全文获取类型
收费全文 | 22222篇 |
免费 | 1269篇 |
国内免费 | 61篇 |
专业分类
电工技术 | 320篇 |
综合类 | 25篇 |
化学工业 | 4968篇 |
金属工艺 | 905篇 |
机械仪表 | 1324篇 |
建筑科学 | 434篇 |
矿业工程 | 6篇 |
能源动力 | 874篇 |
轻工业 | 1867篇 |
水利工程 | 91篇 |
石油天然气 | 17篇 |
无线电 | 3745篇 |
一般工业技术 | 4741篇 |
冶金工业 | 1552篇 |
原子能技术 | 295篇 |
自动化技术 | 2388篇 |
出版年
2024年 | 22篇 |
2023年 | 282篇 |
2022年 | 404篇 |
2021年 | 698篇 |
2020年 | 481篇 |
2019年 | 516篇 |
2018年 | 713篇 |
2017年 | 680篇 |
2016年 | 792篇 |
2015年 | 620篇 |
2014年 | 963篇 |
2013年 | 1420篇 |
2012年 | 1486篇 |
2011年 | 1811篇 |
2010年 | 1314篇 |
2009年 | 1375篇 |
2008年 | 1229篇 |
2007年 | 950篇 |
2006年 | 827篇 |
2005年 | 713篇 |
2004年 | 647篇 |
2003年 | 597篇 |
2002年 | 598篇 |
2001年 | 522篇 |
2000年 | 442篇 |
1999年 | 431篇 |
1998年 | 714篇 |
1997年 | 426篇 |
1996年 | 397篇 |
1995年 | 260篇 |
1994年 | 170篇 |
1993年 | 153篇 |
1992年 | 112篇 |
1991年 | 100篇 |
1990年 | 76篇 |
1989年 | 90篇 |
1988年 | 75篇 |
1987年 | 64篇 |
1986年 | 51篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 26篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1977年 | 24篇 |
1976年 | 33篇 |
1975年 | 17篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We consider a problem of finding a path of an unmanned combat vehicle that patrols a given area by visiting a given set of checkpoints with the objective of minimizing possibility of enemy’s infiltration. In this study, we focus on a situation in which the possibility of enemy’s infiltration at (through) each checkpoint is increased nonlinearly as time passes and the checkpoint may be patrolled multiple times during a planning horizon. We develop two-phase heuristics in which an initial path is constructed in the first phase and then it is improved in the second phase. For evaluation of the performance of the proposed heuristics, computational experiments are performed on randomly generated problem instances, and results show that the heuristics give good solutions in a reasonably short time. 相似文献
72.
Sangseok Yun Bongjin Jun Daijin Kim Jaewoong Kim Sukhan Lee Mun-Taek Choi Munsang Kim Joong-Tae Park Jae-Bok Song 《Journal of Intelligent and Robotic Systems》2012,67(2):79-99
This paper describes a scheme for proactive human search for a designated person in an undiscovered indoor environment without human operation or intervention. In designing and developing human identification with prior information a new approach that is robust to illumination and distance variations in the indoor environment is proposed. In addition, a substantial exploration method with an octree structure, suitable for path planning in an office configuration, is employed. All these functionalities are integrated in a message- and component-based architecture for the efficient integration and control of the system. This approach is demonstrated by succeeding human search in the challenging robot mission of the 2009 Robot Grand Challenge Contest. 相似文献
73.
Kyoung-Su Park Geonyup Lim Young-Pil Park Eo-Jin Hong No-Cheol Park 《Microsystem Technologies》2012,18(9-10):1389-1399
Currently, almost all hard disk drives (HDDs) have adopted a loading/unloading mechanism that increases their recording capacity and improves their reliability. However, these mechanisms still create a few scratches or defects in the loading/unloading zone. Slipping at the dimple–flexure interface was recently reported as one of the causes. In this research, we first analyzed the relative behavior of dimple–flexure based on fretting wear marks. We determined that the dimple–flexure behavior included both slipping and rotating motion simultaneously. We then verified the distinct slipping and rolling phenomenon at the moment of ramp contact using finite-element method (FEM) analysis. An experimental setup was constructed, and an unloading experiment was carried out to obtain the ramp contact characteristics corresponding to various unloading velocities. Based on the verified FEM, the characteristics of dimple–flexure relative behavior were investigated for various suspension design parameters, ramp contact characteristics, and unloading velocities. A higher ramp contact force and shorter contact duration resulted in larger slip displacements and roll angles between the dimple and the flexure. Finally, we analyzed the unloading performance of an HDD for various design parameters using quasi-static approximation while considering the relative behavior between the dimple and flexure. The quasi-static analysis indicated a change of approximately 15?% in the flying height at an unloading velocity of 40?in. per second when the relative motion between the dimple and flexure was considered during the unloading process. Even, slider–disk contact occurred at an unloading velocity of 50 ISP. 相似文献
74.
Kyung-Hoon Hyun Sangkyu Lee Chae-Woong Cho Ungyu Paik Dae-Hwan Kim Eun-Sang Na Jea-Gun Park 《Journal of Electroceramics》2006,17(2-4):351-354
An attempt was made to improve the conventional lamination process in the multilayered ceramic capacitors (MLCCs) fabrication by adapting a solvent treatment on the BaTiO3 green sheets. During the lamination process, additional particle rearrangement in the BaTiO3 green block was stimulated by solvent treatment. This rearrangement resulted in a more compact structure of the BaTiO3 green sheets compared to that obtained through the conventional lamination process. The overall thickness of BaTiO3/Ni/BaTiO3 laminates was also reduced after solvent treatment. It is suggested that miniaturization in the fabrication of MLCCs can be improved by adapting a solvent treatment during the lamination process. 相似文献
75.
