首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   15264篇
  免费   2477篇
  国内免费   1144篇
化学   8832篇
晶体学   478篇
力学   1284篇
综合类   39篇
数学   288篇
物理学   3943篇
无线电   4021篇
  2024年   49篇
  2023年   340篇
  2022年   370篇
  2021年   670篇
  2020年   895篇
  2019年   621篇
  2018年   565篇
  2017年   610篇
  2016年   845篇
  2015年   849篇
  2014年   907篇
  2013年   1112篇
  2012年   844篇
  2011年   969篇
  2010年   892篇
  2009年   879篇
  2008年   1010篇
  2007年   1082篇
  2006年   931篇
  2005年   827篇
  2004年   697篇
  2003年   625篇
  2002年   433篇
  2001年   350篇
  2000年   278篇
  1999年   216篇
  1998年   184篇
  1997年   129篇
  1996年   130篇
  1995年   77篇
  1994年   87篇
  1993年   62篇
  1992年   56篇
  1991年   56篇
  1990年   39篇
  1989年   34篇
  1988年   17篇
  1987年   21篇
  1986年   24篇
  1985年   16篇
  1984年   17篇
  1983年   21篇
  1982年   14篇
  1981年   6篇
  1979年   8篇
  1978年   2篇
  1977年   3篇
  1975年   2篇
  1974年   2篇
  1971年   6篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
71.
用射频磁控溅射结合传统退火的方法制备LiCo0.8M0.2O2 (M=Ni,Zr)阴极薄膜.X射线衍射、拉曼光谱、扫描电子显微镜等手段表征了不同掺杂的LiCo0.8M0.2O2薄膜.结果显示,700℃退火的LiCo0.8M0.2O2薄膜具有类似α-NaFeO2的层状结构.通过对不同掺杂锂钴氧阴极的全固态薄膜锂电池Li/LiPON/LiCo0.8M0.2O2的电化学性能研究表明,电化学活性元素Ni的掺杂使全固态电池具有更大的放电容量(56μAh/cm2μm),而非电化学活性元素Zr的掺杂使全固态电池具有更好的循环稳定性.  相似文献   
72.
Erbium and ytterbium codoped double tungstates NaY(WO4)2 crystals were prepared by using Czochralski (CZ) pulling method. The absorption spectra in the region 290-2000 nm have been recorded at room temperature. The Judd-Ofelt theory was applied to the measured values of absorption line strengths to evaluate the spontaneous emission probabilities and stimulated emission cross sections of Er3+ ions in NaY(WO4)2 crystals. Intensive green and red lights were measured when the sample were pumped by a 974 nm laser diode (LD), especially, the intensities of green upconversion luminescence are very strong. The mechanism of energy transfer from Yb3+ to Er3+ ions was analyzed. Energy transfer and nonradiative relaxation played an important role in the upconversion process. Photoexcited luminescence experiments are also fulfilled to help analyzing the transit processes of the energy levels.  相似文献   
73.
两种蓝色有机电致发光材料   总被引:4,自引:1,他引:3  
重点研究以两种蓝色OEL材料蒽类衍生物JBEM和联苯乙烯衍生物DPVBi分别作基质,以perylene作掺杂剂的器件的电致发光性能,特别研究了它稳定性,在这度和效率方面,两种器件并没有很大差别,然而在稳定性方面却有很大差别,蒽类衍生物JBEM的器件在100cd/m^2初始亮度下,半亮度寿命可达1035h,而DPVBi的器件在同样条件下,半亮度寿命为255h。通过分析两种器件的能级图,认为稳定性的差别可能源于两种蓝光材料本身的热稳定性不同,JBEM优于DPVBi,是一种很有前途的蓝色发光材料。  相似文献   
74.
乳胶厚度对卤化银反射全息图衍射特性的影响   总被引:1,自引:0,他引:1  
实验研究了自制的超细颗粒卤化银乳剂SDUF-1分别在AAC显影、改进的R-10漂白处理及改进的GP-8溶解物理显影处理条件下,其乳胶厚度对反射全息图衍射特性的影响。实验结果表明,在这两种不同处理条件下衍射效率与胶厚的关系有相当大的差别,合适的乳胶厚度分别为12μm和6μm左右。  相似文献   
75.
