全文获取类型
收费全文 | 14758篇 |
免费 | 2202篇 |
国内免费 | 1253篇 |
专业分类
电工技术 | 80篇 |
综合类 | 360篇 |
化学工业 | 3928篇 |
金属工艺 | 232篇 |
机械仪表 | 2015篇 |
建筑科学 | 389篇 |
矿业工程 | 131篇 |
能源动力 | 465篇 |
轻工业 | 6484篇 |
水利工程 | 35篇 |
石油天然气 | 339篇 |
武器工业 | 31篇 |
无线电 | 216篇 |
一般工业技术 | 896篇 |
冶金工业 | 1746篇 |
原子能技术 | 425篇 |
自动化技术 | 441篇 |
出版年
2024年 | 65篇 |
2023年 | 287篇 |
2022年 | 743篇 |
2021年 | 1078篇 |
2020年 | 733篇 |
2019年 | 818篇 |
2018年 | 744篇 |
2017年 | 705篇 |
2016年 | 794篇 |
2015年 | 704篇 |
2014年 | 1031篇 |
2013年 | 1337篇 |
2012年 | 1015篇 |
2011年 | 1154篇 |
2010年 | 717篇 |
2009年 | 688篇 |
2008年 | 597篇 |
2007年 | 781篇 |
2006年 | 638篇 |
2005年 | 570篇 |
2004年 | 467篇 |
2003年 | 435篇 |
2002年 | 345篇 |
2001年 | 209篇 |
2000年 | 167篇 |
1999年 | 170篇 |
1998年 | 159篇 |
1997年 | 127篇 |
1996年 | 139篇 |
1995年 | 126篇 |
1994年 | 86篇 |
1993年 | 77篇 |
1992年 | 68篇 |
1991年 | 57篇 |
1990年 | 52篇 |
1989年 | 41篇 |
1988年 | 30篇 |
1987年 | 28篇 |
1986年 | 31篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 9篇 |
1982年 | 37篇 |
1981年 | 63篇 |
1980年 | 22篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 288 毫秒
71.
大规模定制为生产带来了变革和影响。针对新的生产方式的要求,根据推动大规模定制的过程方法和技术来分析他们对于质量控制产生的影响和要求,给出了大规模定制条件下的质量控制系统的建议,并给出了一个简要的系统模型。 相似文献
72.
73.
Bench-scale reactor experiments were performed to study the dissolution of a binary naphthalene-in-nonane mixture nonaqueous phase liquid (NAPL) pool over a wide range of average pore water velocities, vx (≈0.1–60 m/day). Experimental NAPL pool dissolution flux values were determined using a steady-state mass balance approach. The experimental flux data were compared to model predictions made assuming either local equilibrium or mass-transfer limited conditions. The local equilibrium model could describe the trends in the average effluent concentration and dissolution flux with 0.110?m/day. Data determined to be under mass-transfer limited conditions were fit to the nonequilibrium model to estimate values for an overall mass-transfer coefficient. The calculated overall mass-transfer coefficients had an average value of 0.407 m/day and showed no correlation with vx, probably due to mass-transfer resistance becoming dominated by the diffusional resistance in the NAPL. These results suggest that the nonequilibrium approach is better suited for describing high velocity (vx>10?m/day) dissolution of multicomponent NAPL pools, and that flushing of groundwater at very high velocities may not be an effective approach for enhancing NAPL-pool dissolution flux. 相似文献
74.
75.
本文介绍了用αβ谱仪系统同时测量αβ谱、实现Rn/Th子体补偿、确定超铀α核素气溶胶体积活度及人工放射性气溶胶总β体积活度的技术途径。利用RaA、RaC′a峰的二段时间计数可确定空气中RaA、RaB、RaC的气溶胶体积活度,相应的,也能给出RaB、RaC对总β计数的贡献。根据一般环境条件下的平衡比,用ThC′的。计数修正Th子体对αβ测量的影响。 ̄[239]pu或/和 ̄[241]Am人工核素的α计数,可通过两段时间分别扣除RaA、RaC′拖尾的方法确定;β计数分别扣除Rn/Th子体β贡献即可确定。在本文规定的测量条件下,对室内天然Rn子体水平在15Bq/m ̄3以下,超铀α核素气溶胶体积活度的测量下限可达到0.1Bq/m ̄3;即使在75Bq/m ̄3环境下,人工核素总β的测量下限也可达lBq/m ̄3以下。 相似文献
76.
