全文获取类型
收费全文 | 230434篇 |
免费 | 1550篇 |
国内免费 | 476篇 |
专业分类
化学 | 104916篇 |
晶体学 | 3610篇 |
力学 | 12134篇 |
综合类 | 5篇 |
数学 | 37178篇 |
物理学 | 74617篇 |
出版年
2018年 | 10138篇 |
2017年 | 11053篇 |
2016年 | 5623篇 |
2015年 | 1942篇 |
2014年 | 1459篇 |
2013年 | 4909篇 |
2012年 | 8021篇 |
2011年 | 17730篇 |
2010年 | 10456篇 |
2009年 | 10334篇 |
2008年 | 15291篇 |
2007年 | 19177篇 |
2006年 | 4254篇 |
2005年 | 11413篇 |
2004年 | 7198篇 |
2003年 | 6776篇 |
2002年 | 4560篇 |
2001年 | 3744篇 |
2000年 | 2999篇 |
1999年 | 2238篇 |
1998年 | 1933篇 |
1997年 | 1892篇 |
1996年 | 1982篇 |
1995年 | 1878篇 |
1994年 | 1639篇 |
1993年 | 1615篇 |
1992年 | 1821篇 |
1991年 | 1822篇 |
1990年 | 1752篇 |
1989年 | 1766篇 |
1988年 | 1778篇 |
1987年 | 1765篇 |
1986年 | 1667篇 |
1985年 | 2229篇 |
1984年 | 2364篇 |
1983年 | 1979篇 |
1982年 | 2297篇 |
1981年 | 2112篇 |
1980年 | 2159篇 |
1979年 | 2165篇 |
1978年 | 2296篇 |
1977年 | 2123篇 |
1976年 | 2183篇 |
1975年 | 2103篇 |
1974年 | 1944篇 |
1973年 | 2196篇 |
1972年 | 1322篇 |
1971年 | 1001篇 |
1968年 | 1152篇 |
1967年 | 1133篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Within the framework of a piecewise homogeneous body model, with the use of three-dimensional geometrically nonlinear exact equations of elasticity theory, a method for determining the stress—strain state in unidirectional fibrous composites with locally curved fibers is developed for the case where the interaction between the fibers is neglected. All the investigations are carried out for an infinite elastic body containing a single locally curved fiber. Numerical results illustrating the effect of geometrical nonlinearity on the distribution of the self-balanced normal and shear stresses acting on the interface and arising as a result of local curving of the fiber are presented.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 433–448, July–August, 2005. 相似文献
172.
D. K. Kulshrestha 《The Journal of the Operational Research Society》1987,38(5):447-452
Consider a finite set of demand points which exist anywhere on the boundary of a rectangle contained in the two-dimensional Euclidean space. This paper considers the problem of finding an optimal location (on the boundary of the rectangle) which minimizes the maximum average Euclidean distance to the demand points. The method presented is independent of the number of demand points. 相似文献
173.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
174.
S. S. Dragomir 《Acta Mathematica Hungarica》2005,109(4):331-345
Summary General divergence measures for probability distributions are introduced and their main properties established. Connections
with f-divergence corresponding to a convex function fare explored. 相似文献
175.
V. Yu. Karaev E. M. Meshkov G. N. Balandina E. M. Zuikova V. Yu. Gol'dblat V. I. Titov 《Radiophysics and Quantum Electronics》2005,48(8):587-598
We present the results of data processing of the field experiment devoted to a study of a microwave signal backscattered by
a rough water surface and compare them with the theoretical estimates. The measurements were conducted sequentially using
a radar with parabolic and knife-beam antennas. The radar was mounted on the Molitovsky bridge at a height of 40 m across
the Oka river in Nizhny Novgorod, Russia. For the radar with knife-shaped antenna pattern, we examined the reflected-signal
power and the shift and width of the Doppler spectrum as functions of the azimuthal angle for the nadir sounding. For the
parabolic antenna, we studied the reflected-signal power as a function of the incidence angle. Comparison with the experimental
data shows that the developed theoretical model of a Doppler spectrum is in good agreement with the observations.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 661–673, August 2005. 相似文献
176.
Valery V. Kiselev 《Central European Journal of Physics》2004,2(3):523-534
We calculate the leptonic constant for the pseudoscalar ground state of the B
c
meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy
quark current in nonrelativistic QCD as matched with full QCD. 相似文献
177.
178.
A nonlinear (in the cubic approximation) relaxation equation of state is derived for a rod containing cracks partially filled with an incompressible viscous liquid. The nonlinear effects of the self-action and interaction of low-and high-frequency longitudinal elastic waves propagating in such a rod are studied for the cases of identical and size-varied cracks. Linear and nonlinear acoustic parameters characterizing the self-action and interaction of elastic waves in a cracked rod are determined. 相似文献
179.
H. G. Bohlen W. von Oertzen R. Kalpakchieva B. Gebauer S. M. Grimes A. Lenz T. N. Massey M. Milin Ch. Schulz Tz. Kokalova S. Torilov S. Thummerer 《Physics of Atomic Nuclei》2003,66(8):1494-1500
The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2?, and 3/2?, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C. 相似文献
180.
B.I. Sturman A.S. Gorkunova K.H. Ringhofer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):291-297
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic
states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency
of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to
the periodic states and their apparent characteristics are strongly different for the two limiting cases above.
Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003 相似文献