全文获取类型
收费全文 | 6107篇 |
免费 | 299篇 |
国内免费 | 242篇 |
专业分类
电工技术 | 198篇 |
综合类 | 267篇 |
化学工业 | 493篇 |
金属工艺 | 397篇 |
机械仪表 | 1058篇 |
建筑科学 | 144篇 |
矿业工程 | 113篇 |
能源动力 | 198篇 |
轻工业 | 144篇 |
水利工程 | 31篇 |
石油天然气 | 131篇 |
武器工业 | 82篇 |
无线电 | 950篇 |
一般工业技术 | 504篇 |
冶金工业 | 125篇 |
原子能技术 | 140篇 |
自动化技术 | 1673篇 |
出版年
2024年 | 7篇 |
2023年 | 34篇 |
2022年 | 72篇 |
2021年 | 99篇 |
2020年 | 108篇 |
2019年 | 84篇 |
2018年 | 110篇 |
2017年 | 97篇 |
2016年 | 130篇 |
2015年 | 153篇 |
2014年 | 274篇 |
2013年 | 289篇 |
2012年 | 354篇 |
2011年 | 410篇 |
2010年 | 317篇 |
2009年 | 338篇 |
2008年 | 281篇 |
2007年 | 400篇 |
2006年 | 357篇 |
2005年 | 327篇 |
2004年 | 302篇 |
2003年 | 320篇 |
2002年 | 245篇 |
2001年 | 187篇 |
2000年 | 180篇 |
1999年 | 206篇 |
1998年 | 160篇 |
1997年 | 111篇 |
1996年 | 131篇 |
1995年 | 108篇 |
1994年 | 106篇 |
1993年 | 71篇 |
1992年 | 44篇 |
1991年 | 38篇 |
1990年 | 34篇 |
1989年 | 37篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有6648条查询结果,搜索用时 187 毫秒
101.
An irregular lattice model is used to simulate concrete fracture behavior under dynamic loadings. The numerical approach is based on rigid-body-spring networks, in which a visco-plastic damage model is applied to describe the rate dependency. A direct tensile test is simulated at various strain rates, and the dynamic strength increase is obtained in terms of dynamic increase factor (DIF). The DIFs are compared with a previous experimental and empirical study to calibrate the visco-plastic parameters. Next, a three-point-bending test is conducted numerically under impact and slow loadings, where the mixed-mode fracture is set up with a notch offset from the midspan. The rate-sensitive failure features are shown at the two different loading rates, and the rate effect on the failure mechanism is related with the peak load in the loading history. This study provides qualitative and quantitative understandings of the rate dependent failure behaviors in concrete. 相似文献
102.
主要研究利用图像低位平面数据位的运算来减小对载密图像修改的信息隐藏算法.在嵌入信息时对秘密信息进行连续多次随机变换的同时与载体信息进行位运算,以此求出对载体图像修改量最小的嵌入方式.从而实现在相同嵌入量的条件下尽量减少对载体图像的修改,提高了载密图像的质量.实验结果表明,该算法能有效地减少载体图像的失真,在嵌入大量信息... 相似文献
103.
104.
J.M. Linares G. Goch A. Forbes J.M. Sprauel A. Clément F. Haertig W. Gao 《CIRP Annals》2018,67(2):815-838
In contrast to measurements of the dimensions of machined parts realized by machine tools and characterized by CMMs, software results are not fully traceable and certified. Indeed, a computer is not a perfect machine and binary encoding of real numbers leads to rounding of successive intermediate calculations that may lead to globally false results. This is the case for poor implementations and poorly conditioned algorithms. Therefore, accurate geometric modelling and implementations will be detailed. Based on the works of National Metrology Institutes, the problem of software traceability will also be discussed. Some prospects for this complex task will finally be suggested. 相似文献
105.
针对获各琦铜矿铜Ⅱ矿体赋存特点为沉积变质矿床,具有层位控矿及岩性控矿的特点,铜矿体赋存在石英岩中,并由多条矿体组成,存在较大的选矿难度。笔者通过不同药剂制度下进行了选矿指标必选,获得了较优的选矿指标,可提高Cu回收率3%-5%。 相似文献
106.
一种降低微震定位误差的偏振分析方法 总被引:1,自引:0,他引:1
目前微地震监测技术已成为地球物理界的热门技术之一。对于微地震震源定位,主流的初至时差分析方法由于方程组局部极值、初至拾取困难以及波速恒定假设等问题,极易产生超定或欠定的误差,而且未考虑有效数据不足的情况。为此,利用所测量的检波器姿态信息,计算出参考校正角,并将垂直、径向和切向分量数据校正为标准的三分量数据,以此提取同型波来计算偏振角,所获取的偏振角数据一方面可进行定位求解,另一方面也可对三分量数据进行进一步的校正,以提高时差分析中初至拾取的准确性;综合偏振角极化分析与初至时差分析两种方法建立了最小误差优化模型,实现了更为复杂地质条件下的联合定位,降低了定位误差。最后对数值模拟实验和野外实验结果进行了统计分析,结果表明:最优化联合定位方法能够大大降低定位误差且在有效数据不足的情况下仍能保证较好的定位效果,有效数据在9组以上时的定位误差小于7 m。 相似文献
107.
108.
109.
In order to minimize the transmitted power in the multi-user orthogonal frequency division multiplexing (OFDM) system, a scheme combining the improved particle swarm optimization (POS) algorithm with genetic algorithm (GA) is proposed to optimize the sub-carriers and bits allocation. In the algorithm, a random velocity between the maximum and minimum particle velocity is used as the updating velocity instead of maximum or minimum velocity when the updated particle velocity is higher than the maximum particle velocity or lower than the minimum particle velocity. Then, the convergence population is used as the initial population of the genetic algorithm to optimize the sub-carriers and bits allocation further. Simulation results show that the transmitted power of the proposed algorithm is about 2 dB to 10 dB lower than that of the genetic algorithm, particle swarm optimization algorithm, and Zhang's algorithm. 相似文献
110.
In this paper, we propose a novel methodology to define and estimate a surrogate measure. By imposing a hypothetical disturbance to the leading vehicle, the following vehicle’s action is represented as a probabilistic causal model. After that, a tree is built to describe the eight possible conflict types under the model. The surrogate measure, named Aggregated Crash Index (ACI), is thus proposed to measure the crash risk. This index reflects the accommodability of freeway traffic state to a traffic disturbance. We further apply this measure to evaluate the crash risks in a freeway section of Pacific Motorway, Australia. The results show that the proposed indicator outperforms the three traditional crash surrogate measures (i.e., Time to Collision, Proportion of Stopping Distance, and Crash Potential Index) in representing rear-end crash risks. The applications of this measure are also discussed. 相似文献