全文获取类型
收费全文 | 71912篇 |
免费 | 7934篇 |
国内免费 | 4685篇 |
专业分类
电工技术 | 6369篇 |
技术理论 | 3篇 |
综合类 | 7259篇 |
化学工业 | 10794篇 |
金属工艺 | 4188篇 |
机械仪表 | 8199篇 |
建筑科学 | 5494篇 |
矿业工程 | 2445篇 |
能源动力 | 5452篇 |
轻工业 | 1841篇 |
水利工程 | 5687篇 |
石油天然气 | 4608篇 |
武器工业 | 913篇 |
无线电 | 2610篇 |
一般工业技术 | 6955篇 |
冶金工业 | 3424篇 |
原子能技术 | 1536篇 |
自动化技术 | 6754篇 |
出版年
2024年 | 206篇 |
2023年 | 981篇 |
2022年 | 1768篇 |
2021年 | 2234篇 |
2020年 | 2350篇 |
2019年 | 2041篇 |
2018年 | 1911篇 |
2017年 | 2510篇 |
2016年 | 2785篇 |
2015年 | 2948篇 |
2014年 | 4025篇 |
2013年 | 4679篇 |
2012年 | 4796篇 |
2011年 | 5583篇 |
2010年 | 3907篇 |
2009年 | 4211篇 |
2008年 | 3962篇 |
2007年 | 4783篇 |
2006年 | 4445篇 |
2005年 | 3898篇 |
2004年 | 3234篇 |
2003年 | 2899篇 |
2002年 | 2329篇 |
2001年 | 1968篇 |
2000年 | 1721篇 |
1999年 | 1489篇 |
1998年 | 1146篇 |
1997年 | 1058篇 |
1996年 | 934篇 |
1995年 | 833篇 |
1994年 | 655篇 |
1993年 | 494篇 |
1992年 | 409篇 |
1991年 | 264篇 |
1990年 | 266篇 |
1989年 | 212篇 |
1988年 | 167篇 |
1987年 | 103篇 |
1986年 | 69篇 |
1985年 | 33篇 |
1984年 | 47篇 |
1983年 | 36篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 13篇 |
1979年 | 25篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1959年 | 23篇 |
1951年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
聚合物流变性能对共注射成型的影响 总被引:3,自引:0,他引:3
在共注射成型多相分层流动充模成型机理的基础上,揭示了芯壳层熔体对共注射成型的分层界面形貌和芯层熔体前沿突破的影响,并模拟了芯壳层熔体粘度比对共注射成型的影响,建立了芯壳层熔体粘度与分层界面和前沿移动界面菜貌的关系。本文的模拟研究结果与一些文献的实验结果相吻合。 相似文献
993.
B.S. Cheong 《Chemical engineering science》2004,59(11):2145-2157
The focus of this paper is on the effect of gravity stretching on disturbed capillary jet instability. Break-up and droplet formation under low flows are simulated using finite difference solution of a one-dimensional approximation of disturbed capillary jet instability chosen from the work by Eggers and Dupont (J. Fluid Mech. 155 (1994) 289). Experiments were conducted using water and aqueous glycerol solutions to compare with simulations. We use a gravity parameter, G, which quantifies gravity stretching by relating flow velocity, orifice size and acceleration and is the reciprocal of the Froude number. The optimum disturbance frequency was found to be inversely proportional to G. However, this relationship appears to be complex for the range of G's investigated. At low G, the relationship between and G appears to be linear but takes on a weakly decaying like trend as G increases. As flows are lowered, the satellite-free regime decreases, although experimental observation found that merging of main and satellite drops sometimes offset this effect to result in monodispersed droplet trains post break-up. Viscosity did not significantly affect the relationship between the disturbance frequency and G, although satellite drops could be seen more clearly close to the upper limit for instability at high G's. It is possible to define regimes of satellite formation under low flows by considering local wavenumbers at the point of instability. 相似文献
994.
《Ceramics International》2021,47(21):30531-30535
Al2O3 thin film was deposited on Gorilla glass using an aerosol deposition method to improve the mechanical property of cover glass for mobile electronic device. The deposited Al2O3 film (approximately 1 μm thick) was a polycrystalline structure and showed a high light transmittance of approximately 90% in the visible light region. The CIE color space (L*a*b) measurement also showed a characteristic corresponding to the acceptable optical range of the cover glass. Further, it was confirmed that the bending strength improved by 10 %, as compared with bare Gorilla glass (from 6970 kgf/cm2 to 7704 kgf/cm2), and the Vickers hardness increased to approximately 1700–2000 HV, as compared with that of Gorilla glass (<700 HV). Owing to the improved mechanical properties, the Al2O3 thin film exhibited good anti-scratch properties and is expected to be applied to the cover glass of various display products. 相似文献
995.
A mathematical model has been developed for the simulation of the ammonia oxidation in a reverse flow reactor. Computer simulations were carried out with a kinetic scheme, based upon elementary reaction steps. Aim was to explore the potential of a reverse flow reactor for selective oxidation of NH3 to produce either N2, NO, or N2O via a dedicated operation procedure. Therefore, the conversion of NH3 and the selectivity toward N2, NO, or N2O, were compared for a reverse flow operation and a steady state, once-through operation.A new operation concept of reverse flow operation in combination with a periodically lower feed concentration is proposed. The novel reactor concept shows a better performance compared to normal reverse flow operation and to steady state, once-through operation. The results indicate that reverse flow operation can be applied for manipulation of conversion and selectivity. A periodically lower feed concentration may increase the conversion, even up to levels that exceed the steady state value. 相似文献
996.
