全文获取类型
收费全文 | 53964篇 |
免费 | 3317篇 |
国内免费 | 5509篇 |
专业分类
电工技术 | 2165篇 |
技术理论 | 66篇 |
综合类 | 5627篇 |
化学工业 | 9558篇 |
金属工艺 | 1499篇 |
机械仪表 | 2755篇 |
建筑科学 | 15743篇 |
矿业工程 | 1877篇 |
能源动力 | 2137篇 |
轻工业 | 1461篇 |
水利工程 | 1975篇 |
石油天然气 | 1329篇 |
武器工业 | 759篇 |
无线电 | 2359篇 |
一般工业技术 | 7022篇 |
冶金工业 | 1232篇 |
原子能技术 | 271篇 |
自动化技术 | 4955篇 |
出版年
2024年 | 194篇 |
2023年 | 818篇 |
2022年 | 1053篇 |
2021年 | 1446篇 |
2020年 | 1510篇 |
2019年 | 1188篇 |
2018年 | 1125篇 |
2017年 | 1342篇 |
2016年 | 1562篇 |
2015年 | 1664篇 |
2014年 | 4321篇 |
2013年 | 3237篇 |
2012年 | 3659篇 |
2011年 | 4445篇 |
2010年 | 3498篇 |
2009年 | 3643篇 |
2008年 | 3491篇 |
2007年 | 4067篇 |
2006年 | 3657篇 |
2005年 | 3278篇 |
2004年 | 2914篇 |
2003年 | 2240篇 |
2002年 | 1686篇 |
2001年 | 1239篇 |
2000年 | 1095篇 |
1999年 | 859篇 |
1998年 | 645篇 |
1997年 | 556篇 |
1996年 | 468篇 |
1995年 | 420篇 |
1994年 | 311篇 |
1993年 | 248篇 |
1992年 | 202篇 |
1991年 | 125篇 |
1990年 | 96篇 |
1989年 | 85篇 |
1988年 | 75篇 |
1987年 | 46篇 |
1986年 | 30篇 |
1985年 | 35篇 |
1984年 | 41篇 |
1983年 | 32篇 |
1982年 | 25篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1979年 | 15篇 |
1977年 | 6篇 |
1958年 | 4篇 |
1957年 | 6篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Theoretical predictions using a modified radical species ternary diagram for C–H–O system indicate that addition of sulfur expands the C–H–O gas phase compositional window for diamond deposition. Sulfur addition to no-growth domain increases the carbon super-saturation by binding the oxygen and the addition of sulfur to the non-diamond domain reduces the heavy carbon super-saturation by decreasing CnHm species concentration in the gas phase. The overall effect of sulfur addition to gas phase mixtures is characterized as that of oxygen addition to the C–H system, i.e. expansion of the compositional window over which diamond can be deposited from the gas phase. In addition, the increasing sulfur concentration to diamond domain feed gases beyond 2000 ppm did not affect the steady state gas phase composition but the quality of diamond was reduced. 相似文献
84.
韩选江 《南京建筑工程学院学报》2002,(4):67-74
为有效保护地面上的生态环境,开发利用地下空间资源并营建新世纪的地下水城,在新的21世纪里将会建造更多的地下工程以满足人们生产生活的各种需要。文中介绍了地下工程施工中采用的逆作法、盾构法、新奥法、沉管隧道、顶管工程和大型沉井施工新技术,供同行们参考应用。 相似文献
86.
87.
Pierluigi Guerrini De LucaClaudio Scali 《Chemical engineering science》2002,57(11):2077-2087
Applicability of different temperature oscillation calorimetry algorithms, previously proposed in the literature, for the evaluation of the heat transfer coefficient during the course of the reaction, is analysed by referring to the experimental data from a methyl methacrylate polymerisation reactor.Results are coincident in the nominal case (no errors on data), while differences appear in the elaboration of real data. The effect of uncertainty in the experimental data has been simulated in terms of error on the amplitude and on the phase of reactor and jacket temperature profiles.This approach allows to indicate algorithms having the best robustness properties and to give an explanation of phase errors in terms of a lumped parameter which accounts for different phenomena, not included in the basic hypotheses of the method. Based on this observation, a procedure to eliminate this source of errors from experimental data is proposed for the more general algorithm presented to handle oscillating temperature profiles generated by different techniques. 相似文献
88.
Dmitry Yu. Murzin 《Chemical engineering science》2002,57(8):1299-1306
Several aspects of heterogeneous catalytic kinetics over induced nonuniform surfaces are considered. The reaction mechanism is thought to occur through a surface collision of species, adsorbed on two distinct surface sites, which display nonuniform behavior. The expressions for rates of elementary reactions have been deduced within the framework of the surface electronic gas model, which accounts for the case of inhomogeneous surface. Equations for catalyst activity in the range of medium coverage have been derived and compared with the power-law model. 相似文献
89.
Markus Stolze 《Knowledge》1994,7(4):271-273
System development is strongly influenced by the perspectives used by system developers. Current development methods for knowledge-based systems are based on an information processing perspectives of experts and users which has been criticized by a number of researchers. The paper argues that work-oriented development of knowledge-based systems requires the parallel use of multiple perspectives (including the information processing perspective), and that the use of any single perspective is potentially dangerous. As an example of the importance of using multiple perspectives, thepaper presents the situated action perspective, and shows how it complements the information processing perspective. 相似文献
90.
The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy
(CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a
cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The
products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing
the amount of carbon incorporated into the growing epitaxial layer. 相似文献