全文获取类型
收费全文 | 36298篇 |
免费 | 1515篇 |
国内免费 | 1095篇 |
专业分类
电工技术 | 1346篇 |
技术理论 | 1篇 |
综合类 | 1820篇 |
化学工业 | 7034篇 |
金属工艺 | 4214篇 |
机械仪表 | 1709篇 |
建筑科学 | 907篇 |
矿业工程 | 459篇 |
能源动力 | 1226篇 |
轻工业 | 1387篇 |
水利工程 | 110篇 |
石油天然气 | 704篇 |
武器工业 | 222篇 |
无线电 | 3848篇 |
一般工业技术 | 5607篇 |
冶金工业 | 755篇 |
原子能技术 | 628篇 |
自动化技术 | 6931篇 |
出版年
2024年 | 37篇 |
2023年 | 304篇 |
2022年 | 373篇 |
2021年 | 638篇 |
2020年 | 532篇 |
2019年 | 542篇 |
2018年 | 486篇 |
2017年 | 677篇 |
2016年 | 980篇 |
2015年 | 1225篇 |
2014年 | 1910篇 |
2013年 | 1803篇 |
2012年 | 2007篇 |
2011年 | 3515篇 |
2010年 | 2812篇 |
2009年 | 3006篇 |
2008年 | 2582篇 |
2007年 | 2679篇 |
2006年 | 2301篇 |
2005年 | 2008篇 |
2004年 | 1737篇 |
2003年 | 1731篇 |
2002年 | 1488篇 |
2001年 | 768篇 |
2000年 | 623篇 |
1999年 | 494篇 |
1998年 | 347篇 |
1997年 | 306篇 |
1996年 | 197篇 |
1995年 | 135篇 |
1994年 | 131篇 |
1993年 | 108篇 |
1992年 | 94篇 |
1991年 | 62篇 |
1990年 | 57篇 |
1989年 | 47篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
51.
以废弃的流化催化裂化催化剂(简称SFCC)为载体、β-环糊精为金属络合剂、硝酸镍为镍源,采用湿法浸渍法制备β-环糊精修饰的Ni/SFCC催化剂(简称Ni/SFCC-CD催化剂),考察其对C9石油树脂的催化加氢性能。通过BET比表面积测试、H2程序升温还原、X射线光电子能谱等手段对催化剂的物相结构进行表征,研究β-环糊精的作用机理及其对催化剂加氢性能的影响。研究结果表明:在反应温度为260 ℃、反应压力为7 MPa、反应时间为2.0 h的最优条件下,采用Ni/SFCC-CD催化C9石油树脂加氢,可制得溴值为1.45 gBr/(100 g)、色号(加纳德)小于1的水白色氢化C9石油树脂,催化剂循环使用4次后仍保持良好活性;β-环糊精的作用机理是:β-环糊精与硝酸镍产生络合作用,抑制硝酸镍的分解、控制NiO的结晶过程和增强活性组分Ni与载体之间的相互作用力,从而提高了Ni/SFCC-CD的催化活性和稳定性。 相似文献
52.
Modern refractory castables contain between 3.5 and 5?wt.-% water that is necessary for sufficient flow during emplacement and for the formation of hydrate phases, necessary for the green strength of the material. Prior to the high temperature use of this material, it must be dried very carefully to avoid explosive spalling.This paper will demonstrate that beside conventional drying of pre-shaped materials in resistance furnaces microwave radiation is an energy saving and rapid method to remove pore water as well as hydrate bond water from the castable. In comparison to resistance furnaces, the use of microwave radiation does not affect the castable properties as there are mechanical strength (MOR, CCS), open porosity and pore size distribution. This study proved microwave radiation as valuable alternative with a series of tabular alumina based low cement castables (LLC) in which the water-to-cement-ratio (wcr = 0.64, 0.75, 0.82 and 1.13) was systematically altered by changing the cement concentration at constant mixing water concentration of 4.5%. 相似文献
53.
