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   286774篇
  免费   282699篇
  国内免费   39437篇
耳鼻咽喉   2892篇
儿科学   4608篇
妇产科学   2791篇
基础医学   93248篇
口腔科学   3318篇
临床医学   64205篇
内科学   99282篇
皮肤病学   5198篇
神经病学   23926篇
特种医学   10405篇
外国民族医学   23篇
外科学   45496篇
综合类   60021篇
现状与发展   17篇
一般理论   9篇
预防医学   44450篇
眼科学   19282篇
药学   62315篇
  46篇
中国医学   49285篇
肿瘤学   18093篇
  2022年   4929篇
  2021年   5858篇
  2020年   7900篇
  2019年   14704篇
  2018年   15290篇
  2017年   15876篇
  2016年   14316篇
  2015年   14958篇
  2014年   15213篇
  2013年   14535篇
  2012年   15471篇
  2011年   17276篇
  2010年   18680篇
  2009年   26143篇
  2008年   14034篇
  2007年   10671篇
  2006年   10148篇
  2005年   9847篇
  2004年   11502篇
  2003年   10841篇
  2002年   10969篇
  2001年   12662篇
  2000年   8081篇
  1999年   13406篇
  1998年   14491篇
  1997年   14363篇
  1996年   15241篇
  1995年   15408篇
  1994年   15124篇
  1993年   13647篇
  1992年   13020篇
  1991年   12341篇
  1990年   11303篇
  1989年   11123篇
  1988年   10676篇
  1987年   10002篇
  1986年   9501篇
  1985年   8532篇
  1984年   6599篇
  1983年   6574篇
  1982年   7617篇
  1981年   7151篇
  1980年   6818篇
  1979年   6644篇
  1978年   5819篇
  1977年   6122篇
  1976年   5743篇
  1975年   5483篇
  1974年   5036篇
  1972年   4754篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Previous studies have demonstrated an increase in a low molecular weight angiogenic factor (ESAF) present in the retinae of kittens with oxygen induced retinopathy. The present paper describes differences in the quantity of ESAF extracted from the vitreous humour of control and oxygen treated animals and proposes a mechanism for the induction of intravitreal neovascularisation.  相似文献   
992.
Basal cell carcinomas of the eyelids, especially those in the medial canthal area, may cause extensive local destruction. Recurrent tumours are more aggressive and become progressively more difficult to treat; this is especially true for postirradiated recurrent, medial canthal, basal cell carcinomas. Tumours in this area should thus be treated by a technique which allows tissue sampling in order to gauge the adequacy of the treatment, with the goal being complete extirpation of the tumour. Excision monitored by frozen section control or Mohs' surgery is our recommendation based on a retrospective analyses of 631 eyelid basal cell carcinomas, half of which were primary tumours and half recurrent.  相似文献   
993.
A patient presented with an ipsilateral orbital mass four years after enucleation for a choroidal malignant melanoma. Clinical examination revealed a darkly coloured mass suggestive of recurrent melanoma. CT scanning indicated a locally extensive tumour. Management was by excision without resort to orbital exenteration. Pathological examination revealed a cavernous haemangioma. The natural history of this tumour is discussed.  相似文献   
994.
Evoked potentials were recorded to the occurrence of a disparate stimulus in dynamic random dot stereograms. Seven adult males, all of whom had vision which was normal or corrected to normal, participated in the experiment. Subjects viewed 100 ms duration stimuli which embodied 30 arc min of either crossed or uncrossed disparity under four conditions of spherical overcorrection: -0.25, +1.0, +2.0, +3.0 dioptres. The first condition, essentially normal refraction, yielded reliable behavioural reports of the stimulus and clear evoked potentials to both crossed and uncrossed disparity. With increasing overcorrection the behavioural reports became less reliable, and the evoked potentials were degraded for both conditions of disparity. The responses to the crossed disparity condition, however, showed significantly less degradation in both behavioural and electrophysiological measures. The implications of this finding may be that there are separate cortical subsystems for the processing of crossed and uncrossed disparity and that the former is more robust under non-ideal viewing conditions.  相似文献   
995.
