全文获取类型
收费全文 | 2001篇 |
免费 | 41篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 172篇 |
综合类 | 2篇 |
化学工业 | 309篇 |
金属工艺 | 47篇 |
机械仪表 | 38篇 |
建筑科学 | 37篇 |
矿业工程 | 1篇 |
能源动力 | 45篇 |
轻工业 | 163篇 |
水利工程 | 9篇 |
无线电 | 243篇 |
一般工业技术 | 249篇 |
冶金工业 | 550篇 |
原子能技术 | 43篇 |
自动化技术 | 141篇 |
出版年
2022年 | 24篇 |
2021年 | 42篇 |
2020年 | 18篇 |
2019年 | 13篇 |
2018年 | 32篇 |
2017年 | 20篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 41篇 |
2013年 | 62篇 |
2012年 | 43篇 |
2011年 | 77篇 |
2010年 | 53篇 |
2009年 | 68篇 |
2008年 | 71篇 |
2007年 | 56篇 |
2006年 | 57篇 |
2005年 | 61篇 |
2004年 | 51篇 |
2003年 | 41篇 |
2002年 | 58篇 |
2001年 | 34篇 |
2000年 | 52篇 |
1999年 | 54篇 |
1998年 | 204篇 |
1997年 | 125篇 |
1996年 | 96篇 |
1995年 | 67篇 |
1994年 | 62篇 |
1993年 | 65篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 20篇 |
1976年 | 16篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1967年 | 6篇 |
排序方式: 共有2049条查询结果,搜索用时 15 毫秒
101.
An adaptive antenna array under directional constraint 总被引:1,自引:0,他引:1
The concept of the adaptive system working on the principle of minimizing the output power under the constrained response to specified directions is introduced. Theoretical analysis and computer simulation experiments on this directional constraint system are also presented. By comparison with the computer experiment, the differential equation approach is shown to be useful to predict the behavior of the system. The effect of error in setting the constraint direction is investigated, and it is demonstrated that the system is not very sensitive to such error. This margin can be made even greater by adopting the double directional constraints system. This system is also analyzed theoretically and experimented by computer simulation. History of output power components during adaptation is shown, which enables the comprehension of the behavior of the system. 相似文献
102.
Takano Y Koizumi M Takarada R Kamimura MT Czerminski R Koike T 《Journal of molecular graphics & modelling》2003,22(2):105-114
We have investigated a new approach to efficiently find a novel inhibitor against a serine protease (i.e. an activated coagulation factor X, FXa) by using de novo design programs and the X-ray crystal structure of the target enzyme. FXa is a coagulant enzyme that generates thrombin (a serine protease) and participates in both intrinsic and extrinsic coagulation pathways. We adopted multiple copy simultaneous search (MCSS) and CAVEAT linker search techniques, which disclosed a novel FXa inhibitor (T01312) consisting of two binding moieties (the benzamidinyl and adamantyl groups) and a linker unit (the carboxybenzylamine group). The inhibitory activity of T01312 against FXa was determined to be a small K(i)-value of 48nM, which is two orders of magnitude smaller than that against thrombin. An X-ray crystal analysis of T01312 complexed with trypsin (an analogue of FXa) and docking studies of T01312 with trypsin and FXa showed that: (i) the benzamidinyl group is a predominant binding moiety in the anionic pocket (S1 site) with an asparatic acid residue; (ii) a hydrophobic pocket (S4 site) is the binding site of the adamantyl group; (iii) the carboxylate group of the linker contributes to the selectivity for FXa against thrombin. Thus, the combination of the knowledge of the X-ray crystal structure of the target molecule with MCSS and CAVEAT linker search techniques proved to be an effective hit-finding method that does not require the screening of huge compound libraries. 相似文献
103.
Daikoku M. Morita I. Taga H. Tanaka H. Kawanishi T. Sakamoto T. Miyazaki T. Fujita T. 《Lightwave Technology, Journal of》2007,25(1):139-145
In order to realize a future 100-Gb Ethernet (100 GbE) transport, 100-Gb/s transmission without 100-GHz-class electronics and optical time-division-multiplexing technique was demonstrated. By using a differential quadrature phase-shift-keying (DQPSK) modulation format and commercially available electronics, 2- and 50-km transmissions of 100-Gb/s signal were successfully achieved over a standard single mode fiber. The receiver sensitivity, chromatic dispersion, and differential group delay tolerances of 100-Gb/s DQPSK signal were also evaluated. Through these evaluations, the possibility of DQPSK modulation for future 100-GbE transport is verified 相似文献
104.
