全文获取类型
收费全文 | 755830篇 |
免费 | 9339篇 |
国内免费 | 2697篇 |
专业分类
电工技术 | 14807篇 |
综合类 | 1072篇 |
化学工业 | 112128篇 |
金属工艺 | 29693篇 |
机械仪表 | 25443篇 |
建筑科学 | 19647篇 |
矿业工程 | 2867篇 |
能源动力 | 19075篇 |
轻工业 | 68578篇 |
水利工程 | 6934篇 |
石油天然气 | 8652篇 |
武器工业 | 73篇 |
无线电 | 92597篇 |
一般工业技术 | 146231篇 |
冶金工业 | 134418篇 |
原子能技术 | 12685篇 |
自动化技术 | 72966篇 |
出版年
2021年 | 5457篇 |
2020年 | 4029篇 |
2019年 | 5100篇 |
2018年 | 14696篇 |
2017年 | 15116篇 |
2016年 | 12676篇 |
2015年 | 7041篇 |
2014年 | 11057篇 |
2013年 | 33503篇 |
2012年 | 19938篇 |
2011年 | 30867篇 |
2010年 | 25380篇 |
2009年 | 27084篇 |
2008年 | 28042篇 |
2007年 | 29537篇 |
2006年 | 20839篇 |
2005年 | 21576篇 |
2004年 | 19613篇 |
2003年 | 18805篇 |
2002年 | 17555篇 |
2001年 | 17324篇 |
2000年 | 16672篇 |
1999年 | 17313篇 |
1998年 | 40005篇 |
1997年 | 29045篇 |
1996年 | 22687篇 |
1995年 | 17604篇 |
1994年 | 15847篇 |
1993年 | 15321篇 |
1992年 | 11424篇 |
1991年 | 11063篇 |
1990年 | 10630篇 |
1989年 | 10266篇 |
1988年 | 9832篇 |
1987年 | 8342篇 |
1986年 | 8473篇 |
1985年 | 9974篇 |
1984年 | 9135篇 |
1983年 | 8290篇 |
1982年 | 7631篇 |
1981年 | 7709篇 |
1980年 | 7244篇 |
1979年 | 7013篇 |
1978年 | 6592篇 |
1977年 | 8002篇 |
1976年 | 10645篇 |
1975年 | 5683篇 |
1974年 | 5441篇 |
1973年 | 5360篇 |
1972年 | 4347篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Residual stress as measured quantity in quality assurance The x‐ray method is used in the Volkswagen Automotive Group at different world‐wide locations as a standard procedure to determine residual stress. As an important measured quantity in the quality assurance residual stresses are specified in drawings of different components (e.g. gears, coil springs). Measurements are carried out during quality assurance, production, damage analyse, technical development department and design control of components from suppliers. An optimum efficiency can be achieved, if it exists a unique correlation between residual stress values and loading capacity of components, and if the processes to introduce residual stress can be optimized using residual stress measurements during the production. 相似文献
942.
A. V. Lyutetskii N. A. Pikhtin S. O. Slipchenko N. V. Fetisova A. Yu. Leshko E. G. Golikova Yu. A. Ryaboshtan I. S. Tarasov 《Technical Physics Letters》2003,29(4):290-293
Separate confinement InGaAsP/InP laser heterostructures were grown by metalorganic-hydride vapor-phase epitaxy. High-power single-mode laser diodes of mesastripe design based on these heterostructures operate in a wavelength interval of 1.7–1.8 μm with a maximum continuous room temperature output power of 150 mW. The single-mode lasing regime is maintained up to an output power level of 100 mW. 相似文献
943.
944.
945.
Fe–Co bimetallic metals supported on CaCO3 support have been prepared using three different methods for the preparation of the catalysts; wet impregnation (IMP), deposition–precipitation (DP) and reverse micelle impregnation (RM). By careful choice and optimization of CVD reaction conditions and catalyst preparation procedures, we have tailored the nanofabrication of CNTs using 5 wt.% Fe–Co/CaCO3. High yields of ‘clean’ MWNTs with near 100% selectivity and excellent reproducibility were obtained (1215% and 835% yields for the IMP and DP methods respectively). The RM technique enabled more precise control over the size of the CNTs and a narrower diameter distribution (3–5 nm i.d. and 10–15 nm o.d.) was obtained. 相似文献
946.
