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   7302篇
  免费   391篇
  国内免费   79篇
耳鼻咽喉   86篇
儿科学   62篇
妇产科学   130篇
基础医学   1184篇
口腔科学   178篇
临床医学   491篇
内科学   1347篇
皮肤病学   209篇
神经病学   483篇
特种医学   425篇
外科学   917篇
综合类   27篇
预防医学   241篇
眼科学   97篇
药学   967篇
中国医学   160篇
肿瘤学   768篇
  2024年   4篇
  2023年   49篇
  2022年   171篇
  2021年   282篇
  2020年   124篇
  2019年   149篇
  2018年   230篇
  2017年   156篇
  2016年   272篇
  2015年   418篇
  2014年   414篇
  2013年   490篇
  2012年   812篇
  2011年   712篇
  2010年   408篇
  2009年   338篇
  2008年   445篇
  2007年   356篇
  2006年   338篇
  2005年   365篇
  2004年   305篇
  2003年   227篇
  2002年   182篇
  2001年   106篇
  2000年   104篇
  1999年   70篇
  1998年   29篇
  1997年   32篇
  1996年   23篇
  1995年   14篇
  1994年   16篇
  1993年   8篇
  1992年   14篇
  1991年   25篇
  1990年   13篇
  1989年   10篇
  1988年   13篇
  1987年   9篇
  1986年   8篇
  1985年   7篇
  1984年   3篇
  1981年   4篇
  1979年   3篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1968年   1篇
  1967年   1篇
  1966年   2篇
排序方式: 共有7772条查询结果,搜索用时 15 毫秒
41.
The methanol extracts of the leaves of Crataegus pinnatifida showed potent inhibitory activities against HIV-1 protease at a concentration of 100 micrograms/ml. The subsequent fractionation and isolation of the extract gave two active compounds. Their structures were identified as uvaol (1) and ursolic acid (2) by spectral data. These active compounds inhibit HIV-1 protease with IC50 values of 5.5 and 8.0 microM, respectively.  相似文献   
42.
Kwon BM  Jung HJ  Lim JH  Kim YS  Kim MK  Kim YK  Bok SH  Bae KH  Lee IR 《Planta medica》1999,65(1):74-76
Fifteen lignans were isolated from the fruits of SCHIZANDRA CHINENSIS, the leaves of MACHILUS THUNBERGII, and the flower buds of MAGNOLIA DENUDATA. They were identified as gomisins, schizandrin, wuweizisu, schizantherin, licarins, and machilin, which inhibited rat liver ACAT with IC (50) values of 25-200 microM. Comisin N is the most potent inhibitor with IC (50) value of 25 microM in these lignans.  相似文献   
43.
When liriodendrin or syringin was incubated for 24 h with human intestinal bacteria, two metabolites, (+)-syringaresinol-beta-D-glucopyranoside and (+)-syringaresinol, from liriodendrin and one metabolite, synapyl alcohol, from syringin were produced. The metabolic time course of liriodendrin was as follows: at early time, liriodendrin was converted to (+)-syringaresinol-beta-D-glucopyranoside, and then (+)-syringaresinol. The in vitro cytotoxicities of these metabolites, (+)-syringaresinol and synapyl alcohol, were superior to those of liriodendrin and syringin.  相似文献   
44.
Cytotoxicities of four urushiols, congeners isolated from the sap of Korean lacquer tree (Rhus vernicifera Stokes), to 29 human cancer cell lines originated from 9 organs were evaluated. Their values of 50% growth inhibition were below 4 microg/ml, and showed cell line specific cytotoxicity. The present result is the first report on the cytotoxicity of urushiols suggesting that they would have an anticancer activity to human cancer cells.  相似文献   
45.
PURPOSE: To evaluate the potential of the new prognostic information gained by analyzing the coexpression of epidermal growth factor receptor (EGFR) and cyclooxygenase-2 (COX-2) in cervical cancer patients. EXPERIMENTAL DESIGN: Sixty-eight patients with International Federation of Gynecology and Obstetrics stage IIB squamous cell carcinoma of the uterine cervix, who underwent concurrent chemoradiotherapy between 1993 and 1996, were divided into the following four groups according to their immunoreactivities for EGFR and COX-2 in paraffin-embedded sections: (a). the EGFR-negative/COX-2-negative group (n = 11); (b). the EGFR-negative/COX-2-positive group (n = 8); (c). the EGFR-positive/COX-2-negative group (n = 27); and (d). the EGFR-positive/COX-2-positive group (n = 22). The clinical features, patterns of treatment failure, and survival data in the four groups were compared. RESULTS: Positive immunoreactivity for EGFR and COX-2 was observed in 49 of 68 (72%) and 19 of 68 (28%), respectively. However, no strong correlation was found between the levels of EGFR and COX-2 immunopositivity (R(2) = 0.05, P = 0.07). Patients in the EGFR-positive/COX-2-positive group had a higher likelihood of locoregional recurrence than those in the other three groups (P = 0.02). Of the patients in the four groups, patients positive for both oncoproteins were found to have the worst prognosis with an overall 5-year disease-free survival rate of 55% compared with 91% for the EGFR-negative/COX-2-negative patients, 88% for the EGFR-negative/COX-2-positive patients, and 69% for the EGFR-positive/COX-2-negative patients (P = 0.05, log-rank test). In addition, the synchronous coexpression of the EGFR and COX-2 oncoproteins was found to be an independent prognostic factor by univariate and multivariate analyses (relative risk = 4.0, P = 0.03). CONCLUSIONS: Given these observations, we conclude that the coexpression of EGFR and COX-2 immunoreactivity may be used as a potent molecular risk factor for predicting the poor survival of patients with the International Federation of Gynecology and Obstetrics stage IIB squamous cell carcinoma of the uterine cervix.  相似文献   
46.
