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   252035篇
  免费   17856篇
  国内免费   1130篇
耳鼻咽喉   2787篇
儿科学   6495篇
妇产科学   4596篇
基础医学   32939篇
口腔科学   4557篇
临床医学   25324篇
内科学   53609篇
皮肤病学   3383篇
神经病学   24277篇
特种医学   8399篇
外国民族医学   11篇
外科学   38485篇
综合类   3456篇
一般理论   318篇
预防医学   21402篇
眼科学   6559篇
药学   16966篇
  6篇
中国医学   361篇
肿瘤学   17091篇
  2023年   1339篇
  2022年   2411篇
  2021年   5439篇
  2020年   3261篇
  2019年   5300篇
  2018年   5950篇
  2017年   4470篇
  2016年   4958篇
  2015年   5828篇
  2014年   8604篇
  2013年   11795篇
  2012年   18010篇
  2011年   18900篇
  2010年   10575篇
  2009年   9428篇
  2008年   16595篇
  2007年   17449篇
  2006年   17301篇
  2005年   17276篇
  2004年   16191篇
  2003年   15044篇
  2002年   14063篇
  2001年   2108篇
  2000年   1600篇
  1999年   2319篇
  1998年   3065篇
  1997年   2561篇
  1996年   2183篇
  1995年   2095篇
  1994年   1744篇
  1993年   1572篇
  1992年   1259篇
  1991年   1150篇
  1990年   1002篇
  1989年   974篇
  1988年   966篇
  1987年   945篇
  1986年   950篇
  1985年   963篇
  1984年   1217篇
  1983年   1123篇
  1982年   1365篇
  1981年   1312篇
  1980年   1145篇
  1979年   703篇
  1978年   747篇
  1977年   635篇
  1976年   584篇
  1975年   469篇
  1974年   472篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We have previously reported that immunization of mice with melanoma cells transfected to secrete the superantigen, Staphylococcal enterotoxin A (SEA), increased the production of antibodies to the B700 melanoma antigen, stimulated the production of endogenous interleukin 2 (IL-2), activated the expression of CD4, CD8 and CD25 T cell markers and enhanced NK cell activity. Now we show that immunization of mice with a vaccine of irradiated sea-transfected melanoma cells coupled with IL-2 therapy was even more effective in inhibiting the growth of primary melanoma tumors and the development of lung metastases than was the irradiated melanoma cell vaccine alone or IL-2 alone. The morphological and immunological effectiveness of the therapy was dose-dependent on IL-2.  相似文献   
992.
Summary: It is clear that the development of a safe and effective vaccine for human immunodeficiency virus type 1 (HIV‐1) remains a crucial goal for controlling the acquired immunodeficiency syndrome epidemic. At present, it is not clear what arm of the immune response correlates with protection from HIV‐1 infection or disease. Therefore, a strong cellular and humoral immune response will likely be needed to control this infection. Among different vaccine alternatives, DNA vaccines appeared more than a decade ago, demonstrating important qualities of inducing both humoral and cellular immune responses in animal models. However, after several years and various clinical studies in humans, supporting the safety of the HIV‐DNA vaccine strategies, it has become clear that their potency should be improved. One way to modulate and enhance the immune responses induced by a DNA vaccine is by including genetic adjuvants such as cytokines, chemokines, or T‐cell costimulatory molecules as part of the vaccine itself. Particularly, vaccine immunogenicity can be modulated by factors that attract professional antigen‐presenting cells, provide additional costimulation, or enhance the uptake of plasmid DNA. This review focuses on developments in the coadministration of molecular adjuvants for the enhancement of HIV‐1 DNA‐vaccine potency.  相似文献   
993.
994.
995.
Background:  In recent years, interest has been revived in the possibility of transplanting organs into humans from a phylogenetically disparate species such as the pig (xenotransplantation). Such discordant xenografts, however, are subject to hyperacute rejection (HAR) and activation of host complement plays a major role in this rejection. This problem may be solved through the use of transgenic technology by providing the grafted tissue with molecules that down-regulate the action of host complement.
