全文获取类型
收费全文 | 34734篇 |
免费 | 929篇 |
国内免费 | 178篇 |
专业分类
化学 | 20936篇 |
晶体学 | 211篇 |
力学 | 897篇 |
综合类 | 9篇 |
数学 | 4939篇 |
物理学 | 8849篇 |
出版年
2022年 | 308篇 |
2021年 | 502篇 |
2020年 | 570篇 |
2019年 | 486篇 |
2018年 | 502篇 |
2017年 | 442篇 |
2016年 | 894篇 |
2015年 | 735篇 |
2014年 | 852篇 |
2013年 | 1453篇 |
2012年 | 1763篇 |
2011年 | 2020篇 |
2010年 | 1151篇 |
2009年 | 1066篇 |
2008年 | 1729篇 |
2007年 | 1702篇 |
2006年 | 1590篇 |
2005年 | 1988篇 |
2004年 | 1924篇 |
2003年 | 1377篇 |
2002年 | 1091篇 |
2001年 | 781篇 |
2000年 | 742篇 |
1999年 | 499篇 |
1998年 | 453篇 |
1997年 | 433篇 |
1996年 | 510篇 |
1995年 | 444篇 |
1994年 | 459篇 |
1993年 | 457篇 |
1992年 | 432篇 |
1991年 | 373篇 |
1990年 | 307篇 |
1989年 | 279篇 |
1988年 | 243篇 |
1987年 | 243篇 |
1986年 | 230篇 |
1985年 | 334篇 |
1984年 | 310篇 |
1983年 | 250篇 |
1982年 | 291篇 |
1981年 | 271篇 |
1980年 | 245篇 |
1979年 | 245篇 |
1978年 | 263篇 |
1977年 | 217篇 |
1976年 | 221篇 |
1975年 | 176篇 |
1974年 | 187篇 |
1973年 | 177篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
M. C. Caracoche J. A. Martínez P. C. Rivas M. A. Taylor A. F. Pasquevich S. Barolin O. A. de Sanctis 《Hyperfine Interactions》2007,179(1-3):87-93
The hyperfine quadrupole interaction at Hf sites in films and powders of 14 mol% CaO–HfO2 and 20 mol% CaO–HfO2 has been determined as a function of temperature. Results indicate the formation of a cubic solid solution and other microstructures assigned to the ?1 (CaHf4O9) and ?2 (Ca6Hf19O44) phases. Dynamical effects on the electric field gradient reveal the existence of oxygen vacancies movements in the solid solution. The thermal behavior of the relaxation constant observed in films allowed the determination of activation energies of 0.54 eV and 0.70 eV for the 14 mol% and 20 mol% CaO doped hafnias, respectively. The influence of the microdomains and the stability of the cubic solid solution are discussed. 相似文献
113.
Frank W. Schmidt 《Linear and Multilinear Algebra》1991,30(3):229-230
This section appears from time to time. Contributions are invited, and should be submitted to R. C. Thompson, Mathematics Department, University of California, Santa Barbara, CA 93106. 相似文献
114.
Helga Fetter Berta Gamboa de Buen Jesús García-Falset 《Journal of Mathematical Analysis and Applications》2003,285(2):444-455
We consider a family of spaces wider than r-UNC spaces and we give some fixed point results in the setting of these spaces. 相似文献
115.
E. de A. Gonçalves V. M. de Oliveira A. Rosas P. R.A. Campos 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):127-132
Adaptation of populations takes place with the occurrence and subsequent fixation of mutations that confer some selective
advantage
to the individuals which acquire it. For this reason, the study of the process of fixation of advantageous mutations has a
long history
in the population genetics literature. Particularly, the previous investigations aimed to find out the main evolutionary forces
affecting the strength of natural selection in the populations.
