全文获取类型
收费全文 | 23699篇 |
免费 | 5031篇 |
国内免费 | 1951篇 |
专业分类
化学 | 8506篇 |
晶体学 | 892篇 |
力学 | 1064篇 |
综合类 | 245篇 |
数学 | 3659篇 |
物理学 | 16315篇 |
出版年
2024年 | 53篇 |
2023年 | 195篇 |
2022年 | 527篇 |
2021年 | 538篇 |
2020年 | 593篇 |
2019年 | 494篇 |
2018年 | 543篇 |
2017年 | 798篇 |
2016年 | 851篇 |
2015年 | 855篇 |
2014年 | 1313篇 |
2013年 | 1930篇 |
2012年 | 1453篇 |
2011年 | 1494篇 |
2010年 | 1235篇 |
2009年 | 1476篇 |
2008年 | 1707篇 |
2007年 | 1627篇 |
2006年 | 1511篇 |
2005年 | 1348篇 |
2004年 | 1158篇 |
2003年 | 1086篇 |
2002年 | 1069篇 |
2001年 | 924篇 |
2000年 | 818篇 |
1999年 | 718篇 |
1998年 | 654篇 |
1997年 | 594篇 |
1996年 | 538篇 |
1995年 | 481篇 |
1994年 | 377篇 |
1993年 | 322篇 |
1992年 | 265篇 |
1991年 | 203篇 |
1990年 | 133篇 |
1989年 | 117篇 |
1988年 | 101篇 |
1987年 | 98篇 |
1986年 | 76篇 |
1985年 | 74篇 |
1984年 | 56篇 |
1983年 | 33篇 |
1982年 | 56篇 |
1981年 | 53篇 |
1980年 | 34篇 |
1979年 | 34篇 |
1978年 | 22篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
82.
工程施工中运输网络优化方案 总被引:5,自引:0,他引:5
施工工地运输方案的优化设计可以归结为 :按施工期要求设计运输线路或验证已有线路通行能力 ,计算总线路中影响提高流量的关键路段 ,取得最小费用最大流 .本文运用图论理论这一数学工具把实际问题抽象为有向网络 ,进而建立数学模型 .此方法理论上严密 ,解题步聚直观清晰 ,对水利、公路、水路、铁路等其它运输系统有普遍意义 . 相似文献
83.
J. T. Hoeft M. Polcik D. I. Sayago M. Kittel R. Terborg R. L. Toomes J. Robinson D. P. Woodruff M. Pascal G. Nisbet C. L. A. Lamont 《Surface science》2003,540(2-3):441-456
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding. 相似文献
84.
Mean value in invexity analysis 总被引:1,自引:0,他引:1
In this paper, a generalization of the mean value theorem is considered in the case of functions defined on an invex set with respect to η (which is not necessarily connected). 相似文献
85.
An all-optical fiber nonlinear Fabry-Perot resonator is proposed. The steady-state model for describing this resonator is developed. The transmission and refection bistabilities are shown numerically. Our results show that the bistability in this system is similar to that in a normal nonlinear Fabry-Perot etalon, except that the characteristics of the bistability can be changed not only by the cavity length but also by the phase shifts of the fiber loop mirrors. 相似文献
86.
T. K. Solovykh 《Journal of Applied Spectroscopy》1997,64(5):654-657
The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra
of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on
the optical absorption of orthoferrites that are promising for magnetooptics is studied.
Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072,
Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997. 相似文献
87.
Vincent S. Smentkowski John T. Yates Jr. Xiaojie Chen William A. Goddard III 《Surface science》1997,370(2-3):209-231
The radiation-induced decomposition of C4F9I and CF3I overlayers at 119 K on diamond (100) surfaces has been shown to be an efficient route to fluorination of the diamond surface. X-ray photoelectron spectroscopy has been used for photoactivation as well as for studying the photodecomposition of the fluoroalkyl iodide molecules, the attachment of the photofragments to the diamond surface, and the thermal decomposition of the fluoroalkyl ligands. Measured chemical shifts agree well with ab initio calculations of both C 1s and F 1s binding energies. It is found that chemisorbed CF3 groups on diamond (100) decompose by 300 K whereas C4F9 groups decompose over the range 300 to 700 K and this reactivity difference is rationalized on steric grounds. Both of these thermal decomposition processes produce surface C---F bonds on the diamond. The surface C---F species thermally decompose over a wide temperature range extending up to 1500 K. Hydrogen passivation of the diamond surface is ineffective in preventing free radical attack from the photodissociated products of the fluoroalkyl iodides; I atoms produced photolytically abstract H from surface C---H bonds to yield hydrogen iodide at 119 K allowing diamond fluorination. The attachment of chemisorbed F species to the diamond (100) surface causes band bending as the surface states are occupied as a result of chemisorption. This results in a shift to higher binding energy of the diamond-related C 1s levels present in the surface and subsurface regions which are sampled by XPS on the diamond. The use of photoactivation of fluoroalkyl iodides for the fluorination of diamond surfaces provides a convenient route compared to other methods involving the action of atomic F, molecular F2, XeF2 and F-containing plasmas. 相似文献
88.
89.
提出了折射率温敏式光纤温度传感器的理论模型,包括子午光线和偏射光线的影响,讨论了多模光纤的弯曲损耗,理论的分析和结果与实验相当一致。 相似文献
90.