The urinary excretion of the n-hexane metabolite 2,5-hexanedione (HD) was determined in four shoe factory workers during four workingdays that were preceded by four free days and followed by two free days. The correlation between excretion of HD and the n-hexane concentrations in the workroom air was evaluated. The air concentrations of n-hexane and those of acetone, toluene, and other organic solvents were monitored with charcoal tubes. All the urine from each worker was collected at freely chosen intervals during the experimental period and the following two free days. The samples were analysed by gas chromatography. The relative excretion of HD increased as the exposure to n-hexane increased, although it seemed that HD accumulated progressively in the body at the highest n-hexane concentrations and at higher total solvent concentrations.  相似文献   
996.
A total of 391 male employees in a Swedish pulp and paper company were followed up for 22 years. As a part of a health examination in 1961 back pain reported by the subjects and abnormalities of the back as judged by the physicians were investigated with respect to predictive power regarding sick leave, early retirement, unemployment, labour turnover, and mortality during the follow up period. Univariate analysis showed that abnormalities of the back were better than back pain for predicting early retirement. Neither back pain nor back abnormalities had any predictive power with respect to long term sick leave, labour turnover, or mortality. Multivariate analyses of 26 variables were performed. Both self assessment of general health and back abnormalities were predictive for early retirement with a diagnosis of back disorder on the retirement certificate but self assessed health was a stronger predictor. Age, smoking, and neuroticism were predictors regarding early retirement for all diagnoses. Education had a negative association; neuroticism did not predict early retirement with a diagnosis of back disorder.  相似文献   
997.
为了探讨增产菊胺酯引起小鼠精了生成障碍的可能机理,本文研究了增产菊胺酯对雄性小鼠卵泡刺激素(FSH)、黄体生成素(LH)及睾酮(T)的影响。小鼠经口染毒,隔天一次,连续10次,第35天处死。检验因清FSH、LH没有明显变化,而睾丸组织睾酮含量出现剂理依赖性降低,高剂量组与对照组比较有显著性差异(P〈0.05),结果表明,增产菊胺酯不影响FSH、LH,而影响T的合成和分泌。这可能是增产菊胺酯对小鼠精  相似文献   
998.
Bacteroides fragilis constitutes about 1% of the bacterial flora in intestines of normal humans. Enterotoxigenic strains of B. fragilis have been associated with diarrheal diseases in humans and animals. The enterotoxin produced by these isolates induces fluid changes in ligated intestinal loops and an in vitro cytotoxic response in HT-29 cells. We developed a nested PCR to detect the enterotoxin gene of B. fragilis in stool specimens. After DNA extraction, a 367-bp fragment was amplified with two outer primers. The amplicon from this reaction was subjected to a second round of amplification with a set of internal primers. With these inner primers, a 290-bp DNA fragment was obtained which was confirmed as part of the B. fragilis enterotoxin gene by Southern blotting with a nonradioactive internal probe and a chemiluminescence system. By this approach, B. fragilis enterotoxin gene sequences were detected in eight known enterotoxigenic human isolates and nine enterotoxigenic horse isolates. No amplification products were obtained from DNA extracted from 28 nonenterotoxigenic B. fragilis isolates or B. distasonis, B. thetaiotaomicron, B. uniformis, B. ovatus, Escherichia coli, or Clostridium difficile. The sensitivity of this assay allowed us to detect as little as 1 pg of enterotoxin DNA sequences or 100 to 1,000 cells of enterotoxigenic B. fragilis/g of stool. Enterotoxin production of all isolates was confirmed in vitro in HT-29 cells. A 100% correlation was obtained between enterotoxin detection by cytotoxin assay and the nested PCR assay. This rapid and sensitive assay can be used to identify enterotoxigenic B. fragilis and may be used clinically to determine the role of B. fragilis in diarrheal diseases.  相似文献   
999.
3种氟喹诺酮类药物抗生素后效应的研究   总被引:40,自引:2,他引:38  
应用AVANTAGF分析仪的光密度法测定了环丙沙星(CPLX)、氧氟沙星(OFLX)和氟罗沙星(FLRX)的抗生素后效应(PAE).结果表明氟喹诺酮类抗菌药物对革兰氏阳性球菌和革兰氏阴性杆菌均产生明显的PAE.并随抗菌药物浓度的增大、对受试菌的PAE逐渐延长.呈现了明显的浓度依赖性;3种抗菌药物对铜绿假单胞菌的PAE都较长.MIC均较小.显示了良好的杀菌效果:氯罗沙星对除金葡球菌之外的受试菌的PAE均比其它2药较长.PAE的存在提示在临床设计给药方案时.可适当延长给药间期.减少给药次数与剂量.仍能维持抗菌效果。  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