David Lloyd Suzie Morrell Helle N. Carlsen Hans Degn Phillip E. James Christopher C. Rowlands 《Yeast (Chichester, England)》1993,9(8):825-833
Saccharomyces cerevisiae HSc was grown with ethanol at concentrations up to 10% (v/v). The immediate effects of additions of externally added ethanol on CO2 production and O2 consumption of washed organisms were studied by stopped-flow membrane inlet quadrupole mass spectrometry. Fermentative activities of organisms grown with ethanol (0–5% v/v) showed similar sensitivities to inhibition by ethanol, whereas those grown with 10% (v/v) ethanol had become protected and were markedly less sensitive. The fluidity of subcellular membrane fractions was measured by determination of the temperature dependence of the rotational order parameter of the spin label 5-doxyl stearic acid (free radical) by electron spin resonance. Mitochondria prepared from yeasts grown with 0, 7 and 9% (v/v) ethanol showed similar overall fluidity, although differences in temperature-dependent behaviour indicate altered lipid composition or lateral phase separations. On the other hand the microsomal fraction from organisms grown with 9% ethanol showed a remarkable increase in fluidity. These data suggest that the protective effects of growth with ethanol near the limit of tolerance on fermentative activities may arise from altered plasma membrane fluidity properties. 相似文献
77.
Degassing is a key-step in polymer processing. Low-molecular-weight components are removed from a polymeric system. The transport of these components takes place by diffusion to the polymer-vapour interface. This interface can be formed by free surfaces of single-phase polymer melts or by bubbles. In this study, the transport with and without bubble nucleation is investigated independently from each other in a special designed apparatus similar to a degassing extruder.The mass transport in thin films and in rotating pools with surface renewal is measured. High surface renewal rates and thick films enhance the mass transfer for single phase flow and bubbly flow. Dimensionless mass transfer coefficients are given as a function of the surface renewal rate, the area of the free surface and the total mass of the polymer. The conditions for bubble nucleation and foam formation are investigated. The bubble nucleation is observed in the rotating pool in the area of high shear velocity. 相似文献
78.
《Drying Technology》2007,25(1):85-95
Artificial neural network (ANN) models were developed for the prediction of transient moisture loss (ML) and solid gain (SG) in osmotic dehydration of fruits using process kinetics data from the literature. ANN models for ML and SG were developed based on data over a broad range of operating conditions and ten common processing variables: temperature and concentration of osmotic solution, immersion time, initial water and solid content of the fruit, porosity, surface area, characteristic length, solution-to-fruit mass ratio, and agitation level. The trained models were able to accurately predict the outputs with associated regression coefficients (r) of 0.96 and 0.93, respectively, for ML and SG. These ANN models performed much better than those obtained from linear multivariate regression analysis. The large number of process variables and their wide ranges considered along with their easy implementation in a spreadsheet make them very useful and practical for process design and control. 相似文献
79.
A new catalyst loading method, in which catalyst particles are packed in a reactor with a novel internal, has been studied by measuring pressure drop, RTD, liquid holdup and mass transfer. It can be inferred from experimental results that the internal changes the conventional gas and liquid counter-current flow into a new cross-current flow, so the problems of excessive pressure drop and “flooding” are avoided. When pressure drop, liquid holdup, RTD and mass transfer coefficient are similar, the catalyst loading fraction of the new method is much higher than that of conventional methods. Furthermore, the reactive distillation reactor with the novel internal has advantages such as simple structure, low operating cost, and convenience for installation and removal of the catalyst. 相似文献
80.
A general model, based on double film theory, is developed to study absorption with chemical reactions. In the liquid film region, the model is a set of differential equations that describe the mass transfer accompanying several chemical reactions; the resolution of the system is achieved by the finite difference method using an implicit scheme combined with Newton's method. Continuity equations and equilibrium coefficients are exploited in the treatment of the bulk region, which is based on the Newton‐Raphson method; the results are used directly as boundary conditions in the liquid film equations. Maxwell‐Stefan equations have been used as a rigorous approach in this model. 相似文献