全文获取类型
收费全文 | 193826篇 |
免费 | 15829篇 |
国内免费 | 8629篇 |
专业分类
电工技术 | 11104篇 |
技术理论 | 24篇 |
综合类 | 12761篇 |
化学工业 | 32454篇 |
金属工艺 | 10460篇 |
机械仪表 | 11919篇 |
建筑科学 | 15647篇 |
矿业工程 | 5056篇 |
能源动力 | 5524篇 |
轻工业 | 13704篇 |
水利工程 | 3541篇 |
石油天然气 | 10388篇 |
武器工业 | 1510篇 |
无线电 | 23443篇 |
一般工业技术 | 24213篇 |
冶金工业 | 9218篇 |
原子能技术 | 2196篇 |
自动化技术 | 25122篇 |
出版年
2024年 | 794篇 |
2023年 | 3045篇 |
2022年 | 5464篇 |
2021年 | 7551篇 |
2020年 | 5766篇 |
2019年 | 4899篇 |
2018年 | 5367篇 |
2017年 | 5997篇 |
2016年 | 5759篇 |
2015年 | 7551篇 |
2014年 | 9318篇 |
2013年 | 11131篇 |
2012年 | 12157篇 |
2011年 | 13228篇 |
2010年 | 11465篇 |
2009年 | 10723篇 |
2008年 | 10713篇 |
2007年 | 10196篇 |
2006年 | 10201篇 |
2005年 | 8858篇 |
2004年 | 6385篇 |
2003年 | 5769篇 |
2002年 | 5823篇 |
2001年 | 5109篇 |
2000年 | 4873篇 |
1999年 | 5210篇 |
1998年 | 4492篇 |
1997年 | 3672篇 |
1996年 | 3524篇 |
1995年 | 2847篇 |
1994年 | 2575篇 |
1993年 | 1816篇 |
1992年 | 1381篇 |
1991年 | 1073篇 |
1990年 | 843篇 |
1989年 | 707篇 |
1988年 | 571篇 |
1987年 | 365篇 |
1986年 | 262篇 |
1985年 | 197篇 |
1984年 | 128篇 |
1983年 | 91篇 |
1982年 | 111篇 |
1981年 | 73篇 |
1980年 | 62篇 |
1979年 | 26篇 |
1976年 | 22篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
73.
纳米技术与“纳米涂料”之我见 总被引:11,自引:0,他引:11
概述了纳米技术、纳米材料、“纳米涂料”的现状 ,重点讨论了纳米技术在涂料中应用遇到的问题和建议措施 ,对纳米技术的科研方向及其在涂料中应用的发展提出了看法。 相似文献
74.
75.
通过试验,分析比较了江西Sb2O3、南宁Sb2O3和大连Sb(Ac)3三种缩聚催化剂对聚酯切片质量的影响。试验结果表明,Sb(Ac)3是优良的缩聚催化剂。 相似文献
76.
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
77.
Some methods determine the non-indolyl glucosinolates content in rapeseed as their hydrolysates: the isothiocyanates and the
oxazolidinethiones. These methods in their present form underestimate the amount of the glucosinolates content. In this investigation,
a modified method was developed to give a better quantitative estimate, indicating a glucosinolate level five times that obtained
by a typical existing method. 相似文献
78.
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
79.
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
80.
A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry 相似文献