全文获取类型
收费全文 | 70257篇 |
免费 | 8886篇 |
国内免费 | 5208篇 |
专业分类
电工技术 | 5161篇 |
技术理论 | 7篇 |
综合类 | 9290篇 |
化学工业 | 11659篇 |
金属工艺 | 1947篇 |
机械仪表 | 4004篇 |
建筑科学 | 5011篇 |
矿业工程 | 1136篇 |
能源动力 | 5383篇 |
轻工业 | 3572篇 |
水利工程 | 1662篇 |
石油天然气 | 1844篇 |
武器工业 | 692篇 |
无线电 | 7348篇 |
一般工业技术 | 7707篇 |
冶金工业 | 2062篇 |
原子能技术 | 1238篇 |
自动化技术 | 14628篇 |
出版年
2024年 | 333篇 |
2023年 | 1139篇 |
2022年 | 1894篇 |
2021年 | 2137篇 |
2020年 | 2209篇 |
2019年 | 2049篇 |
2018年 | 1958篇 |
2017年 | 2231篇 |
2016年 | 2448篇 |
2015年 | 2543篇 |
2014年 | 3801篇 |
2013年 | 4503篇 |
2012年 | 4688篇 |
2011年 | 5192篇 |
2010年 | 4002篇 |
2009年 | 4225篇 |
2008年 | 4242篇 |
2007年 | 4884篇 |
2006年 | 4420篇 |
2005年 | 4051篇 |
2004年 | 3306篇 |
2003年 | 2920篇 |
2002年 | 2412篇 |
2001年 | 1994篇 |
2000年 | 1731篇 |
1999年 | 1399篇 |
1998年 | 1222篇 |
1997年 | 1065篇 |
1996年 | 944篇 |
1995年 | 828篇 |
1994年 | 674篇 |
1993年 | 524篇 |
1992年 | 488篇 |
1991年 | 366篇 |
1990年 | 335篇 |
1989年 | 293篇 |
1988年 | 204篇 |
1987年 | 136篇 |
1986年 | 100篇 |
1985年 | 80篇 |
1984年 | 88篇 |
1983年 | 71篇 |
1982年 | 46篇 |
1981年 | 23篇 |
1980年 | 24篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1959年 | 17篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
This study develops a mathematical model for coupled heat and mass transfer in an unsaturated porous slab exposed to a flowing hot gas. Effects of the initial saturation conditions on associated variables, i.e., total pressure, temperature, moisture content, and multiphase flow, are studied. The Newton-Raphson method based on a finite volume technique is applied. This study emphasizes the influence of initial saturation level and gravitational effect in heat and multiphase flow phenomena associated with this system. Gravity enhances the downward flow of liquid within the porous slab. Pressure buildup occurs near the interface between the wet and the dry zone. However, it appears that the order of magnitude to the total pressure is small. This study explains the fundamental mechanism of multiphase flow that involves heat and mass transfer in a heated unsaturated porous slab. 相似文献
62.
We propose a general modeling framework to evaluate the performance of cache consistency algorithms. In addition to the usual hit rate, we introduce the hit* rate as a consistency measure, which captures the fraction of non-stale downloads from the cache. We apply these ideas to the analysis of the fixed TTL consistency algorithm in the presence of network delays. The hit and hit* rates are evaluated when requests and updates are modeled by renewal processes. Classical results on the renewal function lead to various bounds. 相似文献
63.
The main components of thermophotovoltaic (TPV) devices are the primary lens (or mirror), the absorber, the PV cell, and a photon recuperator system. A theory integrating all these components is used in this paper to analyse a particular type of TPV device (plane disk absorber and PV cell). The TPV efficiency is maximized by using three optimization parameters, namely absorber, PV cell temperatures, and cell voltage. Almost ideal operation conditions are envisaged and upper bounds are obtained for the TPV efficiency. They are strongly dependent on PV cell bandgap and radiation concentration. Preliminary results suggest the existence of an optimum solar radiation concentration ratio. The improvement in thermal design quality allows the usage of PV cells based on wide bandgap semiconductors. 相似文献
64.
