全文获取类型
收费全文 | 594篇 |
免费 | 36篇 |
国内免费 | 1篇 |
专业分类
化学 | 414篇 |
晶体学 | 4篇 |
力学 | 34篇 |
数学 | 72篇 |
物理学 | 107篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 11篇 |
2013年 | 30篇 |
2012年 | 25篇 |
2011年 | 45篇 |
2010年 | 18篇 |
2009年 | 15篇 |
2008年 | 35篇 |
2007年 | 36篇 |
2006年 | 34篇 |
2005年 | 35篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1979年 | 3篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1931年 | 2篇 |
1917年 | 1篇 |
排序方式: 共有631条查询结果,搜索用时 15 毫秒
41.
This paper describes a new technique--microscale steady-state kinetic analysis (microSKA)--that enables the rapid and parallel analysis of enzyme kinetics. Rather than physically defining a microscopic reactor through microfabrication, we show how the relative rates of reaction and transport in a macroscopic flow chamber, where the enzyme is immobilized on one wall of the chamber, results in the confinement of an enzyme-catalyzed reaction to a microscopic reactor volume adjacent to this wall. This volume has linear dimensions that are orders of magnitude smaller than the physical dimensions of the system (i.e., micrometer vs millimeter). Conversion within this volume is monitored at steady state as a function of position, rather than time. In this way, limitations due to reactor dead time and mixing are avoided. We use microSKA to determine kinetic parameters for the alkaline phosphatase-catalyzed de-phosphorylation of nonfluorescent methylumbelliferyl phosphate (MUP) to fluorescent 7-hydroxy-4-methylcoumarin (HMC) at two different values of pH. Kinetic parameters measured with microSKA are in good agreement with values obtained using conventional methods, if one takes into account effects of immobilization on enzyme activity. This technique provides a rapid and simple method for determining enzyme kinetics using small amounts of sample material and may be useful for applications in proteomics, drug discovery, biocatalyst development, and clinical diagnostics. 相似文献
42.
Ordered mesoporous organic-inorganic hybrid materials containing microporous functional calix[8]arene amides have been synthesized and characterized for the first time, and are shown to be effective in removal of trace humic acid contaminant from water. 相似文献
43.
Cosper NJ Bienvenue DL Shokes JE Gilner DM Tsukamoto T Scott RA Holz RC 《Journal of the American Chemical Society》2003,125(48):14654-14655
The Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra, of the dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE) from Haemophilus influenzae have been recorded in the presence of one or two equivalents of Zn(II) (i.e. [Zn_(DapE)] and [ZnZn(DapE)]). The Fourier transforms of the Zn EXAFS are dominated by a peak at ca. 2.0 A, which can be fit for both [Zn_(DapE)] and [ZnZn(DapE)], assuming ca. 5 (N,O) scatterers at 1.96 and 1.98 A, respectively. A second-shell feature at ca. 3.34 A appears in the [ZnZn(DapE)] EXAFS spectrum but is significantly diminished in [Zn_(DapE)]. These data show that DapE contains a dinuclear Zn(II) active site. Since no X-ray crystallographic data are available for any DapE enzyme, these data provide the first glimpse at the active site of DapE enzymes. In addition, the EXAFS data for DapE incubated with two competitive inhibitors, 2-carboxyethylphosphonic acid and 5-mercaptopentanoic acid, are also presented. 相似文献
44.
Nathaniel Cain Alexander Haywood George Roberts Douglas Kiserow Ruben Carbonell 《Journal of Polymer Science.Polymer Physics》2011,49(15):1093-1100
The influence of dissolved propane (up to 31.2 wt %) on the phase equilibria of 5 wt % polystyrene (PS) dissolved in 66/34 wt % trans/cis‐decahydronaphthalene (DHN) was measured over the temperature range of 323–423 K. A suitable temperature, pressure, and propane composition operating space was defined to measure intrinsic viscosities of a single fluid phase. Intrinsic viscosities of PS in cosolvent mixtures of propane and trans/cis‐DHN were measured between 323 and 423 K and between 70 and 208 bar. The addition of propane to the isomeric mixture of DHN resulted in a decreased solvent quality for PS, causing a contraction of the PS coil. The most dramatic decrease in solvent quality with the addition of propane occurred at 323 K and 70 bar with approximately a 36% reduction in the viscometric radius with the addition of 45 mol % propane to DHN. At 423 K, the solvent quality was less sensitive to the addition of propane and only a 13% reduction in the viscometric radius was observed at 70 bar and 45 mol % propane in DHN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
45.
46.
We introduce a model motivated by studies of Bose-Einstein condensates (BECs) trapped in double-well potentials. We assume that a mixture of two hyperfine states of the same atomic species is loaded in such a trap. The analysis is focused on symmetry-breaking bifurcations in the system, starting at the linear limit and gradually increasing the nonlinearity. Depending on values of the chemical potentials of the two species, we find numerous states, as well as symmetry-breaking bifurcations, in addition to those known in the single-component setting. These branches, which include all relevant stationary solutions of the problem, are predicted analytically by means of a two-mode approximation, and confirmed numerically. For unstable branches, outcomes of the instability development are explored in direct simulations. 相似文献
47.
48.
Leibfarth FA Schneider Y Lynd NA Schultz A Moon B Kramer EJ Bazan GC Hawker CJ 《Journal of the American Chemical Society》2010,132(42):14706-14709
The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization. 相似文献
49.
50.
Nathaniel T. Rebeck Yifan Li Daniel M. Knauss 《Journal of polymer science. Part A, Polymer chemistry》2013,51(24):1770-1778
Poly(phenylene oxide) block and random copolymers are synthesized by oxidative polymerization of 2,6-dimethylphenol and 2,6-diphenylphenol for potential alkaline exchange membrane application. The copolymers are functionalized on the methyl substituted repeat units through a two-step process to produce pendent quaternary ammonium cationic groups. The amount of quaternary ammonium cations and the ion exchange capacity are quantified through titration measurements. Ionic conductivity of the copolymer membranes is measured by electrochemical impedance spectroscopy. Block copolymers show increased bromide conductivity at higher ion exchange capacities compared with the random copolymer analogs. The bromide conductivity for a block copolymer film with an ion exchange capacity of 1.27 mequiv/g reaches 26 mS/cm at 90 °C and 95% relative humidity. The hydroxide conductivity for the same film was measured to be 84 mS/cm at 80 °C and 95% relative humidity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1770–1778, 2013 相似文献