全文获取类型
收费全文 | 1031篇 |
免费 | 43篇 |
国内免费 | 72篇 |
专业分类
1146篇 |
出版年
2022年 | 11篇 |
2021年 | 21篇 |
2020年 | 5篇 |
2018年 | 5篇 |
2017年 | 10篇 |
2016年 | 29篇 |
2015年 | 69篇 |
2014年 | 46篇 |
2013年 | 47篇 |
2012年 | 86篇 |
2011年 | 140篇 |
2010年 | 94篇 |
2009年 | 32篇 |
2008年 | 32篇 |
2007年 | 35篇 |
2006年 | 15篇 |
2005年 | 68篇 |
2004年 | 69篇 |
2003年 | 39篇 |
2002年 | 22篇 |
2001年 | 30篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 37篇 |
1992年 | 19篇 |
1991年 | 6篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1957年 | 6篇 |
1955年 | 4篇 |
1954年 | 2篇 |
1948年 | 1篇 |
1943年 | 2篇 |
1941年 | 1篇 |
1925年 | 1篇 |
1924年 | 1篇 |
1923年 | 3篇 |
1917年 | 1篇 |
1904年 | 1篇 |
排序方式: 共有1146条查询结果,搜索用时 15 毫秒
961.
Tracey L. Weissgerber Robin E. Gandley Paula L. McGee Catherine Y. Spong Leslie Myatt Kenneth J. Leveno John M. Thorp Jr Brian M. Mercer Alan M. Peaceman Susan M. Ramin Marshall W. Carpenter Philip Samuels Anthony Sciscione Margaret Harper Jorge E. Tolosa George Saade Yoram Sorokin for the Eunice Kennedy Shriver National Institute of Child Health Human Development Maternal-Fetal Medicine Units Network 《PloS one》2013,8(4)
Haptoglobin’s (Hp) antioxidant and pro-angiogenic properties differ between the 1-1, 2-1, and 2-2 phenotypes. Hp phenotype affects cardiovascular disease risk and treatment response to antioxidant vitamins in some non-pregnant populations. We previously demonstrated that preeclampsia risk was doubled in white Hp 2-1 women, compared to Hp 1-1 women. Our objectives were to determine whether we could reproduce this finding in a larger cohort, and to determine whether Hp phenotype influences lack of efficacy of antioxidant vitamins in preventing preeclampsia and serious complications of pregnancy-associated hypertension (PAH). This is a secondary analysis of a randomized controlled trial in which 10,154 low-risk women received daily vitamin C and E, or placebo, from 9-16 weeks gestation until delivery. Hp phenotype was determined in the study prediction cohort (n = 2,393) and a case-control cohort (703 cases, 1,406 controls). The primary outcome was severe PAH, or mild or severe PAH with elevated liver enzymes, elevated serum creatinine, thrombocytopenia, eclampsia, fetal growth restriction, medically indicated preterm birth or perinatal death. Preeclampsia was a secondary outcome. Odds ratios were estimated by logistic regression. Sampling weights were used to reduce bias from an overrepresentation of women with preeclampsia or the primary outcome. There was no relationship between Hp phenotype and the primary outcome or preeclampsia in Hispanic, white/other or black women. Vitamin supplementation did not reduce the risk of the primary outcome or preeclampsia in women of any phenotype. Supplementation increased preeclampsia risk (odds ratio 3.30; 95% confidence interval 1.61–6.82, p<0.01) in Hispanic Hp 2-2 women. Hp phenotype does not influence preeclampsia risk, or identify a subset of women who may benefit from vitamin C and E supplementation to prevent preeclampsia. 相似文献
962.
963.
Diana Espadinha Nuno A. Faria Maria Miragaia Luís Marques Lito José Melo-Cristino Hermínia de Lencastre Médicos Sentinela Network 《PloS one》2013,8(4)
According to the EARS-Net surveillance data, Portugal has the highest prevalence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) in Europe, but the information on MRSA in the community is very scarce and the links between the hospital and community are not known. In this study we aimed to understand the events associated to the recent sharp increase in MRSA frequency in Portugal and to evaluate how this has shaped MRSA epidemiology in the community. With this purpose, 180 nosocomial MRSA isolates recovered from infection in two time periods and 14 MRSA isolates recovered from 89 samples of skin and soft tissue infections (SSTI) were analyzed by pulsed-field gel electrophoresis (PFGE), staphylococcal chromosome cassette mec (SCCmec) typing, spa typing and multilocus sequence typing (MLST). All isolates were also screened for the presence of Panton Valentine leukocidin (PVL) and arginine catabolic mobile element (ACME) by PCR. The results showed that ST22-IVh, accounting for 72% of the nosocomial isolates, was the major clone circulating in the hospital in 2010, having replaced two previous dominant clones in 1993, the Iberian (ST247-I) and Portuguese (ST239-III variant) clones. Moreover in 2010, three clones belonging to CC5 (ST105-II, ST125-IVc and ST5-IVc) accounted for 20% of the isolates and may represent the beginning of new waves of MRSA in this hospital. Interestingly, more than half of the MRSA isolates (8/14) causing SSTI in people attending healthcare centers in Portugal belonged to the most predominant clones found in the hospital, namely ST22-IVh (n = 4), ST5-IVc (n = 2) and ST105-II (n = 1). Other clones found included ST5-V (n = 6) and ST8-VI (n = 1). None of the MRSA isolates carried PVL and only five isolates (ST5-V-t179) carried ACME type II. The emergence and spread of EMRSA-15 may be associated to the observed increase in MRSA frequency in the hospital and the consequent spillover of MRSA into the community. 相似文献
964.
