全文获取类型
收费全文 | 27533篇 |
免费 | 2730篇 |
国内免费 | 1948篇 |
专业分类
电工技术 | 498篇 |
综合类 | 2752篇 |
化学工业 | 3169篇 |
金属工艺 | 5088篇 |
机械仪表 | 914篇 |
建筑科学 | 1558篇 |
矿业工程 | 2793篇 |
能源动力 | 953篇 |
轻工业 | 932篇 |
水利工程 | 154篇 |
石油天然气 | 143篇 |
武器工业 | 45篇 |
无线电 | 1176篇 |
一般工业技术 | 3546篇 |
冶金工业 | 2682篇 |
原子能技术 | 59篇 |
自动化技术 | 5749篇 |
出版年
2024年 | 38篇 |
2023年 | 780篇 |
2022年 | 960篇 |
2021年 | 1038篇 |
2020年 | 1160篇 |
2019年 | 977篇 |
2018年 | 906篇 |
2017年 | 1164篇 |
2016年 | 1195篇 |
2015年 | 1221篇 |
2014年 | 1632篇 |
2013年 | 1966篇 |
2012年 | 2559篇 |
2011年 | 2578篇 |
2010年 | 2065篇 |
2009年 | 2167篇 |
2008年 | 1646篇 |
2007年 | 2264篇 |
2006年 | 1929篇 |
2005年 | 846篇 |
2004年 | 392篇 |
2003年 | 368篇 |
2002年 | 366篇 |
2001年 | 358篇 |
2000年 | 321篇 |
1999年 | 338篇 |
1998年 | 228篇 |
1997年 | 210篇 |
1996年 | 175篇 |
1995年 | 72篇 |
1994年 | 76篇 |
1993年 | 47篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 32篇 |
1989年 | 24篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 3篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
1.
《Ceramics International》2022,48(7):9495-9505
Effects of dopants with different valences on the densification behavior and phase composition of a ZrO2–SiO2 nanocrystalline glass-ceramic (NCGC) during pressureless sintering were investigated in this study. The raw powder of Ca2+, La3+, Ce4+ and Ta5+ ions doped ZrO2–SiO2 (referred to as Ca-ZS, La-ZS, Ce-ZS, Ta-ZS, respectively) and pure ZrO2–SiO2 (PZS) sample were synthesized by sol-gel method, followed by pressureless sintering. Compared with the PZS sample, doping of Ca2+ and La3+ ions significantly promoted the densification of the NCGCs. The “densification promotion” effect was attributed to the formation of oxygen vacancies and the decrease of SiO2 viscosity due to doping of aliovalent cations. The dopants with various valences showed significant effects on the phase compositions of the NCGCs during sintering. Doping of Ca2+ ion accelerated the reaction kinetics between ZrO2 nanocrystallites and amorphous SiO2 to yield ZrSiO4. The La3+ ion acted as destabilizer of t-ZrO2, which resulted in a rapid tetragonal (t) to monoclinic (m) ZrO2 phase transformation during sintering, while in the Ta5+ and Ce4+ ions doped sample, the phase transformation occurred gradually. All the doping ions increased the lattice parameters and the volume of t-ZrO2 unit cell, while the effects of the doping ions on the lattice parameters of m-ZrO2 unit cell were more complex. 相似文献
2.
《Journal of the European Ceramic Society》2022,42(13):5464-5475
In this paper, a new kinetic model considering both oxidation and volatilization kinetics is established and applied to analyze the oxidation of SiC-B4C-xAl2O3 ceramics and other systems in various oxidation conditions. The effects of diffusion area and volume changes during the oxidation process are considered in this model. The physical meaning of each parameter in this model is explicit and simple. According to this model, the diffusion coefficient of species and the corresponding diffusion activation energy are easily available. The practicability of this model is well verified by the experimental data of SiC-B4C-xAl2O3 and other systems oxidized under different conditions. In addition, the practice shows that the model is applicable not only to the systems where oxidation and volatilization coexist, but also to the system where only oxidation plays a major role. We hope the model proposed in this work can be used in other materials with more complex environments. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(81):34376-34386
Searching high-active, stable and abundant bifunctional catalysts to replace noble metals for hydrogen and oxygen evolution reactions (HER and OER) is desired. Herein, petal-like NiCoP sheets were synthesized on carbon paper covered with a 3D nitrogen-doped carbon nanofiber network (NiCoP/CNNCP) by a simple hydrothermal process followed by phosphorization. The HER overpotential in 0.5 M H2SO4 and OER overpotential in 1 M KOH of the NiCoP/CNNCP electrode only required 55 mV and 260 mV to drive a current density of 10 mA cm?2, respectively, which was comparable or even better than most nickel-and cobalt-based phosphide catalysts. The overall water-splitting electrolyzer with an asymmetric electrolyte system assembled using NiCoP/CNNCP as bifunctional electrodes required an extremely low cell voltage of 1.04 V to achieve a current density of 10 mA cm?2, which was much lower than almost all alkaline electrolysis systems. 相似文献
4.
