全文获取类型
收费全文 | 554501篇 |
免费 | 7809篇 |
国内免费 | 1806篇 |
专业分类
电工技术 | 10049篇 |
综合类 | 2671篇 |
化学工业 | 80487篇 |
金属工艺 | 23475篇 |
机械仪表 | 20436篇 |
建筑科学 | 15118篇 |
矿业工程 | 2173篇 |
能源动力 | 12985篇 |
轻工业 | 48119篇 |
水利工程 | 5299篇 |
石油天然气 | 3813篇 |
武器工业 | 14篇 |
无线电 | 69569篇 |
一般工业技术 | 107727篇 |
冶金工业 | 84710篇 |
原子能技术 | 6934篇 |
自动化技术 | 70537篇 |
出版年
2021年 | 2794篇 |
2019年 | 2553篇 |
2018年 | 23531篇 |
2017年 | 23307篇 |
2016年 | 16591篇 |
2015年 | 4529篇 |
2014年 | 6155篇 |
2013年 | 20155篇 |
2012年 | 15260篇 |
2011年 | 30070篇 |
2010年 | 25171篇 |
2009年 | 23917篇 |
2008年 | 25399篇 |
2007年 | 28183篇 |
2006年 | 13368篇 |
2005年 | 16614篇 |
2004年 | 14347篇 |
2003年 | 13778篇 |
2002年 | 12121篇 |
2001年 | 11454篇 |
2000年 | 10697篇 |
1999年 | 11034篇 |
1998年 | 24270篇 |
1997年 | 17816篇 |
1996年 | 14140篇 |
1995年 | 11194篇 |
1994年 | 10009篇 |
1993年 | 9617篇 |
1992年 | 7356篇 |
1991年 | 6976篇 |
1990年 | 6557篇 |
1989年 | 6283篇 |
1988年 | 6001篇 |
1987年 | 5060篇 |
1986年 | 4997篇 |
1985年 | 6185篇 |
1984年 | 5786篇 |
1983年 | 5002篇 |
1982年 | 4645篇 |
1981年 | 4606篇 |
1980年 | 4350篇 |
1979年 | 4231篇 |
1978年 | 3916篇 |
1977年 | 4670篇 |
1976年 | 6220篇 |
1975年 | 3263篇 |
1974年 | 3121篇 |
1973年 | 3001篇 |
1972年 | 2384篇 |
1971年 | 2064篇 |
排序方式: 共有10000条查询结果,搜索用时 806 毫秒
961.
Several companies have made major strides in marketing cellular telephones to children within the past 12 months; more and more children are using cell phones as part of their daily routines. Some fear any disturbance to brain activity in children could lead to impaired learning ability or behavioral problems. Moreover, any lasting biochemical effects could have important consequences, especially in the young, who still have years of development ahead of them. Recently, two studies of the mental process of young users of standard 902 MHz Global System for Mobile Communication (GSM) cellular mobile telephones were published: one paper reported a slight trend toward speeding up of simple reaction time, whereas the other study did not detect any change in cognitive functions. 相似文献
962.
During large scale wildfires, suppression activities are carried out under the direction of an Incident Management Team (IMT). The aim of the research was to increase understanding of decision processes potentially related to IMT effectiveness. An IMT comprises four major functions: Command, Operations, Planning, and Logistics. Four methodologies were used to study IMT processes: computer simulation experiments; analyses of wildfire reports; interviews with IMT members; and cognitive ethnographic studies of IMTs. Three processes were important determinants of IMT effectiveness: information management and cognitive overload; matching component function goals to overall goals; and team metacognition to detect and counter task‐disruptive developments. These processes appear to be complex multi‐person analogues of individual Incident Command processes identified previously. The findings have implications for issues such as: creating IMTs; training IMTs; managing IMTs; and providing decision support to IMTs. 相似文献
963.
A new phenomenon accompanying the electrolysis of salts has been observed, whereby an ordered composite is formed under certain conditions (electrolyte composition, current density). The composite comprises an inorganic salt crystal penetrated by metal nano- and microwires. This phenomenon can serve as a basis for the technology of oriented and ordered nanowire array synthesis. 相似文献
964.
