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   32231篇
  免费   2128篇
  国内免费   34篇
耳鼻咽喉   515篇
儿科学   1348篇
妇产科学   1087篇
基础医学   4490篇
口腔科学   1772篇
临床医学   3094篇
内科学   5633篇
皮肤病学   429篇
神经病学   3005篇
特种医学   1084篇
外科学   4492篇
综合类   156篇
一般理论   2篇
预防医学   2556篇
眼科学   542篇
药学   2206篇
中国医学   37篇
肿瘤学   1945篇
  2022年   222篇
  2021年   371篇
  2020年   375篇
  2019年   486篇
  2018年   636篇
  2017年   540篇
  2016年   565篇
  2015年   593篇
  2014年   695篇
  2013年   1202篇
  2012年   1384篇
  2011年   1401篇
  2010年   864篇
  2009年   901篇
  2008年   1210篇
  2007年   1361篇
  2006年   1359篇
  2005年   1386篇
  2004年   1191篇
  2003年   1164篇
  2002年   1092篇
  2001年   1062篇
  2000年   1025篇
  1999年   962篇
  1998年   377篇
  1997年   327篇
  1996年   297篇
  1995年   303篇
  1994年   284篇
  1993年   227篇
  1992年   764篇
  1991年   713篇
  1990年   756篇
  1989年   736篇
  1988年   692篇
  1987年   674篇
  1986年   604篇
  1985年   557篇
  1984年   504篇
  1983年   389篇
  1982年   243篇
  1981年   214篇
  1979年   362篇
  1978年   263篇
  1977年   215篇
  1976年   205篇
  1975年   237篇
  1974年   257篇
  1973年   223篇
  1972年   210篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Three rapid and two standard developing solutions have been tested. A jaw specimen and an aluminium step wedge were exposed on Kodak Ektaspeed film with a 60 kVp dental x-ray machine. The films were developed during varying times at 21 degrees C under controlled conditions. The image quality was tested with a densitometer as well as visually. The characteristic density curves were constructed and the relative speed, average density, fog and contrast were calculated for each test film. The time at which the contrast specified by the film manufacturer was reached, and beyond which the speed and contrast increased only marginally was regarded as the optimal developing time. With longer developing times no increase in image quality could be perceived visual by three trained observers. The optimal developing time at room temperature 21 degrees C, for the different solutions were found to be Kodak Dental 1:1 1.5 minutes Elfwing Rapid 1:3 1.0 minutes Scanfors Dental 1:2 1.5 minutes Kodak Dental 1:3 3.0 minutes Gevaert G 150 1:5 3.0 minutes The characteristic curves were identical for all developing solutions at the times recommended above and the total fog was below 0.20. However, the image quality was maintained and only an insignificant increase of fog was found even when those times were doubled.  相似文献   
83.
84.
The purpose of this paper is to uncover the dimensional structure of a set of disability items. The analysis is based on a sample of 421 persons aged 75 years and older. Firstly, a factor analysis of the items reveals two distinct dimensions: IADL and ADL. The items with large loadings on the IADL-factor are next submitted to a Guttman analysis. An index is derived which strictly meets the requirements of a Guttman scale, but it is doubtful whether there is a true hierarchical structure among the items. The criterion validity of the index (in different versions) appears to be satisfactory when assessed in terms of the correlation with an outcome variable (home help).  相似文献   
85.
Summary This study determined the energy charge, adenosine and inosine content of human bladder smooth muscle in comparison with striated muscle of the same individual. Biopsies were obtained from 21 women who were subjected to urethrocystopexy because of urinary stress incontinence. We found that the ATP content of bladder smooth muscle was only about one-eighth of that of striated muscle. The energy charge of bladder smooth muscle was 0.78±0.13, which is low compared with striated muscle (0.92±0.02). The adenosine content of bladder smooth muscle was 6.7 times higher than striated muscle and the adenosine/ATP ratio was 1∶9 compared with 1∶450 for striated muscle. These findings were in accordance with our previous studies on uterine smooth muscle.  相似文献   
86.
The tumour antigen expression of ovarian and endometrial endometrioid carcinomas, ovarian clear-cell carcinomas as well as endometrial and cervical clear-cell carcinomas were immunohistochemically compared. Of special interest were potential differences between the endometrioid and clear-cell carcinomas of the ovary. The expression of CEA and CA 19-9 tumour antigens in all these tumour types was heterogeneous, with 10-20% of the cases being positive for CEA and 40-75% being positive for CA 19-9. In contrast, HMFG IIIC 12, a monoclonal antibody originally directed against human milk fat globule (HMFG) membrane antigens, invariably detected a corresponding antigen on every case of these tumour types. Another HMFG antibody, SM IF 3, on the other hand, detected antigenic material on all clear-cell tumour types, but only rarely on endometrioid tumours of the ovary or endometrium. While HMFG IIIC 12 detects an antigen present on all ovarian, endometrial and mammary carcinomas, antibody SM IF 3 thus appears to be more restricted in its staining patterns. Our results with both of these antibodies indicate that ovarian clear-cell carcinomas and ovarian endometrioid carcinomas have antigenic differences, which provides further evidence that they belong to different tumour entities.  相似文献   
87.
