全文获取类型
收费全文 | 3524篇 |
免费 | 20篇 |
国内免费 | 18篇 |
专业分类
化学 | 2188篇 |
晶体学 | 29篇 |
力学 | 77篇 |
数学 | 552篇 |
物理学 | 716篇 |
出版年
2022年 | 27篇 |
2021年 | 27篇 |
2020年 | 35篇 |
2019年 | 21篇 |
2018年 | 27篇 |
2017年 | 21篇 |
2016年 | 49篇 |
2015年 | 45篇 |
2014年 | 51篇 |
2013年 | 172篇 |
2012年 | 151篇 |
2011年 | 174篇 |
2010年 | 130篇 |
2009年 | 101篇 |
2008年 | 178篇 |
2007年 | 172篇 |
2006年 | 199篇 |
2005年 | 206篇 |
2004年 | 170篇 |
2003年 | 143篇 |
2002年 | 115篇 |
2001年 | 60篇 |
2000年 | 59篇 |
1999年 | 44篇 |
1998年 | 47篇 |
1997年 | 57篇 |
1996年 | 55篇 |
1995年 | 36篇 |
1994年 | 55篇 |
1993年 | 53篇 |
1992年 | 28篇 |
1991年 | 28篇 |
1990年 | 38篇 |
1989年 | 25篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 28篇 |
1985年 | 55篇 |
1984年 | 60篇 |
1983年 | 27篇 |
1982年 | 68篇 |
1981年 | 53篇 |
1980年 | 52篇 |
1979年 | 49篇 |
1978年 | 41篇 |
1977年 | 52篇 |
1976年 | 40篇 |
1975年 | 23篇 |
1974年 | 26篇 |
1973年 | 25篇 |
排序方式: 共有3562条查询结果,搜索用时 31 毫秒
51.
Florian Bentivegna Michael Canva Alain Brun Frédéric Chaput Jean-Pierre Boilot 《Journal of Sol-Gel Science and Technology》1997,9(1):33-39
We study herein the rotational mobility of organic dye molecules and their ability to align on a strong optical electric field when they are encaged in the pores of an inorganic silica xerogel matrix. We compare the case of dye molecules simply dispersed in the pores of the gel—and possibly held by hydrogen bonds—to the case of molecules chemically grafted on the inner surface of these pores through covalent bonds. The study is led on hybrid silicon-zirconium based inorganic matrices doped with organic rhodamine B molecules. The stronger holding of the dopants when these are grafted to the matrix enhances the molecular alignment—and thus the induced anisotropy—as well as the remanence of this alignment. Furthermore, we show that submitting the samples to a supplementary drying at higher temperature tends to increase both the alignment anisotropy and its stability. We explain these results in terms of mobility of the molecules, in relation to their immediate environment. 相似文献
52.
Jean-Pierre Costes 《Transition Metal Chemistry》1985,10(5):185-187
Summary The condensation of acetylacetone with ethylenediamine yields 7-amino-4-methyl-5-aza-3-heptene-2-one (AEH). This terdentate (N2O) Schiff base forms various types of ternary complexes, depending on the nature of the second ligand. Examples of five- and six-coordination have been previously reported. The present paper points to the possibility of preparing a less common type of complex,i.e. [MII(AE)Py]+ (M=Ni or Cu) in which the use of a monodentate ligand (pyridine) favours a square planar geometry. 相似文献
53.
Paul Servin Régis Laurent Anne-Marie Caminade Jean-Pierre Majoral 《Tetrahedron letters》2007,48(4):579-583
A series of densely functionalized dendrimers is synthesized using two branched monomers of type AB2 and CD2, in which the A function (NH2) reacts with D (CHO) and the B function (Cl) reacts with C (OH). The reaction has been carried out up to the fourth generation possessing 96 end groups and has been obtained in only four steps. 相似文献
54.
Highly reliable and accurate analytical methods are needed for the determination of magnetic resonance imaging (MRI) contrast agents in complex matrices of clinical interest. We demonstrate the reliability of capillary zone electrophoresis (CZE) coupled with electrospray ionization-mass spectrometry (ESI-MS) for the analysis of MultiHance (gadobenate dimeglumine), a gadolinium-based MRI agent. A sheath liquid interface connected the CE system with an electrospray mass spectrometer equipped with an ion-trap analyzer. CZE with ultraviolet (CZE-UV) and with mass detection (CZE-MS) were compared by analyzing gadobenate dimeglumine and the free ligand diluted in water and in biological fluids (i.e., human serum and urine). The optimization of some relevant CZE-MS parameters was accomplished, like CE buffer composition, sheath liquid composition and flow, and type and length of the separation capillary. CZE-UV was highly influenced by the biological sample components, which hindered a reliable quantification of both gadobenate and free ligand in serum and urine. In CZE-MS, on the other hand, the electrophoretic runs turned out to be independent of the clinical matrices, due to the informative potential and to the selectivity of MS detection. 相似文献
55.
