全文获取类型
收费全文 | 8973篇 |
免费 | 438篇 |
国内免费 | 55篇 |
专业分类
化学 | 6522篇 |
晶体学 | 83篇 |
力学 | 217篇 |
综合类 | 1篇 |
数学 | 1341篇 |
物理学 | 1302篇 |
出版年
2023年 | 71篇 |
2022年 | 60篇 |
2021年 | 194篇 |
2020年 | 187篇 |
2019年 | 192篇 |
2018年 | 158篇 |
2017年 | 125篇 |
2016年 | 303篇 |
2015年 | 285篇 |
2014年 | 314篇 |
2013年 | 631篇 |
2012年 | 687篇 |
2011年 | 723篇 |
2010年 | 409篇 |
2009年 | 308篇 |
2008年 | 544篇 |
2007年 | 545篇 |
2006年 | 565篇 |
2005年 | 533篇 |
2004年 | 440篇 |
2003年 | 373篇 |
2002年 | 303篇 |
2001年 | 114篇 |
2000年 | 92篇 |
1999年 | 84篇 |
1998年 | 76篇 |
1997年 | 85篇 |
1996年 | 106篇 |
1995年 | 65篇 |
1994年 | 63篇 |
1993年 | 67篇 |
1992年 | 54篇 |
1991年 | 33篇 |
1990年 | 29篇 |
1989年 | 31篇 |
1988年 | 41篇 |
1987年 | 27篇 |
1986年 | 33篇 |
1985年 | 71篇 |
1984年 | 49篇 |
1983年 | 29篇 |
1982年 | 54篇 |
1981年 | 34篇 |
1980年 | 26篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 25篇 |
1975年 | 20篇 |
1974年 | 24篇 |
排序方式: 共有9466条查询结果,搜索用时 125 毫秒
111.
Multiphoton laser scanning microscopy offers advantages in depth of penetration into intact samples over other optical sectioning techniques. To achieve these advantages it is necessary to detect the emitted light without spatial filtering. In this nondescanned (nonconfocal) approach, ambient room light can easily contaminate the signal, forcing experiments to be performed in absolute darkness. For multiphoton microscope systems employing mode-locked lasers, signal processing can be used to reduce such problems by taking advantage of the pulsed characteristics of such lasers. Specifically, by recovering fluorescence generated at the mode-locked frequency, interference from stray light and other ambient noise sources can be significantly reduced. This technology can be adapted to existing microscopes by inserting demodulation circuitry between the detector and data collection system. The improvement in signal-to-noise ratio afforded by this approach yields a more robust microscope system and opens the possibility of moving multiphoton microscopy from the research lab to more demanding settings, such as the clinic. 相似文献
112.
The Ramanujan Journal - This paper provides elementary proofs for several types of congruences involving multipartitions and self-convolutions of the divisor function. Our computations use... 相似文献
113.
Nazarov Anatoly Sztrik János Kvach Anna Tóth Ádám 《Methodology and Computing in Applied Probability》2022,24(3):1503-1518
Methodology and Computing in Applied Probability - This paper deals with a retrial queuing system with a finite number of sources and collision of the customers, where the server is subject to... 相似文献
114.
Eric Séré 《Communications in Mathematical Physics》1995,172(2):293-316
Consider a smooth Hamiltonian system in 2N
,
, the energy surface ={x/H(x)=H(0)} being compact, and 0 being a hyperbolic equilibrium. We assume, moreover, that {0} is of restricted contact type. These conditions are symplectically invariant. By a variational method, we prove the existence of an orbit homoclinic, i.e. non-constant and doubly asymptotic, to 0. 相似文献
115.
Logarithmic correction to the probability of capture for dissipatively perturbed Hamiltonian systems
Hamiltonian systems are analyzed with a double homoclinic orbit connecting a saddle to itself. Competing centers exist. A small dissipative perturbation causes the stable and unstable manifolds of the saddle point to break apart. The stable manifolds of the saddle point are the boundaries of the basin of attraction for the competing attractors. With small dissipation, the boundaries of the basins of attraction are known to be tightly wound and spiral-like. Small changes in the initial condition can alter the equilibrium to which the solution is attracted. Near the unperturbed homoclinic orbit, the boundary of the basin of attraction consists of a large sequence of nearly homoclinic orbits surrounded by close approaches to the saddle point. The slow passage through an unperturbed homoclinic orbit (separatrix) is determined by the change in the value of the Hamiltonian from one saddle approach to the next. The probability of capture can be asymptotically approximated using this change in the Hamiltonian. The well-known leading-order change of the Hamiltonian from one saddle approach to the next is due to the effect of the perturbation on the homoclinic orbit. A logarithmic correction to this change of the Hamiltonian is shown to be due to the effect of the perturbation on the saddle point itself. It is shown that the probability of capture can be significantly altered from the well-known leading-order probability for Hamiltonian systems with double homoclinic orbits of the twisted type, an example of which is the Hamiltonian system corresponding to primary resonance. Numerical integration of the perturbed Hamiltonian system is used to verify the accuracy of the analytic formulas for the change in the Hamiltonian from one saddle approach to the next. (c) 1995 American Institute of Physics. 相似文献
116.
We analyze the analytic continuation of the formally divergent one-loop amplitude for scattering of the gravitonmultiplet in the Type II superstring. In particular we obtain explicit double and single dispersion relations, formulas for all the successive branch cuts extending out to +, as well as for the decay rate of a massive string state of arbitrary mass2N into two string states of lower mass. We compare our results with the box diagram in a superposition of 3-like field theories. The stringy effects are traced to a convergence problem in this superposition.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 98. No. 3, pp. 442–455, March, 1994. 相似文献
117.
Eric Bach Richard Lukes Jeffrey Shallit H. C. Williams. 《Mathematics of Computation》1996,65(216):1737-1747
Let be a positive integer. We say looks like a power of 2 modulo a prime if there exists an integer such that . First, we provide a simple proof of the fact that a positive integer which looks like a power of modulo all but finitely many primes is in fact a power of . Next, we define an -pseudopower of the base to be a positive integer that is not a power of , but looks like a power of modulo all primes . Let denote the least such . We give an unconditional upper bound on , a conditional result (on ERH) that gives a lower bound, and a heuristic argument suggesting that is about for a certain constant . We compare our heuristic model with numerical data obtained by a sieve. Some results for bases other than are also given.
118.
Eric Chisolm E. C. G. Sudarshan Thomas F. Jordan 《International Journal of Theoretical Physics》1996,35(3):485-493
Griffiths' quantum trajectories formalism is extended to describe weak decoherence. The decoherence conditions are shown to severely limit the complexity of histories composed of fine-grained events. 相似文献
119.
120.
Eric Berson R. Mane Trupti V. Kurt Svihla C. Hanley Thomas R. 《Applied biochemistry and biotechnology》1998,(1):615-627
Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared
for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level,
fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition
of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on kLa values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and
O transfer. 相似文献