全文获取类型
收费全文 | 197457篇 |
免费 | 23076篇 |
国内免费 | 10697篇 |
专业分类
电工技术 | 10692篇 |
技术理论 | 7篇 |
综合类 | 15750篇 |
化学工业 | 40155篇 |
金属工艺 | 22638篇 |
机械仪表 | 7559篇 |
建筑科学 | 16292篇 |
矿业工程 | 7711篇 |
能源动力 | 4924篇 |
轻工业 | 18379篇 |
水利工程 | 5092篇 |
石油天然气 | 9184篇 |
武器工业 | 1328篇 |
无线电 | 16607篇 |
一般工业技术 | 23250篇 |
冶金工业 | 12989篇 |
原子能技术 | 1761篇 |
自动化技术 | 16912篇 |
出版年
2024年 | 766篇 |
2023年 | 3322篇 |
2022年 | 7111篇 |
2021年 | 8707篇 |
2020年 | 6831篇 |
2019年 | 6259篇 |
2018年 | 6030篇 |
2017年 | 7349篇 |
2016年 | 8694篇 |
2015年 | 9527篇 |
2014年 | 12410篇 |
2013年 | 12532篇 |
2012年 | 13098篇 |
2011年 | 12878篇 |
2010年 | 9793篇 |
2009年 | 10366篇 |
2008年 | 9181篇 |
2007年 | 12393篇 |
2006年 | 11923篇 |
2005年 | 10096篇 |
2004年 | 8127篇 |
2003年 | 7547篇 |
2002年 | 6104篇 |
2001年 | 5029篇 |
2000年 | 4357篇 |
1999年 | 3445篇 |
1998年 | 2644篇 |
1997年 | 2319篇 |
1996年 | 1987篇 |
1995年 | 1783篇 |
1994年 | 1568篇 |
1993年 | 1121篇 |
1992年 | 1032篇 |
1991年 | 814篇 |
1990年 | 793篇 |
1989年 | 686篇 |
1988年 | 409篇 |
1987年 | 301篇 |
1986年 | 241篇 |
1985年 | 243篇 |
1984年 | 230篇 |
1983年 | 131篇 |
1982年 | 148篇 |
1981年 | 124篇 |
1980年 | 127篇 |
1979年 | 64篇 |
1978年 | 38篇 |
1977年 | 35篇 |
1964年 | 41篇 |
1962年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
Mingzhi Zhao Jianwei Cao Zhi Wang Guohua Li 《Journal of the European Ceramic Society》2019,39(7):2427-2435
The crystallization phenomena of spinel in CaO-MgO-Al2O3-SiO2-Fe2O3 glass have received much attention due to the particular role in preparation of glass-ceramic materials, which represent an effective option to manage hazardous waste. In this study, both preliminary spinel and secondary spinel were precipitated in the precursor glass. The formation of these spinel was meticulously assessed by a combination of X-ray diffractometry and scanning electron microscopy. The structure of the microenvironment in the precursor glass was characterized by Raman spectrums. These advanced techniques highlight the potential for one-step crystallization of the glass. The investigation, which focused on one-step crystallization, demonstrated the growth of pyroxene on spinel accompanying a migration of chromium. The results also show the microstructure of the obtained glass-ceramic was very dependent on the heat-treat temperature. This study not only unambiguously reveals the precipitation mechanisms of spinel but also provides more documentation for one-step crystallization in the glass-ceramics field. 相似文献
112.
《Intermetallics》2015
Fine-grained fully-lamellar (FL) microstructure is desired for TiAl components to serve as compressor/turbine blades and turbocharger turbine wheels. This study deals with the process and phase transformation to produce FL microstructure for Mo stabilized beta-gamma TiAl alloys without single α-phase field. Unlike the α + γ two-phased TiAl or beta-gamma TiAl with single α-phase field, the wrought multi-phase TiAl–4/6Nb–2Mo–B/Y alloys exhibit special annealing process to obtain FL microstructure. Short-term annealing at temperatures slightly above β-transus is recommended to produce the desired FL microstructure. The related mechanism is to guarantee the sufficient diffusion homogenization of β stabilizers during single β-phase annealing, and further avoid α decomposition by α → γ + β when cooling through α + β + γ phase field. The colony boundary β phase contributes to fine-grained nearly FL microstructure, by retarding the coarsening of the α phase grains. 相似文献
113.
114.
