全文获取类型
收费全文 | 70750篇 |
免费 | 7869篇 |
国内免费 | 2815篇 |
专业分类
电工技术 | 1063篇 |
技术理论 | 1篇 |
综合类 | 3025篇 |
化学工业 | 26723篇 |
金属工艺 | 10120篇 |
机械仪表 | 1336篇 |
建筑科学 | 1974篇 |
矿业工程 | 1010篇 |
能源动力 | 1358篇 |
轻工业 | 9543篇 |
水利工程 | 373篇 |
石油天然气 | 1341篇 |
武器工业 | 346篇 |
无线电 | 2645篇 |
一般工业技术 | 16512篇 |
冶金工业 | 2915篇 |
原子能技术 | 252篇 |
自动化技术 | 897篇 |
出版年
2024年 | 438篇 |
2023年 | 1657篇 |
2022年 | 2413篇 |
2021年 | 3226篇 |
2020年 | 2989篇 |
2019年 | 2556篇 |
2018年 | 2834篇 |
2017年 | 3238篇 |
2016年 | 3242篇 |
2015年 | 3360篇 |
2014年 | 3972篇 |
2013年 | 5090篇 |
2012年 | 4551篇 |
2011年 | 5582篇 |
2010年 | 3748篇 |
2009年 | 4066篇 |
2008年 | 3392篇 |
2007年 | 3720篇 |
2006年 | 3547篇 |
2005年 | 2809篇 |
2004年 | 2740篇 |
2003年 | 2339篇 |
2002年 | 1915篇 |
2001年 | 1326篇 |
2000年 | 1184篇 |
1999年 | 916篇 |
1998年 | 822篇 |
1997年 | 695篇 |
1996年 | 535篇 |
1995年 | 462篇 |
1994年 | 345篇 |
1993年 | 254篇 |
1992年 | 263篇 |
1991年 | 212篇 |
1990年 | 246篇 |
1989年 | 237篇 |
1988年 | 84篇 |
1987年 | 57篇 |
1986年 | 59篇 |
1985年 | 69篇 |
1984年 | 67篇 |
1983年 | 33篇 |
1982年 | 55篇 |
1981年 | 7篇 |
1980年 | 35篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
The epoxy/polystyrene system is characterized by a poor adhesion between the constituent phases, which determines its mechanical properties. The adhesion can be improved via blends based on epoxy resin and random copolymers, poly(styrene‐co‐allylalcohol) (PS‐co‐PA). In this work, the influence of PS‐co‐PA content and the good adhesion between the phases on the tensile properties and the fracture toughness achieved through instrumented Charpy tests have been investigated. The tensile strength and the deformation at break showed an increase in the PS‐co‐PA content while the Young's modulus remained the same. The tensile fracture surfaces revealed that the improvement of these magnitudes was mainly due to a crack deflection mechanism. Also, the fracture toughness of the blends was superior to that of the pure epoxy resin. The main operating toughening mechanism was crack deflection. The fractographic analysis showed that ~ 80% of the particles were broken, and the crack tended to divert from its original path through the broken PS‐co‐PA particles. The remaining particles were detached from the epoxy resin, and the holes left suffered plastic deformation. Analytical models were used to predict successfully the toughness due to these mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
902.
Electrochromic properties of electrochemically deposited and etched (EDE) WO3−x films have been investigated using voltammetry and nanogravimetry to elucidate the amount of residual stress associated with lattice polarization and deformation in WO3−x nanoparticles. The cathodic WO3−x deposition from pertungstic acid solution and unusual properties of the cathodic electroetching of the oxide in tetraethyl ammonium chloride solution are reported and elucidated on the basis of Electrochemical Quartz Crystal Nanogravimetry (EQCN) measurements. The stress enhanced resonant frequency shift was observed upon WO3−x film coloration. However, the stress enhancement appeared to be much lower (up to 4-6 times) than that measured for films synthesized by other methods. The stress reduction in WO3−x films under study has been attributed to the stress relaxing propensity of EDE film to suppress the compressive stress wave. A considerable isotopic effect has been observed in nanogravimetry of the H+ and D+ ion intercalation into WO3−x films. We have found that the isotopic effect is primarily due to the true mass loading difference between hydrogen and deuterium ions, for the same concentration of color centers (2.65 × 1021 cm−3), since EQCN frequency shifts associated with stress in the film for H+ and D+ are very close to each other. 相似文献
903.
纳米银包覆铜粉体的制备及其导电性能研究 总被引:4,自引:0,他引:4
利用水合肼还原制备出粒径分布均匀的铜纳米粉,并对其表面镀银的方法进行了探索。 相似文献
904.
