全文获取类型
收费全文 | 70435篇 |
免费 | 9147篇 |
国内免费 | 2900篇 |
专业分类
电工技术 | 3473篇 |
技术理论 | 1篇 |
综合类 | 3248篇 |
化学工业 | 15772篇 |
金属工艺 | 2633篇 |
机械仪表 | 2487篇 |
建筑科学 | 6012篇 |
矿业工程 | 1794篇 |
能源动力 | 5961篇 |
轻工业 | 7343篇 |
水利工程 | 1120篇 |
石油天然气 | 1721篇 |
武器工业 | 378篇 |
无线电 | 9785篇 |
一般工业技术 | 9531篇 |
冶金工业 | 2884篇 |
原子能技术 | 2333篇 |
自动化技术 | 6006篇 |
出版年
2024年 | 189篇 |
2023年 | 1436篇 |
2022年 | 2511篇 |
2021年 | 4591篇 |
2020年 | 2501篇 |
2019年 | 2527篇 |
2018年 | 2534篇 |
2017年 | 3442篇 |
2016年 | 4695篇 |
2015年 | 4992篇 |
2014年 | 5532篇 |
2013年 | 5759篇 |
2012年 | 4447篇 |
2011年 | 4212篇 |
2010年 | 3104篇 |
2009年 | 3124篇 |
2008年 | 2757篇 |
2007年 | 3987篇 |
2006年 | 4082篇 |
2005年 | 3359篇 |
2004年 | 2264篇 |
2003年 | 2161篇 |
2002年 | 1615篇 |
2001年 | 1130篇 |
2000年 | 992篇 |
1999年 | 658篇 |
1998年 | 516篇 |
1997年 | 390篇 |
1996年 | 412篇 |
1995年 | 288篇 |
1994年 | 308篇 |
1993年 | 214篇 |
1992年 | 194篇 |
1991年 | 157篇 |
1990年 | 171篇 |
1989年 | 127篇 |
1988年 | 107篇 |
1987年 | 104篇 |
1986年 | 87篇 |
1985年 | 96篇 |
1984年 | 100篇 |
1983年 | 59篇 |
1982年 | 66篇 |
1981年 | 50篇 |
1980年 | 51篇 |
1966年 | 25篇 |
1964年 | 36篇 |
1962年 | 65篇 |
1959年 | 31篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 263 毫秒
71.
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
72.
《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
73.
74.
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
75.
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
76.
《Ceramics International》2019,45(13):16405-16410
Copper Indium Gallium Selenide (Cu(In,Ga)Se2, CIGSe) absorbers with different Ga contents were prepared by sputtering CIGSe ceramic targets and post-annealing. CIGSe solar cell devices were fabricated with other functional layers. The device performances and absorber properties were investigated. Increasing Ga content led to an increase in VOC and a decrease in JSC. Ga was supposed to diffuse towards back contact during the annealing process. The best performance was obtained as the ratio of Ga/(In + Ga) reaches 0.32 with the efficiency of 13.8% and a VOC of 537 mV. 相似文献
77.
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
78.
《Measurement》2015
The modeling of solar radiation for forecasting its availability is a key tool for managing photovoltaic (PV) plants and, hence, is of primary importance for energy production in a smart grid scenario. However, the variability of the weather phenomena is an unavoidable obstacle in the prediction of the energy produced by the solar radiation conversion. The use of the data collected in the past can be useful to capture the daily and seasonal variability, while measurement of the recent past can be exploited to provide a short term prediction. It is well known that a good measurement of the solar radiation requires not only a high class radiometer, but also a correct management of the instrument. In order to reduce the cost related to the management of the monitoring apparatus, a solution could be to evaluate the PV plant performance using data collected by public weather station installed near the plant. In this paper, two experiments are conducted. In the first, the plausibility of the short term prediction of the solar radiation, based on data collected in the near past on the same site is investigated. In the second experiment, the same prediction is operated using data collected by a public weather station located at ten kilometers from the solar plant. Several prediction techniques belonging from both computational intelligence and statistical fields have been challenged in this task. In particular, Support Vector Machine for Regression, Extreme Learning Machine and Autoregressive models have been used and compared with the persistence and the k-NN predictors. The prediction accuracy achieved in the two experimental conditions are then compared and the results are discussed. 相似文献
79.
A fluorene-centered perylene monoimide dimer, PMI-F-PMI with a partly non-coplanar configuration has been developed as a potential non-fullerene acceptor for organic solar cells (OSCs). The optimum power conversion efficiency (PCE) of the OSC based on PMI-F-PMI as acceptor and poly (3-hexyl thiophene) (P3HT) as donor is up to 2.30% after annealing at 150 °C. The PCE of 2.30% is the highest value for the OSCs based on P3HT donor and non-fullerene acceptor lies in that PMI-F-PMI’s lowest unoccupied molecular orbital (LUMO) level around −3.50 eV matches well with the donor P3HT to produce higher open-circuit voltage (Voc) of 0.98 V. Meanwhile, PMI-F-PMI makes remarkable contribution to devices’ light absorption as the maximum EQE (30%) of the devices is at 512 nm, same to the maximum absorption wavelength of PMI-F-PMI. The other favorable characteristics of PMI-F-PMI in bulk heterojunction (BHJ) active layers is proved through the photo current density measures, the relatively balanced electron–hole transport, and the smooth morphology with root mean square (RMS) value of 1.86 nm. For these advantages, PMI-F-PMI overwhelms its sister PMI-F and parent PMI as an acceptor in BHJ solar cells. 相似文献
80.