全文获取类型
收费全文 | 951篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 682篇 |
晶体学 | 3篇 |
力学 | 9篇 |
数学 | 115篇 |
物理学 | 166篇 |
出版年
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 19篇 |
2014年 | 20篇 |
2013年 | 38篇 |
2012年 | 30篇 |
2011年 | 46篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 38篇 |
2007年 | 18篇 |
2006年 | 29篇 |
2005年 | 20篇 |
2004年 | 49篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 27篇 |
2000年 | 28篇 |
1999年 | 15篇 |
1997年 | 7篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 18篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 18篇 |
1976年 | 26篇 |
1975年 | 17篇 |
1974年 | 15篇 |
1973年 | 17篇 |
1972年 | 7篇 |
1971年 | 13篇 |
1970年 | 9篇 |
1968年 | 7篇 |
1943年 | 5篇 |
1939年 | 6篇 |
排序方式: 共有975条查询结果,搜索用时 0 毫秒
11.
SCF calculations utilizing a basis of all s-type Gaussians have been performed to investigate the dimerization of BH3 to B2H6. Localized molecular orbitals and pseudonatural orbitals are calculated. The dimerization energy obtained (11.5 kcal/mole) supports the assumption that the non-Hartree-Fock interactions (electron correlation) play a dominant role (Exp = 40–60 kcal/mole). The energy of the principal type of resonance structure based on the SCF-MO 's of the separated-but-distorted BH3 systems is rigorously calculated and found to be 150 kcal/mole higher in energy than the SCF energy of B2H6. Thus, resonance stabilization (delocalization) is shown to be extremely important to the stability of the “three-center” bonds in B2H6, as has been suspected for many years. 相似文献
12.
Summary A method is described for the determination of nitrated polynuclear aromatic hydrocarbons (nitro-PAHs), in particular 1-nitropyrene, in diesel particulate extracts. The method employs a multidimensional HPLC (column switching) technique with final on-line peak identification by UV-VIS spectral comparison with standards. To achieve exceptional chromatographic selectivity for nitro-PAHs, a new pyrene butyric acid amide phase has been prepared which is capable of forming donor-acceptor complexes with them. With this technique it is possible to confirm the presence of 1-nitropyrene in the range 3–100 ng/mg on filter-collected diesel soot. Its utility was demonstrated with diesel exhaust extracts spiked with varying levels of 1-nitropyrene and proved to be highly selective.Parts of this work have been presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984.Dedicated to Prof. J. F. K. Huber at the occasion of his 60th birthday. 相似文献
13.
14.
15.
16.
17.
18.
A stereoselective ion-pair nonaqueous capillary electrophoresis (NACE) method employing the partial filling technique with N-derivatized amino acids, e.g., (R)- and (S)-3,5-dinitrobenzoyl-leucine (DNB-Leu), as chiral selector for the separation of "pseudoenantiomeric" cinchona alkaloid derivatives and other structurally related basic compounds like the enantiomers of mefloquine is presented. Originating from NACE with cinchona alkaloid derivatives as chiral counterions, this method was developed by application of the reciprocity principle of chiral recognition, which was proven to be valid for stereoselective ion-pair capillary electrophoresis (CE). A variety of basic and amphoteric selectands (SAs) could be well resolved. Thereby, the separation was primarily based on stereoselective ion-pair formation of corresponding SA stereoisomers and mobility differences of free and complexed (ion-paired) SAs. Additionally, in the case of diastereomeric SAs, naturally existing mobility differences between the diastereomers played also a role, but was shown by control experiments with racemic DNB-Leu and without selector (SO) to be of minor contribution to overall separation selectivity. Due to its simplicity, speed, and good reproducibility, the established method can be utilized for fast screening of cationic as well as amphoteric chiral compounds, and therefore is a valuable tool in the development of new chiral selectors and chiral stationary phases. Small sample amounts of the SO (4-5 mg) and only analytical amounts of SAs are needed, and about 20-50 compounds per day can be tested. 相似文献
19.
20.
The localized molecular orbitals for a variety of hydrogen bonded systems are obtained from their INDO and CNDO/2 wavefunctions. The bonding of these systems is qualitatively discussed in light of the localized orbitals. 相似文献