J. Pujara M. A. Siddiqui Z. Liu P. Bjegovic S. S. Takagaki P. Y. Li S. Ramaswamy 《Drying Technology》2008,26(3):341-348
This is part II of a study reported earlier on a method to characterize the air flow and water removal characteristics during vacuum dewatering. This article presents experimental data and analysis of results from the use of a cyclically actuated vacuum dewatering device for removing moisture from wetted porous materials such as paper with the intermittent application of vacuum and accompanying air flow though the material. Results presented include sheet moisture content as a function of residence time and hence water removal rate under a variety of process conditions. Also, experimental results on air flow through the wet porous structure and hence the role and importance of air flow during vacuum dewatering are presented. Vacuum dewatering process conditions include exit solids content between 11 and 20% solid under applied vacuum conditions of 13.5 to 67.7 kPa (4 to 20 in. Hg). Regression analysis indicated that the exit sheet moisture content exhibited a nonlinear relationship with residence time with exit solids reaching a plateau after a certain residence time. Final moisture content correlated linearly with the average overall flow rate of air through the paper sample and the basis weight of the material. 相似文献
947.
Biodiesel has become an attractive diesel fuel substitute due to its environmental benefits since it can be made from renewable resource. However, the high costs surrounding biodiesel production remains the main problem in making it competitive in the fuel market either as a blend or as a neat fuel. More than 80% of the production cost is associated with the feedstock itself and consequently, efforts are focused on developing technologies capable of using lower-cost feedstocks, such as recycled cooking oils and wastes from animal or vegetable oil processing operations. 相似文献
948.
Yu. F. Patrakov E. S. Pavlusha N. I. Fedorova Yu. A. Strizhakova 《Solid Fuel Chemistry》2008,42(1):10-13
The results of the thermal solution of oil shale in benzene in a flow unit under supercritical conditions are reported. It was found that the conversion of shale organic matter into liquid products increased by a factor of 2.5 with an increase in the solvent pressure from 5 to 15 MPa. 相似文献
949.
Ravi Joshi Jörg Engstler P. Kesavan Nair Prathap Haridoss Jörg J. Schneider 《Diamond and Related Materials》2008,17(6):913-919
Carbon nanotubes (CNTs) have been synthesized using the arc discharge method with a rotating graphite disc as the cathode. Arcing was carried out in open air and without the use of catalysts. The current density was maintained constant through out the experiment, while, the rate of rotation of the cathode and atmosphere under which arcing was carried out were changed during experimentation. Characterization of the samples produced indicates that rotation of the cathode has a significant impact on the quality and yield of the process. It is proposed that rotation of the cathode drags plasma formed between two electrodes away from high temperature region. This results in a sudden quenching of the reactive plasma. The time available for nucleation and growth phenomena is significantly reduced and thus leads to the formation of highly graphitic multi walled CNTs (yield 60%) and traces of double walled CNTs. 相似文献
950.
M. Guerioune Y. Amiour W. Bounour O. Guellati A. Benaldjia A. Amara N. E. Chakri M. Ali-Rachedi D. Vrel 《International Journal of Self-Propagating High-Temperature Synthesis》2008,17(1):41-48
Aiming at preparation of shape memory alloys (SMAs), we explored the SHS of Cu1 − x
Zn1 − y
Al1 − z
alloys (0.29 < x < 0.30, 0.74 < y < 0.75, and 0.83 < z < 0.96). The most pronounced shape memory effect was exhibited by the alloys of the following compositions (wt %): (1) Cu(70.6)Zn(25.4)Al(4.0),
(2) Cu(70.1)Zn(25.9)Al(4.0), and (3) Cu(69.9)Zn(26.1)Al(4.0). The effect of process parameters on the synthesis of CuZnAl
alloys was studied by XRD, optical microscopy, and scanning electron microscopy (SEM). The grain size of CuZnAl was found
to depend on the relative amount of the primary CuZn and AlZn phases. Changes in the transformation temperature and heat of
transformation are discussed in terms of ignition intensity and compaction. Mechanism of the process depends on the level
of the temperature attained relative to the melting point of components. At the melting point of AlZn, the process is controlled
by the solid-state diffusion of AlZn into a product layer. The ignition temperature for this system depends on the temperature
of the austenite-martensite transformation in CuZnAl alloys. The composition and structure of the products was found to markedly
depend on process parameters. The SHS technique has been successfully used to prepare a variety of SMAs.
相似文献