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   2344882篇
  免费   175073篇
  国内免费   3314篇
耳鼻咽喉   32050篇
儿科学   75865篇
妇产科学   62671篇
基础医学   348091篇
口腔科学   63672篇
临床医学   211133篇
内科学   456670篇
皮肤病学   51729篇
神经病学   185192篇
特种医学   87998篇
外国民族医学   489篇
外科学   353844篇
综合类   47481篇
现状与发展   12篇
一般理论   848篇
预防医学   182509篇
眼科学   54278篇
药学   175056篇
  10篇
中国医学   4579篇
肿瘤学   129092篇
  2021年   18994篇
  2019年   19552篇
  2018年   27078篇
  2017年   20371篇
  2016年   22757篇
  2015年   25649篇
  2014年   36121篇
  2013年   53980篇
  2012年   74712篇
  2011年   79441篇
  2010年   47073篇
  2009年   44578篇
  2008年   74629篇
  2007年   79501篇
  2006年   80322篇
  2005年   77796篇
  2004年   74377篇
  2003年   71704篇
  2002年   69370篇
  2001年   108740篇
  2000年   111453篇
  1999年   93496篇
  1998年   26990篇
  1997年   23660篇
  1996年   24055篇
  1995年   22715篇
  1994年   20894篇
  1993年   19712篇
  1992年   72001篇
  1991年   70070篇
  1990年   68391篇
  1989年   65666篇
  1988年   60303篇
  1987年   59129篇
  1986年   55219篇
  1985年   53006篇
  1984年   39315篇
  1983年   33397篇
  1982年   19860篇
  1979年   35868篇
  1978年   25653篇
  1977年   21230篇
  1976年   20333篇
  1975年   21818篇
  1974年   26148篇
  1973年   24804篇
  1972年   23200篇
  1971年   22039篇
  1970年   20247篇
  1969年   19315篇
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
971.
Felty's syndrome (FS), the association of rheumatoid arthritis (RA) and idiopathic neutropenia, remains an unexplained phenomenon. HLA-DR4 is found in over 90% of cases. Patients with FS may have a T cell lymphocytosis of CD3+CD8+CD57+ large granular lymphocytes (LGL syndrome). In this study of 47 patients with FS, 19% had clear evidence for LGL expansions, while in total 42% had variable evidence for the LGL syndrome using currently available techniques. Of these T cell expansions, 76% were clonal, as demonstrated by Southern blotting and analysis with T cell receptor (TCR) beta chain constant region probes. This technique may fail to detect clonal populations in some patients. Cytofluorographic analysis using antibodies specific for TCR V beta chains identified patients with clonal LGL expansions with results comparable to those obtained with Southern blotting. No evidence for shared V beta usage among expansions from different patients was seen. The role of LGL in RA and FS is currently unclear, but this technique offers a practical and accessible means of identifying patients with LGL expansions, as a starting point for further investigation.  相似文献   
972.
In 82 CHD male patients aged 35-54 years with well-preserved working capacity (threshold load, 600-750 kgm/min) who had underwent bicycle ergometer test, the time course of changes in the major hemodynamic parameters was found to be significantly similar to that of healthy individuals. The cases who stopped performing bicycle ergometer tests because of anginal attacks, and ST segment depression or either showed a more significant elevation in systolic and diastolic blood pressure at the maximum load rate and lower increase in heart rate than in healthy subjects, which may be regarded as a compensatory mechanism that prevents a further decrease in coronary flow. Diminished increase in stroke index and cardiac index suggests reduced myocardial contractility.  相似文献   
973.
Electrocardiographic symptoms were evaluated in 53 patients with an additional left-ventricular chorda (ALVC), detected by two-dimensional echocardiography. Signs of early ventricular repolarization (EVR) were identified in 45 (84.9%) patients. A transverse ALVC was more common in EVR-free patients (87.5%), as compared to patients with ALVC + EVR combinations (51.1%; p less than 0.05).  相似文献   
974.
975.
