全文获取类型
收费全文 | 15849篇 |
免费 | 1106篇 |
国内免费 | 556篇 |
专业分类
电工技术 | 374篇 |
综合类 | 3549篇 |
化学工业 | 2665篇 |
金属工艺 | 726篇 |
机械仪表 | 928篇 |
建筑科学 | 1289篇 |
矿业工程 | 495篇 |
能源动力 | 658篇 |
轻工业 | 1785篇 |
水利工程 | 201篇 |
石油天然气 | 78篇 |
武器工业 | 27篇 |
无线电 | 812篇 |
一般工业技术 | 2179篇 |
冶金工业 | 147篇 |
原子能技术 | 32篇 |
自动化技术 | 1566篇 |
出版年
2024年 | 61篇 |
2023年 | 599篇 |
2022年 | 657篇 |
2021年 | 581篇 |
2020年 | 620篇 |
2019年 | 468篇 |
2018年 | 376篇 |
2017年 | 413篇 |
2016年 | 406篇 |
2015年 | 421篇 |
2014年 | 699篇 |
2013年 | 789篇 |
2012年 | 1328篇 |
2011年 | 1468篇 |
2010年 | 1213篇 |
2009年 | 1028篇 |
2008年 | 681篇 |
2007年 | 1566篇 |
2006年 | 1363篇 |
2005年 | 606篇 |
2004年 | 410篇 |
2003年 | 267篇 |
2002年 | 393篇 |
2001年 | 152篇 |
2000年 | 103篇 |
1999年 | 106篇 |
1998年 | 84篇 |
1997年 | 137篇 |
1996年 | 125篇 |
1995年 | 79篇 |
1994年 | 61篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 50篇 |
1986年 | 47篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 1篇 |
1976年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
1.
Energy bands, effective mass of carriers, absolute band edge positions and optical properties of tetragonal AgInS2 were calculated using a first-principles approach with the exchange correlation described by B3LYP hybrid functional. The results indicate that tetragonal AgInS2 has a direct band gap of 1.93 eV, which reproduce well experimental value. Calculated effective masses of electrons and holes are both small which are beneficial to separation and migration of electron and hole pairs. This implies that AgInS2 has good photocatalytic performance. The calculated optical characteristics indicate that AgInS2 has a slight anisotropy for both the real and imaginary parts of the dielectric function and exhibits large optical absorption in the visible light region. Furthermore, the calculated band edge positions in (100), (010) and (001) surfaces indicate that tetragonal AgInS2 is beneficial to the reduction and oxidation of water to hydrogen and oxygen under visible light irradiation. 相似文献
2.
3.
This work is devoted to the stress–strain state of isotropic double curved shell with defect system. The construction is weakened by two non-through thickness (internal) cracks of different length and by a circular hole located between cracks. In this study we use the line-spring model. Within the framework of this model cracks are modeled as mathematical cuts of shell’s middle surface. This leads to a two-dimensional problem. The problem is reduced to a system of eight boundary integral equations. To ensure the uniqueness of solution an additional equation is added. In the numerical solution of the problem special quadrature formulas for singular integrals of Cauchy type and the finite difference method are applied. The influence of defects on each other for double curved shell has been investigated. The given theoretical results can be used for the calculation of structural elements with holes, cracks on the strength and fracture toughness in various branches of engineering. 相似文献
4.
The morphology of the photoactive layer critically affects the performance of the bulk heterojunction polymer solar cells (PSCs). To control the morphology, we introduced a hydrophobic fluoropolymer polyvinylidene fluoride (PVDF) as nonvolatile additive into the P3HT:PCBM active layer. The effect of PVDF on the surface and the bulk morphology were investigated by atomic force microscope and transmission electron microscopy, respectively. Through the repulsive interactions between the hydrophilic PCBM and the hydrophobic PVDF, much more uniform phase separation with good P3HT crystallinity is formed within the active layer, resulting enhanced light harvesting and improved photovoltaic performance in conventional devices. The PCE of the conventional device can improve from 2.40% to 3.07% with PVDF additive. The PVDF distribution within the active layer was investigated by secondary ion mass spectroscopy, confirming a bottom distribution of PVDF. Therefore, inverted device structure was designed, and the PCE can improve from 2.81% to 3.45% with PVDF additive. Our findings suggest that PVDF is a promising nonvolatile processing additive for high performance polymer solar cells. 相似文献
5.
This paper discusses the effects of the grinding-induced cyclic heating on the properties of the hardened layer in a plunge cylindrical grinding process on the high strength steel EN26. It was found that a multi-pass grinding brings about a uniform and continuous hardened layer along the circumference of the cylindrical workpiece. An increase of the number of grinding passes, leads to a thicker layer of hardening, a larger compressive residual stress and a deeper plastic deformation zone. Within the plastic deformation zone, the martensitic grains are refined by the thermo-mechanical loading, giving rise to a hardness of 12.5% higher than that from a conventional martensitic transformation. The coupled effects of heat accumulation and wheel wear in the multi-pass grinding are the main causes for the thickening of the hardened layer. A too small infeed per workpiece revolution would result in insufficient grinding heat, and in turn, bring about an undesirable tempered hardened layer and a reduction of its hardness. 相似文献
6.
本文介绍一种智能型、高精度PWR控制器SA4828,其控制实行全数字化产生三相脉宽调制波形.本文采用此器件设计大功率直流电源应用于22KW直流电机测试,对感性负载表现出具有纹波小,响应迅速、硬件电路简洁、控制简单易于编写的优点。 相似文献
7.
研究了某种环氧树脂阻尼灌封胶在热氧老化的作用下分子结构、硬度、断面形貌以及动态力学性能随时间的变化.傅立叶红外光谱图表明,所制备的样品环氧基团反应比较完全,热氧老化后试样表面由仲胺和环氧基团形成的酯键发生了部分断裂和氧化;邵氏硬度的增加、瓦向高温区移动则表明在老化过程中复杂的固化反应仍然继续进行;最大损耗因子(tanδmax)波动较小表明试样老化后分子结构几乎保持不变;SEM图片显示试样的冲击断裂由老化前的韧性转变为老化后的脆性断裂. 相似文献
8.
L. T. MO M. HUURMAN S. P. WU A. A. A. MOLENAAR 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(9):823-831
Tensile fatigue behaviours of bitumen–stone adhesion were investigated using a dynamic mechanics analyser under stress‐controlled mode at two temperatures of 5 and 25°C and various controlled‐stress levels. Failure characteristics including interfacial failure and cohesive failure were examined using image analysis of fracture surfaces. Finite‐element analysis on stress distributions was conducted under different temperatures, film thickness and interfacial bonding conditions. A Coulomb–Mohr like criterion in combination with shear and normal stresses is proposed to deal with the extreme thin adhesive layer, which can be further simplified into an adhesive zone without significant loss of accuracy for stress analysis. 相似文献
9.
迭代回归法计算T型电位滴定中试液含量 总被引:1,自引:0,他引:1
本文将迭代回归法计算T型电位滴定中,叙述了其原理及数学推导,并运算了一批实验数据,结果表明,该法准确度较高,且不需空白溶液校正。 相似文献
10.