全文获取类型
收费全文 | 20532篇 |
免费 | 1391篇 |
国内免费 | 56篇 |
专业分类
耳鼻咽喉 | 129篇 |
儿科学 | 434篇 |
妇产科学 | 270篇 |
基础医学 | 2727篇 |
口腔科学 | 351篇 |
临床医学 | 2566篇 |
内科学 | 3590篇 |
皮肤病学 | 199篇 |
神经病学 | 1823篇 |
特种医学 | 710篇 |
外科学 | 2849篇 |
综合类 | 231篇 |
一般理论 | 28篇 |
预防医学 | 2669篇 |
眼科学 | 430篇 |
药学 | 1593篇 |
中国医学 | 35篇 |
肿瘤学 | 1345篇 |
出版年
2024年 | 20篇 |
2023年 | 136篇 |
2022年 | 243篇 |
2021年 | 488篇 |
2020年 | 308篇 |
2019年 | 435篇 |
2018年 | 514篇 |
2017年 | 390篇 |
2016年 | 432篇 |
2015年 | 582篇 |
2014年 | 743篇 |
2013年 | 974篇 |
2012年 | 1646篇 |
2011年 | 1672篇 |
2010年 | 955篇 |
2009年 | 893篇 |
2008年 | 1465篇 |
2007年 | 1602篇 |
2006年 | 1451篇 |
2005年 | 1455篇 |
2004年 | 1419篇 |
2003年 | 1339篇 |
2002年 | 1155篇 |
2001年 | 147篇 |
2000年 | 108篇 |
1999年 | 163篇 |
1998年 | 219篇 |
1997年 | 151篇 |
1996年 | 132篇 |
1995年 | 101篇 |
1994年 | 111篇 |
1993年 | 88篇 |
1992年 | 49篇 |
1991年 | 44篇 |
1990年 | 29篇 |
1989年 | 34篇 |
1988年 | 24篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 25篇 |
1980年 | 20篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 14篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Universal standardization of forearm bone densitometry. 总被引:4,自引:0,他引:4
John A Shepherd Xiao Guang Cheng Ying Lu Chris Njeh Jorg Toschke Klaus Engelke Michael Grigorian Harry K Genant 《Journal of bone and mineral research》2002,17(4):734-745
As part of an effort to quantify device-dependent differences in forearm bone density, 101 women, aged 20-80 years (approximately 16 women in each age decade), were scanned on six forearm bone densitometers: the Aloka DCS-600EX, the Hologic QDR-4500A, the Lunar PIXI, the Norland pDEXA, the Osteometer DTX-200, and the Pronosco X-posure System. Regression statistics are reported for all similar regions of interest (ROIs). However, comparisons were confounded because of large differences in the ROI size and placement. The number of ROIs reported for a single scan by each device varied from 1 to 12. The correlation coefficients ranged from 0.7 < r < 0.97, with the highest correlation coefficients and lowest SEs for comparisons between the most similar ROIs. Standardized units of bone mineral density are derived for distal (sdBMD), mid-(smBMD), and proximal (spBMD) ROTs that allow for comparable mean bone densities to be derived for patient populations. Five phantoms were scanned and characterized on five of the devices and the precision and mean values were reported. These phantom values will aid in the in vitro cross-calibration between manufacturers to recreate the presented in vivo relationships. Care should be exercised when using these equations for cross-calibrating patient databases or pooling clinical data from different devices because the least significant differences detectable from measurements taken on two different machines can be increased substantially. 相似文献
52.
Chris Clark 《The British journal of general practice》2002,52(480):586-587
53.
54.
Romhild M. Hoogeveen Chris J. G. Bakker Max A. Viergever 《Journal of magnetic resonance imaging : JMRI》1997,7(2):321-330
A problem of current MRA techniques is the inability to accurately depict the vascular anatomy, particularly in areas of disturbed flow. Various reasons, such as intravoxel phase dispersion, saturation, temporal variations, and maximum intensity projection (MIP) nonlinearity, cause a wrong delineation of vessel boundaries. A phase contrast (PC)-based postprocessing operation, the phase derivative (PhD), is introduced to detect phase fluctuations indicating flow. Two-dimensional and three-dimensional angiographic reconstruction algorithms are presented. Mathematical formulas are derived to predict the effect of sampling to flow profiles and the effect on the PhD of these profiles. Numerical, phantom, and preliminary in vivo experiments demonstrate that PhD images do not suffer from phase wraps and allow a velocity dynamic range extension only limited by a differential phase change. It is also shown that PhD MIPs produce higher signal-to-noise ratios than conventional PC angiograms and give a better impression of the anatomy of (stenotic) vessels and of their diameters for both laminar and disturbed flow. 相似文献
55.
