全文获取类型
收费全文 | 144963篇 |
免费 | 15083篇 |
国内免费 | 10629篇 |
专业分类
电工技术 | 7750篇 |
技术理论 | 6篇 |
综合类 | 10462篇 |
化学工业 | 20719篇 |
金属工艺 | 34243篇 |
机械仪表 | 7470篇 |
建筑科学 | 14487篇 |
矿业工程 | 6242篇 |
能源动力 | 2923篇 |
轻工业 | 8494篇 |
水利工程 | 3115篇 |
石油天然气 | 5987篇 |
武器工业 | 1591篇 |
无线电 | 8322篇 |
一般工业技术 | 19962篇 |
冶金工业 | 13230篇 |
原子能技术 | 1378篇 |
自动化技术 | 4294篇 |
出版年
2024年 | 718篇 |
2023年 | 2231篇 |
2022年 | 4040篇 |
2021年 | 5033篇 |
2020年 | 5371篇 |
2019年 | 4377篇 |
2018年 | 4440篇 |
2017年 | 5471篇 |
2016年 | 5508篇 |
2015年 | 5687篇 |
2014年 | 8473篇 |
2013年 | 8376篇 |
2012年 | 10007篇 |
2011年 | 10831篇 |
2010年 | 7758篇 |
2009年 | 8249篇 |
2008年 | 7180篇 |
2007年 | 9533篇 |
2006年 | 9121篇 |
2005年 | 7589篇 |
2004年 | 6536篇 |
2003年 | 5687篇 |
2002年 | 4836篇 |
2001年 | 4333篇 |
2000年 | 3610篇 |
1999年 | 3091篇 |
1998年 | 2315篇 |
1997年 | 1918篇 |
1996年 | 1777篇 |
1995年 | 1365篇 |
1994年 | 1183篇 |
1993年 | 855篇 |
1992年 | 760篇 |
1991年 | 550篇 |
1990年 | 492篇 |
1989年 | 404篇 |
1988年 | 245篇 |
1987年 | 156篇 |
1986年 | 80篇 |
1985年 | 74篇 |
1984年 | 66篇 |
1983年 | 43篇 |
1982年 | 63篇 |
1981年 | 44篇 |
1980年 | 43篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1976年 | 13篇 |
1964年 | 14篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field(BEF) in strained wurtzite Zn O/Mg0:25Zn0:75O quantum dots(QDs), the optical properties of ionized donor-bound excitons(D+, X)are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of(D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of(D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth. 相似文献
2.
3.
4.
文章通过对黑龙江省高效节水现状,存在问题的分析,结合黑龙江省高效节水发展的支撑能力,阐述黑龙江省节水增粮目标、任务及总体布局,为黑龙江省2012—2015年节水增粮实施提供依据。 相似文献
5.
The micromechanics models for composites usually underpredict the tensile strength of polymer nanocomposites. This paper establishes a simple model based on Kelly–Tyson theory for tensile strength of polymer/CNT nanocomposites assuming the effect of interphase between polymer and CNT. In addition, Pukanszky model is joined with the suggested model to calculate the interfacial shear strength (τ), interphase strength (σi) and critical length of CNT (Lc).The proposed approach is applied to calculate τ, σi and Lc for various samples from recent literature. It is revealed that the experimental data are well fitted to calculations by new model which confirm the important effect of interphase on the properties of nanocomposites. Moreover, the derived equations demonstrate that dissimilar correlations are found between τ and B (from Pukanszky model) as well as Lc and B. It is shown that a large B value obtained by strong interfacial adhesion between polymer and CNT is adequate to reduce Lc in polymer/CNT nanocomposites. 相似文献
6.
《Intermetallics》2015
The non-equiatomic FeCoNiAlSi alloy is prepared by the Bridgman solidification (BS) technique at different withdrawal velocities (V = 30, 100, and 200 μm/s). Various characterization techniques have been used to study the microstructure and crystal orientation. The morphological evolutions accompanying the crystal growth of the alloy prepared at different withdrawal velocities are nearly the same, from equiaxed grains to columnar crystals. The transition of coercivity is closely related to the local microstructure, while the saturation magnetization changes little at different sites. The coercivity can be significantly reduced from the equiaxed grain area to the columnar crystal area when the applied magnetic field direction is parallel to the crystal growth direction, no matter what is the withdrawal velocity. In addition, the alloy possesses magnetic anisotropy when the applied magnetic field is in different directions. 相似文献
7.
The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder. 相似文献
8.
Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure. 相似文献
9.
为了实现对微小环片零件的自动化装配,搭建了自动装配系统.通过4根直线导向轴与4个直线轴承来提高系统的导向精度和刚度.采用直线导轨进行各装配作业模块之间的切换,保证了微小环片零件的自动装配与取出.在环片的装配方向上,螺旋升降机和光栅尺实现环片的位置精度控制.在Lab VIEW编程环境中,采用分层软件架构和模块化控制思想,避免了不必要的数据循环检测与丢失,能够达到环片组件的装配精度要求.控制系统分为系统初始化模块、参数设置模块、装配模块和取出模块,自动装配系统通过各个模块间的相互交流配合完成装配任务.采用本文中自动装配系统装配环片的实验结果表明,环片零件装配的最大位置误差为26μm,垂直度误差为17μm,平均装配时间为75 s/片,可满足环片组件所需的精度要求. 相似文献
10.