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   3788篇
  免费   267篇
  国内免费   31篇
耳鼻咽喉   39篇
儿科学   110篇
妇产科学   111篇
基础医学   573篇
口腔科学   53篇
临床医学   633篇
内科学   616篇
皮肤病学   66篇
神经病学   424篇
特种医学   96篇
外科学   354篇
综合类   54篇
一般理论   6篇
预防医学   403篇
眼科学   60篇
药学   231篇
中国医学   1篇
肿瘤学   256篇
  2023年   28篇
  2022年   38篇
  2021年   75篇
  2020年   66篇
  2019年   80篇
  2018年   81篇
  2017年   59篇
  2016年   94篇
  2015年   88篇
  2014年   103篇
  2013年   169篇
  2012年   244篇
  2011年   248篇
  2010年   155篇
  2009年   140篇
  2008年   216篇
  2007年   241篇
  2006年   223篇
  2005年   253篇
  2004年   201篇
  2003年   256篇
  2002年   196篇
  2001年   44篇
  2000年   26篇
  1999年   45篇
  1998年   48篇
  1997年   44篇
  1996年   23篇
  1995年   36篇
  1994年   29篇
  1993年   30篇
  1992年   21篇
  1990年   15篇
  1989年   14篇
  1988年   18篇
  1987年   17篇
  1986年   21篇
  1985年   22篇
  1984年   21篇
  1983年   19篇
  1982年   29篇
  1981年   27篇
  1980年   27篇
  1979年   25篇
  1978年   20篇
  1977年   18篇
  1976年   25篇
  1975年   13篇
  1974年   14篇
  1970年   12篇
排序方式: 共有4086条查询结果,搜索用时 15 毫秒
11.
12.
Background/Aims: This study was designed to assess changes in: (a) neuropsychological tests, measures of memory, quality of life and scores for anxiety and depression; (b) liver function tests; and (c) the relationship between these following transjugular intrahepatic portosystemic stent-shunt.Methods: Twenty-nine patients undergoing transjugular intrahepatic portosystemic stent-shunt for recurrent variceal haemorrhage, 12 matched patients with cirrhosis and variceal haemorrhage manage with variceal band ligation and 16 normal controls were studied. Patients in any of the groups who were clinically encephalopathic were excluded from the study. Serial changes in the conventional liver function tests and Indocyanine green clearance, and psychometric function (Hospital Anxiety Depression Scale, Rivermead Behavioral Memory Test, Quality of Life and the memory and reaction sub-tests of the Cambridge Automated Neuropsychological Test Assessment Battery) were measured prior to and 1, 3, 9 and 15 months following transjugular intrahepatic portosystemic stent-shunt.Results: Over a mean follow up of 9.1 months in the transjugular intrahepatic portosystemic stent-shunt group (range 3–28), one patient (3%) developed clinically detectable encephalopathy. Sixty-seven percent of patients with cirrhosis showed evidence of subclinical encephalopathy as compared with the control population. Significant deterioration occurred in the reaction sub-tests of the Cambridge Automated neuropsychological Test Assessment Battery in patients, both in the transjugular intrahepatic portosystemic stent-shunt group and the controls with cirrhosis, during follow up. Transjugular intrahepatic portosystemic stent-shunt was followed by significant deterioration in levels of anxiety and psychological component of the quality of life. The Rivermead Behavioural Memory Test and the memory sub-test of the Cambridge Automated Neurpsychological Test Assessment Battery did, however, improve significantly at 1 and 15 months after transjugular intrahepatic portosystemic stent-shunt, respectively. Serum alanine aminotransferase, bilirubin and indocyanine green clearance deteriorated significantly following transjugular intrahepatic portosystemic stent-shunt (p<0.001, p<0.001 and p<0.0001, respectively). Significant correlation was observed between changes in the indocyanine green clearance and changes in the complex and simple reaction time subtests of the Cambridge Automated Neuropsychological Test Assessment Battery (r=0.6 and r=0.66, respectively).Conclusions: The results of this study showed that about 67% of patients with cirrhosis were subclinically encephalopathic and that temporary deterioration occurred in the Cambridge Automated Neuropsychological Test Assessment Battery during follow up, both in patients having transjugular intrahepatic portosystemic stent-shunt and in the controls with cirrhosis. These parallel the changes in the liver function tests and indocyanine green clearance. Temporary deterioration was also observed in the Quality of Life and Hospital Anxiety Depression Scale in the transjugular intrahepatic portosystemic stent-shunt group, although the measures of memory improved. Further studies should address the biochemical mechanisms of these changes and the role of prophylactic measures.  相似文献   
13.