Greg A. Breed Paul M. Severns Andrew M. Edwards 《Journal of the Royal Society Interface》2015,12(103)
Lévy flights have gained prominence for analysis of animal movement. In a Lévy flight, step-lengths are drawn from a heavy-tailed distribution such as a power law (PL), and a large number of empirical demonstrations have been published. Others, however, have suggested that animal movement is ill fit by PL distributions or contend a state-switching process better explains apparent Lévy flight movement patterns. We used a mix of direct behavioural observations and GPS tracking to understand step-length patterns in females of two related butterflies. We initially found movement in one species (Euphydryas editha taylori) was best fit by a bounded PL, evidence of a Lévy flight, while the other (Euphydryas phaeton) was best fit by an exponential distribution. Subsequent analyses introduced additional candidate models and used behavioural observations to sort steps based on intraspecific interactions (interactions were rare in E. phaeton but common in E. e. taylori). These analyses showed a mixed-exponential is favoured over the bounded PL for E. e. taylori and that when step-lengths were sorted into states based on the influence of harassing conspecific males, both states were best fit by simple exponential distributions. The direct behavioural observations allowed us to infer the underlying behavioural mechanism is a state-switching process driven by intraspecific interactions rather than a Lévy flight. 相似文献
115.
介绍了PET熔体长距离输送工艺流程,重点分析易对PET熔体输送带来不利影响的因素,如熔体压力降、停留时间、管道粗糙度、焊缝品质等,并针对熔体输送的不利因素,提出了相应的解决方案,对熔体直纺设计、实践提供必要的参考。 相似文献
116.
Isothermal nucleic-acid amplification methods such as Loop-Mediated isothermal AMPlification (LAMP) are increasingly appealing alternatives to PCR for use in portable diagnostic system due to the low cost, weight, and power requirements of the instrumentation. As such, interest in developing new probes and other functionality based on the LAMP reaction has been intense. Here, we report on the development of duplexed LAMP assays for pathogen detection using spectrally unique Assimilating Probes. As proof of principle, we used a reaction for Salmonella enterica as a model coupled with a reaction for λ-phage DNA as an internal control, as well as a duplexed assay to sub-type specific quarantine strains of the bacterial wilt pathogen Ralstonia solanacearum. Detection limits for bacterial DNA analyzed in individual reactions was less than 100 genomic equivalents in all cases, and increased by one to two orders of magnitude when reactions were coupled in duplexed formats. Even so, due to the more robust activity of newly available strand-displacing polymerases, the duplexed assays reported here were more powerful than analogous individual reactions reported only a few years ago, and represent a significant advance for incorporation of internal controls to validate assay results in the field. 相似文献
117.
Measuring nonlinear optical response of a specific material in a mixture, not only leads to investigate the behavior of a particular component in various circumstances, but also can be a way to select suitable combination and optimum concentration of additives and therefore obtaining the maximum nonlinear optical signals. In this work, by using dual-arm Z-scan technique, the nonlinear refractive index of Disperse Red1 (DR1) organic dye molecules inside the core of prepared polymeric nanocapsules was measured among various materials which prepared nanocapsules were made of them. Then the measured value was compared with nonlinear refractive index of DR1 solved in dichloromethane. 相似文献
118.
《Ceramics International》2020,46(8):11846-11853
Cr2AlC and its composites containing α-Al2O3 (6.1 and 15.2 wt %) were prepared by hot pressing and their corrosion behaviors in air-saturated 3.5 wt % NaCl aqueous solution were investigated by electrochemical testing methods. It was revealed that the secondary phase of Al2O3 particles mainly distributed along grain boundaries of Cr2AlC matrix. The potentiodynamic polarization measurements showed that the corrosion current densities of these Cr2AlC composites were lower than that of the pure Cr2AlC. The Aluminum in Cr2AlC was prone to be attacked more easily. When immersed at open circuit potential (OCP), Al readily slipped out from Cr2AlC matrix into NaCl solution in the form of dissoluble species. But in the case of polarization, regardless of potentiostatic polarization or potentiodynamic polarization, more de-intercalated Al, reacted with the electrolyte to form corrosion products of Al2O3 and/or AlOOH and deposited on the sample surface. For Cr2AlC/α-Al2O3 composites, the presence of Al2O3 weakened the corrosion along grain boundaries by partly blocking the permeation of electrolyte and inhibiting the anodic dissolution process. 相似文献
119.
120.
Sumeng Wei Yuling Yang Xiao Feng Shanshan Li Lei Zhou Jingyu Wang Xiaozhi Tang 《International Journal of Food Science & Technology》2020,55(7):2691-2699
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics. 相似文献