全文获取类型
收费全文 | 156704篇 |
免费 | 7234篇 |
国内免费 | 503篇 |
专业分类
耳鼻咽喉 | 2623篇 |
儿科学 | 4671篇 |
妇产科学 | 3598篇 |
基础医学 | 21279篇 |
口腔科学 | 5608篇 |
临床医学 | 9918篇 |
内科学 | 38235篇 |
皮肤病学 | 5085篇 |
神经病学 | 12756篇 |
特种医学 | 3539篇 |
外国民族医学 | 2篇 |
外科学 | 18867篇 |
综合类 | 1000篇 |
一般理论 | 44篇 |
预防医学 | 15345篇 |
眼科学 | 3378篇 |
药学 | 11110篇 |
中国医学 | 890篇 |
肿瘤学 | 6493篇 |
出版年
2023年 | 969篇 |
2022年 | 1383篇 |
2021年 | 4263篇 |
2020年 | 2121篇 |
2019年 | 4010篇 |
2018年 | 5772篇 |
2017年 | 3413篇 |
2016年 | 3269篇 |
2015年 | 3671篇 |
2014年 | 4895篇 |
2013年 | 7013篇 |
2012年 | 11004篇 |
2011年 | 11841篇 |
2010年 | 6223篇 |
2009年 | 4850篇 |
2008年 | 9117篇 |
2007年 | 9654篇 |
2006年 | 8933篇 |
2005年 | 8901篇 |
2004年 | 7974篇 |
2003年 | 7385篇 |
2002年 | 6845篇 |
2001年 | 4445篇 |
2000年 | 5012篇 |
1999年 | 3934篇 |
1998年 | 851篇 |
1997年 | 648篇 |
1996年 | 545篇 |
1995年 | 485篇 |
1994年 | 386篇 |
1993年 | 311篇 |
1992年 | 1516篇 |
1991年 | 1262篇 |
1990年 | 1136篇 |
1989年 | 940篇 |
1988年 | 826篇 |
1987年 | 757篇 |
1986年 | 759篇 |
1985年 | 653篇 |
1984年 | 466篇 |
1983年 | 395篇 |
1979年 | 440篇 |
1975年 | 304篇 |
1974年 | 390篇 |
1973年 | 390篇 |
1972年 | 335篇 |
1971年 | 365篇 |
1970年 | 326篇 |
1969年 | 351篇 |
1968年 | 311篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Marín N Romero B Bosch-Morell F Llansola M Felipo V Romá J Romero FJ 《Mechanisms of ageing and development》2000,119(1-2):63-67
It is known that beta-amyloid peptide (Abeta) contributes to the neurodegeneration in Alzheimer's disease (AD) and operates through activation of an apoptotic pathway. Apoptotic signal is driven by a family of cysteine proteases called caspases. The beta-amyloid precursor protein (APP) is directly and efficiently cleaved by caspases during apoptosis, resulting in elevated beta-amyloid peptide formation. Cerebellar neurons from rat pups were treated with the aged Abeta(25-35) at 1 and 5 microM and fluorescence assays of caspase activity performed over 4 days. We observed an increase in caspase activity after 48 h treatment in both 1 and 5 microM treated cells, then (72-96 h) caspase activity decreased to control values. The data presented support the hypothesis that Abeta(25-35)-induced apoptosis is mediated by the activation of Caspase-3 and that this is a transient effect. 相似文献
942.
González-Griego M Pentón E Delgado G Pérez-Oliva J Ramos V Izquierdo M García G Levy N Cinza Z Valdivia I Trujillo J Delahanty A 《Investigación clínica》2000,41(4):237-244
The follow-up of HBV markers in selected high infection risk populations, in patients from the hemodialysis and peritoneal dialysis services was used to assess the effectiveness of a special vaccination program. Viral infection markers were studied in prevalence cross sections of the whole population of patients, and also by recording the reports of clinical cases of hepatitis B occurred during that period in those groups of patients. The prevention program consisted of the vaccination of all patients negative to the viral markers and the indication of vaccination for the new cases during the period of the kidney disease, just before the start of the treatment at the hemodialysis unit; besides all the persons susceptible to infection that had already been included in the program, regardless of the stage of the disease. The results show the benefit of the vaccination in these patients, but it is more effective in the period before the treatment with dialysis where there is a lower possibility of being exposed to the virus and the immune system is still competent. Once the program was established, after a follow up o 6 years, there have been no reports of new cases of hepatitis B and the incidence of the disease has been declining. 相似文献
943.
944.
