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   35795篇
  免费   3441篇
  国内免费   2688篇
耳鼻咽喉   237篇
儿科学   467篇
妇产科学   264篇
基础医学   3740篇
口腔科学   562篇
临床医学   5035篇
内科学   4766篇
皮肤病学   332篇
神经病学   1534篇
特种医学   979篇
外国民族医学   17篇
外科学   2902篇
综合类   7799篇
现状与发展   13篇
预防医学   2897篇
眼科学   940篇
药学   4166篇
  42篇
中国医学   2697篇
肿瘤学   2535篇
  2024年   138篇
  2023年   595篇
  2022年   1481篇
  2021年   1849篇
  2020年   1464篇
  2019年   1111篇
  2018年   1134篇
  2017年   1168篇
  2016年   1016篇
  2015年   1652篇
  2014年   2140篇
  2013年   1979篇
  2012年   3042篇
  2011年   3203篇
  2010年   2238篇
  2009年   1881篇
  2008年   2202篇
  2007年   2206篇
  2006年   2003篇
  2005年   1737篇
  2004年   1225篇
  2003年   1117篇
  2002年   914篇
  2001年   799篇
  2000年   680篇
  1999年   637篇
  1998年   355篇
  1997年   362篇
  1996年   276篇
  1995年   236篇
  1994年   230篇
  1993年   134篇
  1992年   126篇
  1991年   146篇
  1990年   113篇
  1989年   92篇
  1988年   67篇
  1987年   57篇
  1986年   44篇
  1985年   25篇
  1984年   13篇
  1983年   13篇
  1982年   7篇
  1981年   10篇
  1980年   3篇
  1979年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
目的了解护理本科生临床实习出科考核的现状,为规范实习生出科考核提供依据。方法以《毕业实习鉴定手册》中"内外科出科考试成绩评定表"为问卷设计基础,对8家三级甲等医院160名护理实习生中已进行一轮内科或外科出科考核的80名学生进行调查,将所有参与学生的不同点列出作为问卷的选项,经专家审议和20名学生预试验后成为正式调查问卷,对160名护理本科实习生进行调查。结果护理本科生内外科出科考核内容不规范,评价标准不统一,监管体系欠完善。结论应针对护理本科生内外科出科考核的现状,不断完善学生的出科考核系统,使之更加客观地反映学生临床实践综合能力,促进教学相长。  相似文献   
992.
经者  唐勤 《传染病信息》2006,19(3):121-123
近年来,随着分子生物学检测技术的发展和更昔洛韦等有效抗病毒药物的普遍应用,对巨细胞病毒(cytomegalovirus,CMV)感染的预防和治疗都取得了较大的进展。  相似文献   
993.
Estrogen: one of the risk factors in milk for prostate cancer   总被引:7,自引:0,他引:7  
Studies to elucidate the cause of prostate cancer have met with little success to date. Epidemiological studies suggested that milk consumption is probably as one of the risk factors for prostate cancer. The studies thus focused on the fat and calcium in milk, but reached no definitive conclusion. According to the measurements of estrogen levels in milk by different studies, it was suggested that estrogen in milk was a possible risk to cause prostate cancer. One reason supporting this hypothesis is that Western diet (characterized by milk/dairy products and meat) causes a trend of increasing levels of estrogens, and Western males show a higher incidence rate of prostate cancer than Asia males. Estrogen levels in prostate fluid are also correlated very well with the prostate cancer. During several decades, estrogens, together with testosterone, was commonly used to induce the rodent model of prostate cancer. Our hypothesis also was supported by the presence of estrogen receptors in the prostate gland and the genotoxic role of estrogens on the prostate gland, as possible mechanisms. Therefore, if modern milk consumption does expose consumers to high levels of estrogen and plays an adverse role in prostate cancer, action should be taken to produce the noncontaminant milk.  相似文献   
994.
碱性MAGE家族新成员restin在大肠杆菌中的表达和抗体制备   总被引:2,自引:1,他引:2  
目的:从维甲酸诱导的白血病细胞系HL60中,克隆编码219个氨基酸的新基因restin,构建原核表达载体、制备抗血清并进行初步应用。方法:采用PCR技术,以维甲酸诱导的白血病细胞的cDNA为模板,扩增出restin的编码区。将其克隆入大肠杆菌表达载体中。经过温度诱导获得restin表达蛋白。利用SDS-PAGE纯化的目的蛋白免疫新西兰大白兔,制备该蛋白的抗血清。以该抗体做间接免疫荧光,初步观察restin在COS-7细胞内的表达分布。结果:大肠杆菌中表达的restin蛋白的Mr为26000。将其初步纯化后免疫新西兰白兔制备的抗血清,用Westernblot检测其效价为1∶800。间接免疫荧光显示,restin蛋白主要分布在细胞核内。结论:成功地制备抗restin的抗体,为进一步研究restin蛋白在组织中的表达、细胞内亚定位以及信号转导通路提供了前提条件。  相似文献   
995.
