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   1278485篇
  免费   98226篇
  国内免费   1989篇
耳鼻咽喉   18432篇
儿科学   44359篇
妇产科学   35015篇
基础医学   182175篇
口腔科学   33591篇
临床医学   111252篇
内科学   258306篇
皮肤病学   28022篇
神经病学   100378篇
特种医学   51198篇
外国民族医学   660篇
外科学   196397篇
综合类   27056篇
现状与发展   1篇
一般理论   377篇
预防医学   95720篇
眼科学   27919篇
药学   94776篇
  2篇
中国医学   2423篇
肿瘤学   70641篇
  2018年   13139篇
  2017年   9968篇
  2016年   10901篇
  2015年   12375篇
  2014年   17168篇
  2013年   26214篇
  2012年   36023篇
  2011年   38064篇
  2010年   22806篇
  2009年   21811篇
  2008年   36640篇
  2007年   39248篇
  2006年   39502篇
  2005年   38440篇
  2004年   37595篇
  2003年   36449篇
  2002年   35799篇
  2001年   63989篇
  2000年   66496篇
  1999年   56412篇
  1998年   15131篇
  1997年   13754篇
  1996年   14197篇
  1995年   13452篇
  1994年   12766篇
  1993年   11790篇
  1992年   44554篇
  1991年   43465篇
  1990年   42216篇
  1989年   40113篇
  1988年   36894篇
  1987年   36234篇
  1986年   33619篇
  1985年   32281篇
  1984年   24136篇
  1983年   20268篇
  1982年   11723篇
  1981年   10691篇
  1980年   9516篇
  1979年   21342篇
  1978年   14821篇
  1977年   12532篇
  1976年   11694篇
  1975年   12623篇
  1974年   14661篇
  1973年   14118篇
  1972年   12944篇
  1971年   11730篇
  1970年   11050篇
  1969年   10024篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A total of 186 blood samples from 24 HIV-1 seropositive hemophiliac patients, monitored every four months for 29 months, were investigated for the presence of viral antigen in plasma. In addition, peripheral blood mononuclear cells (PBMC) were cultured for HIV-1, using normal PBMC as a target for replication. Antigenemia was detected in 51 % of the patients and from PBMC in 87.5 % of the patients. The incidence of HIV isolation in asymptomatic patients (42.8 %) was similar to that found in symptomatic patients (51.4 %). Patients with opportunistic infections had a higher incidence of lymphocytic viremia (p<0.05). Plasma viremia was closely associated (p<0.05) with low CD4+ counts and infection progression. The persistence of antigenemia was also a marker of a poor clinical course. In treated patients, plasma viremia was the marker that better correlated with the clinical course, and it did not appear during the first nine months of therapy. Zidovudine doses of >500 mg/day significantly lowered the appearance of antigenemia and lymphocytic viremia (p<0.05).  相似文献   
992.
993.
When administered systemically, glucose attenuates deficits in memory produced by several classes of drugs, including cholinergic antagonists and opiate agonists. Glucose also enhances memory in aged rats, mice, and humans. In addition, glucose ameliorates age-related reductions in paradoxical sleep. Because deficits in paradoxical sleep are most marked in those individual aged rats that also have deficits in memory, treatments which improve one of these functions may similarly improve the other. The present experiments show that glucose attenuates deficits in paradoxical sleep and memory after atropine administration, with similar dose-response curves for both actions. In the first experiment, rats received saline, atropine (1 mg/kg), glucose (100 mg/kg) or combinations of atropine + glucose (10, 100, 250, and 500 mg/kg) 30 min before assessment on a spontaneous alternation task. In the second experiment, 3-h EEGs were assessed for spontaneous daytime sleep in rats administered saline, atropine (1 mg/kg), glucose (100 mg/kg) or combinations of atropine + glucose (10, 100 and 250 mg/kg). In both experiments, glucose significantly attenuated deficits at an optimal dose of 100 mg/kg. A third experiment assessed blood glucose levels after injections of atropine + glucose (100 mg/kg) and determined that blood glucose levels were similar to those produced by other treatments which enhance memory. These results are consistent with the view that paradoxical sleep and at least one test of memory are similarly influenced by atropine and glucose.  相似文献   
994.
