全文获取类型
收费全文 | 4415篇 |
免费 | 124篇 |
国内免费 | 25篇 |
专业分类
化学 | 3673篇 |
晶体学 | 47篇 |
力学 | 47篇 |
综合类 | 1篇 |
数学 | 203篇 |
物理学 | 593篇 |
出版年
2023年 | 24篇 |
2022年 | 25篇 |
2021年 | 48篇 |
2020年 | 68篇 |
2019年 | 56篇 |
2018年 | 37篇 |
2017年 | 35篇 |
2016年 | 72篇 |
2015年 | 91篇 |
2014年 | 98篇 |
2013年 | 212篇 |
2012年 | 229篇 |
2011年 | 299篇 |
2010年 | 161篇 |
2009年 | 159篇 |
2008年 | 336篇 |
2007年 | 272篇 |
2006年 | 314篇 |
2005年 | 281篇 |
2004年 | 260篇 |
2003年 | 235篇 |
2002年 | 210篇 |
2001年 | 67篇 |
2000年 | 85篇 |
1999年 | 67篇 |
1998年 | 42篇 |
1997年 | 51篇 |
1996年 | 54篇 |
1995年 | 48篇 |
1994年 | 38篇 |
1993年 | 43篇 |
1992年 | 46篇 |
1991年 | 31篇 |
1990年 | 33篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 30篇 |
1986年 | 16篇 |
1985年 | 41篇 |
1984年 | 37篇 |
1983年 | 17篇 |
1982年 | 26篇 |
1981年 | 32篇 |
1980年 | 34篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有4564条查询结果,搜索用时 15 毫秒
71.
Yohei Hashimoto Masataka Moriyasu Eiko Kato Masaru Endo Naohiko Miyamoto Hiroshi Uchida 《Mikrochimica acta》1978,70(1-2):159-167
Summary A new type of detector for high-pressure liquid chromatography has been designed. This detector is equipped with a RC resonance circuit, and is similar to the capacitance detector previously reported. It is operated as a capacitance detector with nonpolar eluents; while with polar solvents, it behaves as a conductance detector. Electrolytes such as salts, acids and bases are sensitively detected. The detector was successfully used for the detection of fatty acids and alkaloids.
Zusammenfassung Ein neuartiger Detektor für die Hochdruck-Flüssigchromatographie wurde entwickelt. Dieser ist mit einem Resonanzstromkreis ausgestattet und ähnelt dem kürzlich beschriebenen Kapazitanz-Detektor. Als solcher funktioniert er mit nichtpolaren Eluenten, während er sich mit polaren Lösungsmitteln wie ein Leitfähigkeitsdetektor verhält. Salze, Säuren und Basen werden empfindlich nachgewiesen. Das Gerät wurde zum Nachweis von Fettsäuren und Alkaloiden verwendet.相似文献
72.
Hiroyuki Ohno 《Tetrahedron letters》2006,47(32):5747-5750
The first total synthesis of dapiramicin B, a nucleoside antibiotic, is described. The characteristic N-glycoside linkage in dapiramicin B was effectively constructed by way of the Pd-catalyzed coupling reaction of a heptopyranosylamine with a bromopyrrolopyrimidine derivative. 相似文献
73.
Shinichi Kikkawa Kazuteru Nagasaka Mark Bailey Yoshinari Miyamoto 《Journal of solid state chemistry》2007,180(7):1984-1989
Gallium oxynitride, isostructural to hexagonal gallium nitride (h-GaN), was obtained by ammonia nitridation of a precursor prepared from the addition of citric acid to an aqueous solution of gallium nitrate. Gallium oxynitride produced at 750 °C had a small amount of gallium vacancies, and was formulated as (Ga0.89□0.11) (N0.66O0.34) where the symbol □ stands for gallium vacancy. Both the gallium vacancies and oxygen substituted for nitrogen were randomly distributed within the structure. The amount of vacancies decreased with nitridation temperatures in the range of 750-850 °C. Approximately, 10 at% Li+ was doped into the gallium oxynitride, using a similar preparation with the additional presence of lithium nitrate, resulted in the random substitution of Ga3+ in an atomic ratio of Li/Ga<1 at 750 °C. Oxygen was codoped with lithium and substituted nitrogen in the wurtzite-type crystal lattice. These substitutions reduced the electrical conductivity in the gallium oxynitride semiconductor. A new oxynitride, Li2Ga3NO4, was also obtained with Li2CN2 impurity using similar preparations from a mixture of Li/Ga?1. The crystal structure was isostructural with h-GaN, and was refined as P63mc with a=0.31674(1) nm, and c=0.50854(2) nm. The Ga and Li occupancies at the 2b site were refined to be 0.6085 and 0.3915, respectively, assuming that the other 2b site was randomly occupied with 1/5O and 4/5N. When the new compound was washed for over 1 min for the removal of Li2CN2 impurities, it was decomposed to a mixture of α-GaOOH and α-LiGaO2. The as-prepared product with Li/Ga=1 showed the highest intensity in yellow luminescence among the products under excitation at 254 nm. 相似文献
74.