Zirconium(IV) tungstoiodophosphate has been synthesized under a variety of conditions. The most chemically and thermally stable
sample is prepared by adding a mixture of aqueous solutions of 0·5 mol L−1 sodium tungstate, potassium iodate and 1 mol L−1 orthophosphoric acid to aqueous solution of 0·1 mol L−1 zirconium(IV) oxychloride. Its ion exchange capacity for Na+ and K+ was found to be 2·20 and 2·35 meq g−1 dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, Fourier
transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger
at different temperatures has been studied. The analytical importance of the material has been established by quantitative
separation of Pb2+ from other metal ions. 相似文献
965.
A framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance 总被引:7,自引:0,他引:7
Mechanical mechanisms with clearance abound in technological fields such as robotics, machine and steam turbine industry. The dynamic performance of these mechanisms in working condition can be achieved provided that the effects of the different on the mechanisms (such as mechanism dynamics, technological effects and thermal behaviour) are thoroughly understood. Virtual prototyping provides an integration of multi-domain dynamic simulation for the design and analysis process. In the current paper, a framework of virtual prototyping environment for the design and analysis of mechanical mechanism with clearance is presented. A case study with such a simulation strategy is studied for the optimum design and analysis of the technological parameter. 相似文献
966.
在薄板坯连铸连轧流程上,经过对Ti微合金化技术研究,有效解决了Ti微合金化强度性能波动大的问题,开发出屈服强度450~700MPa高强钢。对试制钢组织性能和工业应用分析研究,表明该产品通板性能良好,通板强度差30MPa左右;成形性能良好,d=0时冷弯测试全部合格;同时还具有良好焊接性能,焊接后,强度波动较小,均在母材部位断开;试制钢显微组织为珠光体和铁素体,晶粒均匀细小,平均尺寸为4~8/μm;实物质量满足集装箱和汽车制造行业要求,具有广阔市场前景。 相似文献
967.
S. V. Ivanova 《Materials Science》2007,43(5):718-724
We have established that technological defects (cracks) in zirconium articles can develop in the course of long-term storage
prior to their mounting in a reactor, which is caused by the action of residual stresses and hydrogen. We have considered
the conditions of after-operation storage of zirconium articles of the fuel core of thermal reactors in water of the cooling
ponds of reactors and in spent-fuel storehouses. The possibility of subsequent hydrogenation of these articles during their
storage has been shown. Finally, we have studied the effect of hydrogen, absorbed in the course of storage, on the crack resistance
of zirconium articles and the development of defects in them due to delayed hydride cracking.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 105–109, September–October, 2007. 相似文献
968.
Most algorithms on receiver autonomous integrity monitoring (RAIM) are under the assumption of a single-satellite fault, because there is an extremely small probability that significant simultaneous multiple-satellite faults may occur. However, after the implementation of the Galileo system in a few years, there will be more satellites in view for the user to utilise together with GPS satellites, and a combination of them will bring better performance for RAIM. On the other hand, with the help of wide area augmentation system and the use of dual-frequency operation, pseudo-range errors will be reduced greatly. Thus, tighter alert limits are required for RAIM, and formerly `small' errors should not be neglected. All of those factors make it necessary to consider simultaneous multiple-satellite faults. A detailed theoretical analysis of RAIM under the condition of two-satellite faults for both vertical and horizontal directions is presented. The characteristic/max slopes for every pair of satellites are then deduced in order to calculate the tighter vertical/horizontal protection level for RAIM 相似文献
969.
A digital signal processor-based control system for the permanent magnet-assisted reluctance synchronous machine, with the emphasis on dynamic performance, is proposed. A classical design approach is used to design the current and speed controllers for the machine. The stator current of the machine is controlled in such a way that the current angle in the dq synchronous reference frame is constant. The load-torque is estimated using a state space observer and compensation current based on the estimated load is used to improve the dynamic performance of the drive. The control system design is machine specific as it relies on data from finite-element analysis. Simulated and measured results on a 110-kW power level show that the resulting control system is stable and robust with good dynamic performance 相似文献
970.
This paper presents an examination of classical scattering models for radar cross sections of deciduous leaves, such as the generalised Rayleigh-Gans (GRG) model and the physical optics (PO) model. The PO model employs the resistive sheet approximation in this study. The validity regions of the analytical models for microwave scattering from deciduous leaves are investigated by comparison with the precise numerical results of the method of moment. It was found that the GRG and PO models extend their validity regions for estimating the scattering amplitudes as the thickness of a lossy dielectric disk decreases. The GRG and PO models can be used alternatively for computing the scattering matrices of natural deciduous leaves at microwave frequencies regardless of the size of the leaves, because of the very small thickness of the leaves (0.2-0.4 mm) 相似文献