全文获取类型
收费全文 | 3862篇 |
免费 | 79篇 |
国内免费 | 23篇 |
专业分类
化学 | 2688篇 |
晶体学 | 32篇 |
力学 | 95篇 |
数学 | 490篇 |
物理学 | 659篇 |
出版年
2022年 | 19篇 |
2021年 | 29篇 |
2020年 | 33篇 |
2019年 | 38篇 |
2018年 | 29篇 |
2017年 | 33篇 |
2016年 | 69篇 |
2015年 | 60篇 |
2014年 | 66篇 |
2013年 | 192篇 |
2012年 | 183篇 |
2011年 | 227篇 |
2010年 | 105篇 |
2009年 | 85篇 |
2008年 | 211篇 |
2007年 | 219篇 |
2006年 | 191篇 |
2005年 | 188篇 |
2004年 | 189篇 |
2003年 | 151篇 |
2002年 | 141篇 |
2001年 | 47篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 44篇 |
1997年 | 48篇 |
1996年 | 68篇 |
1995年 | 68篇 |
1994年 | 63篇 |
1993年 | 54篇 |
1992年 | 41篇 |
1991年 | 40篇 |
1990年 | 53篇 |
1989年 | 44篇 |
1988年 | 47篇 |
1987年 | 48篇 |
1986年 | 45篇 |
1985年 | 84篇 |
1984年 | 57篇 |
1983年 | 56篇 |
1982年 | 68篇 |
1981年 | 57篇 |
1980年 | 63篇 |
1979年 | 43篇 |
1978年 | 38篇 |
1977年 | 41篇 |
1976年 | 25篇 |
1975年 | 27篇 |
1974年 | 35篇 |
1973年 | 35篇 |
排序方式: 共有3964条查询结果,搜索用时 0 毫秒
81.
Wei J Liu Z Chai Z Yuan J Lian J Shen GX 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(2):358-363
In this paper, a digital wireless transmission system based on 802.11b standard for magnetic resonance imaging (MRI) application is designed and built for the first time to eliminate the interference aroused by coil array cables. The analysis shows that the wireless receiver has a very high sensitivity to detect MRI signals. The modulation technique of differential quadrature phase shift keyed (DQPSK) can be applied to MRI data transmission with rate of 2 Mbps and bandwidth of 2 MHz. The bench test verifies that this wireless link has a dynamic range over 86 dB supporting up to 3 T MRI system data transmission. The 2D spin echo imaging of phantom is performed and the SNR of the image obtained by the wireless transmission can be comparable with that got by the coaxial cables. 相似文献
82.
Baltrusaitis RM Becker JJ Blaylock GT Brown JS Bunnell KO Burnett TH Cassell RE Coffman D Cook V Coward DH Cui H Del Papa C Dorfan DE Duncan AL Einsweiler KF Eisenstein BI Fabrizio R Gladding G Grancagnolo F Hamilton RP Hauser J Heusch CA Hitlin DG Köpke L Mockett PM Moss L Mozley RF Nappi A Odian A Partridge R Perrier J Plaetzer SA Richman JD Roehrig JR Russell JJ Sadrozinski HF Scarlatella M Schalk TL Schindler RH Seiden A Sleeman JC Spadafora AL Thaler JJ Toki W Unno Y Villa F Wattenberg A 《Physical review letters》1985,55(17):1723-1726
83.
The perturbation function of a Cd probe atom bound in a hydrogen-decorated vacancy complex in Pt is found to exhibit dynamical
relaxation at 294 K, as measured by the technique of perturbed γ-γ angular correlations. Based on other characteristics of
the complex, a model is proposed for the structure of the complex. In the undecorated state, it consists of a probe atom at
the center of a tetrahedron of vacancies in the fcc structure. In the decorated state at low temperature, the probe atom returns
to one of the four vacant lattice sites. The relaxation at room temperature is attributed to motion of the probe atom in a
cage formed by the four vacant sites. 相似文献
84.
