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   5583篇
  免费   369篇
  国内免费   19篇
耳鼻咽喉   49篇
儿科学   92篇
妇产科学   76篇
基础医学   806篇
口腔科学   80篇
临床医学   540篇
内科学   1204篇
皮肤病学   89篇
神经病学   790篇
特种医学   470篇
外科学   693篇
综合类   60篇
一般理论   1篇
预防医学   282篇
眼科学   114篇
药学   326篇
中国医学   3篇
肿瘤学   296篇
  2024年   7篇
  2023年   64篇
  2022年   87篇
  2021年   163篇
  2020年   91篇
  2019年   123篇
  2018年   134篇
  2017年   127篇
  2016年   149篇
  2015年   157篇
  2014年   206篇
  2013年   262篇
  2012年   417篇
  2011年   432篇
  2010年   252篇
  2009年   203篇
  2008年   370篇
  2007年   374篇
  2006年   352篇
  2005年   316篇
  2004年   310篇
  2003年   248篇
  2002年   248篇
  2001年   87篇
  2000年   67篇
  1999年   81篇
  1998年   67篇
  1997年   61篇
  1996年   32篇
  1995年   27篇
  1994年   28篇
  1993年   22篇
  1992年   34篇
  1991年   41篇
  1990年   30篇
  1989年   34篇
  1988年   29篇
  1987年   26篇
  1986年   24篇
  1985年   32篇
  1984年   21篇
  1983年   19篇
  1982年   17篇
  1981年   5篇
  1979年   19篇
  1978年   12篇
  1977年   7篇
  1976年   11篇
  1974年   5篇
  1967年   4篇
排序方式: 共有5971条查询结果,搜索用时 15 毫秒
941.
This objective of this paper was to verify the relations between the living and infrastructure conditions of municipalities in the State of Paraná, Brazil, and infant mortality rate and its components. An ecological study was carried out having the 399 municipalities of the State being classified into five clusters of living conditions. Infant, neonatal and postneonatal rates were calculated for the period 1997/2001. The mean infant, neonatal and postneonatal mortality rates in the State were, respectively, 19.3, 12.0 and 7.3 per 1,000 live births. Postneonatal mortality rates ranged from 8.7 (cluster of worst living conditions) to 6.3 per 1,000 live births (in the cluster classified as having the best living conditions). Regarding the neonatal component, clusters classified as holding the best and the worst living conditions presented the lowest values: 11.8 and 11.4 per 1,000 live births, respectively. We conclude that the postneonatal component still adequately discriminate living conditions in the State of Paraná. However, there is a need of complementary studies that aim to clarify the causes of similar neonatal mortality rates observed in the richest and in the poorest cluster of municipalities.  相似文献   
942.
943.
To evaluate the long-term effect of mild-early maternal protein malnutrition on weight gain, hematological parameters and macrophage function in rats at adult age, we compared rats whose dams were fed diets containing either 9.5% (low protein-LPD) or 23% protein (normal-NPD) for the first 12 d of lactation. At 80 d of age, the functions of spreading, phagocytosis and killing Candida albicans were determined in resident peritoneal macrophages, whereas leukocytes and red blood cells were counted in peripheral blood. The number of resident peritoneal macrophages from LPD was the same as from NPD, but the ability of spreading and phagocytosing opsonised yeast was impaired. Besides, they were not able to block the germ tube formation or kill C. albicans to the same extent as in the control group. The low protein diet produced a significant reduction in the pups' growth and in hematological parameters although no difference was found in leukocyte counts. Taken together the data suggest that protein malnutrition during early lactation induces permanent alterations in macrophage function, body composition and hematological status, which are not restored completely even after a normal protein diet is supplied.  相似文献   
944.
Endometrial cancer is a heterogeneous tumour with two types which can be distinguished clinically, histologically and pathogenetically:the classical endometrioid cancer (type 1) with a good prognosis and the aggressive histological type 2 with a poor prognosis and early metastatic spread. The most active cytotoxic drugs in advanced or metastatic endometrial cancer are the anthracyclines, the platinum salts and the taxanes. In most studies, combination chemotherapy is superior to monotherapy in terms of response rates. In the last few years there is growing evidence that chemotherapy can prolong overall survival in metastatic endometrial cancer and that adjuvant chemotherapy can reduce recurrence rates in high-risk situations.  相似文献   
945.
Objective: To compare efficacy of intravitreal bevacizumab versus triamcinolone in the treatment of diffuse diabetic macular oedema (DME). Methods: This retrospective nonrandomized study includes 60 patients with diffuse DME treated with at least one intravitreal triamcinolone injection (ITA) or intravitreal bevacizumab injection (IBe). Regression analysis was performed for pretreatment, glycosylated haemoglobin level, visual acuity (VA) at baseline and central macular thickness (CMT) at baseline. Results: After 1‐, 3‐, 6‐ and 9‐month follow‐up, there was no significant change in either VA or CMT treatment in the ITA and IBe groups. There was no statistically significant difference between the two treatment groups. Changes in CMT and VA in the subgroups were not significant. Only predictive factor independent of HbA1c level and VA was CMT at baseline in both treatment groups. The thicker CMT at baseline, the higher was reduction in CMT. After 1 month, the IBe group had a significantly higher decrement than the ITA group. Conclusion: In our study collective, neither IBe nor ITA treatment was able to improve VA during follow‐up, significantly. CMT was reduced in both treatment groups, however not significantly. Our data demonstrates that reduction in CMT with either IBe or ITA treatment was significantly influenced by degree of CMT at baseline.  相似文献   
946.
