全文获取类型
收费全文 | 1810篇 |
免费 | 405篇 |
国内免费 | 47篇 |
专业分类
耳鼻咽喉 | 17篇 |
儿科学 | 91篇 |
妇产科学 | 61篇 |
基础医学 | 165篇 |
口腔科学 | 41篇 |
临床医学 | 238篇 |
内科学 | 403篇 |
皮肤病学 | 104篇 |
神经病学 | 87篇 |
特种医学 | 192篇 |
外科学 | 213篇 |
综合类 | 247篇 |
一般理论 | 1篇 |
预防医学 | 152篇 |
眼科学 | 24篇 |
药学 | 104篇 |
1篇 | |
中国医学 | 9篇 |
肿瘤学 | 112篇 |
出版年
2022年 | 9篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 32篇 |
2017年 | 27篇 |
2016年 | 37篇 |
2015年 | 44篇 |
2014年 | 51篇 |
2013年 | 77篇 |
2012年 | 44篇 |
2011年 | 71篇 |
2010年 | 66篇 |
2009年 | 83篇 |
2008年 | 56篇 |
2007年 | 94篇 |
2006年 | 46篇 |
2005年 | 61篇 |
2004年 | 59篇 |
2003年 | 44篇 |
2002年 | 45篇 |
2001年 | 48篇 |
2000年 | 45篇 |
1999年 | 60篇 |
1998年 | 86篇 |
1997年 | 91篇 |
1996年 | 78篇 |
1995年 | 73篇 |
1994年 | 58篇 |
1993年 | 63篇 |
1992年 | 56篇 |
1991年 | 43篇 |
1990年 | 46篇 |
1989年 | 65篇 |
1988年 | 51篇 |
1987年 | 65篇 |
1986年 | 42篇 |
1985年 | 33篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1974年 | 12篇 |
1969年 | 8篇 |
1968年 | 9篇 |
排序方式: 共有2262条查询结果,搜索用时 15 毫秒
991.
Improved control of image optical density with low-dose digital and conventional radiography in bedside imaging 总被引:1,自引:0,他引:1
Schaefer CM; Greene RE; Oestmann JW; Kamalsky JM; Hall DA; Llewellyn HJ; Robertson CL; Rhea JT; Rosenthal H; Rubens JR 《Radiology》1989,173(3):713-716
The technical and diagnostic performance of simultaneously acquired low-dose (44% of standard dose) storage-phosphor digital radiographs (system resolution = 0.2 mm, 10 bits) were compared with those of standard-dose conventional bedside radiographs of the chest in 32 patients. The mean optical density (OD) of the lungs (800 measurements) was closer to the ideal density with digital radiography (1.45 OD +/- 0.20 [standard deviation] vs 1.75 OD +/- 0.53) and was less often outside the usable range (2.5% vs 42.5%). Receiver operating characteristic analysis for detection of simulated nodules and monitoring devices (nine readers, 4,608 observations) showed that digital radiography was superior to conventional radiography (P less than .05) for four of the nine readers and equivalent to conventional radiography for five readers. The authors concluded that digital radiography produces more consistent and ideal image density and performs at least as well as conventional radiography under phantom test conditions. 相似文献
992.
993.
994.
Reductions of erythrocyte membrane viscoelastic coefficients reflect spectrin deficiencies in hereditary spherocytosis. 总被引:12,自引:0,他引:12 下载免费PDF全文
Hereditary spherocytosis is a common hemolytic anemia associated with deficiencies in spectrin, the principal structural protein of the erythrocyte membrane-skeleton. We have examined 20 different individuals from 10 spherocytosis kindreds and 2 elliptocytosis kindreds to determine the effects of different levels of spectrin deficiency on the viscoelastic properties of the erythrocyte membrane. Micropipettes were used to perform single-cell micromechanical measurements of approximately 1,000 individual cells to determine the membrane elastic shear modulus, the apparent membrane bending stiffness, and whole cell recovery time constant for the different cell populations. The membrane viscosity was calculated by the product of the shear modulus and the recovery time constant. Results show correlation between the fractional reduction in shear modulus and the fractional reduction in spectrin content (determined by spectrin radioimmunoassay) and spectrin density (determined by the ratios of spectrin to band 3 on electrophoresis gels) suggesting that membrane shear elasticity is directly proportional to the surface density of spectrin on the membrane (P less than 0.001). The apparent membrane bending stiffness is also reduced in proportion to the density of spectrin (P less than 0.001). The membrane viscosity is reduced relative to control (P less than 0.001), but the nature of the relationship between spectrin density and membrane viscosity is less clearly defined. These studies document striking relationships between partial deficiencies of erythrocyte spectrin and specific viscoelastic properties of the mutant membranes. 相似文献
995.
Kamal P Dixon-Woods M Kurinczuk JJ Oppenheimer C Squire P Waugh J 《BJOG : an international journal of obstetrics and gynaecology》2005,112(8):1054-1060
OBJECTIVE: To explore the views of health professionals on the factors influencing repeat caesarean section. DESIGN: Qualitative study involving semi-structured interviews with professionals who care for women in pregnancy and labour. SETTING: Acute hospital trust with two maternity units and community midwifery service, Leicestershire, UK. SAMPLE: Twenty-five midwives and doctors. METHODS: Interviews with professionals were undertaken using a prompt guide. All interviews were audiotaped and transcribed verbatim. Analysis was based on the constant comparative method, assisted by QSR N5 software. MAIN OUTCOME MEASURES: Identification of factors influencing professional decision making about repeat caesarean section. RESULTS: Decision making in relation to repeat caesarean is a complex process involving several parties. Professionals identify the relevance of evidence for decision making for repeat caesarean. However, professionals feel that following strict protocols is of limited value because of the perceived substandard quality of evidence in this area, other external pressures and the contingent, unique and often unanticipated features of each case. Professionals also perceive that the organisation of care plays an important role in rates of repeat caesarean. CONCLUSIONS: Decision making for repeat caesarean is a social practice where standardised protocols may have limited value. Attention needs to be given to the multiple parties involved in the decision-making process. Reflective practice, opinion leadership and role modelling may offer ways forward but will require evaluation. 相似文献
996.
