全文获取类型
收费全文 | 22719篇 |
免费 | 2089篇 |
国内免费 | 1327篇 |
专业分类
电工技术 | 1902篇 |
技术理论 | 3篇 |
综合类 | 5568篇 |
化学工业 | 1026篇 |
金属工艺 | 558篇 |
机械仪表 | 1296篇 |
建筑科学 | 1087篇 |
矿业工程 | 268篇 |
能源动力 | 356篇 |
轻工业 | 470篇 |
水利工程 | 302篇 |
石油天然气 | 262篇 |
武器工业 | 168篇 |
无线电 | 2642篇 |
一般工业技术 | 1778篇 |
冶金工业 | 466篇 |
原子能技术 | 132篇 |
自动化技术 | 7851篇 |
出版年
2024年 | 24篇 |
2023年 | 172篇 |
2022年 | 241篇 |
2021年 | 389篇 |
2020年 | 554篇 |
2019年 | 490篇 |
2018年 | 460篇 |
2017年 | 521篇 |
2016年 | 666篇 |
2015年 | 754篇 |
2014年 | 1381篇 |
2013年 | 1461篇 |
2012年 | 1588篇 |
2011年 | 1705篇 |
2010年 | 1336篇 |
2009年 | 1523篇 |
2008年 | 1455篇 |
2007年 | 1588篇 |
2006年 | 1441篇 |
2005年 | 1284篇 |
2004年 | 1093篇 |
2003年 | 1031篇 |
2002年 | 837篇 |
2001年 | 693篇 |
2000年 | 580篇 |
1999年 | 456篇 |
1998年 | 377篇 |
1997年 | 369篇 |
1996年 | 301篇 |
1995年 | 248篇 |
1994年 | 233篇 |
1993年 | 160篇 |
1992年 | 149篇 |
1991年 | 115篇 |
1990年 | 75篇 |
1989年 | 64篇 |
1988年 | 58篇 |
1987年 | 33篇 |
1986年 | 34篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1964年 | 13篇 |
1963年 | 6篇 |
1958年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Spinels with the generic chemical formula AB2O4 have potential applications in nuclear energy and batteries. In both cases, their functionality is related to mass transport through the crystal. Here, using long-time atomistic simulations, we examine the impact of the cation structure on interstitial transport in two spinel chemistries, inverse MgGa2O4 and double MgAlGaO4. We emphasize two aspects of the transport properties: the unit mechanisms that are described by individual barriers, for which we introduce pole-figure-like plots, and the aggregate behavior of those unit mechanisms. Compared to previous work on normal spinels, we find that inversion significantly reduces the rate of interstitial transport in these structures and has an impact on the stability of defects as they move through the lattice. In particular, B cation interstitials are found to be kinetically stable only in the inverse MgGa2O4. These results provide new insight into relationship between structure, chemistry, and transport in spinels. 相似文献
2.
Jiewei Chen Ting Zhang Jingli Wang Ning Zhang Wei Ji Shuyun Zhou Yang Chai 《Advanced functional materials》2021,31(40):2104192
Charge-based field-effect transistors (FETs) greatly suffer from unavoidable carrier scattering and heat dissipation. Analogous to valley degree of freedom in semiconductors, chiral anomaly current in Weyl/Dirac semimetals is theoretically predicted to be nearly nondissipative over long distances, but still lacks experimental ways to efficiently control its transport. Here, field-effect chirality devices are demonstrated with Dirac semimetal PtSe2, in which its Fermi level is close to the Dirac point in the conduction band owing to intrinsic defects. The chiral anomaly is further corroborated by the planar Hall effect and nonlocal valley transport measurement, which can also be effectively modulated by external fields, showing robust nonlocal valley transport with micrometer diffusion length. Similar to charge-based FETs, the chiral conductivity in PtSe2 devices can be modulated by electrostatic gating with an ON/OFF ratio of more than 103. Basic logic functions in the devices are also demonstrated with electric and magnetic fields as input signals. 相似文献
3.
Mingqiang Cheng Erding Zhao Fangjian Jiang Xiaodong Jiang Ze Fang Feng Li Wanneng Ye Yalin Qin Yongcheng Zhang 《Ceramics International》2021,47(13):18417-18423
The materials processing history has a great influence on their properties and finally determines their application effect. In this paper, the ferroelectric, polarization-switching current, and strain properties of Mn-doped 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 ceramics were studied in fresh state, aged state, and poled state, respectively. Compared with the symmetric polarization-electric-field (P-E) hysteresis loops, current-density-electric-field (J-E) curves, and bipolar electric-field-induced strain (S-E) curves in fresh state samples, asymmetric P-E loops, J-E curves, and bipolar S-E curves were obtained in poled state samples. Well-aged-state samples exhibit double hysteresis P-E loop, four peaks J-E curves, and symmetric S-E curves without negative strain. The symmetry-conforming short-range order (SC-SRO) principle of point defects and internal electric field Ei is employed to clarify the different phenomenon of three states. Results indicated that randomly oriented defect polarization PD in aged samples can reverse the spontaneous polarization PS back and result in the double hysteresis P-E loop and four peaks J-E curves. The oriented PD and resulting Ei in poled-state samples will lead to the asymmetric loops and strain memory effect. 相似文献
4.
