全文获取类型
收费全文 | 7274篇 |
免费 | 1294篇 |
国内免费 | 836篇 |
专业分类
电工技术 | 783篇 |
综合类 | 800篇 |
化学工业 | 409篇 |
金属工艺 | 177篇 |
机械仪表 | 478篇 |
建筑科学 | 227篇 |
矿业工程 | 66篇 |
能源动力 | 109篇 |
轻工业 | 103篇 |
水利工程 | 110篇 |
石油天然气 | 339篇 |
武器工业 | 78篇 |
无线电 | 1809篇 |
一般工业技术 | 924篇 |
冶金工业 | 84篇 |
原子能技术 | 35篇 |
自动化技术 | 2873篇 |
出版年
2024年 | 24篇 |
2023年 | 161篇 |
2022年 | 289篇 |
2021年 | 307篇 |
2020年 | 322篇 |
2019年 | 271篇 |
2018年 | 253篇 |
2017年 | 245篇 |
2016年 | 317篇 |
2015年 | 376篇 |
2014年 | 453篇 |
2013年 | 512篇 |
2012年 | 556篇 |
2011年 | 589篇 |
2010年 | 460篇 |
2009年 | 482篇 |
2008年 | 505篇 |
2007年 | 522篇 |
2006年 | 447篇 |
2005年 | 403篇 |
2004年 | 321篇 |
2003年 | 276篇 |
2002年 | 239篇 |
2001年 | 190篇 |
2000年 | 147篇 |
1999年 | 121篇 |
1998年 | 100篇 |
1997年 | 76篇 |
1996年 | 64篇 |
1995年 | 76篇 |
1994年 | 72篇 |
1993年 | 52篇 |
1992年 | 44篇 |
1991年 | 22篇 |
1990年 | 30篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有9404条查询结果,搜索用时 31 毫秒
21.
孙嘉鸿 《石油化工管理干部学院学报》2020,(2):67-70
域名具有重要的品牌价值,研究域名管理体系有利于开展域名注册与保护。现行域名注册规则容易导致域名与字号、商标、姓名等传统权利的冲突。互联网域种类繁多、层级结构复杂,企业应当建立域名注册评估机制、抢注侵权监测机制,加强域名注册与维权保护。 相似文献
22.
Xiang Xia Chunbo Li Jiangtao Zeng Liaoying Zheng Guorong Li 《Journal of the American Ceramic Society》2020,103(4):2694-2701
Due to the feature of domains, ferroelectric materials display hysteresis behavior with respect to the change of the applied electric field. Every ferroelectric material has its own unique hysteresis loop reflecting the information of domain reversal under an electric field. In this work, the scaling behaviors of dynamic hysteresis in relaxor (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) ceramics with different compositions were studied systemically. Our results showed that the evolution of scaling behavior in PMN-PT ceramics can be divided into three stages, which is independent of the phase structure of the ceramics and the testing electric field frequency. The relationship between hysteresis area <A> and field amplitude E0 obeys the power law <A>∝ in the low and high E0 regions, where the reorientations of 180° and non-180° domain are dominant, respectively. However, the dynamic hysteresis area <A> does not follow the power law in the intermediate E0 regions, which is attributed to the interaction of different domain reversal mechanisms. Furthermore, the hysteresis area <A> decreases gradually with increasing frequency at a certain E0 and the time-dependent domain reversal process was also discussed. 相似文献
23.
