全文获取类型
收费全文 | 12076篇 |
免费 | 543篇 |
国内免费 | 113篇 |
专业分类
电工技术 | 252篇 |
综合类 | 198篇 |
化学工业 | 2599篇 |
金属工艺 | 420篇 |
机械仪表 | 439篇 |
建筑科学 | 421篇 |
矿业工程 | 104篇 |
能源动力 | 519篇 |
轻工业 | 927篇 |
水利工程 | 138篇 |
石油天然气 | 171篇 |
武器工业 | 17篇 |
无线电 | 1310篇 |
一般工业技术 | 2668篇 |
冶金工业 | 1183篇 |
原子能技术 | 133篇 |
自动化技术 | 1233篇 |
出版年
2023年 | 150篇 |
2022年 | 279篇 |
2021年 | 406篇 |
2020年 | 312篇 |
2019年 | 298篇 |
2018年 | 389篇 |
2017年 | 340篇 |
2016年 | 362篇 |
2015年 | 308篇 |
2014年 | 431篇 |
2013年 | 814篇 |
2012年 | 545篇 |
2011年 | 667篇 |
2010年 | 510篇 |
2009年 | 468篇 |
2008年 | 425篇 |
2007年 | 387篇 |
2006年 | 353篇 |
2005年 | 282篇 |
2004年 | 252篇 |
2003年 | 244篇 |
2002年 | 221篇 |
2001年 | 190篇 |
2000年 | 237篇 |
1999年 | 236篇 |
1998年 | 313篇 |
1997年 | 271篇 |
1996年 | 245篇 |
1995年 | 201篇 |
1994年 | 191篇 |
1993年 | 177篇 |
1992年 | 151篇 |
1991年 | 159篇 |
1990年 | 109篇 |
1989年 | 110篇 |
1988年 | 119篇 |
1987年 | 114篇 |
1986年 | 99篇 |
1985年 | 135篇 |
1984年 | 126篇 |
1983年 | 140篇 |
1982年 | 103篇 |
1981年 | 101篇 |
1980年 | 84篇 |
1979年 | 91篇 |
1978年 | 79篇 |
1977年 | 72篇 |
1976年 | 76篇 |
1975年 | 58篇 |
1974年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Hari B. Goyal M. O. Garg K. R. Rao R. D. Srivastava 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):49-56
The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid. 相似文献
73.
Uma Maheswar Rao S. S. M. S. Abdul Majeed C. Venkataseshaiah R. Sarathi 《Bulletin of Materials Science》2002,25(6):473-475
In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following
IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric
differential thermal analysis (TG-DTA) studies. The tracking time was different for a.c. and d.c. voltages. 相似文献
74.
This paper draws attention to the basic principles governing reflections in uniform Bragg reflectors (BR) when measured employing optical low coherence reflectometry (OLCR) technique. Using computations based on transfer matrix method (TMM), we first showed a strong spectral dependence of Bragg reflectograms on an OLCR probe spectrum. Later, this dependence is exploited to evaluate, for the first time, the coupling coefficient κ of a Bragg grating in a distributed Bragg reflector (DBR) laser on InP 相似文献
75.
K. Ananthasivan S. Anthonysamy C. Sudha A. L. E. Terrance P. R. Vasudeva Rao 《Journal of Nuclear Materials》2002,300(2-3):217-229
The cations M5+ (M=V, Nb and Ta) were doped in thoria through gel-combustion synthesis using citric acid as fuel. Thorium dioxide feed powders thus prepared were cold compacted without binder or lubricant and sintered to a high density (9.5 Mg m−3) at relatively low temperatures (1623 K). The powders were characterised for the residual carbon, crystallite size, specific surface area, particle size distribution and bulk density. The distribution of the dopant in the thoria matrix was analyzed by electron probe microanalysis. The reactivity of the calcined powders was determined by measuring the density of the sintered compacts prepared from them. For the first time it is demonstrated that apart from niobia, even tantala and vanadia can bring about accelerated sintering in thoria if they are doped through a wet chemical route viz., the gel-combustion procedure. The maximum densities obtained by doping with vanadia (0.02 mol%), niobia (0.50 mol%) and tantala (0.50 mol%) were 9.8 Mg m−3 (1573 K), 9.68 Mg m−3 (1423 K) and 9.69 Mg m−3 (1623 K), respectively. 相似文献
76.
77.
78.
A. Edwards Mulpuri V. Rao B. Molnar A. E. Wickenden W. Holland P. H. Chi 《Journal of Electronic Materials》1997,26(3):334-339
Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown
on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature
activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is
too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases
the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the
damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have
indicated a redistribution in the measured profiles of Mg due to annealing. 相似文献
79.
K. T. Venkateswara Rao W. O. Soboyejo R. O. Ritchie 《Metallurgical and Materials Transactions A》1992,23(8):2249-2257
A study has been made of the role of ductile-phase toughening on the ambient temperature fracture toughness and fatigue-crack
propagation behavior of a molybdenum disilicide intermetallicmatrix composite reinforced with 20 vol pct niobium spheres.
Using disk-shaped compact DC(T) samples, only moderate improvements (∼24 pct) in fracture toughnessK
lcvalues were found for the composite compared to the unreinforced MoSi2 matrix material. Moreover, (cyclic) fatigue- crack propagation was seen at stress intensities as low as 75 to 90 pct ofK
Ic, with growth rates displaying a high dependency (∼14) on the applied stress-intensity range. The lack of significant toughening
due to the incorporation of ductile Nb particles is associated with an absence of crack/particle interactions. This is attributed
to the formation of a weak reaction-layer interface and elastic mismatch stresses at the crack tip between the Nb and MoSi2, both factors which favor interfacial debonding; moreover, the spherical morphology of Nb phase stabilizes cracking around
the particle. Results suggest that increasing the aspect ratio of the distributed Nb rein- forcement phase with attendant
interfacial debonding and eliminating possible Nb-phase em- brittlement due to interstitial impurity contamination are critical
factors for the successful development of tougher Nb/MoSi2 structural composites.
Formerly with McDonnell
Formerly with McDonnell 相似文献
80.
A.Varada Rajulu G. Babu Rao B. Ravi Prasad Rao A. Madhu Sudana Reddy Jiasong He Jun Zhang 《应用聚合物科学杂志》2002,84(12):2216-2221
Studies on some properties such as the density, the degradation temperatures, the morphology and the spectral features of the ligno‐cellulose fiber Hildegardia were carried out in both untreated and alkali treated form. The fibers are found to have good morphology and moderate initial and final degradation temperatures. On alkali treatment, the lignin was found to be eliminated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2216–2221, 2002 相似文献