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   228611篇
  免费   17571篇
  国内免费   7199篇
耳鼻咽喉   1294篇
儿科学   7970篇
妇产科学   1655篇
基础医学   20583篇
口腔科学   3736篇
临床医学   24221篇
内科学   57387篇
皮肤病学   2828篇
神经病学   26429篇
特种医学   6410篇
外国民族医学   4篇
外科学   17196篇
综合类   30311篇
现状与发展   32篇
一般理论   10篇
预防医学   20932篇
眼科学   2466篇
药学   15549篇
  195篇
中国医学   10109篇
肿瘤学   4064篇
  2024年   663篇
  2023年   4970篇
  2022年   8999篇
  2021年   12646篇
  2020年   12171篇
  2019年   8705篇
  2018年   8591篇
  2017年   8470篇
  2016年   8797篇
  2015年   8474篇
  2014年   15884篇
  2013年   17399篇
  2012年   13093篇
  2011年   14180篇
  2010年   11193篇
  2009年   10721篇
  2008年   10707篇
  2007年   10321篇
  2006年   9170篇
  2005年   7618篇
  2004年   6498篇
  2003年   5591篇
  2002年   4694篇
  2001年   4070篇
  2000年   3429篇
  1999年   2909篇
  1998年   2752篇
  1997年   2429篇
  1996年   2177篇
  1995年   1952篇
  1994年   1806篇
  1993年   1537篇
  1992年   1481篇
  1991年   1296篇
  1990年   1021篇
  1989年   878篇
  1988年   820篇
  1987年   752篇
  1986年   653篇
  1985年   752篇
  1984年   630篇
  1983年   387篇
  1982年   455篇
  1981年   382篇
  1980年   286篇
  1979年   252篇
  1978年   191篇
  1977年   165篇
  1976年   137篇
  1975年   50篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Summary The present study demonstrates that the muscarinic antagonist atropine and the -adrenergic agonist clonidine, though ineffective when administered separately, produced a pronounced locomotor stimulation in monoamine-depleted mice when combined. The atropine + clonidine-induced locomotor stimulation was counteracted by both the 2-adrenoceptor antagonist idazoxan and the acetylcholinesterase inhibitor physostigmine. Thus, it is clear that simultaneous manipulations with cholinergic and adrenergic systems are as effective in restoring locomotion in monoamine-depleted mice as increasing central dopaminergic tone. This finding may have implications for the treatment of a movement disorder like Parkinson's disease.  相似文献   
952.
There is a close similarity between the unconventional virus-induced ovine scrapie and human Creutzfeldt-Jakob disease. Since infection might be transmitted orally, the ovine production of an endemically scrapie-infected farm was studied. About 80% of the annual production are sold (50% as butcher-meat, 30% as breeding animals), and scrapie appears in 20% of the sheep kept on the farm. Was the same proportion of butcher-meat animals scrapie-infected? Since the scrapie agent has been detected in “clinically normal” lambs, the same problem occurs with breeding-sheep and “apparently healthy” animals: are they carriers of the pathogenic agent? Are they responsible for the spread of the ovine disease and/or of the human disease?  相似文献   
953.
Globoid cell leukodystrophy (GLD, Krabbe disease) is a severe demyelinating disease caused by a genetic defect of beta-galactocerebrosidase (GALC). To date treatment to GLD is limited to hematopoietic stem cell transplantation. Experimental approaches by means of gene therapy in twitcher mouse, an authentic murine model of human GLD, showed significant but only marginal improvements of the disease. To clarify whether the introduction of GALC could provide beneficial effects on the oligodendrocytes in GLD, we transduced twitcher oligodendrocytes by stereotactically injecting recombinant retrovirus encoding GALC-myc-tag fusion gene into the forebrain subventricular zone of neonatal twitcher mouse. In vivo effects of exogenous GALC on twitcher oligodendrocytes were studied histologically by combined immunostaining for the myc-epitope and the oligodendroglial specific marker, pi form of glutathione-S-transferase, at around 40 days of age. We show here that GALC transduction led to dramatic morphological improvement of the twitcher oligodendrocytes comparing with those in untreated twitcher controls. This study provided direct in vivo evidence that GALC transduction could prevent or correct aberrant morphology of oligodendrocytes in GLD which may be closely related to the dysfunction and/or degeneration of oligodendrocytes and the demyelination in this disease.  相似文献   
954.
