全文获取类型
收费全文 | 25207篇 |
免费 | 3764篇 |
国内免费 | 2195篇 |
专业分类
化学 | 15336篇 |
晶体学 | 539篇 |
力学 | 1378篇 |
综合类 | 289篇 |
数学 | 2274篇 |
物理学 | 11350篇 |
出版年
2024年 | 45篇 |
2023年 | 171篇 |
2022年 | 504篇 |
2021年 | 518篇 |
2020年 | 722篇 |
2019年 | 716篇 |
2018年 | 711篇 |
2017年 | 841篇 |
2016年 | 1090篇 |
2015年 | 1001篇 |
2014年 | 1111篇 |
2013年 | 2544篇 |
2012年 | 1476篇 |
2011年 | 1519篇 |
2010年 | 1275篇 |
2009年 | 1410篇 |
2008年 | 1447篇 |
2007年 | 1456篇 |
2006年 | 1393篇 |
2005年 | 1265篇 |
2004年 | 1220篇 |
2003年 | 1080篇 |
2002年 | 1176篇 |
2001年 | 803篇 |
2000年 | 823篇 |
1999年 | 670篇 |
1998年 | 593篇 |
1997年 | 493篇 |
1996年 | 413篇 |
1995年 | 445篇 |
1994年 | 344篇 |
1993年 | 287篇 |
1992年 | 268篇 |
1991年 | 198篇 |
1990年 | 171篇 |
1989年 | 125篇 |
1988年 | 141篇 |
1987年 | 115篇 |
1986年 | 113篇 |
1985年 | 94篇 |
1984年 | 87篇 |
1983年 | 38篇 |
1982年 | 67篇 |
1981年 | 34篇 |
1980年 | 34篇 |
1979年 | 43篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Peng Ping Wenshou Wang Xuesi Chen Xiabin Jing 《Journal of Polymer Science.Polymer Physics》2007,45(5):557-570
Poly(ε‐caprolactone)‐based segmented polyurethanes (PCLUs) were prepared from poly(ε‐caprolactone) diol, diisocyanates (DI), and 1,4‐butanediol. The DIs used were 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluenediisocyanate (TDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small‐angle X‐ray scattering, and dynamic mechanical analysis were employed to characterize the two‐phase structures of all PCLUs. It was found that HDI‐ and MDI‐based PCLUs had higher degree of microphase separation than did IPDI‐ and TDI‐based PCLUs, which was primarily due to the crystallization of HDI‐ and MDI‐based hard‐segments. As a result, the HDI‐based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard‐segment domains during the sample deformation was responsible for the incomplete shape‐recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 557–570, 2007 相似文献
102.
The paper presents an efficient finite volume method for unstructured grids with rotating sliding parts composed of arbitrary polyhedral elements for both single‐ and two‐phase flows. Mathematical model used in computations is based on the ensemble averaged conservation equations. These equations are solved for each phase and in case of single‐phase flow reduce to the transient Reynolds‐averaged Navier–Stokes (TRANS) equations. Transient flow induced by rotating impellers is thus resolved in time. The use of unstructured grids allows an easy and flexible meshing for the entire flow domain. Polyhedral cell volumes are created on the arbitrary mesh interface placed between rotating and static parts. Cells within the rotating parts move each time step and the new faces are created on the arbitrary interfaces only, while the rest of the domain remain ‘topologically’ unchanged. Implicit discretization scheme allows a wide range of time‐step sizes, which further reduce the computational effort. Special attention is given to the interpolation practices used for the reconstruction of the face quantities. Mass fluxes are recalculated at the beginning of each time step by using an interpolation scheme, which enhances the coupling between the pressure and velocity fields. The model has been implemented into the commercially available CFD code AVL SWIFT (AVL AST, SWIFT Manual 3.1, AVL List GmbH, Graz, Austria, 2002). Single‐phase flow in a mixing vessel stirred by a six‐bladed Rushton‐type turbine and two‐phase flow in aerated stirred vessel with the four‐blade Rushton impeller are simulated. The results are compared with the available experimental data, and good agreement is observed. The proposed algorithm is proved to be both stable and accurate for single‐phase as well as for the two‐phase flows calculations. Copyright 2004 John Wiley & Sons, Ltd. 相似文献
103.
Ryohei Hanayama Kenichi Hibino Shin’ichi Warisawa Mamoru Mitsuishi 《Optical Review》2004,11(5):337-343
Wavelength scanned interferometry allows the simultaneous measurement of top surface shape and optical thickness variation of a transparent object consisting of several parallel surfaces. Interference signals from these surfaces can be separated in frequency space, and their phases are detected by discrete Fourier analysis. However, these signal frequencies are shifted from the detection frequency by the refractive index dispersion of the object and a nonlinearity of the wavelength scanning. The Fourier analysis is sensitive to the detuning of the signal frequency and suffers from the multiple-beam interference noise. Conventional error-compensating algorithms cannot be applied to an object consisting of more than three reflecting surfaces. We derive a new 2N-1 sample error-compensating algorithm, which allows the phase detection of any order of harmonic frequency among the interference signals. The new algorithm suppresses the effect of signal frequency detuning as well as the multiple-beam interference noise and can be applied to the measurement of complex objects consisting of more than three reflecting surfaces. 相似文献
104.
105.
It is shown that the cascaded fifth-order nonlinear phase shifts will increase with energy loss in the cascaded processes. Essentially different from the multi-photon absorption accompanied with inherent material nonlinearities, the loss of fundamental wave in a cascaded process is controllable and suppressible. By introducing difference frequencies generated from the reaction between the fundamental and its second harmonic after the cascaded processes, the fundamental wave can be free of energy loss, while the large cascaded fifth-order nonlinear phase shift is maintained. 相似文献
106.
107.
In this paper,the authors obtain the Backlund transformation on time-like surfaces with constant mean curvature in R2,1.Using this transformation,families of surfaces with constant mean curvature from known ones can be constructed. 相似文献
108.
In this article a new technique was developed to fabricate scaffolds with a unique microstructure by solid–liquid separation in combination with particulate-leaching. Firstly, the effects of polymer concentration, quenching temperature on the porous morphology and the mechanical property of obtained scaffolds during solid–liquid separation have been investigated. Then, salt granules as porogen were introduced into the solid–liquid phase separation to produce the unique pore structure of the scaffold. The pore diameter of the scaffold could be controlled with the particulate size and the wall of pores possessed special microstructure, which enhanced the pore interconnectivity. The cell culture results confirmed that a good interconnectivity of the scaffold prepared by the improved solid–liquid separation was useful for nutrition transportation and cell proliferation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
109.
We use a symmetry approach to solve the classification problem for integrable N-component evolution systems having the form of conservation laws. We obtain complete lists of both isotropic and anisotropic systems of this type and find auto-Bäcklund transformations with a spectral parameter for all systems. 相似文献
110.
Andrei N. Yakunin 《Central European Journal of Physics》2004,2(3):535-555
A cubic structure of polymer colloid complexes is studied. The technique of the research includes i) an analysis of well-known
literature SAXS data; on this basis, ii) constructing a simple model to estimate geometric structure parameters and to obtain
a simulated scattering curve; and iii) comparing the model with the real structure obtained from the SAXS data, using the
reconstruction of electron density distribution. A bicontinuous structure in cubic mesophases is formed.
Dedicated to the memory of Alexander T. Dembo 相似文献