全文获取类型
收费全文 | 746篇 |
免费 | 15篇 |
专业分类
化学 | 629篇 |
晶体学 | 4篇 |
力学 | 4篇 |
数学 | 36篇 |
物理学 | 88篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 25篇 |
2020年 | 19篇 |
2019年 | 27篇 |
2018年 | 36篇 |
2017年 | 28篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 23篇 |
2013年 | 60篇 |
2012年 | 25篇 |
2011年 | 46篇 |
2010年 | 39篇 |
2009年 | 34篇 |
2008年 | 43篇 |
2007年 | 55篇 |
2006年 | 40篇 |
2005年 | 37篇 |
2004年 | 32篇 |
2003年 | 22篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有761条查询结果,搜索用时 312 毫秒
741.
742.
Alexander A. Kuznetsov Anna Yu. Tsegelskaya Michael Yu. Belov Vladimir I. Berendyaev Sergey V. Lavrov Galina K. Semenova Anatoly L. Izyumnikov Nina V. Kozlova Boris V. Kotov 《Macromolecular Symposia》1998,128(1):203-219
Melts of aromatic carboxylic acids are found to be excellent reaction media for 1-pot high molecular weight polyimide synthesis from diamines and tetracarboxylic acid dianhydrides. No reversible reaction of polyamic acids (PAA) formation was observed. The effect of the reactivity equalization was observed for low- and high reactive diamines in acid media. The intrinsic acid catalysis of the imidization reaction was shown to take place also in polycyclization of PAA in concentrated solutions in amic solvents. It is found that the dependence of relative imidization rate (% conv./min) vs. AA/N-MP ratio for model low molecular and oligomeric amic acids (AA) in N-MP at 140–150°C possesses a sharp maximum near the molar ratio 1:1, the imidization rate at the point of the maximum being an order of magnitude higher than that for diluted solutions. A scheme is proposed which includes the opportunity of two reaction channels to occur: A usual one (I) and a catalytic one (II). In diluted solutions and in solid phase experiments with easy evacuation of volatile products, the role of catalytic channel II is low. To the contrary, in high concentrated solutions or in solid phase experiments under the conditions exluding volatile products evacuation, the catalytic channel becomes the key one. It is proposed that the catalytic reaction proceeds via the common acid catalysis mechanism, the solvent and water playing the role of co-catalysts, probably through the mechanism of ionic dissociation of AA or hydrogen- bound complex AA-solvent. It is shown that the water released in the course of solid phase imidization of phtalamic acid at 140°C under the conditions where vaporization is impossible causes a sharp autocatalytic effect after initial 20%-conversion period to obtain entirely imidizied product. 相似文献
743.
Galina Shagisultanova Irina Orlova Luydmila Ardasheva Elena Popova 《Macromolecular Symposia》1998,136(1):91-97
In the present paper we report about the last advances concerning the structure and properties of electrochromic photosensitive metallopolymers based on the complexes of Pt, Pd, Ni, Co, Cu with Schiff's bases. The criteria of selection of the object for the synthesis of new polymers with one-dimensional, reversible, controlled photo- and electroinduced charge transfer was determined. A model for the polymer structure was proposed. The ohmic resistance in the direction parallel and perpendicular to the microelectrode surface of gold-coated α-Al2O3 differs as 1: 106-109 depending on the polymer and film thickness. A qualitative model of the processes of light energy accumulation was proposed. 相似文献
744.
Tatiana Budtova Alexander Vilesov Vladimir Bertsev Galina Elikina Ibragim Suleimenov Yurii Tolmachev 《Macromolecular rapid communications》1996,17(2):87-90
A new optically active medium for lasers — a polyelectrolyte hydrogen swollen in a mixture of water + alcohol + dye — is presented. An anomalous dependence of the absorbance on the composition of the mixture is observed. It shows a maximum which corresponds to the composition when the hydrogel starts to swell as a hydrophilic network. 相似文献
745.
Yuri G. Gololobov Anush S. Oganesyan Galina D. Kolomnikova Svetlana A. Kuznetsova Leonid F. Kasukhin 《Heteroatom Chemistry》1990,1(2):123-134
The new type of α-alkenyl esters of phosphorus acids containing ammonium or phosphonium groups in unsaturated radicals as well as carbonyl or other complexes of Mo, Cr, W, Mn, or Pt with such organophosphorus ligands have been described. The alkenyl phosphates undergo dealkylation upon heating to give betaines. This conversion results in a substantial decrease of an anticholinesterase activity of the compounds and in a sharp rise of their hydrolytic stability. The prototropic rearrangement is observed for the phosphonium betaines. 相似文献
746.
