全文获取类型
收费全文 | 6043篇 |
免费 | 488篇 |
国内免费 | 470篇 |
专业分类
电工技术 | 402篇 |
综合类 | 640篇 |
化学工业 | 655篇 |
金属工艺 | 813篇 |
机械仪表 | 401篇 |
建筑科学 | 206篇 |
矿业工程 | 157篇 |
能源动力 | 158篇 |
轻工业 | 174篇 |
水利工程 | 52篇 |
石油天然气 | 154篇 |
武器工业 | 50篇 |
无线电 | 445篇 |
一般工业技术 | 644篇 |
冶金工业 | 322篇 |
原子能技术 | 46篇 |
自动化技术 | 1682篇 |
出版年
2024年 | 12篇 |
2023年 | 60篇 |
2022年 | 101篇 |
2021年 | 132篇 |
2020年 | 158篇 |
2019年 | 135篇 |
2018年 | 127篇 |
2017年 | 176篇 |
2016年 | 178篇 |
2015年 | 190篇 |
2014年 | 344篇 |
2013年 | 357篇 |
2012年 | 321篇 |
2011年 | 440篇 |
2010年 | 311篇 |
2009年 | 380篇 |
2008年 | 342篇 |
2007年 | 416篇 |
2006年 | 392篇 |
2005年 | 343篇 |
2004年 | 299篇 |
2003年 | 233篇 |
2002年 | 198篇 |
2001年 | 170篇 |
2000年 | 161篇 |
1999年 | 147篇 |
1998年 | 142篇 |
1997年 | 115篇 |
1996年 | 90篇 |
1995年 | 93篇 |
1994年 | 88篇 |
1993年 | 63篇 |
1992年 | 57篇 |
1991年 | 35篇 |
1990年 | 40篇 |
1989年 | 39篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7001条查询结果,搜索用时 31 毫秒
101.
李启朗 《安徽建筑工业学院学报》2014,(6)
如今,相图被广泛用于交通科学领域的研究,取得了重要成果。根据理论分析和计算机模拟,本文构建了十字路口处交通流量相图。该相图是由五个基本区域构成的,本文分析并推导出每个区域的具体流量公式。在周期边界条件下,采用确定性 Fukui-Ishibashi元胞自动机交通模型进行数值模拟,其模拟结果与理论分析精确一致。 相似文献
102.
提出了由二元相图提取定温下无限稀活度系数的方法,分别在正规溶液和Richardson假设条件下,计算了31个二元液态合金体系两组元无限稀活度系数,并与相应的实验值比较,所获得的平均相对误差为:共晶体系为23.2%和20.7%;含固溶体体系为19.4%和18.3%;含化合物体系为39.5%和46.1%;分层体系为25.8%和14.3%.结果表明:由共晶相图、含固溶体相图提取无限稀活度系数,有效性较好,由含化合物相图提取无限稀活度系数有效性较差.引入Richardson假设后,对计算值的精度有所提高.研究表明,运用二元相图提取无限稀活度系数方法提取二元合金体系无限稀活度系数是可行的. 相似文献
103.
通过鱼骨图的方法对现有智能公交投币机存在识别率偏低的问题进行了分析,提出在智能投币机中采用闭式五角叶轮或增加硬币预处理部分,对现有的智能公交投币机进行改进,使智能公交投币机的硬币辨识率得到提高. 相似文献
104.
在气流床气化炉的实际运行中,经常需要寻求最优的进料煤调配方案以调控煤灰的熔融流动特性。借助SiO2-Al2O3-AAEM(CaO+MgO+Na2O+K2O)拟三元等温图,分析了不同组成的宁东煤灰熔融特性,并结合X-射线衍射(XRD)探究了灰在熔化过程中的矿物质转化规律。发现熔融温度在拟三元等温图中呈现U型分布。当SiO2、Al2O3和AAEM质量分数分别为37.5%、25.0%和37.5%时,灰的熔融温度达到最低,流动温度比宁东煤灰降低40 ℃。对灰熔化过程中矿物质转化分析发现,熔化过程中石英与氧化钙会发生矿物质转化反应生成低熔点的钙黄长石和长石,对其熔化具有明显的促进作用;对灰熔化后形成液态熔渣的黏-温特性曲线分析发现,该比例下灰样品同时具有最低的临界黏性温度(TCV=1107 ℃)和最低的黏性流动活化能(Ea=282.86 kJ/mol),可有效降低气化炉的操作温度。研究表明,拟三元等温图对于气化原料配煤方案可起到一定的指导作用。 相似文献
105.
This work investigates the stabilizing impact of MnO on the leaching behavior of hazardous Cr-containing CaO-SiO2-Al2O3-Cr2O3-MnO stainless steel slags after equilibrating at various elevated temperatures and evaluates the potential immobilization of Cr into a MnCr2O4 spinel phase from the existing Cr2O3 phase. The MnCr2O4 spinel phase was found to be an excellent Cr-stabilizer in stainless steel slags, where the leaching tendency of potentially hazardous Cr-related ions decreased with higher MnO content and lower equilibration temperatures within the range of 0 to 15 mass pct. and 1500 to 1300°C, respectively. Thermodynamic calculations by conducting the phase stability diagram also showed that the MnCr2O4 spinel phase was relatively stable and the Ca3Si2O7 (Ca3-xMnxSi2O7) phase was relatively unstable compared with other crystal phases in acid extractant with pH value of 3.2. Combined with the scanning electron microscopy and X-ray powder diffraction results along with the thermodynamic calculations, the leached Cr-related ions was predominantly originating from the unstable amorphous glass phase. 相似文献
106.
