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   242088篇
  免费   20445篇
  国内免费   14385篇
耳鼻咽喉   2175篇
儿科学   3048篇
妇产科学   4881篇
基础医学   28323篇
口腔科学   4210篇
临床医学   30859篇
内科学   39848篇
皮肤病学   2818篇
神经病学   13544篇
特种医学   8546篇
外国民族医学   96篇
外科学   26657篇
综合类   34073篇
现状与发展   48篇
一般理论   45篇
预防医学   15109篇
眼科学   6674篇
药学   24190篇
  164篇
中国医学   10890篇
肿瘤学   20720篇
  2024年   709篇
  2023年   3491篇
  2022年   8685篇
  2021年   11419篇
  2020年   8381篇
  2019年   7559篇
  2018年   7989篇
  2017年   6969篇
  2016年   6664篇
  2015年   10087篇
  2014年   12690篇
  2013年   11883篇
  2012年   17534篇
  2011年   19221篇
  2010年   11717篇
  2009年   9386篇
  2008年   12760篇
  2007年   12803篇
  2006年   12361篇
  2005年   12437篇
  2004年   8602篇
  2003年   7644篇
  2002年   6612篇
  2001年   5999篇
  2000年   6106篇
  1999年   6410篇
  1998年   3655篇
  1997年   3676篇
  1996年   2792篇
  1995年   2584篇
  1994年   2232篇
  1993年   1498篇
  1992年   2291篇
  1991年   1996篇
  1990年   1664篇
  1989年   1458篇
  1988年   1269篇
  1987年   1178篇
  1986年   945篇
  1985年   750篇
  1984年   492篇
  1983年   381篇
  1982年   227篇
  1981年   202篇
  1980年   192篇
  1979年   244篇
  1978年   141篇
  1977年   113篇
  1976年   99篇
  1974年   116篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
With the completion of the human genome project, single-nucleotide polymorphisms (SNPs) have become the focus of intense study in biomedical research. Polymerase-mediated primer extension has been employed in a variety of SNP assays. However, these SNP assays using polymerase without proofreading function are compromised by their low reliability. Using a newly developed short amplicon harboring restriction enzyme site, EcoR-I, we were able to compare the single-base discrimination abilities of polymerases with and without proofreading function in primer extension in a broad range of annealing temperatures. Thermodynamic analysis demonstrated a striking single-nucleotide discrimination ability of polymerases with proofreading function. Using unmodified 3'-end allele-specific primers, only template-dependent products were generated by polymerase with proofreading activity. This powerful single-base discrimination ability of exo(+) polymerases was further evaluated in primer extension using three types of 3' terminally modified allele-specific primers. As compared with the poor fidelity in primer extension of polymerases lacking 3' exonuclease activity, this study provides convincing evidence that the use of proofreading polymerases in combination with 3'-end modified allele-specific primers can be a powerful new strategy for the development of SNP assays.  相似文献   
992.
Four families are described with a t(13q14q) segregating. Two of them were identified through index cases with Down's syndrome; their karotypes revealed the unusual 46,XY, -13, -14, +t(13q14q), +21. The other two families were identified through a chromosomal study of parents with repeated spontaneous abortions. Analysis of data on 3 of these 4 families and on 7 other from the published reports showed no evidence of increased fetal wastage among 13/14 carriers. However, the risk of producing offspring with various types of aneuploidy may be greater among carriers than among persons with a normal chromosome pattern. Qualitative and quantitative differences in D/D translocations may account for the observed variation in clinical findings. These differences add to the problem of determining genetic risks from an analysis of grouped data.  相似文献   
993.
血糖感应型胰岛素给药智能载体的研究进展   总被引:1,自引:0,他引:1  
胰岛素控制释放高分子载体系统一直是国内外科技工作者的研究热点 ,迄今已经研究报道了多种具有不同工作原理的血糖感应型胰岛素给药智能载体。本文基于国内外大量研究文献 ,综述了血糖感应型胰岛素控制释放智能化高分子载体的研究进展。  相似文献   
994.
The cytolethal distending toxin (Cdt) is produced by several Gram-negative bacterial species and causes growth arrest and morphological alterations in mammalian cells. Actinobacillus actinomycetemcomitans, which is involved in the pathogenesis of localized aggressive periodontitis, also produces a Cdt that affects periodontal connective tissue cells. The aim of this study was to investigate in which phase of the cell cycle these cells are arrested and enlarged when challenged with A. actinomycetemcomitans, and to evaluate the involvement of its Cdt. Human gingival fibroblasts and periodontal ligament cells were challenged with A. actinomycetemcomitans extract, or with purified Cdt, and cell cycle analysis was performed by propidium iodide staining and flow cytometry. Cells exposed to an A. actinomycetemcomitans wild-type strain, or to purified Cdt, were arrested in both G1 and G2/M phases, and appeared enlarged compared to the corresponding controls. The cellular enlargement occurred in both G1 and G2/M arrested cells. In contrast, cells exposed to an A. actinomycetemcomitans cdt-knockout mutant strain showed cell cycle phase distribution and size similar to the controls. In conclusion, A. actinomycetemcomitans causes a combined G1 and G2/M growth arrest and enlargement in periodontal connective tissue cells, which is attributed to its Cdt.  相似文献   
995.
