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   49892篇
  免费   3208篇
  国内免费   155篇
耳鼻咽喉   654篇
儿科学   1422篇
妇产科学   860篇
基础医学   5931篇
口腔科学   805篇
临床医学   5065篇
内科学   10718篇
皮肤病学   863篇
神经病学   4653篇
特种医学   2000篇
外国民族医学   1篇
外科学   8723篇
综合类   474篇
一般理论   48篇
预防医学   3135篇
眼科学   881篇
药学   3074篇
中国医学   45篇
肿瘤学   3903篇
  2023年   247篇
  2022年   415篇
  2021年   1084篇
  2020年   625篇
  2019年   1100篇
  2018年   1304篇
  2017年   953篇
  2016年   993篇
  2015年   1173篇
  2014年   1821篇
  2013年   2325篇
  2012年   3750篇
  2011年   3905篇
  2010年   2186篇
  2009年   1872篇
  2008年   3410篇
  2007年   3592篇
  2006年   3572篇
  2005年   3472篇
  2004年   3346篇
  2003年   3107篇
  2002年   2853篇
  2001年   389篇
  2000年   289篇
  1999年   423篇
  1998年   571篇
  1997年   458篇
  1996年   354篇
  1995年   349篇
  1994年   329篇
  1993年   270篇
  1992年   218篇
  1991年   204篇
  1990年   176篇
  1989年   164篇
  1988年   162篇
  1987年   144篇
  1986年   139篇
  1985年   142篇
  1984年   181篇
  1983年   180篇
  1982年   202篇
  1981年   176篇
  1980年   124篇
  1979年   86篇
  1978年   81篇
  1977年   69篇
  1976年   45篇
  1975年   31篇
  1974年   45篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Cytogenetic abnormalities of chromosome 13 (CA 13) and those detected by fluorescence in situ hybridization (FISH 13) have both been associated with poor prognosis in multiple myeloma (MM) patients. The prognostic implications of CA, FISH 13 and other standard laboratory parameters were examined in the first 231 patients enrolled in Total Therapy II, an intensive cytotoxic chemotherapy programme with tandem autotransplants. Three-year projections of event-free survival (EFS) and overall survival (OS) were 71% and 77% respectively. CA 13 was detected in 14% and significantly correlated with FISH 13 (present in 51%), tumour burden, proliferative activity and lactic dehydrogenase (LDH). Both EFS and OS were significantly shorter in patients with CA 13, FISH 13, LDH >or= 190 U/l, beta2 microglobulin >or= 4 mg/l and C reactive protein >or= 4.0 mg/l; other CA was an additional risk factor for OS. Two-thirds of CA 13 patients were identified by FISH 13 and plasma-cell-labelling index (PCLI) >or= 0.4%; however, PCLI failed to identify additional risk groups in FISH subsets. Although present in considerably fewer patients, CA 13 imparted more rapid relapse (61% at 3 years) and death (43% at 3 years) than FISH 13 (38% and 35%; P = 0.02 and 0.1 respectively) and should be part of the initial work-up of patients with MM.  相似文献   
992.
CONTEXT: GH and IGF-I are important regulators of metabolism and body composition. In acromegaly, a state of GH and IGF-I excess, the lipolytic and insulin antagonistic effects of GH may alter adipose tissue (AT) distribution. OBJECTIVES: Our objective was to test the hypothesis that in acromegaly whole-body AT mass is less and to examine for the first time the relationship between GH/IGF-I excess and intermuscular AT (IMAT), an AT depot associated with insulin resistance in other populations. DESIGN, SETTING, AND PATIENTS: We conducted a cross-sectional study in 24 adults with active acromegaly compared with predicted models developed in 315 healthy non-acromegaly subjects. OUTCOME MEASURES: Mass of AT in the visceral AT (VAT), sc AT (SAT), and IMAT compartments from whole-body magnetic resonance imaging and serum levels of GH, IGF-I, insulin, and glucose were measured. RESULTS: VAT and SAT were less in active acromegaly (P < 0.0001); these were 68.2 +/- 27% and 79.5 +/- 15% of predicted values, respectively. By contrast, IMAT was greater (P = 0.0052) by 185.6 +/- 84% of predicted. VAT/trunk AT ratios were inversely related to IGF-I levels (r = 0.544; P = 0.0054). Acromegaly subjects were insulin resistant. CONCLUSIONS: VAT and SAT, most markedly VAT, are less in acromegaly. The proportion of trunk AT that is VAT is less with greater disease activity. IMAT is greater in acromegaly, a novel finding, which suggests that increased AT in muscle could be associated with GH-induced insulin resistance. These findings have implications for understanding the role of GH in body composition and metabolic risk in acromegaly and other clinical settings of GH use.  相似文献   
993.
