全文获取类型
收费全文 | 391250篇 |
免费 | 1991篇 |
国内免费 | 555篇 |
专业分类
化学 | 182533篇 |
晶体学 | 5903篇 |
力学 | 22396篇 |
综合类 | 9篇 |
数学 | 56105篇 |
物理学 | 126850篇 |
出版年
2020年 | 4170篇 |
2019年 | 5059篇 |
2018年 | 7451篇 |
2017年 | 7616篇 |
2016年 | 9532篇 |
2015年 | 4430篇 |
2014年 | 8439篇 |
2013年 | 15854篇 |
2012年 | 12902篇 |
2011年 | 15133篇 |
2010年 | 12626篇 |
2009年 | 12814篇 |
2008年 | 14592篇 |
2007年 | 14385篇 |
2006年 | 12888篇 |
2005年 | 11211篇 |
2004年 | 10844篇 |
2003年 | 10029篇 |
2002年 | 10337篇 |
2001年 | 10476篇 |
2000年 | 8120篇 |
1999年 | 6190篇 |
1998年 | 5689篇 |
1997年 | 5481篇 |
1996年 | 5013篇 |
1995年 | 4464篇 |
1994年 | 4506篇 |
1993年 | 4510篇 |
1992年 | 4586篇 |
1991年 | 5075篇 |
1990年 | 5002篇 |
1989年 | 5049篇 |
1988年 | 4695篇 |
1987年 | 4773篇 |
1986年 | 4461篇 |
1985年 | 5354篇 |
1984年 | 5548篇 |
1983年 | 4726篇 |
1982年 | 4972篇 |
1981年 | 4633篇 |
1980年 | 4286篇 |
1979年 | 4925篇 |
1978年 | 5103篇 |
1977年 | 5300篇 |
1976年 | 5451篇 |
1975年 | 5060篇 |
1974年 | 4887篇 |
1973年 | 5133篇 |
1972年 | 4305篇 |
1971年 | 3944篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
V. G. Lapin 《Radiophysics and Quantum Electronics》1995,38(3-4):195-198
It is shown that the nonstable character of nonlinear interaction of a system of waves similar to that resulting from double stimulated Brillouin scattering is retained upon the oblique incidence of a powerful electromagnetic wave on a layer of supercritical plasma. In this case we have nonlinear back reflection from a layer of supercritical plasma. The threshold intensity of the pump wave is greater than that in the case of subcritical plasma for TE polarization waves but can markedly decrease for waves polarized in the incidence plane. Instability is possible only for a layer of finite thickness.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 298–303, March–April, 1995. 相似文献
42.
43.
A. V. Kashevarov 《Fluid Dynamics》1997,32(6):905-907
It is shown that the exact solution of the problem of convective heat exchange in a low-Prandtl-number fluid flow (Pr ? 1) can be obtained for a two-dimensional body of arbitrary shape provided that the conformal mapping relating the body contour with a circle is known. By way of example, the Joukowsky airfoil is considered. 相似文献
44.
N. V. Pratsevityi 《Ukrainian Mathematical Journal》1998,50(8):1233-1241
We study the fractal properties of a convolution of two Cantor distributions. By using the method of characteristic functions,
we establish sufficient conditions for the singularity of the convolution of an arbitrary finite number of distributions of
random variables with independent s-adic digits. We disprove the hypothesis on the validity of a “singular analog” of the Jessen-Wintner theorem for anomalously
fractal distributions.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 8, pp. 1082–1088, August, 1998.
The present work was partially supported by the International Soros Program of Educational Support in Exact Sciences (grant
No. APU 061086). 相似文献
45.
A model kinetic equation is constructed for the transport of a massless Bose gas. This equation is applied to solve the boundary
value problem for the transport of radiation in the half-space occupied by a dispersive medium that is in local thermal equilibrium
with the radiation. It is shown that the difference in temperature between the dispersive medium and the incident radiation
substantially depends on the character of the scattering properties of the particles in the medium.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 111, No. 3, pp. 462–472, June, 1997. 相似文献
46.
