全文获取类型
收费全文 | 20724篇 |
免费 | 2405篇 |
国内免费 | 4081篇 |
专业分类
化学 | 17634篇 |
晶体学 | 2614篇 |
力学 | 301篇 |
综合类 | 60篇 |
数学 | 138篇 |
物理学 | 6463篇 |
出版年
2024年 | 40篇 |
2023年 | 143篇 |
2022年 | 398篇 |
2021年 | 420篇 |
2020年 | 582篇 |
2019年 | 598篇 |
2018年 | 588篇 |
2017年 | 725篇 |
2016年 | 925篇 |
2015年 | 734篇 |
2014年 | 1113篇 |
2013年 | 2176篇 |
2012年 | 1215篇 |
2011年 | 1190篇 |
2010年 | 1112篇 |
2009年 | 1246篇 |
2008年 | 1346篇 |
2007年 | 1439篇 |
2006年 | 1493篇 |
2005年 | 1356篇 |
2004年 | 1356篇 |
2003年 | 1045篇 |
2002年 | 846篇 |
2001年 | 585篇 |
2000年 | 576篇 |
1999年 | 591篇 |
1998年 | 485篇 |
1997年 | 436篇 |
1996年 | 492篇 |
1995年 | 416篇 |
1994年 | 386篇 |
1993年 | 297篇 |
1992年 | 286篇 |
1991年 | 176篇 |
1990年 | 76篇 |
1989年 | 67篇 |
1988年 | 57篇 |
1987年 | 45篇 |
1986年 | 22篇 |
1985年 | 41篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The centrosymmetric title compound, [Cd2{CH3OC6H4P(OC5H9)S2}4], features an eight‐membered [? Cd? S? P? S? ]2 ring owing to the presence of bridging dithiolate ligands. Tetrahedral coordination geometries for cadmium are completed by chelating ligands. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
42.
Yonggang Shangguan Li Zhao Liyang Tao Qiang Zheng 《Journal of Polymer Science.Polymer Physics》2007,45(13):1704-1712
The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007 相似文献
43.
高压下某些导电高分子色散关系的研究 总被引:1,自引:0,他引:1
利用晶格动力学方法,研究在高压下几种导电高分子具有不同晶格链时的色散关系及其曲线的变化.链间耦合作用的减弱使横波与纵波的ω差值相应增大,且在BZ边界处拉开一个间隙,这是维度作用的结果. 相似文献
44.
H. Sato A. Bensalah N. Solovieva A. Beitlerova A. Vedda M. Martini M. Nikl T. Fukuda 《Radiation measurements》2004,38(4-6):463-466
Two-inch sized KMgF3,BaLiF3 and LiCaAlF6 (LiCAF) single crystals were grown by the Czochralski method under a CF4 atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the ultra-violet and visible spectral regions. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials. It is found that the amplitude of the F-absorption band is suppressed more than a factor of 3 by Mg-doping. For Mg-doped crystals, the optimum doping concentration is about 0.2 mol% of Mg2+. 相似文献
45.
A one‐dimensional zinc(II) coordination polymer has been constructed from zinc(II), 4,4′‐biphenyldicarboxylate and pyridine in which each zinc(II) atom is coordinated by two pyridine ligands and two monodentate 4,4′‐biphenyldicarboxylate ligands that define a distorted tetrahedral geometry. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
46.
47.
Xuming Xie 《Journal of Differential Equations》2004,197(2):349-426
This paper concerns the existence of solutions to a steady needle crystal growth problem in a one-sided model. We rigorously prove that for small nonzero anisotropy γ, analytic symmetric needle crystal solutions exist in the limit of surface tension ε2 if only if the stokes constant S for a relatively simple nonlinear differential equation is zero. This Stokes constant S depends on the parameter β=29/7γε−8/7 and earlier numerical calculations by a number of investigators have shown this to be zero for a discrete set of values of β. It is also proven that for γ=0, there can be no symmetric needle crystal solution in the considered space.The methodology consists of two steps. First, the original problem is reduced to a weak half-strip problem for any γ in a compact set of [0,1) by relaxation of the symmetry condition. The weak problem is shown to have a unique solution in the function space considered for any γ∈[0,γm] for some γm>0. When a symmetry is invoked, the weak problem is shown equivalent to the original needle crystal problem. Next, by considering the behavior of the solution in neighborhood of an appropriate complex turning point for γ∈(0,γm], we extract an exponentially small term in ε as ε→0+ that generally violates the symmetric condition. We prove that the symmetry condition is satisfied for small ε when the parameter β is constrained appropriately. 相似文献
48.
Image potential resonances on the Sn/Ge(1 1 1) α-phase are investigated by two closely related methods: specular electron reflection and so-called selective electron scattering. Electrons from image resonances are detected on this surface at 120 and 300 K, i.e. below and above the phase transition at about 200 K. The dispersion of the image resonances reveals at these two temperatures equivalent effective electron masses, which are characteristic for this type of electronic surface states. The results of the two methods are consistent according to the similarity of the scattering processes. Changes in the loss peak intensity with the annealing temperature are assigned to the surface quality and are reflected by characteristic photoemission intensities. 相似文献
49.
50.
Vladimir B. Arion Alexey A. Nazarov Christian G. Hartinger Gerald Giester Bernhard K. Keppler 《应用有机金属化学》2003,17(9):723-724
For the unsymmetrical title compound, 1‐bromo‐1′‐[(2S)‐N‐(1‐hydroxy‐3‐methylbutane‐2‐yl)]‐ferroceneamide, two independent molecules were found in the asymmetric unit. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献