全文获取类型
收费全文 | 54829篇 |
免费 | 4148篇 |
国内免费 | 176篇 |
学科分类
医药卫生 | 59153篇 |
出版年
2023年 | 363篇 |
2022年 | 523篇 |
2021年 | 1326篇 |
2020年 | 717篇 |
2019年 | 1300篇 |
2018年 | 1550篇 |
2017年 | 1124篇 |
2016年 | 1140篇 |
2015年 | 1399篇 |
2014年 | 2036篇 |
2013年 | 2642篇 |
2012年 | 3988篇 |
2011年 | 4206篇 |
2010年 | 2346篇 |
2009年 | 1957篇 |
2008年 | 3438篇 |
2007年 | 3829篇 |
2006年 | 3645篇 |
2005年 | 3481篇 |
2004年 | 3088篇 |
2003年 | 3031篇 |
2002年 | 2683篇 |
2001年 | 635篇 |
2000年 | 509篇 |
1999年 | 568篇 |
1998年 | 580篇 |
1997年 | 421篇 |
1996年 | 359篇 |
1995年 | 375篇 |
1994年 | 298篇 |
1993年 | 277篇 |
1992年 | 383篇 |
1991年 | 344篇 |
1990年 | 328篇 |
1989年 | 306篇 |
1988年 | 323篇 |
1987年 | 283篇 |
1986年 | 263篇 |
1985年 | 275篇 |
1984年 | 243篇 |
1983年 | 226篇 |
1982年 | 216篇 |
1981年 | 195篇 |
1980年 | 204篇 |
1979年 | 148篇 |
1978年 | 171篇 |
1977年 | 106篇 |
1976年 | 111篇 |
1975年 | 117篇 |
1973年 | 137篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Seymour Solomon Brian M Grosberg Deborah I Friedman Richard B Lipton 《Journal of neuro-ophthalmology》2007,27(3):243-4; author reply 244-5
22.
Neal G Palmer James R Yacyshyn Herbert C Northcott Brian Nebbe Paul W Major 《American journal of orthodontics and dentofacial orthopedics》2005,128(2):163-167
INTRODUCTION: To plan for future acceptance and implementation of computer-related technology, it is necessary to understand orthodontists' current perceptions and attitudes toward emerging technologies. METHODS: An anonymous, self-administered, mail-out survey of Canadian orthodontists was conducted. The response rate was 45.6% (304/667). RESULTS: Most orthodontists indicated that computer technology could improve current practice efficiency and quality of patient care. Only 15% reported that digital models are quite or very useful; 73.6%, 69.1%, 55%, and 37.4% agreed or strongly agreed with using digital and electronic technology to consult with other dental specialists, other orthodontists, general dentists, and the public, respectively. Cost of the technology was reported as a significant or insurmountable obstacle by 54% of the respondents. Interprovincial legislation, unclear consultation remuneration guidelines, and lack of comfort with the technology were not perceived as significant obstacles. Only 36% reported security or privacy issues as a significant or insurmountable obstacle. CONCLUSIONS: Canadian orthodontists seem to view digital and electronic technology as useful and capable of improving their offices' efficiency and production. Although they are sensitive to some potential obstacles, they are willing to overcome these and incorporate the technology into their practices. 相似文献
23.
24.
25.
Brian A Haluska Robert Fathi Leanne Jeffriess Rodel Leano Stephane G Carlier Thomas H Marwick 《Journal of the American Society of Echocardiography》2004,17(2):195-202; quiz 203-4
BACKGROUND: Brachial artery reactivity (BAR), carotid intima-media thickness (IMT), and applanation tonometry for evaluation of total arterial compliance may provide information about preclinical vascular disease. We sought to determine whether these tests could be used to identify patients with coronary artery disease (CAD) without being influenced by their ability to identify those at risk for CAD developing. METHODS: We studied 100 patients and compared 3 groups: 35 patients with known CAD; 34 patients with symptoms and risk factors but no CAD identified by stress echocardiography (risk group); and 31 control subjects. BAR and IMT were measured using standard methods, and total arterial compliance was calculated by the pulse-pressure method from simultaneous radial applanation tonometry and pulsed wave Doppler of the left ventricular outflow. Ischemia was identified as a new or worsening wall-motion abnormality induced by stress. RESULTS: In a comparison between the control subjects and patients either at risk for developing CAD or with CAD, the predictors of risk for CAD were: age (P =.01); smoking history (P =.002); hypercholesterolemia (P =.002); and hypertension (P =.004) (model R = 0.82; P =.0001). The independent predictors of CAD were: IMT (P =.001); BAR (P =.04); sex (P =.005); and hypertension (P =.005) (model R = 0.80; P =.0001). CONCLUSION: IMT, BAR, and traditional cardiovascular risk factors appear to identify patients at risk for CAD developing. However, only IMT was significantly different between patients at risk for developing CAD and those with overt CAD. 相似文献
26.
