全文获取类型
收费全文 | 2205篇 |
免费 | 109篇 |
国内免费 | 8篇 |
专业分类
化学 | 1620篇 |
晶体学 | 13篇 |
力学 | 64篇 |
数学 | 317篇 |
物理学 | 308篇 |
出版年
2023年 | 18篇 |
2022年 | 26篇 |
2021年 | 50篇 |
2020年 | 63篇 |
2019年 | 45篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 72篇 |
2015年 | 52篇 |
2014年 | 67篇 |
2013年 | 114篇 |
2012年 | 157篇 |
2011年 | 204篇 |
2010年 | 113篇 |
2009年 | 94篇 |
2008年 | 156篇 |
2007年 | 155篇 |
2006年 | 151篇 |
2005年 | 131篇 |
2004年 | 116篇 |
2003年 | 85篇 |
2002年 | 73篇 |
2001年 | 44篇 |
2000年 | 22篇 |
1999年 | 18篇 |
1998年 | 22篇 |
1997年 | 29篇 |
1996年 | 28篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1939年 | 3篇 |
1915年 | 4篇 |
1913年 | 3篇 |
1889年 | 3篇 |
1862年 | 2篇 |
排序方式: 共有2322条查询结果,搜索用时 546 毫秒
51.
Conversion of hindered alkenyl boronate esters into the corresponding iodoalkene, or alkenyl chloride can be carried out stereoselectively using ICl. In the presence of NaOMe, direct reaction of ICl is favoured yielding the E-iodoalkene, however, the reaction with ICl followed by NaOMe can be used to give different major alkenyl iodide and chloride products, depending upon reaction temperature, ICl source and alkenyl boronate stereoelectronics. 相似文献
52.
A convenient method for the conjugation of ruthenium complex on oligonucleotides and peptides through chemoselective oxime linkage is reported. Novel Ru(II) complexes sustaining an aminooxy containing ligand were prepared and efficiently coupled with the oligonucleotides and peptides functionalized with the complementary reactive aldehyde group. The method described herein could be a useful tool for preparing a broad range of metal complex-oligonucleotide and peptide conjugates. 相似文献
53.
Sandrine Henry De Hassonville Bruno Perly Géraldine Piel Thierry Van Hees Valéry Barillaro Pascal Bertholet Luc Delattre Brigitte Evrard 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):289-292
Cyproterone acetate (CPA) is a steroidal antiandrogen with a progestogenic activity. Given that this molecule has a very poor water solubility (2.1 g/mL), different cyclodextrins (CDs) were tested to form inclusion complexes and to increase solubility. Two different techniques were compared to study the affinity between CPA and CDs: phase-solubility studies and NMR spectroscopy. The stoichiometry and the stability constant could be determined for most complexes with the aid of phase-solubility studies. The greatest increase in solubility was achieved with the methylated -CDs, but hydroxypropylated - and -CDs also gave enhanced solubilities. 1H-NMR studies showed a solubility increase similar to that found with phase-solubility studies. The proof of inclusion in the2,6-dimethyl--CD (DIMEB) was shown by 1H-NMR and t-ROESY spectra. 相似文献
54.
Valérie Fargeas Myriam Baalouch Jerôme Baffreau Pascal Gosselin Chantal Barthomeuf 《Tetrahedron》2004,60(45):10359-10364
A simple and efficient methodology to introduce an 1,3-diketone motif from various aldehyde precursors in three steps with good overall yields is described using β-ketosulphone 7 as masked equivalent of acetone. 相似文献
55.
We report simulations of laser-driven many-electron dynamics by means of the time-dependent configuration interaction singles (doubles) approach. The method accounts for the correlation of ground and excited states, is capable of describing explicitly time-dependent, nonlinear phenomena, and is systematically improvable. Lithium cyanide serves as a molecular test system in which the charge distribution and hence the dipole moment are shown to be switchable, in a controlled fashion, by (a series of) laser pulses which induce selective, state-to-state electronic transitions. One focus of our time-dependent calculations is the question of how fast the transition from the ionic ground state to a specific excited state that is embedded in a multitude of other states can be made, without creating an electronic wave packet. 相似文献
56.
