全文获取类型
收费全文 | 4508篇 |
免费 | 645篇 |
国内免费 | 393篇 |
专业分类
化学 | 756篇 |
晶体学 | 28篇 |
力学 | 827篇 |
综合类 | 196篇 |
数学 | 542篇 |
物理学 | 3197篇 |
出版年
2024年 | 6篇 |
2023年 | 35篇 |
2022年 | 85篇 |
2021年 | 111篇 |
2020年 | 96篇 |
2019年 | 68篇 |
2018年 | 91篇 |
2017年 | 149篇 |
2016年 | 171篇 |
2015年 | 149篇 |
2014年 | 222篇 |
2013年 | 257篇 |
2012年 | 189篇 |
2011年 | 250篇 |
2010年 | 212篇 |
2009年 | 247篇 |
2008年 | 259篇 |
2007年 | 316篇 |
2006年 | 296篇 |
2005年 | 285篇 |
2004年 | 251篇 |
2003年 | 224篇 |
2002年 | 208篇 |
2001年 | 172篇 |
2000年 | 154篇 |
1999年 | 118篇 |
1998年 | 110篇 |
1997年 | 137篇 |
1996年 | 99篇 |
1995年 | 89篇 |
1994年 | 75篇 |
1993年 | 61篇 |
1992年 | 53篇 |
1991年 | 42篇 |
1990年 | 46篇 |
1989年 | 38篇 |
1988年 | 42篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 19篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有5546条查询结果,搜索用时 31 毫秒
31.
对具有消息恢复的数字签名方案提出了两种攻击方法.此外,对原方案进行了改进,通过对改进方案的安全性分析得出结论:改进方案比原方案更安全,并且消息恢复过程只需要计算一次大数模幂乘和两次单向函数. 相似文献
32.
Let a text of u characters over an alphabet of size σ be compressible to n phrases by the LZ78 algorithm. We show how to build a data structure based on the Ziv–Lempel trie, called the LZ-index, that takes 4nlog2n(1+o(1)) bits of space (that is, 4 times the entropy of the text for ergodic sources) and reports the R occurrences of a pattern of length m in worst case time O(m3logσ+(m+R)logn). We present a practical implementation of the LZ-index, which is faster than current alternatives when we take into consideration the time to report the positions or text contexts of the occurrences found. 相似文献
33.
Thomas Wanner 《Transactions of the American Mathematical Society》2004,356(6):2251-2279
Many interesting and complicated patterns in the applied sciences are formed through transient pattern formation processes. In this paper we concentrate on the phenomenon of spinodal decomposition in metal alloys as described by the Cahn-Hilliard equation. This model depends on a small parameter, and one is generally interested in establishing sharp lower bounds on the amplitudes of the patterns as the parameter approaches zero. Recent results on spinodal decomposition have produced such lower bounds. Unfortunately, for higher-dimensional base domains these bounds are orders of magnitude smaller than what one would expect from simulations and experiments. The bounds exhibit a dependence on the dimension of the domain, which from a theoretical point of view seemed unavoidable, but which could not be observed in practice.
In this paper we resolve this apparent paradox. By employing probabilistic methods, we can improve the lower bounds for certain domains and remove the dimension dependence. We thereby obtain optimal results which close the gap between analytical methods and numerical observations, and provide more insight into the nature of the decomposition process. We also indicate how our results can be adapted to other situations.
34.
Theory and experiment of spatially and temporally partially coherent speckle shearing interferometry
The theory and experiment of spatially and temporally partially coherent speckle shearing interferometry is reported in this rapid communication for the first time. The general requirements for the surface roughness and coherence area of a diffuse object surface in spatially and temporally partially coherent speckle shearing interferometry are discussed. An experimental verification is presented and the results of theory and experiment are in good agreement. 相似文献
35.
36.
37.
G. Romero L. Alvarez E. Alanís L. Nallim R. Grossi 《Optics and Lasers in Engineering》2003,40(1-2):81-90
Real-time electronic speckle pattern interferometry (ESPI) was used for tuning and visualization of natural frequencies of a trapezoidal plate. The plate was excited to resonant vibration by a sinusoidal acoustical source, which provided a continuous range of audio frequencies. Fringe patterns produced during the time-average recording of the vibrating plate—corresponding to several resonant frequencies—were registered. From these interferograms, calculations of vibrational amplitudes by means of zero-order Bessel functions were performed in some particular cases. The system was also studied analytically. The analytical approach developed is based on the Rayleigh–Ritz method and on the use of non-orthogonal right triangular co-ordinates. The deflection of the plate is approximated by a set of beam characteristic orthogonal polynomials generated by using the Gram–Schmidt procedure. A high degree of correlation between computational analysis and experimental results was observed. 相似文献
38.
39.
N. Nishi J. Nishijo K. Judai C. Okabe O. Oishi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):287-290
UV photoexcitation of (t-butylethynyl copper)24
cluster films induces segregation of the crystals into metallic and organic
phases and leads to evolve the metallic sheets sandwiched by organic
polymers. The growth of the metallic crystals in the plane of the
photo-electromagnetic field is attributed due to plasmon-plasmon interaction
among nanoparticles embedded in dielectric polymer matrices. The surface
enhanced photochemical reaction of residual cluster molecules on the photon
incident direction is expected to take an important role for joining the
metal particles to produce a metallic sheet. We can apply this phenomenon
for photolithographic copper pattern generation on a flexible base plate. 相似文献
40.
数码相机原理与系统设计研究 总被引:7,自引:0,他引:7
介绍了数码相机的工作原理 ,分析了数码相机的系统结构 ,提出了设计数码相机的处理流程。典型的数码相机系统有镜头、闪光灯、光学取景器、LCD显示屏、图像数据存储扩展设备接口、图像数据传输接口、供电系统以及核心处理器等八个主要模块。数码相机的数据流向从图像传感器开始 ,止于图像数据的存储和传输。数据流的处理主要包括模数转换、光学黑电平钳位、针对镜头的边缘畸变的运算修正、坏像素处理、白平衡处理、伽马校正、色彩合成处理、边缘检测 (锐度检测 )和伪彩色检测 (伪彩色抑制 )、JPEG压缩和图像存储器等模块 相似文献