全文获取类型
收费全文 | 29907篇 |
免费 | 2760篇 |
国内免费 | 1475篇 |
专业分类
电工技术 | 2014篇 |
技术理论 | 2篇 |
综合类 | 2078篇 |
化学工业 | 4768篇 |
金属工艺 | 1481篇 |
机械仪表 | 2009篇 |
建筑科学 | 2998篇 |
矿业工程 | 807篇 |
能源动力 | 825篇 |
轻工业 | 2410篇 |
水利工程 | 527篇 |
石油天然气 | 1333篇 |
武器工业 | 233篇 |
无线电 | 3653篇 |
一般工业技术 | 3492篇 |
冶金工业 | 1152篇 |
原子能技术 | 399篇 |
自动化技术 | 3961篇 |
出版年
2024年 | 73篇 |
2023年 | 537篇 |
2022年 | 911篇 |
2021年 | 1398篇 |
2020年 | 1020篇 |
2019年 | 844篇 |
2018年 | 898篇 |
2017年 | 998篇 |
2016年 | 933篇 |
2015年 | 1172篇 |
2014年 | 1550篇 |
2013年 | 1782篇 |
2012年 | 2020篇 |
2011年 | 2143篇 |
2010年 | 2003篇 |
2009年 | 1881篇 |
2008年 | 1737篇 |
2007年 | 1641篇 |
2006年 | 1574篇 |
2005年 | 1345篇 |
2004年 | 895篇 |
2003年 | 833篇 |
2002年 | 820篇 |
2001年 | 741篇 |
2000年 | 667篇 |
1999年 | 695篇 |
1998年 | 491篇 |
1997年 | 470篇 |
1996年 | 456篇 |
1995年 | 364篇 |
1994年 | 308篇 |
1993年 | 204篇 |
1992年 | 156篇 |
1991年 | 109篇 |
1990年 | 82篇 |
1989年 | 78篇 |
1988年 | 62篇 |
1987年 | 40篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1977年 | 4篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
72.
73.
LU Xili WU Ye CAI Wei TANG Wenjun 《武汉理工大学学报(材料科学英文版)》2005,20(B12):287-289
A series of random and block poly( L-lactide-co-e-caprolactone ) ( PCLA ) copolymers whh different composition are prepared using stannous octaoate as catalyst.The effects of the amount of initiator on the intrinsic viscosity have been investigated. The structure of the PCLA copolymers is characterized by means of nuclear magnetic resonance( NMR ), Fourier transform infrared spectrum ( FTIR ), differential scanning calorimetry ( DSC ) and X- ray diffraction ( XRD ) methods. It is shown that the synthesis condition and the composition of copolymers obrious influence on the structure of PCLA copolymers. Hydrolytic degradation of the copolymers in a PBS solution of pH 7.4 at 37.0℃ shows that the copolymers of different composhions degrade at different rates. 相似文献
74.
Y. G. Wang H. Q. Ye K. H. Kuo X. J. Feng S. Z. Long G. L. Lao 《Journal of Materials Science》1991,26(23):6325-6330
The microstructures of unhydrated calcium aluminosulphate Ca4Al6SO16 and Ca3SrAl6SO16 have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca3SrAl6SO16 and another phase, possibly Sr3Al2O6 existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced. 相似文献
75.
Xuetian Huang Lei Zhang Min Zhang Peida Ye 《Photonics Technology Letters, IEEE》2005,17(7):1423-1425
The performance degradation of differential quadrature phase-shift keying (DQPSK) wavelength-division-multiplexed (WDM) systems due to self-phase modulation (SPM)- and cross-phase modulation (XPM)-induced nonlinear phase noise is evaluated in this letter. The XPM-induced nonlinear phase noise is approximated as Gaussian distribution and summed together with the SPM-induced nonlinear phase noise. We demonstrate that 10-Gb/s systems, whose walkoff length is larger than 40-Gb/s systems', are more sensitive to XPM-induced nonlinear phase noise than 40-Gb/s systems. Furthermore, DQPSK WDM systems show lower tolerance to both SPM- and XPM-induced nonlinear phase noise than differential phase-shift keying WDM systems. 相似文献
76.
Yu Shichang Wu Shenqing Gong Youjun Gong Yuansheng Lian Mingsheng Ye Gang Cheng Yijun 《中国稀土学报(英文版)》2006,24(1):120-120
Grain growth behavior of 5Cr21Mn9Ni4NRE steel was experimentally studied at various solid solution treatment temperatures and holding for different times. The experimental results show that the 5Cr21Mn9Ni4NRE steel has the feature of sharp austenite grain coarsening after solid solution treatment at the temperature above 1150 ℃. RE added in the steel has the benefit to restrain grain growth and increase grain growth activation energy. 相似文献
77.
A framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance 总被引:7,自引:0,他引:7
Mechanical mechanisms with clearance abound in technological fields such as robotics, machine and steam turbine industry. The dynamic performance of these mechanisms in working condition can be achieved provided that the effects of the different on the mechanisms (such as mechanism dynamics, technological effects and thermal behaviour) are thoroughly understood. Virtual prototyping provides an integration of multi-domain dynamic simulation for the design and analysis process. In the current paper, a framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance is presented. A case study with such a simulation strategy is studied for the optimum design and analysis of the technological parameter. 相似文献
78.
Yu. N. Gornostyrev I. K. Razumov A. Ye. Yermakov 《Journal of Materials Science》2004,39(16-17):5003-5009
Decomposition of solid solution taking into account the grain boundaries segregations is considered in the framework of generalized Cahn-Hilliard model for finite systems. Two types—“stripe” and “drop-wise”—of the surface-directed decomposition found below spinodal depend on concentration of a wetting component. We demonstrate that grain boundaries segregations are able to drastically change the phase equilibrium inside the grain when its size becomes less than the critical value. As a result, decomposition of the solid solutions easily appears for nanograined materials. 相似文献
79.
如何能够在利用网络速度的同时,保护我们的信息安全,这给密码学家提出了一个难题。 公钥密码系统的诞生解决了这个难题。本文在研究了公钥密码学的教学基础上,以椭圆曲线加密 (ECC)为例,把椭圆曲线信息编码成二进制数,把明文加密成密文,把密文还原为明文,完整地研究 了公钥密码系统。 相似文献
80.
介绍了Multisim8的仿真功能的特点,并通过实例说明了用Multisim8进行仿真分析的具体方法,简单介绍了如何设置参数和进行仿真操作。 相似文献