全文获取类型
收费全文 | 21356篇 |
免费 | 1492篇 |
国内免费 | 868篇 |
专业分类
电工技术 | 681篇 |
综合类 | 1242篇 |
化学工业 | 11383篇 |
金属工艺 | 1343篇 |
机械仪表 | 548篇 |
建筑科学 | 1962篇 |
矿业工程 | 182篇 |
能源动力 | 236篇 |
轻工业 | 580篇 |
水利工程 | 112篇 |
石油天然气 | 256篇 |
武器工业 | 77篇 |
无线电 | 917篇 |
一般工业技术 | 3469篇 |
冶金工业 | 396篇 |
原子能技术 | 151篇 |
自动化技术 | 181篇 |
出版年
2024年 | 105篇 |
2023年 | 292篇 |
2022年 | 477篇 |
2021年 | 621篇 |
2020年 | 540篇 |
2019年 | 498篇 |
2018年 | 526篇 |
2017年 | 731篇 |
2016年 | 604篇 |
2015年 | 684篇 |
2014年 | 964篇 |
2013年 | 1217篇 |
2012年 | 1520篇 |
2011年 | 1475篇 |
2010年 | 1143篇 |
2009年 | 1275篇 |
2008年 | 1088篇 |
2007年 | 1354篇 |
2006年 | 1308篇 |
2005年 | 1119篇 |
2004年 | 872篇 |
2003年 | 734篇 |
2002年 | 665篇 |
2001年 | 586篇 |
2000年 | 514篇 |
1999年 | 464篇 |
1998年 | 368篇 |
1997年 | 314篇 |
1996年 | 234篇 |
1995年 | 189篇 |
1994年 | 186篇 |
1993年 | 165篇 |
1992年 | 202篇 |
1991年 | 167篇 |
1990年 | 149篇 |
1989年 | 129篇 |
1988年 | 33篇 |
1987年 | 42篇 |
1986年 | 27篇 |
1985年 | 34篇 |
1984年 | 27篇 |
1983年 | 18篇 |
1982年 | 35篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Keith S. Matlack Tomasz Labuda 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,62(1):91-93
A method for analyzing the fluorine content of glass using a microwave oven to digest the glass is presented. Analysis time and secondary waste generation are reduced using this method, without sacrificing accuracy. 相似文献
22.
Phase separation during polymerization was studied in a model system consisting of a diepoxide based on diglycidyl ether of bisphenol A (DGEBA), variable amounts of ethylenediamine (EDA) and the mass of castor oil (CO) necessary to obtain a mass fraction equal to 0-15 in a final system where the stoichiometric ratio of amine to epoxy equivalents, r, was equal to 1. A two-step polymerization process was performed by curing first a system with r = 0-5, during variable times before phase separation, and then carrying the system to r = 1. Thermodynamic analysis of samples with different r values led to a linear relationship between the Flory-Huggins interaction parameter and r. The concentration (P) and average size (D?) of dispersed-phase particles followed opposite trends, i.e. P increased while D? decreased, when either r was increased or the time of curing in the first step of a two-step process was decreased. This was explained by assuming that the competition between nucleation and growth was determined by the viscosity at the cloud point, ηcp. Low values of ηcp favoured growth over nucleation and led to fewer but larger particles. 相似文献
23.
24.
Nd:碲酸盐玻璃的光谱和激光性质 总被引:2,自引:0,他引:2
对比了各种激光玻璃的光谱性质,指出碲酸盐玻璃是一咱理想的激光介质,并资产在室温下实现了钛宝石激光器泵浦了Nd:碲酸盐块体玻璃的激光发射,激光阈值4.20mJ,斜率效率14.7%。 相似文献
25.
Flory–Huggins interaction parameters, λ, were determined for a series of probes in an amine cured epoxy resin matrix (433–493 K) and its precursors (324–363 K) by inverse gas chromatography (IGC). Hildebrand–Scatchard theory was combined with Flory–Huggins theory in order to estimate infinte dilution solubility parameters (δ2) for the matrix and its precursors at 298 K. It was shown that the value of the solubility parameter for the cured resin matrix lies between those of its precursors. Compared to the majority of published work, an unusual aspect of this application of IGC is that solubility parameters have been determined when the stationery phases are (i) small molecules and (ii) a highly crosslinked polymer. Moreover, all possible attempts have been made to ensure equilibrium conditions between probe and stationary phase, and compensation for asymmetry of peak profile has been applied in determining δ2. The solubility parameters estimated by IGC are in good agreement with those calculated by other methods. 相似文献
26.
Zhen Wang 《Applied Composite Materials》1995,2(4):257-264
A bimodal Weibull distribution function was applied to analyse the strength distribution of glass fibre bundles under tensile impact. The simulation was performed using a one-dimensional damage constitutive model. The results show that there were two concurrent flaw populations in the fracture process. The regression analysis using the bimodal Weibull distribution function was in good agreement with experiment. 相似文献
27.
Mössbauer studies of Fe2+ in water-soaked nafion polymer membranes in the temperature range between 90 K and 250 K have been performed. Above a critical temperature (~ 180 K) the spectra exhibit both elastic narrow absorption lines and quasielastic broad lines. These spectra are typical of bounded diffusion phenomena observed by Mössbauer spectroscopy in macromolecular systems like haemoglobin, myoglobin and ferritin. Similar spectral shapes have been observed by quasielastic neutron scattering from water in nafion membranes. Within 50 K above the critical temperature the total Mössbauer absorption area decreases by an order of magnitude whereas the narrow absorption line decreases by two orders of magnitude. The results are interpreted in terms of bounded diffusive motion of the iron. Using a model based on overdamped harmonically bound Brownian motion, the essential parameters of the iron motion can be derived as a function of temperature. The iron motion most probably reflects the motion of a large Fe2+ complex, e.g. Fe(H2O)2+6, which is attached to the polymer side chains via the sulphonic group. 相似文献
28.
29.
Fracture toughness and fatigue crack propagation (FCP) of plain and modified anhydride-cured epoxy resin (EP) were studied at ambient temperature. Liquid carboxyl-terminated acrylonitrile-butadiene (CTBN) and silicon (SI) rubber dispersions were used as tougheners for the EP. The morphology of the modified EP was characterized by dynamic mechanical analysis (DMA) and by scanning electron microscopy (SEM). The fracture toughness, Kc, of the compositions decreased with increasing deformation rate. Kc of the EP was slightly improved by CTBN addition and practically unaffected by incorporation of the SI dispersion when tests were performed at low cross-head speed, v. Both modifiers improved Kc at high v, and also the resistance to FCP, by shifting the curves to higher stress intensity factor ranges, ΔK, by comparison with the plain EP. It was established that both fracture and fatigue performance rely on the compliance, JR, at the rubbery plateau, and thus on the apparent molecular mass between crosslinks, Mc. The failure mechanisms were less dependent upon the loading mode (fracture, fatigue), but differed basically for the various modifiers. Rubber-induced cavitation and shear yielding of the EP were dominant for CTBN, whereas crack bifurcation and branching controlled the cracking in SI-modified EP. The simultaneous use of both modifiers resulted in a synergistic effect for both the fracture toughness at high deformation rate and the FCP behavior. 相似文献
30.
D Ganguli 《Bulletin of Materials Science》1993,16(6):523-531
The various parameters related to sol-gel processing are discussed with special reference to those which usually attract less
attention but depending on the final product in mind, can play important roles. The versatility of the sol-gel technique in
materials preparation is demonstrated by discussing the various products developed at the author’s laboratory by using this
processing method. 相似文献