全文获取类型
收费全文 | 752篇 |
免费 | 46篇 |
国内免费 | 2篇 |
专业分类
化学 | 626篇 |
晶体学 | 11篇 |
力学 | 4篇 |
数学 | 43篇 |
物理学 | 116篇 |
出版年
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 24篇 |
2015年 | 34篇 |
2014年 | 19篇 |
2013年 | 44篇 |
2012年 | 51篇 |
2011年 | 47篇 |
2010年 | 26篇 |
2009年 | 17篇 |
2008年 | 41篇 |
2007年 | 52篇 |
2006年 | 47篇 |
2005年 | 49篇 |
2004年 | 44篇 |
2003年 | 27篇 |
2002年 | 39篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 4篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有800条查询结果,搜索用时 15 毫秒
91.
92.
93.
Sanz D Claramunt RM Singh SP Kumar V Aggarwal R Elguero J Alkorta I 《Magnetic resonance in chemistry : MRC》2005,43(12):1040-1043
The combined use of 1H NMR spectroscopy with theoretical calculations of chemical shifts (GIAO) and coupling constants (B3LYP/6-311 ++G**) of a 5-hydroxy-5-trifluoromethyl-Delta2-isoxazoline has enabled solving the problem of the assignments of the diastereotopic protons in this compound. This result has been extended to 5-hydroxy-5-trifluoromethyl-Delta2-pyrazolines and the corresponding 5-trichloromethyl derivatives. 相似文献
94.
Electrical measurements are easier and faster than traditional methods for evaluating surface sanitation in the food industry. However, the behavior of sublethally damaged bacteria is different in each method. The electrical method is more sensitive to the presence of disinfectant traces in the samples. These issues lead to low correlations between both methods (r2 < 0.7). The use of smaller sample volumes in electrical measurements, together with the addition of a blend of neutralizers to the sample and the subsequent removal by filtration, provide r2 values > 0.9. The developed protocol shows an excellent correlation with traditional methods and facilitates the adaptation of the electrical method to routine monitoring of surface sanitation. It allows for a reduction in holding times and thereby provides the necessary time to make decisions. 相似文献
95.
96.
Purple arsenomethane crystallises in the orthorhombic system, space group Ima2 (C) with a = 5.81, b = 5.79, c = 13.64 Å and 8 units of CH3As in the cell. The structure is polymeric, the arsenic atoms lying on infinite coplanar ladders parallel to a. The distance between two arsenic atoms on one rung of the ladder is 2.4 Å, the distance between two arsenic atoms on the same upright and adjacent rungs is 2.9 Å, and the shortest distance between two arsenic atoms in neighbouring ladders is 3.4 Å. Each arsenic atom is bonded to one methyl group (1.97 Å), and along the ladder upright or on any one rung these methyl groups lie on alternate sides of the ladder. 相似文献
97.
The stereochemistry of N-bromosuccinimide electrophilic additions to the double bond at the terminal tetrahydropyridazine ring moiety of the 4a,12a-diazatetracyclic compounds 1-4 has been studied. These reactions appear as very regio- and stereoselective. Most the of the results obtained support the hypothesis that the N-bromoamide additions to cyclohexenes and heterocyclic analogous do not occur via the usual AdE2 mechanism, because the nucleophilic step is the rate-limiting one and the main product-determining factor. On the other hand, epoxidation of the double bond in 1-4 and further opening of the oxirane ring take place in accordance with the normal stereochemical rules. 相似文献
98.
ELS has been used to characterize the initial steps in the oxidation of polycrystalline Ta and Nb in an oxygen atmosphere at low pressures (~1.3 × 10?6 Pa) and room temperature. The results are interpreted in terms of transitions to unoccupied states above EF and plasmon losses, and are discussed in the light of previous studies. The results show important changes in the valence band. The O 2s and O 2p bands increase in intensity during oxidation. 相似文献
99.
A quantitative comparative analysis of molecular electrostatic potential (MEP) distributions generated from different wave functions was carried out. Wave functions were computed by using MNDO, AMl, STO-3G, 3-21G, 4-31G, 6-31G, 4-31G*, 6-31G*, and 6-31G** methods. Ten different compounds, which include usual atoms and groups of biomolecules, such as hydroxyl, carbonyl, amine, amide, imine, double and triple bonds, and heteroaromatic rings, were studied. For each compound, MEP values in the points of a common 3-D grid were computed; thereafter, the similarity between each pair of MEP distributions generated by different methods was assessed. Similarities were measured using the Spearman rank correlation coefficient. A similarity matrix was obtained for each compound. Similarity matrices were averaged and a hierarchical cluster analysis was carried out to classify the different quantum chemical methods. In the compounds studied, the main conclusion is the negligible difference between the pattern of MEP distributions generated from all split valence basis sets (with and without polarization functions). © 1993 John Wiley & Sons, Inc. 相似文献
100.
We report on the size, structure and magnetic properties of Ni nanoparticles fabricated with a free-jet sputtering nanoparticle source. It is found how the pressure of the inert gas and the diameter of the source nozzle can control the particle size and coercivity in a wide range. Measurements of the specific magnetic moment of Ni nanoparticles are reported. A particular growing regime is found at high pressures over 1.8 mbar observing a further aggregation process that leads to nanoparticle agglomerates with diameters larger than 100 nm with a low dispersion in size. 相似文献