全文获取类型
收费全文 | 17374篇 |
免费 | 1375篇 |
国内免费 | 659篇 |
专业分类
电工技术 | 994篇 |
技术理论 | 2篇 |
综合类 | 1153篇 |
化学工业 | 3138篇 |
金属工艺 | 886篇 |
机械仪表 | 1083篇 |
建筑科学 | 1460篇 |
矿业工程 | 563篇 |
能源动力 | 440篇 |
轻工业 | 1126篇 |
水利工程 | 282篇 |
石油天然气 | 996篇 |
武器工业 | 95篇 |
无线电 | 1985篇 |
一般工业技术 | 2192篇 |
冶金工业 | 814篇 |
原子能技术 | 296篇 |
自动化技术 | 1903篇 |
出版年
2024年 | 70篇 |
2023年 | 313篇 |
2022年 | 461篇 |
2021年 | 617篇 |
2020年 | 499篇 |
2019年 | 475篇 |
2018年 | 491篇 |
2017年 | 546篇 |
2016年 | 458篇 |
2015年 | 644篇 |
2014年 | 816篇 |
2013年 | 956篇 |
2012年 | 1026篇 |
2011年 | 1040篇 |
2010年 | 909篇 |
2009年 | 990篇 |
2008年 | 911篇 |
2007年 | 901篇 |
2006年 | 946篇 |
2005年 | 797篇 |
2004年 | 608篇 |
2003年 | 549篇 |
2002年 | 562篇 |
2001年 | 531篇 |
2000年 | 453篇 |
1999年 | 534篇 |
1998年 | 371篇 |
1997年 | 348篇 |
1996年 | 354篇 |
1995年 | 289篇 |
1994年 | 262篇 |
1993年 | 161篇 |
1992年 | 126篇 |
1991年 | 92篇 |
1990年 | 73篇 |
1989年 | 67篇 |
1988年 | 51篇 |
1987年 | 35篇 |
1986年 | 21篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
21.
Yang Lüyun 《中国稀土学报(英文版)》2006,24(Z2)
The fabrication of one kind of large core area Nd3 doped silicate glass photonic crystal fiber, and demonstration of the fiber's waveguidence properties were reported. This fiber owns a random air hole distribution in the cladding. The measured minimum loss of this kind of fiber is 10 dB·m-1 at 660 nm. These fibers can sustain only a single mode at least over wavelength ranging from 660 nm to 980 nm. 相似文献
22.
Jun Rong Li Jun Wang Jia Rui Xu Ming Qiu Zhang Min Zhi Rong Qiang Zheng 《Composites Science and Technology》2006,66(16):3126-3131
The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test. 相似文献
23.
Biomimetic synthesis of spherical nano-hydroxyapatite in the presence of polyethylene glycol 总被引:1,自引:0,他引:1
Spherical nano-hydroxyapatite (nano-HA) was synthesized successfully by a biomimetic method using Ca(NO3)2·4H2O and (NH4)3PO4·3H2O as reagents in the presence of polyethylene glycol (PEG). The crystalline phase, microstructure, chemical composition, and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The results show that spherical nano-HA with diameter of 30–50 nm can be synthesized in the presence of a certain concentration (2–6%) of PEG. The crystallinity of HA powder synthesized in the presence of PEG was higher than that synthesized in the absence of PEG, but the crystallinity of HA reduced with increasing the concentration of PEG. The electrical conductivity (EC) of the solution revealed that PEG reduced the transfer rate of Ca2+ in the process of HA crystallization, indicating the interaction between PEG and HA. The possible mechanism of formation spherical nano-HA was discussed. 相似文献
24.
A new efficient numerical method and the dynamic analysis of composite laminates with piezoelectric layers 总被引:1,自引:0,他引:1
Firstly, a numerical method for the inversion of Laplace transform is developed and its accuracy is shown through examples. Then, a state-vector equation for the dynamic problems of piezoelectric plates is deduced directly from a modified mixed variational principle for piezoelectric bodies and its exact solution for the dynamic problems of simply supported rectangle piezoelectric plate is simply given. For multilayered hybrid plates, we derive the solution in terms of the propagator matrices. The techniques accounts for the compatibility of generalized displacements and generalized stresses on the interface both the elastic layers and piezoelectric layers, and the transverse shear deformation and the rotary inertia of laminate are also considered in the global algebraic equation of structure. Meanwhile, there is no restriction on the thickness and the number of layers. As an application of the numerical inversion of Laplace transform presented in this paper, typical numerical examples of the harmonic vibration and transient response are proposed and discussed. Since the highly accurate numerical results, they can serve as benchmarks to test various thick plate theories and various numerical methods, such as the finite and boundary element methods for transient response problems. 相似文献
25.
26.
本研究在简介国际上先进的变参设计几种方法及优点后,叙述了一个国家863/CIMS项目:CAD/CAPP/NCP集成系统中二维尺寸驱动的变参设计子系统的构成与功能;然后着重阐述了本系统采用的尺寸驱动的变参设计思想和几何约束建立的原则,并提供了系统数据结构,最后以几个实例证明了此方法的正确性与工程实用性。 相似文献
27.
随着电力和电子技术的飞速发展,相应的元器件向高频化,小型化,高效率和节能的方向发展,从而对元器件用材料也提出了更高要求。为此,本文概述了冶金部钢铁研究总院近年来所研究的用于开关电源,脉冲变压器,传感器,电流互感器和电感器等方面的非晶软磁合金的性能及其应用概况。 相似文献
28.
The formula for soliton timing jitter due to self-frequency shift and pulse width fluctuations caused by spontaneous-emission noise has been deduced. Such timing jitter is compared with that caused by the carrier frequency shift due to spontaneous-emission noise. It is shown that the timing jitter due to the self-frequency shift can be as large as the timing jitter due to carrier frequency shift when the total transmission distance is 100 times longer than the soliton period 相似文献
29.
Linear periodically time-varying (LPTV) systems are abundant in control and signal processing; examples include multirate sampled-data control systems and multirate filter-bank systems. In this paper, several ways are proposed to quantify aliasing effect in discrete-time LPTV systems; these are associated with optimal time-invariant approximations of LPTV systems using operator norms. 相似文献
30.