全文获取类型
收费全文 | 21820篇 |
免费 | 1277篇 |
国内免费 | 57篇 |
专业分类
电工技术 | 311篇 |
综合类 | 25篇 |
化学工业 | 4898篇 |
金属工艺 | 882篇 |
机械仪表 | 1301篇 |
建筑科学 | 426篇 |
矿业工程 | 7篇 |
能源动力 | 865篇 |
轻工业 | 1851篇 |
水利工程 | 91篇 |
石油天然气 | 16篇 |
无线电 | 3661篇 |
一般工业技术 | 4629篇 |
冶金工业 | 1541篇 |
原子能技术 | 292篇 |
自动化技术 | 2358篇 |
出版年
2024年 | 22篇 |
2023年 | 275篇 |
2022年 | 399篇 |
2021年 | 685篇 |
2020年 | 470篇 |
2019年 | 497篇 |
2018年 | 699篇 |
2017年 | 661篇 |
2016年 | 768篇 |
2015年 | 602篇 |
2014年 | 939篇 |
2013年 | 1390篇 |
2012年 | 1459篇 |
2011年 | 1791篇 |
2010年 | 1300篇 |
2009年 | 1332篇 |
2008年 | 1213篇 |
2007年 | 940篇 |
2006年 | 813篇 |
2005年 | 708篇 |
2004年 | 638篇 |
2003年 | 589篇 |
2002年 | 594篇 |
2001年 | 517篇 |
2000年 | 437篇 |
1999年 | 423篇 |
1998年 | 709篇 |
1997年 | 420篇 |
1996年 | 396篇 |
1995年 | 257篇 |
1994年 | 169篇 |
1993年 | 151篇 |
1992年 | 113篇 |
1991年 | 100篇 |
1990年 | 75篇 |
1989年 | 88篇 |
1988年 | 74篇 |
1987年 | 63篇 |
1986年 | 51篇 |
1985年 | 43篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 31篇 |
1981年 | 26篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1977年 | 22篇 |
1976年 | 33篇 |
1975年 | 17篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
801.
Composite joints are often the weakest elements in composite structures. In this paper, we propose a modified version of the damage zone theory based on the yield strain ratio. We use this framework to predict failure loads for various adhesive joints. Thick aluminum-to-aluminum joint specimens with eight different adhesive lengths and four adhesive thicknesses were manufactured and tested. The strengths of different adhesive lengths could be predicted to within 15.4% using the damage zone ratio method. In addition, the strengths of joints that feature different adhesive thicknesses were predicted to within 16.3% using the damage zone ratio method. 相似文献
802.
Relva C. Buchanan Eusiuk Park Rajesh Surana Harshani Tennakone Kirthi Tennakone 《Journal of Electroceramics》2011,26(1-4):116-121
High electromechanical strains have been developed in this study in Barium Titanate ceramics, suitably doped with Nd and Zr to form a controlled concentration gradient, leading to a dome-like structure on sintering. Compacted pellets constituted of layers of barium titanate powder of varying minor amounts of Nd and Zr powders, incorporated as nitrates precursors, acquire this dome shape on sintering at 1300?C1320oC and cooling to the ambient temperature, the result of the residual thermoelastic strain. The dome structures exhibit high electromechanical responses, and the piezoelectric coefficients (deduced from electric field induced strains measurements in dome-up and dome-down positions) are also found to be exceptionally high. These Nd and Zr doped barium titanate structures could find applications as an environmentally benign material for fabrication of high displacement functionally graded electromechanical actuators in a single sintering step process. 相似文献
803.
Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiNx and Al2O3 capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry. 相似文献
804.
Seungkeun Park Byeong-Gwon Kang 《Communications, IEEE Transactions on》2009,57(8):2198-2203
This letter presents an alternative derivation of the Case IV of Pawula F-function and an approximation for the corresponding probability density function (pdf) in the presence of the Tikhonov distributed phase error. The pdf of Case IV is used to obtain new upper bounds for the conditional and average symbol-error probabilities of M-ary phase shift keying with phase error over additive white Gaussian noise channels. Numerical results demonstrate the validity of the upper bounds. 相似文献
805.
Kyeong‐Yong Park Jinyong Lee Seong Jun Park Jung‐Nyoung Heo Hwan Jung Lim 《Advanced Synthesis \u0026amp; Catalysis》2015,357(18):3917-3926
A series of 1,2‐ and 1,4‐dihydroquinolines has been successfully prepared. The Pd‐catalyzed intramolecular N‐arylation of Z‐enamines, formally prepared by the Horner–Wadsworth–Emmons olefination, proceeded efficiently to furnish the cyclized products. Depending on the cyclization conditions, substituted 1,4‐dihydroquinolines and further isomerized 1,2‐dihydroquinolines were independently obtained in high yields with an excellent control of isomerization of the double bond.
