全文获取类型
收费全文 | 16358篇 |
免费 | 2608篇 |
国内免费 | 1715篇 |
专业分类
化学 | 12268篇 |
晶体学 | 203篇 |
力学 | 845篇 |
综合类 | 75篇 |
数学 | 1607篇 |
物理学 | 5683篇 |
出版年
2024年 | 38篇 |
2023年 | 316篇 |
2022年 | 378篇 |
2021年 | 529篇 |
2020年 | 650篇 |
2019年 | 650篇 |
2018年 | 579篇 |
2017年 | 516篇 |
2016年 | 760篇 |
2015年 | 783篇 |
2014年 | 1002篇 |
2013年 | 1265篇 |
2012年 | 1475篇 |
2011年 | 1583篇 |
2010年 | 1125篇 |
2009年 | 953篇 |
2008年 | 1131篇 |
2007年 | 1018篇 |
2006年 | 905篇 |
2005年 | 787篇 |
2004年 | 595篇 |
2003年 | 495篇 |
2002年 | 461篇 |
2001年 | 333篇 |
2000年 | 316篇 |
1999年 | 268篇 |
1998年 | 229篇 |
1997年 | 201篇 |
1996年 | 189篇 |
1995年 | 145篇 |
1994年 | 188篇 |
1993年 | 131篇 |
1992年 | 126篇 |
1991年 | 97篇 |
1990年 | 92篇 |
1989年 | 87篇 |
1988年 | 45篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 17篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1967年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Takaaki Kakitsuka Shinji Matsuo Seok–Hwan Jeong Toru Segawa Hiroshi Okamoto Yoshihiro Kawaguchi Yasuhiro Kondo Yuzo Yoshikuni Hiroyuki Suzuki 《Optical and Quantum Electronics》2006,38(12-14):1053-1060
We theoretically investigated a digitally tunable laser with a chirped ladder filter and a ring resonator to obtain a wide wavelength tuning range covering the whole C- or L- band. The clear relation between the tuning range and laser structure, especially the ladder filter, is described analytically. The introduction of a chirped structure into a ladder filter is effective in achieving both wide tunability and a stable lasing mode. A numerical simulation based on multimode rate equations shows that a tuning range of over 40 nm and a mode suppression ratio over 40 dB can be achieved by introducing a chirped ladder filter. 相似文献
102.
从运动的荷电粒子产生的流密度出发,研究了在地球偶极磁场中运动的相对论性荷电粒子的辐射能量谱,并对其进行数值计算.分析了相对论性荷电粒子在地球偶极磁场这种特殊磁场中的辐射特点. 相似文献
103.
Cracking of ceramics with tetragonal perovskite grain structure is known to appear at different sites and scale level. The multiscale character of damage depends on the combined effects of electromechanical coupling, prevailing physical parameters and boundary conditions. These detail features are exhibited by application of the energy density criterion with judicious use of the mode I asymptotic and full field solution in the range of r/a=10−4 to 10−2 where r and a are, respectively, the distance to the crack tip and half crack length. Very close to the stationary crack tip, bifurcation is predicted resembling the dislocation emission behavior invoked in the molecular dynamics model. At the macroscopic scale, crack growth is predicted to occur straight ahead with two yield zones to the sides. A multiscale feature of crack tip damage is provided for the first time. Numerical values of the relative distances and bifurcation angles are reported for the PZT-4 ceramic subjected to different electric field to applied stress ratio and boundary conditions that consist of the specification of electric field/mechanical stress, electric displacement/mechanical strain, and mixed conditions. To be emphasized is that the multiscale character of damage in piezoceramics does not appear in general. It occurs only for specific combinations of the external and internal field parameters, elastic/piezoelectric/dielectric constants and specified boundary conditions. 相似文献
104.
105.
Hong Ming ZHANG Xian Hong WANG Xiao Jiang ZHAO Ji LI Fo Song WANG 《中国化学快报》2006,17(4):437-440
A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity. 相似文献
106.
107.
108.
109.
在考虑自由体积和局部临界扩散势能的基础上,提出一种新的计算自扩散系数模型,并给出新模型中各个因子物理含义.同时还提出一种计算局部临界扩散势能的新方法,并应用于新模型.另外将衍生van der Waals状态方程应用于求解自由体积,式中所需径向分布函数由Morsali-Goharshadi方程得到.在相同条件下,新模型比原自由体积模型更准确. 相似文献
110.
Z.X. Cheng S.J. ZhangF. Song H.C. GuoJ.R. Han H.C. Chen 《Journal of Physics and Chemistry of Solids》2002,63(11):2011-2017
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