Takaaki Tsurumi Young-Bae Kil Kouhei Nagatoh Hirofumi Kakemoto Satoshi Wada Sadayuki Takahashi 《Journal of the American Ceramic Society》2002,85(8):1993-1996
The material coefficients of "soft" and "hard" lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least-squares-fitting of immittance data measured for length-extensional bar resonators. The piezoelectric d -constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not "intrinsic" losses, a calculation process to evaluate the "intrinsic" losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ∼50% of the loss of piezoelectric d -constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses. 相似文献
905.
Preliminary evaluation of the anticorrosive properties of aircraft coatings by electrochemical methods 总被引:5,自引:0,他引:5
L. B. Reynolds R. Twite M. Khobaib M. S. Donley G. P. Bierwagen 《Progress in Organic Coatings》1997,32(1-4):31-34
Strict regulations concerning the content of volatile organic compounds (VOCs) and heavy metals (Cr6+) in aircraft coating systems have increased the economic burden of the United States Air Force (USAF) in the area of coating maintenance. To this end, it is critical to have methods to characterize new coating systems in such a manner that the data can be used to predict accurately and reliably the expected lifetime of the coatings in service. Electrochemical noise method (ENM) and electrochemical impedance spectroscopy (EIS) are two techniques used to monitor extent and rate of corrosion. The USAF is currently employing these methods in order to supplement data acquired from traditional salt-spray methods. ENM and EIS are used to evaluate each component of the coating system and its contribution to corrosion prevention. Preliminary evaluations of an aircraft coating system on aluminum substrate (Al 2024-T3) produces resistance noise values of 106 to 107 Ω/cm2. It is hoped that these results will form the basis of coatings that give increased USAF fleet service life and reduction in maintenance manpower and materials costs. 相似文献
906.
Biodegradable plastics (GSD) based on soy dreg (SD) were prepared by compression‐molding, with glycerol as the plasticizer and glutaraldehyde (GA) as the cross‐linker. The structure and properties of the GSD sheets were investigated by Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), scanning electron microscope (SEM), and tensile test methods. The results indicate that when GA content was 6.8%, the tensile strength (σb) of the sheet reached the maximum value of 14.5 MPa. Moreover, the strength and water resistance of the sheets coated with castor‐oil‐based polyurethane/nitrochitosan interpenetrating network (IPN) coating were significantly enhanced to 24.6 MPa in the dry state and 9.8 MPa in the wet state. Simultaneously, the test of biodegradability of the GSD sheet in a mineral salts medium containing microorganisms and agar proved that GSD could be fully biodegradable. This work has provided a novel way to utilize low‐cost SD to prepare biodegradable plastics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 422–427, 2003 相似文献
907.
本文对Al_2O_3/SiC nano ZrO_2(3Y)复相陶瓷的力学性能和微结构进行了研究,探讨了ZrO_2(t)应力诱导相交增韧机制和纳米粒子增韧机制相互迭加的可能性。结果表明:适量的第二相纳米粒子ZrO_2(3Y)加入对材料的微结构有很大影响,同时对材料的力学性能的提高作出贡献。 相似文献
908.
909.
910.
We describe a study of the hot compaction of woven nylon 6,6 multifilaments produced by a patented procedure, developed at the University of Leeds, for creating novel single‐polymer composites. In this process, an assembly of oriented elements, often in the form of a woven cloth, is held under pressure and taken to a critical temperature so that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the single‐polymer composite. This process is therefore a way of producing novel high‐volume‐fraction polymer/polymer composites in which the two phases are chemically the same material. Nylon is an obvious candidate material for this process because oriented nylon multifilaments are available on a commercial scale. The aim of this study was first to establish the conditions of temperature and pressure for the successful hot compaction of oriented nylon 6,6 fibers and second to assess the mechanical properties of the manufactured hot‐compacted nylon sheets. A crucial aspect of this work, not previously examined in hot‐compaction studies of other oriented polymers, was the sensitivity of the properties to absorbed water, with a significant change in the properties measured immediately after hot‐compaction processing and 2 weeks later when 2% water had been absorbed by the compacted nylon sheets. As expected, the water uptake had a greater effect on those properties that depended on local chain interactions (e.g., the modulus and yield strength) and less effect on those properties that depended on the large‐scale properties of the molecular network (e.g., strength). The only negative aspect of the properties of the hot‐compacted nylon sheets was the elevated‐temperature performance of the wet sample, with the modulus falling to a very low value at a temperature of 80°C. However, apart from the elevated‐temperature performance, the majority of the measured properties of the hot‐compacted nylon sheets were comparable to those of hot‐compacted polypropylene and poly(ethylene terephthalate). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 991–997, 2006 相似文献