全文获取类型
收费全文 | 63713篇 |
免费 | 5900篇 |
国内免费 | 3146篇 |
专业分类
电工技术 | 3081篇 |
综合类 | 3882篇 |
化学工业 | 17980篇 |
金属工艺 | 7738篇 |
机械仪表 | 2869篇 |
建筑科学 | 4267篇 |
矿业工程 | 1502篇 |
能源动力 | 2102篇 |
轻工业 | 8629篇 |
水利工程 | 958篇 |
石油天然气 | 2935篇 |
武器工业 | 469篇 |
无线电 | 3898篇 |
一般工业技术 | 7385篇 |
冶金工业 | 2685篇 |
原子能技术 | 874篇 |
自动化技术 | 1505篇 |
出版年
2024年 | 348篇 |
2023年 | 1253篇 |
2022年 | 2209篇 |
2021年 | 2681篇 |
2020年 | 2511篇 |
2019年 | 2271篇 |
2018年 | 2104篇 |
2017年 | 2597篇 |
2016年 | 2567篇 |
2015年 | 2497篇 |
2014年 | 3493篇 |
2013年 | 3897篇 |
2012年 | 4361篇 |
2011年 | 4589篇 |
2010年 | 3154篇 |
2009年 | 3494篇 |
2008年 | 2882篇 |
2007年 | 3566篇 |
2006年 | 3411篇 |
2005年 | 2896篇 |
2004年 | 2389篇 |
2003年 | 2103篇 |
2002年 | 1801篇 |
2001年 | 1585篇 |
2000年 | 1360篇 |
1999年 | 1243篇 |
1998年 | 1013篇 |
1997年 | 871篇 |
1996年 | 647篇 |
1995年 | 645篇 |
1994年 | 484篇 |
1993年 | 398篇 |
1992年 | 322篇 |
1991年 | 229篇 |
1990年 | 175篇 |
1989年 | 142篇 |
1988年 | 112篇 |
1987年 | 80篇 |
1986年 | 56篇 |
1985年 | 57篇 |
1984年 | 58篇 |
1983年 | 39篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 31篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1959年 | 9篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In industrial fluid cokers the feedstock, consisting of heavy bituminous hydrocarbons, is atomized with steam and injected into a hot fluidized bed of coke. Good and uniform contact of the liquid droplets with the solid particles is required to provide heat for the cracking reactions while minimizing mass transfer effects. Experiments in a pilot plant coker have suggested that the initial particle/liquid mixing, in the spray jet, is rather poor. Experiments in a X-ray scanner showed that liquid droplets and entrained particles accumulate just below the tip of the jet plume to form agglomerates.An experimental technique was used to quantitatively determine the quality of mixing with a variety of nozzle configurations including several novel designs. By improving spray stability, redistributing liquid droplets to the solids-rich region of the jet and increasing the surface area of the gas-liquid jet-fluidized bed interface, liquid/solid contact is improved. 相似文献
82.
In the present work, the ohmic resistance of an integrated planar-SOFC (IP-SOFC) has been evaluated by developing a model
whose equations have been solved numerically through an FEM method. The model allows to estimate the distribution of voltage
and current density in the cell. A comparison between simulated and experimental data of area specific resistance is reported,
which shows satisfactory agreement. The mathematical model has also been used to carry out some parametric studies for optimisation
purposes. Indeed, a reduction in cell pitch length and an increase in electrode thickness are predicted to lead to a reduction
in ohmic losses in IP-SOFCs. 相似文献
83.
Defeng Wu Yisheng Zhang Lanfeng Wu Lifeng Jin Ming Zhang Weidong Zhou Changhao Yan 《应用聚合物科学杂志》2008,108(3):1934-1941
Polyarylene ether nitriles (PEN)/thermotropic liquid crystalline polymer (TLCP) blend was prepared via melt mixing. The immiscible phase morphologies, linear and nonlinear, as well as transient viscoelastic properties of the blend were studied using SEM, rheometer, and DMA. The linear dynamic viscoelastic behavior of the blend shows temperature dependence due to further evolution of the immiscible morphology and, as a result, the principle of time‐temperature superposition (TTS) is invalid. In the steady shear flow, the discrete TLCP phase is difficult to be broken up because of the high viscosity ratio of the blend systems, while is easy to be coarsened and followed by elongation, and finally, to form fibrous morphology at high TLCP content and high shear level. During this morphological evolution process, the transient stress response presents step increase and nonzero residual relaxation behavior, leading to increase of the dynamic viscoelastic responses after steady preshear. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
84.
