全文获取类型
收费全文 | 30588篇 |
免费 | 4306篇 |
国内免费 | 2946篇 |
专业分类
电工技术 | 3587篇 |
技术理论 | 2篇 |
综合类 | 4099篇 |
化学工业 | 1769篇 |
金属工艺 | 2444篇 |
机械仪表 | 2300篇 |
建筑科学 | 1447篇 |
矿业工程 | 1233篇 |
能源动力 | 675篇 |
轻工业 | 571篇 |
水利工程 | 647篇 |
石油天然气 | 968篇 |
武器工业 | 400篇 |
无线电 | 4596篇 |
一般工业技术 | 3151篇 |
冶金工业 | 1236篇 |
原子能技术 | 142篇 |
自动化技术 | 8573篇 |
出版年
2024年 | 43篇 |
2023年 | 336篇 |
2022年 | 621篇 |
2021年 | 837篇 |
2020年 | 898篇 |
2019年 | 723篇 |
2018年 | 662篇 |
2017年 | 893篇 |
2016年 | 1030篇 |
2015年 | 1273篇 |
2014年 | 1920篇 |
2013年 | 1854篇 |
2012年 | 2399篇 |
2011年 | 2661篇 |
2010年 | 2150篇 |
2009年 | 2185篇 |
2008年 | 2181篇 |
2007年 | 2685篇 |
2006年 | 2345篇 |
2005年 | 1957篇 |
2004年 | 1519篇 |
2003年 | 1302篇 |
2002年 | 972篇 |
2001年 | 837篇 |
2000年 | 746篇 |
1999年 | 538篇 |
1998年 | 417篇 |
1997年 | 385篇 |
1996年 | 281篇 |
1995年 | 234篇 |
1994年 | 226篇 |
1993年 | 134篇 |
1992年 | 120篇 |
1991年 | 113篇 |
1990年 | 101篇 |
1989年 | 94篇 |
1988年 | 58篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 27 毫秒
11.
Understanding the phase transition behavior of the rhombohedral phase (R) and tetragonal phase (T) of the relaxor ferroelectric PMN–PT single crystals under mechanical load is essential for the potential voltage-free controlled ferroelectric-based nanodevices. Relaxor ferroelectric single crystals PMN–PT, under a local inhomogeneous mechanical load, were studied experimentally by the nanoindentation tests and Raman spectroscopy measurements. The observations show that the rhombohedral phase can be transformed successfully to the tetragonal phase under a mechanical stress, and the tetragonal phase in the PMN–PT single crystals presents a structural stability. The phase transition induced by the mechanical stress with different strain rates further indicates that the relaxor ferroelectric single crystals possess a potential mechanical controllability. The present study reveals the phase transition pathway of the relaxor ferroelectric single crystal under inhomogeneous stress and provides the exciting possibility of the control of mechanically induced phase transition for ferroelectrics. 相似文献
12.
《International Journal of Hydrogen Energy》2022,47(77):32928-32939
The development of efficient and stable electrocatalysts is of great significance for improving water splitting. Among them, transition metal oxyhydroxides show excellent performance in oxygen evolution reactions (OER), but there are certain difficulties in direct preparation. Recently, Metal–organic frameworks (MOFs) as precatalysts or precursors have shown promising catalytic performance in OER and can be decomposed under alkaline conditions. Therefore, using a mild and controllable way to convert MOFs into oxyhydroxides and retaining the original structural advantages is crucial for improving the catalytic activity. Herein, a rapid electrochemical strategy is used to activate well-mixed MOFs to prepare Co/Ni oxyhydroxide nanosheets for efficient OER catalysts, and the structural transformation in this process was investigated in detail by using scanning electron microscope, X-ray diffraction, Raman, X-ray photoelectron spectroscopy and electrochemical methods. It is discovered that electrochemical activation can promote ligand substitution of well-mixed MOFs to form porous oxyhydroxide nanosheets and tune the electronic structure of the metal (Co and Ni), which can lead to more active site exposure and accelerate charge transfer. In addition, the change of structure also improves hydrophilicity, as well as benefiting from the strong synergistic effect between multiple species, the optimal a-MCoNi–MOF/NF has excellent OER performance and long-term stability. More obviously, the porous CoNiOOH nanosheets are formed in situ during electrochemical activation process through structural transformation and acts as the active centers. This work provides new insights for mild synthesis of MOFs derivatives and also provides ideas for the preparation of highly efficient catalysts. 相似文献
13.