H.C. Ji P.K.J. Park Hoon Kim J.H. Lee Y.C. Chung 《Photonics Technology Letters, IEEE》2006,18(8):950-952
We propose and demonstrate a novel technique to monitor the frequency offset between the optical source and delay interferometer (DI) for direct-detection differential phase-shift-keying (DPSK) systems. In this scheme, a phase-modulated tone is applied to DPSK signals at the transmitter and then detected after being converted into an amplitude-modulated tone at the DI to be used for the monitoring signal. Our experimental demonstration shows that the monitoring range and sensitivity of the proposed scheme are measured to be /spl plusmn/2 GHz and /spl sim/10 MHz, respectively, which we believe are good enough to be used either to generate alarm signals for the frequency offset monitoring or to control the feedback loop of the DI. 相似文献
76.
A continuous-wave hybrid AlGaInAs-silicon evanescent laser 总被引:1,自引:0,他引:1
A.W. Fang Hyundai Park R. Jones O. Cohen M.J. Paniccia J.E. Bowers 《Photonics Technology Letters, IEEE》2006,18(10):1143-1145
We report a novel laser architecture, the hybrid silicon evanescent laser (SEL), that utilizes offset AlGaInAs quantum wells (QWs) bonded to a silicon waveguide. The silicon waveguide is fabricated on a silicon-on-insulator wafer using a complimentary metal-oxide-semiconductor-compatible process, and is subsequently bonded with the AlGaInAs QW structure using low temperature O/sub 2/ plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum temperature for CW operation is 60/spl deg/C. The maximum single-sided fiber-coupled CW output power at room temperature is 4.5 mW. 相似文献
77.
A miniature UWB planar monopole antenna with 5-GHz band-rejection filter and the time-domain characteristics 总被引:2,自引:0,他引:2
Young Jun Cho Ki Hak Kim Dong Hyuk Choi Seung Sik Lee Seong-Ook Park 《Antennas and Propagation, IEEE Transactions on》2006,54(5):1453-1460
A planar monopole antenna with a staircase shape and small volume (25/spl times/26/spl times/1 mm/sup 3/) is proposed in this paper. With the use of a half-bowtie radiating element, the staircase-shape, and a modified ground plane structure, the proposed antenna has a very wide impedance bandwidth measured at about 11.6 GHz (2.9-14.5 GHz, bandwidth ratio about 1:5) below VSWR 2 including the WLAN band notched in the vicinity of 5 GHz. An omnidirectional radiation pattern is obtained. The group delay which is an indication of linearity between two proposed antennas is less than 1 ns. The electrical characteristics in terms of frequency and time domains and physical ones of the proposed antenna make it attractive for use in ultrawideband (UWB) systems. 相似文献
78.
Young-Suk Kim Chan-Il Kim Jun-Young Park Kyung-Hoan Na 《Metallurgical and Materials Transactions A》2005,36(1):169-176
The atomic force microscopy (AFM)-based nanolithographic technique is currently used to directly machine material surfaces
and fabricate nanocomponents for microelectromechanical systems (MEMS) devices. In the current study, three-dimensional molecular
dynamic (MD) simulations with potentials based on the Morse function were performed to evaluate the effect of crystallographic
factors and process variables on the nanodeformation characteristics of the nanolithography processing of monocrystalline
copper. Moreover, the effects of process variables (tool shape, cutting speed, and ploughing depth) on the nanostructural
pattern are investigated. The simulation results revealed that the crystal orientation and ploughing direction had a significant
influence on varying the forces (cutting force, thrust force, and width-direction force); the nature of the nanodeformation
ahead of the tool; and the surface quality of the machined material. 相似文献
79.
A new LDPC decoding algorithm aided by segmented cyclic redundancy checks for magnetic recording channels 总被引:2,自引:0,他引:2
Yeong-Hyeon Kwon Mi-Kyung Oh Dong-Jo Park 《IEEE transactions on magnetics》2005,41(7):2318-2320
We introduce a new low-density parity-check (LDPC) decoding algorithm that exploits the cyclic redundancy check (CRC) information of data segments. By using the error detection property of the CRC, we can successively decode data segments of a codeword corrupted by random errors and erasures. The key idea is that the messages from the variable nodes with correct checksum are fixed to deterministic log likelihood ratio values during LDPC iterative decoding. This approach improves the decoding speed and codeword error rate without significant modification of the LDPC decoding structure. Moreover, the CRC is also used for an early stopping criterion of LDPC decoding. Simulation results verify our claims. 相似文献
80.
J. H. Song I. K. Park Y. S. Shin J. H. Kim S. W. Hong B. T. Min H. D. Kim 《Nuclear Engineering and Design》2003,222(1):1051-15
This paper discusses the results of steam explosion experiments using reactor material carried out under “Test for Real cOrium Interaction with water (TROI)” program. About 4–9 kg of corium melt jet is delivered into a sub-cooled water pool at atmospheric pressure. Spontaneous steam explosions are observed in four tests among six tests. The dynamic pressure, dynamic load, and morphology of debris clearly indicate the cases with steam explosion. The initial conditions and results of the experiments are discussed. 相似文献