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   15888篇
  免费   1059篇
  国内免费   557篇
耳鼻咽喉   183篇
儿科学   452篇
妇产科学   213篇
基础医学   1743篇
口腔科学   292篇
临床医学   1623篇
内科学   3189篇
皮肤病学   280篇
神经病学   950篇
特种医学   546篇
外国民族医学   2篇
外科学   1527篇
综合类   1754篇
一般理论   2篇
预防医学   1313篇
眼科学   515篇
药学   1253篇
  7篇
中国医学   581篇
肿瘤学   1079篇
  2024年   24篇
  2023年   133篇
  2022年   271篇
  2021年   477篇
  2020年   316篇
  2019年   381篇
  2018年   562篇
  2017年   418篇
  2016年   387篇
  2015年   540篇
  2014年   653篇
  2013年   778篇
  2012年   1196篇
  2011年   1347篇
  2010年   846篇
  2009年   634篇
  2008年   980篇
  2007年   987篇
  2006年   865篇
  2005年   879篇
  2004年   700篇
  2003年   634篇
  2002年   587篇
  2001年   494篇
  2000年   522篇
  1999年   390篇
  1998年   116篇
  1997年   98篇
  1996年   101篇
  1995年   93篇
  1994年   54篇
  1993年   52篇
  1992年   143篇
  1991年   118篇
  1990年   102篇
  1989年   107篇
  1988年   88篇
  1987年   75篇
  1986年   66篇
  1985年   50篇
  1984年   38篇
  1983年   23篇
  1982年   13篇
  1981年   9篇
  1980年   11篇
  1979年   14篇
  1977年   12篇
  1973年   9篇
  1970年   9篇
  1965年   8篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
The present study in rats evaluates the effects of the ovariectomy (OVX) with and without the simultaneous administration of 17beta-estradiol (17betaE(2)) on oxidative stress and hyperlipidemic nephropathy induced by a single high dose of adriamycin (AD). OVX enhances oxidative stress and worsens nephropathy induced by AD. These changes are prevented by simultaneous administration of 17betaE(2). OVX alone induced oxidative stress and hyperlipidemia without biochemical evidence of renal dysfunction. Our results revealed that ovarian hormones, especially estrogens, have a protective effect against oxidative stress and nephropathy induced by AD. Since the reactive oxygen species plays a role in the pathogenesis of renal lesion, it is important to emphasize that estrogens and their hydroxylated compounds function as biological antioxidants.  相似文献   
142.
BACKGROUND: In developing countries, incomplete resolution of anemia with iron supplementation is often attributed to poor compliance or inadequate duration of supplementation, but it could result from deficiencies of other micronutrients. OBJECTIVE: Our objective was to assess children's hematologic response to supervised, long-term iron supplementation and the relation of this response to other micronutrient deficiencies, anthropometry, morbidity, and usual dietary intake. DESIGN: Rural Mexican children aged 18-36 mo (n = 219) were supplemented for 12 mo with either 20 mg Fe, 20 mg Zn, both iron and zinc, or placebo. Children were categorized as iron-unsupplemented (IUS; n = 109) or iron supplemented (IS; n = 108). Hemoglobin, hematocrit, mean corpuscular volume, mean cell hemoglobin, plasma concentrations of micronutrients that can affect hematopoiesis, anthropometry, and diet were assessed at 0, 6, and 12 mo; morbidity was assessed biweekly. RESULTS: At baseline, 70% of children had low hemoglobin (相似文献   
143.
BACKGROUND: The coexistence of multiple micronutrient deficiencies is a widespread public health problem in many regions of the world. Interactions between zinc deficiency and vitamin A metabolism have been reported but no longitudinal studies have evaluated the effect of iron deficiency on vitamin A. OBJECTIVE: The objective of this study was to investigate the effect of supplementation with iron, zinc, or both on vitamin A and its metabolically related proteins retinol binding protein (RBP) and transthyretin. DESIGN: The study was a longitudinal, double-blind, placebo-controlled trial in which 219 rural Mexican children aged 18-36 mo were randomly assigned to receive 20 mg Zn/d, 20 mg Fe/d, 20 mg Zn/d plus 20 mg Fe/d, or placebo. RESULTS: Six months after supplementation, plasma retinol increased in all supplemented groups. Compared with placebo, zinc supplementation was associated with significantly higher plasma retinol and transthyretin but the increase in RBP was not significant. Iron supplementation significantly increased plasma retinol, RBP, and transthyretin. Supplementation with zinc plus iron significantly increased plasma retinol but not RBP or transthyretin. Children deficient in zinc, iron, or vitamin A (as indicated by nutrient plasma concentration) at the beginning of the study had a significantly greater increase in retinol than did children with adequate nutrient status. CONCLUSIONS: Supplementation with zinc, iron, or both improved indicators of vitamin A status. The results of this study agree with previous observations of a metabolic interaction between zinc and vitamin A and suggest an interaction between iron and vitamin A metabolism.  相似文献   
144.
145.