Integrating Variable Reduction Strategy With Evolutionary Algorithms for Solving Nonlinear Equations Systems 下载免费PDF全文
Aijuan Song Guohua Wu Witold Pedrycz Ling Wang 《IEEE/CAA Journal of Automatica Sinica》2022,9(1):75-89
Nonlinear equations systems (NESs) are widely used in real-world problems and they are difficult to solve due to their nonlinearity and multiple roots. Evolutionary algorithms (EAs) are one of the methods for solving NESs, given their global search capabilities and ability to locate multiple roots of a NES simultaneously within one run. Currently, the majority of research on using EAs to solve NESs focuses on transformation techniques and improving the performance of the used EAs. By contrast, problem domain knowledge of NESs is investigated in this study, where we propose the incorporation of a variable reduction strategy (VRS) into EAs to solve NESs. The VRS makes full use of the systems of expressing a NES and uses some variables (i.e., core variable) to represent other variables (i.e., reduced variables) through variable relationships that exist in the equation systems. It enables the reduction of partial variables and equations and shrinks the decision space, thereby reducing the complexity of the problem and improving the search efficiency of the EAs. To test the effectiveness of VRS in dealing with NESs, this paper mainly integrates the VRS into two existing state-of-the-art EA methods (i.e., MONES and DR-JADE) according to the integration framework of the VRS and EA, respectively. Experimental results show that, with the assistance of the VRS, the EA methods can produce better results than the original methods and other compared methods. Furthermore, extensive experiments regarding the influence of different reduction schemes and EAs substantiate that a better EA for solving a NES with more reduced variables tends to provide better performance. 相似文献
24.
Cell migration is a finely tuned biological process that often involves epithelial-mesenchymal transition (EMT).
EMT is typically characterized by the upregulation of mesenchymal markers such as Snail1. This process has been shown
to be of critical importance to normal developmental processes, including neural crest migration and invasion.
Interestingly, similar mechanisms are utilized in disease processes, such as tumor metastasis and migration. Notably,
EMT and EMT-like processes confer tumor cells with the ability to migrate, invade, and adopt stem cell-like
properties that largely account for immunosuppression and tumor recurrence. Therefore, identifying sensitive EMT
markers may contribute to cancer prognosis and diagnosis in many facets. Previously, we showed that Elp3 plays an
essential role during neural crest migration by stabilizing Snail1. In the current study, we further elucidate the
molecular mechanism underlying colorectal cancer migration. We found that mElp3 exerted an identical function to
xElp3 in modulating neural crest migration, and both HAT and SAM domains are imperative during this migratory
process. Interestingly, overexpression of mElp3 in SW480 cells promoted cell migration and invasion, and we further
showed that Elp3 stabilized Snail1 requiring integrity of both SAM and HAT domains. Our findings warrant further
exploration of the specific target of Elp3 in cancer cells. 相似文献
25.
26.
Nishant SHARMA Kaustubh DASGUPTA Arindam DEY 《Frontiers of Structural and Civil Engineering》2020,14(1):62
This article describes a novel approach for deciding optimal horizontal extent of soil domain to be used for finite element based numerical dynamic soil structure interaction (SSI) studies. SSI model for a 12 storied building frame, supported on pile foundation-soil system, is developed in the finite element based software framework, OpenSEES. Three different structure-foundation configurations are analyzed under different ground motion characteristics. Lateral extent of soil domain, along with the soil properties, were varied exhaustively for a particular structural configuration. Based on the reduction in the variation of acceleration response at different locations in the SSI system (quantified by normalized root mean square error, NRMSE), the optimum lateral extent of the soil domain is prescribed for various structural widths, soil types and peak ground acceleration levels of ground motion. Compared to the past studies, error estimation analysis shows that the relationships prescribed in the present study are credible and more inclusive of the various factors that influence SSI. These relationships can be readily applied for deciding upon the lateral extent of the soil domain for conducting precise SSI analysis with reduced computational time. 相似文献
27.