Jean Pascal Eloundou 《European Polymer Journal》2002,38(3):431-438
Dipolar relaxations in a reactive epoxy-amine system based on diglycidyl ether of bisphenol A with 4,4′-diaminodiphenylsulfone were studied with the Havriliak-Negami function. The system was cured isothermally at 140 °C using simultaneous kinetic and microdielectric studies.The relaxation time was calculated from the frequency fmax of the peak of the loss factor ε′′ versus frequency f. A linear relation exists between the logarithm of the relaxation time τ and the glass transition temperature Tg. Then, logτ follows the Di Benedetto equation revisited by Pascault and Williams allowing the prediction of the relaxation time τ during cure.The unrelaxed permittivity at high frequency εu, the relaxed or static permittivity εs and the skewness parameter β were found independent on the conversion or the curing time. The distribution parameter α decreases as curing time t increases. The difficulty of orientation of dipoles in the electric field due to vitrification is responsible of these behaviours. 相似文献
57.
The preparation of the nickel(II) complex of the diazacyclam ligand 1,3,6,10,12,15-hexaazatricyclo [13.3.1.16,10]eicosane (2) by the reaction of the nickel(II) complex of N-(2-aminoethyl)-1,3-diaminopropane with formaldehyde in MeOH solution is described. The crystal structure of [NiL](ClO4)2 has been determined. The nickel atom is four coordinate and planar with Ni-N bond lengths of 1.969(4) and 1.928(3)Å in a centrosymmetric structure. The basic diazacyclam ring system has a trans III configuration with the two additional six-membered rings fused in a chair conformation.The kinetics of the metal exchange:for the nickel complexes (1) and (2) have been studied in detail. Under the experimental conditions employed, with copper(II) in at least a tenfold excess, the reaction is independent of the copper(II) concentration. The copper(II) effectively scavenges the free ligand as the nickel(II) complex dissociates. For the nickel complex (1) k = 2 × 10–4 s–1 at 60°C and H = 126 ± 5 kJmol–1 and S298 = 61 ± 15 JK–1mol–1. For the complex (2), k = 1.8 × 10–4 s–1 at 60°C and H = 99 ± 6 kJmol–1 and S298 = –21 ± 10 JK–1 mol–1. 相似文献
58.
E. Delée L. Le Garrec I. Jullien S. Béranger J. C. Pascal H. Pinhas 《Chromatographia》1987,24(1):357-359
Summary A routine chiral analysis has been developed to control the optical purity of chiral drugs and to monitor their asymmetric
synthesis. The recent advent of new chiral stationary phases for HPLC enabled us to achieve the direct resolution of chiral
drugs without any derivatization.
The factors affecting chiral resolution on a new alpha1-acid glycoprotein column (EnantioPac, LKB) were assessed with three beta-aminoalcohols. 相似文献
59.
Pascal Brunerie Jean-Pierre Clrier Huguette Petit Grard Lhommet 《Journal of heterocyclic chemistry》1986,23(4):1183-1188
The reaction of acyl chlorides with cyclic five-membered β-enaminoesters gave exclusively N-acylated products while reaction of acyl chlorides with cyclic seven-membered β-enaminoesters gave only C-acylated products. In the case of cyclic six-membered β-enaminoesters, the reaction of acyl chlorides gave a mixture of N-acylated and C-acylated products. 相似文献
60.
Vincent Remusat Thierry Terme Armand Gellis Pascal Rathelot Patrice Vanelle 《Journal of heterocyclic chemistry》2004,41(2):221-225
A new heterocyclic bioreductive bis‐alkylating agent, 2,3‐bis(chloromethyl)benzo[g]quinoxaline‐5,10‐dione, was prepared in a four‐steps synthesis. It was shown to react under electron transfer conditions with 2‐nitropropane anion by an bis‐SRN1 mechanism to give three C‐alkylation products in excellent yields. Extension of this bis‐SRN1 reaction to various nitronate or malonate anions and S‐centered anions led to a new class of potentially active benzo[g]quinoxaline‐5,10‐dione derivatives. 相似文献