全文获取类型
收费全文 | 18633篇 |
免费 | 855篇 |
国内免费 | 1442篇 |
专业分类
化学 | 14779篇 |
晶体学 | 150篇 |
力学 | 342篇 |
综合类 | 10篇 |
数学 | 2349篇 |
物理学 | 3300篇 |
出版年
2023年 | 126篇 |
2022年 | 444篇 |
2021年 | 514篇 |
2020年 | 320篇 |
2019年 | 358篇 |
2018年 | 291篇 |
2017年 | 299篇 |
2016年 | 667篇 |
2015年 | 549篇 |
2014年 | 621篇 |
2013年 | 1342篇 |
2012年 | 1468篇 |
2011年 | 1581篇 |
2010年 | 897篇 |
2009年 | 1124篇 |
2008年 | 1125篇 |
2007年 | 1101篇 |
2006年 | 922篇 |
2005年 | 981篇 |
2004年 | 1231篇 |
2003年 | 862篇 |
2002年 | 799篇 |
2001年 | 383篇 |
2000年 | 317篇 |
1999年 | 240篇 |
1998年 | 219篇 |
1997年 | 196篇 |
1996年 | 201篇 |
1995年 | 165篇 |
1994年 | 121篇 |
1993年 | 146篇 |
1992年 | 121篇 |
1991年 | 82篇 |
1990年 | 82篇 |
1989年 | 69篇 |
1988年 | 67篇 |
1987年 | 62篇 |
1986年 | 70篇 |
1985年 | 91篇 |
1984年 | 96篇 |
1983年 | 67篇 |
1982年 | 59篇 |
1981年 | 62篇 |
1980年 | 53篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 35篇 |
1976年 | 27篇 |
1975年 | 27篇 |
1974年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
941.
Rau María S. Gennero de Chialvo María Rosa Chialvo Abel C. 《Journal of Solid State Electrochemistry》2012,16(5):1893-1900
The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline
smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did
not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting
from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbon monoxide (COad) and hydroxyl (OHad). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species
(θ
CO and θ
OH) and the CO and CO2 pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the
experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences
of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure
of CO and CO2. Thus, it was demonstrated that the Gilman’s mechanism accurately describes the experimental results on steady state of the
COOR on these metals. 相似文献
942.
F. Gonzalez-Muñoz A. Pérez-Oseguera J. Cassani M. Jiménez-Estrada R. Vazquez-Duhalt A. López-Munguía 《Journal of carbohydrate chemistry》2013,32(3):275-283
ABSTRACT The enzymatic synthesis of ß2-2' and ß2-1'-D- fructopyranosyl glycerol was carried out with levansucrase from Bacillus circulans or B.subtilis, using sucrose as fructosyl donor and glycerol. The specificity and efficiency of the enzyme was modified by controlling both the water and the total substrate concentrations. The products were purified by HPLC and analyzed by 1H, 13C NMR and GC-MS. 相似文献
943.
Alma Viso Roberto Fernández de la Pradilla Ana García Carlos Guerrero-Strachan Marta Alonso Mariola Tortosa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1229-1234
Abstract Readily available p-tolylsulfinimines undergo highly stereoselective [3 + 2] cycloadditions with azomethine ylides generated from α -iminoesters and LDA to produce N-sulfinylimidazolidines. In the presence of Lewis acids, p-tolylsulfinimines react with glycine iminoester enolates to produce N-sulfinylimidazolidines, after cyclization of open chain intermediates. These mechanistically diverse processes take place with excellent regio-, stereo-, and facial selectivities, and the latter is opposite to most known reactions involving sulfinimines. Some of the resulting imidazolidines have been transformed into examples of a novel class of nonsymmetrical vicinal diamines using reductive and/or hydrolytic protocols. 相似文献
944.
945.
Whei Oh Lin Vanderléa De Souza 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract As part of our studies in preparation and physical properties of Potential ligands containing l-phosphoryl(P?O)-3-3-carbonyI(C?X, X?NH, O or S) group, we have investigated the intrdinta molecular hydrogen bonding of diisoproxy- phosphorylquanidine[l] as well as the tautomerism of phosphoryl benzylisothiourea. These are of interest as in interpretation of their chelation behavior as well as in development of other potential ligands for specific metal cations. 相似文献
946.
