全文获取类型
收费全文 | 46377篇 |
免费 | 2493篇 |
国内免费 | 41篇 |
专业分类
电工技术 | 314篇 |
综合类 | 38篇 |
化学工业 | 8354篇 |
金属工艺 | 835篇 |
机械仪表 | 870篇 |
建筑科学 | 1415篇 |
矿业工程 | 76篇 |
能源动力 | 1001篇 |
轻工业 | 5737篇 |
水利工程 | 396篇 |
石油天然气 | 180篇 |
武器工业 | 5篇 |
无线电 | 2432篇 |
一般工业技术 | 7793篇 |
冶金工业 | 13126篇 |
原子能技术 | 268篇 |
自动化技术 | 6071篇 |
出版年
2023年 | 372篇 |
2022年 | 440篇 |
2021年 | 987篇 |
2020年 | 794篇 |
2019年 | 742篇 |
2018年 | 1627篇 |
2017年 | 1632篇 |
2016年 | 1691篇 |
2015年 | 1185篇 |
2014年 | 1525篇 |
2013年 | 3009篇 |
2012年 | 2550篇 |
2011年 | 2442篇 |
2010年 | 1912篇 |
2009年 | 1731篇 |
2008年 | 1944篇 |
2007年 | 1711篇 |
2006年 | 1324篇 |
2005年 | 1084篇 |
2004年 | 999篇 |
2003年 | 887篇 |
2002年 | 787篇 |
2001年 | 506篇 |
2000年 | 515篇 |
1999年 | 707篇 |
1998年 | 4143篇 |
1997年 | 2462篇 |
1996年 | 1643篇 |
1995年 | 964篇 |
1994年 | 805篇 |
1993年 | 803篇 |
1992年 | 261篇 |
1991年 | 283篇 |
1990年 | 281篇 |
1989年 | 251篇 |
1988年 | 240篇 |
1987年 | 223篇 |
1986年 | 230篇 |
1985年 | 274篇 |
1984年 | 208篇 |
1983年 | 147篇 |
1982年 | 184篇 |
1981年 | 213篇 |
1980年 | 184篇 |
1979年 | 148篇 |
1978年 | 139篇 |
1977年 | 266篇 |
1976年 | 565篇 |
1975年 | 107篇 |
1973年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
N. Hémono J. Rocherullé M. Le Floch B. Bureau P. Bénard-Rocherullé 《Journal of Materials Science》2006,41(2):445-453
The glass forming region in the B2O3-Al2O3-Y2O3 composition diagram has been determined by a melting and quenching procedure at temperatures up to 1800°C. Different physical
characteristics (density, coefficient of thermal expansion, glass transition and crystallization peak temperatures) have been
determined for a 35B2O3-40Al2O3-25Y2O3 glass composition (in mol.%). By using a predictive model and some NMR structural data, different elastic moduli (Young's
modulus, bulk modulus, shear modulus and Poisson's ratio) have been calculated. The devitrification behaviour has also been
studied. Internal crystallization is the dominant mechanism and a new (Y, Al)BO3 ternary phase has been characterized by X-ray powder diffraction. The temperature and time nucleation dependence have been
determined from DTA experiments as well as the crystallization kinetics (i.e. the Avrami exponent and the activation energy
for crystal growth). 相似文献
123.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
124.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
125.
Joaquín Cortés Eliana Valencia Gonzalo Aguila Esteban Orellana Paulo Araya 《Catalysis Letters》2008,126(1-2):63-71
An experimental study is made of the time decay of activity of the CO–NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models. 相似文献
126.
Formaldehyde is used in ruminant feeding for different purposes including the protection of dietary proteins from ruminal degradation. The formaldehyde content of milk of goats fed various levels of formaldehyde-treated soybean oil-meal has been determined by using a sensitive HPLC method. Results showed a significant linear correlation between ingested formaldehyde and formaldehyde concentration in milk. About 0.02% of ingested formaldehyde was excreted in milk, as free formaldehyde. 相似文献
127.
128.
An increasing amount of laser beam welded T‐joints (e.g. skin‐stringer) of aluminium alloys are now in use in advanced fuselage applications designed as ‘integral structures’ for weight and cost savings. It is known that weld joints generally show lower strength (undermatching) than base metal in both laser beam and friction stir welded joints of 6xxx series Al‐alloys. Damage tolerance considerations in terms of the residual strength of such joints require limit load solutions to be used in engineering fitness‐for‐service (FFS) analysis. The paper, therefore, provides an upper bound limit load solution in closed form for welded T‐joints (idealized) with strength undermatching and subject to a bending moment. In addition to the necessary requirements of the upper bound theorem, the kinematically admissible velocity field chosen leads to a stress field, which satisfies the equilibrium equations and some stress boundary conditions in the plastic zone. This is an advantage of the solution and, therefore, it is expected that the upper bound obtained is close to the exact limit load of such joints. 相似文献
129.
Nicolas Clauvelin Basile Audoly Sébastien Neukirch 《Scientific Modeling and Simulation》2007,14(1):95-101
The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. 相似文献
130.
Mariana Ušáková Jozef Lukáč Rastislav Dosoudil Vladimír Jančárik Anna Grusková Elemír Ušák Jozef Sláma Jan Šubrt 《Journal of Materials Science: Materials in Electronics》2007,18(12):1183-1189
The paper is devoted to the preparation of NiZn ferrite with small substitutions of copper by means of ceramic technology.
The influence of small Cu substitution on the microstructural and magnetic properties of NiZn ferrites have been analysed
by means of various experimental methods and interpreted from the point of view of preparation technology optimisation and
possible applications of such materials. A strong correlation between the substituent content and resulting properties has
been observed, thus allowing preparation of material with the properties tailored for any particular application. 相似文献