全文获取类型
收费全文 | 100560篇 |
免费 | 8272篇 |
国内免费 | 5513篇 |
专业分类
电工技术 | 2235篇 |
技术理论 | 5篇 |
综合类 | 8595篇 |
化学工业 | 10348篇 |
金属工艺 | 21235篇 |
机械仪表 | 4929篇 |
建筑科学 | 23799篇 |
矿业工程 | 3018篇 |
能源动力 | 1518篇 |
轻工业 | 3472篇 |
水利工程 | 2222篇 |
石油天然气 | 3245篇 |
武器工业 | 639篇 |
无线电 | 1220篇 |
一般工业技术 | 10965篇 |
冶金工业 | 15261篇 |
原子能技术 | 551篇 |
自动化技术 | 1088篇 |
出版年
2024年 | 244篇 |
2023年 | 1132篇 |
2022年 | 2614篇 |
2021年 | 3121篇 |
2020年 | 3064篇 |
2019年 | 2516篇 |
2018年 | 2242篇 |
2017年 | 3288篇 |
2016年 | 3411篇 |
2015年 | 3733篇 |
2014年 | 6176篇 |
2013年 | 5913篇 |
2012年 | 7297篇 |
2011年 | 8129篇 |
2010年 | 6130篇 |
2009年 | 6296篇 |
2008年 | 5268篇 |
2007年 | 6629篇 |
2006年 | 6033篇 |
2005年 | 5083篇 |
2004年 | 4270篇 |
2003年 | 3622篇 |
2002年 | 3117篇 |
2001年 | 2645篇 |
2000年 | 2289篇 |
1999年 | 1908篇 |
1998年 | 1521篇 |
1997年 | 1364篇 |
1996年 | 1169篇 |
1995年 | 902篇 |
1994年 | 772篇 |
1993年 | 572篇 |
1992年 | 468篇 |
1991年 | 314篇 |
1990年 | 273篇 |
1989年 | 249篇 |
1988年 | 153篇 |
1987年 | 96篇 |
1986年 | 40篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 32篇 |
1982年 | 38篇 |
1981年 | 25篇 |
1980年 | 50篇 |
1979年 | 19篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1964年 | 4篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Abrasive water jet technology can be used for micro-milling using recently developed miniaturized nozzles. Abrasive water jet (AWJ) machining is often used with both the nozzle tip and workpiece submerged in water to reduce noise and contain debris. This paper compares the performance of submerged and unsubmerged abrasive water jet micro-milling of channels in 316L stainless steel and 6061-T6 aluminum at various nozzle angles and standoff distances. The effect of submergence on the diameter and effective footprint of AWJ erosion footprints was measured and compared. It was found that the centerline erosion rate decreased with channel depth due to the spreading of the jet as the effective standoff distance increased, and because of the growing effect of stagnation as the channel became deeper. The erosive jet spread over a larger effective footprint in air than in water, since particles on the jet periphery were slowed much more quickly in water due to increased drag. As a result, the width of a channel machined in air was wider than that in water. Moreover, it was observed that the instantaneous erosion rate decreased with channel depth, and that this decrease was a function only of the channel cross-sectional geometry, being independent of the type of metal, the jet angle, the standoff distance, and regardless of whether the jet was submerged or in air, in either the forward or backward directions. It is shown that submerged AWJM results in narrower features than those produced while machining in air, without a decrease in centerline etch rate. 相似文献
42.
The micromechanics models for composites usually underpredict the tensile strength of polymer nanocomposites. This paper establishes a simple model based on Kelly–Tyson theory for tensile strength of polymer/CNT nanocomposites assuming the effect of interphase between polymer and CNT. In addition, Pukanszky model is joined with the suggested model to calculate the interfacial shear strength (τ), interphase strength (σi) and critical length of CNT (Lc).The proposed approach is applied to calculate τ, σi and Lc for various samples from recent literature. It is revealed that the experimental data are well fitted to calculations by new model which confirm the important effect of interphase on the properties of nanocomposites. Moreover, the derived equations demonstrate that dissimilar correlations are found between τ and B (from Pukanszky model) as well as Lc and B. It is shown that a large B value obtained by strong interfacial adhesion between polymer and CNT is adequate to reduce Lc in polymer/CNT nanocomposites. 相似文献
43.
