全文获取类型
收费全文 | 41576篇 |
免费 | 1190篇 |
国内免费 | 18篇 |
专业分类
化学 | 23087篇 |
晶体学 | 184篇 |
力学 | 872篇 |
数学 | 6673篇 |
物理学 | 11968篇 |
出版年
2023年 | 221篇 |
2021年 | 335篇 |
2020年 | 517篇 |
2019年 | 349篇 |
2018年 | 476篇 |
2017年 | 459篇 |
2016年 | 1061篇 |
2015年 | 893篇 |
2014年 | 996篇 |
2013年 | 2204篇 |
2012年 | 1754篇 |
2011年 | 2143篇 |
2010年 | 1101篇 |
2009年 | 921篇 |
2008年 | 2014篇 |
2007年 | 1998篇 |
2006年 | 1766篇 |
2005年 | 1553篇 |
2004年 | 1213篇 |
2003年 | 1059篇 |
2002年 | 972篇 |
2001年 | 845篇 |
2000年 | 750篇 |
1999年 | 513篇 |
1998年 | 448篇 |
1997年 | 459篇 |
1996年 | 566篇 |
1995年 | 513篇 |
1994年 | 517篇 |
1993年 | 602篇 |
1992年 | 513篇 |
1991年 | 386篇 |
1990年 | 433篇 |
1989年 | 346篇 |
1988年 | 365篇 |
1987年 | 371篇 |
1986年 | 331篇 |
1985年 | 504篇 |
1984年 | 510篇 |
1983年 | 462篇 |
1982年 | 476篇 |
1981年 | 486篇 |
1980年 | 441篇 |
1979年 | 410篇 |
1978年 | 446篇 |
1977年 | 411篇 |
1976年 | 376篇 |
1975年 | 362篇 |
1974年 | 339篇 |
1973年 | 350篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Automatic segmentation and classification of color images is a problem of great practical interest in different areas. This
paper presents an algorithm for this purpose which is divided in three steps. Firstly, the regions of interest are isolated
from the rest of the image based on threshold functions defined in theYUV andYIQ color spaces, producing a set of connected components. Then, a set of features is computed to enable a quantitative evaluation
of the segmented objects. Finally, the image is classified by means of a decision rule based on the analysis of the differences
between the computed measures and a set of ideally segmented images, according to experts’ assessment. The algorithm was applied
to a decision support tool for estrus detection in cattle. This approach constitutes a valuable alternative to improve this
process, as it may replace the visual observation by the automatic analysis of pictures taken to cows in controlled environments.
Experimental results show that the segmentations obtained with this method are highly satisfactory and they allow a precise
classification of the images with low computational complexity. 相似文献
102.
103.
D. Abbaneo P. Antilogus T. Behnke S.C. Blyth M. Elsing R. Faccini R.W.L. Jones K. Mönig S. Petzold R. Tenchini 《The European Physical Journal C - Particles and Fields》1998,4(2):185-191
Measurements of the forward-backward production asymmetry of heavy quarks in Z decays provide a precise determination of
. The asymmetries are sensitive to QCD effects, in particular hard gluon radiation. In this paper QCD corrections for and are discussed. The interplay between the experimental techniques used to measure the asymmetries and the QCD effects is
investigated using simulated events. A procedure to estimate the correction needed for experimental measurements is proposed,
and some specific examples are given.
Received: 26 February 1998 / Published online: 2 June 1998 相似文献
104.
Th. Mühge Yu. V. Goryunov K. Theis-Bröhl K. Westerholt H. Zabel I. A. Garifullin 《Applied magnetic resonance》1998,14(4):567-582
Magnetic and superconducting properties of Fe/Nb epitaxial bilayers have been studied. Single crystal Fe/Nb (110) bilayers with a Nb thicknessd Nb in the range from 250 to 650 Å and with a Fe thicknessd Fe in the range from 7 to 27 Å were prepared using molecular beam epitaxy techniques. Magnetization measurements showed the existence of a magnetically “dead” Fe-interface layer with a thicknessd NM varying strongly with minor modifications of the growth conditions. For bilayers with a small magnetic layer thicknessd M and a smalld NM the FMR measurements revealed an anomalous decrease of the effective magnetization 4πM eff of the ferromagnetic Fe layer below the superconducting transition temperatureT c. The absolute change of 4πM eff belowT c depends strongly on the actual values ofd M andd NM: upon decreasing bothd M andd NM the effect increases considerably. As a possible mechanism for the anomalous temperature dependence of 4πM eff belowT c we discuss a spatial modulation of ferromagnetic order due to a modification of the RKKY inter-action in the superconducting state. 相似文献
105.
M. A. Morón C. Romero F. R. Ruiz del Portal 《Journal of Optimization Theory and Applications》1996,91(3):643-649
The purpose of this paper is to seek utility functions satisfying a weak condition which guarantees that the utility optimum always belongs to the compromise set. This set is a special subset of the attainable or feasible set, which is generated through the application of the well-known operational research approach called compromise programming. It is shown that there are large families of utility functions satisfying this condition, thus reinforcing the value of compromise programming as a good surrogate of the traditional utility optimum.Thanks are due to the reviewers for their helpful suggestions. The English editing by Ms. Christine Méndez is appreciated. The authors have been supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT), Madrid, Spain. 相似文献
106.
107.
108.
109.
110.