全文获取类型
收费全文 | 1236篇 |
免费 | 141篇 |
国内免费 | 38篇 |
专业分类
化学 | 86篇 |
力学 | 51篇 |
综合类 | 33篇 |
数学 | 987篇 |
物理学 | 258篇 |
出版年
2023年 | 6篇 |
2022年 | 31篇 |
2021年 | 42篇 |
2020年 | 34篇 |
2019年 | 25篇 |
2018年 | 24篇 |
2017年 | 51篇 |
2016年 | 76篇 |
2015年 | 41篇 |
2014年 | 70篇 |
2013年 | 79篇 |
2012年 | 62篇 |
2011年 | 59篇 |
2010年 | 58篇 |
2009年 | 83篇 |
2008年 | 79篇 |
2007年 | 76篇 |
2006年 | 76篇 |
2005年 | 63篇 |
2004年 | 49篇 |
2003年 | 38篇 |
2002年 | 40篇 |
2001年 | 29篇 |
2000年 | 16篇 |
1999年 | 17篇 |
1998年 | 26篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有1415条查询结果,搜索用时 62 毫秒
41.
为了实现对基于自由摆的平板的控制,建立了基于自由摆的平板控制系统.首先分析平板的控制转角与自由摆转角的关系,推导出关系式,再对控制单元、反馈单元进行分析比较给出方案,采用32位LPC2138(ARM7)处理器为平板控制系统的中央控制单元,实现由高精度电位器测量出摆动角度后由步进电机控制的平板在周期摆动中做相应反馈调整,然后在现有器件的基础上编制出控制软件,在设备上进行调试,最后对系统的精度进行分析并进行实际测量.测量结果表明激光笔在摆动中照射在靶板上的光斑偏离基准线最大0.89cm,基本满足对平板的控制要求. 相似文献
42.
带模糊约束的最小费用流问题 总被引:4,自引:1,他引:3
本文首次提出了带模糊约束的最小费用流问题,建立了相应的数学模型并给出了求解这一模型的有关算法。最后,给出了一个具体实例。 相似文献
43.
We study fundamental properties of monotone network enterprises which contain public vertices and have positive and negative
costs on edges and vertices. Among the properties studied are the nonemptiness of the core, characterization of nonredundant
core constraints, ease of computation of the core and the nucleolus, and cases of decomposition of the core and the nucleolus.
Received December 1994/Final version March 1998 相似文献
44.
45.
Karol?Horodecki Micha??HorodeckiEmail author Pawel?Horodecki Jonathan?Oppenheim 《Foundations of Physics》2005,35(12):2027-2040
There are aspects of privacy theory that are analogous to quantum theory. In particular one can define distillable key and
key cost in parallel to distillable entanglement and entanglement cost. We present here classical privacy theory as a particular
case of information theory with adversaries, where similar general laws hold as in entanglement theory. We place the result
of Renner and Wolf—that intrinsic information is lower bound for key cost—into this general formalism. Then we show that the
question of whether intrinsic information is equal to key cost is equivalent to the question of whether Alice and Bob can
create a distribution product with Eve using IM bits of secret key. We also propose a natural analogue of relative entropy of entanglement in privacy theory and show that
it is equal to the intrinsic information. We also provide a formula analogous to the entanglement of formation for classical
distributions.
It is our pleasure to dedicate this paper to Asher Peres on the occasion of his seventieth birthday. 相似文献
46.
47.
48.
Recent studies show that a negative shock in stock prices will generate more volatility than a positive shock of similar magnitude. The aim of this paper is to appraise the hypothesis under which the conditional mean and the conditional variance of stock returns are asymmetric functions of past information. We compare the results for the Portuguese Stock Market Index PSI 20 with six other Stock Market Indices, namely the SP 500, FTSE 100, DAX 30, CAC 40, ASE 20, and IBEX 35. In order to assess asymmetric volatility we use autoregressive conditional heteroskedasticity specifications known as TARCH and EGARCH. We also test for asymmetry after controlling for the effect of macroeconomic factors on stock market returns using TAR and M-TAR specifications within a VAR framework. Our results show that the conditional variance is an asymmetric function of past innovations raising proportionately more during market declines, a phenomenon known as the leverage effect. However, when we control for the effect of changes in macroeconomic variables, we find no significant evidence of asymmetric behaviour of the stock market returns. There are some signs that the Portuguese Stock Market tends to show somewhat less market efficiency than other markets since the effect of the shocks appear to take a longer time to dissipate. 相似文献
49.
We present a scheme for probabilistic remote preparation of an
entangled two-qubit state with three parties from a sender to either
of two receivers. The quantum channel is composed of a partially
entangled two-qubit state and a partially entangled three-qubit
state. We calculate the successful total probabilities of the scheme
in general and particular cases, respectively. We also calculate
total classical communication cost in a general case and two
particular cases, respectively. 相似文献
50.
近年来的雾霾让人们逐渐意识到环境保护的重要性,国网公司基于我国“多煤、少气、贫油”的国情,提出了以电代煤的电能替代方案。本文以在电力和煤炭的使用过程中可获得的热值作为效用,以使用过程中所需要的年费用作为成本,建立了电能替代的成本效用模型,计算出实现电力和煤炭相互替代的排污费临界值,并通过一个算例进行了实证分析。分析结果表明:电价、单位电力排污量、燃煤设备寿命对排污费临界值有正向影响;煤价、单位燃煤排污量、电力设备寿命对其有负向影响。最后,在分析的基础上给出了电能替代的政策建议。 相似文献