We compared the effects of alpha 2- and beta-adrenoreceptor blockade on the central actions of catecholamines and metabolites of alpha-methyldihydroxyphenylalanine, epinephrine, alpha-methylnorepinephrine, and alpha-methylepinephrine were studied. I.c.v. and nucleus tractus solitarii (NTS) injections were carried out under anesthesia. Following i.c.v. injection, both epinephrine and methylepinephrine rapidly reduced blood pressure and heart rate, but the effects of methylnorepinephrine occurred somewhat later. Following microinjection into the nucleus of the solitary tract, epinephrine, methylepinephrine, and methylnorepinephrine all caused hypotension and bradycardia. The hypotensive effects of all 3 amines in the NTS were attenuated in additive fashion by yohimbine, an alpha 2 adrenoreceptor antagonist, and timolol, a beta-adrenoreceptor antagonist, whereas only yohimbine attenuated the bradycardia. The combination of yohimbine and timolol abolished the effects of the amines. These data suggest that in the NTS both alpha 2 and beta adrenoreceptor stimulation contribute to the hypotensive effects of these amines, but that only alpha 2 adrenoreceptors are principally involved in the heart rate response.  相似文献   
976.
Summary. A new apparatus which measures the blood pressure in the finger continuously and yet not invasively was tested for its usefulness during exercise. It was compared with upper arm measurements in 23 volunteers during prolonged bicycle ergometry. Simultaneously, a pulse plethysmogram was recorded from another finger of the same arm, whereas in six additional volunteers Doppler measurements were carried out on the radial artery. The results show that finger systolic pressure ceased to rise at about 40% of maximal exercise; the difference with the continuously rising systolic pressure in the upper arm becoming significant at 140 W. At the same time the amplitude of the finger plethysmogram became significantly higher than its initial value, indicating distinct cutaneous vasodilation, whereas the volunteers also became hot and started to perspire. However, the radial artery ‘flow’, deduced from the Doppler measurements, did not change significantly during exercise. It increased sharply and markedly in the cooling down period. Simultaneously with this increase in flow, HR and both systolic blood pressures fell drastically whereas the plethysmography amplitude remained about stable at its raised level. The results fit in with the idea that a compromise is achieved between the need for muscle activity and the need for temperature regulation. It is concluded that the Finapres functions well during exercise, but that the systolic pressure in the finger is not representative for its more central counterpart during cutaneous vasodilation. It is argued that opening up of AVAs may contribute to this pressure effect.  相似文献   
977.
Serial blood samples were taken at two-hour intervals over a 24-hour period from 25 premenopausal vegetarians (12 vegans and 13 ovolactovegetarians) and from 21 omnivorous controls. All members of the former group had been on a vegetarian diet for a minimum of three years. The mean proportion of estradiol unbound to blood proteins was similar in both vegetarians (1.26%) and meat eaters (1.16%). However, the amount bound to albumin was significantly raised in vegetarians (50.1% vs. 43.1%, p less than 0.009), whereas that bound to sex hormone-binding globulin (SHBG) was correspondingly lower (48.7% vs. 55.8%, p = 0.01). Mean levels of SHBG were similar in vegetarians (59.9 nmole/l) and omnivores (62.0 nmole/l), as was the total amount of free fatty acid (0.42 mmole/l for both). Within the vegetarian group, no differences were detected between vegans and ovolactovegetarians.  相似文献   
978.
979.
980.
Pressure suppresses serotonin release by guinea pig striatal synaptosomes   总被引:1,自引:0,他引:1  
Exposure to high pressure produces neurologic changes in humans which manifest as tremor, EEG changes, and convulsions. Since previous studies have implicated the involvement of the serotoninergic system in these symptoms, it was of interest to study serotonin release at high pressure. Synaptosomes isolated from guinea pig striatum were used to follow serotonin efflux at 68 ATA. The major observation was a decrease in [3H]serotonin release from depolarized striatal synaptosomes at 68 ATA. In view of the role of serotonin as an inhibitory neurotransmitter in this area, the observed decrease in synaptic release leads us to conclude that decreased serotoninergic activity in striatal neurons probably is contributing to the hyperexcitability associated with HPNS.  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