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   2391篇
  免费   191篇
  国内免费   62篇
耳鼻咽喉   9篇
儿科学   75篇
妇产科学   50篇
基础医学   353篇
口腔科学   124篇
临床医学   218篇
内科学   519篇
皮肤病学   20篇
神经病学   158篇
特种医学   138篇
外科学   250篇
综合类   35篇
一般理论   4篇
预防医学   254篇
眼科学   22篇
药学   185篇
中国医学   7篇
肿瘤学   223篇
  2022年   14篇
  2021年   21篇
  2020年   15篇
  2019年   34篇
  2018年   36篇
  2017年   40篇
  2016年   46篇
  2015年   38篇
  2014年   62篇
  2013年   77篇
  2012年   88篇
  2011年   83篇
  2010年   71篇
  2009年   63篇
  2008年   115篇
  2007年   132篇
  2006年   124篇
  2005年   110篇
  2004年   93篇
  2003年   87篇
  2002年   76篇
  2001年   61篇
  2000年   64篇
  1999年   79篇
  1998年   75篇
  1997年   60篇
  1996年   47篇
  1995年   51篇
  1994年   56篇
  1993年   38篇
  1992年   47篇
  1991年   40篇
  1990年   30篇
  1989年   56篇
  1988年   46篇
  1987年   42篇
  1986年   40篇
  1985年   39篇
  1984年   25篇
  1983年   22篇
  1982年   32篇
  1981年   27篇
  1980年   20篇
  1979年   14篇
  1978年   20篇
  1977年   22篇
  1976年   19篇
  1975年   15篇
  1972年   12篇
  1969年   11篇
排序方式: 共有2644条查询结果,搜索用时 31 毫秒
1.
Balloon dacryocystoplasty: indications and contraindications   总被引:3,自引:0,他引:3  
  相似文献   
2.
ABSTRACT: This paper reports on the effectiveness of a teacher development project in promoting implementation of a comprehensive school health education curriculum among inner city elementary school teachers. The longitudinal evaluation design provides empirical data on the efficacy of a strategy to reduce teachers' concerns and promote use of the curriculum at the classroom level. Data were collected at various points throughout the project period from 156 school staff from five schools. Results from analyses of repeated measures of teachers' feelings of preparedness to teach specific health topics, and the observed relationship between both high and improved feelings of preparation and reported health teaching suggest that teacher development efforts including training and ongoing reinforcement to increase teachers' feelings of preparedness can have significant classroom effects.  相似文献   
3.
Several methods for demonstrating antibody to Crimean-Congo haemorrhagic fever virus were compared on serum samples taken from 101 patients during the acute stage of illness and at intervals for up to 59 months thereafter, with emphasis on early detection of the immune response. The deaths of 23 patients on days 5-14 of illness were ascribed to the effects of the disease; two patients died later from other causes. Very few of the patients who died from the acute illness mounted an antibody response detectable by the methods tested. Four patients who died and 18 who recovered were treated with immune plasma collected from recovered patients. Treated patients acquired IgG antibody from the plasma, but it was possible to discern the onset of an endogenous IgM response in those individuals who survived the disease by all of the methods tested. Indirect immunofluorescence (IF) tests detected IgM and/or IgG antibodies at the earliest on day 4 of illness in about 10% of patients who survived the disease, and by day 9 all survivors had antibodies demonstrable by IF. A biotin-streptavidin IF technique offered no advantage over the standard IF test for the early detection of IgG antibody, but demonstrated higher antibody titres and detected IgM antibody earlier in about a quarter of the patients tested. An IgM-capture enzyme-linked immunoassay (ELISA) and an IgG sandwich ELISA demonstrated higher antibody titres than did IF tests, and detected antibody responses at an earlier stage of infection than did IF tests in about one-fifth of patients, but the reverse was true in a similar proportion of instances. A competition ELISA, which detected total antibody activity, produced lower titres than did the IgM and IgG ELISAs, but yielded results which were in close agreement with the findings in IF tests. It was concluded that the IF tests were most convenient for use in making a rapid serodiagnosis of the disease.  相似文献   
4.
The gamma-aminobutyric acid type A (GABAA) receptor gamma 2-subunit is important for benzodiazepine action. In previous studies, two forms of gamma 2-subunit have been found which are generated by RNA alternative splicing (gamma 2L and gamma 2S) and differ by the presence or absence of an 8-amino acid insertion in the major intracellular loop between proposed transmembrane domains M3 and M4. We have used the RNase protection assay to study regulation of expression of the two forms of gamma 2-subunit in mouse brain, as judged from mRNA levels. We find that gamma 2L and gamma 2S are differentially expressed in brain regions and that gamma 2S is expressed at a fairly constant level during brain development while gamma 2L increases dramatically with maturation. Their differentially regulated expression suggests further that gamma 2L and gamma 2S form receptors with important functional differences.  相似文献   
5.
Sex-based differences in CD4 T-cell (CD4) counts are well recognized, but the basis for these differences has not been identified. Conceivably, homeostatic factors may play a role in this process by regulating T-cell maintenance and repletion. Interleukin (IL)-7 is essential for normal T-cell production and homeostasis. We hypothesized that differences in IL-7 might contribute to sex-based differences in CD4 counts. Circulating IL-7 levels were analyzed in 299 HIV-1-infected women and men. Regression analysis estimated that IL-7 levels were 40% higher in women than in men (P = 0.0032) after controlling for CD4 count, age, and race. Given the important role of IL-7 in T-cell development and homeostasis, these findings suggest that higher IL-7 levels may contribute to higher CD4 counts in women.  相似文献   
6.
