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   1909篇
  免费   103篇
  国内免费   2篇
耳鼻咽喉   43篇
儿科学   117篇
妇产科学   302篇
基础医学   221篇
口腔科学   31篇
临床医学   145篇
内科学   393篇
皮肤病学   20篇
神经病学   151篇
特种医学   48篇
外科学   215篇
综合类   8篇
一般理论   3篇
预防医学   103篇
眼科学   55篇
药学   81篇
肿瘤学   78篇
  2024年   4篇
  2023年   15篇
  2022年   21篇
  2021年   51篇
  2020年   41篇
  2019年   64篇
  2018年   60篇
  2017年   47篇
  2016年   68篇
  2015年   59篇
  2014年   90篇
  2013年   105篇
  2012年   153篇
  2011年   150篇
  2010年   85篇
  2009年   65篇
  2008年   128篇
  2007年   121篇
  2006年   146篇
  2005年   109篇
  2004年   116篇
  2003年   72篇
  2002年   81篇
  2001年   14篇
  2000年   11篇
  1999年   9篇
  1998年   11篇
  1997年   7篇
  1996年   9篇
  1995年   4篇
  1994年   6篇
  1993年   7篇
  1992年   3篇
  1991年   6篇
  1990年   5篇
  1989年   3篇
  1988年   8篇
  1987年   4篇
  1986年   4篇
  1985年   10篇
  1984年   8篇
  1983年   4篇
  1982年   2篇
  1981年   6篇
  1976年   3篇
  1975年   3篇
  1974年   3篇
  1972年   3篇
  1970年   2篇
  1967年   3篇
排序方式: 共有2014条查询结果,搜索用时 15 毫秒
81.
82.
83.
In order to reduce the readability level of the Hebrew version of the DACL, a new list of words with high frequency of useage in the Hebrew language was created from the translations of E, F, and G. Ninety-four Ss completed the revised form and the translated standard form E in randomized order; the correlation was 0.90 ( p <0.001). Split-half reliability for the revised form was 0.83 (N = 1,230, p <0.001). The revised DACL was included in a national probability sample survey (N = 1253; 699 femalea and 544 males). T score and percentile norm distributions are skewed toward the left. Raw scores above 20 are rare above 20 are rare.  相似文献   
84.
Endothelin-1 (ET-1) and nitric oxide (NO) play pivotal roles in corpus luteum (CL) function. The present study examined the interplay between NO and ET-1 synthesis in the bovine CL. We found similar inducible and endothelial NO synthase (iNOS and eNOS, respectively) activities in the young CL (d 1-5) expressing the highest levels of both eNOS and iNOS mRNA. These values later declined at mid-cycle (d 8-15) and remained low at later stages (d 16-18). Luteolysis, initiated by prostaglandin F2alpha analog administration, further reduced NOS mRNA and by 24 h, NOS values dropped to approximately 15% of those at mid-cycle. eNOS protein levels followed a similar pattern to its mRNA. Because endothelial cells (ECs) are the main site for ET-1 and NO production in the CL, we examined the direct effects of the NO donor, NONOate on luteal ECs (LECs). Elevated NO levels markedly decreased ET-1 mRNA, and peptide concentrations in cultured and freshly isolated LECs in a dose-dependent manner. In agreement, NOS inhibitor, NG-nitro-l-arginine methyl ester, stimulated ET-1 mRNA expression in these cells. Interestingly, NO also up-regulated prostaglandin F2alpha receptors in LECs. These data show that there is an inverse relationship between NOS and ET-1 throughout the CL life span, and imply that this pattern may be the result of their interaction within the resident LECs. NOS are expressed in a physiologically relevant manner: elevated NO at an early luteal stage is likely to play an important role in angiogenesis, whereas reduced levels of NO during luteal regression may facilitate the sustained up-regulation of ET-1 levels during luteolysis.  相似文献   
85.
86.