Waugh JJ Bell SC Kilby MD Blackwell CN Seed P Shennan AH Halligan AW 《BJOG : an international journal of obstetrics and gynaecology》2005,112(4):412-417
OBJECTIVE: To compare semi-quantitative visual and automated methods of urine testing with fully quantitative point of care urinalysis for the detection of significant proteinuria (0.3 g/24 hours) in pregnancy complicated by hypertension. DESIGN: A prospective comparative study. SETTING: A large teaching maternity hospital. SAMPLE: One hundred and seventy-one pregnant women referred to the obstetric day-care unit for assessment of newly arisen hypertension. METHODS: Early morning urine specimens were tested with four dipstick techniques (Multistix 8SG visual and automated and microalbumin/creatinine ratio visual and automated; Bayer, Elkhart, USA) as well as a fully quantitative measure of the microalbumin creatinine ratio with the DCA 2000 (a point of care assay for albumin; Bayer). These results were compared to a 24-hour urine protein measurement and measures of diagnostic accuracy/prediction are reported. MAIN OUTCOME MEASURES: Significant proteinuria (> or =0.3 g/24 hours) measured by laboratory assay. RESULTS: Automated dipstick urinalysis using the Clinitek 50 has significantly better predictive values for significant proteinuria (LR(+) 4.27, 95% CI 2.78 to 6.56; LR(-) 0.225, 95% CI 0.14 to 0.37) than conventional visual dipstick urinalysis (LR(+) 2.27, 95% CI 1.47 to 3.51; LR(-) 0.635, 95% CI 0.49 to 0.82). Dipstick microalbumin/creatinine ratio testing did not improve overall detection rates with automated or visual testing. Fully quantitative point of care measurement of albumin/creatinine ratio (ACR) was significantly better than any dipstick technique (LR(+) 14.6, 95% CI 6.74 to 31.8; LR(-) 0.069, 95% CI 0.030 to 0.16). CONCLUSIONS: This study confirms that in pregnancy automated dipstick urinalysis is a more accurate screening test for the detection of proteinuria than visual testing. ACR testing can offer a significant improvement over conventional urinalysis if a fully quantitative method of detection is employed that uses pregnancy-specific thresholds. Dipstick assessment of ACR does not improve the detection rate of significant proteinuria. 相似文献
997.
Jason Waugh Stephen C Bell Mark D Kilby Paul Lambert Andrew Shennan Aidan Halligan 《Hypertension in pregnancy》2005,24(3):291-302
OBJECTIVE:To determine what threshold for proteinuria could best predict clinical outcome and whether this threshold could be applied universally to any biochemical assay. DESIGN: A prospective observational study of hypertensive pregnancies referred for further assessment after in a UK University hospital (n=197). Twenty-four hour urine protein was measured by two different assays [benzethonium chloride assay (BCA) and Bradford assay]. The differences between the two assays were calculated from Receiver Operating Characteristic (ROC) curves. Commonly used thresholds for defining preeclampsia (0.3 and 0.5 g/24 hours) were explored for both assays for the prediction of adverse clinical outcomes (severe hypertension, Birthweight<10th percentile, preterm delivery, and a composite biochemical/haematological derangement). RESULTS: The two assays are not equivalent. The prevalence of>300 mg/24 hour proteinuria and, hence, the prevalence of preeclampsia differed between the two assays. ROC curve analysis demonstrates that the two assays are similar in terms of overall performance as predictive tests. However the threshold of 300 mg/24 hours performs poorly as a predictor of clinical risk. Likelihood ratios (LR) for the BCA at the 300 mg/L threshold for each clinical outcome do not achieve statistical significance. At the 500 mg/L threshold, the LR+for the BCA assay does achieve statistical significance for severe hypertension (LR+:1.51 95% CI 0.99-2.28) and for birthweight<10th percentile (LR+:1.72 95% CI 1.11-2.66). For the Bradford assay at the 300 mg/24 hour threshold, the LR+does achieve statistical significance for birthweight<10th percentile (LR+:1.71 95% CI 1.41-4.31). However, at the 500 mg/24 hour threshold, the LR+is significant for severe hypertension (LR+:2.15 95% CI 1.07-4.34), birthweight<10th percentile (LR+:2.79 95% CI 1.4-5.54) and biochemical disease (LR+:2.47 95% CI 1.22-5.01). CONCLUSIONS: This study suggests that thresholds for proteinuria need to be higher (possibly>or=0.5 g/24 hours) and there is the need for a "gold standard" proteinuria assay against which all other measures of quantification can be assessed. 相似文献
998.
Background
There is a considerable body of literature which indicates that contrast thresholds for the detection of sinusoidal grating patterns are abnormally high in glaucoma, though just how these elevations are related to the location of visual field loss remains unknown. Our aim, therefore, has been to determine the relationship between contrast threshold elevation and visual field loss in corresponding regions of the peripheral visual field in glaucoma patients. 相似文献999.
1000.
Marike?RC?HendriksEmail author Jolanda?CM?van Haastregt Joseph?PM?Diederiks Silvia?MAA?Evers Harry?FJM?Crebolder Jacques?ThM?van Eijk 《BMC public health》2005,5(1):6