全文获取类型
收费全文 | 15034篇 |
免费 | 3029篇 |
国内免费 | 2342篇 |
专业分类
化学 | 8249篇 |
晶体学 | 188篇 |
力学 | 1516篇 |
综合类 | 159篇 |
数学 | 1028篇 |
物理学 | 9265篇 |
出版年
2024年 | 29篇 |
2023年 | 139篇 |
2022年 | 459篇 |
2021年 | 533篇 |
2020年 | 579篇 |
2019年 | 497篇 |
2018年 | 472篇 |
2017年 | 625篇 |
2016年 | 705篇 |
2015年 | 547篇 |
2014年 | 836篇 |
2013年 | 1305篇 |
2012年 | 974篇 |
2011年 | 1054篇 |
2010年 | 887篇 |
2009年 | 990篇 |
2008年 | 1032篇 |
2007年 | 945篇 |
2006年 | 970篇 |
2005年 | 775篇 |
2004年 | 755篇 |
2003年 | 647篇 |
2002年 | 563篇 |
2001年 | 536篇 |
2000年 | 483篇 |
1999年 | 355篇 |
1998年 | 396篇 |
1997年 | 326篇 |
1996年 | 301篇 |
1995年 | 255篇 |
1994年 | 237篇 |
1993年 | 198篇 |
1992年 | 186篇 |
1991年 | 130篇 |
1990年 | 114篇 |
1989年 | 96篇 |
1988年 | 107篇 |
1987年 | 73篇 |
1986年 | 50篇 |
1985年 | 40篇 |
1984年 | 46篇 |
1983年 | 17篇 |
1982年 | 35篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
氯代5-氟脲嘧啶卟啉的红外光谱特性的研究 总被引:6,自引:0,他引:6
本文对新合成的对位及间位两类氯代苯基 5 氟脲嘧啶卟啉的红外光谱吸收峰进行了归属和总结 ,讨论了其红外吸收频率随取代基位置变化的规律。指出了苯环上的取代基为电负性强的基团时 ,由于场效应的存在 ,使被测化合物的羰基伸缩振动吸收峰的相对强度发生改变。同时 ,表明了嘧啶环上N原子发生了取代 ,形成单、双取代 5 氟脲嘧啶卟啉化合物的红外光谱特性。 相似文献
102.
Marta Gimnez-Pedrs Ali Aghmiz Carmen Claver Anna M. Masdeu-Bult Denis Sinou 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):157-163
High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO4) as the surfactant or methanol as the co-solvent. 相似文献
103.
The problem of estimating change points in various non-monotonic aging models is considered. A general methodology for consistent estimation of the change point is developed and applied to non-monotonic aging models based on the hazard rate function as well as on the mean residual life function. 相似文献
104.
105.
By means of improved ligand-field theory, the "pure electronic" pressure-induced shifts (PS's) and the PS's due to electron-phonon interaction (EPI) of R1 line and R2 line of YAG:Cr3 have been calculated, respectively.The calculated results are in very good agreement with the experimental data. It is demonstrated that the admixture of |t22(3T1)e4T2> and |t322E> bases in the wavefunction of R1 level of YAG:Cr3 and its change with pressure play a key role for the PS of R1 line. The behaviors of the "pure electronic" PS of R1 line and the PS of R1 line due to EPI are different. It is the combined effect of them that gives rise to the total PS of R1 line, which has satisfactorily explained the experimental results. The systematic analyses and comparisons between the feature of R1-line PS of YAG:Cr3 and the ones of three laser crystals (GSGG:Cr3 , GGG:Cr3 and ruby) have been made, and the origin of the difference between them has been revealed. 相似文献
106.
107.
108.
G. K. Shenoy 《Hyperfine Interactions》2006,170(1-3):5-13
Stanley L. Ruby (1924–2004) made major contributions to Mössbauer spectroscopy and was the first to suggest the feasibility of observing the Mössbauer effect using synchrotron radiation. In this article we recall his scientific legacy that have inspired his scientific colleagues. 相似文献
109.
Due to the Meissner effect, a permanent magnet is levitated, when released above a high temperature superconductor. When there is an inhomogeneous temperature field around the magnet, the magnet might start to oscillate with increasing amplitude until it remains in a continuous rotation. A mathematical model for the described effect is presented which couples heat transfer and electromagnetic forces with the equation of motion, yielding to a multiphysics task. In a detailed analysis it is found, that the torque which drives the rotation of the magnet, is explicitly given in terms of Bessel functions and the Fourier coefficients of order zero and one of the temperature field of the surrounding air. 相似文献
110.
受激拉曼散射和热效应会限制光纤激光器功率的提高。利用高功率光纤激光器的速率方程和热传导方程,理论研究了双端泵浦和分布泵浦下双包层光纤激光器的受激拉曼散射和热效应,得到了光纤中的泵浦光、激光和斯托克斯光的功率分布,光纤激光器的输出特性以及光纤中的温度分布。分析表明,当泵浦功率增大到一定值时,光纤激光器中出现SRS,一部分激光功率会转移给斯托克斯光,影响激光功率进一步提高;与双端泵浦方式相比,分布泵浦下光纤激光器的斜率效率和最大输出功率相差不大,但是,光纤中的温度分布被有效地降低,因此,分布泵浦方式更为有效。 相似文献