全文获取类型
收费全文 | 59122篇 |
免费 | 5870篇 |
国内免费 | 4027篇 |
专业分类
电工技术 | 2316篇 |
技术理论 | 1篇 |
综合类 | 4487篇 |
化学工业 | 9325篇 |
金属工艺 | 5852篇 |
机械仪表 | 2907篇 |
建筑科学 | 7025篇 |
矿业工程 | 1061篇 |
能源动力 | 2284篇 |
轻工业 | 1752篇 |
水利工程 | 956篇 |
石油天然气 | 1593篇 |
武器工业 | 322篇 |
无线电 | 9347篇 |
一般工业技术 | 13010篇 |
冶金工业 | 2044篇 |
原子能技术 | 2448篇 |
自动化技术 | 2289篇 |
出版年
2024年 | 222篇 |
2023年 | 923篇 |
2022年 | 1402篇 |
2021年 | 1735篇 |
2020年 | 2007篇 |
2019年 | 1953篇 |
2018年 | 1782篇 |
2017年 | 2157篇 |
2016年 | 2095篇 |
2015年 | 2083篇 |
2014年 | 3107篇 |
2013年 | 3410篇 |
2012年 | 4130篇 |
2011年 | 4685篇 |
2010年 | 3506篇 |
2009年 | 3738篇 |
2008年 | 3414篇 |
2007年 | 3930篇 |
2006年 | 3584篇 |
2005年 | 2907篇 |
2004年 | 2458篇 |
2003年 | 2245篇 |
2002年 | 1892篇 |
2001年 | 1582篇 |
2000年 | 1382篇 |
1999年 | 1096篇 |
1998年 | 959篇 |
1997年 | 780篇 |
1996年 | 712篇 |
1995年 | 619篇 |
1994年 | 553篇 |
1993年 | 364篇 |
1992年 | 328篇 |
1991年 | 261篇 |
1990年 | 222篇 |
1989年 | 169篇 |
1988年 | 152篇 |
1987年 | 107篇 |
1986年 | 96篇 |
1985年 | 56篇 |
1984年 | 55篇 |
1983年 | 37篇 |
1982年 | 32篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1974年 | 6篇 |
1959年 | 16篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Carbon nanotubes are the most promising reinforcement for high performance composites. Multiwall carbon nanotubes were directly grown onto the carbon fiber surface by catalytic thermal chemical vapor deposition technique. Multi-scale hybrid composites were fabricated using the carbon nanotubes grown fibers with epoxy matrix. Morphology of the grown carbon nanotubes was investigated using field emission scanning electron microscopy and transmission electron microscopy. The fabricated composites were subjected to impact tests which showed 48.7% and 42.2% higher energy absorption in Charpy and Izod impact tests respectively. Fractographic analysis of the impact tested specimens revealed the presence of carbon nanotubes both at the fiber surface and within the matrix which explained the reason for improved energy absorption capability of these composites. Carbon nanotubes presence at various cracks formed during loading provided a direct evidence of micro crack bridging. Thus the enhanced fracture strength of these composites is attributed to stronger fiber–matrix interfacial bonding and simultaneous matrix strengthening due to the grown carbon nanotubes. 相似文献
3.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
4.
Aluminum-doped zinc oxide (ZnO:Al, AZO) electrodes were covered with very thin (∼6 nm) Zn1−xMgxO:Al (AMZO) layers grown by atomic layer deposition. They were tested as hole blocking/electron injecting contacts to organic semiconductors. Depending on the ALD growth conditions, the magnesium content at the film surface varied from x = 0 to x = 0.6. Magnesium was present only at the ZnO:Al surface and subsurface regions and did not diffuse into deeper parts of the layer. The work function of the AZO/AMZO (x = 0.3) film was 3.4 eV (based on the ultraviolet photoelectron spectroscopy). To investigate carrier injection properties of such contacts, single layer organic structures with either pentacene or 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine layers were prepared. Deposition of the AMZO layers with x = 0.3 resulted in a decrease of the reverse currents by 1–2 orders of magnitude and an improvement of the diode rectification. The AMZO layer improved hole blocking/electron injecting properties of the AZO electrodes. The analysis of the current-voltage characteristics by a differential approach revealed a richer injection and recombination mechanisms in the structures containing the additional AMZO layer. Among those mechanisms, monomolecular, bimolecular and superhigh injection were identified. 相似文献
5.
Cyclic tension and bend tests were performed on heat-resistant 12Cr1MoV steel specimens in as-supplied condition as well as after Zr+ ion beam surface irradiation. Distinct differences in strain induced relief, as well in cracking pattern of modified surface layer were observed by optical microscopy and interference profilometry. Changes in subsurface layer are characterized by means of nano- and microindentation and fractography of fracture surfaces (with the help of scanning electron microscopy). It is shown that the main influence on mechanical properties is mostly induced by thermal treatment during irradiation rather than formation of a 2 μm thick layer doped with Zr. The differences in deformation behavior may be explained by physical mesomechanics concepts. 相似文献
6.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
7.
8.
This letter presents a new polarizer which has a simple comb structure inside a circular waveguide. The electrical performance of the proposed comb polarizer is optimized by a circular waveguide radius and by the physical parameters of the comb plates. This polarizer is suitable for providing good performance in millimeter‐band application because of its simple structure and low fabrication cost. In our experiments the dual‐band comb polarizer designed in band 1(K) and band 2(Ka) showed good electrical performance without any tuning elements. 相似文献
9.
10.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献