全文获取类型
收费全文 | 12061篇 |
免费 | 2070篇 |
国内免费 | 1376篇 |
专业分类
化学 | 5541篇 |
晶体学 | 114篇 |
力学 | 2200篇 |
综合类 | 66篇 |
数学 | 1438篇 |
物理学 | 6148篇 |
出版年
2024年 | 30篇 |
2023年 | 158篇 |
2022年 | 308篇 |
2021年 | 531篇 |
2020年 | 548篇 |
2019年 | 508篇 |
2018年 | 396篇 |
2017年 | 438篇 |
2016年 | 634篇 |
2015年 | 537篇 |
2014年 | 686篇 |
2013年 | 1184篇 |
2012年 | 713篇 |
2011年 | 752篇 |
2010年 | 656篇 |
2009年 | 790篇 |
2008年 | 809篇 |
2007年 | 824篇 |
2006年 | 729篇 |
2005年 | 558篇 |
2004年 | 446篇 |
2003年 | 419篇 |
2002年 | 387篇 |
2001年 | 328篇 |
2000年 | 316篇 |
1999年 | 277篇 |
1998年 | 276篇 |
1997年 | 185篇 |
1996年 | 162篇 |
1995年 | 140篇 |
1994年 | 148篇 |
1993年 | 106篇 |
1992年 | 77篇 |
1991年 | 66篇 |
1990年 | 54篇 |
1989年 | 49篇 |
1988年 | 39篇 |
1987年 | 43篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1971年 | 6篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 172 毫秒
61.
For an innovative product characterized by short product lifecycle and high demand uncertainty, investment in capacity buildup has to be done cautiously. Otherwise either the product’s market diffusion is impeded or the manufacturer is left with unutilized capacity. Using the right information for making capacity augmentation decisions is critical in facing this challenge. In this paper, we propose a method for identifying critical information flows using the system dynamics model of a two-echelon supply chain. The fundamental premise of system dynamics methodology is that (system) structure determines (its) behavior. Using loop dominance analysis method we study the feedback loop structure of the supply chain system. The outcome is a set of dominant loops that determine the dynamics of capacity growth. It is revealed that the delivery delay information has little effect while the loop that connects retail sales with production order affects the dynamics significantly. Modifying this loop yields appropriate capacity augmentation decisions resulting in higher performance. What-if analyses bring out effects of modifying other structural elements. In conclusion, we claim that the information feedback based methodology is general enough to be useful in designing decision support systems for capacity augmentation. The limitations of the model are also discussed and possible extensions identified. 相似文献
62.
This paper considers the general synchronization dynamics of coupled Van der Pol–Duffing oscillators. The linear and nonlinear stability analysis on the synchronization process is derived through the Whittaker method and the Floquet theory in addition to the multiple time scales method. A stability map displaying different dynamical states of the system is performed. Numerical simulation is carried out to support and to complement the accuracy of the analytical treatment. 相似文献
63.
Mark Pollicott 《Topology and its Applications》2007,154(12):2365-2375
We study lifts of the stable foliation of a pseudo-Anosov diffeomorphism to abelian covers. Under certain conditions, we show that it is ergodic but not uniquely ergodic and describe the ergodic measures. 相似文献
64.
The melting curve of MgSiO分子动力学 MgSiO3钙钛矿 熔化温度 高压 melting temperature, molecular dynamics, high pressure Project supported by the National Natural Science Foundation of China (Grant Nos 10274055 and 10376021),the Natural Science Foundation of Gansu Province, China (Grant No 3ZS051-A25-027) and the Scientific Research Foundation of Education Bureau of Gansu Province, China (Grant No 0410-01). 2005-01-12 5/8/2005 12:00:00 AM The melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments. 相似文献
65.
66.
A new probabilistic cellular automaton model is introduced to simulate cluster and interface growth in two dimensions. The dynamics of this model is an extension to higher dimensions of the compact directed percolation studied by Essam. Numerical results indicate that the two-dimensional cluster coarsening and growth can be described only approximately by the conventional cluster size scaling due to a crossover in the growth mode. The spreading of the initially flat interface follows a purely diffusional,t
1/2, law. 相似文献
67.
68.
Matthias Heuchel Martin Bhning Ole Hlck Martin R. Siegert Dieter Hofmann 《Journal of Polymer Science.Polymer Physics》2006,44(13):1874-1897
Atomistic packing models have been created, which help to better understand the experimentally observed swelling behavior of glassy polysulfone and poly (ether sulfone), under CO2 gas pressures up to 50 bar at 308 K. The experimental characterization includes the measurement of the time‐dependent volume dilation of the polymer samples after a pressure step and the determination of the corresponding gas concentrations by gravimetric gas‐sorption measurements. The models obtained by force‐field‐based molecular mechanics and molecular dynamics methods allow a detailed atomistic analysis of representative swelling states of polymer/gas systems, with respect to the dilation of the matrix. Also, changes of free volume distribution and backbone mobility are accessible. The behavior of gas molecules in unswollen and swollen polymer matrices is characterized in terms of sorption, diffusion, and plasticization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1874–1897, 2006 相似文献
69.
泊松类型方程边界元解法 总被引:2,自引:0,他引:2
本文采用高阶拉普拉斯算子基本解将泊松类型方程的区域积分全部变换成边界积分,使计算问题的维数减少一维.通过斯托克斯方程的算例,表明本文所用的方法是有效的方法。 相似文献
70.
J. M. Skowronski 《Annals of Operations Research》1992,37(1):423-437
The Liapunov technique has been introduced in differential games in a sequence of works over the last decade. We discuss application of this technique to the interface between two competitive semi-games, each with different qualitative objective. The feedback information for controllers is provided from designed, analytically integrable state predictors with reduced dynamics, which considerably shortens the computing time. The case is illustrated on the scenario of target reaching before being intercepted, and intercepting before target is reached.Deceased. 相似文献