806.
Kyung Hwan Oh Seong Min Kim Mi Jung Lee Jin Kyoon Park 《Advanced Synthesis \u0026amp; Catalysis》2015,357(18):3927-3935
A direct method for the arylation of 1,2‐azolo[1,5‐a]pyridines has been developed. In the process, the fused pyridines react with aryl halides in the presence of the palladium complex Pd(OAc)2(Phen) as a catalyst and copper(I) chloride (CuCl) as a Lewis acid to form arylated derivatives. While pyrazolo[1,5‐a]pyridines and [1,2,4]triazolo[1,5‐a]pyridines are arylated at ortho‐positions of their pyridine rings using this method, in situ ring‐opening of the formed C‐7 arylated [1,5‐a]pyridine takes place to generate the 2,6‐disubstituted pyridine. Also, upon treatment with lithium diisopropylamide (LDA), C‐7 arylated pyrazolo[1,5‐a]pyridine‐3‐carboxylates react to produce diversely substituted 2,6‐disubstituted pyridines. Finally, a sequential C‐3 arylation was accomplished through a two‐step sequence involving hydrolysis of pyrazolo[1,5‐a]pyridine‐3‐carboxylates followed by the bimetallic Pd/Cu‐catalyzed decarboxylative coupling reaction with aryl bromide.
807.
We developed a simple and inexpensive synthesis of a large-scale close-packed monolayer of polystyrene sphere arrays, which have a variety of applications. The influence of three step spin speeds, spinning time, solution quantity and relative humidity is studied in order to achieve a large area close-packed monolayer.A relatively high surface coverage and uniform monolayer of PS spheres in the range of 85%–90% are achieved by appropriate control of the preparative parameters. Also the effect of the oxygen plasma etching process on the reduction of PS spheres has been studied. We conclude that it can be useful in industrial applications, because of the fabrication speed, surface coverage, control over PS spheres and cost of the process. 相似文献
808.
809.
Rocco P. Viggiano III Edward E. Ball Ronald E. Park Karl W. Haider David A. Schiraldi 《应用聚合物科学杂志》2015,132(39)
The feasibility of incorporating ground recycled polyurethane (PU) foam into clay/polymer aerogels was demonstrated, and a range of compositions were prepared and characterized to determine the effect of variation in the formulations on density and mechanical properties of the resulting materials. This study followed a modified combinatorial approach. Initially, experiments were performed in water using either sodium exchanged montmorillonite or laponite clay, poly(vinyl alcohol) (PVOH) solution as the polymer binder, and the recycled PU foam. Freezing and freeze‐drying the aqueous gels produced aerogels, which were characterized through density and mechanical testing, scanning electron microscopy, and thermal gravimetric analysis. The study was expanded by exploring alternative binder chemistries, including the use of an alginate polymer in place of the PVOH or adding a polyisocyanate as a crosslinking agent for PVOH. The effect of recycled PU foam content, clay type and level, and binder type and level on the mechanical properties of the aerogels were determined and will be discussed herein. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42586. 相似文献
810.
Suk‐Joong L. Kang Ji‐Hoon Park Seok‐Young Ko Ho‐Yong Lee 《Journal of the American Ceramic Society》2015,98(2):347-360
Solid‐state conversion of single crystals from polycrystalline materials has the advantages of cost‐effectiveness, chemical homogeneity, and versatility over the conventional melt growth and solution growth methods, particularly for systems with high melting points, incongruent melting, high reactivity (volatility), and phase transformations at high temperature. Nevertheless, for commercial production, this technique has only been successful in a few limited systems, in particular ferroelectric systems. This is mostly because of the difficulty in controlling the microstructure, particularly suppressing grain growth in the polycrystal during its conversion. This article describes the principle and the current status of the solid‐state conversion of single crystals. We first introduce the recently developed principle of microstructural evolution to explain the basis of the microstructure control in polycrystals for solid‐state conversion. We then report recent technical developments in fabricating single crystals by the solid‐state single crystal growth (SSCG) method and their physical properties. The SSCG method is expected to be studied and utilized more widely in fabricating single crystals with complex compositions as a strong alternative to the melt growth and solution growth methods. 相似文献