全文获取类型
收费全文 | 13638篇 |
免费 | 1067篇 |
国内免费 | 561篇 |
专业分类
电工技术 | 716篇 |
技术理论 | 1篇 |
综合类 | 900篇 |
化学工业 | 2508篇 |
金属工艺 | 703篇 |
机械仪表 | 910篇 |
建筑科学 | 910篇 |
矿业工程 | 379篇 |
能源动力 | 388篇 |
轻工业 | 949篇 |
水利工程 | 252篇 |
石油天然气 | 670篇 |
武器工业 | 87篇 |
无线电 | 1499篇 |
一般工业技术 | 1866篇 |
冶金工业 | 629篇 |
原子能技术 | 161篇 |
自动化技术 | 1738篇 |
出版年
2024年 | 60篇 |
2023年 | 239篇 |
2022年 | 336篇 |
2021年 | 516篇 |
2020年 | 438篇 |
2019年 | 344篇 |
2018年 | 410篇 |
2017年 | 449篇 |
2016年 | 374篇 |
2015年 | 509篇 |
2014年 | 652篇 |
2013年 | 829篇 |
2012年 | 791篇 |
2011年 | 793篇 |
2010年 | 769篇 |
2009年 | 685篇 |
2008年 | 651篇 |
2007年 | 731篇 |
2006年 | 716篇 |
2005年 | 580篇 |
2004年 | 419篇 |
2003年 | 462篇 |
2002年 | 543篇 |
2001年 | 430篇 |
2000年 | 356篇 |
1999年 | 368篇 |
1998年 | 323篇 |
1997年 | 286篇 |
1996年 | 248篇 |
1995年 | 193篇 |
1994年 | 165篇 |
1993年 | 114篇 |
1992年 | 100篇 |
1991年 | 82篇 |
1990年 | 63篇 |
1989年 | 48篇 |
1988年 | 42篇 |
1987年 | 25篇 |
1986年 | 31篇 |
1985年 | 10篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Improved integration using product models in a computer aided design and manufacture environment implies that there is an enhanced need to provide information support across a wide range of applications. In a typical situation concerned with mechanical products, these applications are likely to include detail design, process planning and assembly planning. Features have frequently been used to support these and other applications individually, but single feature representations that simultaneously meet the information needs of a number of applications are unusual. Assembly and process planning are two important aspects of an integrated design and manufacture system, and a formal structure for their representation in a feature-based design system is presented. Features are considered to be machined volumes and are described in a hierarchical taxonomy that is designed to be useful across a range of machined components. The assembly structure is also defined hierarchically with the (machining) features forming the basic entities in the assembly. Assembly relationships among features are defined in the form of mating relationships that are carried by the features. A set of mating relationships between pairs of features has been defined after having studied the literature and a number of engineering products. An integrated data structure containing process planning information from earlier research work and the assembly mating relationships is presented and forms the basis of class definitions for each level in the assembly hierarchy. Object-oriented programming techniques have been used to implement a prototype system using the ACIS solid modelling kernel. The research has illustrated the feasibility of using a single feature representation to support a number of activities within a computer integrated manufacturing environment. 相似文献
993.
Zhongquan Wan Chunyang Jia Yandong Duan Ximing Chen Yuan Lin Yu Shi 《Organic Electronics》2013,14(9):2132-2138
In order to increase electron-donating ability of the donor part of the organic dye, two dithiafulvenyl (DTF) units were introduced into a triphenylamine unit to form dithiafulvenyl-substituted triphenylamine hybrid donor for dye-sensitized solar cells (DSSCs) for the first time. Novel donor–acceptor organic dye WD-10 containing this hybrid donor and 2-cyanoacetic acid acceptor has been designed, synthesized and applied in DSSCs. The influence of the substituent unit DTF in the dye on the device performance has been investigated. It was found that the dye with dithiafulvenyl-substituted triphenylamine hybrid donor gave higher photocurrent, open-circuit voltage, and efficiency value. The DSSC based on organic dye WD-10 displayed a short-circuit current (Jsc) of 9.58 mA cm?2, an open-circuit voltage (Voc) of 648 mV, and a fill factor (ff) of 0.71, corresponding to an overall conversion efficiency of 4.41%. An increase in η of about 79% was obtained from simple triphenylamine dye L0 to WD-10. The different photovoltaic behaviors of the solar cells based on the organic dyes were further elucidated by the electrochemical impedance spectroscopy. This work identifies that the introduction of DTF unit into the simple triphenylamine dye could significant improve the photovoltaic performance. 相似文献
994.
