全文获取类型
收费全文 | 35929篇 |
免费 | 5562篇 |
国内免费 | 3617篇 |
专业分类
化学 | 25078篇 |
晶体学 | 342篇 |
力学 | 2184篇 |
综合类 | 241篇 |
数学 | 4272篇 |
物理学 | 12991篇 |
出版年
2024年 | 26篇 |
2023年 | 738篇 |
2022年 | 716篇 |
2021年 | 1204篇 |
2020年 | 1427篇 |
2019年 | 1295篇 |
2018年 | 1118篇 |
2017年 | 1024篇 |
2016年 | 1573篇 |
2015年 | 1552篇 |
2014年 | 1939篇 |
2013年 | 2504篇 |
2012年 | 3204篇 |
2011年 | 3212篇 |
2010年 | 2180篇 |
2009年 | 2051篇 |
2008年 | 2203篇 |
2007年 | 1960篇 |
2006年 | 1842篇 |
2005年 | 1539篇 |
2004年 | 1301篇 |
2003年 | 984篇 |
2002年 | 894篇 |
2001年 | 738篇 |
2000年 | 691篇 |
1999年 | 829篇 |
1998年 | 693篇 |
1997年 | 624篇 |
1996年 | 677篇 |
1995年 | 593篇 |
1994年 | 546篇 |
1993年 | 466篇 |
1992年 | 444篇 |
1991年 | 360篇 |
1990年 | 323篇 |
1989年 | 235篇 |
1988年 | 216篇 |
1987年 | 198篇 |
1986年 | 139篇 |
1985年 | 155篇 |
1984年 | 134篇 |
1983年 | 116篇 |
1982年 | 80篇 |
1981年 | 59篇 |
1980年 | 49篇 |
1979年 | 32篇 |
1978年 | 26篇 |
1976年 | 27篇 |
1975年 | 31篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
脉冲压缩光栅光路调节新方法研究 总被引:2,自引:1,他引:1
介绍了一种简单而实用的大口径脉冲压缩光栅光路调节方法,有效解决了普通光路调节方法中轴向调节精度不高的问题。首先由全息透镜(光栅)成像公式出发,推导出了该光路调节的基本原理。并从光栅记录系统与光栅衍射波像差的关系,结合初级像差理论推导得出叠栅条纹像差为0.4786λ,大约是光栅衍射波像差(0.25λ)的两倍,利用此关系也可对光栅衍射波像差进行实时监测。从数值模拟结果可知,利用叠栅条纹法调节光路可将光栅波像差减至0.06λ,相应的轴向误差量为0.007 mm,可有效提高了轴向调节精度。 相似文献
132.
Tao Jin Feng-Xian Jiang Xiao-Li Li Fang Wang Xiao-Hua Shen Rui-Qiang Zhang Hai-Shun Wu 《Applied Surface Science》2006,253(5):2708-2712
CoPt/Ag and [C/CoPt]n/Ag thin films have been prepared onto the glass substrates by magnetron sputtering. We investigated the evolution of texture and magnetic properties of CoPt/Ag and [C/CoPt]n/Ag films. The results show that C-doping plays an important role in improving (0 0 1) texture, improving the order parameter S, reducing the intergrain interactions, and making the magnetization reversal mechanism more close to Stoner-Wolfarth rotational mechanism. The growth mechanism of (0 0 1) texture also seems to be related strongly to the films thickness. Our results show that the highly (0 0 1)-oriented films with ordered fct phase have a significant potential for the perpendicular media of extremely high-density recording. 相似文献
133.
134.
135.
Investigation of remelting and cladding processing with laminar plasma jets on several metals has been conducted looking for possible development of a new surface modification technique. The remelting tests illustrated that the new method could evidently improve the material microstructure and properties of cast iron. The cladding was done with Al2O3 ceramic powder on stainless steel. The energy dispersive spectra (EDS) analysis was used to determine the distribution of the major cladding element in the plasma-processed layers, for which the microstructure observations and hardness measurements were also performed. 相似文献
136.
137.
The influence of the electron-LO-phonon coupling on energy spectrum of the low-lying states ofan exciton inparabolic quantum dots is investigated as a function of dot size. Calculations are made by using the method of few-bodyphysics within the effective-mass approximation. A considerable decrease of the energy in the stronger confinement rangeis found for the low-lying states of an exciton in quantum dots, which results from the confinement of electron-phononcoupling. 相似文献
138.
将等离子焊接(PAW)电弧和钨极氩弧焊(TIG)电弧串接,相对作用于工件的正反面形成双面电弧焊接(DSAW)系统,可以引导焊接电流沿工件厚度方向流过小孔,补偿等离子电弧穿透工件时消耗的能量,以有效地提高等离子弧的穿透能力.综合考虑影响双面电弧焊接正反面熔池几何形状的力学因素,建立了熔池表面变形的控制方程,以此为基础并采用帖体曲线坐标系建立了DSAW焊接传热的数学模型,分析了DSAW,PAW焊接传热的差异,从传热的角度解释了DSAW焊接熔深增加的原因.焊接工艺实验表明,计算结果与实测结果吻合良好.
关键词:
双面电弧焊接(DSAW)
传热模型
熔池表面变形模型 相似文献
139.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献
140.
An improvement has been made to couple isoelectric focusing (IEF) sample injection and capillary zone electrophoresis in an untreated fused silica capillary. Electroosmotic flow is efficiently prevented by simply using a rubber block at the outlet end of the capillary during IEF sample injection. The experimental conditions that affect the concentration effect are discussed. A concentration enhancement factor of over 100-fold can be easily obtained for two model proteins: lysozyme and ribonuclease A. 相似文献