In the current work, we investigate the dynamics of fixation of beneficial mutations in a subdivided population. The subpopulations
(demes)
can exchange migrants
among their neighbors, in a migration network which is assumed to have either a random graph or a scale-free topology. We
have observed that the migration rate
drastically affects the dynamics of mutation fixation, despite of the fact that the probability of fixation is invariant on
the
migration rate, accordingly to
Maruyama's conjecture. In addition, we have noticed a topological dependence of the adaptive evolution of the population when
clonal interference
becomes effective. 相似文献
116.
Dashan Huang Yoshitaka Kai Frank J. Fabozzi Masao Fukushima 《European Journal of Operational Research》2007
This paper presents a model for optimally designing a collateralized mortgage obligation (CMO) with a planned amortization class (PAC)-companion structure using dynamic cash reserve. In this structure, the mortgage pool’s cash flow is allocated by rule to the two bond classes such that PAC bondholders receive substantial prepayment protection, that protection being provided by the companion bondholders. The structure we propose provides greater protection to the PAC bondholders than current structures during periods of rising interest rates when this class of bondholders faces greater extension risk. We do so by allowing a portion of the cash flow from the collateral to be reserved to meet the PAC’s scheduled cash flow in subsequent periods. The greater protection is provided by the companion bondholders exposure to interest loss. To tackle this problem, we transform the problem of designing the optimal PAC-companion structure into a standard stochastic linear programming problem which can be solved efficiently. Moreover, we present an extended model by considering the quality of the companion bond and by relaxing the PAC bondholder shortfall constraint. Based on numerical experiments through Monte Carlo simulation, we show the utility of the proposed model. 相似文献
117.
In [NR] the authors introduced the notion of superstable operators on a Banach space E using ultrapowers Eu of E. In [HR] this notion was extended to strongly continuous one-parameter semigroups again by means of ultrapowers.It is the aim of the present paper to give an equivalent intrinsic definition of superstability (without the reference to ultrapowers). This definition allows us to improve the results of [NR] as well as of [HR]. We apply our results to semigroups of positive linear operators on Banach lattices and C*-algebras, respectively. 相似文献
118.
In this work preliminary results of amorphous zirconium crystallization using ion beam pulses are presented. Energetic argon- and oxygen-ion beams generated by a plasma focus device were used to promote crystallization on amorphous ZrO2-2.5 mol% Y2O3 film deposited by chemical solution deposition onto silica glass substrate. The films were burnt at 370 °C for 1 h in normal atmosphere previous to plasma irradiation. The irradiation was performed by means of successive pulses of ion beams. The evolution of the surface morphology and crystallization was followed by AFM and X-rays diffraction in a grazing incidence asymmetric Bragg geometry (GIAB), respectively. Argon-irradiated films showed highly nucleated cubic zirconia after 10 pulses. On the other hand, oxygen-irradiated films showed a delayed and less extensive cubic nucleation, but a more ordered structure and well-defined grains. 相似文献
119.
This work presents a formulation based on UPML for truncating conductive media by using a local and non-orthogonal coordinate
system to solve Maxwell’s equations by the FDTD method. The detailed procedure for obtaining the UPML equations for this case
is shown and the complete equation set is provided. 相似文献
120.
Gabor Schmera Adi Bulsara David Pierson Frank Moss Enrico Di Cera 《Journal of statistical physics》1993,71(5-6):1179-1190
We consider the class of experiments which can be characterized by a Fokker-PIanck dynamics corresponding to the overdamped motion of a state point in a suitable stochastic potential. We assume that the general form of the potential is known (or can be guessed with reasonable accuracy), but that its parameters are to be determined experimentally by measurements made with a noisy instrument. This possible method for determining the potential parameters, which exploits the system's own internal stochastic motion in order to explore rapidly its available parameter space, is substantially more efficient than traditional methods involving time averages of single point measurements, and yet does not appear to have been previously considered. The method could be important when, for example, the experiment must be completed in a limited time owing either to the expense of the experimental materials or to the temporary stationarity of the preparation, situations which are commonly encountered in experimental biochemistry and biology. 相似文献