全文获取类型
收费全文 | 508篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
化学 | 248篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 153篇 |
物理学 | 110篇 |
出版年
2022年 | 4篇 |
2021年 | 20篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 11篇 |
2013年 | 30篇 |
2012年 | 28篇 |
2011年 | 24篇 |
2010年 | 26篇 |
2009年 | 16篇 |
2008年 | 14篇 |
2007年 | 19篇 |
2006年 | 9篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 5篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1936年 | 8篇 |
1935年 | 9篇 |
1934年 | 4篇 |
1930年 | 6篇 |
1929年 | 5篇 |
1928年 | 5篇 |
1926年 | 2篇 |
1924年 | 4篇 |
排序方式: 共有525条查询结果,搜索用时 15 毫秒
111.
The solid-phase syntheses of enkephalin and somatostatin analogues with C-terminal OH functions instead of the normal carboxylates are described. The OH function of the N-terminal amino alcohol was acylated with succinic acid and esterified to the solid support. Normal Boc-TFA solid-phase strategy can be applied to build up and cleave these peptides. The succinic ‘handle’ can be removed by mild basic hydrolysis after cleavage. 相似文献
112.
113.
We present a sketch of the construction of the functional measure for theSU(2) quantum chromodynamics with one generation of fermions in two-dimensional space-time. The method is based on a detailed analysis of Wilson loops. 相似文献
114.
Witold Kuran Zbigniew Florjaczyk 《Journal of polymer science. Part A, Polymer chemistry》1978,16(5):861-866
The catalytic activity of various organometallic compounds of the Lewis acid type RmMXn(M = Zn, Cd, B, Al; R = CH3,C2H5, i-C4H9, C6H5CH2, C6H5C2H4; X = Cl, OCH3) in the alternating copolymerization of acrylonitrile with butadiene in bulk and in toluene solution has been studied. The activity of the catalyst was found to depend on its acidity, the strength of its M? R bond, and on the type of substituent R. The results obtained have been discussed in terms of the copolymerizability of the acrylonitrile complexed by RmMXn and in terms of the effect of the RmMXn structure on the initiation rate of the copolymerization. 相似文献
115.
116.
A number of poly(N-isopropylacrylamide) (polyNIPAM) microgels were prepared with dimethacrylate cross-linking agents of various lengths, ether and ester groups in the backbone, and pendant vinylidine functionality. These materials were characterized by examining their morphological patterns using optical and scanning electron microscopy. When ethylene glycol dimethacrylate (EGDMA) was used as a cross-linking agent, microspheres of approximately 1 μm in diameter were obtained. Diethylene glycol dimethacrylate (DEGDMA) cross-linking resulted in relatively large spherical structures (1–5 μm) as well as spherical nanostructures (200 nm). Using triethylene glycol dimethacrylate (TEGDMA) resulted in spheres with diameters between 1 μm and 3 μm. The hydrodynamic particle diameter decreased with the increasing chain length of the dimethacrylate cross-linking agents. The turbidity increased with the temperature of transition points occurring at approximately 31–32°C confirming the thermosensitivity of the obtained polymeric structures. 相似文献
117.
Victor H. Orozco Witold Brostow Wunpen Chonkaew Betty L. López 《Macromolecular Symposia》2009,277(1):69-80
Poly(lactic acid) (PLA) and starch copolymers are obtained by reactive blending - varying the starch compositions from 0 to 60%. PLA is functionalized with maleic anhydride (MA), obtaining PLA-g-MA copolymers using dicumyl peroxide as an initiator of grafting in order to improve the compatibility and interfacial adhesion between the constituents. PLA + starch blends without a compatibilizer do not have sufficient interfacial adhesion. Decomposition temperature of PLA is not affected by grafting. Glass transition temperatures and dynamic mechanical properties are affected since MA has a plasticizing effect. Along with an increasing starch content friction decreases while wear loss volume in pin-on-disk tribometry has a minimum at nominal 15% wt. starch but increases at higher starch concentrations. The residual depth in scratching and sliding wear testing has a maximum at 15% starch; there is a minimum of storage modulus E′ determined in dynamic mechanical testing at the same concentration. Microhardness results also reflect the plasticization by MA. 相似文献
118.
Florinel‐Gabriel Bănică Dariusz Guziejewski Slawomira Skrzypek Witold Ciesielski Dorota Kaźmierczak 《Electroanalysis》2009,21(15):1711-1718
In a 0.02 M borax solution (pH 8.5), basic amino acids (arginine, lysine, and ornithine) react with Ni2+ to form a mono‐ligand complex that is reduced at a mercury electrode at about ?0.85 V vs. Ag|AgCl|KCl (3 M). At a long time scale (staircase voltammetry; scan rate<50 mV s?1), the complex reduction is a catalytic (EC′) process, the rate‐determining step being the regeneration of the reducible species by the reaction of the amino acid with free Ni2+. At a short time scale (differential pulse voltammetry or higher scan rate staircase voltammetry), the reaction rate is controlled by the diffusion of the complex. Although the same kind of complexation occurs with either basic amino acids or glycine, the last one does not induce a similar process. The peculiar effect of basic amino acids is due to the side chain that causes the ligand molecule to adopt a favorable orientation at the electrode surface. The differential pulse voltammetry peak current is proportional to the total amino acid concentration over the concentration range from 2 to 100 μM. Hence a voltammetric method for arginine determination in nutritional supplements was developed and validated using HPLC as reference method. 相似文献
119.
Dr. Witold M. Bloch Prof. Neil R. Champness Prof. Christian J. Doonan 《Angewandte Chemie (International ed. in English)》2015,54(44):12860-12867
Open‐framework materials, such as metal–organic frameworks (MOFs) and coordination polymers have been widely investigated for their gas adsorption and separation properties. However, recent studies have demonstrated that their highly crystalline structures can be used to periodically organize guest molecules and non‐structural metal compounds either within their pore voids or by anchoring to their framework architecture. Accordingly, the open framework can act as a matrix for isolating and elucidating the structures of these moieties by X‐ray diffraction. This concept has broad scope for development as an analytical tool where obtaining single crystals of a target molecule presents a significant challenge and it additionally offers potential for obtaining insights into chemically reactive species that can be stabilized within the pore network. However, the technique does have limitations and as yet a general experimental method has not been realized. Herein we focus on recent examples in which framework materials have been utilized as a scaffold for ordering molecules for analysis by diffraction methods and canvass areas for future exploration. 相似文献
120.
Competition between Nucleophilic Substitution of Halogen (SNAr) versus Substitution of Hydrogen (SNArH)—A Mass Spectrometry and Computational Study 下载免费PDF全文
Kacper Błaziak Prof. Mieczysław Mąkosza Prof. Witold Danikiewicz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(16):6048-6051
The mechanism of intramolecular gas‐phase reactions of N‐(2‐X‐5‐nitrophenyl)‐N‐methylacetamide carbanions (X=H, F, Cl) has been studied using negative ion electrospray mass spectrometry ((?)ESI‐MS) technique and modelled computationally. It was proven that all three anions form cyclic σH adducts, which undergo elimination of water. In the case of X=F, formation of the σF adduct, leading to SNAr reaction, was a competing process. This is the first proof that also in the gas phase formation of σH adduct proceeds faster than σX adduct and only when X=F, rates of these two processes are comparable. The experimental results are in full agreement with quantum chemical calculations. 相似文献