   4篇
预防医学   423篇
眼科学   152篇
药学   370篇
中国医学   4篇
肿瘤学   270篇
  2021年   81篇
  2020年   58篇
  2019年   66篇
  2018年   85篇
  2017年   68篇
  2016年   79篇
  2015年   89篇
  2014年   124篇
  2013年   190篇
  2012年   218篇
  2011年   268篇
  2010年   168篇
  2009年   145篇
  2008年   230篇
  2007年   240篇
  2006年   265篇
  2005年   246篇
  2004年   224篇
  2003年   204篇
  2002年   222篇
  2001年   224篇
  2000年   244篇
  1999年   189篇
  1998年   131篇
  1997年   115篇
  1996年   112篇
  1995年   86篇
  1994年   91篇
  1993年   71篇
  1992年   193篇
  1991年   147篇
  1990年   144篇
  1989年   141篇
  1988年   139篇
  1987年   138篇
  1986年   135篇
  1985年   141篇
  1984年   97篇
  1983年   97篇
  1982年   77篇
  1981年   70篇
  1980年   49篇
  1979年   93篇
  1978年   69篇
  1977年   56篇
  1976年   61篇
  1974年   48篇
  1972年   59篇
  1971年   56篇
  1970年   56篇
排序方式: 共有6905条查询结果,搜索用时 15 毫秒
51.
Eleven strains of eugonic, nonoxidative, gram-negative rods isolated from clinical specimens formed a distinct group that was designated CDC group IIg. Five of the 11 isolates were from wounds. The phenotypic characteristics of CDC group IIg were most similar to those of Weeksella species, with the major difference being that CDC group IIg strains grew on MacConkey agar in 1 to 2 days, did not hydrolyze gelatin, and did not produce urease. All 11 strains of CDC group IIg possessed a distinct fatty acid profile that was characterized by large amounts (19 to 29%) of 18:1 omega 7c, 16:0, and 16:1 omega 7c, moderate amounts (6 to 10%) of 3-OH-14:0 and 14:0, and smaller amounts (1 to 2%) of 18:2, 18:0, and 3-OH-16:0. This fatty acid profile differs from those of Weeksella species by the absence of branched-chain fatty acids. CDC group IIg contains ubiquinone-8, as opposed to menaquinone-6 in Weeksella species. The isolates were susceptible to a variety of antimicrobial agents, including the aminoglycosides, tetracyclines, quinolones, sulfonamides, and polymyxin B.  相似文献   
52.
AIMS--To study the consistency of reporting of abnormal rectal biopsy specimens, especially in the differentiation of inflammatory bowel disease from other causes of abnormality. METHODS--Sixty rectal biopsy specimens were identified from patients presenting with bloody diarrhoea. These were then circulated to the 11 consultant pathologists in the study who filled in a proforma with a list of 12 diagnostic categories and 22 features. RESULTS--Forty one of the 60 cases were examples of inflammatory bowel disease. In 33 of these cases nine or more pathologists had made the diagnosis. Further categorisation into ulcerative colitis and Crohn''s disease showed better recognition of ulcerative colitis. In the 19 cases of non-inflammatory bowel disease recognition of pseudomembranous colitis and solitary rectal ulcer syndrome was good, but the results were poorer in the case of infective colitis. CONCLUSION--The findings suggest that a group of consultant pathologists can differentiate between inflammatory bowel disease and other causes of an abnormal rectal biopsy specimen and can also recognise pseudomembranous colitis and solitary rectal ulcer syndrome satisfactorily.  相似文献   
53.
54.
Although recent epidemiologic studies suggest that silicone augmentation of the breast is not associated with an increased risk of mammary carcinoma, cases of breast carcinoma arising in augmented breasts are being increasingly encountered as a large number of patients who had augmentation are getting older. A case of a 51-year-old woman with a 20-year history of breast augmentation who developed an invasive cribriform carcinoma associated with extensive microcalcification is presented. The patient had submammary silicone implants 20 years ago that were replaced, because of local complications, in subpectoral positions 10 years later. Dispersive X-ray microanalysis failed to demonstrate silicone in sections of the tumor and adjacent breast tissue. Appropriately fixed tumor tissue was available for electron microscopic examination. The tumor cells were rich in mitochondria, and their luminal surfaces were endowed with abundant microvilli, but the cell surfaces that came closest to the calcified microspheriols were devoid of microvilli and had cellular buddings between the microspheriols. It is suggested that the tumor cells might have been actively involved in the process of microcalcification.  相似文献   
55.
Lysosomal enzyme activities were studied in cells derived from the following types of leukaemia: chronic myeloid, acute myeloid, acute myelomonocytic, acute monocytic, non-T, non-B cell acute lymphoblastic, T-cell acute lymphoblastic, B-cell chronic lymphocytic and T-cell chronic lymphocytic. Activities of beta-hexosaminidase and alpha-mannosidase were significantly higher in cells from acute monocytic and acute myelomonocytic leukaemias, and somewhat higher in the other myeloid leukaemias, when compared with control granulocytes. Activities of beta-hexosaminidase, alpha-mannosidase, alpha-fucosidase, beta-glucuronidase and acid phosphatase were markedly lower in B cells of chronic lymphocytic leukaemia when compared with control or other leukaemic lymphoid cells. On isoelectric focusing abnormal patterns of beta-hexosaminidase, alpha-mannosidase and beta-glucuronidase activities were commonly found in myeloid and non-T, non-B cell leukaemias. All patients with acute myeloid leukaemia exhibited a relative decrease in the B form of beta-hexosaminidase activity. The results described show that studies on lysosomal enzymes may assist in the classification of different types of leukaemia.  相似文献   
56.