BackgroundPET myocardial perfusion imaging (MPI) holds several advantages over SPECT for diagnosing coronary artery disease. The short half-lives of prevailing PET-MPI agents hamper wider clinical application of PET in nuclear cardiology; prompting the development of novel PET-MPI agents. We have previously reported on the potential of radiolabeled ammonium salts, and particularly on that of [11C]dimethyl-diphenyl-ammonium ([11C]DMDPA), for cardiac PET imaging. This study was designed to improve the radiosynthesis and increase the yield of [11C]DMDPA, characterize more meticulously the kinetics of radioactivity distribution after its injection via micro-PET/CT studies, and further explore its potential for PET-MPI.MethodsThe radiosynthetic procedure of [11C]DMDPA was improved with respect to the previously reported one. The kinetics of radioactivity distribution following injection of [11C]DMDPA were investigated in juvenile and young adult male SD rats using microPET/CT, and compared to those of [13N]NH3. Furthermore, the metabolic fate of [11C]DMDPA in vivo was examined after its injection into rats.ResultsFollowing a radiosynthesis time of 25–27 min, 11.9 ± 1.1 GBq of [11C]DMDPA was obtained, with a 43.7% ± 4.3% radiochemical yield (n = 7). Time activity curves calculated after administration of [11C]DMDPA indicated rapid, high and sustained radioactivity uptake in hearts of both juvenile and young adult rats, having a two-fold higher cardiac radioactivity uptake compared to [13N]NH3. Accordingly, at all time points after injection to both juvenile and young adult rats, image quality of the left ventricle was higher with [11C]DMDPA compared to [13N]NH3. In vivo stability studies of [11C]DMDPA indicate that no radioactive metabolites could be detected in plasma, liver and urine samples of rats up to 20 min after injection, suggesting that [11C]DMDPA is metabolically stable in vivo.ConclusionsThis study further illustrates that [11C]DMDPA holds, at least in part, essential qualities required from a PET-MPI probe. Owing to the improved radiosynthetic procedure reported herein, [11C]DMDPA can be produced in sufficient amounts for clinical use.  相似文献   
87.
Free fatty acids,insulin resistance,and pregnancy   总被引:15,自引:0,他引:15  
Acute elevation of plasma free fatty acid (FFA) levels causes insulin resistance to rise dose dependently in pregnant and nonpregnant women. Plasma FFA levels are commonly elevated during late pregnancy, partly due to rising blood levels of lipolytic placental hormones, and are a likely cause for much of the increase in insulin resistance occurring at that time in all pregnant women. Plasma FFA levels are similar or higher and the insulin resistance is comparable or more severe in women with gestational diabetes mellitus (GDM) than in nondiabetic pregnant women. In contrast to healthy pregnant women, insulin secretion in women with GDM is defective and, therefore, is unable to rise adequately to compensate for the insulin resistance; the result is hyperglycemia. The mechanism by which elevated plasma FFA levels cause insulin resistance in skeletal muscle includes intramyocellular accumulation of diacylglycerol, which activates protein kinase C (the β II and δ isoforms). This results in reduction of tyrosine phosphorylation of the insulin receptor substrate-1 and inhibits activation of phosphoinositol-3 kinase, an enzyme that is essential for normal insulin-stimulated glucose uptake.  相似文献   
88.
BACKGROUND & AIMS: We tested whether the attenuation of experimental colitis by live probiotic bacteria is due to their immunostimulatory DNA, whether toll-like receptor (TLR) signaling is required, and whether nonviable probiotics are effective. METHODS: Methylated and unmethylated genomic DNA isolated from probiotics (VSL-3), DNAse-treated probiotics and Escherichia coli (DH5 alpha) genomic DNA were administered intragastrically (i.g.) or subcutaneously (s.c.) to mice prior to the induction of colitis. Viable or gamma-irradiated probiotics were administered i.g. to wild-type mice and mice deficient in different TLR or in the adaptor protein MyD88, 10 days prior to administration of dextran sodium sulfate (DSS) to their drinking water and for 7 days thereafter. RESULTS: Intragastric and s.c. administration of probiotic and E. coli DNA ameliorated the severity of DSS-induced colitis, whereas methylated probiotic DNA, calf thymus DNA, and DNase-treated probiotics had no effect. The colitis severity was attenuated to the same extent by i.g. delivery of nonviable gamma-irradiated or viable probiotics. Mice deficient in MyD88 did not respond to gamma-irradiated probiotics. The severity of DSS-induced colitis in TLR2 and TLR4 deficient mice was significantly decreased by i.g. administration of gamma-irradiated probiotics, whereas, in TLR9-deficient mice, gamma-irradiated probiotics had no effect. CONCLUSIONS: The protective effects of probiotics are mediated by their own DNA rather than by their metabolites or ability to colonize the colon. TLR9 signaling is essential in mediating the anti-inflammatory effect of probiotics, and live microorganisms are not required to attenuate experimental colitis because nonviable probiotics are equally effective.  相似文献   
89.