Taro Shimonosono Yoshihiro Hirata Mubin Changgan Syohei Kamei Rina Tokaiya Soichiro Sameshima Toshifumi Yoshidome Katsuhiko Yamaji 《Ceramics International》2018,44(8):8904-8912
This paper reports the performance of porous Gd-doped ceria (GDC) electrochemical cells with Co metal in both electrodes (cell No. 1) and with Ni metal in the cathode and Co metal in the anode (cell No. 2) for CO2 decomposition, CH4 decomposition, and the dry reforming reaction of a biogas with CO2 gas (CH4 + CO2 → 2H2 + 2CO) or with O2 gas in air (3CH4 +?1.875CO2 +?1.314O2 → 6H2 +?4.875CO +?0.7515O2). GDC cell No. 1 produced H2 gas at formation rates of 0.055 and 0.33?mL-H2/(min?m2-electrode) per 1?mL-supplied gas/(min?m2-electrode) at 600?°C and 800?°C, respectively, by the reforming of the biogas with CO2 gas. Similarly, cell No. 2 produced H2 gas at formation rates of 0.40?mL-H2/(min?m2) per 1?mL-supplied gas/(min?m2) at 800?°C from a mixture of biogas and CO2 gas. The dry reforming of a real biogas with CO2 or O2 gas at 800?°C proceeded thermodynamically over the Co or Ni metal catalyst in the cathode of the porous GDC cell. Faraday's law controlled the dry reforming rate of the biogas at 600?°C in cell No. 2. This paper also clarifies the influence of carbon deposition, which originates from CH4 pyrolysis (CH4 → C + 2H2) and disproportionation of CO gas (2CO → C + CO2), on the cell performance during dry reforming. The dry reforming of a biogas with O2 molecules from air exhibits high durability because of the oxidation of the deposited carbon by supplied air. 相似文献
54.
《Ceramics International》2020,46(13):21056-21063
Coprecipitation-derived, sacrificial polymeric (urethane) foam-fabricated bredigite (Ca7MgSi4O16) scaffolds were processed by individual and combined treatments of fluoride doping and poly (lactic-co-glycolic acid) (PLGA) coating and then studied in terms of structure, mechanical strength, bioactivity and cell biocompatibility in vitro. According to scanning electron microscopy and Archimedes porosimetry, the geometrical characteristics of pores for all the scaffolds are in the appropriate range for hard tissue regeneration applications. The apatite-formation ability of the samples immersed in a simulated body fluid is improved by doping for both the bare and coated conditions, based on microscopic and energy-dispersive X-ray spectroscopic analyses. Both the treatments advantageously buffer physiological pH changes imposed due to the fast bioresorption of the ceramic. Also, the biodegradable PLGA coating typically enhances the compressive strength of the scaffolds, which is critical for bone tissue engineering. In accordance with the MTT assay on osteoblast-like cells (MG-63) cultures, both the processes individually enhance the cell viability, while the highest improvement is obtained for the combined application of them. It is finally concluded that fluoride doping and PLGA coating are impressive approaches to improve the bioperformance of bredigite-based scaffolds. 相似文献
55.
The present paper deals with the experimental assessment of the effectiveness of steel fibre reinforcement in terms of punching resistance of centrically loaded flat slabs, and to the development of an analytical model capable of predicting the punching behaviour of this type of structures. For this purpose, eight slabs of 2550 × 2550 × 150 mm3 dimensions were tested up to failure, by investigating the influence of the content of steel fibres (0, 60, 75 and 90 kg/m3) and concrete strength class (50 and 70 MPa). Two reference slabs without fibre reinforcement, one for each concrete strength class, and one slab for each fibre content and each strength class compose the experimental program. All slabs were flexurally reinforced with a grid of ribbed steel bars in a percentage to assure punching failure mode for the reference slabs. Hooked ends steel fibres provided the unique shear reinforcement. The results have revealed that steel fibres are very effective in converting brittle punching failure into ductile flexural failure, by increasing both the ultimate load and deflection, as long as adequate fibre reinforcement is assured. An analytical model was developed based on the most recent concepts proposed by the fib Mode Code 2010 for predicting the punching resistance of flat slabs and for the characterization of the behaviour of fibre reinforced concrete. The most refined version of this model was capable of predicting the punching resistance of the tested slabs with excellent accuracy and coefficient of variation of about 5%. 相似文献
56.
57.