Norbert Boos Daniel Dreier Esther Hilfiker Volker Schade Roland Kreis Josef Hora Max Aebi Chris Boesch 《Journal of orthopaedic research》1997,15(1):141-149
The purpose of this investigation was to determine differences in tissue composition of symptomatic and asymptomatic disc herniations as reflected in T1 and T2 relaxation times (quantitative magnetic resonance investigation of the lumber spine. The longitudinal and transverse magnetic rlaxation times (T1 and T2, respectively) were calculated from a set of 20 images obtained with five single-slice/multi-echo sequences at different repetition time values on a commercial whole-body system (1.5 T). Twenty-two symptomatic and asymptomatic disc herniations could be matched according to age, gender, disc level, and the extent of herniation (protrusion or extrusion) and were compared with regard to T1 and T2 relaxation times. Symptomatic disc herniations exhibited significantly (pT1 < 0.04 and pT2 < 0.003) shorter T1(ΔT1:–182.1 milliseconds, ?15%) and T2(ΔT2: ?11.0 milliseconds, ?21%) relaxation times than matched asymptomatic herniations. Symptomatic disc herniations also exhibited more advanced disc degeneration as graded by Pearce's criteria (p < 0.01). These results suggest that symptomatic and morphologically matched asymptomatic disc herniations differ with regard to disc matrix composition. 相似文献
56.
57.
Philip F. Halloran Joan Urmson Vido Ramassar Anette Melk Lin-Fu Zhu Brendan P. Halloran R. Chris Bleackley 《American journal of transplantation》2004,4(5):705-712
Organ allograft rejection is strongly associated with the presence of alloreactive cytotoxic T cells but the role of cytotoxicity in the pathologic lesions is unclear. Previous studies showed that the principal lesions of kidney rejection - interstitial infiltration, tubulitis, and endothelial arteritis - are T-cell-dependent and antibody-independent. We studied the role of cytotoxic granule components perforin and granzymes A and B in the evolution of the T-cell-mediated lesions of mouse kidney transplant rejection. By real-time RT-PCR, allografts rejecting in wild-type hosts at days 5, 7, 21, and 42 showed massively elevated and persistent expression of perforin and granzymes A and B, but evolution of tubulitis and arteritis did not correlate with increasing granzyme or perforin expression. Allografts transplanted into hosts with disrupted genes for perforin or granzymes A and B showed no change in tubulitis, arteritis, or MHC induction. Thus the development of the histologic lesions diagnostic of T-cell-mediated kidney transplant rejection are associated with but not mediated by perforin or granzyme A or B. Together with previous graft survival studies, these results indicate that the granule-associated cytotoxic mechanisms of T cells are not the effectors of T-cell-mediated allograft rejection. 相似文献
58.
An unusual association with Raynaud's phenomenon 总被引:1,自引:1,他引:0
A 36-yr-old lady with a year of typical Raynaud's and polyarthralgiahad a normal examination other than cold peripheries and bloodpressure of 相似文献
59.
Chris Jarrold Peter Smith Jill Boucher Paul Harris 《Journal of autism and developmental disorders》1994,24(4):433-455
In an attempt to tap underlying competencies, the ability of children with autism to comprehend pretend acts carried out by an experimenter was compared with that shown by controls. These acts consisted of the pouring of a pretend substance from an appropriate container onto a target figure. There was no significant difference in the groups' ability to identify the pretend substance involved, to predict the pretend outcome of the actions, or to reflect on the pretend nature of the episodes. However, the performance of controls on these latter two tasks was surprisingly poor, limiting the implications that might be drawn from the observed absence of group differences in comprehension abilities.We are very grateful to the teachers and headteachers of the following schools for their cooperation and assistance throughout the period of this research: John Worrall School, Sheffield; Doucecroft School, Kelvedon; East Hill First and Middle School, Sheffield; East Hill Second School, Sheffield; Mossbrook School, Sheffield; Priory School, Doncaster; The Rowan School, Dore; St. Mary's School, Sheffield. We also thank James Russell for his helpful comments of earlier drafts of this paper. 相似文献
60.