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   19888篇
  免费   1110篇
  国内免费   160篇
耳鼻咽喉   317篇
儿科学   618篇
妇产科学   331篇
基础医学   2821篇
口腔科学   1609篇
临床医学   1525篇
内科学   4211篇
皮肤病学   493篇
神经病学   1287篇
特种医学   842篇
外科学   2197篇
综合类   117篇
一般理论   3篇
预防医学   2120篇
眼科学   268篇
药学   1362篇
  2篇
中国医学   189篇
肿瘤学   846篇
  2023年   195篇
  2022年   414篇
  2021年   735篇
  2020年   466篇
  2019年   598篇
  2018年   759篇
  2017年   526篇
  2016年   567篇
  2015年   660篇
  2014年   847篇
  2013年   1034篇
  2012年   1433篇
  2011年   1643篇
  2010年   926篇
  2009年   729篇
  2008年   1108篇
  2007年   1098篇
  2006年   915篇
  2005年   827篇
  2004年   668篇
  2003年   591篇
  2002年   498篇
  2001年   409篇
  2000年   367篇
  1999年   331篇
  1998年   233篇
  1997年   227篇
  1996年   199篇
  1995年   146篇
  1994年   162篇
  1993年   130篇
  1992年   165篇
  1991年   153篇
  1990年   118篇
  1989年   149篇
  1988年   130篇
  1987年   98篇
  1986年   123篇
  1985年   101篇
  1984年   78篇
  1983年   56篇
  1982年   50篇
  1981年   49篇
  1980年   52篇
  1979年   48篇
  1978年   34篇
  1977年   40篇
  1976年   54篇
  1975年   34篇
  1969年   25篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Anaplastic large cell lymphomas are associated with chromosomal aberrations involving the anaplastic lymphoma kinase (ALK) gene at 2p23 that result in the expression of novel chimeric ALK proteins with transforming properties. In most of these tumors, the t(2;5)(p23;q35) generates the NPM-ALK fusion gene. However, several studies have now demonstrated that genes other than NPM may be fused to the ALK gene. We have recently described two different ALK rearrangements involving the TRK-fused gene (TFG) in which the same portion of ALK was fused to different length fragments of the 5' TFG region. These two rearrangements encoded chimeric proteins of 85 kd (TFG-ALK(S)) and 97 kd (TFG-ALK(L)), respectively. In this study, we have identified a new ALK rearrangement in which the catalytic domain of ALK was fused to a larger fragment of the TFG gene (TFG-ALK(XL)), encoding for a fusion protein of 113 kd. Genomic analysis of these three TFG-ALK rearrangements revealed that the TFG breakpoints occur at introns 3, 4, and 5, respectively, whereas the ALK breakpoints always occur in the same intron. No homologous regions or known recombination sequences were found in these regions. Transfection experiments using NIH-3T3 fibroblasts showed a similar transforming efficiency of TFG-ALK variants compared with NPM-ALK. In addition, in common with NPM-ALK, the TFG-ALK proteins formed stable complexes with the signaling proteins Grb2, Shc, and PLC-gamma. In conclusion, these findings indicate that the TFG may use a variety of intronic breakpoints in ALK rearrangements generating fusion proteins of different molecular weights, but with similar transforming potential than NPM-ALK.  相似文献   
92.
BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a major health problem with an estimated prevalence of 10-15% among smokers. The incidence of moderate COPD, as defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD), is largely unknown. AIM: To determine the cumulative incidence of moderate COPD (forced expiratory volume in 1 second/forced vital capacity ratio [FEV1/FVC] <0.7 and FEV1 <80% predicted) and its association with patient characteristics in a cohort of male smokers. DESIGN: Prospective cohort study. SETTING: The city of IJsselstein, a small town in the Netherlands. METHOD: Smokers aged 40-65 years who were registered with local GPs, participated in a study to identify undetected COPD. Baseline measurements were taken in 1998 of 399 smokers with normal spirometry (n = 292) or mild COPD (FEV1/FVC <0.7 and FEV1 >or=80% predicted, n = 107) and follow-up measurements were conducted in 2003. RESULTS: After a mean follow-up of 5.2 years, 33 participants developed moderate COPD (GOLD II). This showed an estimated cumulative incidence of 8.3% (95% CI = 5.8 to 11.4) and a mean annual incidence of 1.6%. No participant developed severe airflow obstruction. The risk of developing moderate COPD in smokers with baseline mild COPD (GOLD I) was five times higher than in those with baseline normal spirometry (one in five versus one in 25). CONCLUSIONS: In a cohort of middle-aged male smokers, the estimated cumulative incidence of moderate COPD (GOLD II) over 5 years was relatively high (8.3%). Age, childhood smoking, cough, and one or more GP contacts for lower respiratory tract problems were independently associated with incident moderate COPD.  相似文献   
93.