Yu Chen Jiageng Xu Qian Xu Shaoxiong Xie Qingyuan Wang Jianguo Zhu 《Journal of the American Ceramic Society》2020,103(2):1067-1078
In this work, ferroelastic domain switching and R-curve behavior in lead zirconate titanate (Nb/Ce co-doped Pb(Zr0.52Ti0.48)O3, ab. PZT-NC)-based ferroelectric ceramics were investigated, using the indentation-strength-in-bending (ISB) method. Firstly, Vickers indentation test examined the notable fracture anisotropy of PZT-NC ceramics between the poling direction and its perpendicular direction, and the crack open displacement (COD) profiles in the two directions were also theoretically calculated from the indentation fracture mechanics. And then two kinds of ferroelastic domain switching modes (in-plane and out-of-plane) were used for explaining such anisotropic propagation behavior of indentation cracks. The subsequent three-point bending test illustrated the dependence of fracture strength on indentation load and the rising crack growth resistance curves (R-curves) in two directions. The resulted R-curves were fitted by the Hill's type Growth Function successfully, giving the reasonable values of crack extension exponential (n), plateau fracture toughness (Kmax), and initial fracture toughness (Kini). The in-plane ferroelastic domain switching was identified as a more significant toughening mechanism for PZT-NC ceramics than the out-of-plane switching due to more switchable domains. 相似文献
28.
Hong Fang Lihai Wang Weijie Kuai Juan Du Guicheng Jiang Xiaoyan Lu Minglei Zhao Chunming Wang Wenbin Su Limei Zheng Chunying Wang Chunlei Wang 《Journal of the American Ceramic Society》2020,103(5):3257-3264
Domain wall motions mainly affect all kinds of properties of ferroelectric materials, such as piezoelectricity, dielectric response, and mechanical loss, and the extrinsic contributions associated with domain wall motions have always been an important issue. In this study, the reversible and irreversible extrinsic contributions to the dielectric properties of [011]C-oriented 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystals have been extracted by the Rayleigh analysis. We found that in the unpoled samples, the extrinsic contributions of reversible and irreversible domain wall motions to dielectric properties significantly reduced, whereas after poling, only the irreversible extrinsic contribution decreased. The pinning effect in the 2R domain structure is much weaker than that in the 4R domain structure, leading to the low enhancement of Qm and a slight decrease in piezoelectricity caused by acceptor doping in 2R domain structure. This study explores the domain wall dynamics of acceptor-doped single crystals and mainly guides on further performance optimization in PbTiO3-based relaxor single crystals. 相似文献
29.
Mei Ying Liu Tu Lai Sun Xiao Li Zhu Xiao Qiang Liu He Tian Xiang Ming Chen 《Journal of the American Ceramic Society》2021,104(12):6393-6403
Hexagonal rare-earth ferrites (h-RFeO3) have attracted much scientific attention due to their room-temperature multiferroicity. However, it is still a hard job to obtain h-RFeO3 bulk materials because of the meta-stability of such hexagonal phase, and the evaluation of room-temperature ferroelectric and magnetoelectric characteristics in such materials is also a challengeable issue. In the present work, Yb1−xInxFeO3 ceramics with the stable hexagonal structure were obtained by introducing chemical pressure, where the unique ferroelectric domain structures of sixfold vortex combined with tenfold vortex with a typical size of ~400 nm were determined. Symmetry of the present system evolved from centrosymmetric orthorhombic Pbnm (x = 0–0.4) to non-centrosymmetric hexagonal P63cm (x = 0.5 and 0.6) with a ferroelectric polarization up to 3.2 μC/cm2, and finally to centrosymmetric hexagonal P63/mmc (x = 0.7 and 0.8). The Curie point decreased monotonically from 723 K to a temperature below room temperature with increasing x, and the antiferromagnetic phase transition above room temperature was determined for all compositions. Meanwhile, a large linear magnetoelectric coefficient (αME) up to 0.96 mV/cm Oe was obtained at room temperature, and this indicated the great application potential for magnetoelectric devices. 相似文献
30.
针对当前通信系统入侵行为自动识别技术存在入侵信号样本识别成功率较低、误识别率和漏识别率较高的问题,提出基于 GA-SVM 算法的通信网络入侵信号自动识别技术。利用混沌原理提取通信网络入侵的非平稳信号时域特征,并凭借自回归模型提取对应频域特征,捕捉邻域入侵信号间的非线性时空动作频率,评价相邻行为间的状态关联性,预测入侵信号后续行为,完成入侵信号的识别。实验表明,所提方法识别精度高、误识别率较低,漏识别率非常低,具有可应用于实际的理论价值。 相似文献