全文获取类型
收费全文 | 12694篇 |
免费 | 1230篇 |
国内免费 | 640篇 |
专业分类
化学 | 2972篇 |
晶体学 | 75篇 |
力学 | 2878篇 |
综合类 | 189篇 |
数学 | 4017篇 |
物理学 | 4433篇 |
出版年
2024年 | 22篇 |
2023年 | 89篇 |
2022年 | 250篇 |
2021年 | 306篇 |
2020年 | 358篇 |
2019年 | 277篇 |
2018年 | 289篇 |
2017年 | 363篇 |
2016年 | 442篇 |
2015年 | 371篇 |
2014年 | 476篇 |
2013年 | 968篇 |
2012年 | 551篇 |
2011年 | 611篇 |
2010年 | 506篇 |
2009年 | 671篇 |
2008年 | 676篇 |
2007年 | 717篇 |
2006年 | 740篇 |
2005年 | 602篇 |
2004年 | 504篇 |
2003年 | 576篇 |
2002年 | 489篇 |
2001年 | 438篇 |
2000年 | 511篇 |
1999年 | 381篇 |
1998年 | 405篇 |
1997年 | 243篇 |
1996年 | 231篇 |
1995年 | 207篇 |
1994年 | 149篇 |
1993年 | 147篇 |
1992年 | 149篇 |
1991年 | 102篇 |
1990年 | 93篇 |
1989年 | 64篇 |
1988年 | 98篇 |
1987年 | 77篇 |
1986年 | 56篇 |
1985年 | 84篇 |
1984年 | 67篇 |
1983年 | 26篇 |
1982年 | 48篇 |
1981年 | 27篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
在应变速率为5.56×10-5s-1—5.56×10-3s-1的范围内,在不同温度下(从223K至773K),对3004铝合金进行系列拉伸试验,探索其锯齿屈服规律;通过激活能的计算、内耗研究、微观组织观察和能谱分析,探讨锯齿屈服的机理与物理本质.结果表明,3004铝合金在形变过程中会出现动态应变时效现象;发现了一种“反常”的锯齿屈服现象:在出现锯齿屈服的温区内,存在锯齿屈服临界应变量转变温度Tt,
关键词:
动态应变时效
锯齿屈服
铝合金
内耗 相似文献
92.
We quantify the long-time behavior of solutions to the nonlinear Boltzmann equation for spatially uniform freely cooling inelastic Maxwell molecules by means of the contraction property of a suitable metric in the set of probability measures. Existence, uniqueness, and precise estimates of overpopulated high energy tails of the self-similar profile proved in ref. 9 are revisited and derived from this new Liapunov functional. For general initial conditions the solutions of the Boltzmann equation are then proved to converge with computable rate as t → ∞ to the self-similar solution in this distance, which metrizes the weak convergence of measures. Moreover, we can relate this Fourier distance to the Euclidean Wasserstein distance or Tanaka functional proving also its exponential convergence towards the homogeneous cooling states. The findings are relevant in the understanding of the conjecture formulated by Ernst and Brito in refs. 15, 16, and complement and improve recent studies on the same problem of Bobylev and Cercignani(9) and Bobylev, Cercignani and one of the authors.(11) 相似文献
93.
Robert S. Maier 《Random Structures and Algorithms》1991,2(4):379-420
We analyze the performance of a prototypical scheme for shared storage allocation: two initially empty stacks evolving in a contiguous block of memory of size m. We treat the case in which the stacks are more likely to shrink than grow, but with the probabilities of insertion and deletion allowed to depend arbitrarily on stack height as a fraction of m. New results are obtained on the m → ∞ asymptotics of the stack collision time, and of the final stack heights. The results of Wentzell and Freidlin on the large deviations of Markov chains are used, and the relation of their formalism to the Hamiltonian formulation of classical mechanics is emphasized. Certain results on higher-order asymptotics follow from WKB expansions. 相似文献
94.
95.
Automatic detection and identification of shocks in Gaussian state‐space models: a Bayesian approach
An automatic monitoring and intervention algorithm that permits the supervision of very general aspects in an univariate linear Gaussian state–space model is proposed. The algorithm makes use of a model comparison and selection approach within a Bayesian framework. In addition, this algorithm incorporates the possibility of eliminating earlier interventions when subsequent evidence against them comes to light. Finally, the procedure is illustrated with two empirical examples taken from the literature. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
96.
Vee Ming Ng 《Journal of multivariate analysis》2002,83(2):409
Bayesian inference is considered for the seemingly unrelated regressions with an elliptically contoured error distribution. We show that the posterior distribution of the regression parameters and the predictive distribution of future observations under elliptical errors assumption are identical to those obtained under independently distributed normal errors when an improper prior is used. This gives inference robustness with respect to departures from the reference case of independent sampling from the normal distribution. 相似文献
97.
98.
红外动态图像生成技术概念研究 总被引:4,自引:0,他引:4
红外动态图像生成技术的基本概念包括基本术语及其定义。为了描述红外动态图像生成技术的特性,通常采用如光源类型、光谱波段、阵列规模、空间分辨率、填充因子、时间常数、帧频、闪烁、温度范围、串扰、均匀性、发射率、辐射对比度、动态范围、温度分辨率、调制传递函数、几何畸变及最大温度和最大辐射强度等概念。介绍了描述红外动态图像生成系统性能的基本概念的定义。转换器的指标定义对于转换器的设计和性能指标的测试都有重要的意义。 相似文献
99.
Howel Tong 《应用数学学报(英文版)》2002,18(2):177-184
Abstract I reflect upon the development of nonlinear time series analysis since 1990 by focusing on five majorareas of development. These areas include the interface between nonlinear time series analysis and chaos,thenonparametric/semiparametric approach,nonlinear state space modelling,financial time series and nonlinearmodelling of panels of time series. 相似文献
100.
Recent joint theoretical and experimental investigations of Auger core-core-valence spectra of alkali adatoms on simple metals have revealed that such technique is capable to ascertain contributions from different adsorption environments in the signal [M.I. Trioni, S. Caravati, G.P. Brivio, L. Floreano, F. Bruno, A. Morgante, Phys. Rev. Lett. 93 (2004) 206802]. Consequently, to verify if such an effect is present also for other chemical species, we study theoretically the KLV transition of oxygen either as a bulk impurity or as an adsorbate in/on Al and Ag (jellium-like). We make use of the Fermi golden rule in which the matrix elements of the interaction are calculated within DFT. We verify that the relevant physical quantity of this phenomenon is the excited local density of states (LDOS), calculated within a region centered on the core ionized atom. The Auger rate for oxygen in Ag bulk displays a single asymmetric peak, while for adsorbed oxygen a second smaller feature at lower energies, and very close to the first one, appears. This unexpected result follows from the removal of the degeneracy of the m quantum number of the 2p states of oxygen at the surface. It is only displayed on the electronically less dense metal (Ag), but not on Al. 相似文献