全文获取类型
收费全文 | 1682篇 |
免费 | 88篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 23篇 |
综合类 | 1篇 |
化学工业 | 569篇 |
金属工艺 | 45篇 |
机械仪表 | 44篇 |
建筑科学 | 32篇 |
矿业工程 | 2篇 |
能源动力 | 85篇 |
轻工业 | 112篇 |
水利工程 | 10篇 |
石油天然气 | 14篇 |
无线电 | 183篇 |
一般工业技术 | 307篇 |
冶金工业 | 138篇 |
原子能技术 | 13篇 |
自动化技术 | 201篇 |
出版年
2023年 | 20篇 |
2022年 | 55篇 |
2021年 | 67篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 82篇 |
2017年 | 68篇 |
2016年 | 67篇 |
2015年 | 45篇 |
2014年 | 65篇 |
2013年 | 115篇 |
2012年 | 88篇 |
2011年 | 74篇 |
2010年 | 88篇 |
2009年 | 73篇 |
2008年 | 67篇 |
2007年 | 46篇 |
2006年 | 34篇 |
2005年 | 44篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 38篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 24篇 |
1998年 | 46篇 |
1997年 | 22篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 24篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 21篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有1779条查询结果,搜索用时 15 毫秒
1.
Diffusional limitations (the gel, glass, and cage effects) are manifested in several bulk free radical homopolymerizations as well as in random copolymerizations. These are associated with decreases of several orders of magnitude of the rate constants of termination, propagation, and initiation (the initiator efficiency), respectively. These phenomena have been modeled earlier using the free volume theory for the diffusivities of primary radicals, macro‐radicals, and monomer molecules, and have been applied to homopolymerizations. In this study, a similar model is developed for random bulk copolymerizations. The parameters of the model are fitted using isothermal data on styrene acrylonitrile random copolymerization carried out in small ampoules. Thereafter, best‐fit global correlations have been developed for this system. This enables the model to be used for studying non‐isothermal copolymerizations, as well as for carrying out optimization of industrial reactors, where non‐isothermal conditions are a norm. POLYM. ENG. SCI., 55:2098–2110, 2015. © 2014 Society of Plastics Engineers 相似文献
2.
In this paper, we consider the classical finite mixture model, which is an effective tool for modeling lifetime distributions for random samples from heterogeneous populations. We discuss new results on stochastic comparison for two finite mixtures when each of them is drawn from one of the following semiparametric families, i.e., proportional hazards, accelerated lifetime and proportional reversed hazards. 相似文献
3.
We present a domain decomposition boundary integral equation method for two-dimensional partial differential equations. The overlapping Schwarz method is employed to improve the dual reciprocity boundary element method. The resulting algorithm turns out to be more accurate than a non-overlapping approach previously proposed. Some numerical results showing the improved accuracy and efficiency of the methods are given. 相似文献
4.
The bulk copolymerization of styrene–acrylonitrile monomers using styrene‐N+–montmorillonite complex as a comonomer in the polymerization was studied. The X‐ray diffraction (XRD) analysis showed that part of the styrene‐N+–montmorillonite complex remained non‐dispersed (immiscible) and the copolymer was excluded from the interlayer of the immiscible part of the clay. The successive chemical extraction process revealed that a reasonable amount of the styrene–acrylonitrile copolymer was directly attached to the styrene‐N+–montmorillonite complex and enveloped the clay. Highly exfoliated clay lamella and nanospheres (3–5 nm) were observed by transmission electron microscopy (TEM). The montmorillonite clay assume two different morphologies, immiscible and exfoliated, on the basis of the XRD and TEM data. A simple method of calculation of the ratio of the exfoliated/immiscible amounts of the clay indicated that the amount of the styrene‐N+–montmorillonite complex exfoliated into separate lamella was 40 % (w/w) of the amount of the clay samples containing 2 % of the (styrene‐N+–montmorillonite complex) clay. This amount of exfoliated clay decreases with the increase of the concentration of the clay. The presence of the styrene‐N+–montmorillonite clay in the copolymerization reaction had a minor effect on both the copolymer composition and the molecular weight. Modification of the clay with the derivatized styrene monomer can achieve a nanocomposite using a percentage no more than 4 % (w/w) of complex in the copolymer. Copyright © 2004 Society of Chemical Industry 相似文献
5.
