全文获取类型
收费全文 | 1008篇 |
免费 | 14篇 |
国内免费 | 6篇 |
专业分类
化学 | 677篇 |
晶体学 | 36篇 |
力学 | 23篇 |
数学 | 185篇 |
物理学 | 107篇 |
出版年
2023年 | 4篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 57篇 |
2012年 | 44篇 |
2011年 | 61篇 |
2010年 | 41篇 |
2009年 | 41篇 |
2008年 | 52篇 |
2007年 | 54篇 |
2006年 | 56篇 |
2005年 | 51篇 |
2004年 | 55篇 |
2003年 | 42篇 |
2002年 | 40篇 |
2001年 | 17篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1918年 | 2篇 |
1914年 | 2篇 |
1913年 | 2篇 |
1907年 | 2篇 |
排序方式: 共有1028条查询结果,搜索用时 15 毫秒
991.
Andrzej Gobiowski Kazimierz Stoecki Urszula Prokop Alicja Kumierowska Tadeusz Borowiecki Andrzej Denis Czesawa Sikorska 《Reaction Kinetics and Catalysis Letters》2004,82(1):179-189
The influence of K2O on the amounts of chemisorbed hydrogen on a Ni catalyst, the catalyst activity and its resistance to coking were measured.
Introducing potassium into the commercial catalyst (not into the support) appeared to enhance its resistance to coking. The
best catalytic characteristics was noticed for a system containing ~0.5 wt. % K2O. The investigations show a good agreement between the resistance to coking obtained by the temperature-programmed reaction
(TPReaction) method and by the traditional thermogravimetric method.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
992.
The results in this paper give information about the influence of the zinc sulphide structure and the oxidation conditions on the shape of the crystallites in the oxide phase. Zinc sulphide has regular and hexagonal structures. The cross-sections of the samples have been observed before and after the oxidation at 1223 K.The reaction products are dependent of the temperature, the flow-rate of gases and the oxygen pressure. Showing these dependences the shape of zinc oxide crystallites has been investigated when the oxidation of' regular zinc sulphide was already finished. It was also taken into consideration that the growth of the grain of the sulphide may change the rate of oxidation. The results obtained agree with all the mentioned parameters of the shape of zinc oxide crystallites allowing to interpret the kinetic curves. 相似文献
993.
Abstract— Photoinduced oxygen consumption in systems containing synthetic and natural pheomelanins has been studied by ESR spectroscopy using a nitroxide spin probe to monitor oxygen concentration. Action spectra and quantum yields have been determined for melanin from 5-S-cysteinyldopa and for pheomelanins extracted from red human hair and red chicken feathers. For comparison, data also were obtained for eumelanins from black hair and black feathers. The action spectrum for oxygen consumption by cysteinyldopa melanin is closely related to that previously obtained for eumelanins except that it shows slightly less efficiency at intermediate wavelengths (ca. 300–400 nm). Action spectra for the natural pheomelanins resemble either that for cysteinyldopa melanin or that for eumelanin. In general pheomelanins are no more effective than eumelanins in promoting oxygen consumption, i.e. they are no more susceptible to net photooxidation. 相似文献
994.
995.
Tadeusz Wibig 《Central European Journal of Physics》2007,5(4):528-538
A new feature in the spectrum of ultra high energy cosmic rays (UHECR) has been announced in the paper by Berezinsky, Gazizov
and Kachelrieβ. The ratio of the solution of the exact transport equation to its solution in the continuous energy loss limit
shows intriguing features which, according to the Authors, are related to the very nature of the energy loss processes of
UHECR: the very sharp second dip predicted at 6.3 × 1019 eV can be used as an energy calibration point and also as the UHECR mass indicator for big future cosmic ray experiments.
In the present paper we would like to advocate that this statement is an overinterpretation. The second dip is a result of an inappropriate approximation used, and thus it cannot help to understand the nature of UHECR in any way.
相似文献
996.