Nanometer-sized metallic palladium particles can be synthesized by hydrogen reduction of Pd2+ ions dissolved in the water core of a water-in-CO2 microemulsion. The Pd nanoparticles, stabilized by the micromeulsion and uniformly dispersed in the supercritical fluid phase, are effective catalysts for hydrogenation of olefins. Examples of rapid and efficient hydrogenation of water-soluble and CO2-soluble olefins catalyzed by the Pd nanoparticles in supercritical CO2 are given. 相似文献
75.
Hiroyuki Asanuma Sumie Gotoh Takeshi Ban Makoto Komiyama 《Journal of inclusion phenomena and macrocyclic chemistry》1997,27(3):259-264
Poly(2-vinyl-4,6-diamino-1,3,5-triazine) efficiently binds nucleic acid bases and nucleosides in water by using complementary hydrogen bonding. The binding activity decreases in the order: U, T > A C, G. The corresponding monomer shows virtually no activity, indicating a predominant role of polymer effect for the molecular recognition in water. 相似文献
76.
Synthesis of diphenyl cucurbit[6]uril (CB[6]) has been achieved via co-oligomerization of diphenyl glycoluril and unsubstituted glycoluril. The unsymmetrically substituted CB[6], Ph(2)CB[6], was further converted to a rotaxane incorporating bis(dinitrophenyl)spermine. [reaction: see text] 相似文献
77.
78.
Akitomo Tachibana Hiroyuki Fueno Masaya Yamato Tokio Yamabe 《International journal of quantum chemistry》1991,40(4):435-456
A perturbation theory for normal coordinates of nonadiabatic solvation is presented by means of the “string model” of chemical reactions. The dynamic normal coordinate is introduced for the perturbational treatment of the “intrinsic” normal coordinates that are orthogonal to the reaction path. The reaction is defined as the intrinsic reaction coordinate (IRC ) that is treated as a string. The string is thrown in the external force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of a water molecule for hydration reaction of formaldehyde is calculated. A second-order perturbation effect for the enhancement of the reaction rate is found. 相似文献
79.
David?I?Fisher Jared?L?Cartwright Hideyoshi?Harashima Hiroyuki?Kamiya Alexander?G?McLennanEmail author 《BMC biochemistry》2004,5(1):7
Background
Nudix hydrolases form a protein family whose function is to hydrolyse intracellular nucleotides and so regulate their levels and eliminate potentially toxic derivatives. The genome of the radioresistant bacterium Deinococcus radiodurans encodes 25 nudix hydrolases, an unexpectedly large number. These may contribute to radioresistance by removing mutagenic oxidised and otherwise damaged nucleotides. Characterisation of these hydrolases is necessary to understand the reason for their presence. Here, we report the cloning and characterisation of the DR0975 gene product, a nudix hydrolase that appears to be unique to this organism. 相似文献80.
Takashima H Mimura N Ohkubo T Yoshida T Tamaoki H Kobayashi Y 《Journal of the American Chemical Society》2004,126(14):4504-4505
Distributed computing has been implemented to the solution structure determination of endothelin-1 to evaluate efficiency of the method for NMR constraint-based structure calculations. A key target of the investigation was determination of the C-terminal folding of the peptide, which had been dispersed in previous studies of NMR, despite its pharmacological significances. With use of tens of thousands of random initial structures to explore the conformational space comprehensively, we determined high-resolution structures with good convergences of C-terminal as well as previously defined N-terminal structures. The previous studies had missed the C-terminal convergence because of initial structure dependencies trapped in localized folding of the N-terminal region, which are strongly constricted by two disulfide bonds. 相似文献