全文获取类型
收费全文 | 2747篇 |
免费 | 174篇 |
国内免费 | 22篇 |
专业分类
耳鼻咽喉 | 27篇 |
儿科学 | 59篇 |
妇产科学 | 77篇 |
基础医学 | 265篇 |
口腔科学 | 77篇 |
临床医学 | 338篇 |
内科学 | 455篇 |
皮肤病学 | 22篇 |
神经病学 | 154篇 |
特种医学 | 178篇 |
外科学 | 351篇 |
综合类 | 65篇 |
一般理论 | 4篇 |
预防医学 | 385篇 |
眼科学 | 125篇 |
药学 | 162篇 |
中国医学 | 2篇 |
肿瘤学 | 197篇 |
出版年
2022年 | 21篇 |
2021年 | 51篇 |
2019年 | 56篇 |
2018年 | 54篇 |
2017年 | 35篇 |
2016年 | 38篇 |
2015年 | 50篇 |
2014年 | 65篇 |
2013年 | 101篇 |
2012年 | 90篇 |
2011年 | 113篇 |
2010年 | 102篇 |
2009年 | 94篇 |
2008年 | 105篇 |
2007年 | 104篇 |
2006年 | 110篇 |
2005年 | 95篇 |
2004年 | 88篇 |
2003年 | 80篇 |
2002年 | 96篇 |
2001年 | 57篇 |
2000年 | 80篇 |
1999年 | 74篇 |
1998年 | 48篇 |
1997年 | 47篇 |
1996年 | 44篇 |
1995年 | 46篇 |
1994年 | 33篇 |
1993年 | 34篇 |
1992年 | 43篇 |
1991年 | 48篇 |
1990年 | 47篇 |
1989年 | 47篇 |
1988年 | 43篇 |
1987年 | 36篇 |
1986年 | 42篇 |
1985年 | 34篇 |
1984年 | 41篇 |
1983年 | 60篇 |
1982年 | 60篇 |
1981年 | 49篇 |
1980年 | 60篇 |
1979年 | 35篇 |
1978年 | 33篇 |
1977年 | 28篇 |
1976年 | 21篇 |
1975年 | 18篇 |
1974年 | 22篇 |
1973年 | 18篇 |
1966年 | 22篇 |
排序方式: 共有2943条查询结果,搜索用时 156 毫秒
61.
62.
63.
64.
We measured the accuracy with which subjects judged that a square or circle was perfectly symmetrical i.e. that aspect ratio (a/b) was exactly unity (where a and b were, respectively, the vertical and horizontal dimensions). Errors were remarkably small, ranging from 0.7 to 0.4% for the judgement of squareness and from 1.4 to < 0.1% for the judgement of circularity. Precision in judging aspect ratio was measured by requiring subjects to judge whether the aspect ratio (a/b)TEST of a test rectangle was greater or less than the aspect ratio (a/b)REF of a reference rectangle. Similar measurements were made for elliptical targets. To ensure that subjects based judgements on aspect ratio rather than a, b or (a-b), the area of each successive presentation was varied randomly. The just-discriminable percentage change of aspect ratio was as low as 1.6% at (a/b)REF = 1.0 (i.e. for a square or circular reference), and rose progressively as (a/b)REF was made progressively larger or smaller than 1.0. Aspect ratio discrimination threshold was independent of mean area over a sixteen-fold range of 0.25-4.0 deg2. For both rectangles and ellipses, the best value of aspect ratio discrimination threshold corresponded to a precision of encoding a and b of 14 sec arc or better. In further experiments, the method of constant stimuli was used to measure an aspect ratio aftereffect produced by adapting separately to rectangles of (a/b)ADAPT equal to 1.5, 1.0 and (1/1.5). Similar aftereffects were obtained whether the area of the test stimulus was fixed or varied randomly from trial to trial, and whether the test stimulus was rectangular or elliptical. The aftereffect could not be explained in terms of fatigue of neurons sensitive to linear dimension a or b. Nor could the aftereffect be explained in terms of the "contour repulsion" hypothesis, or in terms of orientation discrimination. We conclude (1) that the same neural mechanism determines aspect ratio discrimination threshold for rectangles and ellipses and (2) that this mechanism is sensitive to aspect ratio independently of linear dimensions. We propose that aspect ratio perception is determined by the balance of excitation of two pools of neurons that are selectively sensitive to different, but overlapping ranges of (a/b). One pool prefers aspect ratios > 1.0 and the others prefer aspect ratios < 1.0. We suppose that the two pools respond identically to changes in area (a * b).(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
65.
66.
67.
68.
69.
MO Livet A Moncla B Delobel MF Croquette N Philip L Vallée 《Archives de pédiatrie》1997,4(12):1231-1237
Smith-Magenis syndrome is caused by a 17p11.2 deletion. It associates mental retardation, facial dysmorphism and brachydactyly; aberrant behavior and major sleep problems are present in 70% of the cases. It is probably under-diagnosed because the facial abnormalities are mild and the behavioral problems with hyperactivity and self-injuries are dominant, leading to the diagnosis of psychiatric pathology. However these behavioral problems are sufficiently characterized to allow the diagnosis of the syndrome and look for a 17p11.2 microdeletion. Otorhinolaryngologic, ophtalmologic, cardiac and renal abnormalities can be associated and their evaluation is necessary. Smith-Magenis syndrome is considered as a contiguous gene syndrome. Genes have been mapped and isolated to the critical region, but their participation in the pathogenesis of the syndrome remains unclear. 相似文献
70.
Bolontrade MF; Stern MC; Binder RL; Zenklusen JC; Gimenez-Conti IB; Conti CJ 《Carcinogenesis》1998,19(12):2107-2113
In this study we have analyzed the vascular response induced in the two-
stage carcinogenesis model in SENCAR mice. The role of angiogenesis has not
been explored in this model, which is the paradigm of multistage
carcinogenesis and a model for neoplastic lesions derived from exophytic
premalignant lesions (e.g. colon carcinoma, bladder papilloma). We
investigated if angiogenesis is involved in the formation of papillomas and
in the progression from papilloma to carcinoma. To this end we analyzed the
vasculature of normal and hyperplastic skin, focal epidermal hyperplasias
that are precursors of papillomas, papillomas at different stages and
squamous cell carcinomas. We also analyzed the vascularization of
papillomas induced in two strains of mice that differ in their
susceptibility to malignant progression. We show here that angiogenesis is
turned on in the earliest stages of papilloma formation. In late stages,
regardless of state of progression, the predominant response is an increase
in the size of blood vessels. Thus, in the SENCAR mouse model,
representative of exophytic tumors, the angiogenesis switch is a very early
event, probably mechanistically related to the development of the primarily
exophytic lesions. Therefore, the density of blood vessels cannot be used
as a predictor of malignant progression in this model.
相似文献