全文获取类型
收费全文 | 115372篇 |
免费 | 14148篇 |
国内免费 | 7851篇 |
专业分类
电工技术 | 11797篇 |
技术理论 | 3篇 |
综合类 | 13059篇 |
化学工业 | 9259篇 |
金属工艺 | 8758篇 |
机械仪表 | 11302篇 |
建筑科学 | 7689篇 |
矿业工程 | 6075篇 |
能源动力 | 5864篇 |
轻工业 | 2106篇 |
水利工程 | 4218篇 |
石油天然气 | 5728篇 |
武器工业 | 3476篇 |
无线电 | 14477篇 |
一般工业技术 | 9838篇 |
冶金工业 | 3370篇 |
原子能技术 | 1626篇 |
自动化技术 | 18726篇 |
出版年
2024年 | 574篇 |
2023年 | 1690篇 |
2022年 | 3214篇 |
2021年 | 3536篇 |
2020年 | 3820篇 |
2019年 | 2799篇 |
2018年 | 2830篇 |
2017年 | 3754篇 |
2016年 | 4527篇 |
2015年 | 5059篇 |
2014年 | 7635篇 |
2013年 | 7342篇 |
2012年 | 9340篇 |
2011年 | 10158篇 |
2010年 | 7461篇 |
2009年 | 7541篇 |
2008年 | 7264篇 |
2007年 | 8908篇 |
2006年 | 7734篇 |
2005年 | 6390篇 |
2004年 | 5228篇 |
2003年 | 4147篇 |
2002年 | 3276篇 |
2001年 | 2711篇 |
2000年 | 2092篇 |
1999年 | 1669篇 |
1998年 | 1266篇 |
1997年 | 1016篇 |
1996年 | 938篇 |
1995年 | 778篇 |
1994年 | 626篇 |
1993年 | 415篇 |
1992年 | 331篇 |
1991年 | 266篇 |
1990年 | 219篇 |
1989年 | 187篇 |
1988年 | 136篇 |
1987年 | 68篇 |
1986年 | 84篇 |
1985年 | 50篇 |
1984年 | 54篇 |
1983年 | 38篇 |
1982年 | 39篇 |
1981年 | 21篇 |
1980年 | 28篇 |
1979年 | 28篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1959年 | 25篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
以重庆市甄子岩29号危岩体为研究对象,基于现场调查和分析解剖,建立UDEC离散元数值计算模型,对其演化变形过程进行模拟分析。研究表明,在巨大的自重作用下,由于基座岩体岩质软,岩体较破碎,且基座外侧为直立的陡崖,具有完整的临空面,从而使基座岩体易发生压缩流变及剪切流变,进而使危岩体存在滑移垮塌的危险。 相似文献
2.
目的研究蛋类礼盒包装结构的缓冲性能。方法以蛋类尺寸为基础,建立可发性聚乙烯(expandable polyethylene. EPE)缓冲单元结构和组合结构,进行静态仿真分析和实验验证,比较结构在形状、叠合层数、组合形式等参数变化时的载荷与位移。结果结构层数变化相同时,单元结构的极限载荷从143N增加到236 N,组合结构的极限载荷从224 N增加到476 N,均呈近线性增长。结论蛋类礼盒包装中,组合结构的承载能力优于单元结构,通过单元结构的组合,可满足不同蛋类的包装要求。 相似文献
3.
4.
大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。 相似文献
5.
现今国内的数字集群网络发展存在局限性、差异性,还远没有达到“网”状分布的程度,因此,共网数字集群发展空间巨大、前景广阔。通过列举共网数字集群系统在龙嘉国际机场和长春雷锋车队的成功应用案例,探讨了我国共网数字集群系统应用的可行性和必要性。 相似文献
6.
7.
Numerical simulation, using SILVACO-TCAD, is carried out to explain experimentally observed effects of different types of deep levels on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates. Two diodes were grown on (311)A and (211)A oriented GaAs substrates using Molecular Beam Epitaxy (MBE). Although, deep levels were observed in both structures, the measured capacitance–voltage characteristics show a negative differential capacitance (NDC) for the (311)A diodes, while the (211)A devices display a usual behaviour. The NDC is related to the nature and spatial distribution of the deep levels, which are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole traps) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation, which calculates the capacitance–voltage characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behaviour. 相似文献
8.
ABSTRACT The concept of digital game-based learning (DGBL) evolves rapidly together with technological enhancements of virtual reality (VR) and smart phones. However, the mental workload (MWL) that VR-training applications demand and motivational qualities originating from user experience (UX) should be identified in order to create effective and enjoyable training/learning challenges that fit with individual users’ capabilities. This study examined the effects of reality-based interaction (RBI) and VR on measures of student motivation and MWL, in a mental arithmetic game for secondary school pupils. In a randomised controlled trial with sixty school children, a mental arithmetic game was tested with three different interaction and two different presentation methods – VR RBI, VR head-mounted-display tapping and tablet flick-gesture. Results found a significant effect of RBI on MWL but no differences in enjoyment of training were found between VR-experience and tablet training-experience. In fact, adding the gaming-context to the mental arithmetic task created an enjoyable, motivating experience regardless of presentation or interaction-style. 相似文献
9.
Tatsuro Tanaka Yoshifumi Maeda Shinji Yamamoto Toru Iwao 《Electrical Engineering in Japan》2019,207(1):15-23
The arc welding has been used in various welding methods because it is inexpensive and high in strength after welding. However, it is a problem that accidents such as collapse of the bridge occur because of the welding defects. The welding of low cost and high productivity is required without the welding defects. The pulsed TIG welding is inexpensive and capable of high‐quality welding. The electromagnetic force contributing to penetration changes because the transient response of arc temperature and iron vapor generated from anode occurs. However, the analysis of pulsed TIG welding with metal vapor has been elucidated only metal vapor concentration near anode with transient phenomenon and heat flux. Thus, the theoretical elucidation of penetration depth with control factor has not been researched. In this paper, the contribution of metal vapor mass at the periphery part of pulsed arc to the electromagnetic force in the weld pool is elucidated. As a result, the iron vapor mass at periphery part decreased with increasing the frequency. The iron vapor was stagnated at axial center within one cycle. The electromagnetic force to the penetration depth direction in weld pool increased at axial center. Therefore, the metal vapor mass at periphery part plays an important role for the electromagnetic force increment at axial center. 相似文献
10.
Paul-Baptiste Rubio François Louf Ludovic Chamoin 《International journal for numerical methods in engineering》2019,120(4):447-472
The motivation of this work is to address real-time sequential inference of parameters with a full Bayesian formulation. First, the proper generalized decomposition (PGD) is used to reduce the computational evaluation of the posterior density in the online phase. Second, Transport Map sampling is used to build a deterministic coupling between a reference measure and the posterior measure. The determination of the transport maps involves the solution of a minimization problem. As the PGD model is quasi-analytical and under a variable separation form, the use of gradient and Hessian information speeds up the minimization algorithm. Eventually, uncertainty quantification on outputs of interest of the model can be easily performed due to the global feature of the PGD solution over all coordinate domains. Numerical examples highlight the performance of the method. 相似文献