全文获取类型
收费全文 | 603178篇 |
免费 | 20929篇 |
国内免费 | 10748篇 |
专业分类
化学 | 313115篇 |
晶体学 | 8759篇 |
力学 | 32395篇 |
综合类 | 521篇 |
数学 | 91411篇 |
物理学 | 188654篇 |
出版年
2022年 | 5311篇 |
2021年 | 6140篇 |
2020年 | 7309篇 |
2019年 | 7362篇 |
2018年 | 17396篇 |
2017年 | 16855篇 |
2016年 | 17216篇 |
2015年 | 9398篇 |
2014年 | 12709篇 |
2013年 | 25617篇 |
2012年 | 25132篇 |
2011年 | 34551篇 |
2010年 | 22672篇 |
2009年 | 22688篇 |
2008年 | 27467篇 |
2007年 | 28889篇 |
2006年 | 20102篇 |
2005年 | 18625篇 |
2004年 | 16931篇 |
2003年 | 15456篇 |
2002年 | 14259篇 |
2001年 | 14575篇 |
2000年 | 11567篇 |
1999年 | 9517篇 |
1998年 | 8365篇 |
1997年 | 8143篇 |
1996年 | 7909篇 |
1995年 | 7109篇 |
1994年 | 6981篇 |
1993年 | 6637篇 |
1992年 | 6956篇 |
1991年 | 7080篇 |
1990年 | 6652篇 |
1989年 | 6338篇 |
1988年 | 6336篇 |
1987年 | 6058篇 |
1986年 | 5760篇 |
1985年 | 7647篇 |
1984年 | 7863篇 |
1983年 | 6516篇 |
1982年 | 6763篇 |
1981年 | 6619篇 |
1980年 | 6505篇 |
1979年 | 6552篇 |
1978年 | 6914篇 |
1977年 | 6704篇 |
1976年 | 6864篇 |
1975年 | 6337篇 |
1974年 | 6363篇 |
1973年 | 6551篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,27(3):311-329
This paper describes topological searches for neutral scalar bosons S0 produced in association with a Z0 boson via the Bjorken process at centre-of-mass energies of 91 GeV and 183-209 GeV. These searches are based on studies of the recoil mass spectrum of
and events and on a search for with and S or photons. They cover the decays of the S0 into an arbitrary combination of hadrons, leptons, photons and invisible particles as well as the possibility that it might
be stable.
No indication for a signal is found in the data and upper limits on the cross section of the Bjorken process are calculated.
Cross-section limits are given in terms of a scale factor k with respect to the Standart Model cross section for the Higgs-strahlung process .
These results can be interpreted in general scenarios independently of the decay modes of the S0. The examples considered here are the production of a single new scalar particle with a decay width smaller than the detector
mass resolution, and for the first time, two scenarios with continuous mass distributions, due to a single very broad state
or several states close in mass.
Received: 13 March 2002 / Published online: 19 February 2003 相似文献
992.
993.
Howard Robinson 《Acta Analytica》2005,20(3):7-10
Nicholas Nathan tries to resist the current version of the causal argument for sense-data in two ways. First he suggests that,
on what he considers to be the correct re-construction of the argument, it equivocates on the sense of proximate cause. Second
he defends a form of disjunctivism, by claiming that there might be an extra mechanism involved in producing veridical hallucination,
that is not present in perception. I argue that Nathan’s reconstruction of the argument is not the appropriate one, and that,
properly interpreted, the argument does not equivocate on proximate cause. Furthermore, I claim that his postulation of a
modified mechanism for hallucinations is implausibly ad hoc. 相似文献
994.
995.
Chris Pollett 《Archive for Mathematical Logic》2003,42(5):469-488
The paper establishes lower bounds on the provability of 𝒟=NP and the MRDP theorem in weak fragments of arithmetic. The
theory I
5
E
1
is shown to be unable to prove 𝒟=NP. This non-provability result is used to show that I
5
E
1
cannot prove the MRDP theorem. On the other hand it is shown that I
1
E
1
proves 𝒟 contains all predicates of the form (∀i≤|b|)P(i,x)^Q(i,x) where ^ is =, <, or ≤, and I
0
E
1
proves 𝒟 contains all predicates of the form (∀i≤b)P(i,x)=Q(i,x). Here P and Q are polynomials. A conjecture is made that 𝒟 contains NLOGTIME. However, it is shown that this conjecture would not be sufficient
to imply 𝒟=N P. Weak reductions to equality are then considered as a way of showing 𝒟=NP. It is shown that the bit-wise less than predicate,
≤2, and equality are both co-NLOGTIME complete under FDLOGTIME reductions. This is used to show that if the FDLOGTIME functions
are definable in 𝒟 then 𝒟=N P.
Received: 13 July 2001 / Revised version: 9 April 2002 /
Published online: 19 December 2002
Key words or phrases: Bounded Arithmetic – Bounded Diophantine Complexity 相似文献
996.
V. Z. Kasimov O. V. Ushakova Yu. P. Khomenko 《Journal of Applied Mechanics and Technical Physics》2003,44(5):612-619
An improved procedure for modeling the operation of a light-gas gun is proposed. The motion of working bodies in both the firing chamber and the light-gas chamber is studied within the framework of the mechanics of heterogeneous media. The problem of barrel heating taking into account its melting and removal of thermal ablation products into the medium inside the bore is solved in a coupled formulation. Heat and mass transfer and friction on the barrel surface are calculated using empirical dependences. The deformable piston is considered compressible and elastoviscoplastic. Allowance is made for the presence of a clearance between the lateral surface of the piston and the barrel bore walls and the associated gas flow between the firing and the light-gas chamber. Calculation results are given. 相似文献
997.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
998.
Zavarzin I. V. Smirnova N. G. Chernoburova E. I. Yarovenko V. N. Krayushkin M. M. 《Russian Chemical Bulletin》2004,53(6):1257-1260
A method for syntheses of previously unknown derivatives of thieno[2,3-d]pyrimidines and quinazolines from monothiooxamides was proposed. 相似文献
999.
We derive a test problem for evaluating the ability of time-steppingmethods to preserve the statistical properties of systems inmolecular dynamics. We consider a family of deterministic systemsconsisting of a finite number of particles interacting on acompact interval. The particles are given random initial conditionsand interact through instantaneous energy- and momentum-conservingcollisions. As the number of particles, the particle density,and the mean particle speed go to infinity, the trajectory ofa tracer particle is shown to converge to a stationary Gaussianstochastic process. We approximate this system by one describedby a system of ordinary differential equations and provide numericalevidence that it converges to the same stochastic process. Wesimulate the latter system with a variety of numerical integrators,including the symplectic Euler method, a fourth-order Runge-Kuttamethod, and an energyconserving step-and-project method. Weassess the methods' ability to recapture the system's limitingstatistics and observe that symplectic Euler performs significantlybetter than the others for comparable computational expense. 相似文献
1000.
M. A. Bertolim M. P. Mello K. A. de Rezende 《Transactions of the American Mathematical Society》2005,357(10):4091-4129
In this article the main theorem establishes the necessity and sufficiency of the Poincaré-Hopf inequalities in order for the Morse inequalities to hold. The convex hull of the collection of all Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data determines a Morse polytope defined on the nonnegative orthant. Using results from network flow theory, a scheme is provided for constructing all possible Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data. Geometrical properties of this polytope are described.