The present study focuses on the sintering of silicon carbide-based ceramics (SiC) by liquid phase sintering (LPS) followed by characterization of the produced ceramics. AlN/Re2O3 mixtures were used as additives in the LPS process. In the first step, the LPS-SiC materials were produced in a graphite resistance furnace in the form of discs at different temperatures. The conditions with the best results regarding real density and relative density were taken as reference for sintering in the form of prismatic bars. In the second step, these samples were evaluated regarding fracture toughness (KIC), by the Single Edge V Notch Beam – SEVNB – method, and flexural strength. KIC behavior was evaluated according to the depth and curvature radius of the notches. Reliable KIC values were presented when the ceramic displayed a small curvature radius at the notch tip. When the radius was large, it did not maintain the square root singularity of the notch tip. Tests were carried out to determine KIC values in atmospheric air and water. KIC results were lower in water than air, with a decrease ranging between 2.56% and 11.26%. The observations indicated a direct grain size correlation between KIC values and fracture strength of the SiC ceramics. 相似文献
58.
In this paper, debonding phenomena between carbon fiber reinforced polymer (CFRP) strips and masonry support were investigated on the basis of single-lap shear tests, considering different dimensions of the bond length. To capture the post-peak response of the CFRP–masonry joint, the slip between the support and the reinforcement strip was controlled using a clip gauge positioned at the end of the reinforcement. The tests were simulated by means of a finite element model able to capture the post-peak snap-back behavior due to the failure process. The numerical model is based on zero-thickness interface elements and on a proper non-linear cohesive law. The comparison between experimental and numerical results was performed in terms of overall response, measured by both the machine stroke and the clip gauge positioned at the free end of the reinforcement. The cases of effective bond length greater and lesser than the minimum anchorage length, suggested by the CNR Italian recommendation, were considered. 相似文献
59.
《Intermetallics》2015
Drop-tube processing was used to rapidly solidify droplets of Ni64.7Fe10Si25.3 and Ni59.7Fe15Si25.3 alloys. In the larger droplets, and therefore at low cooling rates, only two phases, γ-Ni31Si12 and β1-Ni3Si were observed. Conversely, in the smaller droplets, and therefore at higher cooling rates, the metastable phase Ni25Si9 was also observed. The critical cooling rate for the formation of Ni25Si9 was estimated as 5 × 103 K s−1. SEM and TEM analysis reveals three typical microstructures: (I) a regular structure, comprising single-phase γ-Ni31Si12 and a eutectic structure between γ-Ni31Si12 and β1-Ni3Si; (II) a refined lamellar structure with a lamellar spacing <50 nm comprising γ-Ni31Si12 and β1-Ni3Si; (III) an anomalous structure with a matrix of Ni25Si9 and only a very small proportion of a second, and as yet unidentified, phase. These results indicate that there is an extended stability field for Ni25Si9 in the Ni-rich part of the Ni–Fe–Si ternary system in comparison to the Ni–Si binary system. With an increase of cooling rate, an increasing fraction of small droplets experience high undercoolings and, therefore, can be undercooled into the Ni25Si9 stability field forming droplets consisting of only the anomalous structure (III). The Fe atoms are found to occupy different substitutional sites in different phase, i.e. Fe substitutes for Ni in the γ phase and Si in the L12 (β1) phase respectively. 相似文献
60.
Static stresses analysis of carbon nano-tube reinforced composite (CNTRC) cylinder made of poly-vinylidene fluoride (PVDF) is investigated in this study. Non-axisymmetric thermo-mechanical loads are applied on cylinder in presence of uniform longitudinal magnetic field and radial electric field. The surrounded elastic medium is modeled by Pasternak foundation because of its advantages to the Winkler type. Distribution of radial, circumferential and effective stresses, temperature field and electric displacements in CNTRC cylinder are determined based on Mori–Tanaka theory. The detailed parametric study is conducted, focusing on the remarkable effects of magnetic field intensity, elastic medium, angle orientation and volume fraction of carbon nano-tubes (CNTs) on distribution of effective stress. Results demonstrated that fatigue life of CNTRC cylinder will be significantly dependent on magnetic intensity, angle orientation and volume fraction of CNTs. Results of this research can be used for optimum design of thick-walled cylinders under multi-physical fields. 相似文献