947.
Muñoz MP de la Torre MC Sierra MA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(15):4499-4504
Pt versus Au: Platinum-catalysed addition of nucleophiles to allenes follows a distinctly different pathway to the process catalysed by gold(I) complexes; the platinum catalyst leads to different products with indoles involving a bisindolylation reaction, whereas gold(I) gives allyl indoles from a single addition (see scheme). 相似文献
948.
A fast and sensitive method for the simultaneous determination of Sudan dyes (I, II, III, and IV) in food samples was developed for the first time using partial filling micellar electrokinectic chromatography-mass spectrometry (MEKC-MS). The use of MEKC was essential to achieve the separation of these neutral analytes, while the partial filling technique was necessary to avoid the contamination of the ion source with non-volatile micelles. MEKC separation and MS detection conditions were optimized in order to achieve a fast, efficient, and sensitive separation of the four dyes. Filling 25% of the capillary with an MEKC solution containing 40 mM ammonium bicarbonate, 25 mM SDS, and 32.5% (v/v) acetonitrile, a baseline separation of the four azo-dyes was obtained in 10 min. Tandem MS was investigated in order to improve the sensitivity and selectivity of the analysis. Limits of detection (LOD) values 5, 8, 15, and 29 times better were obtained for Sudan III, I, II, and IV, respectively, using partial filling MEKC-MS/MS instead of partial filling MEKC-MS. Under optimized conditions, LOD from 0.05 to 0.2 μg/mL were obtained. The suitability of the developed method was demonstrated through the fast and sensitive determination of Sudan I, II, III, and IV in spiked chilli powder samples. This determination could not be achieved by MEKC-UV due to the existence of several interfering compounds from the matrix. 相似文献
949.
Reboredo S Reyes E Vicario JL Badía D Carrillo L de Cózar A Cossío FP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7179-7188
The catalytic enantioselective [3+2] cycloaddition between azomethine ylides and α,β-unsaturated aldehydes catalyzed by α,α-diphenylprolinol has been studied in detail. In particular, the reaction has been extended to the use of 2-alkenylidene aminomalonates generated in situ as azomethine ylide precursors. These reactions lead to the formation of pyrrolidines containing a 5-alkenyl side chain with potential for chemical manipulation. Moreover, a detailed and concise computational study has been carried out to understand the exact nature of the mechanism of this reaction and especially the consequences derived from the incorporation of the chiral secondary amine catalyst on the reaction pathway. 相似文献
950.
Gao J Lowe MA Conte S Burkhardt SE Abruña HD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8521-8526
Organosulfur compounds with multiple thiol groups are promising for high gravimetric energy density electrochemical energy storage. We have synthesized a poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT)/poly(3,4-ethylenedioxythiophene) (PEDOT) composite cathode for lithium-ion batteries with a new method and investigated its electrochemical behavior by charge/discharge cycles and cyclic voltammetry (CV) in an ether-based electrolyte. Based on a comparison of the electrochemical performance with a carbonate-based electrolyte, we found a much higher discharge capacity, but also a very attractive cycling performance of PDMcT by using a tetra(ethylene glycol) dimethyl ether (TEGDME)-based electrolyte. The first discharge capacity of the as-synthesized PDMcT/PEDOT composite approached 210 mAh g(-1) in the TEGDME-based electrolyte. CV results clearly show that the redox reactions of PDMcT are highly reversible in this TEGDME-based electrolyte. The reversible capacity remained around 120 mAh g(-1) after 20 charge/discharge cycles. With improved cycling performance and very low cost, PDMcT could become a very promising cathode material when combined with a TEGDME-based electrolyte. The poor capacity in the carbonate-based electrolyte is a consequence of the irreversible reaction of the DMcT monomer and dimer with the solvent, emphasizing the importance of electrolyte chemistry when studying molecular-based battery materials. 相似文献