Paul B.C. Ryan Tu Fujita S. Okajima M. Lee T.H. Nishi Y. 《Electron Devices, IEEE Transactions on》2007,54(7):1637-1644
In this paper, we propose a quasi-analytical device model of nanowire FET (NWFET) for both ballistic and drift-diffusion current transport, which can be used in any conventional circuit simulator like SPICE. The closed form expressions for current-voltage (I-V) and capacitance-voltage characteristics are obtained by analytically solving device equations with appropriate approximations. The developed model was further verified with the measured I-V characteristics of an NWFET device. Results show a close match of the model with measured data. 相似文献
105.
N. Fujita K. IshiiH. Ogawa 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(9):1023-1025
We have developed the two-dimensional mapping technique with in-air-PIXE (2D-PIXE) using a metal capillary as a guide to extract ion beam to air. The metal capillary is the conventional injection needle with a 200 μm inside diameter. For the target which is the character made of the copper wires on aluminum basement, 2D-PIXE measurements were performed by irradiating 3 MeV proton beam. As a result, the character was tend to be restored clearly by this method. We discuss about the result of the two-dimensional map from a viewpoint of the signal-to-noise ratio and the resolution. This technique is expected to be applicable to various fields such as biology, nano-technology, archeology and so on. 相似文献
106.
Michiko Fujita Mikio Kajiyama Akio Takemura Hirokuni Ono Hiroshi Mizumachi Shunji Hayashi 《应用聚合物科学杂志》1998,67(2):221-229
Natural rubber (NR) was blended in various ratios with 12 kinds of tackifiers that were prepared from petroleum. The blends were heated to various temperatures (20–120°C) to investigate their miscibility. The blends were visually observed for transparency or opacity at each temperature and further observed under an optical microscope for any existence of phase-separated structure. Miscibility of the blends is illustrated as phase diagrams in this article. NR/aliphatic resin systems and NR/aliphatic-aromatic copolymer systems showed phase diagrams of the lower critical solution temperature type, wherein the blends turned faintly cloudy over the binodal curves. The NR/hydrogenated petroleum resin system also showed a phase diagram of the lower critical solution temperature type. The miscible range of a blend system tends to become smaller as the molecular weight of a tackifier increases. Resins prepared by polymerization of pure aromatic monomers were completely immiscible with NR. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 221–229, 1998 相似文献
107.
Kishino K. Kikuchi A. Yoshizawa M. Fujita N. Kushi K. Sasamoto H. 《IEEE journal of selected topics in quantum electronics》1998,4(3):550-556
Novel growth technologies of III-nitrides for fabricating optical devices by molecular beam epitaxy using RF-plasma excited nitrogen (RF-MBE) were investigated. A relatively high-growth rate, up to 1.4 μm/h of GaN with high-electrical and high-optical quality was obtained. The concept of AlGaN quasi-ternary (QT) compounds, consisting of GaN-AlGaN short period superlattice, was demonstrated and the Al composition was controlled with a shutter control method in the range of 0-0.47. Using the QT technology, a GaN-Al0.07Ga0.933N-Al0.3Ga0.7 N multiquantum-well heterostructure was fabricated to show the effectiveness of the method 相似文献
108.
109.
S. Watanabe T. Fujita M. Sakamoto H. Endo T. Kitazume 《Journal of the American Oil Chemists' Society》1987,64(6):874-875
Monofluoro esters were prepared by the reaction of hydroxy esters with N,N-diethyl-1,1,2,3,3,3-hexafluoro propylamine (PPDA).
Saponification of these monofluoroesters with enzyme (lipase MY) was attempted to give their corresponding monofluorocarboxylic
acids in moderate yields. 相似文献
110.
Muneki Nakada Changho Chong Atsushi Morosawa Keiji Isamoto Takuya Suzuki Hiroyuki Fujita Hiroshi Toshiyoshi 《IEEJ Transactions on Electrical and Electronic Engineering》2014,9(4):448-458
This paper presents a novel device architecture for optically actuated microelectromechanical systems (MEMS) endoscopes for optical coherence tomography (OCT) measurement. A 10‐mW infrared light beam at a wavelength of 1.5 µm is transferred through the single‐mode fiber to provide a scanning MEMS mirror with the drive voltage (maximum 11 V) by exciting a photovoltaic cell, while also providing with a secondary light beam at a wavelength of 1.3 µm for the OCT measurement. An electrostatic vertical comb‐drive optical scanner (1.5 mm × 2.0 mm × 0.5 mm) has been developed by using the deep reactive ion etching (DRIE) of a silicon‐on‐insulator (SOI) wafer. The design of the scanner module is discussed, along with the experimental results of electrostatic operation. An equivalent circuit model for the optical scanner is developed to explain the behavior of the optically powered actuation mechanism, including the hysteresis loop in the frequency response and the voltage dependence of oscillating angle (mechanical peak ±3.2°/7 V around the resonance frequency of 250 Hz). OCT measurement of a tissue is demonstrated to reconstruct the cross‐sectional image of a fingerprint at a resolution of lateral 40 µm × vertical 8 µm and penetration depth of 2.5 mm. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. 相似文献