全文获取类型
收费全文 | 24916篇 |
免费 | 896篇 |
国内免费 | 84篇 |
专业分类
电工技术 | 322篇 |
综合类 | 45篇 |
化学工业 | 5427篇 |
金属工艺 | 579篇 |
机械仪表 | 572篇 |
建筑科学 | 1724篇 |
矿业工程 | 219篇 |
能源动力 | 708篇 |
轻工业 | 2161篇 |
水利工程 | 231篇 |
石油天然气 | 204篇 |
武器工业 | 1篇 |
无线电 | 1652篇 |
一般工业技术 | 4793篇 |
冶金工业 | 3015篇 |
原子能技术 | 323篇 |
自动化技术 | 3920篇 |
出版年
2023年 | 158篇 |
2022年 | 332篇 |
2021年 | 562篇 |
2020年 | 332篇 |
2019年 | 352篇 |
2018年 | 551篇 |
2017年 | 483篇 |
2016年 | 593篇 |
2015年 | 507篇 |
2014年 | 738篇 |
2013年 | 1582篇 |
2012年 | 1146篇 |
2011年 | 1575篇 |
2010年 | 1152篇 |
2009年 | 1098篇 |
2008年 | 1332篇 |
2007年 | 1169篇 |
2006年 | 997篇 |
2005年 | 916篇 |
2004年 | 850篇 |
2003年 | 727篇 |
2002年 | 696篇 |
2001年 | 437篇 |
2000年 | 420篇 |
1999年 | 442篇 |
1998年 | 454篇 |
1997年 | 408篇 |
1996年 | 378篇 |
1995年 | 326篇 |
1994年 | 327篇 |
1993年 | 336篇 |
1992年 | 279篇 |
1991年 | 241篇 |
1990年 | 223篇 |
1989年 | 259篇 |
1988年 | 209篇 |
1987年 | 199篇 |
1986年 | 196篇 |
1985年 | 262篇 |
1984年 | 237篇 |
1983年 | 209篇 |
1982年 | 189篇 |
1981年 | 218篇 |
1980年 | 155篇 |
1979年 | 175篇 |
1978年 | 167篇 |
1977年 | 166篇 |
1976年 | 182篇 |
1975年 | 154篇 |
1974年 | 140篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
PeterThorne 《现代电信科技》2004,(1):61-61,45
2002年,60%的亚洲公司报告了信息安全遭到破坏的事件。2003年上半年,黑客攻击事件的发生率更是上升到77%,2003年亚洲公司报告情况好转的可能性微乎其微。 相似文献
112.
113.
Peter Thorne 《信息安全与通信保密》2004,(2):64-65
2002年,60%的亚洲公司报告了信息安全遭到破坏的事件。2003年上半年,黑客攻击事件发生率猛增至77%,因此,2003年亚洲公司报告情况好转的可能性微乎其微。 相似文献
114.
Gülü Insel Derin Orhon Peter A Vanrolleghem 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(4):437-445
Hydrolysis mechanism plays a dominant role in the delicate balance of electron donor/electron acceptor ratios in BNR and EBPR systems as an important carbon source. In this study, the surface‐saturation‐type hydrolysis kinetics was investigated based on respirometric measurements, within the context of the theoretical and the practical identifiability of mathematical models. The identifiable parameters of a selected model were derived from respirograms. In addition, the information from the experiments was evaluated on the basis of Optimal Experimental Design (OED) methodology for different initial conditions of the batch respirometric experiment. © 2003 Society of Chemical Industry 相似文献
115.
Nondilute athermal and theta solutions of nonadsorbing flexible macromolecules in equilibrium with repulsive slit-like pores were examined by the lattice Monte Carlo simulations. The free energy of confinement ΔA/kT and the force f/kT exerted by polymers on the slit were computed as a function of the slit width D in a wide range of bulk concentrations φ. The free energy and force profiles in nondilute solutions were found to deviate considerably from the ideal chain theory; the perturbation of chains by a presence of the slit walls were substantially reduced in nondilute solutions. The free energy and force functions appropriate for nondilute solutions were derived by fitting the simulation data. Further, the relative pressure pI/pE exerted by the nonadsorbing confined molecules on the slit walls was calculated. The depletion effect relevant to colloid stabilization was found in dilute solutions to be slightly weaker for excluded-volume chains than for ideal chains. The relative pressure equation was modified to cover semidilute solutions, by using the mean-field and scaling expressions of the osmotic pressure. Both the relative pressure pI/pE and the intra-slit concentration profiles φI(x) in tandem display a suppression of the depletion effect with increasing φ in simidilute solutions. 相似文献
116.
L. Todorova T. Angelov Y. Marinov A. G. Petrov 《Journal of Materials Science: Materials in Electronics》2003,14(10-12):817-818
The linear electro-optic response of polymer-dispersed liquid crystal films has been studied. Micrometer-sized droplets of a cyanobiphenyl mixture (E7) were formed in a Norland Optical Adhesive 65 photopolymer by photopolymerization-induced phase separation. Samples with various average nematic droplet sizes were systematically investigated. The temperature dependence of the first-harmonic electro-optic spectra was obtained. Peculiar peaks and double peaks in the phase spectra were found at temperatures close to the clearing point. Samples with narrow distributions of droplet sizes were characterized by a double peak of the amplitude spectra in the low-frequency range. A flexoelectric origin of the first-harmonic spectra in confined nematic systems is discussed. 相似文献
117.
The effects of glycol methacrylate as a dehydrating agent on the dimensional changes of liver tissue
The dimensional changes of liver sections during the course of processing with glycol methacrylate (GMA) or with ethanol are described. Tissue processing with ethanol served as a control. During prolonged processing steps (24 h each), linear shrinkage of tissue specimens dehydrated with GMA at room temperature was 13.2%. Subsequent infiltration with GMA resulted in trivial swelling, and polymerization in slight shrinkage (2.3%). In comparison, processing with cold GMA resulted in shrinkage during dehydration (about 10.8%), a slight swelling in pure GMA, followed by shrinkage during polymerization (2.2%). Short routine processing schedules resulted in similar shrinkage/swelling patterns, although precise values differed slightly. In all experiments, ethanolic dehydration resulted in smaller dimensional tissue changes than did GMA dehydration. The dimensional changes of tissue sections during stretching on water, mounting and drying compensated for the major part of the shrinkage manifested during processing. 相似文献
118.
Translated from Izmeritel'naya Tekhnika, No. 10, pp. 38–39, October, 1992. 相似文献
119.
120.
The constraint satisfaction problem is known to be NP-hard in general, but a number of restrictions of the problem have been identified over the years which ensure tractability. This paper introduces two simple methods of combining two or more tractable classes over disjoint domains, in order to synthesise larger, more expressive tractable classes. We demonstrate that the classes so obtained are genuinely novel, and have not been previously identified. In addition, we use algebraic techniques to extend the tractable classes which we identify, and to show that the algorithms for solving these extended classes can be less than obvious. 相似文献