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   4124篇
  免费   366篇
  国内免费   9篇
耳鼻咽喉   50篇
儿科学   138篇
妇产科学   96篇
基础医学   561篇
口腔科学   165篇
临床医学   514篇
内科学   856篇
皮肤病学   65篇
神经病学   250篇
特种医学   500篇
外国民族医学   1篇
外科学   465篇
综合类   94篇
预防医学   341篇
眼科学   28篇
药学   237篇
  1篇
中国医学   6篇
肿瘤学   131篇
  2022年   27篇
  2021年   48篇
  2019年   50篇
  2018年   44篇
  2017年   38篇
  2016年   46篇
  2015年   74篇
  2014年   99篇
  2013年   164篇
  2012年   133篇
  2011年   142篇
  2010年   92篇
  2009年   108篇
  2008年   158篇
  2007年   154篇
  2006年   138篇
  2005年   148篇
  2004年   127篇
  2003年   121篇
  2002年   105篇
  2001年   120篇
  2000年   121篇
  1999年   90篇
  1998年   109篇
  1997年   104篇
  1996年   112篇
  1995年   97篇
  1994年   71篇
  1993年   83篇
  1992年   81篇
  1991年   81篇
  1990年   89篇
  1989年   130篇
  1988年   107篇
  1987年   94篇
  1986年   98篇
  1985年   114篇
  1984年   74篇
  1983年   61篇
  1982年   52篇
  1981年   48篇
  1980年   52篇
  1979年   45篇
  1978年   46篇
  1977年   44篇
  1976年   39篇
  1975年   36篇
  1972年   24篇
  1971年   26篇
  1968年   24篇
排序方式: 共有4499条查询结果,搜索用时 15 毫秒
991.
Farge D  Nash R  Laar JM 《Autoimmunity》2008,41(8):616-624
Systemic sclerosis (SSc) is a generalised autoimmune disease, of yet unknown origin, with two major clinical subsets: the limited (lcSSc) and the diffuse cutaneous (dcSSc) forms, which can be distinguished by the extent of skin involvement, the autoantibody profile and the pattern of organ involvement. With an incidence of 1/10(5), SSc affects around 250,000 people in Europe and is responsible for significant morbidity with a 5-year mortality rate of at least 30% of all patients. In patients with rapidly progressive dcSSc, the 5-year mortality is estimated to be 40-50%. Hematopoietic stem cell transplantation (HSCT), mostly autologous but also allogeneic in some specific cases, has been employed worldwide since 1996 as a new therapeutic strategy in patients with a poor prognosis. In 2007, 150 HSCT procedures have been reported in the EBMT data base. We review herein both the short and the long-term reports from the various European and North American phase I-II studies, which have shown that autologous HSCT in selected patients with severe dcSSc results in sustained improvement of skin thickening and stabilisation of organ function up to seven years after transplantation. Based on these promising results, ongoing phase III trials have been designed in parallel, both in Europe (ASTIS) and in North America (SCOTT) aiming to analyse the respective benefits from autologous HSCT respectively without or with high dose irradiation. This review reports the current data concerning the effects of HSCT on survival, skin, and major organ function in patients with severe dcSSc.  相似文献   
992.
Low temperature can be expected to increase the resistance to deformation of red blood cells, but the effect of such changes on microcirculatory perfusion are unknown. We therefore analysed resistance to flow through capillary-sized apertures for individual human red blood cells, by micropipette aspiration (approximately 3 μm aperture) and pore transit analysis (approximately 5 μm), as well as average resistance to flow of red cell suspension through multipore filters (5-μm pores). Over a range decreasing from 37 to 0 °C, rates of flow of single cells through the 3- and 5-μm apertures decreased monotonically by 2.5- to 3-fold. The changes were similar in magnitude to that expected for the viscosity of aqueous fluid (2.5-fold increase). Average flow resistance measured by bulk filtration also increased in line with viscosity of water, while tendency to block pores was not increased. Micropipette aspiration of small membrane tongues showed that membrane rigidity increased as temperature was lowered, but by a factor rather less than the viscosity. Cell volume also responded rapidly to change in temperature, with lower temperature being associated with swelling, although this effect was much reduced in plasma compared with saline buffer. We conclude that, although increased resistance to deformation of red cells may impair microcirculation at low temperature, there is no structural change likely to induce more dramatic occlusion of flow. Moreover, the effect is comparable in magnitude to the increase predicted for changes in plasma and blood viscosity. Received: 8 December 1995/Received after revision: 18 March 1996/Accepted: 22 May 1996  相似文献   
993.
