全文获取类型
收费全文 | 40989篇 |
免费 | 3537篇 |
国内免费 | 2577篇 |
专业分类
电工技术 | 1202篇 |
技术理论 | 1篇 |
综合类 | 1993篇 |
化学工业 | 10205篇 |
金属工艺 | 10361篇 |
机械仪表 | 1929篇 |
建筑科学 | 1443篇 |
矿业工程 | 668篇 |
能源动力 | 1338篇 |
轻工业 | 3149篇 |
水利工程 | 113篇 |
石油天然气 | 812篇 |
武器工业 | 409篇 |
无线电 | 2319篇 |
一般工业技术 | 6765篇 |
冶金工业 | 2504篇 |
原子能技术 | 1514篇 |
自动化技术 | 378篇 |
出版年
2024年 | 163篇 |
2023年 | 821篇 |
2022年 | 1289篇 |
2021年 | 1528篇 |
2020年 | 1396篇 |
2019年 | 1358篇 |
2018年 | 1390篇 |
2017年 | 1611篇 |
2016年 | 1418篇 |
2015年 | 1399篇 |
2014年 | 2061篇 |
2013年 | 2414篇 |
2012年 | 2613篇 |
2011年 | 3061篇 |
2010年 | 2332篇 |
2009年 | 2329篇 |
2008年 | 1993篇 |
2007年 | 2616篇 |
2006年 | 2543篇 |
2005年 | 2093篇 |
2004年 | 1891篇 |
2003年 | 1494篇 |
2002年 | 1277篇 |
2001年 | 1075篇 |
2000年 | 954篇 |
1999年 | 753篇 |
1998年 | 622篇 |
1997年 | 521篇 |
1996年 | 470篇 |
1995年 | 351篇 |
1994年 | 291篇 |
1993年 | 242篇 |
1992年 | 211篇 |
1991年 | 137篇 |
1990年 | 85篇 |
1989年 | 92篇 |
1988年 | 43篇 |
1987年 | 14篇 |
1986年 | 26篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 33篇 |
1981年 | 23篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1959年 | 5篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
大直径厚壁气瓶内部淬火时的流动换热过程极其复杂,受到多种因素的影响,而研究气瓶内部压强和温度的变化规律对改善流动换热效果、提高产品组织性能具有重要的理论指导意义。以914 mm厚壁气瓶和瓶内流体为研究对象,建立了二维等效流 固耦合模型;采用多喷嘴系统对气瓶内外进行喷水淬火,研究了气瓶总长、喷水流速及淬火时间对瓶内压强及内壁温度的影响,通过间歇淬火试验验证了数学模型的正确性。结果发现,气瓶长度对瓶内压强和瓶壁温度的影响显著,喷水流速次之,当喷水流速大于8 m/s后,水量对瓶壁的冷却效果大大降低;气瓶内壁长度方向的温度梯度分别随气瓶总长的增加和淬火时间的延长而减小,但基本不受喷水量的影响。 相似文献
32.
采用低温水等离子体技术,在三通道聚氯乙烯(PVC)膜表面接枝了甲基丙烯氧基苄基二甲基氯化铵(DMAE)单体,增强了膜亲水和抗菌性能。通过红外分析,表明DMAE成功接枝到了PVC膜上,水通量提高两倍,PVC-ir-H2O膜(通过水等离子体处理的膜)对牛血清蛋白(BSA)的吸附能力下降67%,对BSA溶液的通量从7.7提高至40 kg?m-2?h-1,并且对BSA的截留能力不变。通过静态及动态抗菌实验,接枝后的PVC膜(PVC-g-PMAE膜)抗菌率达到100%,膜组件运行中的抗菌率也达到82%以上。在保证细菌截留率100%的同时,其渗透通量提高三倍。该膜表面修饰工程技术能实现膜表面的均一化改性,且绿色环保、操作简便、成本低,改性膜在饮用水处理领域,尤其是家用净水器中展现了很好的应用前景。 相似文献
33.
Role of MgO on densification and mechanical properties in spark plasma sintered Os0.9Re0.1B2 ceramic
《Ceramics International》2020,46(3):2612-2617
To promote the densification and therefore the mechanical properties of boride-based ceramics, MgO was added as sintering aid into Os0.9Re0.1B2 powders for densification by using spark plasma sintering (SPS). The Os0.9Re0.1B2 powders were synthesized by mechanochemical method from powder mixture of Os, Re and amorphous B. The role of MgO on densification, phase composition, microstructure and mechanical properties (hardness, fracture toughness and wear behavior) were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM) with energy-dispersive spectroscopy (EDS), micro indentation and ball-on-disk tribometer. The results show that, with the introduction of MgO as sintering aid, the relative density of the Os0.9Re0.1B2 ceramic samples increased. When the MgO content reached 9 wt%, the as-sintered sample is almost fully dense. No obvious regularity was found from the samples with the addition of different content of MgO. Vickers hardness values of the samples with 0, 3 wt% and 9 wt% MgO are found to be very close with each other within the experimental error (~30 GPa), while the sample with the addition of 6 wt% MgO exhibits the highest hardness of ~35 GPa. The fracture toughness of the samples is decreased slightly with the addition of MgO. The friction coefficient and wear rate of the sample with the addition of 6 wt% MgO was also found to be the lowest among all samples, which indicate best wear resistance. As a whole, with the addition content of 6 wt% MgO, the Os0.9Re0.1B2 ceramic sample performs relatively excellent mechanical properties among four groups of samples. 相似文献
34.
