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   34344篇
  免费   2985篇
  国内免费   1505篇
耳鼻咽喉   225篇
儿科学   374篇
妇产科学   456篇
基础医学   3657篇
口腔科学   509篇
临床医学   3065篇
内科学   7286篇
皮肤病学   875篇
神经病学   3362篇
特种医学   1260篇
外国民族医学   10篇
外科学   3522篇
综合类   5480篇
现状与发展   7篇
一般理论   3篇
预防医学   1263篇
眼科学   1407篇
药学   2996篇
  10篇
中国医学   1652篇
肿瘤学   1415篇
  2024年   116篇
  2023年   617篇
  2022年   985篇
  2021年   1327篇
  2020年   1283篇
  2019年   1218篇
  2018年   1099篇
  2017年   1164篇
  2016年   1187篇
  2015年   1338篇
  2014年   2023篇
  2013年   2535篇
  2012年   1812篇
  2011年   1963篇
  2010年   1767篇
  2009年   1704篇
  2008年   1775篇
  2007年   1772篇
  2006年   1707篇
  2005年   1566篇
  2004年   1348篇
  2003年   1183篇
  2002年   1057篇
  2001年   840篇
  2000年   736篇
  1999年   544篇
  1998年   496篇
  1997年   420篇
  1996年   376篇
  1995年   369篇
  1994年   276篇
  1993年   247篇
  1992年   239篇
  1991年   229篇
  1990年   166篇
  1989年   146篇
  1988年   133篇
  1987年   125篇
  1986年   123篇
  1985年   152篇
  1984年   133篇
  1983年   77篇
  1982年   106篇
  1981年   109篇
  1980年   66篇
  1979年   51篇
  1978年   41篇
  1977年   26篇
  1976年   21篇
  1975年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Functional vascular connections must form rapidly to prevent ischemic damage to grafted neural tissues. The temporal sequence by which transplant circulation is re-established provides information about the angiogenic capacity of either intact or damaged CNS blood vessels. This study compares the time course and mechanism of vascular reperfusion in allografts of superior cervical ganglia or adrenal medulla inserted either into the fourth ventricle or directly into the parietal cortex of perinatal rats. Tritiated thymidine was administered to recipients to determine angiogenic patterns at various postoperative time periods. After processing for light microscopic autoradiography, host and graft endothelial labelling indices were determined in order to establish the temporal sequence and location of vascular proliferation. Correlative electron microscopy depicted the morphological changes in transplant vasculature. Some recipients were prelabelled with 3H thymidine prior to transplantation to determine if host vessels invaded the grafts. Intraventricular graft vessels initially collapsed but sustained minimal ischemic damage and were completely reperfused by 24 hours postoperative. Adjacent intact host vessels attained peak 3H thymidine incorporation at 20 hours. Intrinsic graft vessels were radioactively labelled only after 48 hours. Intraparenchymal transplants surrounded by minimal trauma exhibited a similar temporal sequence of reperfusion and host endothelial proliferation. Intrinsic graft vessels in intraparenchymal grafts sustained more severe damage. With increased trauma, a concomitant delay in graft reperfusion time was observed. Grafts within prelabelled hosts rarely contained any labelled endothelium, indicating that anastomotic connections were made between original, intrinsic graft vessels and nearby host vascular sprouts. This study demonstrates that mature autonomic tissue stimulates the growth of adjacent host vessels when transplanted to undamaged brain surfaces. The anastomosis of nascent host vessels with pre-existing graft vessels is responsible for the rapid re-establishment of circulation within the transplants. A similar mechanism occurs within intraparenchymal grafts, although the rapidity of reperfusion appears to be predicated on the amount of trauma present at the graft site.  相似文献   
52.
A neuropathological study on 1540 consecutive autopsy brains ranging from 60 to 107 years of age revealed the following points. (1) Of the of the demented cases of the plaque-predominant type, 93% were complicated with multiple tiny cortical infarcts. They showed a tendency for dementia to develop before or after the appearance or worsening of a systemic disorder such as cardiovascular disease, respiratory infection and cancer. However, there was no case showing Alzheimer-type dementia (ATD). (2) The plaque-predominant type might be an extreme condition of brain aging in terms of senile plaques (SP). It is likely that although the pathological appearance of SP alone is not responsible for dementia, its coexistence with multiple cortical infarcts could be the cause of dementia. Therefore, this type should be distinguished from ATD. (3) Primary hippocampal degeneration could also be an extreme condition of brain aging in terms of neurofibrillary tangles. This condition was different pathologically from the hippocampal lesion in ATD. (4) Several characteristics of old-old and oldest-old patients were clarified.  相似文献   
53.
We evaluated the age distribution of erythrocytes in pregnancy complicated by gestational diabetes class A2 by the density distribution of cells (DDC) method. The values for normal pregnancy and nonpregnant women were obtained from recently published studies. The cumulative density distribution of cells (DDC) of women with gestational diabetes resembled that of normal pregnancy.  相似文献   
54.
