全文获取类型
收费全文 | 2652篇 |
免费 | 55篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 114篇 |
综合类 | 3篇 |
化学工业 | 497篇 |
金属工艺 | 83篇 |
机械仪表 | 43篇 |
建筑科学 | 51篇 |
能源动力 | 56篇 |
轻工业 | 184篇 |
水利工程 | 8篇 |
石油天然气 | 2篇 |
无线电 | 335篇 |
一般工业技术 | 422篇 |
冶金工业 | 704篇 |
原子能技术 | 55篇 |
自动化技术 | 158篇 |
出版年
2022年 | 26篇 |
2021年 | 42篇 |
2020年 | 18篇 |
2019年 | 27篇 |
2018年 | 36篇 |
2017年 | 36篇 |
2016年 | 43篇 |
2015年 | 34篇 |
2014年 | 41篇 |
2013年 | 118篇 |
2012年 | 68篇 |
2011年 | 115篇 |
2010年 | 93篇 |
2009年 | 85篇 |
2008年 | 87篇 |
2007年 | 92篇 |
2006年 | 67篇 |
2005年 | 72篇 |
2004年 | 83篇 |
2003年 | 60篇 |
2002年 | 47篇 |
2001年 | 47篇 |
2000年 | 39篇 |
1999年 | 70篇 |
1998年 | 288篇 |
1997年 | 166篇 |
1996年 | 128篇 |
1995年 | 70篇 |
1994年 | 50篇 |
1993年 | 85篇 |
1992年 | 34篇 |
1991年 | 49篇 |
1990年 | 33篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 36篇 |
1985年 | 31篇 |
1984年 | 21篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 8篇 |
排序方式: 共有2715条查询结果,搜索用时 15 毫秒
991.
Sulfo-group functionalized microporous and mesoporous silica based-on a MCM-41 framework which showed solid acid property were synthesized and characterized by adsorption microcalorimetry. Both the sulfo-functionalized microporous and mesoporous silica (Micro-SO3H and Meso-SO3H) were prepared by the oxidation of thiol group (–SH) included mesoporous silica which was obtained through the hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples have an ordered two-dimensional hexagonal pore array similar to that of MCM-41 as depicted from the XRD patterns. Nitrogen adsorption also shows that both microporous and mesoporous silica have pore characteristics similar to MCM-41, i.e. high surface area and high pore volume. However, pore regularity, surface area and pore volume decreased as the MPTMS loading increased. Solid-state 29Si NMR indicated that the sulfo groups were successfully incorporated into both microporous and mesoporous silica frameworks. This sulfo-functionalized porous silica have high NH3 uptakes and high differential heats of NH3 adsorption, suggesting the presence of strong acidic sulfo groups on the silica surface. Acid catalyses of the samples were characterized by the isomerization reaction of but-1-ene to cis, trans-but-2-ene. 相似文献
992.
Koji Morita Tatsuya Matsumoto Shinpei Nishi Tatsuya Nishikido Songbai Cheng Hirotaka Tagami 《Journal of Nuclear Science and Technology》2016,53(5):713-725
ABSTRACTDuring the material relocation phase of core disruptive accidents in sodium-cooled fast reactors, the rapid quenching and fragmentation of molten materials discharged from the reactor core into the lower plenum region can lead to the formation of debris beds. Coolant boiling may lead to leveling of the mound-shaped beds, which changes both the beds' coolability with decay heat in the fuel and the neutronic characteristics. In this study, a series of experiments using simulant materials were performed to develop an experimental database of self-leveling processes of particle beds in a cylindrical system. To simulate the coolant boiling in the beds in the experiments, a gas injection method was used to percolate nitrogen gas uniformly through the base of a bed with a conical-shaped mound. Time variations in bed height during the self-leveling process were measured for different particle sizes, densities and sphericities, and gas injection velocities. Using a dimensional analysis approach, a new model was proposed. This model correlates the experimental data on transient bed height with an empirical equation using a characteristic time for self-leveling development and an equilibrium bed height. The proposed model reasonably predicts the self-leveling development of particle beds. 相似文献
993.
Cholesteryl 4-(7-diethylamino-2-oxo-2H-1-benzopyran-3-yl)benzoate (1) had an enantiotropic cholesteric phase. The crystal structure of 1 has been determined by X-ray crystallographic analysis. The crystals of 1 had intermolecular CH...pi and CH...O interactions. 7-(Diethylamino)-3-phenylcoumarin derivatives (1) gave a strong emission band at 500 nm in the solid state when excited at 440 nm. 相似文献
994.
Takakuda K Koyama Y Matsumoto HN Shirahama N Akita K Shoji D Ogawa T Kikuchi M Tanaka J 《Journal of nanoscience and nanotechnology》2007,7(3):738-741
Two new bioabsorbable inorganic/organic composite materials were developed for bone regeneration. One material used was beta-TCP/PLGC in which poly(L-lactide-co-glycolide-co-epsilon-caprolactone) and beta-tricalcium phosphate were used as the matrix and filler, respectively. The other material used was HAp/Col-a soft nanocomposite of hydroxyapatite and type I collagen. Using these composites, two bone implants were designed. The efficacy of these implants was investigated by applying them to the critical-sized bone defects that were created in the canine tibia. Although no tissue engineering techniques such as application of growth factors or stem cells was utilized, successful healing was observed. These results suggested that bone regeneration in the critical-sized defects is possible without the use of growth factors or stem cells if the materials and the bone implants are suitably designed. 相似文献
995.