Immunohistochemical classification of non-BRCA1/2 tumors identifies different groups that demonstrate the heterogeneity of BRCAX families. 总被引:1,自引:0,他引:1
Emiliano Honrado Ana Osorio Roger L Milne María F Paz Lorenzo Melchor Alberto Cascón Miguel Urioste Alicia Cazorla Orland Díez Enrique Lerma Manel Esteller José Palacios Javier Benítez 《Modern pathology》2007,20(12):1298-1306
Around 25% of hereditary breast and ovarian cancer families have mutations in the BRCA1 and BRCA2 genes. The search for other genes has until now failed, probably because there is not one single BRCAX gene, but rather various genes that may each be responsible for a small number of breast cancer families and/or may interact according to a polygenic model. We have studied 50 tumors from probands belonging to non-BRCA1/2 breast cancer families (BRCAX), using 25 immunohistochemical markers. The objective was to classify these tumors and confirm that they are heterogeneous. Unsupervised cluster analysis showed the existence of the following two main groups of tumors: high-grade and estrogen receptor (ER)-negative tumors (50%), and low-grade and ER-positive tumors (50%). In addition we identified five subgroups, three among the high-grade and two among the low-grade groups; one overexpressing HER-2 (18%); one with a basal-like phenotype (14%); one with a normal breast-like phenotype (18%); a luminal A subgroup (36%), and a luminal B subgroup (14%). Hypermethylation of the BRCA1 gene was observed in 42% of the cases, spread across all five subgroups, but only 37% of those had loss of heterozygosity as well. These latter cases were all clustered in the high-grade group and the majority of them in the basal-like subgroup. Our results show that familial non-BRCA1/2 tumors are heterogeneous and suggest a polygenic model for explaining the majority of BRCAX families. In addition we have defined a subset of them that have somatic inactivation of the BRCA1 gene. 相似文献
945.
R. Gallego T. García-Caballero A. Beiras M. Fraga J. Forteza 《Virchows Archiv : an international journal of pathology》1995,426(3):317-321
We have analysed the expression of the neural cell adhesion molecule (NCAM) in normal Merkel cells of pig and human skin, and in nine neuroendocrine carcinomas of the skin (Merkel cell carcinomas). NCAM immunoreactivity was observed in virtually all Merkel cells, both in epidermis and vibrissae of pig snout skin and in human epidermis. Immunostaining surrounded the entire surface of Merkel cells and was not restricted to the contact areas between Merkel cells and nerve terminals. All Merkel cell carcinomas studied were also positive for NCAM. The immunostaining pattern of the tumour cells was similar to that observed in normal Merkel cells; the immunoreactivity was confined to the cell membranes. These results suggest that NCAM may be used as an immunohistochemical marker for both Merkel cells and Merkel cell tumours. 相似文献
946.
Lorenzo-Morales J Ortega-Rivas A Foronda P Martínez E Valladares B 《Parasitology research》2005,95(4):273-277
A comprehensive survey to document the presence of free-living amoebae of the genus Acanthamoeba was conducted in tap water and sea water sources related to human environments in Tenerife, Canary Islands, Spain. Acanthamoeba identification was based on the morphology of cyst and trophozoite forms and PCR amplification with a genus-specific primer pair. The pathogenic potential of Acanthamoeba isolates was characterized by temperature and osmotolerance assays and PCR reactions with two primer pairs related to Acanthamoeba pathogenesis. The results demonstrate the presence of potentially pathogenic strains in both sources. Thus, some of the amoebae in these aquatic habitats can act as opportunistic pathogens, could play a role in the diseases of aquatic organisms, and may present a risk to human health. 相似文献
947.
Montes-Rodríguez CJ Alavez S Elder JH Haro R Morán J Prospéro-García O 《Neuroscience letters》2004,360(3):133-136
The human immunodeficiency virus (HIV) induces neuronal death, presumably by apoptosis. This effect may be triggered by the glycoprotein 120 (HIVgp120) released by HIV when infecting a cell, and mediated by tumor necrosis factor alpha (TNF), a pro-inflammatory cytokine. Both molecules, HIVgp120 and TNF, increase sleep when administered acutely in the brain. On the other hand, sleep deprivation increases the levels of several growth factors. In this context, we challenged rats with HIVgp120 or TNF simultaneously with sleep deprivation. Our results indicate that both HIVgp120 and TNF increase neuronal death in the rat cerebral cortex, but not hippocampus, and that this effect is completely prevented by total deprivation of sleep. These results suggest that acute total deprivation of sleep protects against the HIVgp120 and TNF deleterious effects. 相似文献
948.
