全文获取类型
收费全文 | 5681篇 |
免费 | 193篇 |
国内免费 | 30篇 |
专业分类
化学 | 4472篇 |
晶体学 | 53篇 |
力学 | 76篇 |
数学 | 350篇 |
物理学 | 953篇 |
出版年
2023年 | 24篇 |
2022年 | 39篇 |
2021年 | 57篇 |
2020年 | 65篇 |
2019年 | 98篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 110篇 |
2015年 | 98篇 |
2014年 | 135篇 |
2013年 | 293篇 |
2012年 | 318篇 |
2011年 | 387篇 |
2010年 | 213篇 |
2009年 | 243篇 |
2008年 | 385篇 |
2007年 | 381篇 |
2006年 | 420篇 |
2005年 | 373篇 |
2004年 | 344篇 |
2003年 | 275篇 |
2002年 | 277篇 |
2001年 | 88篇 |
2000年 | 70篇 |
1999年 | 61篇 |
1998年 | 70篇 |
1997年 | 71篇 |
1996年 | 67篇 |
1995年 | 56篇 |
1994年 | 36篇 |
1993年 | 45篇 |
1992年 | 32篇 |
1991年 | 40篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 27篇 |
1987年 | 34篇 |
1986年 | 46篇 |
1985年 | 63篇 |
1984年 | 51篇 |
1983年 | 27篇 |
1982年 | 55篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 39篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有5904条查询结果,搜索用时 15 毫秒
991.
992.
Yoshimasa Sakai Mitsuru Ueda Takashi Fukuda Hiro Matsuda 《Journal of polymer science. Part A, Polymer chemistry》1999,37(9):1321-1329
A thermal stable aromatic polyimide (PI) with side‐chain second‐order nonlinear optical (NLO) chromophores has been developed. The PI was prepared by the ring‐opening polyaddition of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride with a new diamine having two N‐ethyl‐N‐[4‐[(6‐chlorobenzothiazol‐2‐yl)diazenyl]phenyl]‐2‐aminoethanol units as the NLO chromophore, followed by poling during or after the thermal imidization process. The resulting PI had number and weight‐average molecular weights (Mn, Mw) of 25,000 and 80,000, respectively, and a relatively high glass transition temperature of 180°C. The second harmonic coefficient (d33) of PI at the wavelength of 1.064 μm was 138 pm/V (329.6 × 10−9 esu) and remained unchanged at elevated temperatures. The corona poling process of the NLO‐substituted poly(amic acid) to the PI was also studied in detail by measuring the second harmonic generation (SHG) from the polymer films. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1321–1329, 1999 相似文献
993.
994.
Langmuir-Blodgett (LB) films consisting of the hybrid of a polymer having the azobenzene (Az) side chain and 4î-pentyl-4-cyanobiphenyl (5CB) are prepared. Microscopic observations and spectroscopic data both indicate that the Az side chain and 5CB are homogeneously mixed at a molecular level without phase separation in the layer. This provides a satisfactory model of the command surface system. Time course accumulation of spectroscopic data for multilayered hybrid films reveals the cooperative nature of the photo-motivated molecular motions. 相似文献
995.
A radical chain addition of allyl bromides 2 to alkenylcyclopropanes 1 resulted in [3+2] annulation to give 2-bromomethylalkenylcyclopentanes 3 in good yields(16 examples). In this reaction, two kinetically fast radical reactions, cyclopropylcarbinyl radical-ring-opening and 5-exo-radical cyclization, preceded the β-fragmentation of a bromine radical to make the formal cycloaddition possible. 相似文献
996.
