全文获取类型
收费全文 | 109000篇 |
免费 | 9553篇 |
国内免费 | 6334篇 |
专业分类
电工技术 | 4260篇 |
技术理论 | 4篇 |
综合类 | 10943篇 |
化学工业 | 14928篇 |
金属工艺 | 8504篇 |
机械仪表 | 6427篇 |
建筑科学 | 20875篇 |
矿业工程 | 4277篇 |
能源动力 | 3852篇 |
轻工业 | 5261篇 |
水利工程 | 2957篇 |
石油天然气 | 5779篇 |
武器工业 | 1031篇 |
无线电 | 8335篇 |
一般工业技术 | 12626篇 |
冶金工业 | 4059篇 |
原子能技术 | 757篇 |
自动化技术 | 10012篇 |
出版年
2024年 | 376篇 |
2023年 | 1469篇 |
2022年 | 2777篇 |
2021年 | 3247篇 |
2020年 | 3185篇 |
2019年 | 2659篇 |
2018年 | 2454篇 |
2017年 | 3148篇 |
2016年 | 3337篇 |
2015年 | 3630篇 |
2014年 | 6522篇 |
2013年 | 5747篇 |
2012年 | 7485篇 |
2011年 | 8479篇 |
2010年 | 6433篇 |
2009年 | 6906篇 |
2008年 | 6314篇 |
2007年 | 7418篇 |
2006年 | 6897篇 |
2005年 | 5850篇 |
2004年 | 4865篇 |
2003年 | 4475篇 |
2002年 | 3737篇 |
2001年 | 3146篇 |
2000年 | 2707篇 |
1999年 | 2226篇 |
1998年 | 1779篇 |
1997年 | 1498篇 |
1996年 | 1140篇 |
1995年 | 996篇 |
1994年 | 880篇 |
1993年 | 629篇 |
1992年 | 566篇 |
1991年 | 434篇 |
1990年 | 340篇 |
1989年 | 250篇 |
1988年 | 187篇 |
1987年 | 107篇 |
1986年 | 72篇 |
1985年 | 81篇 |
1984年 | 62篇 |
1983年 | 61篇 |
1982年 | 69篇 |
1981年 | 30篇 |
1980年 | 64篇 |
1979年 | 21篇 |
1978年 | 12篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
62.
《Ceramics International》2020,46(6):7122-7130
This study examines three novel approaches for enhancing the thermoelectric (TE) properties of atomic-layer-deposited (ALD) ZnO thin films: 1) Hf-doping, which preserved the crystallinity of ZnO and provided effective phonon scattering owing to Hf's similar atomic radius to and large mass difference with Zn, leading to high power factor (PF) and low thermal conductivity (κ); 2) controlling the distribution of Hf into an alternating scattered phase/clustered phase superlattice, which balanced the high PF of the scattered phases with the low κ of the clustered phases, while providing significant energy-filtering effect to raise the Seebeck coefficient; 3) introducing 18O/16O periodicity into the Hf:ZnO films—by alternately using H216O and H218O as oxidants in the ALD processes, which further suppressed κ without compromising PF. The combination of the three approaches resulted in a maximum improvement in ZT of ~1600% over that of the undoped ZnO. 相似文献
63.
64.
Efficient and fully solution-processed blue organic light-emitting diodes (OLEDs) based on fluorescent small-molecule and methanol/water soluble conjugated polymer as electron-injection material are reported. The emitting layer is 3,6-bis(9,9,9′,9′-tetrakis (6-(9H-carbazol-9-yl)hexyl)-9H,9′H-[2,2′-bifluoren]-7-yl)dib-nzo[b, d]thiophene 5, 5-dioxide (OCSoC) with a blue-fluorescent small-molecule, and a methanol/water soluble polymer poly[(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl-fluorene)] (PFN) acted as electron-injection layer (EIL). All the organic layers are spin-coated from solution. The multilayer device structure with emitting layer/electron-injection layer is achieved by solution-processed method without the dissolution problem between layers. The performances of the devices show that the maximum luminous efficiency of the multilayer device is increased about 43%, compared to the single-layer device. PFN acting as the EIL material plays a key role in the improvement of the device performance when used in solution-processed small-molecule OLEDs. 相似文献
65.
