全文获取类型
收费全文 | 3226篇 |
免费 | 116篇 |
国内免费 | 40篇 |
专业分类
化学 | 2047篇 |
晶体学 | 23篇 |
力学 | 79篇 |
综合类 | 3篇 |
数学 | 638篇 |
物理学 | 592篇 |
出版年
2023年 | 20篇 |
2022年 | 99篇 |
2021年 | 119篇 |
2020年 | 88篇 |
2019年 | 113篇 |
2018年 | 110篇 |
2017年 | 96篇 |
2016年 | 149篇 |
2015年 | 115篇 |
2014年 | 135篇 |
2013年 | 235篇 |
2012年 | 248篇 |
2011年 | 244篇 |
2010年 | 148篇 |
2009年 | 114篇 |
2008年 | 174篇 |
2007年 | 145篇 |
2006年 | 138篇 |
2005年 | 133篇 |
2004年 | 92篇 |
2003年 | 67篇 |
2002年 | 69篇 |
2001年 | 37篇 |
2000年 | 43篇 |
1999年 | 37篇 |
1998年 | 32篇 |
1997年 | 25篇 |
1996年 | 31篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 6篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 9篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有3382条查询结果,搜索用时 0 毫秒
1.
Nguyen Minh Chuong Bui Kien Cuong 《Proceedings of the American Mathematical Society》2004,132(12):3589-3597
A class of Cauchy problems for interesting complicated periodic pseudodifferential equations is considered. By the Galerkin-wavelet method and with weak solutions one can find sufficient conditions to establish convergence estimates of weak Galerkin-wavelet solutions to a Cauchy problem for this class of equations.
2.
通过把全息透镜嵌入挡风玻璃,实现全息透镜在车辆中的两种应用,即将具有颜色选择性的窄带全息透镜用于车辆的平视显示,将具有角度选择性的宽带全息透镜用于车辆的阳光防护。 相似文献
3.
Thi Thi Nge Naruhito Hori Akio Takemura Hirokuni Ono Tsunehisa Kimura 《Journal of Polymer Science.Polymer Physics》2003,41(7):711-714
A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003 相似文献
4.
5.
M. Jonathan Fray Paul Allen Paul R. Bradley Clare E. Challenger Michael Closier Tim J. Evans Mark L. Lewis John P. Mathias Carly L. Nichols Yvonne M. Po-Ba Hayley Snow Mark H. Stefaniak Hannah V. Vuong 《Tetrahedron》2006,62(29):6869-6875
The synthesis of ten substituted aminomethylene tetrahydro-isoquinolines is described, proceeding in eight steps from 5-hydroxyisoquinoline via reductive amination of N-Boc tetrahydro-isoquinoline 5-carboxaldehyde. Likewise, reductive amination was used to prepare four substituted dihydro-isoindoles from the corresponding aldehyde. The dihydro-isoindole ring system was conveniently accessed via a 2+2+2 cycloaddition reaction. 相似文献
6.
Tran Quang Minh Léon Christiaens Pierre Grandclaudon Alain Lablache-Combier 《Tetrahedron》1977,33(17):2225-2229
Photoirradiated in presence of acetophenone, benzo[b]selenophene and its 3-methyl derivative add to dimethyl acetylenedicarboxylate. In each ease, the primary reaction product is unstable and has not been isolated. Photoexeited in its triplet state (the energy of which is in the neighbourhood of 69 ) benzo[b]selenophene and its 2- and 3-methyl, 2,3 dimethyl, 3 acetoxy and 2-methyl-3-acetoxy derivatives add to 1,2 dichloroethylene leading to cyclobutanes. Neither cyclo-addition occurs in absence of photosensitiser. Single-crystal X-ray analysis gave the structures of the two adducts of 3-acetoxybenzo[b]selenophene with trans-1,2-dichloroethylene. In both compounds the chlorine atoms are trans. 相似文献
7.
The surface-enhanced Raman scatterings of dimethyl sulfide, diethyl sulfide and dimethyl disulfide have been investigated in silver sol. The dimethyl disulfide molecule decomposes on silver to the corresponding mercaptide implying facile cleavage of its S---S bond. The C---S bond in dialkyl monosulfide appears not to cleave on silver. For diethyl sulfide, the C2 conformation seems to be favorable on silver than other conformations. 相似文献
8.
Pham-Tran NN Bouchoux G Delaere D Nguyen MT 《The journal of physical chemistry. A》2005,109(12):2957-2963
We have investigated the basicity of phosphinine (C5H5P, phosphabenzene) in reevaluating its proton affinity (PA) and gas-phase basicity (GB) and the pK(a) value of its protonated form. As a necessary step, we have first determined its gas-phase proton affinity. Using both mass spectrometric and quantum chemical methods, we have obtained the values PA(C5H5P) = 195.8 +/- 1.0 kcal mol(-1) and GB(298)(C5H5P) = 188.1 +/- 1.0 kcal mol(-1), in good agreement with previous results. We then derived a value of pK(a)(C5H6P+) = -16.1 +/- 1.0 in aqueous solution using three different approaches: the latter markedly differs from the currently available value of -10. The reason for such a discrepancy in the pK(a) of protonated phosphinine in solution is discussed. In the theoretical determination of PAs, evaluation of the basis set superposition error (BSSE) showed that this effect is quite small, being 0.1-0.2 kcal mol(-1) for phosphinine, when a density functional theory (DFT) method in conjunction with a large basis set were used. 相似文献
9.
10.
Study on oxidation of polymers treated by high LET radiation 总被引:2,自引:0,他引:2
Wang Ruiyu Ha Hongfei Wang Yugang Zhao Weijiang Yan Sha Jin Changwen Wang Guanghui Wu Jilan 《Radiation Physics and Chemistry》1998,52(1-6):251-256
The oxidation of medical silicone rubber and segmented polyether urethane which were bombarded with 11.2 MeV Si+ or F+ at the dose of 5 × 1014 ions/cm2 was studied. In XPS measurements, it was found that the oxygen concentration on the surface of the implanted polymeric membranes had been increasing in three months at least. ESR measurement showed that some free radicals existed in these membranes and their quantities decreased with time. Chemical analysis proved that peroxides were generated in the γ irradiated membranes. The reason for the increasing of oxygen concentration was that free radicals combined with oxygen in the air and produced peroxides on the membrane surface. Moreover, in order to demonstrate the radiation mechanism, low LET (γ rays) radiation of such polymeric membranes was carried out for comparison 相似文献