全文获取类型
收费全文 | 273232篇 |
免费 | 2322篇 |
国内免费 | 733篇 |
专业分类
化学 | 127250篇 |
晶体学 | 3991篇 |
力学 | 14547篇 |
综合类 | 7篇 |
数学 | 42175篇 |
物理学 | 88317篇 |
出版年
2021年 | 990篇 |
2020年 | 1110篇 |
2019年 | 1127篇 |
2018年 | 10441篇 |
2017年 | 11408篇 |
2016年 | 6539篇 |
2015年 | 2843篇 |
2014年 | 2611篇 |
2013年 | 7824篇 |
2012年 | 10757篇 |
2011年 | 20851篇 |
2010年 | 12445篇 |
2009年 | 12592篇 |
2008年 | 18265篇 |
2007年 | 21898篇 |
2006年 | 7214篇 |
2005年 | 13888篇 |
2004年 | 9562篇 |
2003年 | 8569篇 |
2002年 | 6396篇 |
2001年 | 6194篇 |
2000年 | 4869篇 |
1999年 | 3520篇 |
1998年 | 2674篇 |
1997年 | 2634篇 |
1996年 | 2749篇 |
1995年 | 2372篇 |
1994年 | 2247篇 |
1993年 | 2107篇 |
1992年 | 2407篇 |
1991年 | 2380篇 |
1990年 | 2093篇 |
1989年 | 2080篇 |
1988年 | 2112篇 |
1987年 | 2042篇 |
1986年 | 1947篇 |
1985年 | 2862篇 |
1984年 | 2850篇 |
1983年 | 2296篇 |
1982年 | 2475篇 |
1981年 | 2360篇 |
1980年 | 2315篇 |
1979年 | 2284篇 |
1978年 | 2358篇 |
1977年 | 2232篇 |
1976年 | 2202篇 |
1975年 | 2169篇 |
1974年 | 2071篇 |
1973年 | 2194篇 |
1972年 | 1234篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
161.
R. A. Ganeev A. I. Ryasnyanskii M. K. Kodirov Sh. R. Kamalov V. A. Li R. I. Tugushev T. Usmanov 《Technical Physics》2002,47(8):991-995
Nonlinear optical parameters (nonlinear refractive indices and nonlinear absorption coefficients) of solutions of polyvinylpyrrolidone doped by cobalt to various concentrations are measured at the lasing and second-harmonic wavelengths of a picosecond Nd:YAG laser (λ=1064 and 532 nm, respectively, and τ=35 ps). Data on optical limitation in these solutions are presented. The absence of nonlinear absorption in the IR spectral range and its significant effect in the visible range are demonstrated. Optical limitation at a wavelength of 1064 nm is related to defocusing, whereas at 532 nm, this effect is caused by two-photon absorption and partially by inverse saturated absorption and defocusing. Nonlinear optical parameters of metal-polymer complexes are reported. 相似文献
162.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
163.
N. Euler W. -H. Steeb L. G. S. Duarte I. C. Moreira 《International Journal of Theoretical Physics》1991,30(9):1267-1271
The techniques of invertible point transformations and the Painlevé analysis can be used to construct integrable ordinary differential equations. We compare both techniques for the second Painlevé transcendent. 相似文献
164.
In intonation research, prominence-lending pitch movements have either been described on a linear or on a logarithmic frequency scale. An experiment has been carried out to check whether pitch movements in speech intonation are perceived on one of these two scales or on a psychoacoustic scale representing the frequency selectivity of the auditory system. This last scale is intermediary between the other two scales. Subjects matched the excursion size of prominence-lending pitch movements in utterances resynthesized in different pitch registers. Their task was to adjust the excursion size in a comparison stimulus in such a way that it lent equal prominence to the corresponding syllable in a fixed test stimulus. The comparison stimulus and the test stimulus had pitches running parallel on either the logarithmic frequency scale, the psychoacoustic scale, or the linear frequency scale. In one-half of the experimental sessions, the test stimulus was presented in the low register, while the comparison stimulus was presented in the high register, and, conversely, for the other half of the sessions. The result is that, in all cases, stimuli are matched in such a way that the average excursion sizes in different registers are equal on the psychoacoustic scale. 相似文献
165.
C M Srivastava 《Pramana》1989,32(3):251-267
A theory of high temperature superconductivity in YBa2Cu3O7_δ compound has been developed on the basis of the momentum pairing of electrons through the relativistic Darwin interaction.
The transport behaviour of electrons is explained in terms of a mechanism of correlated electron transfer arising from the
electron-phonon coupling. A model Hamiltonian has been developed to describe the superconducting properties of the system.
This gives an energy gap which is higher than the BCS value. Attempts have been made to explain the absence of isotope effect,
the linear dependence of specific heat, the presence of larger temperature-independent paramagnetism in the normal phase and
the softening of some of the optic phonon modes observed in this system. 相似文献
166.
167.
S. P. Mukherjee A. K. Chattopadhyay 《The Journal of the Operational Research Society》1989,40(5):489-494
Consider an organization with several categories of staff, each having a specified number of members. The age of entry into service and the age of retirement are both specified. Withdrawals occur at time-independent rates. Under this set-up, the authors have computed the maximum ages at which promotions should take place, assuming that the staff members continuing at various ages are random. Some illustrative calculations have been carried out. 相似文献
168.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed. 相似文献
169.
N. S. Simonović 《Few-Body Systems》2006,38(2-4):139-145
In agreement with the Kohn theorem the relative motion (rel) of three electrons in a two-dimensional parabolic trap separates
from the centre-of-mass (CM) motion. By introducing new coordinates the Hamiltonian for relative motion in the approximation
of non-interacting electrons can be taken to the normal form. The eigenstates of the normalized Hamiltonian are products of
the Fock-Darwin states for normal modes. The energy levels for relative motion are obtained by diagonalizing the exact Hamiltonian
in the eigenbasis for the non-interacting case. In this basis the interaction matrix elements can be obtained in the analytical
form. Since the rank of the Hamiltonian matrix is significantly reduced, the calculations are faster and more accurate than
those for the full (CM + rel) motion. This advantage is especially important for the calculations of excited states and the
analysis of energy spectra. 相似文献
170.
C. Maurel 《Surface science》2006,600(2):442-447
Light emitted in the tunneling junction of a scanning tunneling microscope has been used to establish the electrical characteristics of nanojunctions made of Au islands deposited on flat MoS2 surfaces. It is shown that these characteristics are those of rectifying contacts when the gold islands are isolated and that they evolve toward those of ohmic contacts when the island density increases. It is observed that the rectifying behavior also evolves over time as on infinite metal/semiconductor contacts. Using the STM tip, single gold islands can be manipulated on the MoS2 surface so that their electrical behavior can be changed depending on their position with regard to the other islands. 相似文献