全文获取类型
收费全文 | 16302篇 |
免费 | 1316篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 273篇 |
综合类 | 25篇 |
化学工业 | 3674篇 |
金属工艺 | 470篇 |
机械仪表 | 796篇 |
建筑科学 | 393篇 |
矿业工程 | 6篇 |
能源动力 | 647篇 |
轻工业 | 1389篇 |
水利工程 | 57篇 |
石油天然气 | 14篇 |
无线电 | 3001篇 |
一般工业技术 | 3433篇 |
冶金工业 | 1247篇 |
原子能技术 | 190篇 |
自动化技术 | 2065篇 |
出版年
2024年 | 19篇 |
2023年 | 170篇 |
2022年 | 283篇 |
2021年 | 455篇 |
2020年 | 348篇 |
2019年 | 415篇 |
2018年 | 549篇 |
2017年 | 469篇 |
2016年 | 614篇 |
2015年 | 529篇 |
2014年 | 737篇 |
2013年 | 1134篇 |
2012年 | 950篇 |
2011年 | 1198篇 |
2010年 | 865篇 |
2009年 | 941篇 |
2008年 | 887篇 |
2007年 | 698篇 |
2006年 | 675篇 |
2005年 | 565篇 |
2004年 | 533篇 |
2003年 | 485篇 |
2002年 | 440篇 |
2001年 | 383篇 |
2000年 | 331篇 |
1999年 | 352篇 |
1998年 | 540篇 |
1997年 | 388篇 |
1996年 | 264篇 |
1995年 | 228篇 |
1994年 | 188篇 |
1993年 | 140篇 |
1992年 | 107篇 |
1991年 | 100篇 |
1990年 | 92篇 |
1989年 | 77篇 |
1988年 | 50篇 |
1987年 | 65篇 |
1986年 | 67篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 40篇 |
1982年 | 17篇 |
1981年 | 28篇 |
1980年 | 25篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 28篇 |
1976年 | 35篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Normally a complicated three-dimensional (3-D) approach is needed to study the field pattern of induction machines with skewed rotor bars. In this paper, a time-stepping two-dimensional (2-D) eddy-current finite element method, based on multislice technique, is described to study the steady-state operation and the starting process of skewed rotor induction machines. The fields of the multislices are being solved en bloc simultaneously, and thus, the effects of the eddy current and saturation can be taken into account directly. New forms of the governing equations for the multislice model are derived, which allow the meshes of multislices to be taken as one 2-D mesh so that the algorithm is very similar to that of general 2-D problems. Special techniques required for the mesh generation in the multislice model and the salient structures of the software are also described. The results obtained by using the program being developed have very good correlation with test data 相似文献
72.
The effect of DC flux on the core loss is examined for the practical range of power and frequency. Relevant core loss equations are derived and applied to an optimization algorithm to determine the minimum core loss at a given ratio of s (DC flux density to AC peak flux density). It has been found that the curves of hysteresis loss density versus the ratio of s exhibit a peak at a critical ratio. Below or above this critical ratio, the loss density decreases drastically. On the other hand, the curves of eddy-current loss density versus the ratio of s exhibits a minimum point at a critical ratio. Below or above this critical ratio, the loss density increases gradually 相似文献
73.
Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
74.
75.
This study has explored the potential energy surface on the chemical reaction of CH2OH with NO by using ab initio calculation. We have found the new reaction pathway producing N-hydroxy formamide, which can further decompose to generate isocyanic acid as a reducing agent of hydrocarbons selective catalytic reduction. 相似文献
76.
Carl A. Soderstrom Patricia C. Dischinger Gordon S. Smith J.Richard Hebel David R. McDuff David A. Gorelick Timothy J. Kerns Shiu M. Ho Kathleen M. Read 《Accident; analysis and prevention》1997,29(6):715-721
A structured in-depth interview employing standardized criteria was used to determine the prevalence of lifetime and current alcohol dependence (alcoholism) in unselected consecutive patients admitted to a regional Level I trauma center. Of 629 patients, 157 (25.0%) were current alcoholics at the time of injury. An additional 87 (13.8%) were diagnosed as lifetime non-current alcoholics. There was no significant difference in the rates of current alcohol dependence among patients injured in vehicular crashes (23.5%), other unintentional trauma victims (29.3%), and those injured as a result of violence (24.6%). Of BAC + (blood alcohol concentration positive) patients, 54.5% were current alcoholics. However, 14.4% of alcohol-negative patients were also diagnosed as alcohol dependent. 相似文献
77.
Shye Lin Wu Chung Len Lee Tan Fu Lei Chen C.F. Chen L.J. Ho K.Z. Ling Y.C. 《Electron Device Letters, IEEE》1994,15(4):120-122
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device 相似文献
78.
We analyze and numerically study the code-matching logic module that is the central element in a proposed soliton-based ring network system running at peak rates of 100 Gb/s. The proposed network is packet-switched, and fast logic is required to route each packet. That is the function of the code-matching logic module, and four soliton logic gates that can perform fast logic are the key devices in its design. The behavior of the code-matching logic module is governed by a large set of parameters, and we simulate it by varying many of these parameters. The physical effects that occur in these devices and their significance are analyzed. The results indicate that the logic module will work but within a restricted parameter range 相似文献
79.
The research on optical packet switching (OPS) has witnessed considerable progress in the 1990s. We examine the future potential of OPS in the core network by discussing this switching approach and the current status of a number of its enabling technologies. Many of these technologies are still in the stage of research and experimentation. We see that optical packet switching may be deployed in the long-term future subject to satisfaction of three main conditions/developments. First, additional technological developments have to take place to overcome remaining implementation challenges while making OPS cost-effective to deploy. Second, a rational migration scenario of the network toward gradual deployment of packet-based optical switching approaches should exist. Finally, carriers have to become more interested in packet-based optical switching solutions 相似文献
80.
This paper presents a new push-push voltage-controlled oscillator (VCO) technique that extracts a second harmonic output signal from a capacitive common node in a negative-gm oscillator topology. The generation of the second harmonics is accounted for by the nonlinear current-voltage characteristic of the emitter-base junction diode causing: 1) significant voltage clipping and 2) different rise and fall times during the switching operation of the core transistors. Comparative investigations show the technique is more power efficient in the high-frequency region than a conventional push-push technique using an emitter common node. A prototype 17-GHz VCO realized in GaInP/GaAs HBT technology produces an output power of -6dBm and a phase noise of -110.4dBc/Hz at 1-MHz offset, which is equivalent to a VCO figure-of-merit of -184.3dBc/Hz, while drawing 4.38 mA from a 3.0-V supply 相似文献