全文获取类型
收费全文 | 13175篇 |
免费 | 1309篇 |
国内免费 | 849篇 |
专业分类
电工技术 | 2827篇 |
技术理论 | 1篇 |
综合类 | 1545篇 |
化学工业 | 551篇 |
金属工艺 | 517篇 |
机械仪表 | 850篇 |
建筑科学 | 1360篇 |
矿业工程 | 591篇 |
能源动力 | 282篇 |
轻工业 | 353篇 |
水利工程 | 413篇 |
石油天然气 | 478篇 |
武器工业 | 129篇 |
无线电 | 2293篇 |
一般工业技术 | 1140篇 |
冶金工业 | 385篇 |
原子能技术 | 214篇 |
自动化技术 | 1404篇 |
出版年
2024年 | 53篇 |
2023年 | 109篇 |
2022年 | 253篇 |
2021年 | 333篇 |
2020年 | 349篇 |
2019年 | 251篇 |
2018年 | 252篇 |
2017年 | 354篇 |
2016年 | 439篇 |
2015年 | 436篇 |
2014年 | 833篇 |
2013年 | 767篇 |
2012年 | 972篇 |
2011年 | 1068篇 |
2010年 | 762篇 |
2009年 | 845篇 |
2008年 | 869篇 |
2007年 | 1012篇 |
2006年 | 872篇 |
2005年 | 773篇 |
2004年 | 597篇 |
2003年 | 563篇 |
2002年 | 504篇 |
2001年 | 379篇 |
2000年 | 326篇 |
1999年 | 248篇 |
1998年 | 191篇 |
1997年 | 170篇 |
1996年 | 164篇 |
1995年 | 135篇 |
1994年 | 109篇 |
1993年 | 73篇 |
1992年 | 68篇 |
1991年 | 53篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1966年 | 1篇 |
1962年 | 1篇 |
1959年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
通过引入归一化脉宽P和相对脉冲展宽因子q,提出了一个适用于IM/DD系统中各种眼图恶化量x和归一化脉宽P的色散限制改进公式。通过与其它理论的比较、计算机仿真和对实验数据的分析,验证了该公式的正确性,并给出了其它结果的限制条件。研究表明:当眼图恶化量x为1dB左右时,对2.5Gb/;外调制信号(α=0)而言,非色散位移光纤IM/DD系统的色散因子γ约等于0.79,所对应的系统再生中继距离约为900余公里。 相似文献
12.
K.W. Allen S.M. Smith W.C. Wake A.O. van Raalte 《International Journal of Adhesion and Adhesives》1985,5(1):23-32
The effect of cyclic stressing on the strength of single lap adhesive joints has been studied and a considerable reduction in strength observed when the maximum stress exceeds about 40% of the ultimate tensile strength, but whether or not a true endurance limit exists is not proven. Fallacies are shown in some of the techniques which have been proposed for studying the fatigue behaviour of adhesive joints. 相似文献
13.
An incremental iterative process based on direct energy minimization is presented for a limit analysis of nonlinear elastic lateral displacements and twists of reinforced and prestressed beams. Problems encountered with the constitutive relations are discussed and two possible material models are presented. 相似文献
14.
David Mills 《Granular Matter》2004,6(2-3):173-177
For fine powdered materials, capable of being conveyed in dense phase, a conveying region exists in which instability in flow and pipeline blockage can occur if the pressure gradient available is insufficient to maintain a minimum value of solids loading ratio. A reduction in material flow rate can also lead to pipeline blockage in this region. Conveying trials under-taken with cement are used to illustrate the nature of the problem. 相似文献
15.
Yuji Oie Tatsuya Suda Masayuki Murata Hideo Miyahara 《International Journal of Satellite Communications and Networking》1991,9(5):285-303
One of the most promising approaches for high speed networks for integrated service applications is fast packet switching, or ATM (asynchronous transfer mode). ATM can be characterized by very high speed transmission links and simple, hard-wired protocols within a network. To match the transmission speed of the network links, and to minimize the overhead due to the processing of network protocols, the switching of cells is done in hardware switching fabrics in ATM networks. A number of designs have been proposed for implementing ATM switches. Although many differences exist among the proposals, the vast majority of them are based on self-routeing multistage interconnection networks. This is because of the desirable features of multi-stage interconnection networks such as self-routeing capability and suitability for VLSI implementation. Existing ATM switch architectures can be classified into two major classes: blocking switches, where blockings of cells may occur within a switch when more than one cell contends for the same internal link, and non-blocking switches, where no internal blocking occurs. A large number of techniques have also been proposed to improve the performance of blocking and non-blocking switches. In this paper, we present an extensive survey of the existing proposals for ATM switch architectures, focusing on their performance issues. 相似文献
16.
The strength of case-hardened parts under cyclic loading can be determined in an experimental manner, but this can produce
a large amount of costs due to the expenditure of material and testing time. Therefore, a calculation method is developed,
that strongly reduces the number of experiments. The presented model is based on Weibull's weakest-link concept and allows
to compute the survival probability of a case-hardened part which is loaded close to the fatigue limit. The essential quantities
in this model are the distribution of Vicker's hardness of the material, the exponents of the Weibull distribution of the
volume and the surface, the residual stress state, the surface roughness and the surface oxidation depth. By integrating the
survival probabilities of the surface and the volume, the survival probability of the entire specimen or part can be calculated,
which allows to compute the fatigue limit. The necessary parameters have to be determined from reference specimens. The model
is successfully examined by comparing experimental and calculated results of smooth and notched case-hardened specimens under
alternating torsion, rotating bending, repeated tension and tension-compression.
Received 20 August 2001 / Accepted 11 November 2001 相似文献
17.
TOP开关电源的设计与制作 总被引:3,自引:0,他引:3
利用TOP开关器件设计了一种高精度,输出电压可调的开关电源,并介绍了制作方法。 相似文献
18.
19.
Design optimization of 3D steel structures: Genetic algorithms vs. classical techniques 总被引:1,自引:0,他引:1
María Belén Prendes Gero Antonio Bello García 《Journal of Constructional Steel Research》2006,62(12):1303-1309
In this paper an elitist genetic algorithm (GA) developed by the authors is compared with common commercial solutions for complex structural optimization. After its prior validation on two-dimensional (2D) structures, the GA was tuned and improved in order to obtain structural elements with minimum weights that satisfy the ultimate limit states of the applicable building code. Subsequently, the same spatial structures were optimized using a commercial structural analysis program. Finally, the cost and weight improvements obtained using the GA, although at a higher computational cost, are discussed. 相似文献
20.
针对贵溪冶炼厂建安公司新紫杂铜打包机不良状况及存在的问题进行了改进 ,对整台机组的总配电箱、液压管网、设备的保护接地及建筑主体框架也进行接地。 相似文献