全文获取类型
收费全文 | 44527篇 |
免费 | 4392篇 |
国内免费 | 2522篇 |
专业分类
电工技术 | 836篇 |
技术理论 | 1篇 |
综合类 | 4388篇 |
化学工业 | 8506篇 |
金属工艺 | 4641篇 |
机械仪表 | 1938篇 |
建筑科学 | 9528篇 |
矿业工程 | 2145篇 |
能源动力 | 861篇 |
轻工业 | 3833篇 |
水利工程 | 1796篇 |
石油天然气 | 1801篇 |
武器工业 | 302篇 |
无线电 | 1006篇 |
一般工业技术 | 5565篇 |
冶金工业 | 3084篇 |
原子能技术 | 348篇 |
自动化技术 | 862篇 |
出版年
2024年 | 189篇 |
2023年 | 623篇 |
2022年 | 1181篇 |
2021年 | 1505篇 |
2020年 | 1451篇 |
2019年 | 1281篇 |
2018年 | 1340篇 |
2017年 | 1743篇 |
2016年 | 1802篇 |
2015年 | 1773篇 |
2014年 | 2648篇 |
2013年 | 2955篇 |
2012年 | 3202篇 |
2011年 | 3250篇 |
2010年 | 2392篇 |
2009年 | 2472篇 |
2008年 | 2258篇 |
2007年 | 2736篇 |
2006年 | 2504篇 |
2005年 | 2199篇 |
2004年 | 1870篇 |
2003年 | 1577篇 |
2002年 | 1408篇 |
2001年 | 1190篇 |
2000年 | 1025篇 |
1999年 | 929篇 |
1998年 | 725篇 |
1997年 | 586篇 |
1996年 | 495篇 |
1995年 | 452篇 |
1994年 | 334篇 |
1993年 | 301篇 |
1992年 | 235篇 |
1991年 | 160篇 |
1990年 | 155篇 |
1989年 | 136篇 |
1988年 | 74篇 |
1987年 | 63篇 |
1986年 | 29篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1964年 | 4篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1954年 | 3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.
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
4.
This paper reports the results of an investigation of a set of continuous time, constant demand inventory models under the condition of yield uncertainty. Specifically, the impact of yield improvement programs on lot size, backorder level, and the resulting costs are examined. Models for improving yield rate and reducing yield variability are developed and examined through a series of numerical exercises. In addition, a model for the simultaneous improvement of yield rate and yield variability is presented for the case where there is a relationship between the mean and variance of the yield distribution. In all cases, investment programs improve the picture with respect to manufacturing yield for processes which are not necessarily under statistical control. 相似文献
5.
The tensile elastic modulus (E), yield stress (σY) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry 相似文献
6.
根据石油开采业对石油机械产品的需求 ,利用机械理论基础知识 ,通过实践设计 ,提出了对几何尺寸长的金属管类进行调质处理后的均匀冷却方法 ,以满足其性能要求。 相似文献
7.
8.
9.
介绍了日本川崎制铁公司技术研究所开发出的电焊钢管采用热张力减径工艺的特性 ,及这种钢管的高强度、高延性等基本特性。用这种钢管制造的汽车零部件 ,经弯曲、冲击和疲劳特性等实验 ,证明具有良好的机械加工性能 ,是制造汽车用零部件的优良材料。 相似文献
10.
介绍了利用现有的催化裂化装置 ,通过优化操作及运用MGD技术提高柴油和液化气收率的方法和技术措施。 相似文献