《Geotextiles and Geomembranes》2022,50(3):371-382
Internal stability assessment of geosynthetic-reinforced soil structures (GRSSs) has been commonly carried out assuming plane-strain conditions and dry backfills. However, failures of GRSSs usually show three-dimensional (3D) features and occur under unsaturated conditions. A procedure based on the kinematic limit-analysis method is proposed herein to assess 3D effects and the role of steady unsaturated infiltration on the required geosynthetic strength for GRSSs. A suction stress-based framework is used to describe the soil stress behavior under steady unsaturated infiltration. Based on the principle of energy-work balance, the required geosynthetic strength is determined. A comparison analysis with the prior research is conducted to verify the developed method. Two kinds of backfills, i.e., high-quality backfill and marginal backfill, are considered for comparison in this work. It is shown that accounting for 3D effects and the role of unsaturated infiltration considerably reduces the required geosynthetic strength. The 3D effects are primarily affected by the width-to-height ratio of GRSSs, and the contribution of unsaturated infiltration is mainly influenced by the soil type, flow rate, GRSS's height, and location of the water table. 相似文献
5.
《Ceramics International》2022,48(22):32973-32985
Multilayer structure design is one of the most promising methods for improving the comprehensive performance of AlCrN-based hard coatings applied to cutting tools. In this study, four types of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings, with different modulated thicknesses, were deposited to investigate their microstructure, mechanical, tribological, and oxidizing properties. All multilayer coatings exhibited grain growth along the crystallographic plane of (200) with a NaCl-type face-centered cubic (FCC) structure. The results show that, as the modulation thickness decreases from ~35 nm to ~10 nm, (1) the grain refinement effect is increasingly evident; (2) all multilayer coatings show a hardness of >30 GPa and an elastic modulus of >300 GPa. Both the ability to resist elastic strain to failure and the plastic deformation of multilayer coatings increase. In addition, their resistance to cracking reduces; (3) the wear rates of these multilayer coatings reduce successively from 1.78 × 10?16 m3 N?1 m?1 to 7.7 × 10?17 m3 N?1 m?1. This is attributed to an increase in self-lubricating VOx and a decrease in adhesives from the counterparts; (4) the best high-temperature oxidation resistance was obtained for the multilayer coating with a modulated thickness of ~15 nm. 相似文献
6.
《中国有色金属学会会刊》2021,31(8):2468-2478
An acoustic emission (AE) experiment was carried out to explore the AE location accuracy influenced by temperature. A hollow hemispherical specimen was used to simulate common underground structures. In the process of heating with the flame, the pulse signal of constant frequency was stimulated as an AE source. Then AE signals received by each sensor were collected and used for comparing localization accuracy at different temperatures. Results show that location errors of AE keep the same phenomenon in the early and middle heating stages. In the later stage of heating, location errors of AE increase sharply due to the appearance of cracks. This provides some beneficial suggestions on decreasing location errors of structural cracks caused by temperature and improves the ability of underground structure disaster prevention and control. 相似文献
7.
《中国有色金属学会会刊》2021,31(11):3530-3548
In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements. Three generations of pyrite (Py I, Py II, and Py III) in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central, western, and northern (C_Py, W_Py, and N_Py) mining districts are selected for comparison. Compared with Py I and Py III, the contents of most elements in Py II are apparently higher. The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py. The highest As, Se, and Pb contents were found in W_Py and N_Py. These results indicate the drastic changes in the temperature and fluid mixing during the mineralization. The occurrence of fluctuation and change in temperature and f(O2) was triggered by intermittent pulses of magmatic-hydrothermal fluids, mixing with meteoric water, and water−rock interactions. The sulfur isotopes of all species of pyrite indicated the magmatic source. The change in the f(O2) conditions caused slight differences in the sulfur isotope compositions. Consequently, a metallogenic model was proposed to explain the ore-forming processes. 相似文献
8.
Tao TIAN Chao-lan ZHANG Feng ZHU Shan-xin YUAN Ying GUO Sheng-guo XUE 《中国有色金属学会会刊》2021,31(5):1484-1495
A column experiment was conducted to investigate the effect of phosphogypsum (PG) on the saline- alkalinity, and aggregate stability of bauxite residue. Results showed that: with increasing leaching time, the concentrations of saline-alkali ions decreased while the concentration increased in bauxite residue leachate; compared with CK (control group) treatment, pH, electric conductivity (EC), exchangeable sodium percentage (ESP), sodium absorption ratio (SAR), and exchangeable Na+ content of bauxite residue were reduced following PG treatment; average particle sizes in aggregates following CK and PG treatments were determined to be 155 and 193 nm, respectively. SR-μCT test results also confirmed that bauxite residue following PG treatment acquired larger aggregates and larger pore diameter. These results indicate that the PG treatment could significantly modulate the saline-alkalinity, and simultaneously enhance aggregate stability of bauxite residue, which provides a facile approach to reclaim bauxite residue disposal areas. 相似文献
9.
10.
《中国有色金属学会会刊》2021,31(9):2740-2749
CrAlYN coatings with different Y contents (0, 5 and 12 at.%) were deposited by cathodic arc evaporation to investigate the influence of Y-addition on the structure, mechanical and thermal properties of CrAlN coatings by using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis and nanoindentation. The structural transformation of single phase cubic Cr0.42Al0.58N and Cr0.39Al0.56Y0.05N coatings to cubic–wurtzite mixed Cr0.32Al0.56Y0.12N coating leads to a drop in hardness from (30.2±0.7) GPa of Cr0.42Al0.58N and (32.0±1.0) GPa of Cr0.39Al0.56Y0.05N to (25.2±0.7) GPa of Cr0.32Al0.56Y0.12N. The incorporation of 5 at.% Y retards the thermal decomposition of CrAlN, verified by the postponed precipitation of w-AlN and N-loss upon annealing. Correspondingly, Cr0.39Al0.56Y0.05N coating consistently exhibits the highest hardness value during thermal annealing. Nevertheless, alloying with Y exerts an adverse effect on the oxidation resistance of CrAlN. 相似文献