全文获取类型
收费全文 | 19803篇 |
免费 | 2240篇 |
国内免费 | 1450篇 |
专业分类
电工技术 | 1195篇 |
综合类 | 1627篇 |
化学工业 | 3126篇 |
金属工艺 | 1415篇 |
机械仪表 | 1056篇 |
建筑科学 | 681篇 |
矿业工程 | 366篇 |
能源动力 | 897篇 |
轻工业 | 1144篇 |
水利工程 | 476篇 |
石油天然气 | 1266篇 |
武器工业 | 208篇 |
无线电 | 3066篇 |
一般工业技术 | 2681篇 |
冶金工业 | 388篇 |
原子能技术 | 281篇 |
自动化技术 | 3620篇 |
出版年
2024年 | 54篇 |
2023年 | 399篇 |
2022年 | 643篇 |
2021年 | 770篇 |
2020年 | 860篇 |
2019年 | 760篇 |
2018年 | 688篇 |
2017年 | 767篇 |
2016年 | 797篇 |
2015年 | 868篇 |
2014年 | 1180篇 |
2013年 | 1342篇 |
2012年 | 1175篇 |
2011年 | 1621篇 |
2010年 | 1025篇 |
2009年 | 1217篇 |
2008年 | 1144篇 |
2007年 | 1228篇 |
2006年 | 1025篇 |
2005年 | 878篇 |
2004年 | 747篇 |
2003年 | 636篇 |
2002年 | 564篇 |
2001年 | 422篇 |
2000年 | 375篇 |
1999年 | 360篇 |
1998年 | 298篇 |
1997年 | 279篇 |
1996年 | 233篇 |
1995年 | 225篇 |
1994年 | 181篇 |
1993年 | 123篇 |
1992年 | 109篇 |
1991年 | 99篇 |
1990年 | 88篇 |
1989年 | 57篇 |
1988年 | 58篇 |
1987年 | 27篇 |
1986年 | 30篇 |
1985年 | 24篇 |
1984年 | 10篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1973年 | 3篇 |
1959年 | 5篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
941.
《Intermetallics》2017
Competition between the highly-ordered XA structure and disordered L21B structure in Heusler alloys Mn2CoZ (Z = Al, Ga, Si, Ge, Sb) has been investigated. The relative stability of the two structures strongly depends on the main group element Z. When Z belongs to Al or Ga, the XA structure is stabler, but when Z belongs to Si, Ge or Sb, the L21B structure gains stability and is lower in energy. This is related to the different number of valence electrons in main group element Z, which influences the DOS structure near the Fermi level and changes N(EF). The energy difference ΔE between the XA and L21B structures may be used to estimate the tendency to form L21B structure in different Heusler alloys qualitatively. A large negative ΔE is preferable to retard the A-C site disorder and retain the highly-ordered XA structure. That is just the case in Mn2CoAl. A robust half-metallicity is observed in Mn2CoSi, Mn2CoGe and Mn2CoSb, they are always half-metallic under either XA or L21B structure. But in Mn2CoAl and Mn2CoGa, their spin gapless semiconducting character will be destroyed and replaced by a half-metallic state if L21B disorder occurs. Finally, these results suggest that the L21B structure should be considered together with XA structure when discussing the electronic structure of “inverse” Heusler alloys. 相似文献
942.
《Intermetallics》2014
Based on the density functional theory (DFT), the plane-wave pseudopotential method was used to calculate structural stabilities, electronic structures, and ferromagnetism of Fe3Si, Fe11NiSi4, Fe11CoSi4 and Fe11CrSi4 intermetallic compound. This study showed that the Fe11NiSi4 and Fe11CrSi4 phase are more stable than Fe3Si phase, especially Fe11NiSi4, but decreased with Fe11CoSi4 phase. Calculating the density of states and the Mulliken electronic populations showed that Fe11NiSi4 had the highest structural stability because of its Fermi level, which was close to the bottom of the pseudo-gap. Fe11NiSi4 also had the largest Mulliken population, which increased the metallic bonding of the alloying system. The total magnetic moments of Fe11NiSi4, Fe11CoSi4 and Fe11CrSi4 were 20.04μB, 19.98μB, and 18.81μB, respectively. These magnetic moments mainly originated from the 3d spin polarization of Fe and those of additional atoms. 相似文献
943.
本文介绍了负载限流控制全桥软开关变换器,包括全桥软开关变换器电路结构和过载限流的工作原理,并阐述了如何实现副边整流桥的尖峰电压抑制。在理论分析的基础上,介绍了电路设计,研制了1台样机,并进行实验验证。 相似文献
944.
This paper introduces a novel empirical mode decomposition based anomaly detection in Quadratic frequency modulated thermal wave imaging. Being suited for non-stationary signal analysis, its edge over other contemporary processing modalities in its anomaly detection capability has been verified using experimentation carried over a mild steel specimen with embedded flat bottom holes. It also addresses the effect of size and depth on anomaly detection using the proposed methodology in addition to considering the signal to noise ratio of defects for detection. 相似文献
945.
