全文获取类型
收费全文 | 392篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 329篇 |
晶体学 | 11篇 |
力学 | 5篇 |
数学 | 17篇 |
物理学 | 54篇 |
出版年
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 34篇 |
2012年 | 22篇 |
2011年 | 19篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 22篇 |
2007年 | 12篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有416条查询结果,搜索用时 15 毫秒
41.
Symbiodinolide is a polyol macrolide isolated from the marine dinoflagellate Symbiodinium sp. in 2007. The C14-C24 fragment of symbiodinolide possessing the 17R/18R/21R absolute configuration, which was obtained as one of the degraded products of symbiodinolide, was synthesized stereoselectively from cis-2-butene-1,4-diol. The detailed comparison of the synthetic product with the degraded product in the spectroscopic data confirmed that the stereostructure of the C14-C24 fragment was 17R, 18R, and 21R. 相似文献
42.
Kenji Kashima Masakazu Kato Jun-ichi Imura Kazuyuki Aihara 《The European physical journal. Special topics》2014,223(12):2493-2501
We propose a novel framework for probabilistic evaluation of interconnectable capacity for wind power generation. This is based on mathematical modeling of load frequency control systems, which captures their nonlinear (saturation and rate limiting) dynamical characteristics, and stochastic uncertainty of wind power output deviation. The method called stochastic linearization is used to analyze resulting power quality. The effectiveness of the proposed method is examined by numerical simulation. 相似文献
43.
H. Hiroyoshi H. Yamauchi Y. Yamaguchi H. Yamamoto Y. Nakagawa M. Sagawa 《Solid State Communications》1985,54(1):41-43
Magnetization measurements have been made on a Sm2Fe14B single crystal in magnetic fields up to 140 kOe. The easy direction of the magnetization lies along [100] in the tetragonal structure P42/mnm. Magnetic anisotropy energies at 290K along [110] and [001] have been estimated to be 5.8×106 and 1.1×108 erg/cm3, respectively, both becoming much larger at lower temperature. No evidence of the spin canting of Nd2Fe14B type is observed even at 4.2K. 相似文献
44.
[reaction: see text] Concise synthesis of defucogilvocarcin M was achieved via the [2 + 2 + 2] approach to beta-phenylnaphthalene structure. 相似文献
45.
Hiroyoshi Mitake 《Applied Mathematics and Optimization》2008,58(3):393-410
We study Hamilton-Jacobi equations in a bounded domain with the state constraint boundary condition. We establish a general
convergence result for viscosity solutions of the Cauchy problem for Hamilton-Jacobi equations with the state constraint boundary
condition to asymptotic solutions as time goes to infinity. 相似文献
46.
Distribution constants of 2-thenoyltrifluoroacetone (Htta) and its Ni(II)and Cu(II) chelates between 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (CnmimTf2N; n = 4, 6, and 8) as ionic liquid (IL) and an aqueous phase were determined. The enol fraction of Htta in ILs was spectrophotometrically measured to calculate the distribution constant of the enol form (KD,HE) of Htta. The KD,HE values in ILs were evaluated by comparing those in various molecular solvents such as alkanes, aromatic hydrocarbons, chlorohydrocarbons, ethers, ketones, and esters previously reported on the basis of the regular solution theory (RST). It was elucidated that the IL solutions of Htta (enol) can be taken as apparently regular solutions as expected in the organic solvents. On the other hand, the effect of ILs on the distribution constant of metal(II) chelates (KD,M) was fairly complicated. The Cu(tta)2-IL solutions behaved like the alkane and aromatic hydrocarbon solutions but the Ni(tta)2-IL (C4mimTf2N) like ether and ketone solutions. In the Ni(II) case, some specific interactions between the Ni(II) chelate and IL was suggested. Finally, the solubility parameters of ILs were calculated using KD,HE by RST and were in good agreement with the literature values obtained by the enthalpy of vaporization. 相似文献
47.
To evaluate the superiority of using a task-specific onium salt (TSOS), a novel TSOS reagent 1-methyl-3-[2-(8-quinolinylaminosulfonyl)ethyl]imidazolium chloride (HmimesqCl) was synthesized, and its performance in extraction of different divalent metal cations was investigated. This TSOS reagent has both a cationic imidazolium unit and an anionic (proton-dissociable) complexation unit for the extraction of metal cations into an ionic liquid. In the use of HmimesqCl, relatively high extraction of metals resulted in comparison with the use of its non-imidazolium analogs, without changing the extraction selectivity. 相似文献
48.
We have fabricated novel nanofibrous fluorinated polyimide membranes on a specially designed collector, which is composed of conductive aluminum plates and glass insulator materials and can be removed from the apparatus, using an electrospinning method. We describe the structure and water flux properties of the nanofibrous fluorinated polyimide membranes. The electrospun nanofibers were deposited across the plates and uniaxially aligned to the collector. In addition, the multi‐layer stacked nanofibrous membranes, consisting of three‐dimensionally ordered nanopores, were produced. The pure water fluxes for the stacked membranes were measured, using a stirred dead‐end filtration cell, and were linearly decreased with an increasing deposition time, indicating that the nanopores formed in the nanofibrous membrane were further narrowed due to the regularly accumulated nanofibers. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
49.
Hiroyuki Okamura Hiroki SakaeKeiji Kidani Naoki HirayamaNoboru Aoyagi Takumi SaitoKojiro Shimojo Hirochika NaganawaHisanori Imura 《Polyhedron》2012,31(1):748-753
The extraction constant and the two-phase stability constant (KD,Mβ3) of tris(2-thenoyltrifluoroacetonato)europium(III) between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]) as an ionic liquid and an aqueous phase were determined by considering the extraction equilibria including anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III). Specific solute-solvent interactions between the neutral Eu(III) chelate and [C4mim][Tf2N] molecules were revealed from the relationships between the distribution constant of the enol form of 2-thenoyltrifluoroacetone (Htta) as a proton chelate and the distribution constant (KD,M) of the neutral Eu(III) chelate because the [C4mim][Tf2N] system gave the high KD,Mβ3 value compared with those in conventional molecular solvents such as benzene and 1,2-dichloroethane. The coordination environment of Eu3+ in the neutral Eu(III) chelate in [C4mim][Tf2N] was investigated by time-resolved laser-induced fluorescence spectroscopy and infrared absorption spectroscopy. Both methods consistently indicated that not only the Eu(III) chelate extracted but also Eu(tta)3(H2O)3 synthesized as a solid crystal were almost completely dehydrated in [C4mim][Tf2N] saturated with water. Consequently, the higher KD,M or extractability of the neutral Eu(III) chelate in the [C4mim][Tf2N] system can be ascribed to the dehydration of the Eu(III) chelate, which is caused by the specific solvation with [C4mim][Tf2N] molecules. 相似文献
50.
Hiroyoshi Yamaki 《Proceedings of the American Mathematical Society》2008,136(2):397-402
We will give an estimation of the order of a group of even order by the order of the centralizer of an involution using the classification of finite simple groups.