全文获取类型
收费全文 | 34086篇 |
免费 | 3368篇 |
国内免费 | 1856篇 |
专业分类
电工技术 | 1333篇 |
综合类 | 4265篇 |
化学工业 | 3329篇 |
金属工艺 | 3051篇 |
机械仪表 | 4566篇 |
建筑科学 | 7744篇 |
矿业工程 | 1270篇 |
能源动力 | 578篇 |
轻工业 | 1016篇 |
水利工程 | 1388篇 |
石油天然气 | 1197篇 |
武器工业 | 405篇 |
无线电 | 1137篇 |
一般工业技术 | 4938篇 |
冶金工业 | 1257篇 |
原子能技术 | 221篇 |
自动化技术 | 1615篇 |
出版年
2024年 | 144篇 |
2023年 | 412篇 |
2022年 | 793篇 |
2021年 | 982篇 |
2020年 | 1079篇 |
2019年 | 1006篇 |
2018年 | 1016篇 |
2017年 | 1273篇 |
2016年 | 1357篇 |
2015年 | 1398篇 |
2014年 | 2033篇 |
2013年 | 2175篇 |
2012年 | 2289篇 |
2011年 | 2560篇 |
2010年 | 1837篇 |
2009年 | 1931篇 |
2008年 | 1902篇 |
2007年 | 2251篇 |
2006年 | 2105篇 |
2005年 | 1674篇 |
2004年 | 1415篇 |
2003年 | 1221篇 |
2002年 | 1043篇 |
2001年 | 900篇 |
2000年 | 811篇 |
1999年 | 737篇 |
1998年 | 510篇 |
1997年 | 511篇 |
1996年 | 400篇 |
1995年 | 352篇 |
1994年 | 271篇 |
1993年 | 193篇 |
1992年 | 170篇 |
1991年 | 121篇 |
1990年 | 86篇 |
1989年 | 101篇 |
1988年 | 72篇 |
1987年 | 52篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
G. Ranzi M. A. Bradford B. Uy 《International journal for numerical methods in engineering》2004,61(5):657-672
The use of the conventional semi-analytical stiffness method in finite element analysis, in which interpolation polynomials are used to develop the stiffness relationships, leads to problems of curvature locking when beam-type elements are developed for composite members with partial interaction between the materials of which it is comprised. The curvature locking phenomenon that occurs for composite steel–concrete members is quite well reported, and the general approach to minimizing the undesirable ramifications of curvature locking has been to use higher-order polynomials with increasing numbers of internal nodes. This paper presents an alternate formulation based on a direct stiffness approach rather than starting from pre-defined interpolation polynomials, and which does not possess the undesirable locking characteristics. The formulation is based on a more general approach for a bi-material composite flexural member, whose constituent materials are joined by elastic shear connection so as to provide partial interaction. The stiffness relationships are derived, and these are applied to a simply supported and a continuous steel–concrete composite beam to demonstrate the efficacy of the method, and in particular its ability to model accurately both very flexible and very stiff shear connection that causes difficulties when implemented in competitive semi-analytical algorithms. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
12.
You-Yi Xia 《Materials Letters》2007,61(21):4321-4324
This paper describes a solution-phase approach to the synthesis of selenium nanoparticles by reducing selenious acid solution with ascorbic acid in the presence of silk fibroin. The monodispersed spherical selenium colloid particles obtained were very stable in silk fibroin solution and characterized by Atomic force microscopy and X-ray techniques. The influences of temperature and ultrasonication on the morphology of selenium nanoparticles were also discussed. The experiments showed that the selenium nanoparticles with various morphologies could be obtained under different temperatures and the appropriate ultrasonication time was 60 min. This result indicated that the silk fibroin molecules intimately associated with the surface of the selenium particles and controlled the growth particles. 相似文献
13.
对弹性杆与水下壳体接触冲击问题进行了研究,用有限元法模拟壳体,边界无法模拟无限域流体,通过温面上的耦合条件进行联立求解,文中给出了典型算例,并进行了有关讨论。 相似文献
14.
15.
This paper describes a brushless dc motor system without position or speed sensor. The brushless motor consists of a permanent magnet synchronous motor and a voltage-source inverter capable of controlling the amplitude and frequency of voltage. The rectangular-shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage similarly to chopper control of dc motors. In this paper, two sensorless position detecting methods, i.e., an “indirect method” suited for the lower-speed range and a “direct method” suited for the higher-speed range are proposed. The combination of the two makes it possible to detect the rotor position over a wide-speed range. Furthermore, a speed-sen-sorless PLL control is proposed in applying the principle of the direct method. Experimental results obtained from a prototype brushless dc motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor also is discussed because it is impossible to detect the rotor position at a standstill. 相似文献
16.
17.
高层建筑结构设计特点与剪力墙设计 总被引:6,自引:0,他引:6
围绕高层建筑结构,总结了高层建筑结构设计的特点,提出了剪力墙设计的几个问题,以及高层建筑结构分析和各种体系相对应的方法。 相似文献
18.
19.
从退火态原位TiCp/Fe复合材料的切削力和切屑形状方面分析了其切削性能。研究结果表明其切削力及切削力的波动范围都小于铸态45钢,其切削性能比45钢好。TiCp/Fe复合材料的切屑为C形屑、长紧卷屑和发条状卷屑,在机加工中,产生这几种切屑是比较理想的。从切屑方面看,TiCp/Fe复合材料的切削性能较好。 相似文献
20.
Shunsuke Ohashi 《Electrical Engineering in Japan》2005,150(1):71-77
Magnetic bearing using pinning force of a permanent magnet and a high‐temperature superconductor has been developed. Additional permanent magnet is introduced to increase the levitation force of the magnetic bearing. In this hybrid magnetic bearing system, levitation force is mainly given by the repulsive force of the permanent magnets, and stability for the lateral direction is given by pinning force of the superconductor. The experimental device is developed. A ring‐type superconductor and a bulk one are examined. Levitation characteristics of the hybrid magnetic bearing are measured. The bulk superconductor shows better characteristics of both levitation and lateral stability than the ring one. Levitation force of the hybrid system becomes about twice as large as that of the nonhybrid one. Although, the repulsive force of the permanent magnet decreases the lateral stability of the system, its influence becomes small by choosing an adequate position of the permanent magnets and the superconductor. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 71–77, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10350 相似文献