VATER and hydrocephalus: distinct syndrome?   总被引:2,自引:0,他引:2  
VACTERL association with hydrocephalus is rarely reported, and is thought to be an autosomal recessive uniformly lethal disorder distinct from the VATER association. We have observed 3 patients in a 12-month period with hydrocephalus due to aqueductal stenosis, in addition to vertebral anomalies (3/3), anal anomalies (3/3), cardiac anomalies (3/3), tracheoesophageal fistula (1/3), renal anomalies (3/3), limb anomalies (3/3), single umbilical artery (2/3), hypospadias (1/3), and cryptorchidism (1/2). Chromosomes were normal in all cases. Although one patient died in the neonatal period due to respiratory failure, 2 have survived (30 months and 19 months) with good neurological outcome following early neurosurgical treatment. Although delayed in motor development, both are interactive, social, and continue to make developmental progress. Appropriate surgical treatment, including early ventriculoperitoneal shunting, allowed for the survival of 2 patients with an unexpectedly good outcome. Our experience suggests that the extremely poor prognosis previously ascribed is not universal. We caution against labeling this syndrome as a uniformly lethal, developmentally devastating disorder.  相似文献   
996.
用血清学方法研究显示中国人胰岛素依赖性糖尿病(IDDM)与HLA-DR9相关。鉴于白种人中的研究显示IDDM与HLA-DQβ链第57位氨基酸相关,Asp-57对IDDM呈抗性,non-Asp与IDDM易感性相关。我们用PCR技术扩增了中国人中血清学DR9纯合的IDDM患者和正常对照的HLA-DQB1基因第二外显子并测定了核苷酸顺序,结果未发现IDDM特异HLA-DQB1等位基因,但发现IDDM病人HLA-DQB157位均为天冬氨酸。表明中国IDDM患者中的HLA-DQB157位天冬氨酸不一定具有保护个体抵抗IDDM的足够能力。IDDM易感性可能涉及多个基因位点的变化,另外还可能与其它遗传因素及环境因素有关。  相似文献   
997.
Rat pancreatic cells were dissociated using a combined enzyme and EDTA method, grown on a plastic surface and then overlayed with collagen gel. Our studies have shown that exocrine pancreatic cells grown in this way have the ability to rearrange themselves into a three-dimensional organoid structure in which well defined epithelial lumina have been identified by ultrastructural and light microscopic examination. This in vitro system has advantages in examining the cytodifferentiation of pancreatic cells and may be exploited in studying pancreatic carcinogenesis.  相似文献   
998.
999.
In this article, we proposed a multifunctional telemedicine system supporting both telediagnosis and teleconsultation services. We attempted not only to insure that the implementation of this system satisfied most requirements, but also to evaluate the impact of the system. With regard to system architecture, we designed a unified multimedia database to store all types of data and used two kinds of network (ATM and ISDN) for different possible applications. As for data transmission, the REFRESH and PREFETCH mechanisms were implemented to enhance data transfer efficiency. A total of 1107 consultations employing the telemedicine system were performed during the past 3 years. This technology was used most frequently for radiology consultation (32.7%, n = 362) and ultrasonic examination (19.5%, n = 216). An evaluation of the impact on diagnosis (507 valid cases) indicated that the diagnosis in 80 cases (15.78%) were altered on the basis of second opinions from a medical center; and the number of patients transferred to the medical center was reduced from 24 (4.7%) to eight cases. Most of the rural-site physicians (97%) thought that they did benefit from specialists' experience and knowledge via the telemedicine system. Based on 431 valid questionnaires, the number of the patients with confidence in the telemedicine system at their local healthcare center increased from 72.6% to 87.5%. Overall, more than 90% of patients and physicians believed that the system was valuable and provided satisfactory services.  相似文献   
1000.
急性心肌缺血时冠状窦血浆纤维蛋白原的改变及意义   总被引:2,自引:0,他引:2  
通常人们认为,急性心肌缺血可引起血浆纤维蛋白原(Fg)的增高;但是在缺血区局部Fg的变化并不清楚。本文在17条犬上,以自制微米缩窄器造成冠脉左旋支狭窄与梗塞,观察了冠状窦Fg和血小板数(PC)的改变。结果表明:当冠脉狭窄大于75%后,急性心肌缺血可引起Fg含量的减少,当冠脉大狭窄于90%后,PC也出现减少。病理组织学检查在狭窄部位有内皮细胞的损伤、血小板的粘附及冠状动脉血栓和微血栓的形成。这一结果提示:急性心肌缺血可引起血浆Fg的减少,Fg的减少与血小板的聚集及血栓的形成有关。  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