全文获取类型
收费全文 | 6946篇 |
免费 | 907篇 |
国内免费 | 717篇 |
专业分类
化学 | 2871篇 |
晶体学 | 33篇 |
力学 | 330篇 |
综合类 | 210篇 |
数学 | 2527篇 |
物理学 | 2599篇 |
出版年
2024年 | 16篇 |
2023年 | 71篇 |
2022年 | 268篇 |
2021年 | 335篇 |
2020年 | 300篇 |
2019年 | 266篇 |
2018年 | 259篇 |
2017年 | 321篇 |
2016年 | 380篇 |
2015年 | 308篇 |
2014年 | 421篇 |
2013年 | 599篇 |
2012年 | 375篇 |
2011年 | 422篇 |
2010年 | 324篇 |
2009年 | 404篇 |
2008年 | 390篇 |
2007年 | 400篇 |
2006年 | 354篇 |
2005年 | 318篇 |
2004年 | 296篇 |
2003年 | 234篇 |
2002年 | 209篇 |
2001年 | 181篇 |
2000年 | 142篇 |
1999年 | 135篇 |
1998年 | 129篇 |
1997年 | 90篇 |
1996年 | 92篇 |
1995年 | 95篇 |
1994年 | 59篇 |
1993年 | 53篇 |
1992年 | 41篇 |
1991年 | 37篇 |
1990年 | 31篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 28篇 |
1983年 | 7篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有8570条查询结果,搜索用时 988 毫秒
51.
We consider goodness of fit tests for the Rayleigh distribution with grouped data. New Kolmogrov–Smirnov type tests are suggested and compared with the traditional chi-square and likelihood ratio tests. The results show that some of the suggested tests have a good power performance as compared with the traditional ones. 相似文献
52.
本文首先针对散乱数据拟合的Shepard方法,结合截断多项式、B样条基函数和指数函数来构造其权函数,使新的权函数具有更高的光滑度和更好的衰减性,并且其光滑性和衰减性可以根据实际需要自由调节,从而提高了曲面的拟合质量.同时还给出一种类似的局部插值方法.另外,本文还基于多重二次插值,结合多元样条的思想,给出了两个局部插值算法.该算法较好地继承了多重二次插值曲面的性质,从而保证了拟合曲面具有好地光顺性和拟合精度.曲面整体也具有较高的光滑性. 相似文献
53.
Xie Zhijian Tan Qiulin 《International Journal of Infrared and Millimeter Waves》2006,27(12):1639-1649
To counter the problems of gas accidents in coal mines, family safety resulted from using gas, a new infrared detection system
with integration and miniaturization has been developed. The infrared detection optics principle used in developing this system
is mainly analyzed. The idea that multi gas detection is introduced and guided through analyzing single gas detection is got
across. Through researching the design of cell structure, the cell with integration and miniaturization has been devised.
The way of data transmission on Controller Area Network (CAN) bus is explained. By taking Single-Chip Microcomputer (SCM)
as intelligence handling, the functional block diagram of gas detection system is designed with its hardware and software
system analyzed and devised. This system designed has reached the technology requirement of lower power consumption, mini-volume,
big measure range, and able to realize multi-gas detection. 相似文献
54.
LiNbO3∶Cr∶Cu晶体吸收特性及非挥发全息存储研究 总被引:1,自引:1,他引:0
研究了LiNbO3∶Cr∶Cu晶体的吸收特性,发现LiNbO3∶Cr∶Cu(含0.14 wt.% Cr2O3 和 0.011 wt.% CuO)晶体存在两个明显的吸收峰,中心波长分别位于480 nm和660 nm; 随着Cr的含量逐渐减小,Cu的含量逐渐增大,短波段不存在明显吸收峰,掺Cr的含量越大,中心波长在660 nm处的吸收越大;633 nm红光虽然位于中心波长为660 nm的吸收峰内,但它无助于光折变过程.分别采用390 nm紫外光和488 nm蓝光作为敏化光,514 nm绿光作为记录光的记录方案,实现了非挥发全息记录,掺入适量的Cr( 比如NCr=2.795×1025 m-3,NCr/ NCu=1)有助于全息记录性能的提高. 相似文献
55.
用小型全息设备做傅里叶变换全息图存储资料实验 总被引:1,自引:1,他引:0
阐述了用小型全息设备做傅里叶变换全息图存储资料实验所采用的光路、详细的操作步骤和实验中的关键问题. 相似文献
56.
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
57.
58.
Ching-Cherng Sun You-Nian Lin Shih-Po Yeh Wei-Chia Su Yuh Ouyang 《Optics & Laser Technology》2002,34(7):523-526
High longitudinal selectivity of the shifting multiplexing with spherical reference wave is proposed and demonstrated. A simplified method based on wave optics is used for calculating the selectivity, and the result fits well the experimental measurement. Under the paraxial condition, a simple formula for the longitudinal selectivity is introduced. With use of an object lens with effective NA=0.817, we obtain that an FWHM of selectivity is as small as 1 μm. 相似文献
59.
本主要介绍原木经销商在周期内原木变价销售情况下的最佳期初贮存量的决策方法,在建立期望机会成本的数学模型基础上,探讨原木随机存贮策略的最优化问题。 相似文献
60.
Determination of a control parameter in a one-dimensional parabolic equation using the method of radial basis functions 总被引:3,自引:0,他引:3
In this work, the method of radial basis functions is used for finding the solution of an inverse problem with source control parameter. Because a much wider range of physical phenomena are modelled by nonclassical parabolic initial-boundary value problems, theoretical behavior and numerical approximation of these problems have been active areas of research. The radial basis functions (RBF) method is an efficient mesh free technique for the numerical solution of partial differential equations. The main advantage of numerical methods which use radial basis functions over traditional techniques is the meshless property of these methods. In a meshless method, a set of scattered nodes are used instead of meshing the domain of the problem. The results of numerical experiments are presented and some comparisons are made with several well-known finite difference schemes. 相似文献