Association of Helicobacter pylori Infection with Gastric Adenocarcinoma   总被引:2,自引:0,他引:2  
Gastric adenocarcinoma is the most prevalent cancer in South Korea, and Helicobacter pylori (H. pylori) infection is also common. This study was performed to examine the association between H. pylori infection and gastric cancer, taking into account various other factors. To investigate the association between gastric adenocarcinoma and H. pylori infection, determined by urease-positive reaction in the CLO test, a total of 175 paired specimens (175 tumor and 175 tissues adjacent to tumor) of stomach cancer patients and a total of 113 control specimens were obtained. The positive H. pylori infection rates were 78.9% (138/175) among the patients in specimens of tumor or tissues adjacent to the tumor and 41.6% (47/113) among controls in the CLO test. A positive correlation between H. pylori infection and gastric cancer was observed (age-adjusted odds ratio, 7.0; MH χ2=34.5 with P <0.0005). These data suggest that stomach cancer patients in Korea have high infection rates of H. pylori regardless of site specificity, and this infection might be causally associated with stomach cancer.  相似文献   
146.
Across populations of children, Helicobacter pylori prevalence ranges from under 10% to over 80%. Low prevalence occurs in the U.S., Canada, and northern and western Europe; high prevalence occurs in India, Africa, Latin America, and eastern Europe. Risk factors include socioeconomic status, household crowding, ethnicity, migration from high prevalence regions, and infection status of family members. H. pylori infection is not associated with specific symptoms in children; however, it is consistently associated with antral gastritis, although its clinical significance is unclear. Duodenal ulcers associated with H. pylori are seldom seen in children under 10 years of age. H. pylori-infected children demonstrate a chronic, macrophagic, and monocytic inflammatory cell infiltrate and a lack of neutrophils, as compared with the response observed in adults. The effect of H. pylori infection on acid secretion in children remains poorly defined. The events that occur during H. pylori colonization in children should be studied more thoroughly and should include urease activity, motility, chemotaxis, adherence, and downregulation of the host response. The importance of virulence determinants described as relevant for disease during H. pylori infection has not been extensively studied in children. Highly sensitive and specific methods for the detection of H. pylori in children are needed, especially in younger pediatric populations in which colonization is in its early phases. Criteria for the use of eradication treatment in H. pylori-infected children need to be established. Multicenter pediatric studies should focus on the identification of risk factors, which can be used as prognostic indicators for the development of gastroduodenal disease later in life.  相似文献   
147.
Dietary intake of arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) by the population of Santiago (Chile) was determined using a Total Diet Study in the market basket modality. After conducting a survey of the foods consumed in the last 24 h, the most consumed food products were included in the basket. Subsequently, they were cooked or prepared according to typical Chilean procedures and grouped into 17 food categories according to their chemical characteristics. The fish and shellfish group had the highest contents of As (1351 ng/g wet weight, ww), Cd (277 ng/g ww), and Hg (48 ng/g ww), while the sugar group had the highest content of Pb (251 ng/g ww). For a person with a body weight of 68 kg, the dietary intakes of As (77 microg/day), Cd (20 microg/day), Hg (5 microg/day), and Pb (206 microg/day) are lower than the provisional tolerable weekly intake values established by the FAO/WHO. Consequently, the total intakes of As, Cd, Hg, and Pb in Santiago (Chile) are within the limits estimated as safe.  相似文献   
148.
The clinical presentation and evolution, neuropathological findings, and genotyping of three members of a Spanish family affected with fatal familial insomnia are reported. The mother and two of her offspring developed a rapidly evolving disease with insomnia and behavioural disorders as the initial symptoms and died between 5 and 10 months after the onset of the illness. Frontal brain biopsy in the mother disclosed only non-significant spongiosis, and full neuropathological examination of her offspring showed thalamic and olivary degeneration with isolated focal cortical spongiosis. Genetic examination could only be performed in the contemporary patients and both harboured the prion protein (PrP) 178Asn mutation and homozygous 129 Met/Met genotype.  相似文献   
149.
The localization of nitrergic cells and fibers and cholinergic cells has been analyzed in the spinal cord of the anuran amphibian Rana perezi. Histochemistry for nicotinamide adenine dinucleotide phosphate-diaphorase and nitric oxide synthase immunohistochemistry revealed a concurrent pattern of labeled structures. A large population of nitrergic spinal neurons was found from the level of the obex to the filum terminale. They are abundant in the dorsal horn and intermediate gray matter, but also occur in territories of the ventral horn and, only occasionally, in somatic motoneurons. Numerous nitrergic fibers were present in the spinal white matter, particularly in the dorsal and dorsolateral funiculi. A special arrangement of nitrergic axons is present in Lissauer's tract, where a collateral system is formed. Cholinergic cells, revealed by choline acetyltransferase immunohistochemistry, were observed throughout the spinal cord. The somatic motoneurons were the most conspicuously immunoreactive cells. A large population of cholinergic cells forms a discontinuous column in the intermediate gray, from the third spinal segment to lumbar segments. These cells were organized in a medially located or intercalated cell group, and a laterally located intermediolateral group. Numerous scattered cholinergic cells were present in the central zone of the ventral horn and were absent in the dorsal horn. Double-labeling experiments revealed a high degree of codistribution of nitrergic and cholinergic cells, mainly in the intermediate gray, but colocalization of both markers in the same neurons was not found. This result contrasts with the situation found in mammals and raises the question of whether coexpression of both substances was acquired in spinal cord neurons through evolution only in amniotes or, even, only in mammals.  相似文献   
150.
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