全文获取类型
收费全文 | 790篇 |
免费 | 20篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 20篇 |
综合类 | 31篇 |
化学工业 | 108篇 |
金属工艺 | 131篇 |
机械仪表 | 80篇 |
建筑科学 | 10篇 |
矿业工程 | 5篇 |
能源动力 | 29篇 |
轻工业 | 6篇 |
水利工程 | 2篇 |
石油天然气 | 10篇 |
无线电 | 118篇 |
一般工业技术 | 210篇 |
冶金工业 | 18篇 |
原子能技术 | 22篇 |
自动化技术 | 34篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 19篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 23篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 37篇 |
2013年 | 34篇 |
2012年 | 33篇 |
2011年 | 53篇 |
2010年 | 39篇 |
2009年 | 34篇 |
2008年 | 32篇 |
2007年 | 38篇 |
2006年 | 22篇 |
2005年 | 31篇 |
2004年 | 54篇 |
2003年 | 44篇 |
2002年 | 33篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 31篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 25篇 |
1993年 | 15篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有834条查询结果,搜索用时 0 毫秒
41.
本文论述了用 X 射线衍射法间接测定双■轮刨片机 GCr15钢制刀片的工作温度.用该钢种制成并经不同热处理的八个标样和服役后的刀片,进行衍射线形的测量和半高宽值的测算.通过微机进行的回归分析,得出半高宽值与温度的关系曲线的相关系数为0.995,刀片工作温度为271±10℃.理论分析和实验数据表明:这一间接测定刀片工作温度的方法、简便易行,有一定的准确、可靠性.对某些不能用常规方法测定工作温度的金属零件具有特殊的意义. 相似文献
42.
43.
光栅衍射谱线产生缺级的条件 总被引:1,自引:0,他引:1
蒋夏萍 《华北水利水电学院学报》1995,16(3):25-27
本文对光栅衍射谱线产生缺级的条件进行了讨论,澄清了某些教科书中不确切的叙述。 相似文献
44.
The 2-D problem of diffraction by a gap between two orthogonal semi-infinite barriers is considered. The method of reflections
is applied and the diffraction problem is reformulated as a propagation problem on a multi-sheet surface. An auxiliary problem,
with a single incident wave, is formulated. By applying an embedding formula the auxiliary problem is reduced to that of finding
a set of edge Green’s functions for the surface. The edge Green’s functions are proven to satisfy two sets of differential
equations: the coordinate equations and the spectral equation. Although too complicated to be solved analytically, these ordinary differential equations offer some advantages over partial
differential equations or integral equations. 相似文献
45.
47.
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
48.
P. K. Siwach H. K. Singh N. Khare A. K. Singh O. N. Srivastava 《Journal of Alloys and Compounds》2003,350(1-2):56-61
A new manganite type CMR material, La0.7Hg0.3MnO3 has been successfully synthesized and has been found to exhibit magnetoresistance (≈9%) at low fields (≈1.5 kG). The synthesis has been carried out through a solid state reaction route consisting of the formation of La0.7MnO3 followed by diffusion of Hg leading to La0.7Hg0.3MnO3. The as grown samples are polycrystalline and correspond to an orthorhombic unit cell with the lattice parameters; a=5.5183 Å, b=5.6383 Å and c=7.5368 Å. The typical grain size as revealed by scanning electron microscopy is in the range of 0.5–2 μm. The ρ–T behaviour shows a peak at TIM=227 K. The ρ–T behaviour above this temperature corresponds to that of an insulator and below this to that of a metal. The ρ–T behaviour remains unaltered when a magnetic field (Hdc=1.5 kG) is applied. However, with this magnetic field a drop in the resistivity is observed up to 77 K. At room temperature the magnetoresistance ratio (MRR) is too small but it steadily increases as the temperature is decreased. Thus, MRRs at 227.13 and 77 K are 3.41 and 9.05%, respectively, in an applied field of Hdc=1.5 kG. At a given temperature the variation in MRR with field Hdc is rapid at lower field values (Hdc<1.2 kG) and scales linearly for higher field values (Hdc>1.2 kG). It may be mentioned that the present work on the synthesis and magnetoresistance behaviour of La0.7Hg0.3MnO3, is the first of its type. 相似文献
49.
Michelina Catauro Elisabetta Tranquillo Alessandro Dell’Era Riccardo Tuffi Stefano Vecchio Ciprioti 《Ceramics International》2019,45(2):2771-2778
The thermal behavior of pure ZrO2 and four ZrO2-based organic-inorganic hybrids (OIHs) containing increasing amount (6, 12, 24 and 50?wt%) of poly(ε-caprolactone) (PCL) (named Z, ZP6, ZP12, ZP24 and ZP50 respectively) has been studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The FTIR analysis of the gas mixture evolved at defined temperatures from the samples submitted to the TG experiments identified the mechanism of each thermally activated process. The obtained results suggest that the inorganic matrix of the OIHs prepared by this method exerts a stabilizing effect on the polymer, in particular for poor-PCL hybrid materials. In fact, the different thermal behavior of the ZP50 sample suggests that the polymer is not entirely bonded to the -OH groups of the zirconia matrix due to their saturation. For this reason a part of PCL is not affected by the stabilizing effect of the matrix and is subjected to thermal degradation. Finally, by observing their thermal behavior it was possible to select the most suitable temperatures for thermal pretreatment: 400, 600 and 1000?°C. The structural analysis by X-ray diffraction (XRD) revealed that at 400?°C the materials are amorphous, while at 600?°C they are mostly tetragonal, and the content of the tetragonal phase decreases with increasing the amount of PCL in the OIHs. All the materials treated at 1000?°C are monoclinic, but their crystallinity decreases with increasing the PCL content. 相似文献
50.
《Ceramics International》2017,43(15):12070-12078
It is well documented that biological hydroxyapatite (HA) differs from pure and synthetically produced HA, and contains of a mixture of calcium phosphate (CaP) phases in addition to a range of impurity ions, such as strontium (Sr2+), zinc (Zn2+), magnesium (Mg2+), fluoride (F-) and carbonate(CO32-), but to name a few. Further to this, biological apatite is generally in the form of rod (or needle-like) crystals in the nanometre (nm) size range, typically 60 nm in length by 5–20 nm wide. In this study, a range of nano-hydroxyapatite (nHA), substituted nHA materials and co-substituted nHA (based on Sr2+ and Zn2+) were manufactured using an aqueous precipitation method. Sr2+ and Zn2+ were chosen due to the significant performance enhancements that these substitutions can deliver. The materials were then characterised using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) techniques. The TEM results show that all of the samples produced were nano-sized, with Zn-substituted nHA being the smallest crystals around 27 nm long and 8 nm wide. The FTIR, XRD and XPS results all confirm that the materials had undergone substitution with either Sr2+ and Zn2+, for Ca2+ within the HA lattice (or both in the case of the co-substituted materials). The FTIR results confirmed that all of the samples were carbonated, with a significant loss of hydroxylation as a consequence of the incorporation of Sr2+ and Zn2+ into the HA lattice. None of the materials synthesised here in this study contained any other impurity CaP phases. Therefore this study has shown that substituted and co-substituted nanoscale apatites can be prepared, and that the degree of substitution (and the substituting ion) can have a profound effect of the attendant materials’ properties. 相似文献