A large variety of 5-substituted 2′-deoxyuridines (dUrds) and 2′-deoxyuridylates (dUMPs) have been evaluated for their inhibitory effects on the thymidine (dThd) kinase or thymidylate (dTMP) synthetase isolated from mouse leukemia L1210 cells. The most potent inhibitors of dThd kinase were 5-chloro-, 5-bromo- and 5-iodo-dUrd. Their Ki/Km values ranged from 0.57 to 0.82. All dUrd analogs tested showed competitive kinetics with respect to dThd. However, there was little, if any, correlation between the inhibitory effects of the compounds on L1210 cell growth and their inhibitory activities against dThd kinase (r = 0.16). The most potent inhibitors of dTMP synthetase were (in order of decreasing activity): 5-nitro-dUMP > 5-formyl-dUMP > 5-fluro-dUMP > 5-oxime of 5-formyl-dUMP > 5-azidomethyl-dUMP > (E)-5-(2-bromovinyl)-dUMP. The ki/Km values for these compounds ranged from 0.001 to 0.665. All dUMP analogs tested showed competitive kinetics with respect to dUMP (if not preincubated with the enzyme at 37°). There was a strong correlation (r = 0.833) between the inhibitory effects of these compounds on L1210 cell growth and their inhibitory activities against dTMP synthetase. Thus, the suppressive action of 5-substituted dUrd derivatives on tumor cell growth would involve prior conversion of the nucleoside analogs to the corresponding 5′-monophosphates followed by an inhibition of dTMP synthetase.  相似文献   
947.
In rat pancreatic islets perifused in the presence of 2-cyclohexene-1-one (CHX; 1.0 mM), the secretory response to either D-glucose or 2-ketoisocaproate, but not that evoked by the association of L-leucine and L-glutamine, was severely decreased. This coincided with a decreased stimulation of [45Ca] efflux from prelabelled islets, whereas the inhibitory action of D-glucose or 2-ketoisocaproate upon both [86Rb] and [45Ca] efflux appeared little or not affected. In the presence of D-glucose, the islets exposed to CHX were virtually unresponsive to either forskolin, theophylline or cytochalasin B. A severe decrease in the secretory response to forskolin was also observed in CHX-treated islets exposed to L-leucine and L-glutamine. Except for a somewhat lower sensitivity to NaF, no major change in adenylate cyclase activity or cyclic AMP production was observed in CHX-treated islets. The activity of protein kinase A was decreased in such islets but its responsiveness to cyclic AMP appeared unaltered. Transglutaminase activity was severely decreased in homogenates derived from CHX-treated islets. These findings suggest that CHX, possibly by lowering the GSH content of islet cells, impairs the functional capacity of the effector system for insulin release, in addition to and independently of any effect that it may exert upon nutrient catabolism and cationic fluxes in the islet cells.  相似文献   
948.
PURPOSE: To evaluate which morphologic features of the optic disc are predictive factors for the development or progression of visual field loss in chronic open-angle glaucoma. METHODS: The prospective observational clinical study included 763 eyes of 416 white subjects with ocular hypertension and chronic open-angle glaucoma. During the follow-up time (mean, 67.4 months; median, 65.1; range, 6.2-104.5), all patients underwent repeated qualitative and morphometric evaluation of color stereo optic disc photographs and white-on-white visual field examination. Progression of glaucomatous visual field damage was defined by point-wise regression analysis for each of the 59 locations in the visual field. Outcome measures were qualitative and quantitative morphologic optic nerve head parameters. RESULTS: Development or progression of glaucomatous visual field defects was detected in 106 (13.9%) eyes. At baseline of the study, neuroretinal rim area was significantly (P < 0.002) smaller, the beta zone of parapapillary atrophy (P < 0.003, nasal sector) was significantly larger, and age was significantly higher (P < 0.003) in the progressive study group than in the nonprogressive study group. Both study groups did not vary significantly in size of the optic disc and the alpha zone of parapapillary atrophy. Cox proportional hazard regression analysis revealed that the progression of glaucomatous visual field loss depended significantly on the area of the neuroretinal rim (P < 0.001) and age (P < 0.001), but was independent of diameter of the retinal arterioles and veins. CONCLUSIONS: Morphologic predictive factors for development or progression of glaucomatous visual field defects in whites are small neuroretinal rim area and large beta zone of parapapillary atrophy. Age is an additional nonmorphologic parameter. Progression of glaucomatous optic nerve head changes is independent of the size of the optic disc and alpha-zone of parapapillary atrophy and retinal vessel diameter.  相似文献   
949.
950.
Intravascular iodinated contrast agents are required for a large proportion of computed tomography (CT) studies. Contrast media are indispensable to more clearly differentiate anatomic structures and to detect and characterize abnormalities. Depending on the indication up to 200 ml of these agents are injected during CT. Despite these large amounts adverse effects are rare and have further decreased with the introduction of non-ionic substances. However, it took 10 to 20 years until these non-ionic agents replaced the older ionic agents in clinical practice. In recent years no new substance has been brought to the market. The introduction of rapid scanning using multislice CT technology, however, has led to the development of more sophisticated contrast injection techniques. Current research focuses on optimizing contrast application techniques and on further evaluating the safety profiles of the various substances. The amount of contrast enhancement obtained in individual patients for instance depends on the contrast agent characteristics, such as iodine concentration, and the parameters of the contrast injection protocol, such as iodine flux and iodine dose. Meanwhile, contrast agent characteristics such as osmolality and viscosity play a role in the safety profile of an agent. This paper provides a current overview of CT contrast media, CT contrast dynamics, and CT contrast applications with a special focus on oncological imaging.  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