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   25925篇
  免费   1139篇
  国内免费   122篇
耳鼻咽喉   288篇
儿科学   469篇
妇产科学   474篇
基础医学   3469篇
口腔科学   497篇
临床医学   1523篇
内科学   6176篇
皮肤病学   492篇
神经病学   2320篇
特种医学   1045篇
外科学   4188篇
综合类   122篇
一般理论   6篇
预防医学   809篇
眼科学   527篇
药学   1483篇
中国医学   32篇
肿瘤学   3266篇
  2022年   238篇
  2021年   422篇
  2020年   240篇
  2019年   316篇
  2018年   408篇
  2017年   340篇
  2016年   420篇
  2015年   474篇
  2014年   561篇
  2013年   772篇
  2012年   1217篇
  2011年   1296篇
  2010年   720篇
  2009年   610篇
  2008年   1119篇
  2007年   1244篇
  2006年   1256篇
  2005年   1200篇
  2004年   1187篇
  2003年   1207篇
  2002年   1240篇
  2001年   715篇
  2000年   779篇
  1999年   738篇
  1998年   354篇
  1997年   302篇
  1996年   274篇
  1995年   264篇
  1994年   250篇
  1993年   221篇
  1992年   659篇
  1991年   580篇
  1990年   562篇
  1989年   579篇
  1988年   521篇
  1987年   500篇
  1986年   443篇
  1985年   447篇
  1984年   257篇
  1983年   221篇
  1982年   111篇
  1981年   105篇
  1979年   242篇
  1978年   139篇
  1977年   105篇
  1975年   109篇
  1974年   102篇
  1973年   103篇
  1970年   102篇
  1969年   116篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Expression of six proto-oncogenes (fos, myc, myb, Ki-ras, Ha-ras, and N- ras) in 43 cases of non-Hodgkin's lymphoma was analyzed by means of in situ hybridization. Biotinylated DNA probes of the six oncogenes and those of immunoglobulin H (IgH) gene and T-cell receptor beta (TCR beta) chain gene were used. The results of in situ hybridization performed under blind conditions by IgH gene and TCR beta chain gene probes were compatible with those of typing by cell surface markers. The nuclear protein-related proto-oncogenes, fos, myc, and myb, were expressed in about 70% to 80% of all cases regardless of phenotype, histology, or histologic grade. On the contrary, genes of ras family were expressed in more limited numbers of cases except for the Ki-ras gene, which was more frequently expressed by cases of the T-cell immunophenotype with a high malignancy grade. The results of dot hybridization with RNA extracted from some cases were compatible with those of in situ hybridization, further demonstrating the specificity of in situ hybridization.  相似文献   
72.
Prospective studies suggest that tea may protect against cardiovascular disease. A potential mechanism for such an effect involves inhibition of lipid peroxidation by polyphenolic antioxidants derived from tea. Our objective was to determine whether regular ingestion of tea could inhibit in vivo lipid peroxidation. Two controlled intervention studies assessed the effects of regular ingestion of tea on lipid peroxidation determined by measurement of urinary F(2)-isoprostane excretion. Study 1: The effects of 1000 mL/d of green tea and black tea were compared with hot water containing caffeine in 13 subjects with elevated blood pressure using a randomized 3-period (7 d each) crossover design. Study 2: The effects of 1250 mL/d of black tea were compared with hot water in 22 subjects with mildly raised serum total cholesterol concentrations using a randomized 2-period (4 wk each) crossover design. F(2)-isoprostane excretion was not altered after regular ingestion of green tea (273 +/- 48 pmol/mmol creatinine) or black tea (274 +/- 39 pmol/mmol creatinine) in comparison with hot water (263 +/- 47 pmol/mmol creatinine; Study 1), or by regular ingestion of black tea (334 +/- 71 pmol/mmol creatinine) in comparison with hot water (355 +/- 75 pmol/mmol creatinine; Study 2). These results do not support the suggestion that polyphenolic antioxidants derived from tea inhibit in vivo lipid peroxidation.  相似文献   
73.
The carcinogenic activity of endogenously synthesized N-nitrosobis(2-hydroxypropyl)amine(BHP) was investigated in male Wistar rats administered bis(2-hydroxypropyl)amine(BHPA) mixed in powder diet at a concentration of 1%, and sodiumnitrite (SN) dissolved in distilled water at concentrationsof 0.15 and 0.3%, for 94 weeks. Urinary excretion of BHP wasdetected in rats given 1% BHPA and 0.3% SN but not in the groupsreceiving either of these precursors alone. Nasal cavity, lung,esophagus, liver and urinary bladder tumors were found in animalstreated with combinations of 1% BHPA and 0.15 or 0.3% SN, suggestingthat the target organs of the endogenously synthesized BHP aresimilar to those affected when the carcinogen is administeredexogenously. The incidences of nasal cavity and lung tumorsreached 74 and 58% in rats given 1% BHPA and 0.3% SN, respectively.Tumors at sites other than target organs were only found atlevels similar to those previously reported for spontaneoustumors in male Wistars. The present results clearly indicatedthe tumor inducibility of a nhrosatable amine, BHA, throughan endogenous nitrosation by feeding to rats in conjunctionwith nitrite, and provide further suggestive evidence that endogenousnitrosations of environmental nitrosatable amines can be a potentialrisk factor in human cancer development.  相似文献   
74.
