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   2549337篇
  免费   181178篇
  国内免费   5664篇
耳鼻咽喉   33835篇
儿科学   84314篇
妇产科学   69864篇
基础医学   364212篇
口腔科学   74325篇
临床医学   226567篇
内科学   497141篇
皮肤病学   58180篇
神经病学   199865篇
特种医学   94956篇
外国民族医学   526篇
外科学   379857篇
综合类   57436篇
现状与发展   4篇
一般理论   890篇
预防医学   199128篇
眼科学   60814篇
药学   186292篇
  9篇
中国医学   6237篇
肿瘤学   141727篇
  2021年   19652篇
  2019年   20919篇
  2018年   30725篇
  2017年   22985篇
  2016年   25223篇
  2015年   28603篇
  2014年   39056篇
  2013年   58174篇
  2012年   80810篇
  2011年   85491篇
  2010年   50008篇
  2009年   46082篇
  2008年   78700篇
  2007年   83812篇
  2006年   84266篇
  2005年   80676篇
  2004年   78058篇
  2003年   74216篇
  2002年   71631篇
  2001年   124979篇
  2000年   128328篇
  1999年   106506篇
  1998年   28454篇
  1997年   24999篇
  1996年   25026篇
  1995年   24001篇
  1994年   22085篇
  1993年   20465篇
  1992年   81552篇
  1991年   78982篇
  1990年   76566篇
  1989年   73641篇
  1988年   67008篇
  1987年   66021篇
  1986年   62203篇
  1985年   59307篇
  1984年   43788篇
  1983年   37186篇
  1982年   21395篇
  1979年   39490篇
  1978年   27734篇
  1977年   23692篇
  1976年   22140篇
  1975年   23359篇
  1974年   28415篇
  1973年   27381篇
  1972年   25368篇
  1971年   23543篇
  1970年   21891篇
  1969年   20597篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
This paper suggests that like ethanol, methanol also produces certain changes in the steady state level of monoamines in hypothalamus and striatum of albino rats. Though, the toxic manifestations of methanol are attributed to the metabolic end product of methanol viz. formic acid by several workers, we report here that the methanol-induced brain monoamine changes, at least, could be attributed to the direct action of methanol rather than to its metabolic end products like formaldehyde or formate. Studies in the steady state level of rat brain monoamines have shown that after methanol administration (3 g/kg), there is severe depletion of dopamine level in striatum but a significant increase in the level of dopamine, serotonin and 5-hydroxy indole acetic acid in hypothalamus. At the same time, norepinephrine and epinephrine levels are reduced in hypothalamus as well as in striatum. These effects do not seem to be induced by metabolic acidosis. The changes in monoamine levels are very well correlated with the blood and brain level of methanol as evidenced by maintaining a higher methanol level either by simultaneous administration of ethanol or by blocking methanol metabolism by pretreatment with 4-methyl pyrazole and 3-amino-1,2,4-triazole. It is thus postulated that monoamine changes induced by methanol appear to be the direct effect of methanol per se on the monoaminergic neuronal membranes.  相似文献   
992.
Dietary factors in the risk of bladder cancer   总被引:2,自引:0,他引:2  
The relationship between selected dietary factors and the risk of bladder cancer was investigated in a case-control study conducted in northern Italy. The study included 163 cases and 181 controls who were hospitalized for acute, nonneoplastic or urinary tract diseases. The frequency of consumption of green vegetables and carrots was lower in the cases; thus, the estimated relative risks for the upper vs. the lower tertiles were 0.6 for green vegetables and 0.5 for carrots. Significant inverse trends in risk emerged with estimated carotenoid (as well as retinoid) intake. The apparent protection conveyed by vitamin A was stronger in current smokers. The risk of bladder cancer was not related to scores of fat and measures of alcohol consumption; the risk was elevated in coffee drinkers (although there was no tendency to rise with higher consumption), but it was reduced in tea drinkers. These findings were not explainable in terms of selection, information, or confounding bias. Thus, although available information is too uncertain for any precise definition of specific (micro)nutrients related to bladder cancer risk, the confirmation that several aspects of a less-affluent diet adversely affect the risk is still of interest in terms of a better understanding of bladder carcinogenesis.  相似文献   
993.