Recent studies have demonstrated that α-Smooth Muscle actin expression in glomerular and tubulointerstitial compartments of renal tissue could represent a prognostic marker in several renal diseases. Our objective was to identify the prognostic value of α-SM actin actin expression on the evolution of renal damage in Primary IgA nephropathy (Berger’s Disease). 43 patients followed up from 1988 to 1999 at the University Hospital, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Brazil, was studied. Clinical-laboratory data were obtained from the medical records of the patients using a protocol containing name, race, gender, origin, profession, age at clinical presentation of the disease and personal and family history. The parameters assessed in the approach to IgA nephropathy were serum creatinine, creatinine clearance, serum albumin, total serum protein, 24 hours proteinuria, glycaemia, serum sodium, potassium, calcium and phosphorus ions, analysis of urinary sediment, serum complement profile, blood count, and renal biopsy. Morphological evaluation was performed by renal biopsy using common light and immunofluorescence microscopy. Immunohistochemical studies were performed using a murine monoclonal antibody to α-SM actin. Our data showed that α-SM actin expression in the glomerular and tubulointerstitial compartments are not correlated with unfavorable clinical course of primary IgA nephropathy.  相似文献   
955.
神经生长因子偶联物对老年性痴呆动物模型的保护作用   总被引:7,自引:0,他引:7  
目的 探讨神经生长因子偶联物 (NGF -Tf)对老年性痴呆 (AD)大鼠的影响 .方法 以手术切断大鼠双侧隔 -海马胆碱能通路的方法建立AD动物模型 ,每天从大鼠尾静脉注射NGF -Tf .通过水迷路试验观察大鼠的记忆和方向辨别能力 ;对海马和隔区行神经组织学检查 ;应用酶组织化学技术显示相应区域的ChAT ,采用计算机病理图像分析系统测定酶活性以判断其胆碱能功能状态 .结果 水迷路试验中 ,NGF -Tf组在 10s内抵达平台的正确反应平均数提高 (p <0 .0 5 ) .光镜下 ,NGF -Tf组隔区仅见轻微萎缩性改变 ,而模型组隔区萎缩性改变较明显 ,表现为神经元数目明显减少 ,细胞轮廓不清 ,有胶质细胞增生 ;正常对照组、NGF -Tf组和模型组的海马区未见明显病理性改变 .ChAT染色统计结果显示 ,正常对照组、NGF -Tf组大鼠的海马区及隔区IOD值与模型组比较 ,均有显著性差异 (p <0 .0 1) .结论 NGF -Tf能穿透血脑屏障 ,有效防止模拟AD病变的大鼠的基底前脑胆碱能神经元的变性和死亡 ,改善其记忆和方向辨别能力 ,促进其胆碱能神经元的功能恢复  相似文献   
956.
It is widely known that the tau protein that forms the aggregates found in tauopathies like Alzheimer’s disease (AD) is hyperphosphorylated. Many of the sites that are hyperphosphorylated in AD can also be found phosphorylated in non-pathological control brains, although to a lesser extend. Among the different kinases that are able to phosphorylate tau in these sites, GSK-3 has emerged as a key effector of AD pathogenesis in view of its interaction with many of the proteins involved in the ethiology of AD. In this work, we have tested if control samples show only a decrease in the amount of phosphorylated tau molecules, or if the phosphorylation at different sites occurs in different tau isoforms, whereas in the pathological situation a single tau isoform is modified simultaneously at the different sites. Our results indicate that the second possibility takes place and that the differences in the phosphorylation of different tau isoforms could be due to a different subcellular distribution of these different tau isoforms in a neuron.  相似文献   
957.