Mozammil Hussain Raghu N. Natarajan Amir H. Fayyazi Brian R. Braaksma Gunnar B.J. Andersson Howard S. An 《The spine journal》2009,9(12):1016-1023
Background contextAnterior corpectomy and reconstruction with bone graft and a rigid screw-plate construct is an established procedure for treatment of cervical neural compression. Despite its reliability in relieving symptoms, there is a high rate of construct failure, especially in multilevel cases.PurposeThere has been no study evaluating the biomechanical effects of screw angulation on construct stability; this study investigates the C4–C7 construct stability and load-sharing properties among varying screw angulations in a rigid plate-screw construct.Study designA finite element model of a two-level cervical corpectomy with static anterior cervical plate.MethodsA three-dimensional finite element (FE) model of an intact C3–T1 segment was developed and validated. From this intact model, a fusion model (two-level [C5, C6] anterior corpectomy) was developed and validated. After corpectomy, allograft interbody fusion with a rigid anterior screw-plate construct was created from C4 to C7. Five additional FE models were developed from the fusion model corresponding to five different combinations of screw angulations within the vertebral bodies (C4, C7): (0°, 0°), (5°, 5°), (10°, 10°), (15°, 15°), and (15°, 0°). The fifth fusion model was termed as a hybrid fusion model.ResultsThe stability of a two-level corpectomy reconstruction is not dependent on the position of the screws. Despite the locked screw-plate interface, some degree of load sharing is transmitted to the graft. The load seen by the graft and the shear stress at the bone-screw junction is dependent on the angle of the screws with respect to the end plate. Higher stresses are seen at more divergent angles, particularly at the lower level of the construct.ConclusionThis study suggests that screw divergence from the end plates not only increases load transmission to the graft but also predisposes the screws to higher shear forces after corpectomy reconstruction. In particular, the inferior screw demonstrated larger stress than the upper-level screws. In the proposed hybrid fusion model, lower stresses on the bone graft, end plates, and bone-screw interface were recorded, inferring lower construct failure (end-plate fractures and screw pullout) potential at the inferior construct end. 相似文献
27.
28.
Understanding the minimum clinically important difference: a review of concepts and methods. 总被引:2,自引:0,他引:2
Anne G Copay Brian R Subach Steven D Glassman David W Polly Thomas C Schuler 《The spine journal》2007,7(5):541-546
BACKGROUND CONTEXT: The effectiveness of spinal surgery as a treatment option is currently evaluated through the assessment of patient-reported outcomes (PROs). The minimum clinically important difference (MCID) represents the smallest improvement considered worthwhile by a patient. The concept of an MCID is offered as the new standard for determining effectiveness of a given treatment and describing patient satisfaction in reference to that treatment. PURPOSE: Our goal is to review the various definitions of MCID and the methods available to determine MCID. STUDY DESIGN: The primary means of determining the MCID for a specific treatment are divided into anchor-based and distribution-based methods. Each method is further subdivided and examined in detail. METHODS: The overall limitations of the MCID concept are first identified. The basic assumptions, statistical biases, and shortcomings of each method are examined in detail. RESULTS: Each method of determining the MCID has specific shortcomings. Three general limitations in the accurate determination of an MCID have been identified: the multiplicity of MCID determinations, the loss of the patient's perspective, and the relationship between pretreatment baseline and posttreatment change scores. CONCLUSIONS: An ideal means of determining the MCID for a given intervention is yet to be determined. It is possible to develop a useful method provided that the assumptions and methodology are initially declared. Our efforts toward the establishment of a MCID will rely on the establishment of specific external criteria based on the symptoms of the patient and treatment intervention being evaluated. 相似文献
29.
Limitations of the Panoramic 200 Optomap. 总被引:7,自引:0,他引:7
Brian Chou 《Optometry and vision science》2003,80(10):671-672
30.