目的 构建小鼠白细胞介素-12的融合基因,并进行初号表达,方法 通过重叠序列引物的设计与多聚酶链反应(PCR)技术,将小鼠IL-12的40kPa多肽链基因与35kDa多肽链基因,以甘氨酸接头(Gly4Scr)3序列连接成为晤蛋白编码基因,构建融合蛋白表达载体现,转染小鼠成纤维细胞SVT2,表达具有生物学活性的融合蛋白型IL-12。结果 构建的小鼠IL-12表达载体经测序无突变发生。以G418筛选转  相似文献   
996.
ATP13A2 (PARK9) mutations are related to Kufor-Rakeb syndrome (KRS). We performed genetic analysis of the Ala746Thr variant in an independent cohort of the patients with PD and healthy controls from mainland China. The Ala746Thr variant was present in 1/532 (0.19%) of PD compared with 1/480 (0.21%) of healthy controls (odds ratio = 0.90, 95% CI 0.06, 14.39, P = 1.00). The two subjects carried the heterozygous genotype. Subset analysis in the group ≤50 years of age revealed a prevalence of 0.7% in PD compared with 0% in healthy controls and in the group >50 years of age showed 0% in PD versus 0.3% in healthy controls. We did not observe a significant association between Ala746Thr and Parkinson's disease in Han Chinese population, even after stratification by age at onset. The results suggested that Ala746Thr variant was not a major susceptible factor for PD in Han Chinese people.  相似文献   
997.
IgA nephropathy (IgAN) and Henoch-Schönlein purpura (HSP) are diseases characterized by IgA deposits in the kidney and/or skin. Both may arise after upper respiratory tract infections, but the pathogenic mechanisms governing these diseases remain unclear. Patients with IgAN (n = 16) and HSP (n = 17) were included in this study aimed at examining whether IgA-binding M proteins of group A streptococci could be involved. As M proteins vary in sequence, the study focused on the IgA-binding-region (IgA-BR) of three different M proteins: M4, M22, and M60. Renal tissue from IgAN and HSP patients and skin from HSP patients were examined for deposits of streptococcal IgA-BR by immunohistochemistry and electron microscopy using specific antibodies, and a skin sample from a HSP patient was examined by mass spectrometry. IgA-BR deposits were detected in 10/16 IgAN kidneys and 7/13 HSP kidneys. Electron microscopy demonstrated deposits of IgA-BRs in the mesangial matrix and glomerular basement membrane, which colocalized with IgA. Skin samples exhibited IgA-BR deposits in 4/5 biopsies, a result confirmed by mass spectrometry in one patient. IgA-BR deposits were not detected in normal kidney and skin samples. Taken together, these results demonstrate IgA-BR from streptococcal M proteins in patient tissues. IgA-BR, would on gaining access to the circulation, encounter circulatory IgA and form a complex with IgA-Fc that could deposit in tissues and contribute to the pathogenesis of IgAN and HSP.Tissue deposits containing IgA characterize IgA nephropathy (IgAN) and Henoch-Schönlein purpura (HSP), two conditions affecting kidney function. IgAN is the most common primary glomerulonephritis worldwide. Its predominant clinical feature is episodic macroscopic hematuria usually coinciding with upper respiratory tract infections. Symptoms may, however, vary from microscopic hematuria to a severe nephritic-nephrotic syndrome. End-stage kidney disease occurs in 30% to 40% of patients within 20 years. Histopathologically IgAN is characterized by mesangial cell proliferation and in progressive cases crescent formation as well as glomerular sclerosis, interstitial fibrosis, and tubular atrophy. Ultramorphologic findings show mesangial deposits of immune complexes containing predominantly IgA.1,2HSP is the most common form of vasculitis in childhood. It may affect many organs, but usually presents as skin lesions, varying from purpura to bullous intradermal bleedings, arthritis, gastrointestinal involvement with pain and/or bleeding. Renal involvement occurs in up to 50% of cases3 and is known as Henoch-Schönlein nephropathy (HSN). HSN may manifest as microscopic or macroscopic hematuria as well as glomerulonephritis or nephrotic syndrome. Approximately 20% of HSN cases will develop renal failure.4 The histopathological lesion termed leukocytoclastic vasculitis is characterized by inflammation of small vessels with perivascular polymorphonuclear leukocyte and mononuclear cell infiltrates. Immune deposits in affected organs contain IgA, and renal pathology resembles that seen in IgAN.1,3The IgA mesangial deposits in kidneys of patients with IgAN and HSP are primarily composed of galactose-deficient IgA1.5,6,7 The mechanism by which under-glycosylated IgA1 deposits in the mesangium, possibly