Han Yan Gu Yi Chen Lei Li Bing Liu Xiang Ming Chen 《International Journal of Applied Ceramic Technology》2020,17(2):790-796
SrLa[Ga1−x(R0.5Ti0.5)x]O4 (R = Mg, Zn) ceramics were prepared by a standard solid state sintering method. The single-phase ceramics with K2NiF4-type layered perovskite structure and I4/mmm space group were obtained, indicating that SrLa(R0.5Ti0.5) and SrLaGaO4 can form the unlimited solid solutions. With increasing x for R = Mg and Zn, εr increases monotonously, the Qf value first increases and then decreases, while τf increases from a negative to a positive value. The optimized microwave dielectric properties were obtained as following: εr = 23.3, Qf = 89 400 GHz, τf = −0.8 ppm/°C for SrLa[Ga0.6(Mg0.5Ti0.5)0.4]O4 and εr = 23.3, Qf = 76 200 GHz, τf = 0.2 ppm/°C for SrLa[Ga0.7(Zn0.5Ti0.5)0.3]O4, indicating that the present solid solution ceramics are the promising candidates as microwave resonator materials for the telecommunication applications. 相似文献
66.
67.
The perpetual energy production of a wind farm could be accomplished (under proper weather conditions) if no failures occurred. But even the best possible design, manufacturing, and maintenance of a system cannot eliminate the failure possibility. In order to understand and minimize the system failures, the most crucial components of the wind turbines, which are prone to failures, should be identified. Moreover, it is essential to determine and classify the criticality of the system failures according to the impact of these failure events on wind turbine safety. The present study is processing the failure data from a wind farm and uses the Fault Tree Analysis as a baseline for applying the Design Structure Matrix technique to reveal the failure and risk interactions between wind turbine subsystems. Based on the analysis performed and by introducing new importance measures, the “readiness to fail” of a subsystem in conjunction with the “failure riskiness” can determine the “failure criticality.” The value of the failure criticality can define the frame within which interventions could be done. The arising interventions could be applied either to the whole system or could be focused in specified pairs of wind turbine subsystems. In conclusion, the method analyzed in the present research can be effectively applied by the wind turbine manufacturers and the wind farm operators as an operation framework, which can lead to a limited (as possible) design‐out maintenance cost, failures' minimization, and safety maximization for the whole wind turbine system. 相似文献
68.
In this study, we have proposed an automated classification approach to identify meaningful patterns in wind field data. Utilizing an extensive simulated wind database, we have demonstrated that the proposed approach can identify low‐level jets, near‐uniform profiles, and other patterns in a reliable manner. We have studied the dependence of these wind profile patterns on locations (eg, offshore vs onshore), seasons, and diurnal cycles. Furthermore, we have found that the probability distributions of some of the patterns depend on the underlying planetary boundary layer schemes in a significant way. The future potential of the proposed approach in wind resource assessment and, more generally, in mesoscale model parameterization improvement is touched upon in this paper. 相似文献
69.
70.
《International Journal of Hydrogen Energy》2020,45(29):14964-14971
Sr3Fe2O7-δ (SFO) with two-layer Ruddlesden-Popper (R–P) structure has recently been proved to be a promising material for the single phase cathode in proton conducting solid oxide fuel cells (P–SOFCs). To investigate the hydration reactions and proton conducting mechanisms of SFO and cobalt doped SFO (SFCO), both bulk and surface properties were calculated. We conclude that R–P structures have advantages in P–SOFCs. The unique Sr–O–M layer can facilitate the hydration process. Although in Sr–O–F and Sr–O–N layers, it is difficult for the formation and migration of oxygen vacancies, protons are most stable. Furthermore, cobalt doping can not only improve the electronic conductivity but also enhance surface properties of SFCO. The easily exposed Co–Fe–O surface can also facilitate the hydration reactions on the surface. Our work could give an informative insight into the relationships among the doped elements, the R–P structures, the hydration process and the proton conducting properties. 相似文献