全文获取类型
收费全文 | 522985篇 |
免费 | 6671篇 |
国内免费 | 1552篇 |
专业分类
化学 | 248056篇 |
晶体学 | 6707篇 |
力学 | 19390篇 |
综合类 | 13篇 |
数学 | 52033篇 |
物理学 | 137943篇 |
无线电 | 67066篇 |
出版年
2021年 | 4882篇 |
2020年 | 5208篇 |
2019年 | 5597篇 |
2018年 | 6930篇 |
2017年 | 6724篇 |
2016年 | 10445篇 |
2015年 | 6579篇 |
2014年 | 10365篇 |
2013年 | 23144篇 |
2012年 | 18295篇 |
2011年 | 22240篇 |
2010年 | 15947篇 |
2009年 | 16508篇 |
2008年 | 21791篇 |
2007年 | 21879篇 |
2006年 | 20592篇 |
2005年 | 18693篇 |
2004年 | 17326篇 |
2003年 | 15478篇 |
2002年 | 15054篇 |
2001年 | 16375篇 |
2000年 | 12976篇 |
1999年 | 10480篇 |
1998年 | 8958篇 |
1997年 | 8596篇 |
1996年 | 8313篇 |
1995年 | 7446篇 |
1994年 | 7323篇 |
1993年 | 6971篇 |
1992年 | 7565篇 |
1991年 | 7615篇 |
1990年 | 7253篇 |
1989年 | 6898篇 |
1988年 | 6701篇 |
1987年 | 6080篇 |
1986年 | 5698篇 |
1985年 | 7266篇 |
1984年 | 7312篇 |
1983年 | 5860篇 |
1982年 | 5866篇 |
1981年 | 5856篇 |
1980年 | 5372篇 |
1979年 | 5700篇 |
1978年 | 5820篇 |
1977年 | 5709篇 |
1976年 | 5597篇 |
1975年 | 5170篇 |
1974年 | 5140篇 |
1973年 | 5149篇 |
1972年 | 3645篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
M. Z. Rovinskii 《Functional Analysis and Its Applications》1991,25(1):74-77
M. V. Lomonosov Moscow State University. Translated from Funktsional'nyi Analiz i Ego Prilozheniya, Vol. 25, No. 1, pp. 88–91, January–March, 1991. 相似文献
942.
E. R. Bauminger E. Fibach A. M. Konijn S. Ofer E. A. Rachmilewitz 《Hyperfine Interactions》1991,66(1-4):11-23
Mössbauer studies in murine (MEL) and human K-562 erythroleukemia cell lines have been utilized to study the fate of iron during intracellular Hb synthesis and denaturation. The results showed that ferritin can serve as an intermediate iron pool for Hb synthesis and for storage of iron released during intracellular Hb denaturation. 相似文献
943.
Bera L.K. Ray S.K. Mukhopadhyay M. Nayak D.K. Usami N. Shiraki Y. Maiti C.K. 《Electron Device Letters, IEEE》1998,19(8):273-275
Growth of ultrathin (<100 Å) oxynitride on strained-Si using microwave N2O and NH3 plasma is reported. X-ray photoelectron spectroscopy (XPS) results indicate a nitrogen-rich layer at the strained-Si/SiO2 interface. The electrical properties of oxynitrides have been characterized using a metal-insulator-semiconductor (MIS) structure. A moderately low value of insulator charge density (6.1×1010 cm-2) has been obtained for NH3 plasma treated N2O oxide sample. Nitrided oxide shows a larger breakdown voltage and an improved charge trapping properties under Fowler-Nordheim (F-N) constant current stress 相似文献
944.
P. Kurpas A. Oster M. Weyers A. Rumberg K. Knorr W. Richter 《Journal of Electronic Materials》1997,26(10):1159-1163
Reflectance anisotropy spectroscopy (RAS) has been used to study As-by-P exchange during metalorganic vapor phase epitaxy.