Previous DNA relatedness and enzyme electrophoretic mobility studies indicated heterogeneity among strains of Legionella pneumophila serogroups 1, 4, 5, and Lansing 3 (a new, as yet unnumbered serogroup). In this study 60 L. pneumophila strains were studied by DNA hybridization (hydroxyapatite method) to assess their genomic relatedness. These strains were also studied biochemically and serologically to determine whether they formed one or more phenotypic groups. DNA relatedness studies identified three groups. DNA group 1 contained the type strain Philadelphia 1 and strains from serogroups 1 through 14 of L. pneumophila. The average relatedness of DNA group 1 strains was 88% at 60 degrees C with 1.1% divergence in related sequences and 85% at 75 degrees C. DNA group 2 contained strain Los Angeles 1, the reference strain of serogroup 4, and strains of serogroups 1, 4, 5, and Lansing 3, an unnumbered serogroup. Average relatedness of DNA group 2 strains was 84% at 60 degrees C with 0.7% divergence and 87% at 75 degrees C. Reciprocal relatedness of DNA groups 1 and 2 was approximately 67% at 60 degrees C with 6.0% divergence and 48% at 75 degrees C. DNA group 3 strains were in serogroup 5. They were 98% related at 60 degrees C with 0.5% divergence and 97% related at 75 degrees C. Reciprocal relatedness of DNA group 3 and DNA group 1 was approximately 74% at 60 degrees C with 5.3% divergence and 43% at 75 degrees C, and reciprocal relatedness of DNA groups 3 and 2 was 66% at 60 degrees C with 5.7% divergence and 55% at 75 degrees C. The DNA groups could not be separated biochemically or serologically or by cell wall fatty acid and isoprenoid quinone composition. Three subspecies of L. pneumophila are proposed to accommodate the three DNA groups: L. pneumophila subsp. pneumophila subsp. nov. for DNA group 1, L. pneumophila subsp. fraseri subsp. nov. for DNA group 2, and pneumophila subsp. pascullei subsp. nov. for DNA group 3.  相似文献   
57.
58.
We have conducted a population-based association study of substance abuse and a microsatellite at the dopamine D5 receptor locus (DRD5) in a sample of European–American males and females with substance dependence (SA) or without any psychiatric disorder. Overrepresentation of the most frequent allele (148 bp) was found in males in the SA group (OR = 2.2, P= .02); this finding was reproduced in females (OR = 5.4, p< .001). The difference in the frequencies of this allele between SA males and SA females was statistically significant. The genotype coded in accordance with the dose of this allele correlated with substance abuse liability in males and females (stronger in females) and with novelty seeking in females. There was no evidence of correlation between the genotypes of spouses that could be induced by assortative mating for the liability to substance abuse. The data suggest that the DRD5 locus is involved in the variation and sex dimorphism of substance abuse liability.CEDAR is a consortium between St. Francis Medical Center and the University of Pittsburgh.  相似文献   
59.
Epidermal mosaicism and Blaschko''s lines.   总被引:1,自引:1,他引:1       下载免费PDF全文
To test the hypothesis that epidermal rather than dermal mosaicism determines Blaschko's lines in hypomelanosis of Ito (HI), we studied the distribution of chromosomal mosaicism in four patients. In two, mosaicism had not been detected in lymphocytes or dermal fibroblasts, but was clearly shown in epidermal keratinocytes; furthermore, the abnormal cell line was confirmed to the hypopigmented epidermis and the normal epidermis contained only normal cells. Negative findings in the other two patients might be because of mosaicism which was undetected either because it was submicroscopic or because it was present in melanocytes, which have not yet been studied. These preliminary results support the ideas that (1) Blaschko's lines represent single clones of epidermal cells; (2) in patients with HI and severe neurological involvement mosaicism, if detectable, is best shown in keratinocytes; and (3) the cytogenetic defect in epidermal cells may be directly responsible for the failure of pigmentation in HI.  相似文献   
60.
Microorganisms detected in situ on the distal tip of central venous catheters (CVC) within 90 min of insertion were investigated using pulsed-field gel electrophoresis to analyse genomic fragments obtained with theSmaI restriction enzyme. Thirty patients received a triple lumen CVC, which was inserted directly through the skin using the Seldinger technique. In a further 30 patients a triple lumen CVC was inserted through a Swan sheath, thereby avoiding direct contact of the CVC with the skin. Staphylococci were isolated from the distal tips of the catheters in 6 patients (5 who had the CVC inserted directly through the skin and 1 who had the CVC inserted via a Swan sheath.) Twenty-three staphylococcal isolates were also isolated from the insertion equipment and the skin swabs surrounding the insertion site of these six patients. All the isolates were genotyped. In one of the patients the organisms isolated from the skin were identical to those on the CVC tip. In two further patients similar organisms were isolated from the insertion equipment and the patients' skin. These results, in addition to the reduced colonisation rates observed when catheters were introduced through a Swan sheath, support the hypothesis that microorganisms from the skin are impacted onto the CVC tip and the CVC insertion equipment at catheter insertion.  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