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   35815篇
  免费   2739篇
  国内免费   1543篇
耳鼻咽喉   334篇
儿科学   493篇
妇产科学   395篇
基础医学   5659篇
口腔科学   3026篇
临床医学   4487篇
内科学   4526篇
皮肤病学   699篇
神经病学   1519篇
特种医学   1690篇
外国民族医学   8篇
外科学   5390篇
综合类   4712篇
现状与发展   10篇
预防医学   1049篇
眼科学   532篇
药学   2267篇
  10篇
中国医学   1152篇
肿瘤学   2139篇
  2024年   102篇
  2023年   556篇
  2022年   884篇
  2021年   1179篇
  2020年   1252篇
  2019年   1182篇
  2018年   1215篇
  2017年   1153篇
  2016年   1203篇
  2015年   1294篇
  2014年   2283篇
  2013年   3172篇
  2012年   1941篇
  2011年   2274篇
  2010年   1755篇
  2009年   1776篇
  2008年   1851篇
  2007年   1876篇
  2006年   1673篇
  2005年   1537篇
  2004年   1333篇
  2003年   1149篇
  2002年   849篇
  2001年   778篇
  2000年   583篇
  1999年   550篇
  1998年   435篇
  1997年   424篇
  1996年   373篇
  1995年   334篇
  1994年   299篇
  1993年   230篇
  1992年   248篇
  1991年   234篇
  1990年   198篇
  1989年   180篇
  1988年   178篇
  1987年   158篇
  1986年   131篇
  1985年   184篇
  1984年   141篇
  1983年   106篇
  1982年   133篇
  1981年   141篇
  1980年   123篇
  1979年   87篇
  1978年   73篇
  1977年   57篇
  1976年   76篇
  1972年   30篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
树突状细胞在胆囊癌组织内浸润的研究   总被引:2,自引:0,他引:2  
目的通过对胆囊癌组织中树突状细胞浸润情况的研究,阐述树突状细胞与肿瘤免疫之间的关系。方法采用免疫组化SP法。结果树突状细胞在胆囊癌组织的浸润程度与年龄、性别和病理组织学类型无关,与病理分化程度呈负相关关系(P<005)。结论树突状细胞在胆囊癌组织的浸润程度与病理分化程度、Nevin分期、肝浸润及淋巴结转移存在密切的关系。树突状细胞的定量检测可作为估计胆囊癌预后的标志。  相似文献   
72.
Summary The effects of beta-adrenergic agonists such as isoproterenol, norepinephrine and epinephrine upon the adenylate cyclase activity of human fat cell ghosts were tested, each alone and in combination with the beta-blocking agent propranolol. Saturating concentrations of these agents showed a 2–6.5-fold increase of enzyme activity without addition of any artificial cofactors. Isoproterenol was more potent in stimulating the enzyme system than epinephrine and nor-epinephrine. Propranolol caused a dose-dependent rightward shift of the log-dose response curve of these beta-adrenergic agonists. The assay of human fat cell adenylate cyclase in vitro may provide a simple and convenient assay system for the screening of beta-adrenergic drugs of potential therapeutic importance.Herrn Prof. Dr. Dr. h.c. G. Schettler zum 60. Geburtstag gewidmet  相似文献   
73.
Due to the nonlinear, viscoelastic material properties of brain, its mechanical response is dependent upon its total strain history. Therefore, a low strain rate, large strain will likely produce a tissue injury unique from that due to a high strain rate, moderate strain. Due to a lack of current understanding of specific in vivo physiological injury mechanisms, a priori assumptions cannot be made that a low strain rate injury induced by currently employed in vitro injury devices is representative of clinical, nonimpact, inertial head injuries. In the present study, an in vitro system capable of mechanically injuring cultured tissue at high strain rates was designed and characterized. The design of the device was based upon existing systems in which a clamped membrane, on which cells have been cultured, is deformed. However, the present system incorporates three substantial improvements: (1) noncontact measurement of the membrane deflection during injury; (2) precise and independent control over several characteristics of the deflection; and (3) generation of mechanical insults over a wide range of strains (up to 0.65) and strain rates (up to 15s–1). Such a system will be valuable in the elucidation of the mechanisms of mechanical trauma and determination of injury tolerance criteria on a cellular level utilizing appropriate mechanical injury parameters.  相似文献   
74.
The TGF-1(–/–) mouse is a murine model for systemic autoimmune disease. The aim of this study is to elucidate the immunological mechanism that leads to multifocal tissue inflammation and autoantibody production in TGF-1(–/–) mice. Heart, lung, liver, and salivary gland from TGF-1(–/–) were assessed for CD154 expression by RT-PCR and immunohistochemistry. Compared to wild-type littermates, CD154 expression was elevated in all tissues studied. Furthermore, IL-12 mRNA was expressed in the salivary gland and heart of TGF-1(–/–) mice and not in wild-type littermates. This suggests that the CD154 pathway is activated in these tissues. This shows that TGF-1 regulates CD154 expression leading to spontaneous IL-12 production and autoimmunity.  相似文献   
75.
