全文获取类型
收费全文 | 1514篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 1014篇 |
晶体学 | 9篇 |
力学 | 31篇 |
数学 | 297篇 |
物理学 | 178篇 |
出版年
2014年 | 14篇 |
2013年 | 27篇 |
2012年 | 35篇 |
2011年 | 37篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 41篇 |
2007年 | 34篇 |
2006年 | 34篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 33篇 |
2002年 | 32篇 |
2001年 | 23篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1994年 | 13篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 26篇 |
1985年 | 19篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 35篇 |
1981年 | 36篇 |
1980年 | 21篇 |
1979年 | 29篇 |
1978年 | 18篇 |
1977年 | 23篇 |
1976年 | 26篇 |
1975年 | 23篇 |
1938年 | 15篇 |
1937年 | 17篇 |
1934年 | 21篇 |
1933年 | 19篇 |
1932年 | 12篇 |
1931年 | 24篇 |
1930年 | 19篇 |
1929年 | 20篇 |
1928年 | 29篇 |
1927年 | 18篇 |
1926年 | 19篇 |
排序方式: 共有1529条查询结果,搜索用时 15 毫秒
61.
Erich Tobler 《Helvetica chimica acta》1969,52(2):408-418
2-Dimethylaminoethanol reacts with 1,2-epoxyoctane presumably via a hydrogen-bonded complex to form a quaternary ammonium compound which exhibits a fair stability at lower temperatures. At higher temperatures the quaternary structure decomposes with the resulting formation of a wide variety of products. Most of the products have been identified and a reasonable mechanistic picture for their formation is presented. The main products of the reaction are 1-(ß-dimethylaminoethoxy)-2-octanol (IIIa) and 1-dimethylamino-2-octanol (IV), the latter being formed according to several pathways concurrently with ethylene oxide, 2-methyl-4-hexyl-1, 3-dioxolane (VI), and 2-hexyl-1, 4-dioxane (VII). Some of the higher molecular weight products are secondary products resulting from the action of epoxide on the primary reaction products IIIa and IV. The relative amount of each product formed depends on the ratio of starting materials and reaction temperature. In the presence of an additional hydroxylic solvent such as ethanol, the solvent enters also into the reaction. 相似文献
62.
Gerhard Wendlberger Liljana Mladenova-Orlinova Walter Göhring Regina Scharf Erich Wünsch 《Monatshefte für Chemie / Chemical Monthly》1981,112(11):1297-1312
The synthesis of the tetratriacontapeptide amide corresponding to the revised primary structure of human big gastrin I is described. For this purpose the fragments were designed in view of the maximum use of those utilized in our previous synthesis of human big gastrin I according to the first sequence proposal. Consequently the key tripeptide-Pro-Pro-His- (sequence 7–9) was prepared in suitably protected form to be used as amino or carboxyl component for assembly of the segments 1–9 and 1–14, respectively. Final condensation of the latter nona- and tetradecapeptide derivatives with the C-terminal segments 10–34 and 15–34 via the azide and the dicyclohexylcarbodiimide/N-hydroxysuccinimide procedure, respectively, leads to crude fully protected human big gastrin I. Upon deprotection by exposure to trifluoroacetic acid in presence of ethanedithiol-(1,2) as scavanger, ion exchange chromatography and partition chromatography, the desired tetratriacontapeptide amide was isolated in satisfactory yield with a high degree of purity. The identical immunological behaviour of the synthetic material, if compared with that of natural human big gastrin I, represents ulterior strong evidence for the correctness of the newly proposed structure for this putative prohormonal form of the gastrins.
Kurzmitteilung:Wünsch E., Wendlberger G., Mladenova-Orlinova L., Göhring W., Jaeger E., Scharf R., Gregory R. A., Dockray G. J., Hoppe-Seyler's Z. Physiol. Chem.362, 179 (1981). 相似文献
63.
Bailey BC Fan H Baum EW Huffman JC Baik MH Mindiola DJ 《Journal of the American Chemical Society》2005,127(46):16016-16017
The transient titanium alkylidyne complex (PNP)TiCtBu (PNP = N-[2-P(CHMe2)2-4-methylphenyl]2-), prepared from alpha-hydrogen abstraction of the corresponding alkylidene-alkyl species (PNP)Ti=CHtBu(CH2tBu), can readily undergo intermolecular 1,2-addition of C-H bonds of benzene and SiMe4. Synthesis and reactivity, isotopic labeling, kinetics, and theoretical studies strongly favor an alkylidyne pathway and the alpha-H abstraction step to be the rate-determining step. 相似文献
64.