目的 从秩序与非秩序理论出发,研究文创产品卡通形象的设计方法.方法 对秩序与非秩序理论的视觉机制和创制理论进行梳理,结合实例,阐述了其与文创产品卡通形象设计之间的联系,分析文创产品卡通形象中的秩序与非秩序的表现形式,提出基于秩序与非秩序理论文创产品卡通形象设计的主要原则,归纳出一套基于秩序与非秩序理论的文创产品卡通形象设计流程与方法,指导设计实践,并验证这些理论方法在设计实践中有效性与可行性.结论 通过对秩序与非秩序理论的研究,文创产品卡通形象设计时应注意提高辨识度、亲和力和便于衍生设计的原则.探索基于秩序与非秩序理论的设计流程与方法,按照界定主题、主体形象设计、主体形象拓展、衍生品应用四个环节开展整体方案设计,为文创产品卡通形象设计提供新的思路与方法. 相似文献
5.
A multiphase dc‐dc converter is effective for miniaturization and achieving high‐power density in a switching power supply. However, its mathematical modeling becomes complex as the phase number of the circuit increases. This study proposes a new modeling method to derive a reduced‐order method in a simple manner. The frequency characteristics of the reduced‐order model are fit to those of the original mathematical model of the multiphase dc‐dc converter. Therefore, the efficacy of the proposed method is validated. 相似文献
6.
Hao Yuan Haifeng Dai Wei Wu Jiaping Xie Jun Shen Xuezhe Wei 《International Journal of Hydrogen Energy》2021,46(7):5714-5728
In a vehicular fuel cell system, alternative load and frequent purge action can lead to anode pressure varies with the hydrogen mass flow fluctuation. It's crucial to control the pressure difference between anode and cathode within a reasonable range to avoid adverse phenomena such as membrane failure, reactant starvation, or even water management fault. In this paper, an improved proportional integrative (PI) controller by the fuzzy logic technique that considers the engineer experience and knowledge on the hydrogen supply system behavior is proposed for hydrogen pressure control, in which the PI parameters are tuned by a fuzzy decision process. Furthermore, load current and purge action regarded as input disturbances are applied for feedforward compensation to reduce the pressure response hysteresis. A hydrogen supply subsystem based on the proportional valve is modeled, and corresponding parameters are determined by analyzing the response time and steady pressure fluctuation. The performance of the conventional PI controller, the fuzzy logic PI (FLPI) controller and fuzzy logic PI with feedforward (FLPIF) controller is validated. The presented results indicated that the FLPI controller significantly improves the dynamic response of hydrogen pressure compared to the PI controller, and the FLPIF controller can further reduce overshoot caused by disturbance. Finally, the proposed FLPIF controller is implemented on a rapid prototype platform of the hydrogen supply subsystem and an actual fuel cell system, exhibiting satisfactory performance. 相似文献
7.
美育作为素质教育的重要组成部分,与德育、智育、体育相辅相成,互相促进。在高职计算机基础教学中渗透
美育,有助于学生综合素质的提升。对高职美育工作现状及美育载体进行了总结,同时探讨了美育如何在计算机基础教学中
渗透。 相似文献
8.
Wei Xu Ziping Huang Weimin Han Wenbin Chen Cheng Wang 《Computers & Mathematics with Applications》2019,77(10):2596-2607
In this paper numerical approximation of history-dependent hemivariational inequalities with constraint is considered, and corresponding Céa’s type inequality is derived for error estimate. For a viscoelastic contact problem with normal penetration, an optimal order error estimate is obtained for the linear element method. A numerical experiment for the contact problem is reported which provides numerical evidence of the convergence order predicted by the theoretical analysis. 相似文献
9.
Conventional geostatistical prediction methods can be used to carry out resource classification in ore beds and for reliability measurements. A field investigation based on lignite thickness data was conducted for resource classification in Eskisehir-Mihaliccik-Koyunagili coal basin. Moreover, a fuzzy logic-based resource classification method has been recently proposed to eliminate the uncertainties encountered in the conduct of conventional resource classification procedure. Fuzzy logic-based classification provides gradual transitions between two adjacent resource classes. In addition, the proposed method can classify each block by assigning a membership degree for handling decision-making problems encountered in conventional resource classification methods. 相似文献
10.