Franco R Rodríguez R Pasantes-Morales H 《Pflügers Archiv : European journal of physiology》2004,449(2):159-169
Reducing osmolarity by 35% increased 3H-taurine efflux from Swiss 3T3 fibroblasts from 0.5% to a peak of 5.7%. The presence of ATP (10–100 µM; EC50 1.5 µM) increased taurine efflux up to 10%, and decreased the set point for hyposmotically stimulated taurine release (HTR). ATP potentiation was mimicked by UTP, reduced by addition of suramin and pyridoxal phosphate-6-azophenyl-2,4-disulphonic acid (PPADS) and unaffected by ADP, ,-methylene-ATP (,-ATP) or 2-methylthio-ATP (Me-ATP), suggesting its mediation by purinergic P2Y2 and P2Y4 metabotropic receptors. Under isosmotic conditions ATP increased the cytosolic [Ca2+] ([Ca2+]i) markedly, but did not increase taurine release. HTR was independent of external Ca2+ but was reduced (by 56–59%) by BAPTA-AM, thapsigargin-induced depletion of intracellular Ca2+ stores, or phospholipase C (PLC) inhibition. Blockade of calmodulin (CaM) or calmodulin kinase II (CaMKII) reduced HTR by 54% and 76%, respectively. The ATP-mediated potentiation was prevented fully by all these treatments. HTR was reduced by 30–50% by blockers of protein tyrosine kinases (AG18), phosphoinositide 3-kinase (PI3K) (wortmannin), p21rho (toxin B), p21rho-kinase (Y27632) and the stress-activated kinase p38 (PD169316). ATP-mediated potentiation was reduced similarly by these blockers. Simultaneous inhibition of PI3K and CaMKII abolished HTR. Altogether, these results suggest a modulatory effect of ATP, probably exerted by a potentiation of the Ca2+-dependent fraction of HTR. This fraction has as signalling elements a PLC-dependent [Ca2+]i increase, resulting from Ca2+ released from thapsigargin-sensitive internal stores, followed by activation of CaM/CaMKII reactions. The Ca2+/ATP effect operates only when the Ca2+-independent, tyrosine kinase-mediated pathway is already activated. Suggested elements of cross-talk between the two pathways are PLC, PI3K and CaMKII. 相似文献
949.
The medicinal leech is one of the few parasitic invertebrates widely used in medicine and as a scientific model object. Because of a dramatic decline in its natural populations, it is subject to considerable conservation effort. Despite all attention, there is confusion regarding the taxonomic status of different morphological forms. The prevailing view is that all varieties of medicinal leech in Europe represent the same species, Hirudo medicinalis. However, the present study based on RAPD molecular markers demonstrates that a second European taxon, H. verbana, forms a distinct species. Phenetic clustering and principal coordinate analysis of eight populations revealed the same basic structure, reflecting taxonomic rather than geographic subdivision. Variation between species explained 60% of the total molecular variance (CT=0.60, P<0.001). Both taxa displayed a significant number of specific RAPD markers. Conversely, no specific fragment supporting the geographic association of both taxa was found. Since the stronghold of commercially exploited medicinal leech populations in southeastern Europe and Turkey belongs to H. verbana, most medicinal and scientific applications probably use this species, not H. medicinalis. Appropriate taxonomic correction of international conservation conventions and legislation is essential. 相似文献
950.
Marruchella G Di Leonardo M Di Guardo G Romanucci M Marà M G Tiscar P Mosca F Della Salda L 《Journal of comparative pathology》2004,131(1):10-17
Heat shock proteins (HSPs), known to play a key role in cellular homeostasis, may also play a role in the defensive mechanisms of gastric mucosa. By means of appropriate immunohistochemical and immunobiochemical techniques, the expression of HSP27, HSP72 and HSP73 within the epithelium of normal and pre-ulcerative (hyperkeratinized) mucosa of the pars oesophagea of abattoir pigs was assessed. In normal mucosa, HSP72 and HSP73 expression was mainly limited to the basal epithelial cell layer, whereas HSP27 expression was consistently detected within the superficial epithelial cell layers. In hyperkeratinized mucosa, HSP72 and HSP73 immunoreactivity appeared to be more widespread, becoming very intense within epithelial cells affected by hydropic degeneration. Hyperkeratinized mucosa also showed HSP27 immunoreactivity, which was particularly intense in epithelial areas affected by hydropic degeneration. Western blot analysis confirmed HSP27, HSP72 and HSP73 expression in normal and in pre-ulcerative mucosa of the pars oesophagea. Semi-quantitative analysis showed that for all three HSPs the immunoreactivity was more intense in pre-ulcerative mucosa than in normal mucosa. The different expression patterns observed may have functional significance; further studies are needed, however, to define the role of HSPs in swine oesophagogastric lesions, the aetiology and pathogenesis of which are largely unknown. 相似文献