全文获取类型
收费全文 | 5646篇 |
免费 | 115篇 |
国内免费 | 31篇 |
专业分类
化学 | 3216篇 |
晶体学 | 51篇 |
力学 | 173篇 |
数学 | 966篇 |
物理学 | 1386篇 |
出版年
2020年 | 55篇 |
2019年 | 50篇 |
2018年 | 34篇 |
2016年 | 85篇 |
2015年 | 65篇 |
2014年 | 91篇 |
2013年 | 246篇 |
2012年 | 227篇 |
2011年 | 291篇 |
2010年 | 142篇 |
2009年 | 130篇 |
2008年 | 242篇 |
2007年 | 219篇 |
2006年 | 245篇 |
2005年 | 235篇 |
2004年 | 179篇 |
2003年 | 158篇 |
2002年 | 157篇 |
2001年 | 137篇 |
2000年 | 118篇 |
1999年 | 83篇 |
1998年 | 56篇 |
1997年 | 68篇 |
1996年 | 88篇 |
1995年 | 81篇 |
1994年 | 104篇 |
1993年 | 111篇 |
1992年 | 97篇 |
1991年 | 91篇 |
1990年 | 79篇 |
1989年 | 94篇 |
1988年 | 67篇 |
1987年 | 83篇 |
1986年 | 66篇 |
1985年 | 109篇 |
1984年 | 90篇 |
1983年 | 54篇 |
1982年 | 81篇 |
1981年 | 82篇 |
1980年 | 64篇 |
1979年 | 74篇 |
1978年 | 78篇 |
1977年 | 60篇 |
1976年 | 68篇 |
1975年 | 66篇 |
1974年 | 71篇 |
1973年 | 103篇 |
1972年 | 39篇 |
1966年 | 44篇 |
1965年 | 52篇 |
排序方式: 共有5792条查询结果,搜索用时 187 毫秒
1.
2.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
3.
The new Antiproton Accumulator Complex is now in operation at CERN. We consider the possibility of using this facility to
create and store antideuterons and conclude that we could achieve an accumulation rate of about 2·106 particles/day. No major rebuild of the rings is envisaged, but it is thought that modification to existing components and
becoming operational would take about 5 to 6 months. We stress, however, that the operation of such a facility and the use
of any stack of antideuterons for particle physics would be extremely taxing. 相似文献
4.
J. R. Lindle W. W. Bewley I. Vurgaftman J. R. Meyer J. L. Johnson M. L. Thomas W. E. Tennant 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):558
A self-referencing, optical modulation technique was used to measure the negative luminescence efficiencies of an array of mid-wave infrared HgCdTe photodiodes with cutoff wavelength 4.6 μm as a function of sample temperature. The internal efficiency at a wavelength of 4 μm was 93% at 295 K, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction >50 K at room temperature and >30 K at 240 K. Moreover, the reverse-bias saturation current density was only 0.13 A/cm2. The measured transmission and emission spectra were simulated using empirical HgCdTe absorption formulas from the literature. 相似文献
5.
In this note we show how 1-factors in the middle two layers of the discrete cube can be used to construct 2-factors in the
Odd graph (the Kneser graph of (k − 1)-sets from a (2k − 1)-set). In particular, we use the lexical matchings of Kierstead and Trotter, and the modular matchings of Duffus, Kierstead
and Snevily, to give explicit constructions of two different 2-factorisations of the Odd graph.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
6.
Periodica Mathematica Hungarica - 相似文献
7.
N. Srinivasan R.C. Johnson N. Kasthurikrishnan P. Wong R.G. Cooks 《Analytica chimica acta》1997,350(3):128-271
An overview of membrane introduction mass spectrometry (MIMS) is presented and comparisons are made with other direct sample introduction techniques. Special attention is given to the unique advantages and the limitations of newer variants on the MIMS technique, including affinity MIMS, reverse-phase and trap MIMS. The salient features of the interfaces used in MIMS are summarized and the various membrane materials commonly used are delineated. The applicability of MIMS is illustrated via discussion of
- 1. (i) bioreactor monitoring (represented by yeast fermentation),
- 2. (ii) environmental monitoring (illustrated by analysis of contaminated ground water samples) and
- 3. (iii) on-line chemical reaction monitoring (exemplified by the photolysis of aryl esters).
8.
9.
The hyperfine constants for muonium in elemental and binary inorganic solids suggest formation of three different families
of defect centre, with distinct electronic structures. The overall range of values, spanning nearly five orders of magnitude,
and their correlation with host properties such as band gap and electron affinity, reveal a deep-to-shallow instability which
has profound implications for the electrical properties of hydrogen impurity in electronic materials, both semiconducting
and dielectric. 相似文献
10.
Marianne Gerny Burkhard Alpers 《International Journal of Computers for Mathematical Learning》2004,9(1):25-57
In this article we describe a mathematical microworld for investigating car motion on a racing course and its use with a group of grade 12 students. The microworld is concerned with the mathematical construction of courses and functions which describe car motion. It is implemented in the computer algebra system, Maple®, which provides the means to represent courses and functions symbolically and graphically. We describe the learning opportunities offered by the microworld in relation to the research literature on functions. Various facets and layers of the function concept are addressed in the microworld, and we suggest how work in the microworld might help in overcoming some well-known misconceptions.This revised version was published online in September 2005 with corrections to the Cover Date. 相似文献