The effects of 2.0 g of clofibrate and 15, 20 and 30 g of colestipol on plasma lipid and lipoprotein levels were evaluated in adult patients with Type IIa hyperlipoproteinemia. Clofibrate treatment was associated with decreases of 11.0% in plasma cholesterol, 15.2% in LDL cholesterol, 26.1% in triglycerides, and an 11.3% increase in HDL cholesterol. The reductions in total cholesterol with the various doses of colestipol ranged from 11.9 to 17.8% and reductions in LDL cholesterol ranged from 16.1 to 27.3%. Colestipol treatment was not associated with any significant change in HDL cholesterol levels and minor increases in triglycerides. The addition of clofibrate to patients receiving colestipol resulted in a significant increase in HDL cholesterol and a decrease in triglycerides, but no additional reduction in total or LDL cholesterol.  相似文献   
994.
995.
A case of localized filiform polyposis of the colon is presented. This lesion was part of a more generalized inflammatory bowel disease with clinicopathological features indicative of Crohn's disease. An unusual feature of this case was profuse rectal bleeding, initially from a solitary sigmoid ulcer and later from the area of filiform polyposis. A step by step clinicopathological follow-up emphasizing the development of filiform polyps is provided.  相似文献   
996.
Up-regulation of connexin45 in heart failure   总被引:3,自引:0,他引:3  
INTRODUCTION: Heart failure is associated with reduced expression of the major gap junction protein connexin43 (Cx43), which may contribute to arrhythmias and sudden cardiac death in this patient population. Other cardiac connexins may be altered as well. Because connexin45 (Cx45) has been shown to colocalize with Cx43, we determined whether the number, size, or distribution of Cx45 gap junctions is altered in the failing heart. METHODS AND RESULTS: Cx45 expression levels were measured by immunoblotting and quantitative immunostaining in failing and control human left ventricles. Total Cx45 protein was significantly (P = 0.021) up-regulated 1.8-fold in failing hearts. Cx45 immunohistochemical signal was increased by 80% (P = 0.005) due to a 3.5-fold increase in the number of gap junctions containing Cx45. Cx45 mRNA was not altered in failing hearts, suggesting reduced degradation of Cx45 protein in the failing heart. Cx43 signal, on the other hand, was reduced by 49% in failing hearts. Double-label experiments demonstrated colocalization of Cx45 and Cx43 in the same gap junctions. CONCLUSION: Cx45 is markedly enhanced in the failing heart. Up-regulation of Cx45 in conjunction with down-regulation of Cx43 could result in abnormal impulse propagation and generation of ventricular arrhythmias, thereby predisposing patients in heart failure to sudden cardiac death.  相似文献   
997.
The Mars Organic Analyzer (MOA), a microfabricated capillary electrophoresis (CE) instrument for sensitive amino acid biomarker analysis, has been developed and evaluated. The microdevice consists of a four-wafer sandwich combining glass CE separation channels, microfabricated pneumatic membrane valves and pumps, and a nanoliter fluidic network. The portable MOA instrument integrates high voltage CE power supplies, pneumatic controls, and fluorescence detection optics necessary for field operation. The amino acid concentration sensitivities range from micromolar to 0.1 nM, corresponding to part-per-trillion sensitivity. The MOA was first used in the lab to analyze soil extracts from the Atacama Desert, Chile, detecting amino acids ranging from 10-600 parts per billion. Field tests of the MOA in the Panoche Valley, CA, successfully detected amino acids at 70 parts per trillion to 100 parts per billion in jarosite, a sulfate-rich mineral associated with liquid water that was recently detected on Mars. These results demonstrate the feasibility of using the MOA to perform sensitive in situ amino acid biomarker analysis on soil samples representative of a Mars-like environment.  相似文献   
998.
