全文获取类型
收费全文 | 1445篇 |
免费 | 23篇 |
国内免费 | 9篇 |
专业分类
化学 | 844篇 |
晶体学 | 5篇 |
力学 | 35篇 |
数学 | 248篇 |
物理学 | 345篇 |
出版年
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 18篇 |
2017年 | 12篇 |
2016年 | 19篇 |
2015年 | 17篇 |
2014年 | 19篇 |
2013年 | 63篇 |
2012年 | 54篇 |
2011年 | 81篇 |
2010年 | 30篇 |
2009年 | 27篇 |
2008年 | 66篇 |
2007年 | 57篇 |
2006年 | 70篇 |
2005年 | 68篇 |
2004年 | 48篇 |
2003年 | 69篇 |
2002年 | 42篇 |
2001年 | 33篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 17篇 |
1997年 | 11篇 |
1996年 | 23篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 15篇 |
1986年 | 21篇 |
1985年 | 30篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 28篇 |
1975年 | 25篇 |
1974年 | 23篇 |
1973年 | 18篇 |
1970年 | 10篇 |
1968年 | 9篇 |
排序方式: 共有1477条查询结果,搜索用时 0 毫秒
41.
42.
43.
44.
An infrared spectral investigation of a number of pyrimidine and pyrimidone hexachloroantimonates is reported. Typical aromatic absorption bands found in pyrimidinium salts were absent in the pyrimidone cations. 2-And 4-Pyrimidone hexachloroantimonates, as well as their N-methyl- and N,N'-dimethyl derivatives, exhibit intense carbonyl absorption bands between 1720–1729 cm?1 (solid state) which corroborates N-protonation of pyrimidones. 相似文献
45.
The SER spectrum is reported for N-methylpyridinium iodide, an organic cation with no unshared electron pair available for interaction with the electrode. Both Raman- and infrared-active bands are observed with small frequency shifts. No SERS is observed for N-methylpyridinium chloride until trace amounts of iodide are added to the solution. 相似文献
46.
Following the newly-discovered UV absorption spectrum of Br2Si, its reactions with oxygen and nitric oxide in the gas phase have been quantitatively investigated using the flash photolysis-kinetic
absorption spectroscopy technique. The room temperature bimolecular rate constants are:
相似文献
47.
Given a reaction mechanism we show how a symbolic computation approach can be used to develop the kinetic equations by identifying the reaction scheme with an equivalent matrix. Our method is also applicable in cases where the stoichiometric matrix approach fails. The specific algorithm that is written applies to schemes where individual reactions are at most ternary, but the way to generalize the procedure is also discussed. By using symbolic computing it is possible to determine general properties of the system. We demonstrate this by showing how to use the matrix to determine the system's conservation laws, which in turn can be used to reduce the number of equations in the system. As another application it is shown how to determine some of the species which have a zero equilibrium state. To illustrate the procedure, example reaction schemes are investigated. 相似文献
48.
The rheological properties of a nanosized alumina powder coated with fatty acid steric stabilizers of varying chain length were investigated. The storage and loss moduli of the complex modulus were measured to characterize the behavior of the flocculated systems. As chain length increased, there was a transition from an elastic response to fluid behavior. However, the fluid system developed elastic characteristics at relatively low volume fractions of 22%. The length of the steric barrier required to produce the fluid dispersion was estimated to be approximately 2 nm and correlates with attractive interactions on the order of the system thermal energy. Moreover, in the flocculated systems, the storage modulus was found to be higher than reported previously in the literature. These higher values were related to the additional attractive forces due to van der Waals attractions between the hydrocarbon tails of the adsorbed fatty acid layers. 相似文献
49.
Interpolation methods such as the nudged elastic band and string methods are widely used for calculating minimum energy pathways and transition states for chemical reactions. Both methods require an initial guess for the reaction pathway. A poorly chosen initial guess can cause slow convergence, convergence to an incorrect pathway, or even failed electronic structure force calculations along the guessed pathway. This paper presents a growing string method that can find minimum energy pathways and transition states without the requirement of an initial guess for the pathway. The growing string begins as two string fragments, one associated with the reactants and the other with the products. Each string fragment is grown separately until the fragments converge. Once the two fragments join, the full string moves toward the minimum energy pathway according to the algorithm for the string method. This paper compares the growing string method to the string method and to the nudged elastic band method using the alanine dipeptide rearrangement as an example. In this example, for which the linearly interpolated guess is far from the minimum energy pathway, the growing string method finds the saddle point with significantly fewer electronic structure force calculations than the string method or the nudged elastic band method. 相似文献
50.
The IR and resonance Raman spectra of the nickel(II) complexes of dibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TAA) and 5,7,12,14-tetramethyldibenzo[b,i][1,4,8,11]tetraaza[14]annulene (TMTAA) have been measured and compared with ab initio calculations of the vibrational wavenumbers at the B3-LYP level using the LanL2DZ basis set. An excellent fit is found between the experimental and calculated data, enabling precise vibrational assignments to be made. Surface-enhanced resonance Raman spectra were obtained following adsorption on Ag electrodes, with potentials in the range -0.1 to -1.1 V vs Ag/AgCl. There is evidence for contributions from both the electromagnetic and charge transfer (CT) surface enhancement mechanisms. The data indicate that variations in band intensities with electrode potential can be interpreted in terms of the CT mechanism. 相似文献