全文获取类型
收费全文 | 2905篇 |
免费 | 288篇 |
国内免费 | 79篇 |
专业分类
电工技术 | 11篇 |
综合类 | 202篇 |
化学工业 | 1021篇 |
金属工艺 | 712篇 |
机械仪表 | 79篇 |
建筑科学 | 47篇 |
矿业工程 | 66篇 |
能源动力 | 33篇 |
轻工业 | 232篇 |
水利工程 | 16篇 |
石油天然气 | 79篇 |
武器工业 | 14篇 |
无线电 | 33篇 |
一般工业技术 | 266篇 |
冶金工业 | 422篇 |
原子能技术 | 27篇 |
自动化技术 | 12篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 54篇 |
2021年 | 84篇 |
2020年 | 85篇 |
2019年 | 59篇 |
2018年 | 68篇 |
2017年 | 87篇 |
2016年 | 87篇 |
2015年 | 93篇 |
2014年 | 138篇 |
2013年 | 184篇 |
2012年 | 233篇 |
2011年 | 182篇 |
2010年 | 126篇 |
2009年 | 170篇 |
2008年 | 127篇 |
2007年 | 183篇 |
2006年 | 178篇 |
2005年 | 169篇 |
2004年 | 121篇 |
2003年 | 120篇 |
2002年 | 120篇 |
2001年 | 111篇 |
2000年 | 78篇 |
1999年 | 56篇 |
1998年 | 54篇 |
1997年 | 47篇 |
1996年 | 34篇 |
1995年 | 35篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有3272条查询结果,搜索用时 15 毫秒
51.
The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolu-tion characteristic with an increase of chromium content There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel However, chromium improves the corrosion resistance of the stainless steel re-markably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wr% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels. 相似文献
52.
Chromium ore fines containing coal (COFCC) can be rapidly heated by microwave to conduct the voluminal reduction, which lays
a foundation of getting sponge ferrochromium powders with a lower content of C. Under the conditions of COFCC with n(O):n(C) (molar ratio) as 1.00:0.84 and n(SiO2):n(CaO) as 1.00:0.39, the samples were heated by 10 kW microwave power to reach the given temperatures and held for different
times respectively. The results show that the low-C-Cr ferrochromium metal phase in the reduced materials forms before the
high-C-Cr ferrochromium metal phase does. With increasing temperature the C content of ferrochromium metals is in a positive
correlation with the content of Cr. The C content of ferrochromium metal in reduced materials is 0–10.07% with an average
value of 4.68%. With the increase of holding time the Cr content in ferrochromium metals is in a negative correlation with
the content of C, while the content of Fe changes in the contrary way. In the microwave field the kinetic conditions of carburization
are closely related with the temperature of microwave heating, holding time and carbon fitting ratio.
Foundation item: Project(50474083) supported by the National Natural Science Foundation of China; Project supported by the Baoshan Iron &
Steel Co. Ltd. of China 相似文献
53.
《水科学与水工程》2020,13(1):65-73
This study investigated the removal of hexavalent chromium(Cr(VI)) in aqueous solutions using pomelo peel(PP) and FeCl_3-modified pomelo peel(FPP) as novel biomass adsorbents.Batch adsorption experiments were performed to evaluate the effects of pH,time,temperature,initial concentration,and adsorbent dose on Cr(VI) removal by PP and FPP.The results show that the maximum adsorption capacity of Cr(VI)was 21.55 mg/g for FPP and 0.57 mg/g for PP at a pH of 2.0 and a temperature of 40℃.The surface shape,microstructure,and chemical composition of FPP were analyzed with scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),and energy dispersive spectroscopy(EDS),and compared with those of PP.The results show that the adsorption performance of FPP was much better than that of PP,indicating that FPP can be an alternative high-efficiency adsorbent for Cr(VI) removal. 相似文献
54.
Effect of vanadium and chromium on the microstructural features of V–Cr–Mn–Ni spheroidal carbide cast irons 总被引:2,自引:0,他引:2
V.G.Efremenko ;K.Shimizu ;A.P.Cheiliakh ;T.V.Kozarevskaya ;K.Kusumoto ;K.Yamamoto 《北京科技大学学报(英文版)》2014,(11):1096-1108
The objective of this investigation is to study the influence of vanadium(5.0wt%–10.0wt%) and chromium(0–9.0wt%) on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys' microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic(based on M7C3), pearlite, martensite, and austenite. Their combinations and area fraction(AF) ratios are reported to be influenced by the alloys' chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic(γ-Fe + М7С3), preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure. 相似文献
55.