Zhi-Hua Yin Yun-Ze Long Chang-Zhi Gu Mei-Xiang Wan Jean-Luc Duvail 《Nanoscale research letters》2009,4(1):63-69
In this paper, we focus on current–voltage (I–V) characteristics in several kinds of quasi-one-dimensional (quasi-1D) nanofibers to investigate their electronic transport
properties covering a wide temperature range from 300 down to 2 K. Since the complex structures composed of ordered conductive
regions in series with disordered barriers in conducting polymer nanotubes/wires and CdS nanowires, all measured nonlinear
I–V characteristics show temperature and field-dependent features and are well fitted to the extended fluctuation-induced tunneling
and thermal excitation model (Kaiser expression). However, we find that there are surprisingly similar deviations emerged
between the I–V data and fitting curves at the low bias voltages and low temperatures, which can be possibly ascribed to the electron–electron
interaction in such quasi-1D systems with inhomogeneous nanostructures. 相似文献
995.
996.
997.
提出了一种新颖的用于测量微结构力学性能的弯曲测试法——微射流驱动的弯曲测试法(microjet-driving microbending test method,JDBT)。该方法利用气体微射流连续冲击微结构,使之发生弯曲变形,通过获取结构的尺寸参数和形变位移,并代入结构的变形公式,从而反解出材料的力学性能参量。利用动量定理推导了微射流作用力公式,对某型号石英摆片式加速度计的敏感结构进行了理论建模,并用COMSOL MULTIPHYSICS有限元软件对理论公式进行了修正,接着通过JDBT实验得到了不同流量下的结构位移,最后将结构尺寸和结构形变位移代入修正后的理论公式,从而得到了石英玻璃的弹性模量约为71GPa,比纳米压痕仪测试的结果要小14%左右,与文献中提到的结果吻合较好。 相似文献
998.
999.
Xiao-Jin Wan Lin HuaXu-Feng Wang Qi-Ze PengXun-peng Qin 《International Journal of Machine Tools and Manufacture》2011,51(3):221-229
Producing an accurate part mainly depends on the position and orientation of the cutting tool with respect to the workpiece which is mainly influenced by the rigid body motion of the workpiece and the elastic deformation of workpiece-fixture-cutter system. For the purpose of minimizing the machining error, a new modification strategy of the nominal tool path is not that directly compensate the control commands of the machine tools, but that modify the cutter location source file (CLSF) from the computer aided manufacturing (CAM) system by means of the proposed modification model on the basis of the prediction deviation, namely, the deviation of the cutting tool relative to the workpiece in computer numerical control (CNC) machining operation. Therefore, it is not only simpler, but also easier implemented by common manufacturing engineer. The effectiveness of the proposed strategy is verified by a machining example. 相似文献
1000.
Neng-Hui Zhang Jian-Zhong Chen Shu-Xiao Wan 《International Journal of Thermophysics》2009,30(2):648-660
The influence of the hybridization exothermic effect on nanomechanical deflections of DNA chips in label-free biodetections
is investigated. First, from the related experimental curves, the thermal variation of the biolayer during the linkage of
DNA base pairs is estimated by Breslauer’s method and the Langmuir adsorption isotherm. Second, the temperature field of the
chip is obtained by the lumped parameter model and the classical Fourier’s method. Third, the nanomechanical deflection of
the chip is predicted by an alternative model for thermoelastic problems of laminated cantilever beams. The effect of a DNA
base sequence on thermal deflection of chips is also investigated. In the case of adiabatic conditions, numerical results
show that the theoretical predicted value of 1.5 nm to 2 nm deflection is within the scope of the optical-beam-deflection
readout system’s accuracy. 相似文献