Burt DW 《Genome research》2005,15(12):1692-1698
The chicken genome sequence is important for several reasons. First, the chicken shared a common ancestor with mammals approximately 310 million years ago (Mya) at a phylogenetic distance not previously covered by other genome sequences. It therefore fills a gap in our knowledge and understanding of the evolution and conservation of genes, regulatory sequences, genomes, and karyotypes. The chicken is also a major source of protein in the world, with billions of birds used in meat and egg production each year. It is the first livestock species to be sequenced and so leads the way for others. The sequence and the 2.8 million genetic polymorphisms defined in a parallel project are expected to benefit agriculture and cast new light on animal domestication. Also, as the first bird to be sequenced, it is a model for the 9600 avian species thought to exist today. Many of the features of the chicken genome and its biology make it an ideal organism for studies in development and evolution, along with applications in agriculture and medicine.  相似文献   
7.
We present the pathological findings in a case of acquired immunodeficiency syndrome (AIDS) in a patient with no known risk factor. Postmortem examination showed klebsiella lung abscess, generalised cytomegalovirus infection, cerebral toxoplasmosis, and a primary cerebral lymphoma. An additional feature was the presence of dilatation of the intrahepatic large bile ducts in association with an atypical distribution of cytomegalovirus. The relation between this case and previously reported cases of AIDS is discussed.  相似文献   
8.
We have studied changes in the pattern of intrinsic hepatic innervation in sequential liver biopsies from 16 patients who underwent orthotopic liver transplantation. Seventy-one needle biopsies were used, including specimens obtained at the time of transplantation (time zero) and up to 4 years post-transplantation; five transplant hepatectomy tissue blocks removed 3-32 months after transplantation were also assessed. Paraffin sections were immunostained with anti-PGP 9.5 and anti-S-100 to identify nerve fibres. All 'time zero' biopsies contained portal nerves and all but two showed staining of parenchymal fibres. After 1 week, no subsequent biopsies contained parenchymal fibres. The disappearance of portal fibres was less rapid and showed greater variability between patients, but they had all disappeared by 6 weeks and there was no positive staining between 6 and 60 weeks. Thereafter, a minority of biopsies showed innervation of a few small portal tracts. Samples from the porta hepatis, hepatectomy specimens, and needle biopsies containing large tracts showed persistence of major nerve trunks at all stages. Abnormally large nerve bundles were seen in some of these areas. The pattern of nerve staining showed no obvious relationship to the intensity of rejection changes. Our results suggest that there is a limited, delayed capacity for regeneration of portal, but not parenchymal, fibres in the transplanted human liver. The physiological significance of this long-term parenchymal denervation in transplanted livers remains to be determined.  相似文献   
9.
G Z Hastings  D S Burt    D R Stanworth 《Immunology》1988,65(1):149-151
A mouse monoclonal antibody (mAb) has been produced by conventional cell fusion methods against a synthetic peptide, p123, representative of a portion of the CH4 domain of rat immunoglobulin E (IgE). This monoclonal antibody was reactive with both peptide and purified rat IgE (p.rat IgE) by indirect enzyme immunosorbent assay (ELISA), and its binding to p.rat IgE was found to be inhibitable by pre-incubation with rat ascitic fluid containing the immunocytoma 162 (IR162) IgE. Heating of the immunocytoma IgE in solution at 56 degrees for 1 hr resulted in its enhanced binding of the mAb. The effect of this treatment was investigated further using p.rat IgE heated at 56 degrees for various time intervals between 0 and 60 min. The mAb showed enhanced binding to IgE heated for as little as 10 min, a similar level of binding being shown by samples heated for 30 and 60 min. The degree of aggregation of the IgE molecules brought about by the heat treatments was measured by differential UV absorption. This revealed a decrease in the proportion of monomeric IgE with an accompanying increase in the percentage of dimer and larger aggregates with increased time of heating at 56 degrees. These absorption data, together with the ELISA inhibition data, suggest that, rather than inducing changes mediated by aggregation of the IgE molecules in solution, heating at 56 degrees causes subtle alterations in the conformation of individual IgE molecules at specific sites within their CH4 domains, one of which is detected by this mAb.  相似文献   
10.
AIM--To determine the composition of the inflammatory infiltrate and to check for the presence of cytomegalovirus (CMV) and Epstein-Barr virus (EBV) in nine cases of post-infantile giant cell hepatitis. METHODS--The clinical, serological, and histological features of the nine cases were reviewed. Immunohistochemistry was used on liver biopsy specimens from six cases to: (i) characterise the lymphocytic infiltrate; (ii) assess the monocyte/macrophage response; (iii) detect "activated" perisinusoidal cells; and (iv) detect CMV and EBV antigens. Electron microscopic examination was carried out in two cases. RESULTS--Four patients had serological features suggestive of autoimmune chronic active hepatitis; in the other five cases the aetiology was obscure. Two patients presented with neurological symptoms. Hepatitis resolved completely in one patient; two patients showed clinical improvement; and one remained stable. Cirrhosis developed in three patients, one of whom proceeded to liver transplantation, and three patients died. Portal inflammation was present in all cases and lymphocytic piecemeal necrosis in eight cases, but intra-acinar inflammation associated with hepatocyte necrosis was observed in only five cases. The inflammatory infiltrate was composed predominantly of T lymphocytes; an increase in monocyte/macrophage cells was also observed. Mallory bodies, often with associated neutrophilic infiltrate, were present in four cases, and bilirubinostasis was a feature in four cases. "Activated" perisinusoidal cells were present, especially in relation to areas of inflammation, necrosis, and fibrosis. There was severe fibrosis or cirrhosis in five cases. Paramyxoviral nucleocapsids were not seen in the two cases examined ultrastructurally. CONCLUSIONS--Post-infantile giant cell hepatitis should be viewed as a heterogeneous clinical and aetiological entity encompassing cases of hepatitis with extensive giant cell hepatocyte transformation.  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