研究正火温度对新型高铬铸铁组织、硬度(HRC)及冲击韧性的影响。实验结果表明高铬铸铁在800~950℃正火时,其组织由珠光体+少量铁素体+网状共晶碳化物组成;在1 000~1 050℃正火时,碳化物溶解析出,珠光体球化,得到铁素体基体上分布的粒状碳化物+共晶碳化物+少量珠光体,硬度略有降低;在1 100~1 150℃正火时,共晶碳化物溶解得更多,冷却过程中奥氏体中析出弥散碳化物,冷却后得到马氏体(过饱和铁素体)基体上弥散碳化物+共晶碳化物,硬度明显升高,并在1 150℃时硬度达到最大值,在800~1 150℃正火加热温度范围内,冲击韧性在4.2~4.7 Jcm2之间波动,总体变化不大。 相似文献
56.
Erosion-corrosion investigation of high chromium cast irons using newly designed jet type tester 总被引:1,自引:0,他引:1
A jet type erosion-corrosion tester was developed for the erosion-corrosion investigation of high-chromium cast irons. During tests the size and the shape of particles in the slurry can be maintained stable. The jet velocity and attack angle can be accurately controlled. The repeatability and ranking consistency of the test results are satisfactory. The test parameters can be adjusted in a wide range, so that the tester can simulate various practical working conditions. Electrochemical test data can be automatically collected and processed. Dynamic polarization curves can be obtained during erosion-corrosion test, which can be used to study the dynamic corrosion characteristics.Two high chromium cast irons were studied in hot concentrated alkaline slurry. The results show that the erosioncorrosion mass loss rate and dynamic corrosion rate of 295Cr26 iron is lower than that of 185Cr13 under the conditions similar to alumyte processing. The mechanism of erosion-corrosion of 295Cr26 and 185Cr13 was studied by using the tester. The interaction between erosion and corrosion was also quantitatively evaluated. 相似文献
57.
研究了低铬耐磨铸铁经40%热变形及不同方式冷却后的组织与耐磨性的关系。结果表明:该铸铁经热变形后的组织与耐磨性有良好的对应关系,其耐磨性随硬度的增加而增大,同时也与组织中碳化物的形状、大小及分布有关。 相似文献
58.
利用电弧离子镀设备在1Cr11Ni2W2MoV不锈钢基体上沉积了CrN涂层,对涂层的抗氧化性能进行了研究。结果表明,CrN氧化生成Cr2O3,氧化反应激活能小于Cr和Cr2N的氧化反应激活能,具有低的氧化速率常数,抗氧化性能良好。氧化过程中发生CrN向Cr2N的相转变,涂层中大的压应力的存在对这一转变起了关键作用。 相似文献
59.
研究了高铬马氏体耐热钢(0.09C-10.2Cr-0.52Ni-1.52Mo-0.22V-0.07Nb-3.0Co-0.01Ti-0.0129N-0.0033B)的显微组织和力学性能.结果表明该钢经1100℃×1h空冷正火处理 750℃×1h空冷回火处理后的显微组织为板条状马氏体,在原奥氏体晶界和板条间分布有M23C6碳化物,并有少量1~3μm的M3B2颗粒,马氏体板条内部有10~30 nm的MX型析出相.短期蠕变试验数据显示其在650℃的蠕变性能优于P92钢. 相似文献
60.
Qin Lu 《Oxidation of Metals》1993,40(5-6):421-432
The initial oxidation of pure, polycrystalline-chromium metal with gas mixtures of oxygen-labeled water, H2
18O, and oxygen,16O2, at temperatures 300–730 K has been studied in situ with secondary ion mass spectrometry, SIMS. The fraction of O in secondary ion species: CrO+, Cr2O+, CrOH+, Cr2OH+, CrOH2
+, and Cr2OH2
+ originating from water and oxygen was found. The reaction of water and oxygen in the oxygen/water gas mixture with Cr is then revealed. The dissociation of water in its reaction with Cr in such a gas mixture was analyzed. Oxide growth on cleaned Cr surfaces during the reaction with H2O, O2 and H2O/O2 gas was also studied in situ with X-ray photoelectron spectroscopy, XPS. A correlation between a chemical shift in XPS and the OH content in the oxide is discussed. 相似文献