全文获取类型
收费全文 | 35242篇 |
免费 | 3290篇 |
国内免费 | 1373篇 |
专业分类
电工技术 | 2452篇 |
技术理论 | 1篇 |
综合类 | 3198篇 |
化学工业 | 7063篇 |
金属工艺 | 855篇 |
机械仪表 | 1088篇 |
建筑科学 | 4576篇 |
矿业工程 | 1901篇 |
能源动力 | 1402篇 |
轻工业 | 3535篇 |
水利工程 | 1305篇 |
石油天然气 | 1143篇 |
武器工业 | 297篇 |
无线电 | 2200篇 |
一般工业技术 | 2012篇 |
冶金工业 | 2484篇 |
原子能技术 | 246篇 |
自动化技术 | 4147篇 |
出版年
2024年 | 115篇 |
2023年 | 372篇 |
2022年 | 697篇 |
2021年 | 861篇 |
2020年 | 904篇 |
2019年 | 779篇 |
2018年 | 781篇 |
2017年 | 1046篇 |
2016年 | 1234篇 |
2015年 | 1313篇 |
2014年 | 2045篇 |
2013年 | 1816篇 |
2012年 | 2334篇 |
2011年 | 2592篇 |
2010年 | 1922篇 |
2009年 | 2167篇 |
2008年 | 1897篇 |
2007年 | 2360篇 |
2006年 | 2239篇 |
2005年 | 1805篇 |
2004年 | 1515篇 |
2003年 | 1489篇 |
2002年 | 1258篇 |
2001年 | 1041篇 |
2000年 | 824篇 |
1999年 | 659篇 |
1998年 | 452篇 |
1997年 | 376篇 |
1996年 | 279篇 |
1995年 | 252篇 |
1994年 | 237篇 |
1993年 | 157篇 |
1992年 | 133篇 |
1991年 | 102篇 |
1990年 | 105篇 |
1989年 | 72篇 |
1988年 | 69篇 |
1987年 | 66篇 |
1986年 | 32篇 |
1985年 | 146篇 |
1984年 | 253篇 |
1983年 | 288篇 |
1982年 | 205篇 |
1981年 | 309篇 |
1980年 | 120篇 |
1979年 | 40篇 |
1978年 | 38篇 |
1977年 | 13篇 |
1975年 | 21篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The specific heat at constant pressure, C
p, of aluminum measured by Ditmars, Plint, and Shukla has been reduced to the volume V
0 appropriate for 0 K employing the Murnaghan equation. The C
v0 thus obtained is compared with the theoretical C
v0 calculated in the harmonic and the lowest-order anharmonic approximation from three different pseudopotentials (Harrison, Ashcroft, and Dagens-Rasolt-Taylor) as well as a phenomenological Morse potential. The higher-order (
4) anharmonic contributions are calculated from the same nearest-neighbor Morse potential as in the lowest-order anharmonic theory. The role of the vacancy and the higher-order anharmonic contributions to C
v0 has been examined and we conclude that the
4 contributions to C
v0 are much smaller than the vacancy contribution. After removal of the vacancy contribution, the reduced C
v0 is found to be in excellent agreement with the Ashcroft and Harrison pseudopotentials as well as the Morse potential including the
2 and
4 contributions to C
v0. 相似文献
102.
粉煤灰基混凝剂的制备及在大麻废水中的应用 总被引:6,自引:0,他引:6
采用酸溶法以粉煤灰为基础原料 ,通过添加一定量的硫铁矿烧渣 ,制备成粉煤灰基复合混凝剂 ,确定了最佳工艺条件 .实验结果表明 ,影响混凝剂制备的主要因素是粉煤灰与硫铁矿渣的质量比、酸用量、浸取时间和温度 .此混凝剂对大麻废水中 CODcr去除率达 88% ,色度去除率可达 96.6%以上 ,具有沉淀快和污泥体积小等优点 . 相似文献
103.
104.