This paper identifies various kinds of risk and uncertainty observable in rural areas of developing countries and explains the relative importance of those pertaining to disability and old age. It compares the modern system (based on old age pensions and social security) for mitigating or coping with these risks with the traditional intrafamilial support mechanisms. The paper concludes that, when the traditional system is functioning smoothly, it can address these needs at far lower cost than the modern system. The efficiency and viability of the traditional system can be considerably enhanced by the presence of social norms, on the one hand, and of strategic instruments in the hands of household heads, on the other. Since both of these defenses are often undermined prematurely by modernizing influences, the paper identifies possible actions for avoiding or postponing the effects of such influences.The author expresses his appreciation to Richard Anker, Mussadegh Chowdhury, Richard Easterlin, Jeremy Evans and one of the editors for useful comments and suggestions and to the US Agency for International Development for financial support for some earlier research upon which this paper is partially based.  相似文献   
999.
Study objective: We sought to characterize the ECG changes associated with symptomatic β-blocker overdose. Methods: The study population consisted of a prospective cohort of patients reporting to 2 regional poison centers with β-blocker overdose. Each patient received an ECG on presentation and a structured follow-up. The inclusion criteria for symptomatic overdose included heart rate of less than 60 beats/min or systolic blood pressure of less than 90 mm Hg; symptoms consistent with decreased end-organ perfusion; therapeutic intervention with cardioactive medication; and corroboration by 2 of the authors that this was a clear-cut case of symptomatic β-blocker overdose with cardiovascular toxicity. Exclusion criteria included cardioactive coingestants, age younger than 6 years, and no available ECG. Results: Of 167 patients, 13 were determined to have symptomatic exposures. First-degree heart block (>200 ms) was the most common ECG finding (10/12) and also had the greatest likelihood ratio (5.31) when comparing those with symptomatic exposures with those with asymptomatic exposures. Comparing the asymptomatic with the symptomatic groups, the mean PR interval was 167 ms (95% confidence interval [CI] 162 to 171 ms) versus 216 ms (95% CI 193 to 238 ms), the mean QRS interval was 89 ms (95% CI 87 to 91 ms) versus 112 ms (95% CI 92 to 132 ms), the mean QTc interval was 422 ms (95% CI 417 to 428) versus 462 ms (95% CI 434 to 490 ms), and the mean heart rate was 72 beats/min (95% CI 69 to 74 beats/min) versus 66 beats/min (95% CI 59 to 73 beats/min). Two cases of symptomatic acebutolol exposure appeared unique by demonstrating disproportionate prolongation of the QTc interval, an RaVR height of 3 mm or greater, and associated ventricular tachydysrhythmia. Conclusion: The majority of clinically significant β-blocker intoxications demonstrate negative dromotropic effects on ECG. Several ECG differences in acebutolol intoxication might reflect unique pathophysiologic processes relative to other β-blockers. [Ann Emerg Med. 2002;40:603-610.]  相似文献   
1000.
Caspase-12 is a dominant-negative regulator of caspase-1 (IL-1beta-converting enzyme) and an attenuator of cytokine responsiveness to septic infections. This molecular role for caspase-12 appears to be akin to the role of cFLIP in regulating caspase-8 in the extrinsic cell death pathway; however, unlike cFLIP/Usurpin, we demonstrate here that caspase-12 is catalytically competent. To examine these catalytic properties, rat caspase-12 was cloned, and the recombinant enzyme was used to examine the cleavage of macromolecular and synthetic fluorogenic substrates. Although caspase-12 could mediate autoproteolytic maturation of its own proenzyme, in both cis and trans, it was not able to cleave any other polypeptide substrate, including other caspase proenzymes, apoptotic substrates, cytokine precursors, or proteins in the endoplasmic reticulum that normally undergo caspase-mediated proteolysis. The dearth of potential substrates for caspase-12 also was confirmed by whole-cell diagonal-gel analysis. Autolytic cleavage within the caspase-12 proenzyme was mapped to a single site at the large-small subunit junction, ATAD(319), and this motif was recognized by caspase-12 when incorporated into synthetic fluorogenic substrates. The specific activity of caspase-12 with these substates was several orders of magnitude lower than caspases-1 and -3, highlighting its relative catalytic paucity. In intact cells, caspase-12 autoproteolysis occurred in the inhibitory complex containing caspase-1. We propose that the proteolytic activity of caspase-12 is confined to its own proenzyme and that autocleavage within the caspase-1 complex may be a means for temporal limitation of the inhibitory effects of caspase-12 on proinflammatory cytokine maturation.  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