The current study presents both longitudinal behavioral data and functional activation data documenting the effects of early focal brain injury on the development of spatial analytic processing in two children, one with prenatal left hemisphere (LH) injury and one with right hemisphere (RH) injury. A substantial body of evidence has shown that adults and children with early, lateralized brain injury show evidence of spatial analytic deficits. LH injury compromises the ability to encode the parts of a spatial pattern, while RH injury impairs pattern integration. The two children described in this report show patterns of deficit consistent with the site of their injury. In the current study, their longitudinal behavioral data spanning the age range from preschool to adolescence are presented in conjunction with data from a functional magnetic resonance imaging (fMRI) study of spatial processing. The activation results provide evidence that alternative profiles of neural organization can arise following early focal brain injury, and document where in the brain spatial functions are carried out when regions that normally mediate them are damaged. In addition, the coupling of the activation with the behavioral data allows us to go beyond the simple mapping of functional sites, to ask questions about how those sites may have come to mediate the spatial functions.  相似文献   
14.
Summary Antigenic relationships between adenoviruses of subgenus D were determined by neutralization tests in HeLa cell cultures by CPE inhibition. For cross-testing, several antisera of the same species were tested against the prototype viruses 39 wild strains belonging to 12 different virus species were also studied. Marked variation in the degree of cross-neutralization between individual sera of the same species was often observed. However, virus strains within a species mostly showed identical serological reactions. Hence, antigenic specificity appears to be a fairly constant property of any one species.Strong cross-neutralizations between species are presumably due to a relationship of the (hexon) antigen, whereas weak cross-neutralizations found between viruses related by hemagglutination-inhibition are due to the (fiber) antigen.Viruses related to adenovirus 15(Mastadenovirus h 15) showed a variety of cross-reactions in neutralization tests. In view of the new species definitions of adenoviruses and to facilitate identification, changes in the classification of Ad 15, 25, 29, and 15/H9 are proposed. The prototypes of Ad 13, 15, 25, 29, and 30 have been cloned by terminal dilution.Aided by a grant from the Bundesministerium für Jugend, Familie und Gesundheit.  相似文献   
15.
The aim of the double-blind, placebo-controlled study was to investigate the effects of a continuous combined estrogen-progestogen treatment (Climodien, Lafamme) as compared with estrogen alone on vigilance in insomniac postmenopausal syndrome patients, objectified by EEG mapping. METHODS: In a 3-arm, 2-month parallel group design phase, patients received a combination of estradiol valerate 2 mg and the novel progestogen dienogest 3 mg (Climodien 2/3) or estradiol valerate 2 mg alone or placebo. In a subsequent open-label phase, all patients received estradiol valerate 2 mg+dienogest 2 mg (Climodien 2/2). EEG mapping was carried out before and after the 2-month double-blind phase as well as after the 2-month open-label treatment. RESULTS: As compared with placebo, Climodien 2/3 induced a marked and highly significant increase in absolute power in all frequency bands, specifically in alpha-2 activity. Moreover, a significant increase in relative alpha-2 power, a decrease in relative delta and beta power as well as an acceleration of the dominant frequency and of the delta and alpha centroids suggested a marked improvement in vigilance. In contrast, under estradiol valerate 2 mg alone, only a slight augmentation of alpha and attenuation of relative delta and beta power occurred, suggesting only a slight vigilance improvement as compared with placebo. Thus, dienogest 2 mg increased the estrogen effect, which was also confirmed by a statistical evaluation of the differences between Climodien 2/3 and estradiol valerate alone (augmentation of alpha-2, attenuation of relative beta, acceleration of the dominant frequency). Moreover, Climodien 2/2 also markedly increased alpha-2 power, decreased relative beta-2 power and accelerated the alpha centroid. Finally, comparing Climodien 2/3 with Climodien 2/2, there was even a dose-efficacy relation. CONCLUSIONS: Estradiol valerate 2 mg improves vigilance slightly, thereby confirming previous findings. The additional administration of dienogest does not minimize the effect of estrogen, but on the contrary increases it, which makes the combination superior to both placebo and estradiol valerate alone. Vigilance improvement may be of great therapeutic benefit to menopausal syndrome patients at a time when increased adaptability is needed to adjust to increasing sexual, marital, occupational and social difficulties known to occur specifically in this period of life.  相似文献   
16.
IgE antibody specific for AgE (IgE—AgE) was eluted from human basophils at acid pH and quantified by its binding of 125I AgE in antigen excess. The quantity of Ige—AgE recovered from 30 ml of blood ranged from 0.08 ng to 10.3 ng representing 500 to 56,000 molecules IgE—AgE per basophil. The number of molecules of IgE—AgE per basophil was compared to plasma IgE—AgE, total plasma IgE and leucocyte histamine release in response to AgE.

