全文获取类型
收费全文 | 77201篇 |
免费 | 6092篇 |
国内免费 | 6690篇 |
专业分类
化学 | 43578篇 |
晶体学 | 796篇 |
力学 | 5263篇 |
综合类 | 711篇 |
数学 | 14142篇 |
物理学 | 25493篇 |
出版年
2024年 | 86篇 |
2023年 | 714篇 |
2022年 | 1262篇 |
2021年 | 1838篇 |
2020年 | 2056篇 |
2019年 | 2046篇 |
2018年 | 1821篇 |
2017年 | 2184篇 |
2016年 | 2432篇 |
2015年 | 2038篇 |
2014年 | 2899篇 |
2013年 | 5054篇 |
2012年 | 3514篇 |
2011年 | 3940篇 |
2010年 | 3235篇 |
2009年 | 4704篇 |
2008年 | 4761篇 |
2007年 | 5149篇 |
2006年 | 4462篇 |
2005年 | 3701篇 |
2004年 | 3389篇 |
2003年 | 3315篇 |
2002年 | 4090篇 |
2001年 | 2782篇 |
2000年 | 2533篇 |
1999年 | 2119篇 |
1998年 | 1991篇 |
1997年 | 1306篇 |
1996年 | 1323篇 |
1995年 | 1166篇 |
1994年 | 1202篇 |
1993年 | 877篇 |
1992年 | 937篇 |
1991年 | 596篇 |
1990年 | 539篇 |
1989年 | 442篇 |
1988年 | 411篇 |
1987年 | 376篇 |
1986年 | 308篇 |
1985年 | 286篇 |
1984年 | 294篇 |
1983年 | 155篇 |
1982年 | 248篇 |
1981年 | 266篇 |
1980年 | 215篇 |
1979年 | 244篇 |
1978年 | 180篇 |
1977年 | 149篇 |
1976年 | 104篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
M. M. Krayushkin M. A. Kalik L. G. Vorontsova E. Yu. Zvezdina M. G. Kurella 《Russian Chemical Bulletin》1993,42(7):1204-1208
9-Methyl-3,3a,4,5-tetrahydro-6H-thieno[2,3-b]thiocino[4,5-c]isoxazole and 9-hydroxyimino-2-methyl-7-methylene-6, 7,8,9-tetrahydro-5H-thieno[2,3-b]thiocine have been prepared for the first time by the oxidation of 2--alkenylthio-3-thiophenecarbaldoximes with NaOCl. X-ray structural investigations of thieno[2,3-b]thiocine and 2-homomethallylthio-5-methyl-3-thiophenecarbaldoxime have been carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1262–1266, July, 1993. 相似文献
992.
Summary The application of capillary SFC for SIMDIST investigations of paraffins and waxes is reported. Pressure, density and temperature of the mobile phase are optimized to obtain high chromatographic resolution of complex mixtures of industrial products. Isothermal linear pressure programming and asymptotic pressure and density programming are used in the range from 15 to 35 MPa in the isothermic mode above 100°C. SFC chromatograms of natural and synthetic paraffins, microcrystalline wax and candle wax are compared. The retention behaviour of paraffin mixtures and waxes has been investigated on methyl/phenyl and biphenyl capillary columns. The polarity of the stationary phases influences the absolute retention time more than it influences the chromatographic resolution. 相似文献
993.
O. S. Filipenko S. M. Aldoshin G. V. Shilov N. I. Makarova V. A. Kharlanov M. I. Knyazhanskii 《Russian Chemical Bulletin》1995,44(2):287-292
The molecular structures of the initial compounds and the products of photocyclization involving amino and azomethine groups in perchlorates ofN-amino (1) andN-azomethine (2) derivatives of 2,4,6-triphenylpyridinium cations were studied. Cations1 and2 have an essentially non-coplanar arrangement of the -Ph rings, and the product of photocyclization of2, cation3, is characterized by a flattened structure. It was found that the orientation of the lone electron pair of the N atom with respect to one of the planes of the -Ph rings in molecule1 is more favorable for monocyclization involving the amino group. The structure of molecule2 allows two routes of the photoreaction,viz., O N proton transfer and monocyclization with an -Ph ring. However, the structural features of molecule2 are more favorable for photocyclization.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 296–301, February, 1995. 相似文献
994.
Summary Inverse gas chromatography is shown to be suitable for the study of the oxidation of vegetable oils. With air as carrier gas
characteristic plots of retention index versus time are obtained for hydroxylic test solutes that are consistent with the
oxidation behaviour of vegetable oils. Shifts of retention are found to be accompanied by changes of column efficiency due
to the oxidative crosslinking of polyunsaturated vegetable oils. The technique also leads to useful information concerning
the oxidation of antioxidant inhibited systems.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
995.
Summary Four different techniques to quantify unresolved chromatographic peaks with known spectral features combined with photodiode array detection, are investigated as regards their efficiency for the accurate and precise determination of drugs in the low g-range. The comparison includes peak suppression utilising difference chromatograms, first-order derivative chromatograms, selective chromatograms, generated by the calculation of orthogonal polynomial shares, and the powerful least-squares multicomponent analysis approach. Each of these methods uses UV-spectra taken throughout, the peak. The results presented and conclusions reached should enable the chromatographer to come to a decision about the reasonable use of these options now provided by multichannel detection in HPLC. 相似文献
996.
Summary 2,8-Dihydroxyadeninuria and xanthinuria are inborn enzyme disorders which must be under lifelong therapeutic control. Quantitative
determination of 2,8-DHA and xanthine using reversed phase HPLC was performed. A new application for the separation of purines
shortens analysis-time. Examples of the determination of 2,8-DHA and xanthine before and under certain therapies are shown.
Long term monitoring of the patients offers the possibility of a reliable prophylaxis against stone recurrence. 相似文献
997.
998.
H. Hanabata T. Matsuo H. Suga 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(3):325-333
Heat capacities of crystalline-cyclodextrin undecahydrate have been measured in the temperature range between 13 and 300K by use of a miniaturized adiabatic low-temperature calorimeter. A first-order phase transition occurred at 226K with a discontinuous entropy change of 45.0 ± 1.0J
K
–1 mol–1. The highly disordered nature of the high temperature phase was considered in relation to the entropy contribution. A glass transition phenomenon observed around 150K was ascribed to the freezing of a configurational change of the protons engaged in the four-membered hydrogen-bonded ring which appeared only in the low temperature phase. 相似文献
999.
The aim of this research work was to clarify the role of the mixed emulsifier in the structure formation and water binding
mode in the case of o/w creams prepared with different surfactants. The swelling behavior of mixed emulsifiers was examined
by means of direct investigation methods such as transmission electron microscopy (TEM) and X-ray diffraction. The detailed
structure image of the creams was created with the help of the latter. The influence of the structure of the hydrophilic gel
phase, and the structural changes during storage were studied with rheological methods. On the basis of the results, it can
be stated that the investigated creams had different structures from those mentioned in the literature: surfactant did not
create a mixed bilayer with the structure to furnish fatty amphiphile; instead, micelles were formed. These results correlated
well with the results of the rheological tests. 相似文献
1000.