全文获取类型
收费全文 | 113949篇 |
免费 | 9811篇 |
国内免费 | 5975篇 |
专业分类
电工技术 | 6632篇 |
技术理论 | 3篇 |
综合类 | 9362篇 |
化学工业 | 18484篇 |
金属工艺 | 6396篇 |
机械仪表 | 7335篇 |
建筑科学 | 7896篇 |
矿业工程 | 2912篇 |
能源动力 | 3143篇 |
轻工业 | 9094篇 |
水利工程 | 2086篇 |
石油天然气 | 5223篇 |
武器工业 | 878篇 |
无线电 | 13718篇 |
一般工业技术 | 13254篇 |
冶金工业 | 5457篇 |
原子能技术 | 1460篇 |
自动化技术 | 16402篇 |
出版年
2024年 | 459篇 |
2023年 | 1599篇 |
2022年 | 2926篇 |
2021年 | 4169篇 |
2020年 | 3151篇 |
2019年 | 2856篇 |
2018年 | 3028篇 |
2017年 | 3279篇 |
2016年 | 3173篇 |
2015年 | 4323篇 |
2014年 | 5539篇 |
2013年 | 6678篇 |
2012年 | 7507篇 |
2011年 | 8243篇 |
2010年 | 7322篇 |
2009年 | 7196篇 |
2008年 | 7220篇 |
2007年 | 6776篇 |
2006年 | 6792篇 |
2005年 | 5607篇 |
2004年 | 4439篇 |
2003年 | 3992篇 |
2002年 | 4490篇 |
2001年 | 3920篇 |
2000年 | 2932篇 |
1999年 | 2425篇 |
1998年 | 1761篇 |
1997年 | 1477篇 |
1996年 | 1327篇 |
1995年 | 1133篇 |
1994年 | 853篇 |
1993年 | 609篇 |
1992年 | 489篇 |
1991年 | 408篇 |
1990年 | 339篇 |
1989年 | 261篇 |
1988年 | 207篇 |
1987年 | 162篇 |
1986年 | 88篇 |
1985年 | 103篇 |
1984年 | 78篇 |
1983年 | 67篇 |
1982年 | 48篇 |
1981年 | 41篇 |
1980年 | 44篇 |
1979年 | 31篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 33篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
逆向工程技术在机械领域的应用 总被引:2,自引:0,他引:2
逆向工程技术已成为联系新产品开发过程中各种先进技术的纽带,并成为实现新产品快速开发的重要技术手段.介绍了逆向工程的概念、技术流程、测量系统、常用软件以及实际应用. 相似文献
52.
Xiaojun Xie Yonghong Cheng Hong Wang Qian Wang Xiaolin Chen Caixin Sun 《Ceramics International》2008,34(4):689-693
In the ideal A2B2O6O′ pyrochlore structure, the x-value of O atom position is a variable parameter. In Bi1.5ZnNb1.5−xTaxO7 (BZNT) cubic pyrochlores, the x-values alter with the different compositions of Nb/Ta. In this work, a series of initial models for BZNT were established by analyzing X-ray diffraction data. Then three structure modifying methods, including Rietveld refinement, Rietveld refinement with energy and geometry optimization based on quantum mechanics, were employed to obtain the precise models using Materials Studio. Moreover, the reflectivities of BZNT were computed by quantum mechanical simulation based on the refined models. Comparing the simulation results from different modifying models with the experimental results, it is found that Rietveld refinement with energy optimization is the most accurate method for BZNT pyrochlores. According to the simulation results, the different reflectivities correspond well with various x-values of O atom positions in BZNT pyrochlores. 相似文献
53.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
54.
Youngmo Han 《IEEE transactions on systems, man, and cybernetics. Part A, Systems and humans : a publication of the IEEE Systems, Man, and Cybernetics Society》2007,37(6):854-863
This paper is about gaze control in active vision. The problem to tackle is, given a camera imaging a particular 3-D point, to place the 3-D point at the center of the image by rotating the camera about its own optical center. For separating this procedure from structure estimation, we use a normalized camera coordinate system, which leads to formulation defined on the unit sphere. In designing the algorithm, we try to avoid the disadvantages of local coordinates or approximation. For this purpose, we design the algorithm by considering the intrinsic geometric properties of the underlying space, not using any kinds of parameterization or approximation. The proposed algorithm is simple and of a closed form, and that makes it suitable for real-time application. 相似文献
55.
56.
Jin‐Hong Kim 《Polymer Engineering and Science》2008,48(1):97-101
Polyetherimide (PEI) substrate for next‐generation high density optical data storage is fabricated and characterized. Cover‐layer incident or first‐surface recording configurations do not require optical properties of the substrate, which are the prerequisite conditions for the conventional material of polycarbonate (PC). Instead of the optical properties, good mechanical properties with a sufficient transcribability are required. Even though PEI has higher glass transition temperature than that of PC, a microscopic transcribability of PEI is comparable with PC by laminating a thermal insulation layer on the backside of a stamper to retard the heat flow. A macroscopic warpage of PEI substrate is smaller than that of PC substrates, which reduces tilt and servo burden. The lowest critical speed coupled with the flutter of PEI substrate is larger than that of PC substrate because of the mechanical properties of PEI. POLYM. ENG. SCI., 48:97–101, 2008. © 2007 Society of Plastics Engineers 相似文献
57.
On Ultra-Fine Leak Detection of Hermetic Wafer Level Packages 总被引:1,自引:0,他引:1
Theoretical and practical ranges of leak rates measurable by the helium mass spectrometer are characterized. The effect of noise due to: 1) background helium present in the spectrometer and 2) desorption of helium that attaches itself to the specimen surface during bombing is quantified experimentally. The results guide a framework to extract the true leak rate from the measured leak rate profile. An optical interferometry based hermeticity measurement technique for ultra-fine leaks is proposed. The setup to implement the technique is described and a preliminary experimental result is reported. 相似文献
58.
Bin Xie Shi X.Q. Han Ding 《Components and Packaging Technologies, IEEE Transactions on》2008,31(2):361-369
In an anisotropic conductive adhesive (ACA) assembly, the electrical conduction is usually achieved with the conductive particles between the bumps of integrated circuit (IC) and corresponding conductive tracks on the glass substrate. Fully understanding of the mechanical and electrical characteristics of ACA particles can help to optimize the assembly process and improve the reliability of ACA interconnection. Most conductive particles used in the ACA assembly are with cracks in the metal coating of the particles after the ACA bonding. This paper introduced the fracture analysis by applying the cohesive elements in the numerical model of the nickel-coated polymer particle and further simulating the cracks initiation and propagation in the nickel coating during the ACA bonding. The simulation results showed that the stress distribution on the nickel-coated particle with cracks was significantly different from that on the nickel-coated particle without crack, indicating that the stress analysis by taking the crack into consideration is very important for the reliability assessment of the ACA interconnection. The stress analysis of cohesive elements indicated that the cracks initiated at the central area of the nickel coating and propagated to the polar area. Furthermore, by the introduction of a new parameter of the virtual resistance, a mathematical model was established to describe the electrical characteristics of the nickel-coated particle with cracks. The particle resistance of the nickel-coated particle with cracks was found to be much higher than that of the particle without crack in the optimized bonding pressure range, indicating that it is necessary to take the crack into consideration for the particle conduction analysis as well. Therefore, the fracture analysis on the conductive particle by taking the crack into consideration could accurately evaluate the reliability of ACA interconnection and avoid serious reliability issues. 相似文献
59.
60.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献