The study focuses on the processes occurring during switching from GaAs to GaInP, especially the effect of purging PH3 over a GaAs surface. GaAsP/GaAs superlattices of different periodicity were grown and the P-content was determined by high-resolution
x-ray diffraction and correlated to the RAS spectra. From the temperature dependence of the P-content, an activation energy
of 0.56 eV was estimated for the incorporation mechanism. In addition to the insights into the processes at mixed group-V
heterointerfaces, our study demonstrates the reproducibility of RAS transients that thus can be used for process monitoring. 相似文献
945.
M. Carme Calderer 《Mathematical Methods in the Applied Sciences》1994,17(3):171-188
This article deals with flow phenomena in liquid crystal materials. The model that I analyse is that due to Ericksen for liquid crystals with variable degree of orientation. One of the goals is understanding the role of the order parameter in the model. I examine the multiplicity of solutions, phases, that occur in shear flow regimes and analyse their stability under physically realistic conditions. In particular, I show that ellipticity of the linearized system of governing equations is a consequence of the Clausius–Duhem inequality. 相似文献
946.
H. M. Soroush 《The Journal of the Operational Research Society》1994,45(3):287-300
The classical PERT approach uses the path with the largest expected duration as the critical path to estimate the probability of completing a project by a given deadline. However, in general, such a path is not the ‘most critical’ path and does not provide the smallest estimate for the probability of completion time. This paper studies the ‘most critical path’ problem and formulates it as an optimal path problem in a deterministic network with a two-attribute fractional objective function. An exact solution approach is presented for the optimal path problem which also gives the solution to the most critical path problem. The illustrative examples as well as our computational results demonstrate that the proposed algorithm provides estimates for the probabilities of completion time that are much more accurate than those of the classical approach. 相似文献
947.
We estimate the possible influence of spectral line profile (Lorentz profile, Van Vleck–Weisskopf profile, and profile obtained by solving kinetic equation) on the rotation part of the dielectric permittivity of water-vapor monomers. Spectral regions corresponding to long-wavelength (static) and high-frequency (optical) limiting cases as well as regions in close proximity to resonances of various intensities are considered. The studied effects are compared with the corresponding effects on water-vapor absorption coefficient, which are related to factors determining the line-shape structure. 相似文献
948.
The results of a study of photoluminescence excited by a nitrogen laser in the space charge region of Ni-ZnSe contacts are
presented. It is found that the photoluminescence intensity is modulated not only in the presence of an external voltage but
also in its absence, and that it depends on the diode switching regime: no load or short circuit. A physical interpretation
of the results is given.
Fiz. Tekh. Poluprovodn. 32, 1210–1212 (October 1998) 相似文献
949.
S. M. Lenzi C. H. Dasso M. A. Nagarajan H. M. Sofia A. Vitturi 《Acta Physica Hungarica A》1997,6(1-4):95-98
The existence of a neutron skin in neutron-rich nuclei is discussed in connection with the excitation of isovector dipole and quadrupole giant modes via isoscalar nuclear probes. In the case of large neutron excess, important contributions are obtained from the nuclear excitation, which may even become predominant according to proper kinematical conditions. At variance with the usual situation encountered in inelastic processes, constructive interference can be found between nuclear and Coulomb contributions. 相似文献
950.
Based on the SU(n)-algebra the Markoff master equation in discrete product space is reformulated to explicitly deal with composite systems. The resulting local (single node) and nonlocal (multi-node) state parameters allow a systematic approach to non-classical features of the state, like variance and covariance tensors. For local optical driving forces, inter-node interactions, and local damping channels the solution of the master equation is unraveled into stochastic quantum trajectories. Sampling leads to a joint distribution function in terms of those state parameters. Its linear moments define the ensemble-density matrix. The average variance and covariance are in terms of non-linear moments, which should be distinguished from their entirely statistical counterpairs. Non-classicality of the network dynamics is shown to reflect itself in the luminescence-photonstatistics. 相似文献