全文获取类型
收费全文 | 117776篇 |
免费 | 11427篇 |
国内免费 | 5983篇 |
专业分类
电工技术 | 8056篇 |
技术理论 | 2篇 |
综合类 | 8370篇 |
化学工业 | 17872篇 |
金属工艺 | 6647篇 |
机械仪表 | 6984篇 |
建筑科学 | 9000篇 |
矿业工程 | 2671篇 |
能源动力 | 3487篇 |
轻工业 | 9916篇 |
水利工程 | 2517篇 |
石油天然气 | 4897篇 |
武器工业 | 1132篇 |
无线电 | 15267篇 |
一般工业技术 | 14549篇 |
冶金工业 | 5289篇 |
原子能技术 | 1505篇 |
自动化技术 | 17025篇 |
出版年
2024年 | 280篇 |
2023年 | 1925篇 |
2022年 | 3470篇 |
2021年 | 5411篇 |
2020年 | 3781篇 |
2019年 | 3132篇 |
2018年 | 3404篇 |
2017年 | 3874篇 |
2016年 | 3373篇 |
2015年 | 4928篇 |
2014年 | 6180篇 |
2013年 | 7650篇 |
2012年 | 8352篇 |
2011年 | 9181篇 |
2010年 | 8026篇 |
2009年 | 7708篇 |
2008年 | 7485篇 |
2007年 | 6976篇 |
2006年 | 6531篇 |
2005年 | 5380篇 |
2004年 | 3686篇 |
2003年 | 3026篇 |
2002年 | 3094篇 |
2001年 | 2666篇 |
2000年 | 2276篇 |
1999年 | 2177篇 |
1998年 | 1941篇 |
1997年 | 1625篇 |
1996年 | 1452篇 |
1995年 | 1238篇 |
1994年 | 971篇 |
1993年 | 794篇 |
1992年 | 618篇 |
1991年 | 484篇 |
1990年 | 390篇 |
1989年 | 310篇 |
1988年 | 257篇 |
1987年 | 184篇 |
1986年 | 162篇 |
1985年 | 135篇 |
1984年 | 97篇 |
1983年 | 69篇 |
1982年 | 68篇 |
1981年 | 61篇 |
1980年 | 62篇 |
1979年 | 41篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 54篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
2.
寒区河道凌汛灾害河势“弯道效应”的量化评估十分重要。基于分形理论提出河道横断面-纵剖面-平面多维度河势分形维数计算方法及其物理机制,并探讨黄河内蒙古段不同维度河势演变分形特征及其与凌汛灾害的关联关系。结果表明,黄河内蒙古段不同维度河势均具有多尺度自相似分形特征,且具有多年记忆周期的长程相关性;冰坝(严重性冰塞)发生频次与河道主槽弯曲分形维数呈正相关指数型函数关系,与河相系数、深泓点高程和河段平均底坡分形维数负相关,与水深-面积分形维数正相关,总体表明冰坝灾害更易发生于主槽偏移摆动大、蜿蜒曲折、河湾发育程度高的宽浅型弯曲河道,研究成果可为凌汛期冰塞冰坝灾害易发河段诊断及预测提供重要理论依据。 相似文献
3.
5.
6.
This paper investigates PID control design for a class of planar nonlinear uncertain systems in the presence of actuator saturation. Based on the bounds on the growth rates of the nonlinear uncertain function in the system model, the system is placed in a linear differential inclusion. Each vertex system of the linear differential inclusion is a linear system subject to actuator saturation. By placing the saturated PID control into a convex hull formed by the PID controller and an auxiliary linear feedback law, we establish conditions under which an ellipsoid is contractively invariant and hence is an estimate of the domain of attraction of the equilibrium point of the closed-loop system. The equilibrium point corresponds to the desired set point for the system output. Thus, the location of the equilibrium point and the size of the domain of attraction determine, respectively, the set point that the output can achieve and the range of initial conditions from which this set point can be reached. Based on these conditions, the feasible set points can be determined and the design of the PID control law that stabilizes the nonlinear uncertain system at a feasible set point with a large domain of attraction can then be formulated and solved as a constrained optimization problem with constraints in the form of linear matrix inequalities (LMIs). Application of the proposed design to a magnetic suspension system illustrates the design process and the performance of the resulting PID control law. 相似文献
7.
Applied Composite Materials - In this paper, the low-velocity impact deformation behavior of biaxial warp-knitted flexible composite was investigated. A simplified finite element model (FEM) of the... 相似文献
8.
Yixuan ZHOU Huajie WANG Yi YU Yihang CHEN Rui KE Min XU Chijie XIAO Zhanhui WANG Jiquan LI Xuru DUAN Minyou YE 《等离子体科学和技术》2021,23(7):75105-52
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel. 相似文献
9.
北极地区战略地位的提高促进了极区各种应用的快速发展,冰下水声通信成为其中一个热点问题。为了研究冰下单载波水声通信性能,在黄海冰区开展冰下试验。重点分析了内嵌锁相环的多通道判决反馈均衡(Multi-channelDecision Feedback Equalization, M-DFE)技术在冰下水声通信中抗多途时延的能力,研究比较了改进比例归一化最小均方(Improved Proportional normalized Least Mean Square, IPNLMS)算法和递归最小二乘(Recursive Least Squares,RLS)算法的均衡性能。试验结果表明IPNLMS和RLS都能克服信道多途效应带来的影响。在牺牲计算复杂度的前提下,RLS具有更好的均衡效果,M-DFE在冰下环境中能够有效消除码间干扰。 相似文献
10.
Tao Feng Mingde Tong Shuotian Yao Hejun Li Shifeng Wen Hongjiao Lin 《Journal of the European Ceramic Society》2021,41(1):158-166
Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface. 相似文献