王震西  胡伯平 《物理》2002,31(7):422-429
简要回顾了20世纪20年代以来我国现代磁学研究的历史。20世纪80年代初期正值我国改革开放浪潮之时,科技人员纷纷走上科技成果产业化道路。建立于1985年的中国科学院三环公司就是一个成功的代表,同时好也是我国现代磁学研究结出的一颗硕果。  相似文献   
76.
This paper analyses and models the dynamic interaction among permeable multi-cracks in a piezoelectric strip under anti-plane shear waves by the Schmidt method. The Fourier transform is applied and then two pairs of triple integral equations can be solved using the Schmidt method. The results show that the stress and the electric displacement intensity factors of cracks depend on not only the crack length and the piezoelectric coefficient, but also the thickness of the piezoelectric strip, the distance between multi-cracks and the frequency of incident wave.  相似文献   
77.
The dynamic Young modulus (E) of magnetic Nd2Fe14B+αFe nanocomposites is investigated with mechanical spectroscopy techniques (vibrating reed configuration, f≈1.5 kHz <10−6). Reduced values of E are obtained (88–152 GPa) as compared with that predicted by the rule of mixtures for the composite (164 GPa). Three contributions to this reduction are briefly discussed: a large volume fraction of the specimen with grain boundary like structure; internal pores, resulting from the high cooling rate during processing (106 K/min) and magneto-mechanical effects. Even when porosity is identified as the principal cause of modulus reduction, magnetic effects are also detected.  相似文献   
78.
Summary Glass formation in nature and materials science is reviewed and the recent recognition of polymorphism within the glassy state, polyamorphism, is discussed. The process by which the glassy state originates during the continuous cooling or viscous slowdown process, is examined and the three canonical characteristics of relaxing liquids are correlated through the fragility. The conversion of strong liquids to fragile liquids by pressure-induced coordination number increases is discussed, and then it is shown that for the same type of system it is possible to have the same conversion accomplished via a first-order transition within the liquid state. The systems in which this can happen are of the same type which exhibit polyamorphism, and the whole phenomenology can be accounted for by a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The concept of complex amorphous systems which can lose a significant number of degrees of freedom through weak first-order transitions is then used to discuss the relation between native and denatured hydrated proteins, since the latter have much in common with plasticized chain polymer systems. Finally, we close the circle by taking a short-time-scale phenomenon given much attention by protein physicists,viz., the onset of an anomaly in the Debye-Waller factor with increasing temperature, and showing that for a wide variety of liquids, including computer-simulated strong and fragile ionic liquids, this phenomenon is closely correlated with the experimental glass transition temperature. This implies that the latter owes its origin to the onset of strong anharmonicity in certain components of the vibrational density of states (evidently related to the boson peak) which then permits the system to gain access to its configurational degrees of freedom. The more anharmonic these vibrational components, the closer to the Kauzmann temperature will commence the exploration of configuration space and, for a given configurational microstate degeneracy, the more fragile the liquid will be. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.  相似文献   
79.
含氰基的酚醛树脂,具有优异的耐高温性能和高温下的机械强度,在315℃下性能变化甚小;不着火,发烟量低,有良好的加工成型性能。热固化过程中氰基成三嗪环而交联,没有小分子脱出,是一类具有广泛发展前景的新型热固性树脂。  相似文献   
80.
Polypropylenes of differing morphologies were examined by differential thermal analysis. The problems of reordering during the programmed heating are discussed. Four potential procedures by which the reordering could be inhibited are considered, and three of these are experimentally assessed. Their advantages and deficiencies are identified. Two pretreatments, an etching and a crosslinking, are recognised as able to qualitatively characterise the initial morphology, with a preference for the former. A test to identify the occurrence of reordering is identified. In celebration of the 60th birthday of Dr. Andrew K. Galwey  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号