External cephalic version (ECV) using tocolysis is a widely recognized low-risk intervention in cases of breech presentation, particularly in areas where resources are scarce and the perinatal mortality is high in vaginal breech deliveries. In such a setting, pregnant women were trained to make regular self-assessments of the presenting fetal part after ECV in order to detect spontaneous reversions to breech presentation. It was found that such maternal involvement could significantly improve the final results of ECV.  相似文献   
88.
Spinal cord restitution following compression injuries in rats   总被引:22,自引:0,他引:22  
Spinal cord compression injuries were produced in rats by applying weights to a plate 2.2 x 50 mm in size, placed on the exposed midthoracic dura covering the spinal cord. The influence of force and duration of compression was studied by using 3 different weights, 20, 35 and 50 g, applied for 1, 5 and 10 min. Postoperative neurological function was tested by the inclined plane method and the rats were observed for 3 weeks. Neurological impairment increased with force and duration of compression. It is therefore reasonable to conclude that patients suffering from spinal cord injury should be investigated immediately for signs of persistent cord compression. If this is present, early decompression might be of value, although nothing is known in man concerning the limits of force and duration of compression permitting postoperative neurological recovery.  相似文献   
89.
Serial sections of formalin-fixed, paraffinembedded blocks from two asymptomatic, non-AIDS cases of progressive multifocal leukoencephalopathy (PML) were stained with a double-label immunocytochemical method for detection of glial fibrillary acidic protein and JC virus (JCV) capsid proteins and with luxol fast blue/hematoxylin-eosin. In case 1 small, rounded lesions of about 1-mm diameter were seen within a restricted area in the posterior part of the superior frontal gyrus of both cerebral hemispheres, suggesting an early manifestation of the disease. Fully developed demyelinated lesions of the classical type with JCV-infected oligodendrocytes appeared in the white matter and along its border with the cortex. Lesswell-developed lesions, believed to be precursors to the fully developed ones, were seen in the gray and white matter. Of special interest were areas which contained small collections of enlarged, glial fibrillary acidic protein (GFAP)-positive astrocytes without capsid antigen and which seemed to lack destruction of myelin as judged from the appearance of matching serial sections stained for myelin. Large lesions in the brain of case 2 showed the well-known features of advanced PML. The close relation between some astrocytes and oligodendrocytes with viral antigen raises the possibility of early intercellular passage of virus. Vacuolation, seen within or near lesions in both cases, has previously been noted in the CNS infected by HIV, but not in PML. It is suggested that PML, a disease of both oligodendrocytes and astrocytes, may actually begin in astroglial cells which, under the influence of a restricted JCV infection, become reactive, express GFAP and pass on virus to the more highly susceptible oligodendrocytes with which they are in contact.Supported in part by a grant N.S.07596 from the National Institute of Neurological Disorders and Stroke. The work was carried out in the Laboratory of Experimental Neurophathology, NINDS, and in the Department of Pathology II, Karolinska Institute, Stockholm  相似文献   
90.
The development of photoreceptors and two putative neurotransmitter systems in the pineal organ and retina was studied during embryogenesis in the three-spined stickleback Gasterosteus aculeatus L. The investigation was performed by aid of immunocytochemistry using well characterized antisera to the retinal proteins alpha-transducin (TD alpha) and S-antigen (SA) (photoreceptor-markers), antisera against L-glutamic acid decarboxylase (GAD), gamma-aminobutyric acid (GABA), choline-O-acetyltransferase (ChAT) and with acetylcholinesterase (AChE) histochemistry (neurotransmitter-markers). It was possible to set up the following developmental time-table concerning the first appearance of positive immuno- and enzyme-reactive cells in the pineal organ and retina: I AChE-activity and TD alpha- and SA-immunoreactive cells in the pineal organ; II GAD- and GABA-immunoreactive cells in the pineal organ and retina; ChAT immunoreactivity and AChE activity in the retina; III hatching; IV SA-immunoreactive cells in the retina. The obtained results provide good evidence that while photoreceptor cells develop much earlier in the pineal organ than in the retina, neurons develop simultaneously in the pineal organ and retina.  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