支承或连接构件对梁结构的动力学性能有至关重要影响,必须保证其在振动过程中不发生破坏或者失效。通过合理设计和布局附加弹性支承可以实现对这些重要连接构件所承受约束反力的控制。应用微分变换法推导含附加支承的梁结构支承约束反力及其对于附加支承位置和刚度的灵敏度表达式,并通过优化设计附加支承位置和刚度实现具有弹性约束端的简支梁结构各支承约束反力的平衡,可提高结构的动力学性能。 相似文献
14.
《Ceramics International》2022,48(4):4401-4423
Nano-zirconia has been widely applied due to its excellent physical and chemical properties (e.g., high strength, corrosion resistance, oxygen ion conductivity). Existing preparation methods of nano-zirconia tend to require long reaction time, and the sizes of final particles are large with uneven distributions. Sub-/supercritical hydrothermal synthesis of nanoparticles is favored by researchers owing to controllable reaction process, uniform particle size distribution, good reproducibility, short reaction time, high conversion rate and harmlessness to environment. In this paper, the characteristics and mechanisms of dissolution, crystallization and growth of nano-zirconia during sub-/supercritical hydrothermal synthesis are systematically reviewed. The influences of process and material parameters on the size and purity of particles are analyzed. Then, the reaction mechanism and product phase transition mechanism during hydrothermal synthesis of zirconia are summarized to provide a theoretical reference for the oriented preparation. Finally, the improvement and commercialization of sub-/supercritical hydrothermal synthesis technology are evaluated, and the future research topics are proposed. 相似文献
15.
Multi-channel and single-channel image denoising are on two important development fronts. Integrating multi-channel and single-channel image denoisers for further improvement is a valuable research direction. A natural assumption is that using more useful information is helpful to the output results. In this paper, a novel multi-channel and single-channel fusion paradigm (MSF) is proposed. The proposed MSF works by fusing the estimates of a multi-channel image denoiser and a single-channel image denoiser. The performance of recent multi-channel image denoising methods involved in the proposed MSF can be further improved at low additional time-consuming cost. Specifically, the validity principle of the proposed MSF is that the fused single-channel image denoiser can produce auxiliary estimate for the involved multi-channel image denoiser in a designed underdetermined transform domain. Based on the underdetermined transformation, we create a corresponding orthogonal transformation for fusion and better restore the multi-channel images. The quantitative and visual comparison results demonstrate that the proposed MSF can be effectively applied to several state-of-the-art multi-channel image denoising methods. 相似文献
16.
Coline Grisotto Janice Taïl Cynthia Planesse Nicolas Diotel Marie-Paule Gonthier Olivier Meilhac David Couret 《International journal of molecular sciences》2021,22(9)
Background: Stroke in context of type 2 diabetes (T2D) is associated with a poorer outcome than in non-diabetic conditions. We aimed at creating a new reproducible mouse model of stroke in impaired glucose tolerance conditions induced by high-fat diet. Methods: Adult C57BL6 mice were fed for 2 months with either normal diet (ND) or high-fat diet (HFD). We used a model of Middle Cerebral Artery Occlusion (MCAO) for 90 min. Oral Glucose Tolerance Test (OGTT) and Insulin Tolerance Test (ITT) were used to assess pre-diabetic status. Brain infarct volume, hemorrhagic transformation (HT) as well as systemic and cerebral inflammatory markers were evaluated. Results: HFD was associated with an increased body weight and glycemia following OGTT. The HFD group presented a significant increase in brain infarct volume (38.7 (IQR 30–46.7%) vs. 28.45 (IQR 21–30%); p = 0.016) and HT (HFD: 2 (IQR 1–5) vs. ND: 0 (IQR 0–1); p = 0.012) and higher levels of IL-6 and MCP-1 in infarcted hemisphere compared to the ND group. Conclusion: Two months of HFD in adult mice were sufficient to alter the lipid profile and the control of hyperglycemia. These metabolic perturbations were significantly associated with increased infarct volume and hemorrhagic complications. 相似文献
17.