Heart failure causes significant morbidity and mortality. Distinguishing risk factors for incident heart failure can help identify at-risk individuals. Orthostatic hypotension may be a risk factor for incident heart failure; however, this association has not been fully explored, especially in nonwhite populations. The Atherosclerosis Risk in Communities Study included 12363 adults free of prevalent heart failure with baseline orthostatic measurements. Orthostatic hypotension was defined as a decrease of systolic blood pressure ≥20 mmHg or diastolic blood pressure ≥10 mmHg with position change from supine to standing. Incident heart failure was identified from hospitalization or death certificate disease codes. Over 17.5 years of follow-up, orthostatic hypotension was associated with incident heart failure with multivariable adjustment (hazard ratio: 1.54 [95% CI: 1.30-1.82]). This association was similar across race and sex groups. A stronger association was identified in younger individuals ≤55 years old (hazard ratio: 1.90 [95% CI: 1.41-2.55]) than in older individuals >55 years old (hazard ratio: 1.37 [95% CI: 1.12-1.69]; interaction P=0.034). The association between orthostatic hypotension and incident heart failure persisted with exclusion of those with diabetes mellitus, coronary heart disease, and those on antihypertensives or psychiatric or Parkinson disease medications. However, exclusion of those with hypertension somewhat attenuated the association (hazard ratio: 1.34 [95% CI: 1.00-1.80]). We identified orthostatic hypotension as a predictor of incident heart failure among middle-aged individuals, particularly those 45 to 55 years of age. This association may be partially mediated through hypertension. Orthostatic measures may enhance risk stratification for future heart failure development.  相似文献   
90.
Objective:There is strong evidence supporting internet-delivered cognitive behaviour therapy (iCBT) and consequently growing demand for iCBT in Canada. Transdiagnostic iCBT that addresses both depression and anxiety is particularly promising as it represents an efficient method of delivering iCBT in routine care. The Online Therapy Unit, funded by the Saskatchewan government, has been offering transdiagnostic iCBT for depression and anxiety since 2013. In this article, to broadly inform implementation efforts, we examined trends in utilization, patient characteristics, and longitudinal improvements for patients receiving transdiagnostic iCBT over 6 years.Methods:Patients who completed telephone screening between November 2013 and December 2019 were included in this observational study. Patients provided demographics and mental health history at screening and completed measures at pre-treatment, post-treatment and at 3- to 4-month follow-up. Treatment engagement and satisfaction were assessed.Results:A total of 5,321 telephone screenings were completed and 4,283 of patients were accepted for treatment over the 6-year period (80.5% acceptance). The most common reason for referral to another service was high suicide risk/severe symptoms (47.1%). Examination of trends showed growing use of transdiagnostic iCBT over time (37% increase per year). There was remarkable stability in patient characteristics across years. Most patients were concurrently using medication (57.3%) with 11.9% reporting using iCBT while on a waiting list for face-to-face treatment highlighting the importance of integrating iCBT with other services. Consistent across years, large improvements in depression and anxiety symptoms were found and maintained at 3- to 4-month follow-up. There was strong patient engagement with iCBT and positive ratings of treatment experiences.Conclusions:As there is growing interest in iCBT in Canada, this large observational study provides valuable information for those implementing iCBT in terms of likely user characteristics, patterns of use, and improvements. This information has potential to assist with resource allocation and planning in Canada and elsewhere.  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