全文获取类型
收费全文 | 522篇 |
免费 | 27篇 |
专业分类
化学 | 366篇 |
晶体学 | 8篇 |
力学 | 9篇 |
数学 | 59篇 |
物理学 | 107篇 |
出版年
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 28篇 |
2020年 | 18篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 13篇 |
2013年 | 30篇 |
2012年 | 50篇 |
2011年 | 45篇 |
2010年 | 17篇 |
2009年 | 24篇 |
2008年 | 26篇 |
2007年 | 33篇 |
2006年 | 30篇 |
2005年 | 29篇 |
2004年 | 20篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 10篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有549条查询结果,搜索用时 265 毫秒
11.
Lara BianchiCarlo Dell'Erba Massimo MaccagnoAngelo Mugnoli Marino NoviGiovanni Petrillo Fernando SancassanCinzia Tavani 《Tetrahedron》2003,59(51):10195-10201
1-(Methyl-p-tolyl-amino)-3-phenoxy-2-azetidinones 4-COX and 4-R substituted (COX: X=Me, Et, Ph, NMe2, NEt2, OBut; R=Me, Et, Ph) were smoothly prepared from the corresponding α-(methyl-p-tolyl)hydrazonylated ketones, amides and esters via [2+2] cycloaddition with phenoxyketene. The reaction was generally high-yielding and diastereoselective, leading to β-lactams with a cis relationship between the PhO and the COX moieties, except for R=Ph, where an opposite stereoselectivity was instead observed. The azetidinones represent interesting intermediates which couple protection at N(1) and functionalization at position 4 of the ring. Deprotection of N(1) can be easily attained by oxidative N-N cleavage with magnesium monoperoxyphthalate. 相似文献
12.
Ilia A. Guzei Frankline K. Keter Lara C. Spencer James Darkwa 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(8):o481-o483
Five distinct strong hydrogen‐bonding interactions of four kinds (N—H...Cl, N—H...O, O—H...N, and O—H...Cl) connect molecules of the title compound, C9H18N3+·Cl−·H2O, in the crystal structure into corrugated sheets stacked along the a axis. The intermolecular interactions are efficiently described in terms of the first‐ through fifth‐level graph sets. A two‐dimensional constructor graph helps visualize the supramolecular assembly. 相似文献
13.
14.
Electrical Impedance Spectroscopy (EIS) was used to study the electrical properties of the (1???x)CsHSeO4–xKHSeO4 binary system with concentrations x?=?0.0 and 0.1. The results show a higher proton-conduction phase above 80°C for both concentrations, however, while DC conductivity of CsHSeO4 shows a gradual change to higher values in the 80–118°C temperature range, the 0.9CsHSeO4–0.1KHSeO4 concentration reveals an abrupt change at about 80°C to an intermediate temperature phase. The observed behavior for the doped sample was modeled using a trial free-energy density, based on the concentration of mobile ions, that takes into account the formation of defects, configurational and phonon entropies, and defect-defect interactions. By minimising the free-energy density one obtains two roots for the carrier concentration at a given temperature, which corresponds to a stable and metastable configuration. It is possible to characterise the phase behavior of the system by means of temperature and two model parameters, which depend on the crystalline properties of the system, but not on temperature. One can successfully explain the conductivity behavior of the system by changing the model parameters if it is assumed that its variations are due to the carriers density. 相似文献
15.
A CdSe-ZnS quantum dot (QD) has been surface functionalised by a place exchange reaction with p-mercaptomethyl benzoate synthesized by a three-step procedure. The resulting lumophore-spacer-receptor QD-conjugate was characterized by IR, UV-visible and fluorescence spectroscopy. The emission profile of the QD reveals a narrow emission peak centred at 542 nm. Addition of hydroxide to the solution containing the QD-conjugate results in quenching of the original fluorescence, which is attributed to a photoinduced electron transfer reaction from the electron-rich benzoate moiety to the QD valence band. This is the first reported example of fluorescent quenching of a CdSe-ZnS QD luminescence by an aryl carboxylate moiety. 相似文献
16.
17.
Martín A. Iglesias Arteaga Roxana Pérez Gil Vivian Leliebre Lara Carlos S. Pérez Martinez Francisco Coll Manchado Arístides Rosado Pérez 《合成通讯》2013,43(8):1381-1386
The synthesis of a plant growth promoter furostanol which bears the characteristic functionality of teasterone on rings A and B is described. 相似文献
18.
Due to the widespread use of acoustic arrays, optimisation techniques for array design, focused on improving array performance, have been widely published. This paper exploits the statistical relation between different measures of sidelobe levels and the spacing of elements in random linear arrays made up of a small number of sensors. This paper defines the methodology to obtain maximum probability functions, associating array geometry and performance. These maximum probability functions allow a pre-selection of those array geometries that are more likely to be associated to specified sidelobe level values. This pre-selection results in a significantly reduced computational burden. 相似文献
19.