Tadeusz M. Krygowski Marcin Palusiak Anna Płonka Joanna E. Zachara‐Horeglad 《Journal of Physical Organic Chemistry》2007,20(5):297-306
Molecular geometry of 10 isomeric nitronaphtholate ions (excluding peri‐ and ortho‐type substituted systems), 1‐ and 2‐naphtholate ions, 1‐ and 2‐nitronaphthalene, meta‐ and para‐nitrophenolate, phenolate, and nitrobenzene were optimized at B3LYP/6‐311G** level of approximation. Substituent effect stabilization energy (SESE), geometry‐based aromaticity index HOMA, magnetism‐based indices NICS, NICS(1), NICS(1)zz, and parameters characterizing Bond Critical Points (BCP) (ρ, ?2ρ, ellipticity, ion/cov) of the Bader AIM theory were used to characterize transmitting properties for substituent effect through the naphthalene moiety. It results from our study that the studied systems could be clearly divided into two groups, (i) a para‐type group, where the intramolecular charge transfer between the π‐electron donating and π‐electron accepting substituents can be described by canonical forms with charge separation (as in the case of para‐nitrophenolate) and (ii) a meta‐type group, where this transfer requires using canonical forms with double charge separation (as in the case of meta‐nitrophenolate). Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
997.
Andrzej Maślanskiewicz Tadeusz Glowiak Henryk Chojnacki Leszek Skrzypek Adam Niedbala 《Journal of chemical crystallography》1995,25(4):165-169
The crystal and molecular structures of two isomeric 3,4- and 4,3-chloro-(methylthio)quinolines have been determined. For 3-chloro-4-(methylthio)-quinoline (3-Cl–4-MeS–Q); triclinic, space group
,a=7.199(3),b=7.919(3),c=8.921(3) Å, =89.74(3), =74.29(3), =78.55(3)°. For 4-chloro-3-(methylthio)quinoline (4-Cl–3-MeS–Q): monoclinic, space group P21/n,a=12.860(4),b=5.424(2),c=13.434(4) Å, =90.84(3)°. The values of the Cl...S distance as well as those for the Cl–C–C(S) and (Cl)C–C–S angles indicate the attractive interaction between ortho-situated heteroatoms in isomer 4-Cl–3-MeS–Q contrary to the effects observed in the case of 3-Cl–4-MeS–Q. The conclusions were confirmed by calculations of atomic charges withab initio method 4-31G basis set, which show positively charged sulfur atom in 4-Cl–3-MeS–Q and negatively charged sulfur in 3-Cl–4-MeS–Q.Part XXX in the series of Azinyl Sulfides. 相似文献
998.
Krystian Pluta Andrzej Maślankiewicz Tadeusz Głbwiak 《Journal of chemical crystallography》1993,23(4):285-290
The title compound (C20H16N2S3) is triclinic, witha=9.494(3)b=9.890(3),c=19.456(5)Å,a=90.26(3)°,°=100.47(3)°, =99.18(3)°,Z=4 and space groupP¯1. The structure was solved by direct methods and refined toR=0.045 for 6076 reflections. There are two nonequivalent molecules in the unit cell. Two pairs of sulfur atoms in ortho-positions remain in very close contact. The S-methyl groups are nearly coplanar to the quinoline moieties and turned to the orthoposition, 2. CP MAS spectrum shows two conformers in the solid state but1H and13C NMR spectra in CDCl3 solution show rapid equilibrium of the conformers giving rise to average NMR data.Part XX in the series of Azinyl Sulfides. 相似文献
999.
In a series of our previous papers we have investigated the influence of various variables on retention/migration of peptides in various high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) systems. Here we present a correlation of the selectivity of peptide separation in similar, as well as in various HPTLC and PPEC systems investigated before. Our results show that the selectivity in similar HPTLC and PPEC systems is quite different. This results from the share of electrophoresis in separation of solutes by PPEC. The results suggest that combination of HPTLC and PPEC, with properly selected separation conditions (the same, or even better—different for each technique), may be used for efficient two-dimensional separation of peptides. The best separation can be obtained if PPEC is carried out in two opposite directions (toward the cathode and the anode) simultaneously. 相似文献
1000.
We prove that the set of all complex series which are nonabsolutely convergent is c-algebrable. We establish a similar result for the set of all divergent complex series with bounded partial sums. 相似文献