Mohamed M. El Nady Naira M. Lotfy Doaa A. Mousa 《Petroleum Science and Technology》2016,34(16):1496-1502
The authors aimed to examine a multivariate statistical analysis approach for monitoring the hydrocarbon potentiality of source rocks in the North Western Desert to recognize the potentiality of source rocks and subsequently investigate the maturation level of the proven potential source formations for oil preservation. To achieve this aim, they applied multivariate statistics analysis (principle component analysis [PCA], cluster analysis, and correlation coefficient) and Rock-Eval pyrolysis analyses. The results showed that both PCA and cluster analyses have showed two types of source rocks. The first is classified as poor to fair source rock and immature to marginally mature source rock, the second is considered as fair to good source rock and mature to post mature source rock. PCA extracted two independent factors, which explained 81.87% of the total variance. The first type of source rock was responsible for 50% of the total variance and was best represented by variables TOC, S2, OI, and Ro, and the second one was responsible for 31.65% of the total variance and was represented by the HI variable. Pearson correlation coefficient showed a significant positive correlation between TOC and S2 or Ro. A positive correlation between S2 and HI or OI and also between OI and Ro was observed, while no significant correlation was noticed between HI and Ro. 相似文献
946.
《Calphad》2016
Thermodynamic optimization of the Au–Sc and Fe–Sc systems was carried out by means of the CALPHAD (CALculation of PHAse Diagram) method on the basis of the available experimental data in literature. Redlich–Kister polynomials were used to describe the excess Gibbs energy of solution phases, and all the compounds are treated as stoichiometric ones. The Au–Sc system was described thermodynamically for the first time, and the Fe–Sc system was re-optimized by considering the new experimental data about enthalpies of mixing of the liquid phase. A set of self-consistent parameters was obtained for each of these two binary systems, respectively. 相似文献
947.
Mixtures of experts (ME) model are widely used in many different areas as a recognized ensemble learning approach to account for nonlinearities and other complexities in the data, such as time series estimation. With the aim of developing an accurate tourism demand time series estimation model, a mixture of experts model called LSPME (Lag Space Projected ME) is presented by combining ideas from subspace projection methods and negative correlation learning (NCL). The LSPME uses a new cluster-based lag space projection (CLSP) method to automatically obtain input space to train each expert focused on the difficult instances at each step of the boosting approach. For training experts of the LSPME, a new NCL algorithm called Sequential Evolutionary NCL algorithm (SENCL) is proposed that uses a moving average for the correlation penalty term in the error function of each expert to measure the error correlation between it and its previous experts. The LSPME model was compared with other ensemble models using monthly tourist arrivals to Japan from four markets: The United States, United Kingdom, Hong Kong and Taiwan. The experimental results show that the estimation accuracy of the proposed LSPME model is significantly better than the other ensemble models and can be considered to be a promising alternative for time series estimation problems. 相似文献
948.
《Calphad》2021
Metallic coatings can improve the high temperature resistance of superalloys serving in the gas turbines. In general they are Al–Co–Cr–Ni alloys with small Y additions to improve oxide scale adherence.In order to complete the construction of a thermodynamic database for coatings, thermodynamic assessments of four ternary systems have been performed by means of the CALPHAD method, namely Al–Co–Y, Al–Ni–Y, Al–Cr–Y and Co–Ni–Y. All of the experimental phase diagrams and thermodynamic data available in the literature were critically reviewed. The liquid, fcc, bcc and hcp phases were modeled as substitutional solutions. The order-disorder model has been adopted to describe the A1/L12 and A2/B2 phase relations. A series of ternary compounds have been modeled during the present work according to the crystal structure or composition. As a result a satisfactory agreement was obtained between our calculations and the experimental data used in the assessment.Finally, interaction parameters calculated in this work have been merged in the thermodynamic database for the simulation of Al–Co–Cr–Ni–Y alloys. This has been validated by comparing our calculations with experimental data regarding selected Ni-based and Co-based alloy coatings. 相似文献
949.
The article presents how to increase electrical efficiency and power output of photovoltaic (PV) panel with the use of a phase change material (PCM). The focus of the work is in experimental setup and simulation heat extraction from the PV panel with the use of TRNSYS software. A modification of PV panel Canadian Solar CS6P-M was made with a phase change material RT28HC. The actual data of cell temperature of a PV panel with and without PCM were given and compared. A simulation of both PV panels in TRNSYS software was performed, followed by the comparison of results with the simulation and experimental actual data. The experimental results show that the maximum temperature difference on the surface of PV panel without PCM was 35.6 °C higher than on a panel with PCM in a period of one day. Referring to experimental results the calculation of the maximum and average increase of electrical efficiency was made for PV-PCM panel with TRNSYS software. Final results of simulation shows that the electricity production of PV-PCM panel for a city of Ljubljana was higher for 7.3% in a period of one year. 相似文献
950.
《Calphad》2019
The C-Co-Mo-W and C-Mo-Ni-W quaternary systems have been critically evaluated by means of the CALPHAD approach, in which the Co-Mo-W system was readjusted to ensure the model consistency. The thermodynamic models of Gibbs energies for individual phases in the ternary and quaternary systems are described, including substitutional solution model, sublattice model and linear compound model. The modeling covers the whole temperature and composition ranges, and a set of self-consistent thermodynamic parameters for the C-Co-Mo-W and C-Mo-Ni-W quaternary systems is obtained. According to the comprehensive comparisons between the reported and calculated phase diagram data, the reliable equilibria information is satisfactorily accounted for by the modeling. Based on the present work together with the previously reported assessments of binary, ternary and quaternary sub-systems, a thermodynamic database for the C-Co-Mo-Ni-W quinary system is constructed and applied to calculate the sintering region phase equilibria of the (W,Mo)C-(Co,Ni) cemented carbides. 相似文献