全文获取类型
收费全文 | 32977篇 |
免费 | 4748篇 |
国内免费 | 2913篇 |
专业分类
电工技术 | 7639篇 |
综合类 | 3782篇 |
化学工业 | 1746篇 |
金属工艺 | 591篇 |
机械仪表 | 2104篇 |
建筑科学 | 3282篇 |
矿业工程 | 825篇 |
能源动力 | 1017篇 |
轻工业 | 523篇 |
水利工程 | 930篇 |
石油天然气 | 1037篇 |
武器工业 | 315篇 |
无线电 | 3570篇 |
一般工业技术 | 1888篇 |
冶金工业 | 666篇 |
原子能技术 | 168篇 |
自动化技术 | 10555篇 |
出版年
2024年 | 78篇 |
2023年 | 460篇 |
2022年 | 911篇 |
2021年 | 1060篇 |
2020年 | 1134篇 |
2019年 | 1041篇 |
2018年 | 914篇 |
2017年 | 1255篇 |
2016年 | 1310篇 |
2015年 | 1569篇 |
2014年 | 2275篇 |
2013年 | 2031篇 |
2012年 | 2569篇 |
2011年 | 2619篇 |
2010年 | 2040篇 |
2009年 | 2166篇 |
2008年 | 2111篇 |
2007年 | 2452篇 |
2006年 | 2014篇 |
2005年 | 1763篇 |
2004年 | 1600篇 |
2003年 | 1290篇 |
2002年 | 1068篇 |
2001年 | 879篇 |
2000年 | 715篇 |
1999年 | 635篇 |
1998年 | 493篇 |
1997年 | 376篇 |
1996年 | 342篇 |
1995年 | 313篇 |
1994年 | 237篇 |
1993年 | 193篇 |
1992年 | 138篇 |
1991年 | 108篇 |
1990年 | 83篇 |
1989年 | 83篇 |
1988年 | 61篇 |
1987年 | 47篇 |
1986年 | 35篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 24篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1962年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
1.
为了监测绕组变压器的静态应力场和发生短路等故障时的动态应力变化,设计了一种用于电气设备状态监测的新式FBG传感器。该传感器由聚醚醚酮材料封装的FBG构成,通过内部圆锥形空腔结构实现将轴向应力集中于FBG敏感位置。通过仿真对不同压力强度下传感器结构的应力场部分及形变趋势进行了计算与分析,论证了设计的合理性。实验分别对静态载荷和动态冲击进行测试,结果显示,在静态压载测试中,当100 N相似文献
2.
3.
A Pitot tube is a popular device used for the measurements of flow fields. To control the accuracy of the Pitot tube coefficient, the international standard organization (ISO), the American Society for Testing and Materials (ASTM), and the Japanese Industrial Standards (JIS) issued guidelines that recommended the shape and working conditions of these devices. However, many Pitot tubes on the market do not follow these guidelines. In the present study, various types of Pitot tubes in the market were tested at the National Metrology Institute of Japan (NMIJ) to determine the effects of the geometry and flow characteristics. The results revealed certain limitations in the existing ISO and JIS standards, specifically with regard to the recommended design parameters of the AMCA Pitot tube, the reference coefficient value for the JIS Pitot tube, and the redefinition and limitation of Reynolds numbers pertaining to Pitot tube working conditions. 相似文献
4.
Edge Computing is one of the radically evolving systems through generations as it is able to effectively meet the data saving standards of consumers, providers and the workers. Requisition for Edge Computing based items have been increasing tremendously. Apart from the advantages it holds, there remain lots of objections and restrictions, which hinders it from accomplishing the need of consumers all around the world. Some of the limitations are constraints on computing and hardware, functions and accessibility, remote administration and connectivity. There is also a backlog in security due to its inability to create a trust between devices involved in encryption and decryption. This is because security of data greatly depends upon faster encryption and decryption in order to transfer it. In addition, its devices are considerably exposed to side channel attacks, including Power Analysis attacks that are capable of overturning the process. Constrained space and the ability of it is one of the most challenging tasks. To prevail over from this issue we are proposing a Cryptographic Lightweight Encryption Algorithm with Dimensionality Reduction in Edge Computing. The t-Distributed Stochastic Neighbor Embedding is one of the efficient dimensionality reduction technique that greatly decreases the size of the non-linear data. The three dimensional image data obtained from the system, which are connected with it, are dimensionally reduced, and then lightweight encryption algorithm is employed. Hence, the security backlog can be solved effectively using this method. 相似文献
5.