Miyuki Uno Shunsuke NishimotoYoshikazu Kameshima Michihiro Miyake 《International Journal of Hydrogen Energy》2013
The purpose of this study is to clarify the physicochemical properties of Ti2O3 for hydrogen production. The hydrogen production properties of Ti2O3 before and after milling in pure water were investigated in a flat-bottomed reaction vessel made of a Pyrex glass cell which was attached to a closed-gas circulation system under an Ar atmosphere at room temperature using three different types of stirring rod. Ti2O3 was found to be a new material for mechano-chemical hydrogen production, although it did not exhibit photocatalysis or mechano-catalysis for hydrogen production. 相似文献
996.
T.H. Barnes K. Matsumoto T. Eiju K. Matsuda N. Ooyama 《Journal of Modern Optics》2013,60(11):1849-1863
Abstract We have recently developed a new type of liquid-crystal spatial light-modulator which acts as a phase-only spatial light-modulator for coherent light. The use of this device as a flexible filter in the Fourier plane of an optical correlation system is described, and it is shown how it may also be used as a flexible interconnect capable of simultaneously providing continuous amplitude and binary phase modulation. 相似文献
997.
Relatively high transconductance in bipolar devices contributes to the economy of power dissipation on analog integrated circuits. Recently, a high-speed transistor, such as the HBT attracts attention of researchers and developers in electronic communication industries and is expected to be applied to RF circuits. In this paper, high-efficiency bipolar transconductors are presented. The proposed circuits are composed of a hyperbolic function circuit with an intermediate voltage terminal and a triple-tail cell. The parameter values for linearisation are all integers. The values can be realised precisely. The linearity of the proposed transconductors is superior to the triple-tail cell. The linear input range is 1.5 times as wide as that of the conventional triple-tail cell. Nevertheless, the power dissipation is lower than the triple-tail cell. Further, sensitivity analysis shows that the proposed transconductors have lower sensitivity than the triple-tail cell. These properties are confirmed by SPICE simulation. 相似文献
998.
Integrators are useful analogue function blocks. A representative application of integrators is a continuous-time filter on an integrated circuit. Excess phase shift of integrators is one of the most severe problems, because excess phase shift at the unity gain frequency degrades the frequency characteristics of the filters. This paper describes a feedforward excess-phase cancellation technique. The proposed technique is applied to integrators which have feedback with an amplifier. The proposed idea is verified by experiment. It is shown that the excess-phase shift due to the gain-bandwidth product of operational amplifiers is cancelled. The proposed technique is useful for realization of integrated continuous-time filters using integrators because extra capacitors are unnecessary. An integrator with the excess-phase cancellation and a third-order leapfrog filter using the integrator are designed and demonstrated by HSPICE simulation. The integrator has a parasitic pole whose frequency is proportional to the unity gain frequency. The simulation results show that the phase characteristics are improved by the proposed technique over the wide range of the unity gain frequency. 相似文献
999.
Atsushi Matsumoto Hiroshi Taninaka Kengo Hashimoto 《Journal of Nuclear Science and Technology》2013,50(8):782-792
The possibility of prompt neutron emission during acceleration of fission fragments (FFs) was examined by means of Monte Carlo method and statistical neutron emission model. Multimodal random neck-rapture model was used to describe the initial distribution of mass, charge, and total kinetic energy of the primary fragments. Statistical model was used to simulate the de-excitation process of the fragments from the moment of scission until full acceleration. By random number sampling, the fission process was simulated in order to obtain the basic physical quantities, and their correlations were analyzed to verify the adequacy of the model. It was found that, on the average, ~10% and ~16% of prompt neutrons for 235U(n th,f) and 252Cf(sf), respectively, were emitted before reaching 90% of the final fragment kinetic energy. 相似文献
1000.
In this nonsalt type of solar pond, the nonconvecting layer is composed of a viscous polymer solution partitioned by a number of transparent films. An advantage of partitioning is that a thinner polymer solution can be used and that the light transmittance increases. Results of experimental and theoretical investigations on the performance of this solar pond are summarized as follows:
- 1. 1. Ionized polyacrylamide solution was chosen as the thickener based on tests about solubility, viscosity, light transmittance and stability.
- 2. 2. The critical temperature difference for the onset of convection in the polymer layer (ΔT/L)cr [°C/m] was given by the following formula based on the measurements in various thicknesses of the polymer layers (L) [m] and various concentrations (ζ) [%], (ΔT/l)cr=(55−185lnL)exp(4.66L0.505lnζ
- 3. 3. An outdoor model pond, 200 × 150 cm surface and 100 cm depth, was constructed in Osaka. Four types of model ponds were tested, and the availability of membrane type with partition films was confirmed.
- 4. 4. The theoretical temperature rise of the pond using a one-dimensional model was calculated by solving the equations of the heat balance in the pond. As a result, the optimum values of thickness of polymer layer and number of films was determined