全文获取类型
收费全文 | 324145篇 |
免费 | 2138篇 |
国内免费 | 886篇 |
专业分类
化学 | 136127篇 |
晶体学 | 4786篇 |
力学 | 18916篇 |
综合类 | 3篇 |
数学 | 69436篇 |
物理学 | 97901篇 |
出版年
2020年 | 1408篇 |
2019年 | 1568篇 |
2018年 | 18579篇 |
2017年 | 19200篇 |
2016年 | 11757篇 |
2015年 | 3404篇 |
2014年 | 3501篇 |
2013年 | 8078篇 |
2012年 | 12546篇 |
2011年 | 26405篇 |
2010年 | 16086篇 |
2009年 | 16516篇 |
2008年 | 21535篇 |
2007年 | 26406篇 |
2006年 | 6454篇 |
2005年 | 12989篇 |
2004年 | 9588篇 |
2003年 | 9473篇 |
2002年 | 6647篇 |
2001年 | 5572篇 |
2000年 | 4421篇 |
1999年 | 3132篇 |
1998年 | 2697篇 |
1997年 | 2531篇 |
1996年 | 2536篇 |
1995年 | 2311篇 |
1994年 | 2242篇 |
1993年 | 2155篇 |
1992年 | 2415篇 |
1991年 | 2369篇 |
1990年 | 2306篇 |
1989年 | 2242篇 |
1988年 | 2255篇 |
1987年 | 2254篇 |
1986年 | 2143篇 |
1985年 | 2759篇 |
1984年 | 2821篇 |
1983年 | 2513篇 |
1982年 | 2621篇 |
1981年 | 2427篇 |
1980年 | 2417篇 |
1979年 | 2563篇 |
1978年 | 2599篇 |
1977年 | 2432篇 |
1976年 | 2515篇 |
1975年 | 2425篇 |
1974年 | 2385篇 |
1973年 | 2606篇 |
1972年 | 1679篇 |
1971年 | 1356篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
E. Mathieu Y. Foucher P. Dellamonica J. P. Daures 《Methodology and Computing in Applied Probability》2007,9(3):389-397
In AIDS control, physicians have a growing need to use pragmatically useful and interpretable tools in their daily medical
taking care of patients. Semi-Markov process seems to be well adapted to model the evolution of HIV-1 infected patients. In
this study, we introduce and define a non homogeneous semi-Markov (NHSM) model in continuous time. Then the problem of finding
the equations that describe the biological evolution of patient is studied and the interval transition probabilities are computed.
A parametric approach is used and the maximum likelihood estimators of the process are given. A Monte Carlo algorithm is presented
for realizing non homogeneous semi-Markov trajectories. As results, interval transition probabilities are computed for distinct
times and follow-up has an impact on the evolution of patients.
相似文献
942.
943.
Joseph Shipman 《Mathematical Intelligencer》2007,29(4):9-14
Theorems 2 and 3 establish the minimum algebraic conditions necessary for a field to be algebraically closed, and they can
therefore be said to “optimize” the Fundamental Theorem of Algebra. But each specific“degree implication” is a first-order
consequence of the axioms for fields, and could have been discovered two centuries ago; the existence of these finitary relationships
appears to have been unsuspected by practically everyone, with one important exception. 相似文献
944.
T. Hansel J. Müller C. Falldorf C. von Kopylow W. Jüptner R. Grunwald G. Steinmeyer U. Griebner 《Applied physics. B, Lasers and optics》2007,89(4):513-516
Digital holographic shape measurements using femtosecond laser pulses are reported. For contouring of very fast moving objects,
the simultaneous generation of at least two spectrally separated ultrashort pulses is required. To deliver this particular
spectral signature at high pulse energies, a chirped-pulse Ti:sapphire laser amplifier was modified to emit two spectrally
separated pulses with energies above 1 μJ each. The wavelength separation of these pulses was adjustable within the 50 nm
gain bandwidth, cutting out two distinct wavelength peaks by a variable double-slit assembly in a prism sequence. A Michelson-type
interferometer was employed to perform the two-wavelength contouring. The phases of the holograms and the phase differences
are calculated numerically, which allow us to deduce the contour lines of the topology of the object. The suitability of the
light source for digital holography is demonstrated with contouring of stationary objects and the potential for high-speed
applications is indicated.
PACS 42.40.-i; 42.60.By 相似文献
945.
Ling-yan Tang Song-he Song 《应用数学学报(英文版)》2007,23(2):303-310
In this paper,we use Daubechies scaling functions as test functions for the Galerkin method,and discuss Wavelet-Galerkin solutions for the Hamilton-Jacobi equations.It can be proved that the schemesare TVD schemes.Numerical tests indicate that the schemes are suitable for the Hamilton-Jacobi equations.Furthermore,they have high-order accuracy in smooth regions and good resolution of singularities. 相似文献
946.
A. M. Kharitonov 《Thermophysics and Aeromechanics》2007,14(1):3-11
Sergey Alekseevich Khristianovich is one of the famous Russian mechanical engineers of the 20th century together with N.E.
Zhukovsky, S.A. Chaplygin, N.E. Kochin, and others. He made an immense contribution to some aspects of mechanics, such as
aerogasdynamics, rock mechanics, theory of plasticity, filtration theory, and environmental power engineering. All this was
preceded by a long, hard, and fruitful life full of outstanding events. 相似文献
947.
Phase synchronization in a system of three virtual-cathode microwave oscillators (vircators) simulated by coupled van der Pol oscillators is studied. The phasing dynamics of the vircators is visualized with the phase portraits of the system in the triangular coordinates. Different phasing conditions are found. 相似文献
948.
The viscosity behavior, index of refraction, and density of dilute polycaproamide solutions in DMAc containing lithium chloride have been studied. On the basis of temperature dependences of the index of refraction and the density of solutions, the θ-condition of polycaproamide solutions in DMAc containing 2.5% lithium chloride is estimated as 21.3°C. From intrinsic viscosity [η] measurements, the coefficients of swelling of a polymer coil, the mean-square distance between chain ends, and other parameters of macromolecules in solution are calculated. 相似文献
949.
Chaotic dynamics in open systems produces fractals. This can be seen, for example, in the ionization of an electron from a
hydrogen atom in applied parallel electric and magnetic fields. We summarize some of our recent work on the order that can
be found in these fractals. 相似文献
950.
N.A. Buznikov A.S. Antonov A.B. Granovsky C.G. Kim C.O. Kim X.P. Li S.S. Yoon 《Journal of magnetism and magnetic materials》2006
The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau–Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material. 相似文献