全文获取类型
收费全文 | 260898篇 |
免费 | 33957篇 |
国内免费 | 27955篇 |
专业分类
电工技术 | 35781篇 |
技术理论 | 14篇 |
综合类 | 18520篇 |
化学工业 | 46995篇 |
金属工艺 | 13877篇 |
机械仪表 | 15649篇 |
建筑科学 | 14668篇 |
矿业工程 | 5774篇 |
能源动力 | 7986篇 |
轻工业 | 18659篇 |
水利工程 | 4367篇 |
石油天然气 | 8397篇 |
武器工业 | 2627篇 |
无线电 | 37079篇 |
一般工业技术 | 26675篇 |
冶金工业 | 9079篇 |
原子能技术 | 4208篇 |
自动化技术 | 52455篇 |
出版年
2024年 | 931篇 |
2023年 | 4027篇 |
2022年 | 7024篇 |
2021年 | 9416篇 |
2020年 | 9222篇 |
2019年 | 8093篇 |
2018年 | 7533篇 |
2017年 | 10198篇 |
2016年 | 11195篇 |
2015年 | 12822篇 |
2014年 | 14325篇 |
2013年 | 16717篇 |
2012年 | 20156篇 |
2011年 | 22048篇 |
2010年 | 15901篇 |
2009年 | 15946篇 |
2008年 | 16785篇 |
2007年 | 19241篇 |
2006年 | 18156篇 |
2005年 | 15433篇 |
2004年 | 12968篇 |
2003年 | 10597篇 |
2002年 | 8394篇 |
2001年 | 6749篇 |
2000年 | 5574篇 |
1999年 | 4602篇 |
1998年 | 3624篇 |
1997年 | 2870篇 |
1996年 | 2355篇 |
1995年 | 1909篇 |
1994年 | 1655篇 |
1993年 | 1227篇 |
1992年 | 1002篇 |
1991年 | 782篇 |
1990年 | 652篇 |
1989年 | 480篇 |
1988年 | 382篇 |
1987年 | 241篇 |
1986年 | 212篇 |
1985年 | 275篇 |
1984年 | 226篇 |
1983年 | 158篇 |
1982年 | 214篇 |
1981年 | 112篇 |
1980年 | 120篇 |
1979年 | 28篇 |
1978年 | 20篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
织物-树脂复合材料层压板的准静态侵彻机理 总被引:4,自引:1,他引:3
本文利用MTS得到了芳纶和高强维纶织物复合材料层压板受尖头侵彻体穿孔的准静态侵彻曲线 ,比较和分析了不同类型纤维集合体与热固性树脂和热塑性树脂复合材料的破坏模式 ,并考察了芳纶织物复合材料层压板侵彻的逐步破坏过程 ,揭示了复合材料层压板的准静态侵彻机理。 相似文献
992.
993.
电阻式电压传感器结构设计及误差特性研究 总被引:2,自引:0,他引:2
从路的角度分析了电阻式电压传感器的误差特性 ,从场的角度比较了几种结构方案的幅值误差、相角误差及最大场强 ,优化出最佳方案 ,并分析了该方案幅值误差的频率特性 相似文献
994.
One of the main problems faced while configuring or reconfiguring manufacturing systems is to rank alternative designs taking into account all the different aspects involved (both tangible and intangible). For this purpose the Analytic Hierarchy Process (AHP) is a well-known decision making support method that addresses this problem. A major drawback of AHP is that uncertainty in the judgments of the decision makers and the resulting impact on the ranking is not considered. In real situations, however, judgments based on perceived future scenarios are almost always uncertain. To solve this problem in this paper we present the first complete probabilistic extension to the AHP method. The new method provides the decision maker not only with information on the ranking of the alternatives but also the probability that the ranking remains stable even in presence of uncertainty in the judgements. We verified the validity of the new method in a real application developed for the Ferrari racing team. 相似文献
995.
Compact Airborne Spectrographic Imager (CASI) hyperspectral data is used to investigate the effects of topography on the selection of spectral end members, and to assess whether the topographic correction improves the discrimination of rock units for lithologic mapping. A publicly available Digital Elevation Model (DEM), at a scale of 1:50,000, is used to model the radiance variation of the scene as a function of topography, assuming a Lambertian surface. Skylight is estimated and removed from the airborne data using a dark object correction. The CASI data is corrected on a pixel-by-pixel basis to normalize the scene to a uniform solar illumination and viewing geometry. The results show that topography has the effect of expanding end member clusters at times resulting in the overlap of clusters and that the correction process can effectively reduce the variation in detected radiance due to changes in local illumination. When topographic effects are embedded in the hyperspectral data, methods typically used for the selection of end members, such as the convex hull method, can miss end members or result in the selection of nonrepresentative pixels as end members. Thus, end members selected by some conventional methods are very likely “incomplete” or “nonrepresentative” if the topographic effect is embedded in the data. As shown in this study, the topographic correction can reveal hidden end members and achieve a better representation of end members via the statistical center of isolated clusters. 相似文献
996.
997.
利用透射电子显微镜观察了铜在高纯净钢中的析出过程,发现早期析出阶段有类B2结构的亚稳相出现,分析了铜在高纯净钢中的析出贯序,研究结果对分析铜在高纯净钢中的时效强化机理具有重要意义。 相似文献
998.
Polyethylene‐g‐polyacrylamide membranes were prepared by graft polymerization of acrylamide onto polyethylene films using a preirradiation method. The ion‐exchange membranes were obtained by the hydrolysis of grafted films so as to transform amide groups into carboxyl groups. The fraction of amide groups transformed into carboxyl groups was limited to ~0.5. The characterization and thermal behavior of membranes with different degrees of grafting were evaluated by FTIR, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) measurements. The heat of fusion and the crystallinity of polyethylene decreased considerably in the hydrolyzed membranes depending on the degree of grafting. It was found that the grafting of acrylamide led to the reduction in crystallinity due to disruption of the crystallites (crystal defects) and dilution of the inherent crystallinity (dilution effect). The contribution of the hydrolysis step to the crystallinity decrease was negligible. The thermal stability of the membranes as obtained from TGA showed considerable enhancement after hydrolysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 149–154, 2003 相似文献
999.
Numerical Modeling of Silicon Photodiodes for High-Accuracy Applications Part I. Simulation Programs
Jon Geist Deane Chandler-Horowitz A. M. Robinson C. R. James 《Journal of research of the National Institute of Standards and Technology》1991,96(4):463-469
The suitability of the semiconductor-device modeling program PC-1D for high-accuracy simulation of silicon photodiodes is discussed. A set of user interface programs optimized to support high-accuracy batch-mode operation of PC-1D for modeling the internal quantum efficiency of photodiodes is also described. The optimization includes correction for the dark current under reverse- and forward-bias conditions before calculating the quantum efficiency, and easy access to the highest numerical accuracy available from PC-1D, neither of which is conveniently available with PC-1D’s standard user interface. 相似文献
1000.