Two series of semiflexible random thermotropic copolymers containing 8‐(3‐hydroxy phenyl) octanoic acid (HPOA) with either 3‐chloro‐4‐hydroxy benzoic acid or 3,5‐dibromo‐4‐hydroxy benzoic acid were prepared by melt polycondensation techniques. The copolyesters were characterized with Fourier transform infrared spectroscopy, dilute solution viscometry, hot‐stage polarized light microscopy, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction. Studies revealed that the amount of HPOA as a disruptor incorporated into the backbone of substituted 4‐hydroxy benzoic acids had a detrimental effect on the liquid‐crystalline behavior. Mesophase‐transition temperatures were observed between 210 and 250°C, and the optical textures were of typical nematic phases. The degree of crystallinity decreased with an increase in the HPOA content. The thermal stability of the copolymers was in the range of 310–370°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
85.
We have calculated thermal conductivity of alumina nanofluids (with water and ethylene glycol as base fluids) using temperature
as well as concentration-dependent viscosity, η. The temperature profile of η is obtained using Gaussian fit to the available experimental data. In the model, the interfacial resistance effects are incorporated
through a phenomenological parameter α. The micro-convection of the alumina nanoparticle (diameter less than 100 nm) is included through Reynolds and Prandtl numbers.
The model is further improved by explicitly incorporating the thermal conductivity of the nanolayer surrounding the nanoparticles.
Using this improved model, thermal conductivity of copper nanofluid is calculated. These calculations capture the particle
concentration-dependent thermal conductivity and predict the dependence of the thermal conductivity on the size of the nanoparticle.
These studies are significant to understand the underlying processes of heat transport in nanofluids and are crucial to design
superior coolants of next generation. 相似文献
86.
87.
A method of current drive with Ion Cyclotron Range of Frequency (ICRF) on Experimental Advanced Superconducting Tokomak (EAST) is described. A variety of liquid silicon oil heights in the phase shifter will bring the phase difference to the current drive. It is found that the current drive can be achieved by using the phase shifter. The liquid phase shifter is one of the impedance matching systems too. 相似文献
88.
对T形线路的故障测距,现有方法都是先判断故障支路,再将3端线路等效成2端线路进行测距。但在 T节点附近短路,尤其是经高阻短路时,现有的测距方法由于无法正确判别故障支路而存在一定范围的测距死区。针对上述缺陷,分别假设故障发生在某一支路,由假定正常的2段支路端的电压、电流推算求得 T节点电压和注入假定故障支路的电流,从而分别求得3个故障距离。经证明,求得的3个故障距离有且仅有1个在0和对应支路总长度之间,该距离就是真实的故障距离,故障发生在对应支路上。该方法无需事先判别故障支路即可测距,在 T节点附近经高阻故障时无测距死区。其测距精度理论上不受过渡电阻和故障类型影响,无需故障前数据,且对滤波无高要求。EMTP仿真结果表明该方法正确、有效,测距精度高。 相似文献
89.
Dynamics of the explosive growth of a vapor bubble in microgravity is investigated by direct numerical simulation. A front tracking/finite difference technique is used to solve for the velocity and the temperature field in both phases and to account for inertia, viscosity, and surface deformation. The method is validated by comparison of the numerical results with the available analytical formulations such as the evaporation of a one-dimensional liquid/vapor interface, frequency of oscillations of capillary waves, and other numerical results. Evolution of a three-dimensional vapor nucleus during explosive boiling is followed and a fine scale structure similar to experimental results is observed. Two-dimensional simulations yield a similar qualitative instability growth. 相似文献
90.
E. Gorges L. M. Raez A. Schillings I. Egry 《International Journal of Thermophysics》1996,17(5):1163-1172
Electromagnetic levitation is a useful tool for measuring thermophysical properties of high-temperature melts such as liquid metals. Due to its noncontact nature, the undercooled regime is also accessible. Density and thermal expansion of a levitated drop can be derived from volume measurements, if its mass is known. Assuming cylindrical symmetry, the volume of a drop can be determined from its cross section. Using photography, such measurements on liquid metals have been performed in the past. Here we present an improvement of this method, which replaces the photographic camera with a CCD videocamera and subsequent digital image processing. This reduces the time effect required to obtain the results and allows one to average over disturbing surface oscillations. The specific problems of digital image processing, namely resolution and edge detection, are addressed and results on nickel are presented.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1991, Köln, Germany. 相似文献