全文获取类型
收费全文 | 1487篇 |
免费 | 24篇 |
国内免费 | 3篇 |
专业分类
化学 | 685篇 |
晶体学 | 13篇 |
力学 | 58篇 |
数学 | 140篇 |
物理学 | 618篇 |
出版年
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 20篇 |
2019年 | 16篇 |
2018年 | 22篇 |
2017年 | 28篇 |
2016年 | 38篇 |
2015年 | 23篇 |
2014年 | 36篇 |
2013年 | 92篇 |
2012年 | 78篇 |
2011年 | 87篇 |
2010年 | 55篇 |
2009年 | 53篇 |
2008年 | 77篇 |
2007年 | 64篇 |
2006年 | 45篇 |
2005年 | 61篇 |
2004年 | 50篇 |
2003年 | 41篇 |
2002年 | 47篇 |
2001年 | 28篇 |
2000年 | 31篇 |
1999年 | 32篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 23篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有1514条查询结果,搜索用时 15 毫秒
131.
The spinel FeCoCrO4 has been studied between 4.2 and 538°K. Characteristic Mossbauer spectra of paramagnetic, magnetic and electronic relaxation types have been observed. The Mossbauer parameters for Fe3+ ions situated at tetrahedral (A) and octahedral (B) sites have been calculated. The cation distribution in magnetic and paramagnetic phases is found to be approximately Fe0.53+Co0.52+[Co0.52+Fe0.53+Cr3+]O4. The Neel temperature been determined by the temperature scanning method to be 310±5°K. 相似文献
132.
In this paper an attempt has been made to find the solution of the boundary layer equations for two-dimensional laminar steady motion of a viscous incompressible fluid in a convergent channel (sink flow) with suction at the wall. Suction velocity v0 (x) ~ 1/x has been imposed at the wall and an approximate solution has been obtained with the help of similarity transformation. A solution valid at a large distance from the wall and a series solution valid near the wall have been obtained and the two solutions have been joined at a suitable point. It is seen that the boundary layer thickness diminishes as the value of the suction parameter\(\lambda ( = v_0 x/\sqrt {u_1 v} )\) increases. The velocity profile and the boundary layer parameters for solid wall (λ = 0) obtained from this solution are found to be in close agreement with the profile and the parameters calculated from the known exact solution for the solid wall problem. 相似文献
133.
Hu X Jiao X Narayanan S Jiang Z K Sinha S Lurio LB Lal J 《The European physical journal. E, Soft matter》2005,17(3):353-359
We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion. 相似文献
134.
We report a novel application of an ultrathin-polymer-film-based, resonance-enhanced x-ray waveguide as a real-time nanoprobe for elucidating dilute, yet disordered, gold nanoparticles embedded in the polymer matrix. This nanoprobe promises a sensitivity enhancement of several orders of magnitude, hence revealing in real time the lateral nanoparticle distribution with subnanometer spatial resolution. We observed that the motion of the nanoparticles is strongly anisotropic, with in-plane coalescence taking place more rapidly than out-of-plane diffusion, which can ultimately facilitate the formation of two-dimensional structures. 相似文献
135.
Seweryniak D Woods PJ Carpenter MP Davinson T Janssens RV Jenkins DG Lauritsen T Lister CJ Ruiz C Shergur J Sinha S Woehr A 《Physical review letters》2005,94(3):032501
The level structure of (22)Mg has been studied with high-sensitivity gamma-ray spectroscopy techniques. A complete level scheme is derived incorporating all subthreshold states and all levels in the energy region relevant for novae burning. The excitation energy of the most important astrophysical resonance is measured with improved accuracy and found to differ from previous values. Combining the present result with a recent resonance energy measurement of this state leads to a derived (22)Mg mass excess of -400.5(13) keV. 相似文献
136.
Braunisch H Habashy TM Sinha BK Pabon J Kong JA 《The Journal of the Acoustical Society of America》2004,115(1):269-279
The problem of inferring unknown geometry and material parameters of a waveguide model from noisy samples of the associated modal dispersion curves is considered. In a significant reduction of the complexity of a common inversion methodology, the inner of two nested iterations is eliminated: The approach described does not employ explicit fitting of the data to computed dispersion curves. Instead, the unknown parameters are adjusted to minimize a cost function derived directly from the determinant of the boundary condition system matrix. This results in an efficient inversion scheme that, in the case of noise-free data, yields exact results. Multimode data can be simultaneously processed without extra complications. Furthermore, the inversion scheme can accommodate an arbitrary number of unknown parameters, provided that the data have sufficient sensitivity to these parameters. As an important application, we consider the sonic guidance condition for a fluid-filled borehole in an elastic, homogeneous, and isotropic rock formation for numerical forward and inverse dispersion analysis. We investigate numerically the parametric inversion with errors in the model parameters and the influence of bandwidth and noise, and examine the cases of multifrequency and multimode data, using simulated flexural and Stoneley dispersion data. 相似文献
137.
Gutt C Ghaderi T Chamard V Madsen A Seydel T Tolan M Sprung M Grübel G Sinha SK 《Physical review letters》2003,91(7):076104
We report measurements of propagating capillary waves on a liquid water surface at T=5 degrees C with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the q region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions g(1)(tau) and g(2)(tau). 相似文献
138.
We present a method for solving the wormlike-chain (WLC) model for twisting semiflexible polymers to any desired accuracy. We show that the WLC free energy is a periodic function of the applied twist with period 4pi. We develop an analogy between WLC elasticity and the geometric phase of a spin-1 / 2 system. These analogies are used to predict elastic properties of twist-storing polymers. We graphically display the elastic response of a single molecule to an applied torque. This study is relevant to mechanical properties of biopolymers such as DNA. 相似文献
139.
In this article, we first investigate the bending of light rays in 4D line elements representing spherically symmetric, static on–brane geometries. The amount of bending in these four dimensional, strong and weak field solutions is derived. Signatures, which appear in the bending formulae, due to the presence of extra dimensions are discussed. Subsequently, as a separate exercise, we calculate the bending of null geodesic trajectories in a bulk five dimensional spacetime with a Schwarzschild line element on the 3-brane section. We interpret the deviation of null trajectories as that of gravitational signals or five dimensional photons, which are, unlike light rays confined to four dimensions, allowed to propagate along the fifth (extra) dimension. Features of the presence of extra dimensions in the effective potentials and the bending formula are analysed in this context. 相似文献
140.
Phytochemical investigation of the leaves of Bidens pilosa lead to the isolation and characterization of a new disubstituted acetylacetone (1) named as 3-Propyl-3-(2,4,5-trimethoxy)benzyloxy-pentan-2,4-dione. 相似文献