Magnani A Marchettini N Ristori S Rossi C Rossi F Rustici M Spalla O Tiezzi E 《Journal of the American Chemical Society》2004,126(37):11406-11407
The present work deals with the spatially extended oscillatory Belousov Zhabotinsky reaction-diffusion system carried out in an anisotropic environment of phosphatidylcholines/water binary system, which presents layered aqueous domains separated by lipid bilayers. We report the occurrence of stable Turing patterns, spiral waves, and other exotic structures in phospholipids bilayers that are generally used as a models for cell plasma membranes. 相似文献
56.
Marchand P Griffe L Caminade AM Majoral JP Destarac M Leising F 《Organic letters》2004,6(8):1309-1312
The functionalization of phosphorus-containing dendrimers was easily achieved through thioacylation reactions involving new dendrimers capped with dithioester end groups and various functionalized amines. These reactions were successfully applied to the first generation (12 end groups) and the third generation of the dendrimer (48 end groups) and allowed their functionalization by various primary or secondary amines, alcohols, glycols, and azides. [reaction: see text] 相似文献
57.
In order to analyse metal complexation with polyfunctional phenolic compounds as ligand models of natural substances, a detailed examination is described for five simple binary complexes and three ternary mixed ligand complexes at 25°C (μ = 0.1 M NaClO4). The ligands are tyrosine, 4,5-dihydroxy-1,3-benzene disulfonic acid, disodium salt (tiron), 3,4-dihydroxycinnamic acid (caffeic acid), 3,4,5-trihydroxy-1 -cyclohexene-1 -carboxylic acid (shikimic acid) and 1,3,4,5-tetrahydroxycyclohexanecarboxylic acid 3-(3,4-dihydroxycinnamate) (chlorogenic acid). The ternary systems are Cu(II)/HqA/tiron, where HqA is tyrosine, caffeic or chlorogenic acids. Potentiometric data were used successively to evaluate the protonation of each individual ligand, to detect simple and mixed complexes (including protonated species) and to determine their stability constants (a set of 33 values of constants with several original data is provided). The calculated distribution (speciation) of each species as a function of pH is indicated. Mixed coordination enhances the stability of complexes and the stabilization is expressed in terms of various parameters. The results emphasize that mixed ligand complex formation is essential to studies of multiple equilibria. 相似文献
58.
Perturbative solution of the RPA equation. An application to the calculation of rotational strengths
The RPA equation is solved by perturbation in Møller-Plesset (MP) and Epstein-Nesbet (EN) partitions, which are first compared on a specific example. To still accelerate the faster one (EN), a third scheme is proposed, which involves preliminary diagonalization within a limited subset
, followed by usual EN perturbation between
and the rest of the whole configuration space. Criteria for the choice of
are given. 相似文献
59.
Cecilia Bartolucci Luciano Cellai Concetta Martuccio Andrea Rossi Anna Laura Segre Simona Rizea Savu Luigi Silvestro 《Helvetica chimica acta》1996,79(6):1611-1619
Glycosylrifamycins, a new type of semisynthetic rifamycin derivatives, can be easily obtained by reaction of 3-(2-aminoethylthio)rifamycin SV ( 2 ) with a glycosyl compound carrying a coupling group, such as isothicyanate or carboxy. We prepared O-acetylated and free glucopyranosyl and arabinopyranosyl derivatives of rifamycin S and SV (see 3–10 ). Additionally, derivatives with D -saccharo-1,4-lactone and with shikimic acid were obtained (see 11–15 ). Glycosylrifamycins show an interesting inhibitory power on Gram-positive bacteria (Table). 相似文献
60.
Roger Azria Yvonnick Le Coat Jean-Pierre Ziesel Jean-Pierre Guillotin Brahim Mharzi Michel Tronc 《Chemical physics letters》1994,220(6):417-422
Absolute kinetic energy distributions and yields associated with ground state 3P and excited state 1D oxygen atoms have been obtained for O− anion electron stimulated desorption from condensed O2 in the electron energy range 6–15 eV. The observed yields are understood as resulting essentially from dissociative electron attachment reactions via the two lowest 2Σ+g O−2 resonance states through adiabatic and non-adiabatic transitions to the limits O−(2P) + O(3P) and O−(2P) + O(1D). The kinetic energy distributions show the prominent role of electron multiple collision processes and post-dissociation interactions of the O− anions in the condensed phase. 相似文献