全文获取类型
收费全文 | 137325篇 |
免费 | 15865篇 |
国内免费 | 8839篇 |
专业分类
电工技术 | 10991篇 |
技术理论 | 4篇 |
综合类 | 16068篇 |
化学工业 | 11263篇 |
金属工艺 | 11462篇 |
机械仪表 | 16934篇 |
建筑科学 | 14213篇 |
矿业工程 | 6881篇 |
能源动力 | 7196篇 |
轻工业 | 2374篇 |
水利工程 | 5646篇 |
石油天然气 | 6824篇 |
武器工业 | 3817篇 |
无线电 | 9532篇 |
一般工业技术 | 16651篇 |
冶金工业 | 4452篇 |
原子能技术 | 1925篇 |
自动化技术 | 15796篇 |
出版年
2024年 | 263篇 |
2023年 | 1685篇 |
2022年 | 3429篇 |
2021年 | 3982篇 |
2020年 | 4269篇 |
2019年 | 3364篇 |
2018年 | 3422篇 |
2017年 | 4466篇 |
2016年 | 5337篇 |
2015年 | 6006篇 |
2014年 | 8951篇 |
2013年 | 8856篇 |
2012年 | 11140篇 |
2011年 | 12163篇 |
2010年 | 8778篇 |
2009年 | 9004篇 |
2008年 | 8409篇 |
2007年 | 10371篇 |
2006年 | 8925篇 |
2005年 | 7242篇 |
2004年 | 6095篇 |
2003年 | 4861篇 |
2002年 | 3914篇 |
2001年 | 3172篇 |
2000年 | 2599篇 |
1999年 | 2114篇 |
1998年 | 1670篇 |
1997年 | 1378篇 |
1996年 | 1285篇 |
1995年 | 1105篇 |
1994年 | 890篇 |
1993年 | 611篇 |
1992年 | 524篇 |
1991年 | 397篇 |
1990年 | 337篇 |
1989年 | 266篇 |
1988年 | 199篇 |
1987年 | 107篇 |
1986年 | 97篇 |
1985年 | 51篇 |
1984年 | 54篇 |
1983年 | 33篇 |
1982年 | 37篇 |
1981年 | 26篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1959年 | 24篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
Effect of heat loss on the syngas production by fuel-rich combustion in a divergent two-layer burner
《International Journal of Hydrogen Energy》2022,47(34):15270-15281
The effect of heat loss on the syngas production from partial combustion of fuel-rich in a divergent two-layer burner is numerically studied using two-dimensional model with detailed kinetics GRI-Mech 1.2. Both the radiation and wall heat losses to the surrounding are considered in the computations. It is shown that two types heat losses have different effects on the syngas production. The radiation heat loss has significant effect on the syngas temperature and the syngas temperature is dropped as radiation heat loss is increased, but it has neglected effect on the reforming efficiency and methane conversion efficiency. The wall heat loss has a comprehensive effect on the syngas production. The wall heat loss not only reduces the conversion efficiency, but also significantly decreases the syngas temperature. The effect of wall heat loss becomes weak as the equivalence is increased. The reforming efficiency drops from 0.440 to 0.424 for equivalence ratio of 2 and mixture velocity of 0.17 m/s for the predictions between adiabatic wall and non-adiabatic conditions. 相似文献
14.
Qian-Yun Han Fang Liu Yuan-Ying Ni 《International Journal of Food Science & Technology》2022,57(2):920-930
The gene sequence coding for the membrane-bound polyphenol oxidase (mPPO) with a length of 1761 bp was cloned by PCR method and shown to contain one highly conserved sequence encoding a di-copper-binding region. The predicted three-dimensional structure of mPPO indicated that the active site was located near two copper ions and composed of a typical bundle of four α-helices. Each of the two catalytic copper ions was coordinated with three histidine residues in the hydrophobic pocket, yielding His 180, His 201, His 210, His 332, His 336 and His 366. Docking studies showed that 4-methylcatechol and chlorogenic acid have different binding models due to different ligand sizes and binding sites in the active centre, and it was found that the smaller compound exhibited a higher affinity for mPPO. Molecular dynamic simulation results indicated that Phe 353 is important in controlling enzymatic activity through influencing substrate coordination in the active site. 相似文献
15.
《Soils and Foundations》2022,62(3):101156
In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% < VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses. 相似文献
16.
17.
Ya-Nan Yang Yin-Ning Zhou Bo Ouyang Yi-Yang Wu Xi-Bao Zhang Zheng-Hong Luo 《American Institute of Chemical Engineers》2022,68(5):e17645
The computational fluid dynamics (CFD) and kinetic-based moment methods coupled approach is adopted to simulate the bulk copolymerization of styrene–acrylonitrile (SAN) in a stirred tank reactor. Numerical simulations are carried out to investigate the impacts of impeller speed, monomer ratio, initiator ratio, and initial reaction temperature on the copolymerization process and product properties. Particularly, the Chaos theory is selected as a criterion for evaluating the occurrence of the thermal runaway. The Flory's and Stockmayer's distributions are employed to calculate chain length distribution and copolymer composition distribution of copolymer. The simulation results highlight that the appearance of thermal runaway can be postponed by properly increasing the rotation speed, decreasing the initiator loadings, initial acrylonitrile contents and initial reactor temperature. Furthermore, significant differences exist in the product properties that predicted by the ideal and non-ideal models, which demonstrates that the temperature heterogeneity plays a crucial role in SAN copolymerization. This study could offer references for the safe operation and design of polymerization processes. 相似文献
18.
Pengcheng Li Xiuxia Xu Junjie Zhao Pragati Awasthi Xusheng Qiao Jincheng Du Xianping Fan Guodong Qian 《中国稀土学报(英文版)》2022,40(2):169-192
Significant developments have been made in the past few decades for lanthanide(Ln)ions doped fluorosilicate glass-ceramics(Flusi-GCs).As novel generation of luminescence materials with a wide range of applications,Flusi-GCs as a single host combine the advantages of glass and ceramics/crystals as well as fluorides and silicates.In this review,the chemical design principles and experimental procedures of Flusi-GCs are summarized in detail.Flusi-GCs are categorized as those containing PbxCd1-xF2,RF3(R=Y,La,Gd),MF2(M=Ca,Sr,Ba),xMF2-yRF3(R=Y,La-Lu),mAF-nRF3(A=Li,Na,K),KTF3(T=Zn,Mn)and K2 SiF6 nanocrystals(NCs).Theoretical breakthroughs mainly by molecular dynamic(MD)simulation have been recapitulated as efficient routes for composition-design,nano-crystallization-prediction,and performance-optimization of Flusi-GCs containing target fluoride NCs.Essential research progresses pertaining photonic applications have been made in random lasers,communication amplifiers,optical fibers,spectral converters,white light-emitting-diodes(WLEDs),and thermal sensors.In the end,we propose three future research directions for Flusi-GCs. 相似文献
19.
Xuan-Tao Ji Si-Yuan Luo Yu-He Huang Kun Zhu Jin Zhu Xiao-Yu Peng Min Xiao Xiao-Dong Wang 《核技术(英文版)》2022,33(1):13-23
The muon radiography imaging technique for high-atomic-number objects(Z) and large-volume objects via muon transmission imaging and muon multiple scattering imaging remains a popular topic in the field of radiation detection imaging. However, few imaging studies have been reported on low and medium Z objects at the centimeter scale. This paper presents an imaging system that consists of three layers of a position-sensitive detector and four plastic scintillation detectors. It acquires data by co... 相似文献