We report a case of benign osteoblastoma arising in the temporal bone of a 28-year-old woman. Plain radiography showed a mass with an amorphous calcified matrix and a thin radiolucent marginal zone. CT and MR imaging were useful in delineating the extent of the tumor, and angiography showed its hypervascularity. Preoperative transarterial embolization was effective in reducing bleeding during surgery.  相似文献   
75.
Clinical value and limitation of resting reinjection of small dose of thallium (37 MBq) for the assessment of myocardial viability were evaluated. The results were compared with the degree of wall motion improvement by revascularization to infarcted myocardium supplied by chronic total vessels in 12 patients with old myocardial infarction. Thallium uptake was visually scored and judged as normal, reversible defect (Group 1), new fill in after reinjection (Group 2A), and no fill in even after reinjection (Group 2B). Among 53 segments with initial perfusion abnormality, 21 segments reverted to almost normal, while 32 segments remained abnormal on redistribution images. New fill in after reinjection was observed in 11 segments of 32 segments showing persisting defect on stress and delayed image (37%). Wall motion score index of Group 2A improved significantly higher than Group 2B (p less than 0.01) and almost equal to Group 1, suggesting the utility of reinjection for the assessment of tissue viability which may be underestimated by conventional imaging. But significant wall motion improvement (greater than or equal to 0.6 mean SD/chords) was observed in 6 segments (29%) of 21 segments showing neither redistribution nor fill in after reinjection. These data indicate that small dose of thallium reinjection may enhance detection of viable but jeopardized myocardium, although some underestimation of viability remained to be resolved.  相似文献   
76.
Six heterogeneous common variable immunodeficiency (CVID) patients were analysed for germ-line DNA, DNA rearrangements, and RNA expressions of immunoglobulin (Ig) gene by Southern or northern blotting using appropriate probes. We detected no polymorphism in neutrophil DNA hybridized to a C mu and a C gamma probe. In three patients, both serum Ig and Ig-bearing cells were scarcely detected, and by northern hybridization methods, neither mu mRNA, gamma mRNA, alpha mRNA nor kappa mRNA was detected. However, one Epstein-Barr virus-transformed B lymphoblastoid cell line (LCL) of these three patients was different from the germ line in the region of JH, C gamma, and C kappa, and expressed mu mRNA at a higher level. The B cell defects of these three patients lay on the B cell maturation stage similar to X-linked agammaglobulinaemia (XLA). In two others among the six CVID patients, serum IgM and IgM-bearing cells were detected to a certain degree, and by northern hybridization, mu mRNA was detected at a lower level, but neither mu mRNA, alpha mRNA, nor kappa mRNA was detected. One LCL of these two patients could express mu mRNA at the normal level. In the last patient, the serum IgM was normal, serum IgG and IgA were somewhat low, Ig-bearing cells were normal, mu mRNA and kappa mRNA were detected at the normal level, and gamma mRNA and alpha mRNA were detected at a lower level. The defect of this patient affected the class switch stage. These results showed that primary B cell defects in CVID occurred at several B cell differentiation stages which could be classified by expression of the Ig gene, and at the degree of clonal diversity in the B cell repertoire. Furthermore, this study provides support for the idea that the CVID defect is related to a more generalized cellular function, such as regulating the proliferation and/or clonal expansion of cells of the B lymphoid lineage.  相似文献   
77.
The effects of direct revascularization of the bronchial artery after bronchoplasty were estimated by laser Doppler velocimetry and india ink injection in dogs. Bronchoplastic surgery at the right main bronchus was performed in all dogs, and the bronchial artery was reconstructed using the internal thoracic artery in the reconstruction group. The mucosal blood flow was measured at the distal side of the anastomosis. India ink was injected into the aorta in the nonreconstruction group and into the internal thoracic artery in the reconstruction group. The peripheral blood flow had diminished immediately after surgeries to 59% of the baseline value and took 14 days to recover to the baseline value in the nonreconstruction group. However, in the reconstruction group, the blood flow recovered at once to 78% of the baseline value and had returned to that value in 5 days. Statistically significant differences were noted between the groups from just after operation to day 7. India ink data confirmed these findings. In the nonreconstruction group, no ink was observed in the peripheral bronchial vessels on day 3; it was noted in part of the vessels on day 7 and in most on day 14. On the other hand, a relatively large number of vessels were stained just after operation in the reconstruction group. Thus reconstruction of the bronchial artery by means of the anastomosis with the internal thoracic artery can be said to be a useful and effective method for preventing airway ischemia.  相似文献   
78.
79.
Intraperitoneal injection of free valproic acid (VPA) suppressed amygdaloid-kindled seizure 1 h after injection in rats, but had no effect at 24 h. VPA entrapped in positively charged liposomes showed a prolonged anticonvulsant effect lasting for 2 days, while the effect evaluated at 1 h was not different from that with free VPA. VPA entrapped in negatively charged liposomes exerted a significantly stronger effect at 1 h than did free VPA, while it had no significant effect at 24 h. These results suggest that surface charges on liposomes play an important role in modifying the anticonvulsant effect of VPA.  相似文献   
80.
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