《Ceramics International》2020,46(15):23417-23426
Yttria stabilized hafnia (Hf0.84Y0.16O1.92, YSH16) coatings were sprayed by atmospheric plasma spraying (APS). The effects of thermal aging at 1400 °C on the microstructures, mechanical properties and thermal conductivity of the coatings were studied. The results show that the as-sprayed coating was composed of the cubic phase, and the nano-sized monoclinic (M) phase was precipitated in the annealed coating. The presence of M phase effectively constrained the sintering of the coating due to its superior sintering-resistance. The Young's modulus kept at a nearly same level of ~78 GPa even after annealing, and the coating annealed for 6 h yielded a maximum value of hardness but revealed a declining tendency in the Vicker's hardness with prolonged sintering time. The thermal conductivity increased from 0.8-0.95 W m-1 K-1 at as-sprayed state to 1.6 W m-1 K-1 after annealing at 1400 °C for 96 h. The dual-phase coating is promising to serve at temperatures above 1400 °C due to its excellent thermal stability and mechanical properties. 相似文献
35.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions. 相似文献
36.
37.
38.
Shengyue Gu Shouyang Zhang Fei Liu Wei Li 《Journal of the European Ceramic Society》2018,38(15):5082-5091
Y2Hf2O7 possesses low thermal conductivity and high melting point, which make it promising for a new anti-ablation material. For evaluating the thermal stability and the potential applications of Y2Hf2O7 on anti-ablation protection of C/C composites, Y2Hf2O7 ceramic powder was synthesized by solution combustion method and Y2Hf2O7 coating was prepared on the surface of SiC coated C/C composites using SAPS. Results shown that the coating exhibits good ablation resistance under the heat flux of 2.4?MW/m2 with the linear and mass ablation rates are 0.16?μm?s?1 and ?0.028?mg?s?1, respectively, after ablation for 40?s. With the prolonging of the ablation time, the increasing thermal stress causes the increase of cracks. Moreover, the chemical erosion from SiO2 and the physical volatilization of low temperature molten products aggravate failure of the Y2Hf2O7 coating. 相似文献
39.
目的: 建立快速灵敏的LC-MS/MS法测定人血浆中阿莫西林浓度,并用于两种阿莫西林胶囊的一致性评价。方法: 采用岛津公司LCMS-8060型LC-MS/MS仪,以MRM模式测定阿莫西林(m/z 366.00/114.00)的浓度,d4-阿莫西林作内标(m/z 370.10/114.05),离子源为ESI源。色谱柱选用Waters ACQUITY BEH C18(2.1×50 mm,1.7 μm),梯度洗脱。血浆样本加入内标,经甲醇沉淀蛋白后取上清液进样检测。结果: 所建方法经验证,其线性、准确度、精密度、最低定量限、提取回收率、特异性、基质效应、稳定性等各项指标均符合CFDA的指导原则及最新核查标准要求,并较文献报道中的方法有处理简单、灵敏度高、色谱峰形好的优点。结论: 所建方法快速、灵敏,适用于人血浆中阿莫西林浓度的检测。用于一致性评价的样本实测,两种制剂生物等效。 相似文献
40.
Mohan B. Ponnuchamy G. Mohan Muralikrishna Venkateswara Rao Mannava G. Srinivas Reddy 《Ceramics International》2018,44(13):15019-15023
Nanocrystalline nickel oxide (NiO) was prepared from nickel hydroxide by Spark plasma sintering (SPS) and the mechanisms involved in the densification of NiO were studied. Reverse precipitated nickel hydroxide powders were SPS processed at 400, 600 and 700?°C with 70?MPa pressure. Pure NiO with 12?nm crystallite size formed after 400?°C sintering process. However NiO grains had grown to 18 and 38?nm after 600 and 700?°C sintering respectively. NiO pellets prepared using 600 and 700?°C SPS sintering schedules had relative densities of 83% and 94% respectively. Two displacement rate regimes were observed during densification of NiO in both 600 and 700?°C sintering processes. Decomposition of nickel hydroxide and particle sliding of NiO led to first displacement rate maximum while inverse Hall-Petch based plastic deformation facilitated densification during the constant second displacement rate regime. No densification occurred during sintering holding times indicating the limited role that diffusion played during densification. 相似文献