994.
To navigate into and within tissues, leukocytes require guidance cues that enable them to recognize which tissues to enter and which to avoid. Such cues are partly provided at the time of extravasation from blood by an endothelial address code on the luminal surface of the vascular endothelium. Here, we review the evidence that fibroblasts help define an additional stromal address code that directs leukocyte behaviour within tissues. We examine how this stromal code regulates site-specific leukocyte accumulation, differentiation and survival in a variety of physiological stromal niches, and how the aberrant expression of components of this code in the wrong tissue at the wrong time contributes to the persistence of chronic inflammatory diseases.  相似文献   
995.
Antineutrophil cytoplasm antibodies (ANCA) activate neutrophils to undergo a series of coordinated interactions, leading to transendothelial migration, eventually culminating in vascular destruction. The molecular events underlying neutrophil recruitment in ANCA-associated vasculitis need to be defined to enable effective therapeutic manipulation. A flow-based adhesion assay was used to investigate the role of beta2 integrins (CD11a/CD18 and CD11b/CD18) and chemokine receptors [CXC chemokine receptor (CXCR)1 and CXCR2] in neutrophil migration through the endothelium. Two endothelial models were used: a highly activated model stimulated with 100 U/ml tumor necrosis factor alpha (TNF-alpha) and a minimally activated model stimulated with 2 U/ml TNF-alpha and in which ANCA was present as a secondary neutrophil stimulus. CD11a/CD18, CD11b/CD18, and CXCR2 contributed to adhesion and transendothelial migration in both models. However, when the endothelium was minimally activated with TNF-alpha, CD11b/CD18 played an important role in stabilizing adhesion induced by ANCA immunoglobulin G (IgG). Analysis of beta2 integrins and chemokine receptors demonstrated that ANCA IgG had no effect on expression levels at the neutrophil surface but enabled an active conformational change of CD11b/CD18. Similar molecular mechanisms control neutrophil adhesion and migration through highly or minimally TNF-alpha-activated endothelium. However, the direct ANCA-mediated neutrophil stimulation is needed to drive migration through minimally activated endothelium, and CD11b/CD18 is recruited for greater stability of adhesion during this process and can undergo an activatory, conformational change in response to ANCA IgG.  相似文献   
996.
In defining the genetic profiles in cancer, cytogenetically aberrant cell lines derived from primary tumors are important tools for the study of carcinogenesis. Here, we present the results of a comprehensive investigation of 15 established colorectal cancer cell lines using spectral karyotyping (SKY), fluorescence in situ hybridization, and comparative genomic hybridization (CGH). Detailed karyotypic analysis by SKY on five of the lines (P53HCT116, T84, NCI‐H508, NCI‐H716, and SK‐CO‐1) is described here for the first time. The five lines with karyotypes in the diploid range and that are characterized by defects in DNA mismatch repair had a mean of 4.8 chromosomal abnormalities per line, whereas the 10 aneuploid lines exhibited complex karyotypes and a mean of 30 chromosomal abnormalities. Of the 150 clonal translocations, only eight were balanced and none were recurrent among the lines. We also reviewed the karyotypes of 345 cases of adenocarcinoma of the large intestine listed in the Mitelman Database of Chromosome Aberrations in Cancer. The types of abnormalities observed in the cell lines reflected those seen in primary tumors: there were no recurrent translocations in either tumors or cell lines; isochromosomes were the most common recurrent abnormalities; and breakpoints occurred most frequently at the centromeric/pericentromeric and telomere regions. Of the genomic imbalances detected by array CGH, 87% correlated with chromosome aberrations observed in the SKY studies. The fact that chromosome abnormalities predominantly result in copy number changes rather than specific chromosome or gene fusions suggests that this may be the major mechanism leading to carcinogenesis in colorectal cancer. Published 2009 Wiley‐Liss, Inc.  相似文献   
997.
998.
