全文获取类型
收费全文 | 1164篇 |
免费 | 37篇 |
国内免费 | 15篇 |
专业分类
化学 | 816篇 |
晶体学 | 12篇 |
力学 | 20篇 |
数学 | 251篇 |
物理学 | 117篇 |
出版年
2023年 | 7篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 32篇 |
2013年 | 32篇 |
2012年 | 30篇 |
2011年 | 49篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 56篇 |
2007年 | 52篇 |
2006年 | 65篇 |
2005年 | 58篇 |
2004年 | 49篇 |
2003年 | 31篇 |
2002年 | 35篇 |
2001年 | 29篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 30篇 |
1997年 | 31篇 |
1996年 | 18篇 |
1995年 | 28篇 |
1994年 | 16篇 |
1993年 | 24篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 21篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 20篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 16篇 |
1974年 | 5篇 |
1972年 | 7篇 |
排序方式: 共有1216条查询结果,搜索用时 15 毫秒
81.
We provide conditions for which the round functions of an ?-bit Rijndael-like block cipher generate the alternating group on the set {0,1}?. These conditions show that the class of Rijndael-like ciphers whose round functions generate the alternating group on their message space is large, and includes both the actual Rijndael and the block cipher used by the compression function of the Whirlpool hash function. The result indicates that there is no trapdoor design for a Rijndael-like cipher based on the imprimitivity of the group action of its proper round functions which is difficult to detect. 相似文献
82.
83.
Rüdiger Brandt Hanskarl Müller-Buschbaum 《Monatshefte für Chemie / Chemical Monthly》1986,117(11):1239-1244
Solid state reaction of BaCO3, FeC2O4·2H2O and Nb2O5 gave single crystals of Ba6FeNb9O30. The crystal structure was solved by X-ray investigations (a=12.597,c=3.990Å, space group P 4 bm-C
4v
2
,Z=1). Ba6FeNb9O30 crystallyzes in the tetragonal bronze type with a statistical distribution of Fe3+ and Nb5+ in the octahedral framework. The anisotropic temperature factors of barium are discussed with respect to the oxygen coordination. 相似文献
84.
85.
86.
Six different calixarene-bonded phases were characterized by analyzing 36 and 26 solutes at pH 3 and 7, respectively. Dolan and Snyder's multiple term linear equation was used to correlate retention factors k' to parameters of the solutes and columns. The column parameters have been related to molecular properties of the stationary phases and new suggestions were made for the interpretation of steric selectivity. Ionic and polar interactions have been found dependent on pH value, while steric interactions are less dependent and hydrophobic interactions remain unchanged. Distinct differences of the supported interactions were confirmed between the calixarene-bonded and the common alkyl-bonded silicas. By use of the parameters, values of k' can be estimated with an average deviation of 2.50 and 7.92% at low and neutral pH-value, respectively. 相似文献
87.
88.
Imines in the Titanium Coordination Sphere – Transformation of Imidoyl Chlorides to Nitrilium Ions
下载免费PDF全文
![点击此处可从《无机化学与普通化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In the reaction of TiCl4 in benzene as solvent with the imidoyl chloride p‐Tolyl(Cl)C=NPh ( 1 ) the abstraction of the chloride substituent is observed, leading to the nitrilium salt [p‐Tolyl–C≡N–Ph]+[Ti2Cl9]– ( 2 ) in quantitative yield. The highly electrophilic salt 2 is characterized by IR‐ and NMR spectroscopy. The observed band for the C≡N stretching mode of 2 clearly indicates the formation of a nitrilium ion. Especially a characteristic line broadening of the 13C{1H}‐NMR signals related to carbon atoms next to the nitrogen is observed. By 15N,1H‐HMBC NMR experiments it is shown that the nitrogen signal of 2 is significantly shifted to high‐field in relation to nitriles and imines. The molecular structure of 2 was confirmed by single‐crystal X‐ray diffraction. The C≡N bond length and the linearity of the C–C≡N–C unit in 2 confirm the triple bond character of this bond. 相似文献
89.
Activation of Molecular Hydrogen by Bis(η5,η1‐pentafulvene)‐titanium Complexes – Efficient Formation of Titanium(III)hydrides
下载免费PDF全文
![点击此处可从《无机化学与普通化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The synthesis and crystal structures of two dinuclear titanocene hydride complexes are reported. Both complexes, namely bis(η5‐(di‐para‐tolylmethyl)cyclopentadienyl)titanium hydride dimer, [(η5‐C20H19)2Ti(μ‐H)]2 ( 2a ), and bis(η5‐2‐adamantylcyclopentadienyl)‐titanium hydride dimer, [(η5‐C15H19)2Ti(μ‐H)]2 ( 2b ), are formed via activation of molecular hydrogen by the corresponding bis(η5,η1‐pentafulvene)titanium complexes 1a and 1b at ambient temperatures and pressures in high yields. The hydride complexes 2a and 2b exhibit planar [Ti2H2] cores and, as a result of the heterolytic cleavage of molecular hydrogen, substituted Cp Ligands were formed during the reaction. 相似文献
90.
Ralf Zimmermann Uwe Freudenberg Rüdiger Schweiß David Küttner Carsten Werner 《Current Opinion in Colloid & Interface Science》2010,15(3):196-202
The propensity of hydroxide and hydronium ions to accumulate at interfaces is the subject of ongoing scientific debate. Electrokinetic and surface force measurements suggest elevated interfacial concentrations of hydroxide ions across a wide range of pHs. Contrary to this, however, surface-sensitive spectroscopic techniques and molecular dynamic (MD) simulations indicate that hydronium ions have strong surface affinity under similar conditions. Here we review results obtained for gas/water, oil/water and solid/water interfaces. Emphasis is placed on ion adsorption phenomena occurring on polymer films of different hydrophobicity and structure. The results clearly show that asymmetric water ion adsorption is independent of the hydrophobicity of the solid surface. Recently obtained data reveal significant effects of the hydroxide and hydronium ions even on the charging of hydrophobic polymers in the presence of multivalent electrolytes and on the charging of zwitterionic lipid membranes. 相似文献