全文获取类型
收费全文 | 63711篇 |
免费 | 1736篇 |
国内免费 | 814篇 |
专业分类
化学 | 30737篇 |
晶体学 | 1067篇 |
力学 | 3399篇 |
综合类 | 78篇 |
数学 | 5076篇 |
物理学 | 25904篇 |
出版年
2022年 | 696篇 |
2021年 | 658篇 |
2020年 | 616篇 |
2019年 | 600篇 |
2018年 | 748篇 |
2017年 | 632篇 |
2016年 | 1130篇 |
2015年 | 884篇 |
2014年 | 1235篇 |
2013年 | 2822篇 |
2012年 | 2785篇 |
2011年 | 3528篇 |
2010年 | 2429篇 |
2009年 | 2486篇 |
2008年 | 3071篇 |
2007年 | 2860篇 |
2006年 | 2698篇 |
2005年 | 2372篇 |
2004年 | 2151篇 |
2003年 | 1867篇 |
2002年 | 1789篇 |
2001年 | 3102篇 |
2000年 | 2253篇 |
1999年 | 1658篇 |
1998年 | 1170篇 |
1997年 | 1157篇 |
1996年 | 966篇 |
1995年 | 860篇 |
1994年 | 764篇 |
1993年 | 695篇 |
1992年 | 989篇 |
1991年 | 1006篇 |
1990年 | 891篇 |
1989年 | 780篇 |
1988年 | 746篇 |
1987年 | 809篇 |
1986年 | 672篇 |
1985年 | 897篇 |
1984年 | 839篇 |
1983年 | 579篇 |
1982年 | 569篇 |
1981年 | 535篇 |
1980年 | 496篇 |
1979年 | 621篇 |
1978年 | 650篇 |
1977年 | 660篇 |
1976年 | 576篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
W. Z. Chen Y. F. Zhao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2054-2063
In this article, we used the Atherton–Todd reaction to synthesize amino acid methyl ester 5′-phosphoamidates of uridine as prodrugs. Their structures were confirmed by 1H NMR, 31P NMR, 13C NMR, IR, and mass spectrometry. Supplemental materials are available for this article. Go to the publisher′s online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
912.
G. F. D'alelio W. A. Fessler Y. Giza D. M. Feigl A. Chang M. Saha 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(1):159-185
Transamidation reactions of nonpolymerizing systems involving benzamides, phthalimides, arylsulfonamides, benzenedisulfonamides and -disulfonim-ides, and saccharins are described. The study includes reactions of both N-substituted and unsubstituted amides and imides with anilines and aniline hydrochlorides. An evaluation of the results of these reactions, aimed at establishing the optimum conditions for transamidations in polymerizing systems, is also presented. 相似文献
913.
The photoreduction behavior of alkyl viologen compounds in a PVA matrix was investigated. The initial photoreduction of alkyl viologens and related polyviologens follows second-order reaction kinetics, and the respective rate constants, which vary only slightly with alkyl chain length, were determined. While the polymer effect was not remarkable in a PVA matrix, the association behavior of radical cations was similar to that found in a 2-propanol aqueous solution. 相似文献
914.
Poly[3,3-bis(chloromethyl)] oxetane in vacuo, after λ-irradiation at 77°K and room temperature, showed ESR spectra consisting of a triplet (hfs of 22.0G) and a doublet (hfs of 17.8G), respectively. The triplet ESR spectrum is attributed to the -CH2-C(CH2Cl)-CH2 -O- radical and the doublet ESR spectrum is attributed to the -CH2-C(CH2Cl)2-CH-O- radical. The G values for formation of radicals are estimated to be 0.3 and 0.5 at 298 and 77°K, respectively. 相似文献
915.
C. Bauvais F. Barbault Y. Zhu M. Petitjean 《SAR and QSAR in environmental research》2013,24(3):253-264
A theoretical investigation was carried out on the retention and separation of enantiomeric molecules including nonsteroidal anti-inflammatory drugs, anti-neoplastic compounds and N-derivatized amino acids by capillary electrophoresis using macrocyclic antibiotics, a new class of chiral selectors, as stationary phase. Firstly docking methods were used to study the enantiorecognition in chiral electrophoresis. The molecular dynamics simulations of the two diastereoisomer complexes were then performed in order to understand how these antibiotics recognize the enantiomers. Another approach was applied in this study to establish a quantitative structure-enantioselectivity relationship (QSER) model, able to describe the resolution of a series of chiral compounds in capillary electrophoresis using vancomycin as the resolving agent. 相似文献
916.
