全文获取类型
收费全文 | 85302篇 |
免费 | 8355篇 |
国内免费 | 2168篇 |
专业分类
电工技术 | 616篇 |
综合类 | 3656篇 |
化学工业 | 40272篇 |
金属工艺 | 4124篇 |
机械仪表 | 1250篇 |
建筑科学 | 1150篇 |
矿业工程 | 1947篇 |
能源动力 | 10613篇 |
轻工业 | 4936篇 |
水利工程 | 200篇 |
石油天然气 | 1885篇 |
武器工业 | 650篇 |
无线电 | 3804篇 |
一般工业技术 | 14954篇 |
冶金工业 | 1980篇 |
原子能技术 | 418篇 |
自动化技术 | 3370篇 |
出版年
2024年 | 253篇 |
2023年 | 3495篇 |
2022年 | 2949篇 |
2021年 | 3434篇 |
2020年 | 4752篇 |
2019年 | 3741篇 |
2018年 | 3199篇 |
2017年 | 4006篇 |
2016年 | 4286篇 |
2015年 | 4649篇 |
2014年 | 6741篇 |
2013年 | 7251篇 |
2012年 | 6755篇 |
2011年 | 6644篇 |
2010年 | 4929篇 |
2009年 | 5072篇 |
2008年 | 2652篇 |
2007年 | 4342篇 |
2006年 | 3616篇 |
2005年 | 1896篇 |
2004年 | 1028篇 |
2003年 | 1113篇 |
2002年 | 1250篇 |
2001年 | 1086篇 |
2000年 | 719篇 |
1999年 | 802篇 |
1998年 | 413篇 |
1997年 | 209篇 |
1996年 | 347篇 |
1995年 | 305篇 |
1994年 | 202篇 |
1993年 | 181篇 |
1992年 | 182篇 |
1991年 | 170篇 |
1990年 | 202篇 |
1989年 | 234篇 |
1988年 | 383篇 |
1987年 | 863篇 |
1986年 | 823篇 |
1985年 | 241篇 |
1984年 | 52篇 |
1983年 | 30篇 |
1982年 | 47篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1974年 | 16篇 |
1973年 | 17篇 |
1951年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
Coupled large eddy simulation and the discrete element method are applied to study turbulent particle–laden flows, including particle dispersion and agglomeration, in a channel. The particle–particle interaction model is based on the Hertz–Mindlin approach with Johnson–Kendall–Roberts cohesion to allow the simulation of van der Waals forces in a dry air flow. The influence of different particle surface energies, and the impact of fluid turbulence, on agglomeration behaviour are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with a positive relationship observed between the two. Particle agglomeration is found to be enhanced in two separate regions within the channel. First, in the near-wall region due to the high particle concentration there driven by turbophoresis, and secondly in the buffer region where the high turbulence intensity enhances particle–particle interactions. 相似文献
92.
In this work, ZnO nanostructures are electrodeposited on a transparent conducting glass from chloride baths. The influence of H2O2 concentration on the electrochemical characteristics has been studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. From the analysis of the current transients on the basis of the Scharifker–Hills model, it is found that nucleation mechanism is progressive with a typical three-dimensional (3D) nucleation and growth process; independently with the concentration of H2O2. However, the nucleation rate of the ZnO changes with the increase of H2O2 concentration. The Mott–Schottky measurements demonstrate an n-type semiconductor character for all samples with a carrier density varying between 5.14×1018 cm−3 and 1.47×1018 cm−3. Scanning electron microscopy (SEM) observations show arrays of vertically aligned ZnO nanorods (NRs) with good homogeneity. The X-ray diffraction (XRD) patterns show that the ZnO deposited crystallises according to a hexagonal Würtzite-type structure and with the c-axis perpendicular to the electrode surface. The directional growth along (002) crystallographic plane is very important for deposits obtained at 5 and 7 mM of H2O2. The high optical properties of the ZnO NRs with a low density of deep defects was checked by UV–vis transmittance analyses, the band gap energy of films varies between 3.23 and 3.31 eV with transparency around 80–90%. 相似文献
93.