If M is an isoparametric hypersurface in a sphere S
n
with four distinct principal curvatures, then the principal curvatures κ1, . . . , κ4 can be ordered so that their multiplicities satisfy m
1 = m
2 and m
3 = m
4, and the cross-ratio r of the principal curvatures (the Lie curvature) equals −1. In this paper, we prove that if M is an irreducible connected proper Dupin hypersurface in R
n
(or S
n
) with four distinct principal curvatures with multiplicities m
1 = m
2 ≥ 1 and m
3 = m
4 = 1, and constant Lie curvature r = −1, then M is equivalent by Lie sphere transformation to an isoparametric hypersurface in a sphere. This result remains true if the
assumption of irreducibility is replaced by compactness and r is merely assumed to be constant.
相似文献
85.
Bahram Alidaee Fred Glover Gary Kochenberger Haibo Wang 《European Journal of Operational Research》2007
The unconstrained quadratic binary program (UQP) is proving to be a successful modeling and solution framework for a variety of combinatorial optimization problems. Experience reported in the literature with several problem classes has demonstrated that this approach works surprisingly well in terms of solution quality and computational times, often rivaling and sometimes surpassing more traditional methods. In this paper we report on the application of UQP to the maximum edge-weighted clique problem. Computational experience is reported illustrating the attractiveness of the approach. 相似文献
86.
Blood analysis by Raman spectroscopy 总被引:1,自引:0,他引:1
Concentrations of multiple analytes were simultaneously measured in whole blood with clinical accuracy, without sample processing, using near-infrared Raman spectroscopy. Spectra were acquired with an instrument employing nonimaging optics, designed using Monte Carlo simulations of the influence of light-scattering-absorbing blood cells on the excitation and emission of Raman light in turbid medium. Raman spectra were collected from whole blood drawn from 31 individuals. Quantitative predictions of glucose, urea, total protein, albumin, triglycerides, hematocrit, and hemoglobin were made by means of partial least-squares (PLS) analysis with clinically relevant precision (r(2) values >0.93). The similarity of the features of the PLS calibration spectra to those of the respective analyte spectra illustrates that the predictions are based on molecular information carried by the Raman light. This demonstrates the feasibility of using Raman spectroscopy for quantitative measurements of biomolecular contents in highly light-scattering and absorbing media. 相似文献
87.
Carl Bracken Eimear Byrne Gary McGuire Gabriele Nebe 《Designs, Codes and Cryptography》2011,61(3):261-272
Establishing the CCZ-equivalence of a pair of APN functions is generally quite difficult. In some cases, when seeking to show
that a putative new infinite family of APN functions is CCZ inequivalent to an already known family, we rely on computer calculation
for small values of n. In this paper we present a method to prove the inequivalence of quadratic APN functions with the Gold functions. Our main
result is that a quadratic function is CCZ-equivalent to the APN Gold function x2r+1{x^{2^r+1}} if and only if it is EA-equivalent to that Gold function. As an application of this result, we prove that a trinomial family
of APN functions that exist on finite fields of order 2
n
where n ≡ 2 mod 4 are CCZ inequivalent to the Gold functions. The proof relies on some knowledge of the automorphism group of a code
associated with such a function. 相似文献
88.
89.
The macroscopic thermodynamic stability of a system of 108 diatomic molecules undergoing planar Couette flow far from equilibrium is reported. The system is perturbed from the steady state using a nondissipative variable colour field which induces a polarization in the system. It is found that the steady state for the system corresponds to an extremum in the generalized free energy and entropy production. However, while the free energy is always a minimum, the entropy production may be either a minimum or a maximum depending upon the direction of the colour field. These results, for a molecular system, are fundamentally different from those for an equivalent atomic system. 相似文献
90.
Gary Gordon 《Discrete Mathematics》1984,52(1):51-65
For a given prime p, we construct a collection of 2p matroids Gp,a with (1) χpf(Gp,a)={p}, and (2) Gp,a is an excluded minor for rational representability. The motivating construction (Section 2) disproves a conjectures of Reid [4], using relatively high-rank, high cardinality matroids. The general construction (Section 3) makes use of ordered partitions (χpf(G) denotes the prime-field characteristic set of G, i.e., the set of prime fields over which G may be represented, while G can be represented over fields of no other characteristic.) Finally, Section 4 offers another construction with the same properties–a kind of projective dual to Section 2. 相似文献