Self-efficacy and the maintenance of exercise participation in older adults   总被引:10,自引:0,他引:10  
The role played by exercise self-efficacy in the maintenance of exercise participation of previously sedentary middle-aged adults 4 months after the termination of a formal exercise program is reported. Correlational and multiple regression analyses examined the influence of self-efficacy, physiological (aerobic capacity, sex, body composition), and behavioral (past exercise frequency and intensity) parameters in the maintenance of exercise participation. Self-efficacy significantly predicted exercise behavior at follow-up when controlling for biological and behavioral influences. Aerobic capacity, exercise efficacy, and exercise behavior in combination were significantly related to current energy expenditure in aerobic physical activity. The discussion focuses on the need to examine the impact of different correlates of exercise behavior at different stages of the exercise process.This project was funded by Grant AG07907 from the National Institute on Aging.  相似文献   
55.
During (January) 1986–(May) 1988, we examined 272 eyes in 136 rhesus monkeys in the closed Cayo Santiago colony of the Caribbean Primate Research Center of the University of Puerto Rico. Seventy-eight eyes were less than 10 years of age. One hundred and ninety-four were aged 10–28 years. The fundi were examined and photographed. Fluorescein angiography was performed in some eyes. Selected cases were evaluated for acuity loss by recording of pattern-evoked retinal and cortical signals. Light and electron microscopy were used to evaluate the pigment epithelium of some animals. Thirty-eight percent of all eyes had posterior pole drusen. Incidence was highly age-related. When late-stage lesions were found, we did not see neovascularization, but late hyperfluorescence was consistent with degenerative scarring and atrophy. Electrophysiology demonstrated moderately reduced acuity in the presence of numerous macular drusen. Electrooculograms were low normal. Histopathology showed changes identical to those reported in human age-related macular degeneration. No eyes less than 10 years of age had confluent drusen or disciform-like lesions. The incidence of drusen in samples of some social groups was much higher than others.  相似文献   
56.
57.
We have previously shown that tumor necrosis factor-α (TNF-α), which is an important angiogenesis-related factor, was over-secreted in male BALB/c mice under social isolation stress as compared with the control, and closely associated with a remarkable elevation of tumor invasion and metastasis of colon 26-L5 carcinoma cells. In the present study, we explored the effect of isolation stress on the angiogenesis caused by colon 26-L5 carcinoma cells in vivo and in vitro. Social isolation lead to the enhancement of tumor growth after intrahepatic implantation with a fragment of colon 26-L5 tumor. Angiogenic response (number of vessels oriented towards tumor mass) and tumor growth (size) were significantly increased in the socially isolated mouse relative to that in the group-housed mice. Furthermore, higher protein level of hepatic TNF-α was found in the stressed mice than that in the control. Expression of mRNA for vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were also elevated in the tumor regions and liver tissues of the stressed mice in comparison with that in group-housed mice. On the other hand, hepatic sinusoidal endothelial (HSE) cells treated with TNF-α exhibited a marked promotion of the migration, invasion, expression of mRNA for matrix metalloproteinase (MMP)-9, and tube-like formation, but no cytotoxicity against the cells in vitro. The above data suggest that the social isolation stress augmented the tumor-induced angiogenesis probably by up-regulating the angiogenesis-related factors, including TNF-α, VEGF and HGF, and consequently mediating the functions of endothelial cells such as migration, invasion, and tube-like formation.  相似文献   
58.
We report a family with two cases of severe pre-eclampsia/eclampsia in which very high levels of Lp(a) lipoprotein were found. The serum level of Lp(a) lipoprotein is genetically determined and the Lp(a) apolipoprotein has a close homology to plasminogen. Very high levels of Lp(a) lipoprotein might interfere with the fibrinolytic/thrombolytic process in man. A previous report suggested that a high maternal serum Lp(a) lipoprotein level can cause fetal growth retardation, and it is proposed that very high levels might lead to increased deposition of fibrin in the uterine spiral arteries in pregnancy, which is central in the pathogenesis of pre-eclampsia. If confirmed, a very high Lp(a) lipoprotein level could be one risk factor for pre-eclampsia that is genetically determined.  相似文献   
59.
对84例周围血管病(脉管炎68例,静脉炎16例)和25例正常健康人进行了足甲襞微循环的对比观察。结果:患病组足甲襞微循环的血管形态、流态、管周状态均较正常健康组有明显差异(P<0.01)。提示:更接近病变部位的局部微循环观察更能代表病变的程度,对临床医生判断病情、选择用药和疗效观察都有很大帮助和参考价值。  相似文献   
60.
目的:探讨内皮细胞清除补体攻膜复合物(MAC)的途径及其清除动力学,方法:原代培养的人脐静脉内皮细胞以RH414荧光标记质膜双层,0℃组装亚溶剂量的MAC,37℃复苏后,LSCM实时监MAC沉积诱导的质膜囊泡化形成和胞吞,胞吐情况,流式细胞仪定量检测内皮细胞表面MAC抗原的清除情况,结果:MAC沉积后,内皮细胞有的质膜囊泡化形成,囊泡以胞吞和胞吐2种方式离开细胞,并以前者占优,37度条件下,内皮细胞清除表面MAC的半衰期约为5min。结论:内皮细胞可通过胞吞和胞吐2种机制清除细胞表面沉积的MAC,并以胞吞方式为主。  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