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   15530篇
  免费   1116篇
  国内免费   73篇
耳鼻咽喉   121篇
儿科学   420篇
妇产科学   270篇
基础医学   2600篇
口腔科学   344篇
临床医学   1335篇
内科学   3529篇
皮肤病学   347篇
神经病学   1780篇
特种医学   365篇
外科学   1531篇
综合类   72篇
一般理论   10篇
预防医学   1093篇
眼科学   145篇
药学   1103篇
中国医学   49篇
肿瘤学   1605篇
  2024年   21篇
  2023年   144篇
  2022年   349篇
  2021年   669篇
  2020年   373篇
  2019年   491篇
  2018年   550篇
  2017年   424篇
  2016年   472篇
  2015年   509篇
  2014年   624篇
  2013年   774篇
  2012年   1211篇
  2011年   1258篇
  2010年   709篇
  2009年   598篇
  2008年   948篇
  2007年   967篇
  2006年   859篇
  2005年   827篇
  2004年   787篇
  2003年   665篇
  2002年   636篇
  2001年   153篇
  2000年   152篇
  1999年   177篇
  1998年   145篇
  1997年   137篇
  1996年   88篇
  1995年   88篇
  1994年   62篇
  1993年   54篇
  1992年   89篇
  1991年   74篇
  1990年   79篇
  1989年   60篇
  1988年   55篇
  1987年   47篇
  1986年   55篇
  1985年   43篇
  1984年   19篇
  1983年   29篇
  1982年   22篇
  1981年   17篇
  1979年   21篇
  1978年   25篇
  1977年   12篇
  1974年   12篇
  1973年   17篇
  1966年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Immunization with cells expressing endogenous antigens can stimulate long-lived CD8(+) T cell memory. In many cases, the response is also stimulated by host antigen-presenting cells (APC) that have processed antigen from internalized apoptotic cells or cell fragments. This study investigated whether immunization with peptide-pulsed dendritic cells (DC) could prime long-lasting, peptide-specific CD8(+) T cell immunity in the absence of cross-priming by host APC. C57BL / 6 female mice immunized with syngeneic male splenic DC pulsed with the H-2K(b)-restricted ovalbumin peptide OVA(257 - 264) made memory CD8(+) CD44(high) T cell responses to OVA(257 - 264) and the male antigen HY more than 1 year after immunization. Establishment and maintenance of peptide-specific CD8(+) T cell memory did not require antibody or B cells. Immunization of H-2(bxd) mice with OVA(257 - 264)-pulsed minor-incompatible H-2(b) or H-2(d) DC demonstrated that CD8(+) T cells were primed exclusively by the injected cells, and not by peptide transferred to host APC, even though there was very effective cross-priming for CD8(+) T cell responses to the minor antigens expressed by the DC. Thus peptide-pulsed DC can prime long-lasting CD8(+) memory responses without any requirement for cross-priming by other APC.  相似文献   
63.
Enteroinvasive Escherichia coli (EIEC), a distinctive pathogenic form of E. coli causing dysentery, is similar in many properties to bacteria placed in the four species of Shigella. Shigella has been separated as a genus but in fact comprises several clones of E. coli. The evolutionary relationships of 32 EIEC strains of 12 serotypes have been determined by sequencing of four housekeeping genes and two plasmid genes which were used previously to determine the relationships of Shigella strains. The EIEC strains were grouped in four clusters with one outlier strain, indicating independent derivation of EIEC several times. Three of the four clusters contain more than one O antigen type. One EIEC strain (an O112ac:H- strain) was found in Shigella cluster 3 but is not identical to the Shigella cluster 3 D2 and B15 strains with the same O antigen. Two forms of the virulence plasmid pINV have been identified in Shigella strains by using the sequences of ipgD and mxiA genes, and all but two of our EIEC strains have pINV A. The EIEC strains were grouped in two subclusters with a very low level of variation, generally not intermingled with Shigella pINV A strains. The EIEC clusters based on housekeeping genes were reflected in the plasmid gene sequences, with some exceptions. Two strains were found in the pINV B form by using the ipgD sequence, with one strain having an mxiA sequence similar to the divergent sequence of D1. Clearly, EIEC and Shigella spp. form a pathovar of E. coli.  相似文献   
64.
To determine the prevalence of antibodies to feline coronavirus (FCoV) serotypes 1 and 2 in Switzerland and their association with different disease manifestations, a serological study based on immunofluorescence tests was conducted with Swiss field cats using transmissible gastroenteritis virus (TGEV), FCoV type 1 and FCoV type 2 as antigens. A total of 639 serum samples collected in the context of different studies from naturally infected cats were tested. The current study revealed that, with an apparent prevalence of 83%, FCoV serotype 1 is the most prevalent serotype in Switzerland. FCoV type 1 viruses induced higher antibody titers than FCoV type 2, and were more frequently associated with clinical signs and/or feline infectious peritonitis. The antibody development in seven cats experimentally infected with FCoV type 1 revealed that, with progressing duration of infection, antibodies to FCoV type 1 significantly increased over those to FCoV type 2. There was a significant relationship between antibody titers against TGEV, FCoV 1, and FCoV 2 and TGEV antigen detected the highest proportion of seropositive cats. We conclude that a vaccine against FCoV should be based on FCoV type 1-related antigens and that for serodiagnosis of FCoV infection TGEV should be used to attain the highest diagnostic efficiency. When serology is used in addition to clinical signs, hematology, and clinical chemistry results as an aid to diagnose clinical FIP, TGEV shows a diagnostic efficiency equal to that of a FCoV antigen.  相似文献   
65.