The symmetrical and asymmetrical electrodes made of Mg were studied in 0.1-M NaCl electrolyte adjusted at pH 12. The statistical and wavelet methods were employed for analyzing the electrochemical current noise (ECN) signals. The asymmetric configuration was used for electrochemical detection of filiform corrosion on Mg electrode. The real time scale of the dominant transients of the asymmetric electrodes was detected on the basis of the maximum peak in the SDPS plots. The SDPS values of the real time scale crystals of the ECN signals resulting from asymmetrical electrodes increased with the increase in immersion time due to the onset of filiform corrosion. 相似文献
18.
Wenhui Zhu Haizhen Huan Ying Bu Xuepeng Li David Shiuan Jianrong Li Xiaotao Sun 《International Journal of Food Science & Technology》2019,54(6):2159-2168
Protein oxidation is considered as an important issue in food preservation process. In the present study, the potential influence of protein oxidation on water holding capacity and protein structure of jumbo squid (Dosidicus gigas) mantle was investigated. After the hydroxyl radical oxidation, it was found that the carbonyl, surface hydrophobicity and dityrosine content of myofibrillar protein significantly increased (P < 0.05), while the content of total sulphydryl decreased significantly (P < 0.01). Meanwhile, the fluorescence intensity of squid was weakened, and the maximum absorption peak of fluorescence red shift as the H2O2 concentration increased. The sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed that not only the protein cross-linking but also degradation could have occurred. The content of α-helix decreased, the content of β-sheet, β-turn and the unordered structures increased after oxidation. In addition, oxidation resulted in a decrease in water holding capacity. Taken together, oxidation resulted in the damage of the myofibrillar structure, the increase in muscle loss rate and the decrease in water holding capacity. 相似文献
19.
《Journal of the European Ceramic Society》2019,39(14):4338-4346
Yttria, yttria-ceria and yttria-ceria-lanthana stabilized zirconia powders were prepared by coprecipitation. Their tetragonal-to-monoclinic phase (t→m) transformation was investigated by calcining the powders in a temperature range of 400–1400 °C for 2 h. The results show that after doping with 0.1 to 0.3 mol.% La2O3 and calcining at 1400 °C in air, unusual redox behaviours of cerium were detected in the 1.5 mol.% Y2O3+5.5 mol.% CeO2 co-stabilized zirconia. Grain refinement and a sharp reduction in oxygen vacancy concentration were observed simultaneously. The t→m transition was not found in the 0.1 mol.% La2O3 doped zirconia but appeared in the cases with a higher dopant content. The changes are discussed with regards to the grain size, valence change of cerium, presence of oxygen vacancies, and segregation of the dopants at grain boundaries. 相似文献
20.
《Journal of the European Ceramic Society》2022,42(4):1354-1361
Core–rim structures were observed as common features in Y-α-SiAlON ceramics hot-pressed between 1550?1950 °C. We found most dopants were taken into α’-rims, and a transition layer grown first on α-cores from liquid-phase over-saturated with metal solutes. Elongated β’-grain were formed as minor phase with α’- or AlN-cores thus only after the α’ matrix had consumed up all Y solutes, revealing that the α’ → β’ transformation is controlled by the transient liquid-phase and similar defects and dangling bonds could be detected in both SiAlON phases by cathodoluminescence. Quantitative assessment of Ym/3Si12?(m+n)Alm+nOnN16?n demonstrates the multiphase evolution, initiated by over-saturation of Y solutes at low temperatures thus retaining α-phase as cores to lower the infra-red transmittance, dictated by homogenization of Al solutes at higher temperature. The elimination of those phase boundaries leads to better dopant and sintering design for achieving transparent and high-performance SiAlON ceramics. 相似文献