We report the clinical, SPET, immunohistochemical and DNA features of an early-onset familial Alzheimer's disease (FAD) in an Argentine pedigree of South American indian ethnic background. Pedigree spans 5 generations comprising more than 110 biological relatives. Clinical data supported the diagnosis of early onset FAD (mean age at onset 38.9 years) in 10 family members, including 3 with pathological confirmation (mean age at death 48.5). The pattern of transmission suggested autosomal dominant inheritance. Prominent features were mood changes, early language impairment, myoclonus, seizures and cerebellar signs. SPET displayed bilateral frontal, temporo-parietal and cerebellar hypoperfusion in early stages and in an asymptomatic member at risk, suggesting that SPET may have predictive value in this family. Immunohistochemistry showed β amyloid deposits within neuritic plaques and vessel walls and no anti-PrP immunoreactivity. DNA analysis showed no abnormalities in the β amyloid precursor protein gene. The identification of additional genetic defects in well characterized independent FAD pedigrees will contribute to the understanding of the pathogenesis of Alzheimer's disease.  相似文献   
995.
A 30-year-old presented In 1984 with a clinically nonfunctional tumour which subsequently developed Into a metastatic corticotrophlnoma from which he died despite surgery In 1984,1986 and 1991 and external radiotherapy In 1986. Molecular genetic analysis of tumour and metastatic tissue revealed loss of heterozygosity at loci on the autosomes 1p, 3p, 10q26,11q13 and 22q12. Tissue taken at surgery In 1986 also revealed positive cytoplasmic Immunostalning for p53 protein. No such staining was evident in tissue taken at first surgery in 1984. Further analysis of Invasive pituitary adenomas may reveal loci associated with such behaviour, enabling better prediction of subsequent clinical outcome than is possible using standard histological techniques, and delivery of early, aggressive treatment to those tumours which show molecular markers associated with a poor prognosis.  相似文献   
996.
997.
998.
Summary Rats were treated with desipramine 5mg/kg, nomifensine 10mg/kg, zimelidine 25 mg/kg or with 0.9% sodium chloride once a day during the second and third weeks after birth, and brain stem, caudate/putamen and cortical monoamines, and caudate/putamen dopamine D1 (3[H]SCH 23390) and D2 (3[H]spiroperidol) receptor binding were measured when rats were at two months of age. In the brain stem, the concentration of 3-methoxy-4-hydroxy-phenyl glycol was increased in nomifensine rats and the ratio of 5-hydroxyindoleacetic acid to 5-hydroxytryptamine was increased in zimelidine rats. In the caudate/putamen, the concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid and the ratio of homovanillic acid to dopamine were increased in desipramine rats; neither3[H]SCH 23390 nor3[H]spiroperidol binding were affected by any of the three monoamine uptake inhibiting antidepressants studied. In the cortex, the ratio of 5-hydroxyindoleacetic acid to 5-hydroxytryptamine was increased in desipramine and zimelidine rats. The findings suggest that desipramine but not nomifensine increases the metabolism of dopamine in the caudate/ putamen and nomifensine but not desipramine increases the metabolism of norepinephrine in the brain stem, and furthermore that the metabolism of serotonin is affected by desipramine as well as by zimelidine. It is possible that also treatment of women with these drugs during late pregnancy causes long-lasting changes in the brain of human fetus.  相似文献   
999.
The ethanol extracts of the roots of T. cordifolia Miers and C. asiatica Linn were observed to induce a marked protective action against an 8 h restraint stress induced ulcerization, the activity being comparable to that of diazepam.  相似文献   
1000.
This report explores the possibility of redefining risk factors so as to improve their observed associations with prevalent coronary heart disease (CHD). A large cross-sectional community study of 5,895 white males and females aged 25-64 years yielded 240 cases of confirmed angina pectoris and 361 of confirmed myocardial infarction. Odds ratios for CHD end-points by level of risk factors when risk factors were expressed in the conventional manner (e.g. total cholesterol, systolic and diastolic blood pressure or current smoking) were often low and not statistically significant. Redefinition of risk factor variables in a manner that improved their specificity or compensated to some extent for the decreased risk factor exposure as a result of a CHD event (e.g. stopping smoking after a myocardial infarct) improved the strength of association. In this study, the most useful cholesterol variable was total cholesterol minus high-density lipoprotein cholesterol; for blood pressure the most useful variable was a blood pressure of 160/95 mmHg or above and/or being on anti-hypertensive treatment; and for smoking the most useful variable was the total duration of smoking (previous and current). Strong associations with CHD end-points were also found for conventionally expressed serum uric acid, diabetes prevalence (females) and family history of CHD. The study suggests that appropriate redefinition of risk factor variables and CHD end-points in cross-sectional studies yields associations similar in strength and direction to those found in prospective studies.  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