In this work, the kinetics and mechanism of free-radical polymerisation of glycidyl methacrylate (GMA) using potassium peroxydisulphate
(PDS) as water soluble initiator in the presence of synthesized 1, 4-Bis (tributyl methyl ammonium) benzene dichloride (TBMABDC)
as multi-site phase transfer catalyst (MPTC) was studied. The polymerisation reactions were carried out under inert and unstirred
conditions at constant temperature of 60 ± 1°C in cyclohexane/water biphase media. The role of concentrations of monomer,
initiator, catalyst and volume fraction of aqueous phase, solvent polarity and temperature on the rate of polymerisation (Rp)
was ascertained. The order with respect to monomer and initiator was found to be unity. The order with respect to catalyst
was found to be 0.51. The rate of polymerisation is independent of ionic strength and pH of the medium. However, an increase
in the polarity of solvent has slightly increased the Rp value. Based on the results obtained, a suitable kinetic scheme has
been proposed to account for the experimental observations and its significance discussed. 相似文献
65.
裂齿矩形翅片板翅式换热器优化设计的分析 总被引:2,自引:0,他引:2
对裂齿矩形翅片板翅式换热器中的裂齿矩形翅片的传热效率作了分析,并以单位质量材耗的换热能力最大为目标函数,分析研究了在不同雷诺数(Re)的操作条件下裂齿矩形翅片间角度、翅片厚、长度、宽度及极厚之间的关系。结果表明:在气体换热的场合下,当Re在某一范围时翅片可有效地起到强化传热的作用。当板厚为5mm,翅片厚为3mm,翅片间夹角为45°~70°,Re为2×10~3~8×10~3,最佳翅片纵向间距与翅片长度和翅片厚度乘积的平方根的比为1.5~2.5,最佳翅片尺寸系数为3~5时,传热强化效果较好。 相似文献
66.
L. M. CRUZ-ORIVE 《Journal of microscopy》2005,219(1):18-28
A new principle is presented to generate isotropic uniform random (IUR) test lines hitting a geometric structure in three-dimensional space (3D). The principle therefore concerns the estimation of surface area, volume, membrane thickness, etc., of arbitrary structures with piecewise smooth boundary. The principle states that a point-sampled test line on an isotropic plane through a fixed point in 3D is effectively an invariant test line in 3D. Particular attention is devoted to the stereology of particles, where an alternative to the surfactor method is obtained to estimate surface area. An interesting case arises when the particle is convex. The methods are illustrated with synthetic examples. 相似文献
67.
The effect of pressure on combustion and heat transfer is analyzed. The research is based on the basic combustion and heat
transfer theorem. A correction for the heat calculation method for pressurized furnace is made on the basis of the normal
pressure case. The correction takes the effect of pressurizing into account. The results show that the correction is reasonable
and the method is applicable to combustion and heat transfer of the marine supercharged boiler. 相似文献
68.
MIP-CGP工艺专用催化剂CGP-1的开发与应用 总被引:11,自引:3,他引:8
阐述了生产汽油组分满足欧Ⅲ排放标准并多产丙烯的催化裂化工艺(简称MIP-CGP)专用催化剂(简称CGP-1)的研究开发与工业应用结果。CGP-1催化剂的基质具有良好的容炭性能,使活性组元受到良好保护,其优势作用在第二反应区得以充分发挥,具有更高的氢转移活性和强的汽油小分子烯烃裂化活性。中国石化九江分公司和镇海炼化公司的MIP-CGP工业试验标定结果表明,与常规FCC相比,采用CGP-1催化剂的MIP-CGP技术在生产烯烃体积分数小于18%的汽油组分的同时,丙烯产率达到8%以上。此外,汽油诱导期大幅提高,抗爆指数增加;总液体收率有所提高,干气产率下降,焦炭选择性良好。 相似文献
69.
Camacho Christopher J.; Higgins E. Tory; Luger Lindsay 《Canadian Metallurgical Quarterly》2003,84(3):498
People experience regulatory fit (E. T. Higgins, 2000) when the strategic manner of their goal pursuit suits their regulatory orientation, and this regulatory fit feels right. Fit violation feels wrong. Four studies tested the proposal that experiences of fit can transfer to moral evaluations. The authors examined transfer of feeling wrong from fit violation by having participants in a promotion or prevention focus recall transgressions of commission or omission (Studies 1 and 2). Both studies found that when the type of transgression was a fit violation, participants expressed more guilt. Studies 3 and 4 examined transfer of feeling right from regulatory fit. Participants evaluated conflict resolutions (Study 3) and public policies (Study 4) as more right when the means pursued had fit. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
70.
Gabriel Nivasch 《Information Processing Letters》2004,90(3):135-140
We present an algorithm for detecting periodicity in sequences produced by repeated application of a given function. Our algorithm uses logarithmic memory with high probability, runs in linear time, and is guaranteed to stop within the second loop through the cycle. We also present a partitioning technique that offers a time/memory tradeoff. Our algorithm is especially well suited for sequences where the cycle length is typically small compared to the length of the acyclic prefix. 相似文献