Herle V Fischer P Windhab EJ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(20):9051-9057
An equimolar mixture of a cationic surfactant, cetylperidinium chloride (CPyCl), and salt sodium salicylate (NaSal) forms wormlike micelles in aqueous solutions. Under shear, the solution shows a pronounced shear-thickening behavior, which is coupled with oscillations in shear rate and the apparent viscosity. In this shear-thickening regime shear bands form, which also oscillate in position and intensity. These shear bands are visualized by direct imaging and Rheo-small angle light scattering methods. Temporal intensity fluctuations of the shear bands were evaluated using image analysis. Fourier transformations (FT) of the oscillating shear rate and intensity of the shear bands showed a single dominating frequency in the power spectrum analysis. This characteristic frequency as well as the amplitude of shear rate fluctuation was found to increase with stress. From the rheological and optical measurements, we propose that a stress driven mechanism is responsible for the formation of shear bands. Experiments performed in transparent parallel-plate geometry show dampening of the shear rate oscillations and increase in the characteristic frequency with decrease in the gap. Power spectrum analysis and the SALS measurements confirm the formation of different structures as a function of gap size in the parallel-plate geometry. 相似文献
65.
Erich Ziegler Hans Junek Hildegrad Kroboth 《Monatshefte für Chemie / Chemical Monthly》1976,14(1):317-324
Thermolysis ofMeldrum acid in the presence of cycloalkanones leads to dioxaspiro-alkanediones (3 a–c) by the elimination of acetone. With increasing temperature an additional dehydratation is observed and with two moles ofMeldrum acid pyrano-cycloalkano-pyranediones (6 a–b) are formed. The reaction of dialkylMeldrum acids with cyclic 1,3-diones is investigated. 相似文献
66.
Daniel Krois Mario Simonetti Erich Wünsch 《Monatshefte für Chemie / Chemical Monthly》1989,120(11):1029-1041
Summary For the identification of a protein predicted by DNA sequence analysis of the TTV1 virus from the archaebacteriumThermoproteus tenax, the trieicosapeptide H-Thr-Pro-Thr-Pro-Thr-Pro-Thr-Tyr-Asp-Ile-Thr-Tyr-Val-Val-Phe-Asp-Val-Thr-Pro-Ser-Pro-Thr-Pro-OH, corresponding to the protein fragment 79–101, was prepared by conventional methods of peptide synthesis. This sequence portion may possibly represent a suitable protein specific immunepitope.
Zur Hypothese eines TTV1 Virus/Thermoproteus tenax F154-Proteins. Teil II: Synthese des Protein-fragments 79–101
Zusammenfassung Für den Nachweis der Expression des Proteins F154 — nach einer Sequenzanalyse des Genoms des TTV1 Virus im ArchaebakteriumThermoproteus tenax postuliert — wurde das Peptid H-Thr-Pro-Thr-Pro-Thr-Pro-Thr-Tyr-Asp-Ile-Thr-Tyr-Val-Val-Phe-Asp-Val-Thr-Pro-Ser-Pro-Thr-Pro-OH (Proteinfragment 79–101) mit Hilfe konventioneller Peptidsynthese hergestellt. Diese Peptidsequenz sollte ein geeignetes proteinspezifisches Immunepitop darstellen.相似文献
67.
68.
Jinsong Zhang Chris Taylor Erich Bowman Leo Savage-Low Michael W. Lodewyk Larry Hanne Guang Wu 《Tetrahedron letters》2013
A process for synthesizing 1,4-benzodioxin, through oxidation of a phenol to an o-quinone followed by treatment with an enamine, has been developed. Adduct stereochemistry is found to be retained via this one-pot reaction. The method uses hypervalent iodine reagent under mild conditions and is compatible with a wide scope of phenols and enamines. 相似文献
69.
A magnetic balance was used for measuring the susceptibility of metals and alloys, in an atmosphere of purified argon, up to 1800°c. Comparison of the susceptibilities of liquid Fe, Co and Ni gives information on the liquid state. The changes in the susceptibilities of Ge, Sn and Te on melting are typical of semi-metallic elements and semiconductors, but their behaviour differs according to the degree of symmetry in the solid state. 相似文献
70.
Coupled Hartree-Fock theory is used to compute and map the current density induced in planar hydrocarbons by an external magnetic field. Results of useful accuracy can be obtained with modest (6-31G**) basis sets by employing a continuous gauge transformation. Maps are presented and discussed for benzene, naphthalene, anthracene, tetracene, pentacene, heptacene, and biphenylene. © 1996 John Wiley & Sons, Inc. 相似文献