Surface-modified δ-MnO2 with a hierarchical structure was synthesized via a hydrothermal redox reaction between toluene and KMnO4. Toluene is oxidized to produce benzoic acid which rapidly adsorbs onto the surface of δ-MnO2. The δ-MnO2 sample prepared with toluene exhibited a much higher catalytic activity for the Fenton-like oxidation of methylene blue in aqueous solution than that prepared without toluene. The enhanced catalytic activity might be attributed to the surface-bound persistent free radicals produced from the electron transfer from the adsorbed C6H5–COO− to Mn(IV). 相似文献
94.
《Carbon》2015
In this work, three dimensional (3D) NixCo1−xS2/graphene composite hydrogels with different Ni contents (denoted as NixCo1−xS2/GH (x = 0, 0.31, 0.56, 0.66, 1)) have been synthesized by a simple one-step hydrothermal method and utilized as the active materials of supercapacitors. The as-prepared samples present a 3D interconnected porous network with the pore sizes in the range of several to tens micrometers. Interestingly, the NixCo1−xS2 particles are uniformly located on the graphene network and the particle size is evolved from ∼50 nm to ∼1.5 μm with the increase of Ni content. The electrochemical measurements revealed that the specific capacitance, rate capability and cyclability of different NixCo1−xS2/GH electrodes are strongly affected by their different Ni content. Among these, the 3D Ni0.31Co0.69S2/GH composite has the highest specific capacitance of 1166 F/g at a current density of 1 A/g. Furthermore, a specific capacitance of 559 F/g can be still maintained at high current density of 20 A/g. After 1000 charge–discharge cycles at 5 A/g, the specific capacitance remains a high value of 755 F/g. 相似文献
95.
Enas Taha Sayed Hussain Alawadhi A.G. Olabi Aisha Jamal Menna Salah Almahdi Juiaria Khalid Mohammad Ali Abdelkareem 《International Journal of Hydrogen Energy》2021,46(8):5975-5983
Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm?2 to 381 mWm?2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements. 相似文献
96.
97.
98.
《Calphad》2020
This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga0.75Li0.25)1-xGex, (Ge0.50Li0.50)1-xGax, (Ga0.50Li0.50)1-xGex, (Ga0.25Li0.75)1-xGex. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature. 相似文献
99.
The lack of consensus on the meaning of energy security and how it should be measured hinders the evaluation of alternatives for improving the Cape Verdean energy sector. The objective of the paper is to develop an energy security index adjusted to the country's context. The methods used are the multi-criteria analysis and the Delphi survey. Different alternatives to improve energy security are assessed: electrically interconnect Cape Verde's islands, increase the share of renewable energy, and a combination of the previous alternatives. The results of our analysis indicate that increasing renewable energy is the optimal alternative for Cape Verde. 相似文献
100.
The influence of the environment on the excited state transitions of meso-tetrakis(p-sulfonatophenyl) porphyrin (TPPS) is reported. TPPS was investigated in protonated and non-protonated forms, and in the presence of the cationic cetyltrimethylammonium bromide (CTAB) micelles. The singlet excited-state absorption spectra were measured by using the white-light continuum Z-scan technique and the triplet–triplet absorption spectra were acquired employing an association of laser flash photolysis and Z-scan techniques. Our results show that the perseveration of the molecular symmetry, upon excitation, depends on the state of multiplicity of the molecules, as well as on the environment and structural characteristics of the porphyrin. Additionally, it was observed that for excited molecules, the ring distortion caused by the protonation of porphyrin ring has great influence on the changes observed for the symmetry and vibronic structure. The results clearly show that the porphyrin investigated is a promising candidate for optical limiting applications for all investigated environments. 相似文献