PURPOSE: Sphingolipid metabolites, such as sphingosine and ceramide, are highly bioactive compounds and are involved in diverse cell processes, including cell-cell interaction, cell proliferation, differentiation, and apoptosis. However, the physiological roles of phytosphingosine are poorly understood. In this study, we report that phytosphingosine can potently induce apoptotic cell death in human cancer cells via caspase activation and caspase-independent cytochrome c release. EXPERIMENTAL DESIGN: Phytosphingosine-induced apoptosis was determined by Hoechst 33258 staining, flow cytometric analysis, and DNA fragmentation assay. Involvement of caspases was determined by immunoblot analysis and cell death detection assays after treatment with synthetic inhibitor z-Val-Ala-Asp-fluoromethyl ketone, z-DEVD-fmk, or z-IETD-fmk. Death receptor (DR) dependency was analyzed by examining expression of DRs (Fas, DR4, DR5, TNFR1, and R2), and interaction of Fas-associated death domain and caspase 8. Involvement of the mitochondria pathway was examined by monitoring of the mitochondria membrane potential, cytochrome c release, and Bax translocation. RESULTS: Phytosphingosine-treated cells displayed several features of apoptosis, including increase of sub-G(1) population, DNA fragmentation, and poly(ADP-ribose) polymerase cleavage. We observed that phytosphingosine cause activation of caspase 8 in a DR-independent fashion. Phytosphingosine also induced activation of caspase 9 and 3, loss of mitochondrial membrane potential, and the cytochrome c release from mitochondria. However, we failed to detect Bid cleavage. Moreover, caspase 8 inhibitor z-IETD-fmk did not affect phytosphingosine-induced cytochrome c release and caspase 9 activation, suggesting that phytosphingosine-induced cytochrome c release is caused by caspase 8-independent manner. Phytosphingosine induced mitochondrial translocation of Bax from the cytosol without changes in the protein levels of Bcl-2, Bcl-xL, and Bax. In addition, Bcl-2/Bax interaction was diminished after addition of phytosphingosine. CONCLUSION: These findings indicate that phytosphingosine induces apoptotic cell death in human cancer cells by direct activation of caspase 8, and by mitochondrial translocation of Bax and subsequent release of cytochrome c into cytoplasm, providing a potential mechanism for the anticancer activity of phytosphingosine.  相似文献   
47.
48.
In magnetic resonance angiography, contrast agents are frequently used to help highlight arteries over background tissue. Unfortunately, enhancing veins hamper the visualization of arteries when data are collected over a long period of time after the arterial phase of the contrast agent. To overcome this problem, we have developed a novel imaging and postprocessing method that is capable of eliminating veins by utilizing the susceptibility difference between veins and surrounding tissue. This method was applied in the peripheral vasculature where the vessels are predominantly parallel to the main field and where the blood oxygen level-dependent effect is most pronounced. Results are presented for both long (15.8 msec) and short echo times (7.8 msec) and for sequential and centrally reordered acquisition schemes. The short echo scan approach appears to be the most promising, making it possible to obtain good suppression of the venous signal even when the timing is not perfect or when repeat scans are necessary.  相似文献   
49.
Choi BK  Cho SH  Bai GH  Kim SJ  Hyun BH  Choe YK  Bae YS 《Diabetes》2000,49(9):1459-1467
The D variant of encephalomyocarditis (EMC-D) virus causes diabetes in susceptible mice by direct cytolysis of pancreatic beta-cells. cDNA covering the major outer capsid protein (VP1) of the EMC-D virus was cloned into Mycobacterium bovis bacillus Calmette-Guerin (BCG). None of the SJL/J mice immunized with live recombinant BCG-VP1 (rBCG-VP1) became diabetic when challenged with the highly diabetogenic EMC-D virus, but the control mice inoculated with normal BCG developed diabetes during the same challenge. VP1-specific antibodies (including neutralizing antibodies) were markedly increased over time and reached the maximum titer at week 10 after a single immunization. The plateau of the titer lasted longer than 4 weeks. Mice and guinea pigs immunized with live rBCG-VP1 showed strong delayed-type hypersensitivity to the VP1 of the EMC-D virus. The preventive immunity still worked effectively 10 months after the primary immunization. At that time, the VP1-specific antibody was almost undetectable in the bloodstream, but a large number of VP1-specific lymphocytes was found in the spleen of the immunized mice. Our results show that live rBCG-VP1 elicits effective humoral and long-lasting cellular immune responses against EMC-D virus infection that results in the prevention of virus-induced diabetes in susceptible mice.  相似文献   
50.
Our aim was to translate and cross-culturally adapt the fibromyalgia impact questionnaire into Korean (KFIQ), and then evaluate its reliability and validity. The FIQ was translated into Korean by three translators and then independently translated back into English by three different translators. A total of 62 women patients with fibromyalgia (FM) were studied for the psychometric properties of the KFIQ. The mean age of the patients was 47.1 (25-73) years, and all were female. The mean KFIQ score was 48.3 (17-91), and the mean Korean health assessment questionnaire (KHAQ) score was 0.4 (0-1.7). The test-retest reliability of the KFIQ yielded an intraclass correlation coefficient of 0.85 (0.53-0.96). For the construct validity, the Spearman rank correlations of KFIQ with patient global assessments using visual analog scale (pain, 0.58; morning stiffness, 0.45; fatigue, 0.48; depression, 0.43; anxiety, 0.56; global well-being, 0.46; disease severity, 0.49; impact on life, 0.51), KHAQ (0.44), and tender points (0.60) were high and statistically significant. The KFIQ might be a reliable and valid instrument for measuring health status and physical functioning in Korean women patients with FM, but needs further study.  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