全文获取类型
收费全文 | 67506篇 |
免费 | 2913篇 |
国内免费 | 2122篇 |
专业分类
电工技术 | 2251篇 |
技术理论 | 6篇 |
综合类 | 1780篇 |
化学工业 | 10927篇 |
金属工艺 | 4559篇 |
机械仪表 | 2962篇 |
建筑科学 | 2874篇 |
矿业工程 | 946篇 |
能源动力 | 2100篇 |
轻工业 | 4146篇 |
水利工程 | 823篇 |
石油天然气 | 2883篇 |
武器工业 | 155篇 |
无线电 | 6966篇 |
一般工业技术 | 13750篇 |
冶金工业 | 8509篇 |
原子能技术 | 1061篇 |
自动化技术 | 5843篇 |
出版年
2023年 | 519篇 |
2022年 | 975篇 |
2021年 | 1377篇 |
2020年 | 1121篇 |
2019年 | 1075篇 |
2018年 | 1433篇 |
2017年 | 1537篇 |
2016年 | 1532篇 |
2015年 | 1597篇 |
2014年 | 2148篇 |
2013年 | 3951篇 |
2012年 | 3202篇 |
2011年 | 3851篇 |
2010年 | 2952篇 |
2009年 | 3190篇 |
2008年 | 3057篇 |
2007年 | 3182篇 |
2006年 | 2774篇 |
2005年 | 2361篇 |
2004年 | 1934篇 |
2003年 | 1780篇 |
2002年 | 1818篇 |
2001年 | 1708篇 |
2000年 | 1532篇 |
1999年 | 1617篇 |
1998年 | 2610篇 |
1997年 | 2056篇 |
1996年 | 1827篇 |
1995年 | 1306篇 |
1994年 | 1064篇 |
1993年 | 973篇 |
1992年 | 749篇 |
1991年 | 691篇 |
1990年 | 614篇 |
1989年 | 553篇 |
1988年 | 421篇 |
1987年 | 439篇 |
1986年 | 392篇 |
1985年 | 393篇 |
1984年 | 324篇 |
1983年 | 310篇 |
1982年 | 318篇 |
1981年 | 304篇 |
1980年 | 358篇 |
1979年 | 343篇 |
1978年 | 299篇 |
1977年 | 418篇 |
1976年 | 633篇 |
1975年 | 310篇 |
1973年 | 312篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
烧结材料孔隙形态与分布对离子氮碳共渗层组织结构的影响 总被引:1,自引:0,他引:1
研究了烧结材料孔隙形态与分布对离子氮碳共渗层组织结构的影响。试验表明,随试样孔隙数量的增加,γ'相含量和扩散层深度增加。由于试样的正压制面与侧压制面的孔隙形态及分布不同,导致化合物层深度和相组成不同。还观察讨论了氮原子在氮碳共渗层的分布状态。 相似文献
992.
DEFORMATIONBEHAVIOUROFCu-Zn-AlALLOYSANDITSEFFECTONTRANSFORMATIONHYSTERESISWangMingpu;XuGenyin;YinZhiming(DepartmentofMaterial... 相似文献
993.
994.
Terry C. Lowe Ruslan Z. Valiev 《JOM Journal of the Minerals, Metals and Materials Society》2004,56(10):64-68
Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive
properties. Today, SPD techniques are rapidly developing and are on the verge of moving from lab-scale research into commercial
production. This paper discusses new trends in the development of SPD techniques suchas high-pressure torsion and equal-channel
angle pressing, as well as new alternative techniques for introducing SPD. The paper also contains a comparative analysis
of SPD techniques in terms of their relative capabilities for grain refinement, enhancement of properties, and potential to
economically produce ultrafine-grained metals and alloys.
For more information, contact Terry C. Lowe, Science and Technology Base Programs, Los Alamos National Laboratory, Los Alamos,
NM 87545; (505) 667-7824; fax (505) 665-3199; e-mail tlowe@lanl.gov. 相似文献
995.
This paper presents an integrated simulation model for full digital controlled PMIG/MAG welding system with Matlab/Simulink, and it consists of power inverter, digital control system and dynamic arc-load model. An integrated simulation study was done for fuU digital PMIG/MAG welding, and a method of connecting dynamic arc-load model to the system with controlled current source was presented, in addition, the simulation results were utilized to study the issues of digital control PMIG/MAG welding in this paper. The experimental results validated the developed simulation model, and this simulation study can be applied in implementation of the full digital PMIG/MAG welding and analysis of system dynamic process. 相似文献
996.
The dissolution rate of mild steel in 1 N H2SO4 without and with different additions of Cl?, Br? and I? has been measured. Analysis of the results indicates that halide ions adsorbed on the metal surface inhibit the dissolution reaction. Adsorption occurs according to the Frumkin isotherm. 相似文献
997.
The objective of this study is to experimentally investigate the cutting mechanisms of polycrystalline diamond compacts (PDC) using two different lasers: (a) a near infrared Nd:YAG laser (Neodymium-doped Yttrium Aluminum Garnet) of 1064 nm wavelength and 100 μs pulse width; and (b) a green light KTP (Potassium Titanyl Phosphate)/Nd:YAG laser of 532 nm wavelength and 120 ns pulse width. To realize the objective, the study applies polishing, lapping and etching processes to the cut-surfaces of the PDC samples. It further observes and analyzes the processed cut-surfaces with scanning electron microscopy (SEM) and Raman spectroscopy. A discussion is provided to reveal the underlying physics of the laser cutting mechanisms, and a conclusion is drawn based on the outcomes from the experimental investigation and the discussion. 相似文献
998.
Ennoblement of stainless steel (SS) by microbially deposited manganese oxides can lead to pitting corrosion at low chloride concentrations, causing unexpected material failures. We exposed 316L SS to manganese oxidizing bacteria Leptothrix discophora under well-defined laboratory conditions, and then placed the ennobled coupons in a 0.5 M sodium chloride solution until pitting developed. Using time-of-flight secondary ion mass spectroscopy we demonstrated that the pits and their immediate vicinity associated with microbial influenced corrosion had different chemical signatures than those associated with electrochemically induced pitting, suggesting a possibility that the microorganisms were directly involved in pit initiation. Based on the differences in the chemical signatures we were able to distinguish the microbially induced pits from those induced by anodic polarization. 相似文献
999.
Conclusion In the process of heat treatment at the austenitization temperature, on the grain boundaries of steel 10 segregations of manganese and of substitutional impurities form, the adsorbed layers being about 200 nm thick. Long-term aging (up to 250,000 h) at 245°C does not lead to a noticeable change in the concentration of these layers.Leningrad Technological Institute of the Refrigeration Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 54–56, October, 1987. 相似文献
1000.
An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (∼90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements. 相似文献