Large aggregation interval asymptotics are used to investigate the relation between Granger causality in disaggregated vector autoregressions (VARs) and associated contemporaneous correlation among innovations of the aggregated system. One of our main contributions is that we outline various conditions under which the informational content of error covariance matrices yields insight into the causal structure of the VAR. Monte Carlo results suggest that our asymptotic findings are applicable even when the aggregation interval is small, as long as the time series are not characterized by high levels of persistence. 相似文献
997.
Saziye Ugur Ayse Alemdar Önder Pekcan 《Journal of Coatings Technology and Research》2005,2(7):565-575
This study reports a steady-state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene
(PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles
and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature
(t3) of polystyrene. During the annealing processes, the transparency of the film improved considerably. Scattered light (Is) and fluorescence intensity (Ip) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite
films was monitored by using photon transmission intensity, Itr. Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite films. Minimum
film formation temperature, Tq, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It
was observed that both activation energies increased as the percent of SNaM was increased in composite films. 相似文献
998.
The contact time of particles at the walls of gas fluidized beds has been studied using a radioactive particle tracking technique to monitor the position of a radioactive tracer. The solids used were sand or FCC particles fluidized by air at room temperature and atmospheric pressure at various superficial velocities, covering both bubbling and turbulent regimes of fluidization. Based on the analysis of tracer positions, the motion of individual particles near the walls of the fluidized bed was studied. The contact time, contact distance and contact frequency of the particles at the wall were evaluated from these experimental data. It was found that in a bed of sand particles, the mean wall contact time of the fluidized bed of sand particles decreases by increasing the gas velocity in the bubbling and increases in the turbulent fluidization. In other words, the particle-wall contact time is minimum at the onset of turbulent fluidization in the bed of sand particles. However, the mean wall contact time is almost constant in both regimes of fluidization in the bed of FCC particles. All the existing models in the literature predict a decreasing contact time when the gas velocity in the bed is increased. It was also shown that the contact distance increases monotonously by increasing the gas velocity in the bed of sand particles, while it is almost constant for the bed of FCC particles. Contact frequency has a trend similar to that of the contact time for both sand and FCC particles. 相似文献
999.
Y.T. Makkawi 《Chemical engineering science》2003,58(10):2035-2051
Here, an experimental investigation on the effective drag force in a conventional fluidized bed is presented. Two beds of different particle size distribution belonging to group B and group B/D powders were fluidized in air in a diameter column. The drag force on a particle has been calculated based on the measurement of particle velocity and concentration during pulse gas tests, using twin-plane electrical capacitance tomography. The validity of the voidage function “correction function”, (1−εs)n, for the reliable estimation of the effective drag force has been investigated. The parameter n shows substantial dependence on the relative particle Reynolds number , and the spatial variation of the effective static and hydrodynamic forces. It is also illustrated that, a simple correlation for the effective drag coefficient as function of the particle Reynolds number (Rep), expressed implicitly in terms of the interstitial gas velocity, can serve in estimating the effective drag force in a real fluidization process. Analysis shows that, the calculated drag force is comparable to the particle weight, which enables a better understanding of the particle dynamics, and the degree of spatial segregation in a multi-sized particle bed mixture. The analogy presented in this paper could be extended to obtain a generalized correlation for the effective drag coefficient in a fluidized bed in terms of Rep and the particle physical properties. 相似文献
1000.
Mohit Singh 《Chemical engineering science》2003,58(1):1-18
The interplay of viscous, gravity and capillary forces determines the flow behavior of two or more phases through porous materials. In this study, a rule-based dynamic network model is developed to simulate two-phase flow in three-dimensional porous media. A cubic network analog of porous medium is used with cubic bodies and square cross-section throats. The rules for phase movement and redistribution are devised to honor the imbibition and drainage physics at pore scale. These rules are based on the pressure field within the porous medium that is solved for by applying mass conservation at each node. The pressure field governs the movement and flow rates of the fluids within the porous medium. Film flow has been incorporated in a novel way. A pseudo-percolation model is proposed for low but non-zero capillary number (ratio of viscous to capillary forces). The model is used to study primary drainage with constant inlet flow rate and constant inlet pressure boundary conditions. Non-wetting phase front dynamics, apparent wetting residuals (Swr), and relative permeability are computed as a function of capillary number (Nca), viscosity ratio (M), and pore-throat size distribution. The simulation results are compared with experimental results from the literature. Depending upon the flow rate and viscosity ratio, the displacement front shows three distinct flow patterns—stable, viscous fingering and capillary fingering. Capillary desaturation curves (Swr vs. Nca) depend on the viscosity ratio. It is shown that at high flow rates (or high Nca), relative permeability assumes a linear dependence upon saturation. Pseudo-static capillary pressure curve is also estimated (by using an invasion percolation model) and is compared with the dynamic capillary pressure obtained from the model. 相似文献