Nash P  Eriksson UJ 《Placenta》2007,28(5-6):505-515
Previously maternal and fetal alterations resembling human pre-eclampsia were induced in pregnant rats by injections of the angiogenesis inhibitor Suramin. These alterations were aggravated by maternal diabetes and partly rectified by vitamin E supplementation. In the present study we evaluated the morphology of placentae and kidneys in this model. Non-diabetic and streptozotocin-induced diabetic pregnant rats of two rat strains (U and H) were treated with Suramin or saline, and given standard or vitamin E-enriched food. On gestational day 20 one placenta and the left kidney of the mother were collected for morphological and stereological analysis. In the placental trophospongium Suramin treatment caused cysts, which were further enhanced by maternal diabetes. Vitamin E treatment had no effect on the vacuolization. In the placental labyrinth of the non-diabetic rats Suramin treatment restricted maternal placental blood volume and increased the interface between maternal and fetal circulation. These changes were reversed by vitamin E treatment. Diabetes increased slightly the interface between the circulations in both rat strains. Suramin treatment decreased the interface, and vitamin E further decreased the interface in the diabetic U rats, whereas neither treatment affected the maternal-fetal interface in the diabetic H rats. The kidneys of Suramin-treated and diabetic rats were heavier compared to controls. Suramin treatment and maternal diabetes damaged renal glomeruli to a similar extent. Vitamin E treatment diminished the Suramin- and diabetes-induced glomerular damage in U rats, but not in H rats. The average cell count per glomerulus was decreased by Suramin in the U rats. Vitamin E treatment did not affect cell number per glomerulus in any group. We conclude that Suramin-injected pregnant rats constitute a valid animal model for placental dysfunction and pre-eclampsia, also from the histological perspective. The present work supports the notion that one important effect of untreated maternal diabetes may be impaired placentation, leading to oxidative stress, morphological damage, and compromised placental function.  相似文献   
999.
Background: A limited range of evidence suggests that children with specific language impairment (SLI) have difficulties with higher order thinking and reasoning skills (executive functioning, EF). This study involved a comprehensive investigation of EF in this population taking into account the contributions of age, nonverbal IQ and verbal ability. Methods: Ten separate measures of EF were assessed in 160 children: 41 had SLI; 31 had low language/cognitive functioning but did not fulfil the criteria for SLI (low language functioning or LLF); and 88 were typically developing with no language difficulties. Group differences in performance were assessed after controlling for age, nonverbal IQ and verbal ability in a series of regression analyses. Results: Children with SLI and LLF had significantly lower performance than typical children on 6 of the 10 EF tasks once age and nonverbal IQ had been controlled (verbal and nonverbal executive‐loaded working memory, verbal and nonverbal fluency, nonverbal inhibition and nonverbal planning). Performance on these EF tasks remained lower for those in the SLI group even when verbal IQ was entered in the regressions. Conclusions: Children with language impairments showed marked difficulties on a range of EF tasks. These difficulties were present even when adjustments were made for their verbal abilities.  相似文献   
1000.
OBJECTIVE: To estimate whether alterations in plasma levels of the proangiogenic proteins placental growth factor (PlGF) and vascular endothelial growth factor-A (VEGF-A), and the antiangiogenic protein soluble fms-like tyrosine kinase-1 (sFlt1) were more pronounced in early-onset than in late-onset preeclampsia. METHODS: A cross-sectional study was conducted to estimate the levels of sFlt1, PlGF, and VEGF-A in plasma in a control group of nonpregnant women, in an early control group of women at 24-32 weeks of gestation, in a late control group of women at 36-42 weeks of gestation, and in cases of women with early-onset (before 32 weeks of gestation) and late-onset (after 35 weeks of gestation) preeclampsia. RESULTS: Women with early-onset preeclampsia had a 43 times higher median plasma sFlt1 level than early controls (P<.001). Women with late-onset preeclampsia had a three times higher median plasma sFlt1 level than late controls (P<.001). Women with early-onset preeclampsia had a 21 times lower median plasma PlGF level than early controls (P<.001). Women with late-onset preeclampsia had a five times lower median plasma PlGF level than late controls (P=.01). The median level of VEGF-A in plasma was less than 15 pg/mL in all groups of pregnant women. CONCLUSION: Both early- and late-onset preeclampsia are associated with altered plasma levels of sFlt1 and PlGF. The alterations are more pronounced in early-onset rather than in late-onset disease.  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