全文获取类型
收费全文 | 39062篇 |
免费 | 4731篇 |
国内免费 | 3551篇 |
专业分类
化学 | 20500篇 |
晶体学 | 284篇 |
力学 | 1944篇 |
综合类 | 273篇 |
数学 | 3280篇 |
物理学 | 10620篇 |
无线电 | 10443篇 |
出版年
2024年 | 147篇 |
2023年 | 907篇 |
2022年 | 999篇 |
2021年 | 1370篇 |
2020年 | 1358篇 |
2019年 | 1277篇 |
2018年 | 1096篇 |
2017年 | 1044篇 |
2016年 | 1506篇 |
2015年 | 1593篇 |
2014年 | 1936篇 |
2013年 | 2552篇 |
2012年 | 3091篇 |
2011年 | 3120篇 |
2010年 | 2115篇 |
2009年 | 2141篇 |
2008年 | 2272篇 |
2007年 | 2146篇 |
2006年 | 1998篇 |
2005年 | 1720篇 |
2004年 | 1246篇 |
2003年 | 1134篇 |
2002年 | 1012篇 |
2001年 | 805篇 |
2000年 | 859篇 |
1999年 | 940篇 |
1998年 | 843篇 |
1997年 | 771篇 |
1996年 | 869篇 |
1995年 | 689篇 |
1994年 | 629篇 |
1993年 | 537篇 |
1992年 | 505篇 |
1991年 | 409篇 |
1990年 | 323篇 |
1989年 | 239篇 |
1988年 | 186篇 |
1987年 | 159篇 |
1986年 | 156篇 |
1985年 | 131篇 |
1984年 | 100篇 |
1983年 | 67篇 |
1982年 | 46篇 |
1981年 | 38篇 |
1980年 | 21篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1975年 | 34篇 |
1974年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
The In-Sn-Ni alloys of various compositions were prepared and annealed at 160°C and 240°C. No ternary compounds were found;
however, most of the binary compounds had extensive ternary solubility. There was a continuous solid solution between the
Ni3Sn phase and Ni3In phase. The Sn-In/Ni couples, made of Sn-In alloys with various compositions, were reacted at 160°C and 240°C and formed
only one compound for all the Sn-In alloys/Ni couples reacted up to 8 h. At 240°C, Ni28In72 phase formed in the couples made with pure indium, In-10at.%Sn and In-11at.%Sn alloys, while Ni3Sn4 phase formed in the couples made of alloys with compositions varied from pure Sn to In-12at.%Sn. At 160°C, except in the
In/Ni couple, Ni3Sn4 formed by interfacial reaction. 相似文献
12.
Analysis of multiple FSS screens of unequal periodicity using an efficient cascading technique 总被引:1,自引:0,他引:1
In this paper, we present an efficient cascading procedure for analyzing frequency selective surface (FSS) systems consisting of multiple FSS screens of unequal periodicity embedded in multiple dielectric layers. In this procedure, we first find a global period for the FSS system by studying the composite in its entirety. Next, we compute the scattering matrix [S] of each of the FSS subsystems for the global Floquet harmonics by applying a relationship we establish that maps the [S] matrix of the subsystem for the individual Floquet harmonics to that for the global harmonics. This mapping-cum-filling process substantially reduces the effort needed to compute the [S] matrix of a subsystem. Finally, we compute the [S] of the entire system by applying a modified cascading formulation, in which one matrix inversion step is eliminated, resulting in a reduction in the total computing resource requirement as well as time. Two numerical examples are given to illustrate the efficiency and effectiveness of the technique. 相似文献
13.
Supplementary proof for "Exact and approximate construction of digital phase modulations by superposition of AMP" by P. A. Laurent 总被引:1,自引:0,他引:1
Kaibin Huang 《Communications, IEEE Transactions on》2005,53(2):234-237
In this letter, we supplement the derivation in Laurent's paper by mathematically proving that combining binary continuous phase modulation (CPM) signals in different bit durations results in the decomposed CPM expression consisting of a set of continuous amplitude-modulated pulse functions. 相似文献
14.
勿庸置疑,课堂只是学生腾飞的基地,社会才是学生飞翔的天空.如何架设课堂与社会之间的桥梁,使学生从理论走向实践,从空想走向实际,是每位教师必须思考的问题.就物理教学而言,实验是架设课堂和社会的桥梁之一.那就是通过物理实验来实现. 相似文献
15.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
16.
A Low-Power CMOS Linear-in-Decibel Variable Gain Amplifier With Programmable Bandwidth and Stable Group Delay 总被引:1,自引:0,他引:1
Tsou S.-C. Li C.-F. Huang P.-C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1436-1440
This brief presents a new circuit architecture for linear-in-decibel, constant-bandwidth variable gain amplifier (VGA). To obtain high linearity under low-voltage operation, this VGA is a closed-loop structure. In loop amplifier design, two techniques are applied: first, the loop amplifier is given finite input impedance. This arrangement keeps the VGA bandwidth constant under different gain setting. Second, a current-buffered compensation is applied for loop stability. Compared to the Miller compensation, this method achieves wider bandwidth. The prototype chip using 0.18-mum CMOS technology demonstrates that -10- to 20-dB gain and 0.5- to 30-MHz bandwidth can be programmed independently. The group delay difference within 30-dB gain control range is smaller than 1%. The total circuit dissipates 1.35 mA from a 1.8-V supply 相似文献
17.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
18.
Current methodologies used for the inference of thin film stress through curvature measurement are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single layer of thin film deposited on a substrate subjected to the non-uniform misfit strain in the thin film. Such methodologies are further extended to multi-layer thin films deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain. We derive relations between the stresses in each thin film and the change of system curvatures due to the deposition of each thin film. The interface shear stresses between the adjacent films and between the thin film and the substrate are also obtained from the system curvatures. This provides the basis for the experimental determination of thin film stresses in multi-layer thin films on a substrate. 相似文献
19.
20.