The ratio of plasma IgE—AgE to basophil bound IgE—AgE ranged from 100 to 4000, indicating that there are a limited number of IgE receptors on the basophil surface as contrasted to the concentration of IgE in the plasma. There was no correlation between IgE—AgE in plasma and the number of molecules of IgE—AgE per basophil. However there was a significant correlation between the ration of IgE—AgE to total IgE in plasma and the number of IgE—AgE molecules per basophil.

Two measures of leucocyte histamine release in response to AgE, cell reactivity (maximum per cent histamine release attainable) and sensitivity (lowest antigen dose leading to 50% release), were compared to the number of IgE—AgE molecules per basophil. Cell reactivity was dependent on the number of IgE—AgE molecules per basophil. Only 2500 molecules IgE—AgE per basophil were required to reach a cellular reactivity of 50%. Cell sensitivity to AgE was not correlated with the number of molecules IgE—AgE per basophil which indicated that other factors played a role in determining the sensitivity of a population of basophils to antigenic stimulation by AgE.

  相似文献   
17.
Resting CD4(+) T cells in the lymphoid tissue (LT) are essential producers of virions at the beginning of HIV infection in vivo. We previously developed a model that allowed in vitro infection of non-prestimulated T lymphocytes in the presence of autologous B lymphocytes and complement. In this study, we try to clarify the mechanism(s) responsible for virus transmission in unstimulated autologous B cell/T cell co-cultures. Ex vivo analyses of patient plasma samples revealed that HIV was opsonized. Flow cytometry showed that opsonized virus preferentially bound to complement receptor (CR)-2 on B lymphocytes in primary B cell/T cell co-cultures. As indicated by cytokine measurements and transwell experiments, soluble factors seemed to play a minor role in enabling infection. Rather, direct interaction between B and T lymphocytes and direct binding of opsonized virus to CR2 on B cells turned out to be essential for productive infection. Antibodies blocking cell-cell adhesion inhibited p24 antigen production. An anti-CR2 antibody blocking C3d-CR2 binding also significantly reduced viral replication. Since the infection of unstimulated T cells by opsonized primary HIV isolates in the presence of B cells was highly efficient independent of the tropism of the virus, this mechanism may be critical in the pathogenesis of HIV.  相似文献   
18.
19.
We have recently shown that 'alloimmune sera' derived from polytransfused patients (PTP sera) are able to recognise and neutralise HIV in vitro. In this study we try to identify the protein(s), which are recognised by the PTP sera and elucidate mechanisms responsible for the neutralising capacity of these sera. The PTP sera allowed immunoprecipitation (IP) of HLA class II molecules on HIV-infected cells. To detect a potential cross-reactivity of alloreactive antibodies (Ab) with the HIV envelope protein gp160 or its subunits gp120/gp41 and HLA proteins, ELISA and FACS analyses were performed. The lack of reactivity of the PTP sera against rsgp160 in ELISA or FACS analysis indicated that recognition of cells was independent of HIV infection. To clarify whether interaction of the PTP sera with target cells has any effect on the infection process, virus neutralisation assays were performed. Inhibition of HIV infection was observed only when virus was pre-incubated with the PTP sera. Complement enhanced neutralisation of HIV-1 significantly. This enhancement was not due to complement-mediated lysis, because pre-incubation of the target cells with PTP sera did not inhibit HIV replication. Therefore, the neutralising effect of the Ab was due to blocking of the viral attachment/fusion process and not to negative signalling after infection. Since steric hindrance is possible only when HLA and gp120/gp41 are in close vicinity, isolation of rafts and IP assays were performed. These experiments revealed that gp120 and MHC class II molecules are indeed co-localised. The close physical association of gp120/gp41 and HLA strongly supports a mechanism for neutralisation of HIV by anti-HLA-Ab based on steric hindrance.  相似文献   
20.
To determine the basis of susceptibility and resistance to human monocytic ehrlichiosis (HME), immunocompetent and immunocompromised mice were infected with Ehrlichia chaffeensis and bacterial loads were measured by PCR and by immunohistochemistry. Immunocompetent (C.B-17 and C57BL/6) mice cleared the bacteria within 10 days, but immunocompromised SCID and SCID/BEIGE mice developed persistent infection in the spleen, liver, peritoneal cavity, brain, lung, and bone marrow and became moribund within 24 days. Both immunocompromised strains lack T and B lymphocytes, but the SCID/BEIGE strain is also deficient in natural killer (NK) cell function. During advanced stages of disease, the infections were associated with wasting, splenomegaly, lymphadenopathy, liver granulomas and necroses, intravascular coagulation, and granulomatous inflammation. Histochemical and immunohistochemical localization studies confirmed the presence of bacteria in tissues, and viable bacteria were cultured from infected animals. The data reveal that T and/or B cells play an essential role during resistance of immunocompetent mice to infection with E. chaffeensis and demonstrate the utility of immunocompromised mice as an experimental model for the study of HME.  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