狭翅雏蝗Chorthippus dubius是我国北方草原的重要蝗种之一,在大发生年对牧草的威胁很大。它对牧草的损失至今尚无较准确的定量估算。本文通过测定不同发育阶段狭翅雏蝗的取食率、掉落毁损率,结合野外自然种群数据,对内蒙古草原三种植物群落中狭翅雏蝗造成的牧草损失进行了估测,并对三种草场蝗虫的经济阈值进行了计算。主要研究结果如下: 1.狭翅雏蝗对羊草、冷蒿、大针茅的取食率相似;取食率与虫体体重存在显著的线性相关。 2.狭翅雏蝗每个个体在一生中平均造成牧草损失487.55—784.4mg(干重),每日消耗与浪费的牧草为7.64—11.45mg。 3.狭翅雏蝗种群造成的牧草损失在冷蒿群落、羊草-大针茅-羊草群落、羊草-大针茅群落分别为1.52,1.65,0.76g/m,占地上初级生产量的2.96%、1.18%、0.42%,表现为越退化的草场,狭翅雏蝗对牧草的压力越大。其累积损失量的季节程式可以刚logisuc方程拟合。 4.狭翅雏蝗的经济阈值在羊草、羊草+大针茅+冰草、冷蒿草原分别为每平方米18.5、19.4、11.8头四龄为主个体。 相似文献
965.
Kuster SP Tuite AR Kwong JC McGeer A;Toronto Invasive Bacterial Diseases Network Investigators Fisman DN 《PLoS medicine》2011,8(6):e1001042
Background
The wintertime co-occurrence of peaks in influenza and invasive pneumococcal disease (IPD) is well documented, but how and whether wintertime peaks caused by these two pathogens are causally related is still uncertain. We aimed to investigate the relationship between influenza infection and IPD in Ontario, Canada, using several complementary methodological tools.Methods and Findings
We evaluated a total number of 38,501 positive influenza tests in Central Ontario and 6,191 episodes of IPD in the Toronto/Peel area, Ontario, Canada, between 1 January 1995 and 3 October 2009, reported through population-based surveillance. We assessed the relationship between the seasonal wave forms for influenza and IPD using fast Fourier transforms in order to examine the relationship between these two pathogens over yearly timescales. We also used three complementary statistical methods (time-series methods, negative binomial regression, and case-crossover methods) to evaluate the short-term effect of influenza dynamics on pneumococcal risk. Annual periodicity with wintertime peaks could be demonstrated for IPD, whereas periodicity for influenza was less regular. As for long-term effects, phase and amplitude terms of pneumococcal and influenza seasonal sine waves were not correlated and meta-analysis confirmed significant heterogeneity of influenza, but not pneumococcal phase terms. In contrast, influenza was shown to Granger-cause pneumococcal disease. A short-term association between IPD and influenza could be demonstrated for 1-week lags in both case-crossover (odds ratio [95% confidence interval] for one case of IPD per 100 influenza cases = 1.10 [1.02–1.18]) and negative binomial regression analysis (incidence rate ratio [95% confidence interval] for one case of IPD per 100 influenza cases = 1.09 [1.05–1.14]).Conclusions
Our data support the hypothesis that influenza influences bacterial disease incidence by enhancing short-term risk of invasion in colonized individuals. The absence of correlation between seasonal waveforms, on the other hand, suggests that bacterial disease transmission is affected to a lesser extent. Please see later in the article for the Editors'' Summary 相似文献966.
Zhen Li Zhou Tan Shiying Hao Bo Jin Xiaohong Deng Guang Hu Xiaodan Liu Jie Zhang Hua Jin Min Huang John T. Kanegaye Adriana H. Tremoulet Jane C. Burns Jianmin Wu Harvey J. Cohen Xuefeng B. Ling Emergency Medicine Kawasaki Disease Research Group 《PloS one》2016,11(2)
Objectives
Kawasaki disease (KD) is an acute pediatric vasculitis of infants and young children with unknown etiology and no specific laboratory-based test to identify. A specific molecular diagnostic test is urgently needed to support the clinical decision of proper medical intervention, preventing subsequent complications of coronary artery aneurysms. We used a simple and low-cost colorimetric sensor array to address the lack of a specific diagnostic test to differentiate KD from febrile control (FC) patients with similar rash/fever illnesses.Study Design
Demographic and clinical data were prospectively collected for subjects with KD and FCs under standard protocol. After screening using a genetic algorithm, eleven compounds including metalloporphyrins, pH indicators, redox indicators and solvatochromic dye categories, were selected from our chromatic compound library (n = 190) to construct a colorimetric sensor array for diagnosing KD. Quantitative color difference analysis led to a decision-tree-based KD diagnostic algorithm.Results
This KD sensing array allowed the identification of 94% of KD subjects (receiver operating characteristic [ROC] area under the curve [AUC] 0.981) in the training set (33 KD, 33 FC) and 94% of KD subjects (ROC AUC: 0.873) in the testing set (16 KD, 17 FC). Color difference maps reconstructed from the digital images of the sensing compounds demonstrated distinctive patterns differentiating KD from FC patients.Conclusions
The colorimetric sensor array, composed of common used chemical compounds, is an easily accessible, low-cost method to realize the discrimination of subjects with KD from other febrile illness. 相似文献967.
Design of lifestyle intervention trials to prevent excessive gestational weight gain in women with overweight or obesity 下载免费PDF全文
968.
969.
970.