In this study, 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors. 相似文献
44.
《Ceramics International》2021,47(22):31413-31422
Based on reactive air brazing (RAB), we designed a new type of sealant (Ag–xCuAlO2) for joining 3 mol.% yttria-stabilized zirconia (YSZ) ceramics and AISI 310S stainless steel. The CuAlO2 content affected the wettability of the sealant on the YSZ surface, and the joints had a high shear strength when Ag–2 wt.%CuAlO2, which had a small contact angle on the YSZ substrate, was used as the sealant. In addition, the thickness of the oxide layer was reduced compared to that for the Ag–CuO sealant. The effects of the processing parameters on the microstructure and shear strength of the joints were investigated, and the as-brazed joints reached their highest shear strength (93.7 MPa) when brazed at 1040 °C for 30 min. After high-temperature oxidation at 800 °C for 200 h, the shear strength of the joints remained at 50 MPa, and no apparent change in the microstructure was observed, proving that the joints possessed excellent oxidation resistance. 相似文献
45.
《Ceramics International》2021,47(22):31268-31276
The relationship between the tensile strength of corroded domestic second-generation (2ed-gen) SiC fibers at various temperatures for 500 h in 46.5LiF-11.5NaF-42.0KF (mol. %) eutectic salt and the typical microstructure was studied. Weibull theory was used to analyze the critical defects that caused the tensile fracture, and the microstructure of fibers before and after corrosion was characterized. It is concluded that the decrease of tensile strength after corrosion at 800 °C is caused by the surface injury of fibers, which led to the shift of critical defects from the internal defects of virgin fibers to surface defects. Moreover, corrosion at higher temperature accelerates the corrosion process and dissolve the surface O-contained layer thoroughly. This shifts the critical defects back to the internal defects and will be helpful for the recovery of tensile strength of corroded fibers at the higher temperature. 相似文献
46.
47.
Musculoskeletal injuries are well-known disorders among the agricultural tractor operators. Overexertion is a critical factor which can agitate these injuries. Physical body characteristics should be measured for an ergonomically best-fit-optimal design for the operators. In this study, a designed setup was employed to derive the applied forces by tractor operators on the control tools. The different muscle strengths including leg/foot strength, hand push/pull strength, and torque strength applied by both hands were measured. A comparison was made for the obtained values for different strengths by considering the effects of hand dominance. The obtained data were used to estimate the maximum allowed forces in these tools. In contrast to the previous studies, the minimum allowed actuating forces of the pedals were calculated using reasonable assumptions. These values could provide more comfort and less exhaustion for the tractor operators. The obtained ranges were benchmarked against corresponding recommended values in some standards (ISO, ISIRI, and ASABE family). The results revealed the unsuitability of evaluated standards for a proper design and the excessive overestimation of those recommended values (in some cases more than 3 times). In all of the design procedure, a suitable attention was paid to accommodate it with more than 90% of target population.Relevance to industryA prosperous industry which considers ergonomic factors in the design of agricultural machine workplace can overcome the disorders and generate more comfort. Evaluating more exact mechanical forces can result in a suitable design of workplace. 相似文献
48.
49.
Longbang Qing Yuehua Cheng Ru Mu 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(11):2533-2543
Based on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at the crack tip of the composite. The equivalent initial fracture toughness was used to characterize the crack initiation of SFRC. A simplified method for determining the of SFRC was proposed based on a linear regression method. Fracture tests were conducted on three‐point bending notched beams with different steel fibre volume fractions and specimen sizes to study the crack initiation behaviour of aligned steel fibre reinforced cementitious composite (ASFRC). of ASFRC was calculated, and the size effect of was analysed. The results showed that slightly increased with the steel fibre volume fraction and gradually became stable. For the tested specimens, whose heights varied between 40 and 100 mm, the specimen size had little impact on the . 相似文献
50.
Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI ... 相似文献