B. I. Sokil 《Ukrainian Mathematical Journal》1997,49(11):1777-1781
On the basis of periodic Ateb functions, in the resonance and nonresonance cases, we construct the asymptotic approximation of one-frequency solutions of a boundary-value problem for a nonlinear nonautonomous equation. 相似文献
47.
V. Ye. Zaichick 《Fresenius' Journal of Analytical Chemistry》1995,352(1-2):219-223
The contents of 21 chemical elements (Ag, Br, Ca, Cl, Co, Cr, Cs, Fe, Hg, K, Mg, Mn, Na, P, Rb, Sb, Sc, Se, Sr, Zn, Zr) in synthetic reference materials (SRMs) were compared with those in natural reference materials (NRMs) using short- and long-lived radionuclides. SRMs called synthetic standards (SSs) and synthetic standards, biological (SSBs) were prepared on the basis of phenol-formaldehyde resol resins in the Institute of Physics, Georgian Academy of Science. The NRMs included such IAEA reference materials as H-4 (animal muscle), A-13 (animal blood), H-5 (animal bone), SL-1 (lake sediment), SOIL-7 (soil), A-9 (mixed human diet), and IAEA-153 (milk powder). It was shown that SSB-SRMs possessed good representativity of the 30–50 mg tablets, high precision, operational convenience, and could be recommended for the INAA of a wide range of medico-biological and bioecological objects. 相似文献
48.
The microwave subsidiary absorption threshold in tangentially magnetized yttrium-iron-garnet (YIG) films was measured as a function of the static magnetic field, film thickness and decrease in the 0.3–3 μm range is observed. The effect is explained quantitatively by using modified Damon-Eshbach dispersion relations which take into account exchange interactions.
The effect of temperature on hcrit, the smallest threshold field amplitude, in the 250<T< 450 K temperature range can be expressed by an empirical relationship hcrit Ms(T)-1.6 where Ms is the saturation magnetization. This hcrit vs Ms relationship is similar to that obtained for the magnetization dependence of parallel pump thresholds in Li-Ti ferrite compounds. 相似文献
49.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
50.
J.-L. Hainaut V. Englebert J. Henrard J.-M. Hick D. Roland 《Applied Categorical Structures》1996,3(1-2):9-45
This paper analyzes the requirements that CASE tools should meet for effective database reverse engineering (DBRE), and proposes
a general architecture for data-centered applications reverse engineering CASE environments. First, the paper describes a
generic DBMS-independent DBRE methodology, then it analyzes the main characteristics of DBRE activities in order to collect
a set of desirable requirements. Finally, it describes DB-MAIN, an operational CASE tool developed according to these requirements.
The main features of this tool that are described in this paper are its unique generic specification model, its repository,
its transformation toolkit, its user interface, the text processors, the assistants, the methodological control and its functional
extensibility. Finally, the paper describes five real-world projects in which the methodology and the CASE tool were applied.
This is a heavily revised and extended version of “Requirements for Information System Reverse Engineering Support” by J.-L.
Hainaut, V. Englebert, J. Henrard, J.-M. Hick, D. Roland, which first appeared in the Proceedings of the Second Working Conference
on Reverse Engineering, IEEE Computer Society Press, pp. 136–145, July 1995. This paper presents some results of the DB-MAIN
project. This project is partially supported by the Région Wallonne, the European Union, and by a consortium comprising ACEC-OSI (Be), ARIANE-II (Be), Banque UCL (Lux), BBL (Be), Centre de recherche public H.
Tudor (Lux), CGER (Be), Cockerill-Sambre (Be), CONCIS (Fr), D'Ieteren (Be), DIGITAL, EDF (Fr), EPFL (CH), Groupe S (Be), IBM,
OBLOG Software (Port), ORIGIN (Be), Ville de Namur (Be), Winterthur (Be), 3 Suisses (Be). The DB-Process subproject is supported
by the Communauté Fran?aise de Belgique. 相似文献