N. E. Wijeysundera M. N. A. Hawlader Chan Wee Boon Andy M. Kamal Hossain 《International Journal of Refrigeration》2004,27(5):1997
An ice slurry generation system was developed using direct contact heat transfer between water and the coolant, Fluroinert FC-84. The location of the coolant nozzle is an important design consideration to avoid clogging due to freezing of water. An ice fraction of up to about 40 percent was obtained with the nozzle located at the bottom of the ice slurry tank and the jet directed upwards into the water. Two simplified model were developed to extract the heat transfer coefficient between the coolant drops and the water. The first model requires as input the average drop diameter and the residence time while the second model uses the measured drop diameter distribution. The estimated heat transfer coefficients are much smaller than those computed using single-sphere correlations. 相似文献
6.
S. Vaidyanathan K. M. Kavadia L. P. Borkar S. P. Mahajan 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):121-128
With a view to evaluate the effects of hydraulic retention time and volatile solids loading rate on methane production using water hyacinth, experiments were conducted in a 160 dm3 capacity, well-mixed continuous digestion unit at ambient temperature. The optimal design of biogas plant using water hyacinth was elucidated, to provide a unit giving a maximum methane yield of 0.16 nm3 kg?1 volatile solids added, which was 60% greater than the conventional plant using cowdung. The calculations of optimal design factors were based on reactor size, hydraulic retention time and volatile solids loading rate; considerations were made of capital cost, running costs and operational revenue. 相似文献
7.
A generalized equation was derived to calculate the melting temperatures of homopolymers and copolymers. The Gibbs‐Thomson equation for homopolymers and a modified application to copolymers were derived using the proposed equation. The melting temperature Tm0 in the Flory equation corresponds to the melting temperature TmC,∞ of copolymer crystals with stems of infinite length. Also, TmC,n*, the melting temperature for copolymer crystals with stems containing the maximum possible number of structural units, n*, should be used instead of Tm0 as the basis of supercooling in crystallization. The proposed equation shows good agreement with experimental data for α‐alkene‐ethylene homogeneous copolymers. 相似文献
8.
9.
Ulla I. Brimberg Afaf Kamal‐Eldin 《European Journal of Lipid Science and Technology》2003,105(2):83-91
The influence of minor amounts of pro‐ and anti‐oxidants on the kinetics of the autoxidation of fat has been evaluated. The reaction rates of oxygen with the substrates were found to follow the same basic equation, hitherto established for pure substrates. There is evidence that the surface of the reaction vessel also acts as a reaction catalyst and its effect is proportional to the area of glass in contact with lipids. Oxidation is enhanced by trace metal ions as well as by surface‐active compounds (e.g. hydroperoxides and sterols). Antioxidants such as α‐tocopherol and butylated hydroxyanisole inhibit the oxidation by delaying the start of oxygen consumption (the induction period) while retarders like amino acids only decrease the rate of oxidation. Thus pro‐ and anti‐ oxidants affect either the start or the rate of oxygen consumption. The empirical formula dx/dt = k [O2] (1‐x/n) f′(t) was found applicable to the different stages of oxidation. 相似文献
10.
Simple pseudo-steady state relations between the hydraulic and nozzle pressures of an injection molding machine were presented and verified experimentally. A simulation study was performed to evaluate the performance of simple controllers using dynamic models developed for the hydraulic and nozzle pressures. The controllers chosen were the discrete proportional, proportional-integral (PI), and proportional-integral-derivative (PID) types, tuned according to the ITAE criterion. The control of hydraulic pressure simulation showed that the PI controller had the best overall performance, whereas the result of nozzle pressure control loop simulation showed that the PID controller performance was better than that of the PI controller. All the controllers, in both loops, gave responses that were about an order of magnitude more rapid than the open loop response. 相似文献