This paper presents a control design for the one‐phase Stefan problem under actuator delay via a backstepping method. The Stefan problem represents a liquid‐solid phase change phenomenon which describes the time evolution of a material's temperature profile and the interface position. The actuator delay is modeled by a first‐order hyperbolic partial differential equation (PDE), resulting in a cascaded transport‐diffusion PDE system defined on a time‐varying spatial domain described by an ordinary differential equation (ODE). Two nonlinear backstepping transformations are utilized for the control design. The setpoint restriction is given to guarantee a physical constraint on the proposed controller for the melting process. This constraint ensures the exponential convergence of the moving interface to a setpoint and the exponential stability of the temperature equilibrium profile and the delayed controller in the norm. Furthermore, robustness analysis with respect to the delay mismatch between the plant and the controller is studied, which provides analogous results to the exact compensation by restricting the control gain. 相似文献
6.
This reported paper presents the design and analysis of wideband nature inspired planar antenna of 46 × 18 × 1.6 mm3 size, designed using FR4 (Flame Retardant) substrate. The antenna patch is delineated from the growth pattern of sneezewort plant with supplementary notion of golden ratio in branching and branch width. The total number of branches in each stage follows the Fibonacci series and the branch width is calculated from the golden ratio concept. Starting from one feed line and two branches, the maximum numbers of branches are increased to 20. There has been significant enhancement in the radiation performance of proposed geometry by increasing the number of branches to 21 and by modifying ground with T‐shaped slot. The antenna covers wide impedance bandwidth of 8.2 to 16.5 GHz by possessing stable radiation characteristics. 相似文献
7.
通过解析矿用提升机制动器制动的工作原理,分析影响安全制动的因素,可以在工作中尽快找出影响安全制动的原因,并采用相应的解决方法使提升机在有效制动范围内运行。 相似文献
8.
Chung-Hao Chiang Hsiu-Hsien Su Ying-Chien Fang Sheng-Yuan Chu 《Ceramics International》2018,44(6):6278-6284
In this paper, Ca6BaP4O17:Sm3+ and Li+ co-doped Ca6BaP4O17:Sm3+ phosphors were synthesized in air and argon atmospheres using a solid-state reaction method. The phosphor morphologies and crystal structure were studied using scanning electron microscopy and X-ray diffraction, respectively. The emission and absorption characteristics were investigated using photoluminescence emission spectroscopy and diffuse reflectance spectroscopy. The surface states and composition of phosphor were investigated using X-ray photoelectron spectroscopy. The emission integrated intensities of the phosphors sintered in an argon atmosphere increased 3.5 fold than the ones sintered in air atmosphere, with Li+ ions becoming embedded in the lattice of the Ca6BaP4O17:Sm3+ phosphor. This occurs because there are fewer defect/oxygen vacancies and less of the secondary phase forms, leading to better Sm3+ emission. The results suggest that sintering a mixture of the raw materials of a phosphor in an argon atmosphere is a good approach for synthesizing Ca6BaP4O17:Sm3+ phosphor powders. The color purity and CIE values of an optimized phosphor sample sintered in an argon atmosphere with an Li+ ion compensator were calculated to be ~ 99.6% and (0.612,0.386) in the orange–red region under 405-nm excitation, respectively. Moreover, the solid solubility of Sm3+ ions in the Ca6BaP4O17 host can be enhanced by using an argon atmosphere in the synthesis process. 相似文献
9.
本文建立了PC结构施工全过程的BIM模型及有限元分析模型,对施工过程进行数值模拟与动态、静态监测,对装配式结构进行了结构性能评价,为结构可视化施工监测提供了技术支持。 相似文献
10.
针对实体产业对科技资源的服务需求,以服务效应作为资源文本分类标准,提出一种基于多元神经网络融合的分布式资源空间文本分类模型。设计了包含词嵌入层、卷积层、双向门控循环单元层、注意力机制层和softmax层的多元神经网络通路;在此基础上采用基于需求—效应—资源分类策略,完成了从定性科技资源需求到定量资源服务效应求解,再到定性科技资源输出的映射变换,重点解决了分布式科技资源局部和全局语义特征形式多样、文本长距离依赖特征显著、重要资源信息难以准确识别的问题,进而从分布式科技资源空间中快速准确地获取效应知识,提升实体产业产品研发效率和创新能力;通过万方专利科技资源数据集验证了所提方法的可行性和有效性,为更加全面地挖掘资源文本特征和按需服务实体产业提供了一种新的思路和手段。 相似文献