全文获取类型
收费全文 | 6711篇 |
免费 | 664篇 |
国内免费 | 566篇 |
专业分类
化学 | 1503篇 |
晶体学 | 23篇 |
力学 | 214篇 |
综合类 | 60篇 |
数学 | 3517篇 |
物理学 | 2624篇 |
出版年
2024年 | 5篇 |
2023年 | 50篇 |
2022年 | 64篇 |
2021年 | 133篇 |
2020年 | 131篇 |
2019年 | 151篇 |
2018年 | 168篇 |
2017年 | 173篇 |
2016年 | 258篇 |
2015年 | 168篇 |
2014年 | 292篇 |
2013年 | 725篇 |
2012年 | 354篇 |
2011年 | 377篇 |
2010年 | 330篇 |
2009年 | 391篇 |
2008年 | 410篇 |
2007年 | 471篇 |
2006年 | 365篇 |
2005年 | 313篇 |
2004年 | 261篇 |
2003年 | 280篇 |
2002年 | 238篇 |
2001年 | 249篇 |
2000年 | 199篇 |
1999年 | 162篇 |
1998年 | 143篇 |
1997年 | 114篇 |
1996年 | 112篇 |
1995年 | 125篇 |
1994年 | 113篇 |
1993年 | 68篇 |
1992年 | 51篇 |
1991年 | 70篇 |
1990年 | 46篇 |
1989年 | 42篇 |
1988年 | 46篇 |
1987年 | 30篇 |
1986年 | 49篇 |
1985年 | 46篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 7篇 |
排序方式: 共有7941条查询结果,搜索用时 31 毫秒
1.
2.
The existence of a homoclinic orbit in dynamical systems implies chaotic behaviour with positive entropy. In this work, we determine explicitly the Markov shifts associated to certain Smale horseshoe homoclinic orbits which allow us to compute a lower bound for the topological entropy that such a system can have. It is done associating a heteroclinic orbit which belongs to the same isotopy class and then determining the Markov partition of the dynamical core of an end periodic mapping. 相似文献
3.
高能重带电粒子能直接穿透靶原子核外电子层,与原子核发生直接碰撞,发生散裂反应,产生一系列具有放射性的剩余产物核.重带电粒子诱发靶材放射性剩余核与辐射防护和人员安全有着密切联系,当前,大部分剩余核产额主要依靠蒙特卡罗粒子输运程序进行模拟计算,其准确程度亟需通过实验测量进行准确评估.本文利用能量为80.5 MeV/u的(12)^C6+粒子对薄铜靶开展了辐照实验与伽玛射线测量,结合伽玛谱学分析方法,得出了辐照产生的18种放射性剩余产物的初始活度和产生截面值,并与PHITS模拟结果进行对比.结果表明,PHITS模拟程序对放射性剩余核种类的估计具有较高可靠性,在其绝对产额方面,与实验测量仍具有较大偏差. 相似文献
4.
5.
S. Sidi Ahmed G. Dimitri Ngantso M. Boujnah A. Benyoussef A. El Kenz 《Physics letters. A》2019,383(2-3):121-126
By using the density functional theory (DFT) and Monte Carlo simulations (MCS) with the Heisenberg model, we have studied magnetic properties of the bulk perovskite YCrO3. The exchange couplings of the Heisenberg model and the magnetic anisotropy are investigated. The 110 direction in the crystalline structure of the compound has shown the minimum energy, it is the easy magnetic direction. Using Monte Carlo simulations, the magnetizations behavior, the effects of system parameters and the critical exponents of the compound YCrO3 are implemented. It is shown that the bulk perovskite YCrO3 belongs to the 3D Heisenberg universality class. 相似文献
6.
Chikashi Shinagawa Yusuke Morikawa Shin-ichi Nishimura Hiroshi Ushiyama Atsuo Yamada Koichi Yamashita 《Journal of computational chemistry》2019,40(1):237-246
Na2FePO4F is a promising cathode material for a Na-ion battery because of its high electronic capacity and good cycle performance. In this work, first principle calculations combined with cluster expansion and the Monte Carlo method have been applied to analyze the charge and discharge processes of Na2FePO4F by examining the voltage curve and the phase diagram. As a result of the density functional theory calculation and experimental verification with structural analysis, we found that the most stable structure of Na1.5FePO4F has the P21/b11 space group, which has not been reported to date. The estimated voltage curve has two clear plateaus caused by the two-phase structure composed of P21/b11 Na1.5FePO4F and Pbcn Na2FePO4F or Na1FePO4F and separated along the c-axis direction. The phase diagram shows the stability of the phase-separated structure. Considering that Na2FePO4F has diffusion paths in the a- and c-axis directions, Na2FePO4F has both innerphase and interphase diffusion paths. We suggest that the stable two-phase structure and the diffusion paths to both the innerphase and interphases are a key for the very clear plateau. We challenge to simulate a nonequilibrium state at high rate discharge with high temperature by introducing a coordinate-dependent chemical potential. The simulation shows agreement with the experimental discharge curve on the disappearance of the two plateaus. © 2018 Wiley Periodicals, Inc. 相似文献
7.
Palle E.T. Jorgensen Erin P.J. Pearse 《Journal of Mathematical Analysis and Applications》2019,469(2):765-807
Motivated by applications to machine learning, we construct a reversible and irreducible Markov chain whose state space is a certain collection of measurable sets of a chosen l.c.h. space . We study the resulting network (connected undirected graph), including transience, Royden and Riesz decompositions, and kernel factorization. We describe a construction for Hilbert spaces of signed measures which comes equipped with a new notion of reproducing kernels and there is a unique solution to a regularized optimization problem involving the approximation of functions by functions of finite energy. The latter has applications to machine learning (for Markov random fields, for example). 相似文献
8.
《Physics letters. A》2019,383(22):2594-2603
In this work, we address the systematic biases and random errors stemming from finite step sizes encountered in diffusion simulations. We introduce the Effective Geometry Monte Carlo (EG-MC) simulation algorithm which modifies the geometry of the receiver. We motivate our approach in a 1D toy model and then apply our findings to a spherical absorbing receiver in a 3D unbounded environment. We show that with minimal computational cost the impulse response of this receiver can be precisely simulated using EG-MC. Afterwards, we demonstrate the accuracy of our simulations and give tight constraints on the single free parameter in EG-MC. Finally, we comment on the range of applicability of our results. While we present the EG-MC algorithm for the specific case of molecular diffusion, we believe that analogous methods with effective geometry manipulations can be utilized to approach a variety of problems in other branches of physics such as condensed matter physics and cosmological large scale structure simulations. 相似文献
9.
10.
Understanding the complicated failure mechanisms of hierarchical composites such as fiber yarns is essential for advanced materials design. In this study, we developed a new Monte Carlo model for predicting the mechanical properties of fiber yarns that includes statistical variation in fiber strength. Furthermore, a statistical shear load transfer law based on the shear lag analysis was derived and implemented to simulate the interactions between adjacent fibers and provide a more accurate tensile stress distribution along the overlap distance. Simulations on two types of yarns, made from different raw materials and based on distinct processing approaches, predict yarn strength values that compare favorably with experimental measurements. Furthermore, the model identified very distinct dominant failure mechanisms for the two materials, providing important insights into design features that can improve yarn strength. 相似文献