全文获取类型
收费全文 | 4097篇 |
免费 | 633篇 |
国内免费 | 259篇 |
专业分类
电工技术 | 342篇 |
综合类 | 229篇 |
化学工业 | 663篇 |
金属工艺 | 274篇 |
机械仪表 | 250篇 |
建筑科学 | 315篇 |
矿业工程 | 145篇 |
能源动力 | 115篇 |
轻工业 | 292篇 |
水利工程 | 90篇 |
石油天然气 | 256篇 |
武器工业 | 44篇 |
无线电 | 565篇 |
一般工业技术 | 493篇 |
冶金工业 | 196篇 |
原子能技术 | 94篇 |
自动化技术 | 626篇 |
出版年
2024年 | 46篇 |
2023年 | 97篇 |
2022年 | 250篇 |
2021年 | 315篇 |
2020年 | 236篇 |
2019年 | 163篇 |
2018年 | 182篇 |
2017年 | 214篇 |
2016年 | 180篇 |
2015年 | 215篇 |
2014年 | 279篇 |
2013年 | 303篇 |
2012年 | 294篇 |
2011年 | 333篇 |
2010年 | 268篇 |
2009年 | 208篇 |
2008年 | 200篇 |
2007年 | 200篇 |
2006年 | 211篇 |
2005年 | 137篇 |
2004年 | 100篇 |
2003年 | 74篇 |
2002年 | 69篇 |
2001年 | 49篇 |
2000年 | 48篇 |
1999年 | 67篇 |
1998年 | 34篇 |
1997年 | 36篇 |
1996年 | 45篇 |
1995年 | 33篇 |
1994年 | 26篇 |
1993年 | 30篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有4989条查询结果,搜索用时 31 毫秒
91.
城市发展更新的加快,使我国历史文化名城遭受不同程度的破坏。通过比较国内外有关的实践经验,作者认为应将历史街区作为保护的重点。并力图探索一条如何在传统与现代,整治与保护以及资金短缺等矛盾中实施保护的切实可行之路。 相似文献
92.
针对以ADSP-BF561芯片为核心的目标跟踪系统中显示目标运动及提示信息的需要,提出了基于ADSP-BF561的英文字符库的设计方案.该字符库中包括26个小写英文字符(a~z)、10个数字(0~9),以及“:”和空格共计38个符号.该字符库通过使用存储在ADSP-BF561的L2存储器上的数据类型为布尔型、大小为16... 相似文献
93.
多层卫星网络是卫星星座发展的一种理想组网模式,组网的关键技术在于路由协议的选取和设计。本文介绍了多层卫星网络的概况,按照不同的标准对现有多层卫星网络路由协议进行了分类,详细分析了现有的几类典型的路由协议,指出了存在的问题,并对以后的研究方向作了展望。 相似文献
94.
95.
The SCOLE model is a coupled system consisting of a flexible beam (modelled as an Euler–Bernoulli equation) with one end clamped
and the other end linked to a rigid body. Its inputs are the force and the torque acting on the rigid body. It is well-known
that the SCOLE model is not exactly controllable with L
2 input signals in the natural energy state space H
c
, because the control operator is bounded from the input space
\mathbbC2{\mathbb{C}^2} to H
c
, and hence compact. We regard the velocity and the angular velocity of the rigid body as the output signals of this system.
Using the theory of coupled linear systems (one infinite-dimensional and one finite-dimensional) developed by us recently
in another paper, we show that the SCOLE model is well-posed, regular and exactly controllable in arbitrarily short time when
using a certain smoother state space X ì Hc{\mathcal{X}\subset H^c}. 相似文献
96.
Xiaowei Yang Jie Lu Guangquan Zhang 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2010,14(7):667-680
As a new version of support vector machine (SVM), least squares SVM (LS-SVM) involves equality instead of inequality constraints and works with a least squares cost function. A well-known drawback in the LS-SVM applications is that the sparseness is lost. In this paper, we develop an adaptive pruning algorithm based on the bottom-to-top strategy, which can deal with this drawback. In the proposed algorithm, the incremental and decremental learning procedures are used alternately and a small support vector set, which can cover most of the information in the training set, can be formed adaptively. Using this set, one can construct the final classifier. In general, the number of the elements in the support vector set is much smaller than that in the training set and a sparse solution is obtained. In order to test the efficiency of the proposed algorithm, we apply it to eight UCI datasets and one benchmarking dataset. The experimental results show that the presented algorithm can obtain adaptively the sparse solutions with losing a little generalization performance for the classification problems with no-noises or noises, and its training speed is much faster than sequential minimal optimization algorithm (SMO) for the large-scale classification problems with no-noises. 相似文献
97.
基于System Generator的帧同步设计与实现 总被引:1,自引:0,他引:1
通过对帧同步系统的设计,主要包括巴克码识别器和帧同步保护的设计,大大减小了假同步和漏同步概率,从而提高了帧同步系统的性能;重点阐述采用Xilinx公司推出的快速可编程门阵列(FPGA)开发环境System Generator系统设计工具进行帧同步设计与实现的方法,并在Lyrtech SFF SDR DP(Lyrtech小型软件无线电开发平台)上进行硬件协同仿真与验证,同时给出了相应的仿真波形;仿真结果在软件无线电技术及应用方面有着重要的理论研究价值.在开发设计上可大幅度地缩短开发周期,节约成本,有着巨大的社会效益和经济效益. 相似文献
98.
Jing Zhao Weinan Wang Yinping Liu Jinming Ma Xiaowei Li Yu Du Geyu Lu Author vitae 《Sensors and actuators. B, Chemical》2011,160(1):604
Ordered mesoporous SnO2 and mesoporous Pd/SnO2 have been successfully synthesized via nanocasting method using the hexagonal mesoporous SBA-15 as template. Two different procedures, impregnation technique and direct synthesis, were utilized for the doping of Pd in the mesoporous SnO2. The results of small angle X-ray diffraction (SAXD), nitrogen adsorption–desorption and transmission electron microscopy (TEM) demonstrate that the SnO2 and Pd/SnO2 display ordered mesoporous structures and high surface areas. Wide angle X-ray diffraction (WAXD) and X-ray photoelectron spectroscopy (XPS) reveal tetragonal structure of SnO2 and the existence of Pd element. The sensing properties of mesoporous SnO2 and mesoporous Pd/SnO2 for H2 were detected. The sensor utilizing mesoporous Pd/SnO2 via direct synthesis method exhibits excellent response and recovery behavior and much higher sensitivity to H2, compared to those using mesoporous SnO2 and mesoporous Pd/SnO2 via impregnation technique. It is believed that its high gas sensing performance is derived from the large surface area, high activity and well dispersion of Pd additive, as well as high porosity, which lead to highly effective surface interaction between the target gas molecules and the surface active sites. 相似文献
99.
100.
In this paper, a MEMS-based monolithic three-axis fiber-optic acceleration sensor is proposed, consisting of three optical fiber collimators and a three-axis acceleration sensing chip. The novel acceleration sensor includes two horizontal sensing units and one vertical sensing unit integrated on a single silicon substrate. Three optical fiber collimators are on the same side of the three-axis sensing chip, thus reducing the package size and cost. In each sensing unit, the micromirror, suspended on a pair of torsion beams, has a torsional angle in response to acceleration in sensing direction. The torsion angle is monitored using fiber-optic detection technique. The sensing system operation principle has been analyzed theoretically, its mechanical performances were simulated using the FEM simulation, and its fabricated process flow was proposed. Using bulk micromachining technologies, the horizontal and the vertical sensing units were successfully fabricated. Finally the individual fabricated sensing units were packaged and tested. 相似文献