Analytical and numerical studies of the boundary slip in the immersed boundary‐thermal lattice Boltzmann method
下载免费PDF全文
![点击此处可从《国际流体数值方法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We analytically and numerically investigate the boundary slip, including the velocity slip and the temperature jump, in immersed boundary‐thermal lattice Boltzmann methods (IB‐TLBMs) with the two‐relaxation‐time collision operator. We derive the theoretical equation for the relaxation parameters considering the effect of the advection velocity on the temperature jump of the IB‐TLBMs. The analytical and numerical solutions demonstrate that the proposed iterative correction methods without the computational cost of the sparse matrix solver reduce the boundary slip and boundary‐value deviation as effectively as the implicit correction method for any relaxation time. Because the commonly used multi‐direct forcing method does not consider the contributions of the body force to the momentum flux, it cannot completely eliminate the boundary slip because of the numerical instability for a long relaxation time. Both types of proposed iterative correction methods are more numerically stable than the implicit correction method. In simulations of flow past a circular cylinder and of natural convection, the present iterative correction methods yield adequate results without the errors of the velocity slip, the temperature jump, and the boundary‐value deviation for any relaxation time parameters and for any number of Lagrangian points per length. The combination of the present methods and the two‐relaxation‐time collision operator is suitable for simulating fluid flow with thermal convection in the multiblock method in which the relaxation time increases in inverse proportion to the grid size. 相似文献
997.
Hidemitsu Aoki Makoto Hara Takuro Masuzumi Motaharu K. Mazumder Naoki Ooi Daisuke Watanabe Chiharu Kimura Takashi Sugino 《Applied Surface Science》2009,255(6):3719-3722
Cu electroplating is required for the fabrication of Cu/low-k interconnections. The permeation of a plating solution into low-k films during Cu electroplating is a serious challenge for 45-nm nodes and more complex devices. We investigated the influence of Cu electroplating solutions on boron carbon nitride (BCN) as a low-k film. After dipping it into a Cu electroplating solution that contained additives, the BCN film's hydrophilic surface changed to a hydrophobic surface, and the incorporation of water into the BCN film was suppressed by surfactant adsorption. Sulfuric residue was detected on the BCN sample by thermal desorption spectroscopy after treatment in the Cu electroplating solution with additives; however, it was found through electrical measurements that this solution did not affect the leakage current or the dielectric constant of the BCN film. We successfully fabricated an electroplating Cu layer on a BCN film with good adhesion, and we believe that this BCN film is a sufficiently useful material for Cu/BCN integration in LSI. 相似文献
998.
Keiko Matsunouchi Naoyoshi Komatsu Chiharu Kimura Hidemitsu Aoki Takashi Sugino 《Applied Surface Science》2009,255(9):5021-5024
YAlO films are synthesized on (1 0 0)-oriented Si substrates by RF magnetron sputtering method. Al2O3 wafer is used as a target material, and some small pieces of Y bulk material are put on the Al2O3 target to synthesize YAlO films. Y composition ratio is varied from 0 to 34%. Amorphous YAlO films are characterized. An electrical resistivity as high as 3.4 × 1014 Ω-cm is achieved for the YAlO film with Y composition ratio of 10%. The dielectric constant increases with increasing Y composition ratio, and the YAlO film with Y composition ratio of 34% has a dielectric constant of 10.2. The bandgap energy of the YAlO film is suggested to be wider than 6.5 eV. YAlO films with a surface roughness of 0.4-1.3 nm are obtained irrespective of the Y composition ratio. 相似文献
999.
The applicability of laser processing for small-lot micro-electromechanical system devices is discussed in this paper. This simple process could replace conventional complex processes designed with mass production in mind. Ablation, protrusions or surface modification is revealed to occur by argon ion laser scanning into silicon. Which of them occurs depends on the laser power. It is found that the protrusions are covered by a thin layer of oxide; however, oxidation of the modified surface is not established even though some results suggest it. Surface modification is more applicable to surface patterning than coarse protrusion is because the laser-modified surface can be used as a mask in KOH etching to make sharp patterns. The applicability of this method is indicated by demonstrating pattern width control, patterning over a large area and the fabrication of a 16-bit linear scale. 相似文献
1000.
Takashi Nagatani 《Physica A》2009,388(14):2911-2921
We study the dynamic behavior of vehicular traffic through a series of traffic lights on selected paths in a two-dimensional (2d) traffic network. The city traffic network is made of one-way perpendicular streets arranged in a square lattice with traffic signals where vertical streets are oriented upwards and horizontal streets are oriented rightwards. A vehicle moves through the series of signals on a path selected by the driver. The selected path is one of the straight, zigzag, and random paths in a 2d traffic network. The vehicular motion on a selected path is presented by the nonlinear-map model. Vehicular traffic exhibits very complex behavior with varying selected paths, cycle times, and vehicular density. The dependence of the arrival time on cycle time, selected path, and density is clarified for 2d city traffic. 相似文献