94.
Rotavirus strains causing gastroenteritis in Brazilian children were characterized by PCR-based typing assays. In addition to strains bearing the major human G and P types, large numbers of strains bearing P3 (M37-like), P6 (HCR3-like), untypeable P and G types, and complex mixtures of P and G types not previously recognized were present in the community.  相似文献   
95.
Summary We present a case with a characteristic magnetic resonance image (MRI) of bilateral open-lipped schizencephaly and atypical clinical presentation. The patient is still alive and in good health in her forties, she has never presented seizures, and although the motor dysfunction is well correlated with cerebral lobe involvement, neurobehavioral dysfunction is not proportional to the MR image of the cerebral malformation.
Un cas inhabituel de schizencéphalie bilatérale
Résumé Nous présentons un cas de schizencéphalie bilatérale ouverte caractérisé par une présentation clinique atypique et une imagerie par résonance magnétique nucléaire caractéristique. La patiente est encore vivante, en bonne santé, à plus de 40 ans, elle n'a jamais présenté de crise comitiale et, bien que les troubles moteurs soient bien corrélés aux altérations cérébrales, les troubles neuro-comportementaux ne sont pas proportionnels aux images IRM de cette malformation cérébrale.
  相似文献   
96.
Summary. We have previously reported on the use of a tobacco mosaic virus (TMV) vector TMV-30B to express foreign viral antigens for use as experimental immunogens. Here we describe the development of an improved TMV-30B vector that adds a sequence of 7 histidine residues to the C-terminus of recombinant proteins expressed in the vector. We used this TMV-30B-HISc vector to express the VP8* fragment of the VP4 protein from bovine rotavirus (BRV) strain C-486 in plants. Recombinant VP8* protein was purified from N. benthamiana leaves at 7 days post-inoculation by immobilized metal affinity chromatography. The plant-produced VP8* was initially detected using anti-His tag mAb and its antigenic nature was confirmed using both monoclonal and polyclonal specific antisera directed against BRV. Adult female mice, inoculated by the intraperinoteal route with an immunogen containing 4µg of recombinant VP8*, developed a specific and sustained response to the native VP8* from the homologous BRV. Eighty five percent of suckling mice from immunized dams that were challenged with the homologous virus at the fifth day of age were protected from virus as compared to 35% of the pups from mothers immunized with a control protein. These results demonstrate that the plant-produced VP8* was able to induce passive protection in the new born through the immunization of dams. This suggests that the technology presented here provides a simple method for using plants as an inexpensive alternative source for production of recombinant anti-rotavirus antigens.Authors contributed equally to the results presented in this report.  相似文献   
97.
98.
99.
Lymphocytes from healthy volunteers seropositive for cytomegalovirus (CMV) demonstrated strong lymphoproliferative responses to CMV-infected and glutaraldehyde-fixed foreskin fibroblasts (CMVFFx) when cocultured for 6 days. Addition of the immunosuppressive drug cyclosporine (CsA) to the cultures resulted in a 10-fold reduction (P less than 0.001) in counts per minute of [3H]thymidine uptake. The proliferative response to noninfected fixed fibroblasts was also reduced 10-fold. Kinetic studies showed an inhibition of the lymphoproliferative response and not an alteration in the time course kinetics in CsA-treated cultures. Cytotoxicity to CMV-infected and unfixed fibroblasts by lymphocytes primed by CMVFFx in the presence of 0.5 micrograms of CsA per ml was significantly reduced (P less than 0.01) as compared with untreated cultures but remained significantly above background level (P less than 0.01). The cytotoxic response was still present but reduced at concentrations of greater than or equal to 1.0 micrograms/ml. Cytotoxicity to noninfected fibroblasts by CMVFFx-primed lymphocytes could be eliminated by as little as 0.5 micrograms of CsA per ml. Stimulation of lymphocytes by CMVFFx but not by noninfected fixed fibroblasts resulted in the in vitro generation of suppressor cells. CsA at a final concentration of 1.0 or 2.5 micrograms/ml did not significantly impair the induction of cells capable of suppressing the lymphoproliferative response of fresh autologous mononuclear cells to CMVFFx. The findings described above may have important clinical implications in that a degree of protective immunity to CMV-infected cells is maintained even in the presence of CsA.  相似文献   
100.
We validated a commercial enzyme-linked immunosorbent assay for the detection of anti-CagA antibodies in Brazilian patients with Helicobacter pylori infection. The test presented high sensitivity (97.4%) and specificity (88.9%) when employed in patients without gastric carcinoma. However, in gastric carcinoma patients, the test was neither sensitive nor specific enough to detect cagA-positive H. pylori infection.  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