W. Chen X. L. Xu P. Zhou Y. M. Cui Y. G. Li 《Russian Journal of Coordination Chemistry》2013,39(3):301-304
Two silver(I) compounds, [Ag(R,R-hxn)](C7H4BrO2) · 2H2O (I) (Chxn = 1,2-diaminocyclohexane) and [Ag(C5H6N2)2]2(C8H4O4) · 10H2O (II), were synthesized and complex I was structurally characterized by X-ray crystallography. Compound I contains a catena-(trans-1,2-diaminocyclohexane) silver polycation ([Ag(Chxn)]∞) in a roughly linear fashion, while II possesses a linear-type silver monocation. Compounds I and II were evaluated for their inhibitory activities against Helicobacter pylori urease in vitro. Both were found to have strong inhibitory activities against H. pylori urease comparable to that of acetohydroxamic acid. 相似文献
917.
Y. E. Du Z. Q. Xing Y. F. Liang Z. B. Han 《Russian Journal of Coordination Chemistry》2013,39(1):114-118
A new metal-organic coordination polymer [Zn(Pydc)(Dppz)] n (I) (H2Pydc = 2,6-pyridinedicarboxylic acid, Dppz = dipyrido[3,2-a:2′,3′-c]phenazine) was hydrothermally synthesized and characterized by elemental analysis, IR and X-ray single-crystal diffraction. The X-ray diffraction analysis reveals that I crystallizes in the monoclinic system, space group P21/c. The Pydc2? ligands adopt O,N,O′-tridentate chelating and monodentate bridging coordination mode to link two adjacent Zn2+ ions to form a one-dimensional (1D) zigzag chain. The adjacent chains are further linked through hydrogen bonds and π-π stacking interactions, forming a three-dimensional (3D) supramolecular framework. The unit cell parameters for I: a = 7.332(3) Å, b = 36.023(9) Å, c = 7.8838(13) Å, β = 105.65(3)○, V = 2005.1(10) Å3, Z = 4. 相似文献
918.
Density functional theory (DFT) and the dispersion corrected DFT have been used to investigate the hygroscopicity of ammonium dinitramide (ADN). Calculation results show that the gaseous ADN has a strong hydrogen bond. But the ionic pair structure NH4 + · N(NO2)? is stabilized upon the addition of water molecules. Natural bond orbital calculations suggest that the intra- and intermolecular orbital interactions LP(O) → σ*(N–H) or LP(O) → σ*(O–H) make the system stabilized as a whole. En energy decomposition analysis reveals that the interactions between ADN and H2O are dominated by the electrostatic and orbital interactions. The formation reactions become more spontaneous with the increasing number of water molecules but can be weakened by the growing temperature from 200 to 400 K. Moreover, the molecular dynamic method is applied to explore a more realistic cluster model to study the interactions between ADN and H2O. 相似文献
919.
F. Yang J. Mao X. W. He L. X. Chen Y. K. Zhang 《Analytical and bioanalytical chemistry》2013,405(21):6639-6648
In this study, a boronate-silica hybrid affinity monolith was prepared for specific capture of glycoproteins at neutral pH condition. The monolith was synthesized via a facile one-pot procedure in a stainless steel column by concurrently mixing hydrolyzed alkoxysilanes tetramethoxysilane and vinyltrimethoxysilane, organic monomer 3-acrylamidophenylboronic acid and initiator 2,2′-azobisisobutyronitrile together. The polycondensation of alkoxysilanes and copolymerization of organic monomer and vinyl-silica monolith were carried out successively by reacting at different temperatures. After optimizing the preparation conditions, the resulting hybrid affinity monolith was systematically characterized and exhibited excellent affinity to both cis-diol-containing small molecules and glycoproteins at neutral and physiological pH, including adenosine, horseradish peroxidase, transferrin and ovalbumin. The binding capacity of ovalbumin on monolith was measured to be 2.5 mg g?1 at pH 7.0. Furthermore, the hybrid affinity monolith was applied to the separation of transferrin from bovine serum sample at a physiological condition. Good repeatability was obtained and the relative standard deviations of retention time were 1.15 and 4.77 % (n?=?5) for run-to-run and column-to-column, respectively. 相似文献
920.
The methyl pheophorbide-a and methyl pheophorbide-b were used as starting materials and converted to purpurin-18 ester by ring-opening and rearrangement reaction in their exocyclic ring. N-Substituted purpurin-18 imides were obtained from purpurin-18 ester through amidation reaction of six-membered cyclic anhydride. Further chemical modifications along their peripheries were carried out by a variety of common reactions, including electrophilic substitution, Wittig reaction, allomerization and Vilsmeier reaction, to afford the title compounds with long-wavelength absorption. The structures of all new chlorins were characterized by elemental analysis, IR, UV–vis and 1H NMR spectra. 相似文献