全文获取类型
收费全文 | 1078篇 |
免费 | 40篇 |
国内免费 | 1篇 |
专业分类
化学 | 894篇 |
晶体学 | 3篇 |
力学 | 10篇 |
综合类 | 1篇 |
数学 | 72篇 |
物理学 | 139篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 14篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 18篇 |
2017年 | 9篇 |
2016年 | 22篇 |
2015年 | 33篇 |
2014年 | 19篇 |
2013年 | 53篇 |
2012年 | 82篇 |
2011年 | 92篇 |
2010年 | 36篇 |
2009年 | 41篇 |
2008年 | 63篇 |
2007年 | 86篇 |
2006年 | 62篇 |
2005年 | 59篇 |
2004年 | 52篇 |
2003年 | 55篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 17篇 |
1996年 | 5篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1969年 | 3篇 |
1930年 | 3篇 |
排序方式: 共有1119条查询结果,搜索用时 15 毫秒
31.
Yang J Gitlin I Krishnamurthy VM Vazquez JA Costello CE Whitesides GM 《Journal of the American Chemical Society》2003,125(41):12392-12393
Proteins are functional biopolymers; viewed as molecules, they are also monodisperse polyamides with chemically reactive side chains. This paper describes the use of proteins as starting materials for the synthesis of monodisperse polymers with nonbiological functionalities attached to the side chains. It demonstrates the complete derivatization of amine groups (lysine side chains and N-termini) on three different proteins by addition of activated carboxylate reagents in aqueous solutions containing sodium dedecyl sulfate (SDS), under denaturing conditions. Several different acylating reagents were used to generate derivatized proteins; the resulting compounds constitute a new class of monodisperse, semisynthetic polymers, having the potential for wide variation in the structure of the backbone and of the side chains. Modification of lysozyme on a gram scale demonstrated that the method can generate useful quantities of material. 相似文献
32.
Corinna Kerst Rabah Boukherroub William J. Leigh 《Journal of photochemistry and photobiology. A, Chemistry》1997,110(3):215-246
The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λmax 255 nm. Characteristic rapid quenching is observed for the silene with methanol (kMcOH = (4.9 ± 0.2) × 109 M−1 s−1), tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1 s−1) and oxygen (kO2 = (2.0 ± 0.5) × 108 M−1 s−1). The Arrhenius activation parameters for the reaction with methanol have been determined to be Ea = −2.6 ± 0.6 kcal mol−1 and log A = 7.7 ± 0.3. 相似文献
33.
The river Elbe has been one of the most contaminated rivers with regard to mercury for many years. In 1991 a length-profile has been measured for mercury and methylmercury (CH3Hg+) from Obristvi, Czech Republic, to the German bight. Total mercury has been measured by cold vapor atomic absorption spectrometry (CVAAS). The organo mercury compounds have been separated by high performance liquid chromatography (HPLC) connected on-line to an atomic fluorescence spectrometer (AFS) by a continuous flow-system. Total mercury up to 120 mg Hg+/kg and CH3Hg+ concentrations up to 130 μg CH3 Hg+/kg could be detected in special sites. The formation of CH3Hg+ in sediments can be caused besides the methylation of mercury, by sulphate reducing or methanogenic bacteria and transmethylation reactions with organometals. Atmospheric mercury concentrations have been measured at three different European sites. Samples have been collected on goldcoated glass balls or on quartz wool, respectively. After thermal desorption mercury has been determined using the two step amalgamation technique with AFS detection. Compared to natural background concentrations of total gaseous mercury (TGM), slightly increased levels could be detected at a rural site in Germany. This increase can probably be explained by long-range transport processes. Within the vicinity of a inactivated mercury production plant high concentrations of up to 13.5 ng/m3 particle associated mercury (Hgpart) have been detected. Consequently, dry deposition of mercury in the particulate form can intensify the total deposition flux close to Hg-emitting sources. 相似文献
34.
Chung‐Cheng Chang Kuo‐Ching Yang Jeng‐Gong Guo Leigh‐May Huang Li‐Chyung Wang Gene‐Hsiang Lee Shie‐Ming Peng 《中国化学会会志》2003,50(5):965-971
The insertion reaction of CS2 with Mg(NR2)2 (R= Et, iPr), MgR′2 (R′= Et, Ph) and R″MgBr (R″= iPr, Ph) respectively lead solid products, Mg(S2CNR2)2(THF)n ( 1 : R= Et, n=2; 2 : R= iPr, n=1), Mg(S2C′R)2(THF)2 ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S2C″R) (THF)3 ( 5 : ″R= iPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with 1H, 13C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography. 相似文献
35.
Mendoza SM Whelan CM Jalkanen JP Zerbetto F Gatti FG Kay ER Leigh DA Lubomska M Rudolf P 《The Journal of chemical physics》2005,123(24):244708
Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface. 相似文献
36.
37.
38.
39.
40.