in complex with IgG,8,9 has not been determined. Environmental antigens have been proposed to contribute to the disease but have not been consistently associated with mesangial deposits.9 Although the etiology of IgAN and HSP is unclear, these diseases are often preceded by infections, primarily of the upper respiratory tract, and an infectious agent has therefore been suspected. There is circumstantial evidence for involvement of group A streptococcus (GAS, Streptococcus pyogenes),10,11,12,13,14,15 but infections with other bacteria16,17 as well as viruses18 have been implicated as well.In this study we hypothesized that GAS infection could trigger IgAN and/or HSN, because GAS is a very common cause of upper respiratory tract infection, and because many GAS strains bind IgA-Fc.19,20,21 The ability of a GAS strain to bind human IgA results from the presence of an IgA-binding region (IgA-BR) in the surface-localized M protein.22,23 The fibrillar M protein, which is a major virulence factor of GAS, varies in sequence between strains24 allowing classification of GAS isolates into more than 120 M serotypes.25 The exact function of the IgA-BR in an M protein is not known, but there is evidence that it contributes to bacterial phagocytosis resistance.26 The IgA-BR of an M protein represents a distinct domain that can be studied in isolated form, as a peptide that binds IgA.27,28 Such IgA-binding peptides, designated Sap (streptococcal IgA-binding peptide), were used in the experiments described herein.To analyze whether IgA-binding streptococcal M proteins are present in affected tissues of patients with IgAN and/or HSP, and colocalize with IgA, we used antibodies to the IgA-BR of three different M proteins M4, M22, and M60. Of note, M4 and M22 are among the most common serotypes of clinical GAS isolates.29 As the IgA-BRs of different M proteins vary extensively in sequence,22,23 the use of antibodies to three different serotypes enhanced our chances to detect tissue deposition of an IgA-BR.  相似文献   
998.
Thirty Newcastle disease virus (NDV) strains isolated from outbreaks in China during 1996 to 2005 were characterized pathotypically and genotypically. All strains except one were velogenic. An analysis of the variable region (nucleotides 47 to 420) of the F gene indicated that 6 isolates belonged to genotype II, 3 to genotype III, 1 (isolated from a pigeon) to genotype VI, and 20 to genotype VII. Isolates belonging to genotype VII were further divided into five subtypes, VIIa, VIIb, VIIc, VIId, and VIIe, and subtype VIId was made up of VIId1 to VIId5. These results showed that genotype VII isolates might have been the most prevalent in China during the past two decades. Genotype VII isolates shared high homology, but the homology was less than that between genotype VII viruses and the vaccine virus LaSota. Among these NDV isolates, 25 isolates had the velogenic motif 112R/K-R-Q-K/R-R-F117 that is consistent with results of the biological tests. However, four of five LaSota-type isolates that contained the lentogenic motif 112G-R-Q-G-R-L117 were velogenic, except SY/03, in the view of the biological test. The majority of genotype VII isolates had lost one or two N-glycosylation sites. Finally, a cross-protection experiment in which specific-pathogen-free chickens vaccinated with LaSota were challenged by six NDV isolates showed that more than three isolates were antigenic variants that could be responsible for recent outbreaks of Newcastle disease.  相似文献   
999.
F gene recombination between genotype II and VII Newcastle disease virus   总被引:2,自引:1,他引:2  
Qin Z  Sun L  Ma B  Cui Z  Zhu Y  Kitamura Y  Liu W 《Virus research》2008,131(2):299-303
A velogenic Newcastle disease virus (NDV) strain, designated as SRZ03, was isolated from an egg layer flock with NDV vaccine immunization failure in China in 2003. Recombination was found in the F gene of SRZ03. Complete genome sequences analysis indicated that the N-terminal of SRZ03 F gene originated from a genotype II NDV strain, whereas the C-terminal of F gene and the rest of the genes originated from a prevalent velogenic genotype VII NDV strain. It provides us valuable information for understanding the recombination of nonsegmented negative-sense RNA viruses.  相似文献   
1000.
为了研究性能更好的EIT图像重构算法,我们对基于敏感性定理的EIT图像重构算法进行了计算机仿真研究,并与几种常用图像重构算法进行比较,提出对基于敏感性定理的EIT图像重构算法的改进措施。  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