Results: Transgenesis with a yeast artificial chromosome (YAC) was used to produce transgenic mice with the complete genomic gene of the human complement regulator membrane cofactor protein (MCP). Transgenic mice were obtained that exhibit full regulation of MCP as normally observed in humans. Hearts from these mice were shown to be significantly protected from HAR caused by human serum in an in vivo experimental procedure.
Conclusions:  We conclude that MCP can protect discordant xenografts from HAR caused by human serum and that transgenic mice can be used effectively as in vivo models for the study of the role of human complement regulatory molecules in xenotransplantation.  相似文献   
996.
Signal Transduction in Human T Lymphocytes   总被引:11,自引:0,他引:11  
  相似文献   
997.
Aspartylglucosaminuria in the United States   总被引:2,自引:0,他引:2  
Aspartylglucosaminuria (AGU) was diagnosed in two unrelated males with progressive mental retardation, coarse facies and skeletal abnormalities. Until now, this disorder has been described in predominantly Finnish populations with only one previous case reported in the U.S. We conclude that AGU may be more common in nowFinnish populations than the number of reported cases would indicate and should be included in the differential diagnosis in patients with suspected lysosomal storage disorders regardless of their geographical or ethnic backgrounds.  相似文献   
998.
Cerebral lateralization in the voluntary increase of heart rate was investigated in a biofeedback experiment involving 20 right-handed female subjects randomly assigned to one of two groups: right or left ear input of stimulus and biofeedback information. The stimulus was a 1000 Hz tone which signalled the start and duration of 30 20-sec training trials. Feedback was a click presented every time an interbeat interval was shorter than a criterion established through a shaping schedule. A monetary bonus provided additional reinforcement at the end of each trial. Subjects given right ear feedback increased their heart rate significantly more than subjects given left ear feedback. The largest difference between the group means (7 bpm) was recorded after the first 20 training trials. The results are discussed in terms of hemispheric perceptual and functional differences.  相似文献   
999.
On the classification of the acrocephalosyndactyly syndromes   总被引:2,自引:0,他引:2  
This report describes a family in which two different types of acrocephalosyndactyly (ACS) were clinically identified. The proband presented with the classic stigmata of Pfeiffer syndrome, while her cousin was considered to be a typical case of Apert syndrome. Seven other family members also have unusually shaped heads and the facial appearance reminiscent of Crouzon disease.
Observations made in this family and from previous reports in the literature, we feel there is substantial reason to re-evaluate the ACS classification and to consider that the Apert and Pfeiffer types of ACS may be one and the same.  相似文献   
1000.
Weak transcranial direct current stimulation (tDCS) of the human motor cortex results in excitability shifts which occur during and after stimulation. These excitability shifts are polarity-specific with anodal tDCS enhancing excitability, and cathodal reducing it. To explore the origin of this excitability modulation in more detail, we measured the input–output curve and motor thresholds as global parameters of cortico-spinal excitability, and determined intracortical inhibition and facilitation, as well as facilitatory indirect wave (I-wave) interactions. Measurements were performed during short-term tDCS, which elicits no after-effects, and during other tDCS protocols which do elicit short- and long-lasting after-effects. Resting and active motor thresholds remained stable during and after tDCS. The slope of the input–output curve was increased by anodal tDCS and decreased by cathodal tDCS. Anodal tDCS of the primary motor cortex reduced intracortical inhibition and enhanced facilitation after tDCS but not during tDCS. Cathodal tDCS reduced facilitation during, and additionally increased inhibition after its administration. During tDCS, I-wave facilitation was not influenced but, for the after-effects, anodal tDCS increased I-wave facilitation, while cathodal tDCS had only minor effects. These results suggest that the effect of tDCS on cortico-spinal excitability during a short period of stimulation (which does not induce after-effects) primarily depends on subthreshold resting membrane potential changes, which are able to modulate the input-output curve, but not motor thresholds. In contrast, the after-effects of tDCS are due to shifts in intracortical inhibition and facilitation, and at least partly also to facilitatory I-wave interaction, which is controlled by synaptic activity.  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