全文获取类型
收费全文 | 63572篇 |
免费 | 18651篇 |
国内免费 | 1741篇 |
专业分类
化学 | 67289篇 |
晶体学 | 225篇 |
力学 | 3075篇 |
综合类 | 67篇 |
数学 | 4661篇 |
物理学 | 8647篇 |
出版年
2024年 | 422篇 |
2023年 | 4320篇 |
2022年 | 2117篇 |
2021年 | 3188篇 |
2020年 | 5245篇 |
2019年 | 3021篇 |
2018年 | 2944篇 |
2017年 | 1173篇 |
2016年 | 6455篇 |
2015年 | 6309篇 |
2014年 | 5912篇 |
2013年 | 6445篇 |
2012年 | 4839篇 |
2011年 | 2759篇 |
2010年 | 4482篇 |
2009年 | 4378篇 |
2008年 | 2192篇 |
2007年 | 1765篇 |
2006年 | 1083篇 |
2005年 | 854篇 |
2004年 | 649篇 |
2003年 | 468篇 |
2002年 | 467篇 |
2001年 | 372篇 |
2000年 | 294篇 |
1999年 | 415篇 |
1998年 | 300篇 |
1997年 | 375篇 |
1996年 | 361篇 |
1995年 | 385篇 |
1994年 | 293篇 |
1993年 | 425篇 |
1992年 | 239篇 |
1991年 | 225篇 |
1990年 | 184篇 |
1988年 | 202篇 |
1981年 | 178篇 |
1980年 | 222篇 |
1979年 | 194篇 |
1978年 | 203篇 |
1977年 | 321篇 |
1976年 | 378篇 |
1975年 | 471篇 |
1974年 | 484篇 |
1973年 | 299篇 |
1972年 | 374篇 |
1971年 | 361篇 |
1970年 | 548篇 |
1969年 | 421篇 |
1968年 | 470篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Gallin Peter Prof. Dr. 《ZDM》2003,35(3):110-119
In order to emphasize functional thinking in mathematical education, arguments are brought forward for an early and frequent use of tree diagrams in teaching stochastics. Since set and tree diagrams can be regarded as two sides of the same matter, Bayes’ theorem, which is strongly associated with predicative set diagrams, need not be dealt with explicitly any longer. Set diagrams are replaced by tree diagrams that are labelled in detail and by tree inversion as a functional instrument of dealing with conditioned probabilities. This technique is demonstrated by three typical problems in the context of conditioned probability. Finally, two letters by Pascal to Fermat are analysed in order to illustrate that predicative and functional approaches were already pursued in the early stages of probability calculus in the 17th century. 相似文献
22.
23.
在GS-221高速摄影测量仪中,测角信息采集与处理速度的快慢是重要性能指标之一。本文讨论了如何在尽可能短的时间内对测角信息进行采集和处理的软件实现方法。 相似文献
24.
Phenylene vinylene‐based electroluminescent polymers with electron transport block in the main chain
Honghao Sun Chongyu Mei Quanguo Zhou Ze Liu Dongge Ma Lixiang Wang Xiabin Jing Fosong Wang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(11):3469-3478
We report a new route for the design of soluble phenylene vinylene (PV) based electroluminescent polymers bearing electron‐deficient oxadizole (OXD) and triazole (TZ) moieties in the main chains with the aryloxy linkage. Both series of the PV‐based polymers were prepared by Wittig reaction. By properly adjusting the OXD and/or TZ content through copolymerization, we can achieve an enhanced balance of hole‐ and electron injections, such that the device efficiency is significantly improved. Light‐emitting diodes fabricated from P1, P2, P3, P4, P5, P6, and P7 with the configuration of Indium–Tin Oxide (ITO)/Poly (styrene sulfonic acid) doped poly (ethylenedioxythiophene) (PEDOT)/polymer/Ca/Al, emit bright green light with the maximum peak around 500 nm. For the device using the optimal polymer (P4) as emitting layer, a maximum brightness of 1300 cd/m2 at 20 V and a maximum luminance efficiency of 0.325 cd/A can be obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3469–3478, 2006 相似文献
25.
26.
Zhicheng Xiao Ying Li Dongling Ma Linda S. Schadler Yvonne A. Akpalu 《Journal of Polymer Science.Polymer Physics》2006,44(7):1084-1095
Small‐angle light scattering (SALS) measurements were used to study the structure of titanium dioxide (TiO2)/low‐density polyethylene (LDPE) nanocomposites. The results showed that the scattering from LDPE crystalline structures and the scattering from TiO2 nanoparticles can be resolved and separated. It is shown that the independent effects of crystallization conditions and the presence of nanoparticle aggregates on the spherulitic structure of the LDPE matrix can be determined by analyzing the scattering patterns using the methods proposed. From the SALS results, we conclude that the nanoparticle surface chemistry affects both nucleation of spherulites and their structure particularly under rapid cooling conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1084–1095, 2006 相似文献
27.
激光感生碰撞能量转移的四能级理论模型 总被引:6,自引:2,他引:4
首次考虑了两个中间态对激光感生碰撞能量转移的影响,发展了激光感生碰撞能量转移的四能级理论模型,推导出态振幅的运动方程,并给出碰撞截面的近似表达式,通过对Eu-Sr和Cs-Sr系统的数值计算表明,当频率差│ω21│大小和│ω43│可以相比时,利用三能级近似理论就难以获得令人满意的计算结果,而四能级理论模型则适合于任何情况下的激光感生碰能量转移。 相似文献
28.
The picosecond degenerate four-wave mixing reflectivity of semi-insulating gallium arsenide at 1.06 m is calculated in this paper. The dependence of the reflectivity on the pump and signal fluences is measured. Reflectivities of more than one are possible. The Fourier components of the excited-carrier densities are calculated as a function of the pump fluence. The wavefront-correction property of this reflectivity is demonstrated with a lens group in the signal beam. 相似文献
29.
K. Rohlena K. Mašek E. G. Balabanova I. Paulička 《Czechoslovak Journal of Physics》1988,38(6):622-637
Systematic calculations of maximum inversion were performed for iodine photodissociation laser in dependence on the mixture composition. The flash-lamp radiation was modelled as emanating from an optically thin Xe plasma. Duration of the pumping pulse is about 300 s. The sensitivity of the model to the values of kinetic constants was also tested. 相似文献
30.