The toenails and the rest of the human foot are constantly sandwiched in shoes, traumatized, and poorly supplied with blood that is necessary for normal morphology and function, resulting in more abnormal changes of the toenails (onychopathies). This article discusses briefly the following: (1) the conditions that are commonly seen in feet by podiatric practitioners; (2) clinical signs, symptoms, and etiology; and (3) differential diagnosis and care of the conditions.  相似文献   
994.
A case of tumoral calcinosis simulating osteomyelitis and associated with bunion formation in a 20-year-old female is presented. The most striking findings in this patient were the soft tissue calcifications. There was no evidence of any of the known causes of heterotopic calcifications. This kind of simulation between tumoral calcinosis bunion formation and osteomyelitis has not been previously described.  相似文献   
995.
996.
A topical formulation of ketoprofen, a widely used nonsteroidal antiinflammatory drug, has recently been developed. Ten healthy young subjects (mean age 23.5 +/- 2.5 years) received daily 15 g of 2.5% ketoprofen gel, corresponding to 375 mg on the skin of the back over an area of 750 cm2. Plasma samples were collected after the first dose and after 10 days of chronic treatment. Urine was also collected. Ketoprofen was assayed by HPLC. The peak plasma concentration was 144 +/- 91 ng/ml after the first administration with apparent absorption and elimination half-lives of 3.2 +/- 2.4 h and 27.7 +/- 18.0 h, respectively. The total quantities of ketoprofen eliminated in the urine represented about 2.6% of the first dose applied. At the end of the study, the apparent half-life of unchanged ketoprofen was 17.1 +/- 9.1 h, and there was no accumulation. In this study, no sign of local intolerance was seen.  相似文献   
997.
This study demonstrated the existence of specific binding sites for [3H]Ro 19-6327 in human platelet membranes. This compound is a novel, time-dependent inhibitor of monoamine oxidase type B (MAO-B) and is structurally closely related to [3H]Ro 16-6491. The density of the sites labelled with high affinity by [3H]Ro 19-6327 was similar to that observed in previous studies with [3H]Ro 16-6491 as ligand. Binding was reversible at 20 degrees C and showed a relatively slow dissociation (t1/2 = 220 min). The dissociation rate was markedly decreased (t1/2 = greater than 24h) at 0 degrees C. MAO-B, but not MAO-A inhibitors, effectively prevented the binding of [3H]Ro 19-6327. Like [3H]Ro 16-6491, [3H]Ro 19-6327 is recognized as a substrate by MAO-B, being eventually deaminated by the enzyme. Since the deaminated aldehyde derivative of Ro 19-6327 did not inhibit MAO-B, a still unidentified reversible adduct, formed at the MAO-B active site, might explain the high potency and selectivity of [3H]Ro 19-6327. Incubation of the radioligand-enzyme complex from platelet and brain membranes with NaBH3CN and acetic acid (to pH 4.5) caused the irreversible incorporation of the radioactivity into a single polypeptide as shown by SDS-PAGE analysis. This polypeptide had a molecular weight identical to that of the MAO-B subunit, i.e. 58,000. The presence of unlabelled MAO-B inhibitors in the incubation mixture prevented the covalent incorporation of [3H]Ro 19-6327. The irreversible MAO-B inhibitor, [3H] pargyline, labelled a protein with a molecular weight identical to the protein labelled by [3H]Ro 19-6327.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
998.
Herniation of a thoracic disc in an acromegalic giant is reported. Degenerative changes in the spine in association with dorsal kyphosis, and the additional strain, resulted in the disc prolapse.  相似文献   
999.
The effect of zinc supplementation on the metabolism of tryptophan conversion to niacin was studied in 14 alcoholic patients with pellagra and in 7 male control subjects aged 21-45 y. The pellagrins received chemically defined diets based on crystalline amino acids through an enteral tube for 7 d. Patients were divided into two groups (A and B), both receiving a diet from which tryptophan, Zn, and niacin were excluded. Patients in group B, however, received 220 mg Zn sulfate orally. Upon admission the pellagra patients had low plasma Zn levels and low urinary excretion values of N'methylnicotinamide (N'MN) and N'methyl-2-pyridone-5-carboxamide (2-PYR) in relation to the control subjects (p less than 0.01). During the experimental period there was an increase in plasma Zn levels (p less than 0.005) and in urinary N'MN (p less than 0.05) and 2-PYR (p less than 0.05) excretion in the patients receiving Zn supplementation (group B). These results suggest that Zn interacts with niacin metabolism in alcoholic patients with pellagra through a probable mediation by vitamin B-6.  相似文献   
1000.
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