Rhinosinusitis is diagnosed frequently in clinical practice, but the term may in fact encompass a wide spectrum of diseases. Inflammation of the nasal and sinus mucosa can arise from various causes and lead to different sequelae. Moreover, the term rhinosinusitis is more accurate than sinusitis. Causes range from a viral infection leading to the common cold to an invasive, fungal infection. An accurate diagnosis is important because effective therapy is available if recognized early and if specific therapy is used. Importantly, there is a close relationship between upper and lower airway disease and each have unique structural and functional differences that make an understanding of rhinosinusitis important not only for upper airway disease, but also for the management of asthma. All too often, rhinosinusitis becomes chronic and this becomes a challenge because medical therapy may not be sufficient to control disease. Finally, we should note that the differential diagnosis of rhinosinusitis is extensive and physicians should place heavy emphasis not only on the history, but also on appropriate imaging studies. A normal exam does not rule out the possibility or rhinosinusitis. Finally, we should emphasize that effective treatment is dependent on the etiology of the symptoms but also dependent on whether it is acute or chronic.  相似文献   
958.
Nie X  Singh RP 《Virus genes》2003,26(1):39-47
A North American (NA) isolate of tobacco veinal necrotic strain of Potato virus Y (PVYN) (N-Jg) and a NA isolate of potato tuber necrotic strain of Potato virus Y (PVYNTN) (Tu 660) were tested for their phenotypes by inoculation to potato plants of three potato cultivars. Upon inoculation with Tu 660, tubers of the cultivars Norchip and Ranger Russet developed potato tuber necrotic ringspot disease (PTNRD) but not the tubers of Russet Burbank. N-Jg failed to induce PTNRD in the tested cultivars. The genomic RNAs of both strains were completely sequenced and analysed. High homology (98% and 99% identity on nucleotide and polyprotein, respectively) was found between Tu 660 and N-Jg. When polyproteins were compared with other isolates, high identity was observed between Tu 660 and an European (Eu) PVYN-605 (98%) and with an Eu-PVYNTN-H (96%). However, when individual mature proteins were compared, much lower identities (86.5–94%) were found between Tu 660 and PVYNTN-H compared to 98–99.5% between Tu 660 and PVYN-605 in the P3, 6K1 and CI regions. Further sequence analysis indicated that the PVYNTN-H is a hybrid molecule of the genomic RNA recombination of PVYO and Eu-PVYN as shown by Glais et al. (Arch Virol 147, 363–378), whereas NA-PVYNTN Tu 660 is free of recombination points. Phylogenetic analysis confirmed this observation, and suggested that, in light of high homology, the Tu 660 might have evolved from NA-PVYN by mutations rather than the genome recombinations. The non-recombinant nature of NA-PVYNTN Tu 660 strongly suggests that the recombinant structure of genome is not a necessary prerequisite for the PTNRD phenotype.  相似文献   
959.
DNA vaccination is an efficient way to induce CD8+ T cell memory, but it is still unclear to what extent such memory responses afford protection in vivo. To study this, we induced CD8+ memory responses directed towards defined viral epitopes, using DNA vaccines encoding immunodominant MHC class I-restricted epitopes of lymphocytic choriomeningitis virus covalently linked to beta2-microglobulin. This vaccine construct primed for a stronger recall response than did a more conventional minigene construct. Despite this, vaccinated mice were only protected against systemic infection whereas protection against the consequences of peripheral challenge was limited. Phenotypic analysis revealed that DNA vaccine-primed CD8+ T cells in uninfected mice differed from virus-primed CD8+ T cells particularly regarding expression of very-late antigen (VLA)-4, an adhesion molecule important for targeting T cells to inflammatory sites. Thus, our DNA vaccine induces a long-lived memory CD8+ T cell population that provides efficient protection against high-dose systemic infection. However, viral replication in solid non-lymphoid organs is not curtailed sufficiently fast to prevent significant virus-induced inflammation. Our results suggest that this is due to qualitative limitations of the primed CD8+ T cells.  相似文献   
960.
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