全文获取类型
收费全文 | 1446篇 |
免费 | 41篇 |
国内免费 | 90篇 |
专业分类
化学 | 791篇 |
晶体学 | 37篇 |
力学 | 41篇 |
综合类 | 16篇 |
数学 | 199篇 |
物理学 | 493篇 |
出版年
2021年 | 11篇 |
2020年 | 20篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 23篇 |
2014年 | 30篇 |
2013年 | 80篇 |
2012年 | 52篇 |
2011年 | 73篇 |
2010年 | 43篇 |
2009年 | 43篇 |
2008年 | 63篇 |
2007年 | 68篇 |
2006年 | 54篇 |
2005年 | 72篇 |
2004年 | 54篇 |
2003年 | 51篇 |
2002年 | 53篇 |
2001年 | 48篇 |
2000年 | 38篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 38篇 |
1996年 | 31篇 |
1995年 | 17篇 |
1994年 | 32篇 |
1993年 | 36篇 |
1992年 | 27篇 |
1991年 | 45篇 |
1990年 | 25篇 |
1989年 | 21篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 8篇 |
1973年 | 18篇 |
1972年 | 7篇 |
排序方式: 共有1577条查询结果,搜索用时 46 毫秒
1.
The method described in this paper allows an investigator to determine the intrinsic stress of a polymer layer in a way that
does not result in damage to devices or test structures. The method requires that a small area of the polymer be released
from the substrate to form a diaphragm. The diaphragm is stimulated with acoustic white noise and the diaphragm movement is
monitored with a laser vibrometer. The first few resonance frequencies of the diaphragm are obtained using a laser vibrometer
and then those frequencies are used to calculate the membrane intrinsic bi-axial tension. 相似文献
2.
乐毅 《宁波大学学报(理工版)》2004,17(4):437-440
从正交各向异性三维弹性动力学的控制方程出发,在求得四边简支矩形板自由振动频率和位移振型的基础上,构造了受迫振动的位移函数;利用自由振动位移振型的正交性,将控制方程的空间变量和时间变量分离,得到了广义质量、广义力和频率表示的关于时间的2阶常微分方程,从而得到了正交各向异性弹性矩形板在受迫振动下的位移场和应力场.给出了本文方法与薄板理论的算例. 相似文献
3.
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
4.
5.
Whereas glucose oxidase and related proteins are encapsulated readily in silica sol–gels, α-hydroxy enzymes such as lactate
oxidase (LOx), are reported to be damaged by electrostatic interaction with these matrices. Based on a previous report, poly(ethyleneimine),
PEI, was evaluated as a protecting compound under conditions suited to analytical measurements. With LOx and PEI co-encapsulated
in a silica sol–gel, the enzyme retained 62% of its initial activity after 20 days. In the absence of PEI, activity was lost
during the processing. Batch analytical measurements with enzyme-doped sol–gel yielded a linear response over the range 0.5–2.0 mM
lactate and a detection limit of 0.03 mM lactate. Both simple incorporation of LOx in a silica sol–gel and an alternative
protection method, blocking the ion-exchange sites on silica with La(III), failed. These negative results supported the hypothesis
that the efficacy of PEI was related to its formation of a protective sheath around the enzyme.
Author for correspondence. E-mail: coxja@muohio.edu
Received July 29, 2002; accepted December 15, 2002
Published online May 19, 2003 相似文献
6.
7.
Endoscopic illumination systems conduct light down a built-in fibre-optic bundle to illuminate the object. Many modern endoscopes employ wide-field imaging optical systems and therefore require an illuminating beam of large divergence. This is commonly provided by placing a strong diverging lens at the far end of the fibre bundle, but it results in a poor uniformity of illumination in the object space. This paper describes the design of a telescopic illumination system to overcome this problem. 相似文献
8.
S J Cox 《The Journal of the Operational Research Society》2007,58(1):2-9
The UK nuclear industry is currently undergoing a series of dramatic changes. Important, among many is the establishment of the Nuclear Decommissioning Authority (NDA) with an associated impact on service delivery. At the same time, the debate on the future of our energy supply in the UK is increasingly focused on the question of the nuclear option. Issues of safety and reliability are paramount for the nuclear industry given both the nature of the hazard and the associated public perceptions of the associated risks. This paper explores linked developments in human factors and the management of safety in the nuclear industry in the context of unprecedented change. 相似文献
9.
M. G. Cox 《Numerical Algorithms》1993,5(3):133-154
This paper addresses a fundamental problem in mathematics and numerical analysis, that of determining a polynomial interpolant to specified data. The data is taken as consisting of a set of points (abscissae), at each of which is specified a function value. Additionally, at each point, any number of leading derivative values of the function may be given.
Mathematically, this problem is solved. The classical Lagrangian interpolation formula applies in the derivative-free case, and the Newton form of the interpolating polynomial in general.Numerically, few reliable algorithms are available; most published algorithms concentrate on speed of computation. This paper describes an algorithm that delivers the required polynomial in Chebyshev form. It is based on the repeated use of the Newton representation, with a data ordering strategy and iterative refinement to improve accuracy, using a carefully devised merit function to measure success. The algorithm attempts to provide a polynomial that is stable in the sense of backward error analysis, i.e. that is exact for slightly perturbed data.Implementations of the algorithm have been in use since the early 1980s in the NAG Library and NPL's Data Approximation Subroutine Library (DASL). In addition to providing polynomial interpolants in their own right, these implementations are used as computational modules in the NAG and DASL routines for constrained least-squares polynomial data fitting.This paper constitutes the first detailed presentation of the algorithm. 相似文献
10.
E. A. Davis A. Singh S. F. J. Cox S. R. Kreitzman T. L. Estle B. Hitti R. L. Lichti R. DuVarney 《Hyperfine Interactions》1994,86(1):705-710
Studies of the muonium fractions in the amorphous oxide a-SiO have been carried out by RF resonance at TRIUMF, Canada and LF repolarization techniques at RAL, U.K. The resonance measurements confirm the presence of the interstitial Mu centre in this intermediate oxide of silicon. Analysis of the data gathered at RAL, using a recently-developed fitting technique, reveals that the Mu* state is present here as well, but with lower relative fractions than in a-Si. However, as in the latter material, but in contrast to c-Si, this bond-centre species appears to be stable up to room temperature. 相似文献