全文获取类型
收费全文 | 212517篇 |
免费 | 1999篇 |
国内免费 | 635篇 |
专业分类
化学 | 107625篇 |
晶体学 | 3378篇 |
力学 | 9586篇 |
综合类 | 5篇 |
数学 | 24043篇 |
物理学 | 70514篇 |
出版年
2021年 | 1933篇 |
2020年 | 2030篇 |
2019年 | 2201篇 |
2018年 | 2872篇 |
2017年 | 2745篇 |
2016年 | 4125篇 |
2015年 | 2619篇 |
2014年 | 3929篇 |
2013年 | 9554篇 |
2012年 | 7815篇 |
2011年 | 9389篇 |
2010年 | 6426篇 |
2009年 | 6237篇 |
2008年 | 8438篇 |
2007年 | 8580篇 |
2006年 | 8188篇 |
2005年 | 7324篇 |
2004年 | 6800篇 |
2003年 | 5929篇 |
2002年 | 5756篇 |
2001年 | 6534篇 |
2000年 | 4996篇 |
1999年 | 3872篇 |
1998年 | 3101篇 |
1997年 | 3130篇 |
1996年 | 2864篇 |
1995年 | 2677篇 |
1994年 | 2525篇 |
1993年 | 2381篇 |
1992年 | 2731篇 |
1991年 | 2703篇 |
1990年 | 2629篇 |
1989年 | 2421篇 |
1988年 | 2482篇 |
1987年 | 2478篇 |
1986年 | 2302篇 |
1985年 | 2998篇 |
1984年 | 3252篇 |
1983年 | 2658篇 |
1982年 | 2836篇 |
1981年 | 2793篇 |
1980年 | 2661篇 |
1979年 | 2750篇 |
1978年 | 2840篇 |
1977年 | 2836篇 |
1976年 | 2895篇 |
1975年 | 2677篇 |
1974年 | 2652篇 |
1973年 | 2780篇 |
1972年 | 1768篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The general theory on the transformation of elastic waves at a rigid nodal junction of an arbitrary number of thin plates is considered. The notion of transformation marix is introduced, and a way for computing it and numerical examples are given. Properties of the transformation matrix resulted from the reciprocity principle and the energy conservatin law are studied. In particular, a new relation that expresses the energy conservation low for the case where a wave damped in the direction of the joint of plates is a source of a field is obtained. Bibliography: 18 titles. 相似文献
112.
Problem-structuring techniques are an integral aspect of ‘Soft-OR’. SSM, SAST, Strategic Choice, and JOURNEY Making, all depend for their success on a group developing a shared view of a problem through some form of explicit modelling. The negotiated problem structure becomes the basis for problem resolution. Implicit to this process is an assumption that members of the group share and build their knowledge about the problem domain. This paper explores the extent to which this assumption is reasonable. The research is based on detailed records from the use of JOURNEY Making, where it has used special purpose Group Support software to aid the group problem structuring. This software continuously tracks the contributions of each member of the group and thus the extent to which they appear to be ‘connecting’ and augmenting their own knowledge with that of other members of the group. Software records of problem resolution in real organisational settings are used to explore the sharing of knowledge among senior managers. These explorations suggest a typology of knowledge sharing. The implications of this typology for problem structuring and an agenda for future research are considered. 相似文献
113.
D.E. ShalómH. Pastoriza 《Solid State Communications》2003,126(7):379-383
We present kinetic inductance measurements in current driven Josephson junction arrays. Measurements performed with circular coils indicate that this technique is very sensitive to the vortex mobility. Results obtained with anisotropic detection coils provide experimental evidence for the anisotropic response of a driven vortex lattice. Anisotropic behavior is obtained when rising the temperature or the mean vortex velocity as indicated by the loss of the superconducting shielding capability, first in the direction of vortex motion and then in the perpendicular direction. 相似文献
114.