76.
A new immunoelectron microscopy procedure was developed by remaking the fixed-frozen tissue specimens into LR White resin blocks suitable for postembedding colloidal gold immunolabeling, and used to examine 16 cases of small round cell soft tissue sarcomas. In rhabdomyosarcoma, ultrastructural double-immunogold staining demonstrated a coexpression of muscle specific actin and desmin in the same tumor cell. In both Ewing's sarcoma and peripheral neuroepithelioma, the heterogeneous expression of MIC2 gene product (p30/32MIC2) in each tumor cell was demonstrated as well. In peripheral neuroepithelioma, the colloidal gold immunolabeling for neurofilament demonstrated the intermediate filaments surrounding microtubules. The procedure for ultrastructural colloidal gold immunolabeling using fixed-frozen tissue is thus considered to be useful not only for tumor diagnosis, but also for investigating various subcellular structures.  相似文献   
77.
In-vitro NMR spectroscopic examinations of tissue extracts can be combined with appropriate pattern-recognition and visualization techniques in order to monitor characteristic metabolic differences between tissue classes. In the present study, such techniques are applied to a set of 88 breast-tissue samples with the intention of identifying typical differences between various tissue classes. The set contains 49 breast-tumor samples of various tumor grades and 39 samples of healthy tissue. The metabolite compositions of the tissue extracts were investigated using a dual extraction technique and high-resolution (1)H-NMR spectroscopy. The spectra of the hydrophilic and the lipophilic compounds were assigned to three groups according to different malignancy grades of the respective tissue samples. The group characteristics were analyzed using the k-nearest-neighbor method and self-organizing-map visualizations. The results show an increase of UDP-hexose, phosphocholine and phosphoethanolamine concentrations according to the tumor grade. Higher concentrations of taurine were detected in the malignant samples. Myo-inositol and glucose content were elevated in control samples compared with malignant tissue. Both compounds also characterized different subgroups in the pool of unaffected tissue samples depending upon fat content or fibrosis. Several lipid metabolites showed a characteristic elevation with high malignancy.  相似文献   
78.
Microscopic aneurysmal-like structures (ALS) develop spontaneously in the convoluted rat testicular artery and have been previously proposed as a model relevant to cerebral aneurysms. The effect of defects in connective tissue fibres on ALS formation was investigated by microscopy using two approaches: (i) the study of the effect of β-aminopropionitrile (BAPN), an inhibitor of the cross-linking of elastic and collagen fibres, on the incidence, size and morphology of ALS in spontaneously hypertensive rats (SHR) and their normotensive controls (WKY). The straight spermatic artery was studied for comparison. (ii) The determination of the incidence of spontaneous ALS in Brown Norway (BN) and Long Evans (LE) rats which are highly susceptible (BN) or resistant (LE) to the spontaneous rupture of the arterial internal elastic lamina. (i) BAPN increased the number and size of ALS in SHR and WKY rats and had no effect on the straight spermatic artery and (ii) ALS were more numerous and of greater size in BN than in LE rats. Taken together, these results show that defective connective tissue fibres may favour the formation and induce the enlargement of aneurysmal-like structures. By analogy, these data suggest that a lack of connective tissue fibre integrity may be of importance in cerebral aneurysm formation and development.  相似文献   
79.
Calretinin is a calcium-binding protein expressed in different normal and neoplastic tissues. Early studies suggested that calretinin is a useful marker to differentiate adenocarcinomas from malignant mesotheliomas of the lung, but subsequent work has shown that calretinin can be expressed in several other tumor types. To systematically investigate the epidemiology of calretinin expression in normal and neoplastic tissues, we used tissue microarrays (TMAs) to analyze the immunohistochemically detectable expression of calretinin in 5233 tissue samples from 128 different tumor categories and 76 different normal tissue types. At least 1 case with weak expression could be found in 74 of 128 (58%) different tumor types and 46 entities (36%) had at least 1 tumor with strong positivity. In normal tissues, a particularly strong expression was found in Leydig cells of the testis, neurons of the brain, theca-lutein and theca interna cells of the ovary, and mesothelium. In tumors, strong calretinin expression was most frequently found in malignant mesotheliomas (6 of 7), Leydig cell tumors of the testis (5 of 5), adenomas of adrenal gland (5 of 9), and adenomatoid tumors (4 of 9). In summary, calretinin is frequently expressed in many different tumor types. Metastases of various different origins must be included in the differential diagnosis of calretinin-positive pleura tumors.  相似文献   
80.
Summary We describe a purification method for tissue culture-grade trypsin that yields an enzyme mixture with reproducible activities of trypsin, elastase, and chymotrypsin and eliminates amylase and lipase.  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