全文获取类型
收费全文 | 13748篇 |
免费 | 1186篇 |
国内免费 | 849篇 |
专业分类
电工技术 | 713篇 |
综合类 | 1181篇 |
化学工业 | 1981篇 |
金属工艺 | 2076篇 |
机械仪表 | 288篇 |
建筑科学 | 1371篇 |
矿业工程 | 732篇 |
能源动力 | 274篇 |
轻工业 | 312篇 |
水利工程 | 595篇 |
石油天然气 | 419篇 |
武器工业 | 61篇 |
无线电 | 583篇 |
一般工业技术 | 1268篇 |
冶金工业 | 3472篇 |
原子能技术 | 138篇 |
自动化技术 | 319篇 |
出版年
2024年 | 23篇 |
2023年 | 339篇 |
2022年 | 474篇 |
2021年 | 533篇 |
2020年 | 524篇 |
2019年 | 417篇 |
2018年 | 442篇 |
2017年 | 315篇 |
2016年 | 360篇 |
2015年 | 354篇 |
2014年 | 565篇 |
2013年 | 581篇 |
2012年 | 754篇 |
2011年 | 860篇 |
2010年 | 676篇 |
2009年 | 701篇 |
2008年 | 657篇 |
2007年 | 784篇 |
2006年 | 808篇 |
2005年 | 727篇 |
2004年 | 615篇 |
2003年 | 640篇 |
2002年 | 512篇 |
2001年 | 503篇 |
2000年 | 423篇 |
1999年 | 467篇 |
1998年 | 340篇 |
1997年 | 281篇 |
1996年 | 232篇 |
1995年 | 202篇 |
1994年 | 164篇 |
1993年 | 133篇 |
1992年 | 109篇 |
1991年 | 77篇 |
1990年 | 59篇 |
1989年 | 36篇 |
1988年 | 19篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1975年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
51.
The aim of the present work is to study magnetization processes in the spring-exchange magnetic composites containing magnetically soft, hard and ultra-high coercive phases, experimentally found in Tb-Fe-B-Nb group of alloys. In order to modeling hysteresis loops a special Monte Carlo procedure,suitable for irregular geometry of the composites, was applied. The obtained results indicate that sufficiently strong coupling between soft and hard magnetic phase leads to collective, single-phase-like movement of such phases, which in turn, causes increase of the coercivity and internal magnetic energy. 相似文献
52.
Ranulfo Benedito de Paula Miranda Roger Borges Juliana Marchi Nelson Batista de Lima Paulo Francisco Cesar 《International Journal of Applied Ceramic Technology》2019,16(5):1979-1988
The addition of bioactive glasses to a Y:TZP matrix represents a feasible alternative to provide bioactivity to this material and optimize osseointegration. This work evaluated the effect of the BG concentration (0 and 10 wt%) and the sintering temperature (1200°C and 1300°C) on the microstructure, relative density, and flexural strength of the composite Y:TZP/BG. The Y:TZP and Y:TZP/BG powders were uniaxially pressed and sintered at 1200°C or 1300°C for 1 h. The microstructure was characterized by X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray Spectroscopy. Relative density was calculated from density values obtained using the Archimedes’ principle. For the flexural strength, specimens (n = 6) were fractured in a biaxial flexural setup using a piston-on-three-balls fixture in a universal testing machine. Bioactivity test was performed in simulated body fluid solution. The results suggested that BG addition decreased the grain size of the composite, increased porosity and caused a significant decrease in the relative density and flexural strength. Crystalline phases of calcium stabilized cubic zirconia and sodium zirconium silicate were formed after the addition of BG. Finally, it was concluded that composite specimens sintered at 1300°C showed the highest density values and larger grains compared to those sintered at 1200°C. 相似文献
53.
《中国稀土学报(英文版)》2020,38(7):742-748
We report the fabrication of bulk anisotropic(SmCo+FeCo)/NdFeB multicomponent nanocomposite magnets using high-pressure thermal compression(HPTC).The correlations among microstructure,magnetic properties,heating temperature and composition of the HPTC nanocomposite magnets were studied.The HPTC magnet made under variable temperatures(VT),with 19 wt% of FeCo phase,exhibits a maximum energy product of 32 MGOe,which is much higher than that(14 MGOe) for the HPTC magnet made under a constant temperature(CT).When the FeCo content increases to~23 wt%,the HPTC magnet made under VT still remains a high energy product of about 25 MGOe.With increasing NdFeB content,the(SmCo+FeCo)/NdFeB multicomponent nanocomposite magnets exhibit an enhanced magnetic anisotropy and coercivity.This work is beneficial to fabricating high-performance and low-cost permanent magnets for practical applications. 相似文献
54.
《中国稀土学报(英文版)》2020,38(10):1086-1092
Mesoporous GdPO_4:Eu@SiO_2@mSiO_2 core-shell nanorods(NRs) were prepared by a facile two-step method.First,the monodispersed GdPO_4:Eu NRs were obtained on a large scale via a facile precipitation method,then mesoporous silica was wrapped onto their surface through hydrolysis of tetraethylorthosilicate(TEOS).The XRD result indicates that the as-prepared GdPO_4:Eu NRs core has hexagonal phase.The FTIR and the N_2 adsorption/desorption isotherm analysis confirm the successful coating of mesoporous silica.The TEM images show that the obtained GdPO_4:Eu@SiO_2@mSiO_2 NRs exhibit uniform monodisperse core-shell structure with a nanorod core(length of 200 nm;width of 20 nm),and mesoporous silica shell of 15 nm.Under excitation of 274 nm,GdPO_4:Eu@SiO_2@mSiO_2 NRs show strong red luminescence from ~5 D_0→~7 F_J(J=1,2,3 and 4) transitions of Eu~(3+).Furthermore,the GdPO_4:Eu@-SiO_2@mSiO_2 NRs exhibit obvious T_1 enhancement effect due to paramagnetism of Gd~(3+).The drug loading capacity and pH-sensitive releasing behavior of the as-prepared GdPO_4:Eu@SiO_2@mSiO_2 NRs were studied by using doxorubicin(DOX) as model drug.The excellent biocompatibility of GdPO_4:Eu@-SiO_2@mSiO_2 NRs was demonstrated by MTT assay.Taken together,the mesoporous GdPO_4:Eu@-SiO_2@mSiO_2 NRs may be potentially applied in fields of drug delivery and dual-modal imaging. 相似文献
55.