The shape of lines in the radiospectroscopic (NMR and EPR) and dielectric spectra of materials formed by nanoparticles (hereafter, nanomaterials) is analyzed theoretically. The theory is developed in the framework of the core and shell model according to which a nanoparticle consists of two regions whose properties are affected and unaffected by the surface, respectively. The changes in the resonance frequency, the relaxation time, and the static permittivity due to the surface tension are taken into account, and the Gaussian and Lorentzian shapes of homogeneously broadened lines are considered. The inhomogeneous broadening of the spectral lines is examined for several types of nanoparticle size distributions. It is demonstrated that the splitting of the initial lines in the spectra of bulk systems into pairs of lines with a decrease in the particle size is a specific feature of the spectra of nanoparticles. The intensities and half-widths of the lines are investigated as functions of the parameters of the size distribution of nanoparticles. The results of theoretical calculations are compared with recent experimental data on the 17O and 25Mg NMR spectra of nanocrystalline MgO. The theoretical dependences of the intensity, the resonance frequency, and the half-width of the spectral lines are in good agreement with the experimental data. The proposed theory offers a satisfactory explanation of the behavior of the static permittivity in BaTiO3 ceramic materials with nanometer-sized grains. 相似文献
115.
Given one or more vibrational modes of a membrane, the free vibration equation can be applied to infer the mass surface density. This paper considers determining the surface density of an inhomogeneous membrane from digitized holographic projections (interferograms) of the modeshapes. Spatially discrete numerical models of the membrane surface are presented, which can be used to solve both forward and inverse vibration problems. The accuracy of the discrete models is examined for exactly solvable free vibration problems involving inhomogeneous membranes. For the solution of the inverse problem, error estimates are given for the mass surface density deduced from modeshape interferograms. The practicability of the method is investigated using simulated experimental data for membranes with composite and continuously inhomogeneous density profiles. Strategies are discussed for reducing errors in the reconstructed densities. 相似文献
116.
Dinesh Topwal U. Manju Sugata Ray S. Raj D. D. Sarma S. R. Krishnakumar M. Bertolo S. La Rosa G. Cautero 《Journal of Chemical Sciences》2006,118(1):87-92
Disordered Sr2FeMoO6 shows a drastic reduction in saturation magnetization compared to highly ordered samples, moreover magnetization as a function
of the temperature for different disordered samples shows qualitatively different behaviours. We investigate the origin of
such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish
that extensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples, is
responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with
composition fluctuations of the type Sr2Fe1+x
Mo1-x
O6 with Fe-rich (x > 0) and Mo-rich (x < 0) regions.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
117.
D. Barrios Rolanía G. Lpez Lagomasino E. B. Saff 《Journal of Approximation Theory》2003,124(2):263-281
Using a convergence theorem for Fourier–Padé approximants constructed from orthogonal polynomials on the unit circle, we prove an analogue of Hadamard's theorem for determining the radius of m-meromorphy of a function analytic on the unit disk and apply this to the location of poles of the reciprocal of Szeg
functions. 相似文献
118.
119.
Fabry-Perot resonators have long been advocated to improve the limited contrast ratio of multiple quantum well optical modulators used in photonic switches based on self electrooptic effect devices (SEEDs) and in other array based optical interconnection schemes. Using data on field dependent GaAs/AlGaAs quantum well absorption and refraction, we have modelled the reflectivity, modulation depth and contrast ratio of resonant modulators. Our results are generally valid for any quantum well modulator and demonstrate 23the important role played by electro-refraction even in regions of strong absorption. Resonators give large contrast ratios but there are trade-offs in the maximum reflectivity change achievable with Fabry-Perot resonators compared to simple modulators. The model gives the optimum number of quantum wells and reflectivity values required to make a resonator at any wavelength for a given quantum well structure. Understanding the limits of Fabry-Perot quantum well modulator performance is important for their application in symmetric self electrooptic effectiveness for photonic switching where modulation and detection properties are both used and for optical interconnection systems. 相似文献
120.
An interconnection strategy with built-in adaptive controllersis presented which achieves synchronization of scalar linearsystems: the closed-loop network forces all outputs to followthe same signal asymptotically while maintaining the open-loopcharacteristics. In the design of the output feedback controllers,no knowledge of system parameters is assumed, but each systemmust have the same poles and be high-gain-stable. The proofof the main theorem relies critically on derived systems-theoreticresults and the special system topology as a network of interconnectedsystems. The topology is explained by first solving the simplerproblem of signal synchronization. 相似文献