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   29567篇
  免费   2647篇
  国内免费   955篇
耳鼻咽喉   340篇
儿科学   440篇
妇产科学   589篇
基础医学   5725篇
口腔科学   404篇
临床医学   2530篇
内科学   3892篇
皮肤病学   384篇
神经病学   931篇
特种医学   1106篇
外国民族医学   1篇
外科学   2805篇
综合类   4484篇
现状与发展   2篇
预防医学   1256篇
眼科学   144篇
药学   2277篇
  6篇
中国医学   828篇
肿瘤学   5025篇
  2025年   31篇
  2024年   374篇
  2023年   418篇
  2022年   827篇
  2021年   977篇
  2020年   911篇
  2019年   665篇
  2018年   659篇
  2017年   773篇
  2016年   844篇
  2015年   853篇
  2014年   1671篇
  2013年   1775篇
  2012年   1680篇
  2011年   1807篇
  2010年   1535篇
  2009年   1460篇
  2008年   1530篇
  2007年   1558篇
  2006年   1405篇
  2005年   1275篇
  2004年   1177篇
  2003年   1028篇
  2002年   851篇
  2001年   844篇
  2000年   678篇
  1999年   666篇
  1998年   530篇
  1997年   518篇
  1996年   455篇
  1995年   440篇
  1994年   418篇
  1993年   283篇
  1992年   245篇
  1991年   183篇
  1990年   223篇
  1989年   176篇
  1988年   139篇
  1987年   125篇
  1986年   101篇
  1985年   167篇
  1984年   188篇
  1983年   96篇
  1982年   133篇
  1981年   105篇
  1980年   94篇
  1979年   89篇
  1978年   46篇
  1977年   43篇
  1976年   50篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
PROBLEM: Previous studies have revealed the presence of a unique population of CD45R+ granulated cells in the sheep uterine epithelium. In the present study, dramatic changes in this cell population and in the nongranulated lymphocytes in the uterine and endometrial glandular epithelium of non-cycling, cycling, pregnant, and postparturient sheep are described. In noncycling and cycling sheep, the granules in the granulated intraepithelial cells were small. From days 55 to 134 of pregnancy, the granules in these cells were large, and there was a significant increase (P < 0.01) in the proportion of this cell population in the uterine epithelium but not in the endometrial glandular epithelium located in the deeper region of the stroma. The number of these cells declined dramatically (P < 0.01) from 2 to 15 days after parturition. Both the tissue distribution and the time of activation of these cells suggests they are different from the granulated lymphocytes described in placentae of mice and man. CONCLUSIONS: It is concluded that this unique population of granulated cells is derived from lymphocytes, and that these cells become metabolically active from mid- to late-pregnancy and may play a physiological role during pregnancy or birth. In contrast, the number of nongranulated intraepithelial lymphocytes were suppressed throughout pregnancy and they probably do not play a role in pregnancy.  相似文献   
32.
33.
Association between HLA and Japanese patients with rheumatoid arthritis   总被引:12,自引:0,他引:12  
Japanese patients with rheumatoid arthritis (RA) were observed to have a statistical association with HLA-DR4, MT3. Strong association between the clinical severity of RA and HLA was also observed. Male patients had a stronger association with HLA than female patients. Males are more resistant to RA than females. This suggested that the threshold of liability for RA is higher in males than in females. Japanese patients with RA with systemic vasculitis were negative for HLA-Bw44 and had antilymphocytotoxic autoantibody, indicating that RA with systemic vasculitis is different in etiology from RA without systemic vasculitis.  相似文献   
34.
35.
36.
This retrospective study involved 463 breast cancer patients treated by radiotherapy alone at the Princess Margaret Hospital and at the Institut Gustave-Roussy. These patients either had operable tumors, but were unfit for general anesthesia, or had inoperable tumors due to local contraindications to surgery. Results were analyzed according to tumor response, local recurrence rate, tumor size, tumor fixation, nodal fixation and tumor dose. Conventional statistical analysis of local control showed two significant factors: tumor dose and tumor size. Multivariate analysis permitted to define an "individual risk" (IR) of local recurrence according to three independent factors: tumor size, tumor fixation, and nodal fixation. It was shown that the IR was a good prognostic factor for local control. Increase in tumor dose gave a similar effect in the local recurrence relative risk for all the IR groups. According to the slope of the dose-effect curve, it was deduced that a dose increase of 15 Gy can decrease the relative risk of local recurrence 2-fold. In fact, it was shown that tumor dose was the most significant independent factor on local control, able to produce up to a 10-fold increase compared to 2-fold decrease for tumor size. If the IR of local recurrence is known, a theoretical predictive value on local control, taking into account the tumor dose, can be determined according to the present data.  相似文献   
37.