Pavel P. Fedorov Alexander A. Alexandrov Valery V. Voronov Mariya N. Mayakova Alexander E. Baranchikov Vladimir K. Ivanov 《Journal of the American Ceramic Society》2021,104(6):2836-2848
Phase formation in the SrF2–LaF3 system was studied at temperatures ranging from 300°C to 450°C using nitrate flux. The solubility of LaF3 in SrF2 decreases with decreasing temperature. The equilibrium width of the solid solution region Sr1−xLaxF2+x at 400°C, it is 44.6 ± 0.4 mol% LaF3 (x = 0.446), at 350°C — 38.3 ± 0.7 mol% LaF3 (x = 0.383), and decreases almost to zero at 300°C. 相似文献
107.
《Journal of the European Ceramic Society》2021,41(14):7005-7013
The lead-free piezoelectric material sodium bismuth titanate (NBT, Na0.5Bi0.5TiO3) has attracted considerable attention owing to its promising dielectric, piezoelectric, and electrical properties. However, the literature on the binary subsystems is contradictory and there are only limited data for the ternary system. The present work surveys all of the reports of the binary subsystems Bi2O3 – TiO2 and Na2O – TiO2 and synthesizes these data into inclusive revised versions. The compatibilities for the ternary system Na2O – Bi2O3 – TiO2 were determined experimentally, thus enabling the construction of a complete isothermal section at 800 °C. The compatibilities associated with the problematic binary subsystem Na2O – Bi2O3, which experiences extreme volatilisation, were determined through the generation of the absent standard-state thermodynamic functions for the relevant binary and ternary phases, thus providing a full suite of thermodynamic data for this system. The thermodynamic stability diagrams for Na2O, Bi2O3, and TiO2 thus were calculated. The isothermal section also addresses the contradictions in the literature concerning the formation of solid solutions of Bi12TiO20-x / Bi12-xTi1+xO20+0.5x, pyrochlore (Bi2Ti2O7 / NawBi2-xTi2-yO7-z), BTO (Bi4Ti3O12 / NaxBi4Ti3O12+0.5x), and NBT (Na0.5Bi0.5TiO3 / Bi1±xNaxTiO3.5±x). Further, it was observed that the congruent melting point of NBT, which was determined to be 1225 °C, was preceded by the onset of gradual structural destabilization at 940 °C. Also, the NBT rhombohedral → tetragonal phase transformation was observed at an onset temperature of ∼250 °C. The present work thus provides platform data for the fabrication and reactivities of materials in the ternary system Na2O – Bi2O3· TiO2 and its binary subsystems. 相似文献
108.
109.
Solid state phase equilibria in the ternary Fe–Ga–Sb diagram were determined at 600 °C using experimental techniques such as X-ray diffraction, electron probe microanalysis and scanning electron microscopy. Very limited solid solutions were measured in the binary constituent Fe–Ga and Fe–Sb compounds except for the -phase (Fe≈2.55Sb2) which extends from 42 to 48 at.% Sb. In the Fe-rich part of the diagram, a ternary phase FetGa2−xSbx (2.15≤t≤2.80) was evidenced which corresponds in fact to a solid solution into which Ga and Sb substitute one another on the same hexagonal sublattice. This phase, which can be truly considered as a pseudo-binary one since its origin results from the -phase, shows an extended homogeneity range with a Ga-rich limit corresponding to the formula FetGa0.8Sb1.2. Moreover, it crystallizes in hexagonal symmetry with a disordered structure derivative from the NiAs-type (B81). This pseudo-binary phase is in thermodynamic equilibrium with all the binaries of the system except FeGa3. The main result of the ternary Fe–Ga–Sb diagram remains the existence of a diphasic region between the FetGa2−xSbx phase (1.2≤x≤1.6; 2.15≤t≤2.80) and the semiconductor GaSb. Nevertheless, at 600 °C, this pseudo-binary phase does not extend up to the Fe3GaSb composition which is stoichiometric in Ga and Sb. Finally, a comparative study has been made with the three other ternary systems Fe–Ga–As, Ni–Ga–As and Ni–Ga–Sb previously reported, and the consequences for the solid state interdiffusions in Metal/III–V semiconductor heterostructures are discussed. 相似文献
110.
Key experiments were carried out on the three Al–R–Mg (R=Gd,Dy,Ho) systems and the results obtained used for the thermodynamic optimisation reported in a separate paper in this issue [Caccasmani G, De Negri S, Saccone A, Ferro R. Intermetallics this issue.]. The samples were characterized by differential thermal analysis (DTA), X-ray powder diffraction (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM) and quantitative electron probe microanalysis (EPMA). The isothermal sections at 400 °C are all characterized by extended homogeneity regions at a constant rare earth content. The extension of the (Mg,Al)R solid solution, cP2-CsCl type, varies with the R atomic number. Ternary compounds (τ) of Al2(R,Mg) stoichiometry (hexagonal Laves phases with MgNi2-type structure) have been found to exist at 400 °C in all the systems. Their temperatures of formation were detected by DTA measurements. 相似文献