全文获取类型
收费全文 | 39996篇 |
免费 | 3724篇 |
国内免费 | 1488篇 |
学科分类
工业技术 | 45208篇 |
出版年
2024年 | 125篇 |
2023年 | 684篇 |
2022年 | 947篇 |
2021年 | 1576篇 |
2020年 | 1154篇 |
2019年 | 1154篇 |
2018年 | 1310篇 |
2017年 | 1322篇 |
2016年 | 1437篇 |
2015年 | 1508篇 |
2014年 | 1947篇 |
2013年 | 2426篇 |
2012年 | 2580篇 |
2011年 | 2973篇 |
2010年 | 2387篇 |
2009年 | 2361篇 |
2008年 | 2266篇 |
2007年 | 2046篇 |
2006年 | 1921篇 |
2005年 | 1684篇 |
2004年 | 1342篇 |
2003年 | 1366篇 |
2002年 | 1556篇 |
2001年 | 1339篇 |
2000年 | 969篇 |
1999年 | 881篇 |
1998年 | 783篇 |
1997年 | 618篇 |
1996年 | 545篇 |
1995年 | 429篇 |
1994年 | 308篇 |
1993年 | 250篇 |
1992年 | 210篇 |
1991年 | 154篇 |
1990年 | 121篇 |
1989年 | 113篇 |
1988年 | 83篇 |
1987年 | 79篇 |
1986年 | 52篇 |
1985年 | 45篇 |
1984年 | 28篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
91.
This letter investigates the scattering characteristic of the rivets on aircraft.The electric Field Integral Equation (EFIE)is used with the moment to calculate the current distribution on the surface of the rivet.With the application of Gaussian integral corresponding triangular cell,the time to fill the Z matrix is greatly reduced.Finally,the RCS of a type of rivet on aircraft is analyzed. 相似文献
92.
T.J. ChungJ.H. Park C.K. Choi D.-Y. Yoon 《International Journal of Heat and Mass Transfer》2002,45(14):3061-3064
The onset of convective instability in a fluid-saturated porous layer between the two horizontal plates heated isothermally from below has been analyzed theoretically by using propagation theory. In the analysis the thermal dispersion coefficient is assumed to be proportional to the streamwise velocity. The results show that both inertia and thermal dispersion stabilize the system. 相似文献
93.
94.
95.
96.
A hybrid finite element method/method of moments (FEM/MoM) technique is used to analyze a printed circuit board power bus structure where the source and observation points are in the near field. The FEM is used to model the lossy region between the planes of the board including the source. The MoM is used to model the region outside the planes and provide a radiation boundary condition to terminate the FEM mesh. Numerical results for a bridged power bus structure are compared with measurements. A nonphysical interior resonance of the electric field integral equation is observed. The problem can be avoided by using a hybrid technique based on a combined field integral equation 相似文献
97.
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
98.
We present a new iterative alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method. By recognizing the ADI-FDTD method as a special case of a more general iterative approach to solve the Crank-Nicolson (CN) FDTD scheme, the splitting error in ADI-FDTD can be reduced systematically. Numerical examples are used to illustrate the improved accuracy of this method. 相似文献
99.
为扩大我省工程咨询业在国外的影响,进一步加强工程咨询企业的国际合作,学习和借鉴发达国家在城市规划与建设领域的先进理念和经验,受美国、加拿大相关部门的的邀请,经省发展改革委批准,由江苏省工程咨询协会组织的业内领导及工程咨询专业技术骨干赴美国、加拿大考察团一行9人,于6月15日至27日对美国、加拿大城市规划与建设情况进行了学习考察. 相似文献
100.
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