Non-specific mental retardation (NSMR) is a common human disorder characterized by mental handicap as the only clinical symptom. Among the recently identified MR genes is GDI1, which encodes alpha Gdi, one of the proteins controlling the activity of the small GTPases of the Rab family in vesicle fusion and intracellular trafficking. We report the cognitive and behavioral characterization of mice carrying a deletion of Gdi1. The Gdi1-deficient mice are fertile and anatomically normal. They appear normal also in many tasks to assess spatial and episodic memory and emotional behavior. Gdi1-deficient mice are impaired in tasks requiring formation of short-term temporal associations, suggesting a defect in short-term memory. In addition, they show lowered aggression and altered social behavior. In mice, as in humans, lack of Gdi1 spares most central nervous system functions and preferentially impairs only a few forebrain functions required to form temporal associations. The general similarity to human mental retardation is striking, and suggests that the Gdi1 mutants may provide insights into the human defect and into the molecular mechanisms important for development of cognitive functions.  相似文献   
66.
67.
Psychiatric symptoms and medical utilization in primary care patients   总被引:1,自引:0,他引:1  
In two studies, the authors evaluated the impact of psychiatric disorders on medical care utilization in a primary care setting. In the first study, 526 consecutive patients in a teaching hospital primary care practice completed the 18-item RAND Mental Health Inventory to identify clinically significant depression and/or anxiety and a questionnaire about the use of psychiatric treatment and psychoactive medications. The medical utilization of those patients defined as depressed and/ or anxious was compared with those defined as not depressed and/or anxious. Patients identified as depressed and/or anxious reported significantly increased medical utilization, but this was not confirmed by the hospital's computerized record system. In the second study, the authors analyzed medical care utilization for the years before and after the first outpatient psychiatry appointment of a sample of 91 patients referred from the same primary care practice to the hospital's outpatient psychiatry clinic over a 1-year period. In both studies there was not a statistically significant difference in medical utilization among those patients receiving psychiatric treatment. The findings demonstrate the difficulties in examining cost offset in a primary care population and raise questions about it as a realistic outcome measure of the effect of psychiatric treatment.  相似文献   
68.
Acquired immunodeficiency syndrome (AIDS)-related non-Hodgkin's lymphomas (AIDS-NHLs) consistently derive from B cells, are histologically heterogeneous, and are associated with distinct molecular pathways depending upon histology. Recently, it has been proposed that inactivating mutations of the bax death agonist may contribute to the pathogenesis of human tumors. In particular, among B-cell malignancies, BAX mutations have been detected at a certain frequency in Burkitt lymphomas. This study is aimed at defining the status of the BAX gene throughout the clinicopathologic spectrum of AIDS-NHL (n = 54), including AIDS-related Burkitt lymphoma (n = 14), AIDS-related Burkitt-like lymphoma (n = 8), AIDS-related diffuse large cell lymphoma (n = 15), AIDS-related primary central nervous system lymphoma (n = 6), and AIDS-related primary effusion lymphoma (n = 11). All 6 BAX exons and flanking sequences were subjected to mutational analysis by polymerase chain reaction-single strand conformation polymorphism followed by DNA direct sequencing of positive cases. Mutations of BAX among AIDS-NHL were restricted to a cell line of AIDS-related primary effusion lymphoma, which harbored a frameshift mutation causing the introduction of a proximal stop codon. All other AIDS-NHL displayed wild-type BAX alleles. In order to investigate whether BAX inactivation in AIDS-NHL may occur through mechanisms other than gene mutation, bax protein expression was investigated by Western blot analysis or immunohistochemistry in selected cases. All AIDS-NHL analyzed expressed normal bax proteins. Overall, this study indicates that deregulation of apoptotic control in AIDS-NHL is not caused by BAX alterations. Genes Chromosomes Cancer 27:177-182, 2000.  相似文献   
69.
70.
Epidemiological and pathogenetic evidences suggest a strong association between vascular risk factors and sporadic Alzheimer's disease (sAD). In agreement with the vascular hypothesis of AD, the role of various candidate genes for atherosclerosis has been investigated, leading to conflicting results. In order to clarify the significance of angiotensin-converting enzyme (ACE) gene insertion (I)/deletion (D) polymorphism in a group of patients with sAD, we conducted a case-control study including 149 cases and 149 age and sex matched controls. All subjects were genotyped for ACE and Apolipoprotein E (APOE). There were no significant differences in ACE genotype or allele frequencies between cases and controls, even after stratification for APOE4 carrier status. Our data suggest that the ACE I/D polymorphism is not associated to genetic susceptibility in sAD patients.  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