分别以“散样重装”和保持矿体原样的离子型稀土矿为原料,开展植物浸取剂浸出稀土的小试和“原地浸出”中试模拟试验。探讨了试验动力学,探索了植物浸取剂浓度和用量对浸出的影响,并它的渗透性和浸取性能与硫酸铵为浸出剂时的进行了对比。结果表明,植物浸取剂浸出稀土过程的动力学符合“收缩未反应核模型”;128.2 kg浓度为2%植物浸取剂浸出451 kg稀土矿是合适的;保持矿体原样的稀土矿渗透性较差,植物浸取剂的水平平均渗透速度、垂直平均渗透速度、浸出率分别为0.141 cm/min、0.213 cm/min、94.40%,均好于硫酸铵的。 相似文献
56.
《中国稀土学报(英文版)》2020,38(5):523-530
A multidisciplinary approach for the production and characterization of a series of high concentration Er~(3+)activated SrLaGa_3 O_7(abbreviated as Er:SLGO) crystal fibers is shown to have a great promise for implementation in mid-infrared laser applications.The current approach includes the design and formation of unique layered tetrahedral network structures with several kinds of rare earth(RE) ions including Er ions distributing statistically between layers,such as Er:SLGO,Er,Nd:SLGO,Er,Yb,Ho:SLGO,Er,Eu:SLGO and Er,Ho:SLGO.Five kinds of Er:SLGO crystal fibers were designed to grow via a micropulling down method.Spectroscopic analyses show that Er,Yb,Ho:SLGO and Nd,Er:SLGO crystal fibers were superiorly endowed with inhomogeneous broadening absorption and strong emission.The unique structural components design enables the generation of improved absorption and emission recombination,and the inhibition of self-termination as well.Generally,the use of structural components design may warrant high-efficiency emissions in RE-doped crystal fibers. 相似文献
57.
《中国稀土学报(英文版)》2020,38(3):265-273
This study presents the influence of Zn and Nd co-substitution on structure,morphology,AC susceptibility and ZFC-FC magnetizations of Sr nanohexaferrites(NHFs),SrFe_(12-x)(Zn,Nd)_xO_(19)(0.0≤x≤1.0),which was produced by sol-gel approach.XRD powder patterns,scanning electron microscopy(SEM) and high-resolution transmission electron spectroscopy(HR-TEM) approve the synthesis of Sr M-type hexaferrite.Mossbauer spectra show that Zn~(2+)ions occupy 2 b and 4f_1 sites while Nd~(3+)ions locate at 2 a,4f_2 and 12 k sites.The magnetic properties of the produced Sr-NHFs were investigated also by ZFC-FC magnetizations and AC susceptibility.According to the M_(FC)-M_(ZFC) results(between 2 and 400 K),no blocking temperature was detected which indicates the ferromagnetic(FM) behavior of NHFs.At lower temperatures,a super-spin glass like behavior is discerned.The AC susceptibility indicates that the magnetic interactions are improved due to the inclusion of low content(x=0.1) of Nd~(3+)and Zn~(2+)ions into the Sr-NHFs.However,with further increasing the Nd~(3+)and Zn~(2+)contents(x=0.9),the magnetic interactions are weakened. 相似文献
58.
59.
White-light-emitting phosphors based on phosphate host matrix, KSrPO_4 doped with Dy~(3+), were prepared by solid state reaction and their VUV luminescent properties were firstly investigated. The excitation band peaking at 125-153 nm corresponding to the absorption of PO_4~(3-) group exhibits very strong absorption. The phosphors emit warm-white luminescence under vacuum ultraviolet excitation of 147 nm, which consists of three main emission peaks located at 475, 570 and 662 nm, respectively.According to the luminescence and color chromaticity of the optimal sample KSrPO_4:1 mol%Dy~(3+),1.3 mol%Li~+, it can be a potential candidate for mercury-free fluorescent lamps. 相似文献
60.
采用湿化学法制备了Eu~(3+)掺杂Y_2P_4O_(13)荧光材料,通过X射线粉末衍射(XRD)、傅里叶变换红外光谱(FT-IR)和荧光光谱(FL)等手段表征制备产物的物相结构、荧光性能,并对合成原料中稀土与磷的比例(n(Y+Eu)/n(P))和pH调节剂种类对制备样品的物相结构及性能的影响进行分析。结果表明:合成原料中n(Y+Eu)/n(P)比值和pH调节剂种类直接影响着制备产物的物相结构与性能。在n(Y+Eu)/n(P)=12.1、以NH_4HCO_3为pH调节剂调节pH为6的条件下可获得正交晶系的Eu~(3+)掺杂Y_2P_4O_(13)荧光材料。所制备的Y_2P_4O_(13):2at%Eu~(3+)荧光材料在395nm光的激发下可发射出橙红光。 相似文献