To measure the rate of protein synthesis in human neoplasms by positron emission tomography, we prepared no carrier added DL-(1-11C)-tyrosine by 11C-carboxylation of the appropriate -lithioisocyanide followed by hydrolysis of the isocyanide function and removal of the protecting methoxy group. The purification, resolution and solvent switch to saline was performed by high performance liquid chromatography (HPLC). DL-(1-11C)-Tyrosine in 0.1 N NaH2PO4 buffer was prepared with a radiochemical yield of 8%–16% (EOS, 35 min). The enantiomeric separation and solvent switch to saline were achieved in 5 min and 10 min respectively. Consequently L-(1-11C)-tyrosine in physiological saline was obtained in 2%–4% radiochemical yield. Tumor accumulation in rats with the experimental WALKER 256 carcinosarcoma was observed for both the L- and D-isomer. Using positron emission tomography a tumor/muscle ratio of two was observed for the L-isomer 15 min after injection. The corresponding figure for the D-isomer was 2.5. The first clinical results with DL-(1-11C)-tyrosine show accumulation of radioactivity in meningioma, a primary breast carcinoma and in liver metastases of a colonic carcinoma.  相似文献   
38.
We report a case of chronic myelogenous leukemia (CML) associatedwith pronounced peripheral lymphadenopathy, with the cells havingthe Philadelphia (Phl) chromosome and T-cell features. A 23-year-oldman who was diagnosed as having CML and treated with busulfanwas admitted to our hospital because of increasing hepatosplenomegalyand pronounced lymphadenopathy. An axillary lymph node biopsydisclosed that the malignant cells formed rosettes with neuraminidase-treatedsheep red blood cells (En) (95.0%) and were positive for Leu1 (91.8%). Of the cytochemical reactions, peroxidase was negativeand periodic acid-Shiff, acid -naphthyl acetate esterase andß-glucuronidase were all positive. The karyotype ofthe bone marrow cells was 46 XY Phl positive (22q–), andthat of the lymph node cells was 51 XY Phl positive +8, +9,+18, +19, +21, 22q–. He was treated with various anti-leukemicagents and irradiation. Despite such treatments, he died ofpneumonia. This is a report of a CML patients with blast crisisand tumor formation characterized by T-cell features.  相似文献   
39.
The metastatic process is characterized by a complex series of sequential steps involving constant interactions (mutual cross-talks) of metastasized tumor cells with their microenvironment (lymphocyte, macrophages, endothelial cells, etc.) in target organs. These interactions determine the outcome of metastasis (either the eradication of metastatic cells or their increased proliferation and invasion). Recently developed methods of tumor and host cell analysis at the molecular level allow better elucidation of molecular mechanisms of metastasis and of immune mechanisms involved in antitumor responses. Direct modulation of these processes will probably increase the success of clinical cancer treatment. Here we review data (a) on the expression of some costimulatory (MHC class II, CD80, sialoadhesin) and adhesion (LFA1, ICAM-1, VLA-4) molecules on both metastasized tumor cells and host cells and (b) on the production of a cytotoxic molecule, nitric oxide, by in situ activated Kupffer and endothelial cells in the process of liver metastasis. This study was performed with well-characterized murine ESbL T lymphoma cells transduced with the bacterial lacZ gene, which allows detection and quantification of metastases at the single cell level throughout lymphoma growth and metastasis. Experimental results are discussed in the context of recent literature.Abbreviations APC Antigen-presenting cells - hCRP Human C-reactive protein - ICAM Intercellular adhesion molecule - IFN Interferon - IL Interleukin - iNOS Inducible NO synthase - LFA Leukocyte function associated antigen - SER Sheep erythrocyte receptor - TA Tumor-associated rejection antigens - TNF Tumor necrosis factor - VCAM Vascular cell adhesion molecule - VLA Very late activated antigen  相似文献   
40.
Types of chromosomal aberrations in cultures of human lymphocytes exposed to the combined action of various concentrations of thiophosphamide and dipin, with different proportions of each, were studied. The mutagens acted on the G0 stage. The range of concentrations used was from 3.17·10–5 to 22.19·10–5M. Equimolar concentrations of thiophosphamide inhibited more chromatid exchanges and fewer sister-strand (isolocus) unions than dipin, and it also induced a greater proportion of single breaks and a greater proportion of breaks in chromatid exchanges relative to the total number of chromosome breaks. Both the absolute and the relative frequencies of chromosomal aberrations depended on the concentration of the mutagens. A change in the ratio between thiophosphamide and dipin, if the total number of molecules of the two mutagens at the different concentration levels remained constant, gave rise to an effect whose level was between the effects of action of equimolar concentrations of the pure mutagens. This effect depended on the proportion of each mutagen in the combined treatment. It is concluded that the action of thiophosphamide and dipin is additive.Laboratory of Mutagenesis, Institute of Medical Genetics, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. V. Smol'yannikov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 1, pp. 79–81, January, 1978.  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