Galina F. Makhaeva Nadezhda V. Kovaleva Natalia P. Boltneva Elena V. Rudakova Sofya V. Lushchekina Tatiana Yu. Astakhova Igor V. Serkov Alexey N. Proshin Eugene V. Radchenko Vladimir A. Palyulin Jan Korabecny Ondrej Soukup Sergey O. Bachurin Rudy J. Richardson 《Molecules (Basel, Switzerland)》2022,27(3)
Using two ways of functionalizing amiridine—acylation with chloroacetic acid chloride and reaction with thiophosgene—we have synthesized new homobivalent bis-amiridines joined by two different spacers—bis-N-acyl-alkylene (3) and bis-N-thiourea-alkylene (5) —as potential multifunctional agents for the treatment of Alzheimer’s disease (AD). All compounds exhibited high inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity for BChE. These new agents displayed negligible carboxylesterase inhibition, suggesting a probable lack of untoward drug–drug interactions arising from hydrolytic biotransformation. Compounds 3 with bis-N-acyl-alkylene spacers were more potent inhibitors of both cholinesterases compared to compounds 5 and the parent amiridine. The lead compounds 3a–c exhibited an IC50(AChE) = 2.9–1.4 µM, IC50(BChE) = 0.13–0.067 µM, and 14–18% propidium displacement at 20 μM. Kinetic studies of compounds 3a and 5d indicated mixed-type reversible inhibition. Molecular docking revealed favorable poses in both catalytic and peripheral AChE sites. Propidium displacement from the peripheral site by the hybrids suggests their potential to hinder AChE-assisted Aβ42 aggregation. Conjugates 3 had no effect on Aβ42 self-aggregation, whereas compounds 5c–e (m = 4, 5, 6) showed mild (13–17%) inhibition. The greatest difference between conjugates 3 and 5 was their antioxidant activity. Bis-amiridines 3 with N-acylalkylene spacers were nearly inactive in ABTS and FRAP tests, whereas compounds 5 with thiourea in the spacers demonstrated high antioxidant activity, especially in the ABTS test (TEAC = 1.2–2.1), in agreement with their significantly lower HOMO-LUMO gap values. Calculated ADMET parameters for all conjugates predicted favorable blood–brain barrier permeability and intestinal absorption, as well as a low propensity for cardiac toxicity. Thus, it was possible to obtain amiridine derivatives whose potencies against AChE and BChE equaled (5) or exceeded (3) that of the parent compound, amiridine. Overall, based on their expanded and balanced pharmacological profiles, conjugates 5c–e appear promising for future optimization and development as multitarget anti-AD agents. 相似文献
747.
Journal of Solid State Electrochemistry - 相似文献
748.
A system involving homopolymerisation of a 3‐functional monomer has been studied by using an off‐lattice long‐range percolation model. The elementary reaction steps were controlled by substitution effects and by local concentrations of units. The latter were controlled by setting a constant value to a range‐of‐reaction parameter called the capture radius. The critical conversion at gelation in the system turned to the classical one as the value of capture radius increased. 相似文献
749.
Vladimir I. Lozinsky Roman V. Ivanov Elena V. Kalinina Galina I. Timofeeva Alexei R. Khokhlov 《Macromolecular rapid communications》2001,22(17):1441-1446
The radical polymerisation of acrylamide initiated with a persulfate/tertiary amine redox pair was performed in liquid (+5 to +35°C) and moderately frozen (–10 to –30°C) aqueous solutions. The reaction in frozen systems resulted in the pronounced increase in the molecular weight of the polymer. The temperature dependence of the yield and molecular weight of cryogenically produced polyacrylamide were of extreme character with a maximum for both parameters in the vicinity of –12.5°C. 相似文献
750.
Sergei S. Sheiko Gabi Eckert Galina Ignat'eva Aziz M. Muzafarov Jochen Spickermann Hans J. Rder Martin Mller 《Macromolecular rapid communications》1996,17(5):283-297
Adsorption and aggregation of carbosiloxane dendrimers on mica and pyrolytic graphite were investigated by scanning force microscopy (SFM). The aggregation process started from (i) single molecules which coagulated to (ii) clusters and (iii) fluid droplets followed by formation of (iv) a complete layer on the solid substrate. The molecules were displayed as a globular particle with a diameter of about 2.5 nm. Tapping SFM of the liquid was possible due to the fact that the dendrimer undergoes a transition to a viscoelastic state below the tapping frequency of about 360 kHz. Dynamic shear compliance experiments have shown a plateau of 5 · 10−7 Pa−1 around this frequency. Dendrimer droplets slowly spread into polygonal lamellae with a thickness of two molecular layers. The structures indicate a rather regular dense packing of the globular molecules. 相似文献