全文获取类型
收费全文 | 197413篇 |
免费 | 40108篇 |
国内免费 | 27910篇 |
专业分类
化学 | 131473篇 |
晶体学 | 2408篇 |
力学 | 13174篇 |
综合类 | 723篇 |
数学 | 24018篇 |
物理学 | 93635篇 |
出版年
2024年 | 627篇 |
2023年 | 3036篇 |
2022年 | 4935篇 |
2021年 | 4968篇 |
2020年 | 5857篇 |
2019年 | 6073篇 |
2018年 | 5450篇 |
2017年 | 5576篇 |
2016年 | 7962篇 |
2015年 | 7830篇 |
2014年 | 9036篇 |
2013年 | 12879篇 |
2012年 | 14942篇 |
2011年 | 16806篇 |
2010年 | 16317篇 |
2009年 | 16128篇 |
2008年 | 10857篇 |
2007年 | 9757篇 |
2006年 | 8909篇 |
2005年 | 8130篇 |
2004年 | 7421篇 |
2003年 | 5946篇 |
2002年 | 5568篇 |
2001年 | 5446篇 |
2000年 | 4309篇 |
1999年 | 4930篇 |
1998年 | 4187篇 |
1997年 | 3901篇 |
1996年 | 4346篇 |
1995年 | 4333篇 |
1994年 | 4302篇 |
1993年 | 4031篇 |
1992年 | 3562篇 |
1991年 | 3095篇 |
1990年 | 2598篇 |
1989年 | 2443篇 |
1988年 | 2296篇 |
1987年 | 1530篇 |
1986年 | 1607篇 |
1985年 | 1211篇 |
1984年 | 1236篇 |
1983年 | 532篇 |
1982年 | 1034篇 |
1981年 | 848篇 |
1980年 | 848篇 |
1979年 | 570篇 |
1978年 | 565篇 |
1977年 | 665篇 |
1976年 | 1079篇 |
1972年 | 553篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
Chongyu Mei Junqiao Ding Bing Yao Yanxiang Cheng Zhiyuan Xie Yanhou Geng Lixiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1746-1757
Two orange phosphorescent iridium complex monomers, 9‐hexyl‐9‐(iridium (III)bis(2‐(4′‐fluorophenyl)‐4‐phenylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐PIr) and 9‐hexyl‐9‐(iridium(III)bis(2‐(4′‐fluorophenyl)‐4‐methylquinoline‐N,C2′)(tetradecanedionate‐11,13))‐2,7‐dibromofluorene (Br‐MIr), were successfully synthesized. The Suzuki polycondensation of 2,7‐bis(trimethylene boronate)‐9,9‐dioctylfluorene with 2,7‐dibromo‐9,9‐dioctylfluorene and Br‐PIr or Br‐MIr afforded two series of copolymers, PIrPFs and MIrPFs, in good yields, in which the concentrations of the phosphorescent moieties were kept small (0.5–3 mol % feed ratio) to realize incomplete energy transfer. The photoluminescence (PL) of the copolymers showed blue‐ and orange‐emission peaks. A white‐light‐emitting diode with a configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/PIr05PF (0.5 mol % feed ratio of Br‐PIr)/Ca/Al exhibited a luminous efficiency of 4.49 cd/A and a power efficiency of 2.35 lm/W at 6.0 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.46, 0.33). The CIE coordinates were improved to (0.34, 0.33) when copolymer MIr10PF (1.0 mol % feed ratio of Br‐MIr) was employed as the white‐emissive layer. The strong orange emission in the electroluminescence spectra in comparison with PL for these kinds of polymers was attributed to the additional contribution of charge trapping in the phosphorescent dopants. © 2007 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 45: 1746–1757, 2007 相似文献
994.
Hilbert空间上线性算子的Drazin可逆性 总被引:1,自引:0,他引:1
主要研究了Hilbert空间上两个Drazin可逆算子和的Drazin可逆性.同时,对上三角算子矩阵的Drazin可逆性也给出了详细的讨论. 相似文献
995.
Li-Min Wang 《Semigroup Forum》1995,50(1):141-160
Communicated by F. Pastijn 相似文献
996.
To satisfy the volatile nature of today’s markets, businesses require a significant reduction in product development lead times. Consequently, the ability to develop precise product sales forecasts is of fundamental importance to decision-makers. Over the years, many forecasting techniques of varying capabilities have been introduced. The precise extent of their influences, and the interactions between them, has never been fully clarified, although various forecasting factors have been explored in previous studies. Accordingly, this study adopts the Taguchi method to calibrate the controllable factors of a forecasting model. An L9(34) inner orthogonal array is constructed for the controllable factors of data period, horizon length, and number of observations required. An experimental design is then performed to establish the appropriate levels for each factor. At the same time, an L4(23) outer orthogonal array is used to consider the inherited parameters of forecasting method as the noise factors of Taguchi method simultaneously. An illustrated example, employing data from a power company, serves to demonstrate the thesis. The results show that the proposed model permits the construction of a highly efficient forecasting model through the suggested data collection method. 相似文献
997.
本文在经典风险模型的基础上,将索赔到达过程推广为更新过程,索赔可以批量到达,且带有常数利息力和Brown运动干扰项,得到一个新的风险模型,运用Markov骨架过程的方法,得出盈余过程的瞬时分布和生存概率. 相似文献
998.
Humberto César Chaves Fernandes Arthur Rodrigo Barros da Rocha 《International Journal of Infrared and Millimeter Waves》2003,24(7):1171-1176
The use of photonic materials has been used in the theory of optical waves. The PBG (Photonic Band Gap) theory and material, was developed recently for optical frequencies and can be easily applied to millimeter waves, microwaves and planar antenna frequencies. The presence of photonic materials as substrate in antennas has some good characteristics such as, supression of light spontaneous emission and suppression of surface waves, allowing the application in planar antenna array. In this work an elaborate analysis using the full wave Transverse Transmission Line - TTL method, that provides efficient and concise results is applied to the planar antennas array with PBG substrate. 相似文献
999.
1000.
Xiaowei Sun Zijiang Liu Qifeng Chen Chengwei Wang 《Journal of Physics and Chemistry of Solids》2007,68(2):249-255
Molecular dynamics (MD) method is used to investigate the behavior of the pressure-volume-temperature (P-V-T) relationship, lattice constant and thermal expansivity for ZnO with rock-salt structure at high pressures and temperatures. The interionic potential is taken to be the sum of pair-wise additive Coulomb, van der Waals attraction, and repulsive interactions. The isothermal and isobaric properties are discussed from the corresponding P-V-T relationship, and it is shown that the MD simulation is successful in reproducing the measured volumes of ZnO over a wide range of temperature and pressure. Meanwhile, the equations of state parameters including lattice constant, linear thermal expansion coefficient, and isothermal bulk modulus are calculated and compared with the available experimental data and the latest theoretical results. At an extended pressure and temperature range, P-V-T relationship, lattice constant, and linear thermal expansion coefficient have been predicted. The structural and thermodynamic properties of ZnO with rock-salt structure are summarized in the pressure 0-100 GPa ranges and the temperature up to 3100 K. 相似文献