全文获取类型
收费全文 | 72555篇 |
免费 | 6223篇 |
国内免费 | 3109篇 |
专业分类
电工技术 | 4077篇 |
技术理论 | 4篇 |
综合类 | 4337篇 |
化学工业 | 12555篇 |
金属工艺 | 3835篇 |
机械仪表 | 4868篇 |
建筑科学 | 4774篇 |
矿业工程 | 1315篇 |
能源动力 | 2149篇 |
轻工业 | 5586篇 |
水利工程 | 1273篇 |
石油天然气 | 2654篇 |
武器工业 | 484篇 |
无线电 | 9908篇 |
一般工业技术 | 10392篇 |
冶金工业 | 3173篇 |
原子能技术 | 923篇 |
自动化技术 | 9580篇 |
出版年
2024年 | 254篇 |
2023年 | 1041篇 |
2022年 | 1927篇 |
2021年 | 2811篇 |
2020年 | 1993篇 |
2019年 | 1843篇 |
2018年 | 1999篇 |
2017年 | 2237篇 |
2016年 | 2291篇 |
2015年 | 2838篇 |
2014年 | 3547篇 |
2013年 | 4449篇 |
2012年 | 4735篇 |
2011年 | 5322篇 |
2010年 | 4631篇 |
2009年 | 4327篇 |
2008年 | 4309篇 |
2007年 | 3883篇 |
2006年 | 3775篇 |
2005年 | 3291篇 |
2004年 | 2509篇 |
2003年 | 2361篇 |
2002年 | 2643篇 |
2001年 | 2171篇 |
2000年 | 1777篇 |
1999年 | 1557篇 |
1998年 | 1421篇 |
1997年 | 1114篇 |
1996年 | 978篇 |
1995年 | 820篇 |
1994年 | 705篇 |
1993年 | 540篇 |
1992年 | 394篇 |
1991年 | 316篇 |
1990年 | 239篇 |
1989年 | 209篇 |
1988年 | 161篇 |
1987年 | 112篇 |
1986年 | 78篇 |
1985年 | 71篇 |
1984年 | 48篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 31篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We have investigated the effect of extended dislocations (0.5-3 μm) on charge distribution in GaN epilayer grown by metalorganic chemical vapor deposition on (0001) sapphire using atomic force microscopy (AFM) and scanning surface potential microscopy (SSPM). It has been observed for the surface at the extended dislocations present in undoped GaN film to be negatively charged showing 0.04-0.2 V higher potential relative to regions that contain no dislocations. In addition to the higher potential at the dislocation core, the surrounding surfaces, including the edge of the dislocations, are also negatively charged in a symmetric way around the dislocations revealing crater-shaped higher potential regions (∼0.04 V) relative to surrounding dislocation-free area. The experimental results show that the protrusion-type of dislocation is also negatively charged and its potential is dependent on the size of dislocation. 相似文献
72.
A kind of complex additive mainly containing Al, Mg, F, and O was prepared. The synthetical performances of the property-modified prebaked anodes containing additives were tested in laboratory. On the basis of ideal testing results obtained, a large number of industrial prebaked property-modified anodes are prepared in a large-scale aluminum company. Further more, they are all used in 160 kA prebaked anode aluminum electrolysis cells. The statistic result show that, compared with common anodes, the property-modified ones enhance current by 11.6 kg per ton aluminum averagely. 相似文献
73.
套管侧钻分支井钻井工程设计及应用原则 总被引:8,自引:3,他引:5
利用老井开窗侧钻分支井,可以提高原油采收率,增加产能和降低成本。对与分支井相关的分式设计。轨迹优化设计,钻柱设计,斜向器开窗方位的优化。开窗技术。轨迹控制应用等方面的主要原则进行了阐述。对进一步推广应用分支井技术,提高我国分支井钻井技术水平有一定的推动作用。 相似文献
74.
Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling 总被引:1,自引:0,他引:1
Montrose M.I. Er-Ping Li Hong-Fang Jin Wei-Liang Yuan 《Electromagnetic Compatibility, IEEE Transactions on》2005,47(2):227-233
This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results. 相似文献
75.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters. 相似文献
76.
The transmission mode of holographic polymer‐dispersed liquid crystals (HPDLCs) was developed an under electric field. It is reported that orientation of LC molecules under an electric field induces orientation of oligomer molecules giving rise to low off‐state diffraction and small grating shrinkage. Copyright © 2005 Society of Chemical Industry 相似文献
77.
Biodegradable multiblock poloxamers (BMPs) with gel duration of 8 h to several weeks were prepared by varying their molecular weights from 4000 to 40 000 g mol?1. The molecular weight of the BMP was controlled by changing the poloxamer to coupling agent ratio. Assuming a micelle packing model of the BMP gel, as in the case of a poloxamer gel, the micelle properties and critical gel concentration of BMPs were investigated on the basis of the scaling concept. The findings suggest that the control of molecular weight by hydrolyzable groups can be a facile approach to optimize the gel properties for biomedical applications. Copyright © 2005 Society of Chemical Industry 相似文献
78.
Colour Centres and Energy Transfer in BaF2-xClx:Eu2+ Phosphors 总被引:1,自引:1,他引:0
The optical absorption spectra of BaF2-xClx:Eu2 after ultraviolet (UV) light excitation were investigated.The differences between the absorption spectra after and before excitation (DAS) were observed.The DAS increase at both the high and the low energy side of F band in BaF2-xClx:Eu2 after 245 nm UV light excitation.The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres (association of F(Cl-) centres), whose absorption band matches the HeNe laser better, may explain the latter.In the write-in process, the transfer of electrons is via tunneling.In the readout process, the transfer of electrons captured in F(F-) and Fa centres is more likely via tunneling, and that of F(Cl-) centres is more likely via conduction band. 相似文献
79.
利用引进的制造技术和设备,制作出了 APT(STLRI)—1.78型系列化光纤连接器。 相似文献
80.
Jong-Hwan Kim Yeon-Chan Hong Sung-Jun Lee Keh-Kun Choi 《Industrial Electronics, IEEE Transactions on》1989,36(3):361-364
A direct adaptive control scheme is proposed for nonminimum-phase systems in which controller parameters are estimated from the recursive least-squares algorithm and additional auxiliary parameters are obtained from the proposed polynomial identity. A local convergence is guaranteed without any extra condition. Integral action is incorporated into the adaptive controller to eliminate the steady-state error and to satisfy a condition of the unique solution for the polynomial identity. The control law used in this scheme is based on the set-point-on-I-only proportional-integral-derivative (PID) structure 相似文献