Mass transfer rates were determined in a 3.4 cm i.d. trickle-bed reactor in the absence of reaction by absorption measurements and in presence of reaction. Gas flow rates were varied from 0-100 l/h and liquid flow rates from 0-1.5 l/h. The catalyst particles were crushed to an average diameter of 0.054 and 0.09 cm. Mass transfer coefficients remained unaffected by change in gas flow rate but increased with liquid rate. The data from absorption measurements were evaluated with predictions based upon plug-flow and axial dispersion model. Mass transfer coefficients were found greater in case of axial dispersion model than that of plug-flow model specially at low Reynolds number (Re1 < 1).Hydrogenation of α-methylstyrene to cumene using a Pd/Al2O3 catalyst was taken as a model reaction. Intrinsic kinetic studies were made in a laboratory-stirred-autoclave. Mass transfer coefficients were determined using these intrinsic kinetic data from the process kinetic measurements in trickle-bed reactor. Mass transfer coefficients under reaction conditions were found to be considerably higher than those obtained by absorption measurements.Correlations were suggested for predicting mass transfer coefficients at low Reynolds number.The gas to liquid mass transfer coefficients for lower gas and liquid flow rates were determined in a laboratory trickle-bed reactor. The effect of axial dispersion on mass transfer was considered in order to evaluate the experimental data. Three correlations were formulated to calculate the mass transfer coefficients, which included the effect of liquid loading, particle size and the properties of the reacting substances. The gas flow rate influences the gas to liquid mass transfer only in the region of low gas velocities. In the additional investigations of gas to liquid mass transfer without reaction in trickle-bed reactor, the mass transfer coefficients were determined under reaction conditions and the intrinsic kinetics was studied in a laboratory scale stirred autoclave with suspended catalyst. A few correlations are formulated for the mass transfer coefficients. A comparison with the gas-liquid mass transfer coefficient obtained by absorption measurements showed considerable deviations, which were illustrated phenomenologically. 相似文献
105.
106.
In manufacturing industries, the quality of a product depends on the combined effect of multiple input variables working singly or together and therefore attention has been given on process capability indices to shift from single to multivariate domain. In case of multivariable domain the capability to incorporate uncertainties at the time of decision making becomes necessary. Fuzzy system is introduced to take care of this requirement. In this article the process parameters of soap manufacturing industries have been analyzed. The process capability is determined using Fuzzy Inference System rule editor based on a set of justified if then statements as applicable for the process. The data has been collected in linguistic form to derive its process capability, using a set of justified rules and the effect of each factor has been determined using Design of Experiments (DoE) and analysis of variance technique (ANOVA) for improving the soap quality from perspective of its softness. This article ventures to propose a new methodology by integrating Fuzzy with DoE providing better result followed by DoE and Fuzzy Inference system in isolation. 相似文献
107.
通过对济宁市防治水污染技术研究, 提出水污染防治在政策措施上实施治污抓源头, 杜绝不达标排放; 在城市
建设规划上, 把河湖生态湿地建设、 改善居住生活环境与城市建设有机结合; 在河湖治理上, 坚持工程、 生物措施并
举; 在工程管护上, 坚持依法治水。利用南水北调东线工程建设, 实施水污染防治建设, 通过对济宁市水污染防治成
果的阐释, 为今后水污染治理提供成功的经验和做法。 相似文献
108.
This paper addresses the problem of designing controllers that are robust to a great uncertainty in a time constant of the plant. Plants must be represented by minimum phase rational transfer functions of an arbitrary order. The design specifications are: (1) a phase margin for the nominal plant, (2) a gain crossover frequency for the nominal plant, (3) zero steady state error to step commands, and (4) a constant phase margin for all the possible values of the time constant (T): 0<T<∞. We propose a theorem that defines the structure of the set of controllers that fulfil these specifications and show that it is necessary for these robust controllers to include a fractional-order PI term. Examples are developed for both stable and unstable plants, and the results are compared with a standard PI controller and a robust controller designed using the QFT methodology. 相似文献
109.
A systematic strategy is developed for the location of the source and the rectification of gross, biased measurement errors in a chemical process. The proposed strategy proceeds in three levels: (a) A structural analysis of the balance equations identifies subsets of balances with measurements which are suspected to possess gross errors. (b) A sequential analysis of the balance equations with suspect measurements further reduces the size of the problem. Statistical criteria are used in this step. (c) Finally, a sequential analysis of the suspect measurements appearing in the reduced set of balances leads to the identification of the source of the gross errors.The proposed strategy: (i) reduces the size of the data reconciliation problem significantly, even for large-scale chemical processes, (ii) is computationally simple and (iii) it conforms with the general process of variable monitoring in a chemical plant.Numerical examples are presented to clarify the elements of the procedure involved and demonstrate their value and effectiveness in dealing with realistic situations. 相似文献
110.
The kinetics of methane hydrate formation, after commencement of nucleation, were studied using a semibatch stirred tank reactor. The temperatures studied in the experiments were from 274 to 284 K over a pressure range of 3–10 MPa. The results of the experiments revealed that the formation kinetics were dependent on the interfacial area, pressure, temperature and degree of supercooling. The history of water sample affected the induction delay times for nuclei formation, but it had no observable effects on the overall kinetics of hydrate formation after the nucleation had commenced. A consistent semi-empirical model was formulated to correlate the experimental kinetic data. 相似文献