全文获取类型
收费全文 | 985篇 |
免费 | 47篇 |
国内免费 | 4篇 |
专业分类
化学 | 626篇 |
晶体学 | 16篇 |
力学 | 11篇 |
数学 | 139篇 |
物理学 | 244篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 36篇 |
2015年 | 23篇 |
2014年 | 33篇 |
2013年 | 50篇 |
2012年 | 58篇 |
2011年 | 58篇 |
2010年 | 44篇 |
2009年 | 48篇 |
2008年 | 70篇 |
2007年 | 55篇 |
2006年 | 46篇 |
2005年 | 44篇 |
2004年 | 34篇 |
2003年 | 28篇 |
2002年 | 39篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 4篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1036条查询结果,搜索用时 31 毫秒
21.
F. M. Bautista J. M. Campelo A. Garcia D. Luna J. M. Marinas A. A. Romero M. R. Urbano 《Reaction Kinetics and Catalysis Letters》1997,62(1):47-54
The vapor-phase catalytic alkylation of phenol with methanol and dimethyl carbonate on a series of differently prepared CrPO4 (Cr/P=1) and CrPO4-AlPO4 (CrAIP) catalysts, has been studied at different temperatures (473–673 K). The reaction is first order in phenol, giving
a mixture of O- and C-alkylated products (C-alkylation taking place preferentially at theortho-position). Moreover, dimethyl carbonate is a better methylating agent than methanol. 相似文献
22.
Ignés-Mullol J Claret J Albalat R Crusats J Reigada R Romero MT Sagués F 《Langmuir : the ACS journal of surfaces and colloids》2005,21(7):2948-2955
Preparation of Langmuir monolayers of a mixture of trans- and cis-isomers of an azobenzene derivative, 4-[4-[(4-octylphenyl)azo]phenoxy]butanoic acid, results in the segregation of birefringent trans-isomer domains embedded in an isotropic medium of cis-isomers. Brewster angle microscopy observations allow us to identify different textures inside the domains depending on surface pressure, temperature, and domain size. The evolution of the monolayer in the dark, from initial droplets formed after spreading to a stable stripe texture, is described. The dynamics of domain coalescence and some morphological transitions induced by temperature and surface pressure changes are also discussed. A simple theoretical model is included to supplement some of these experimental observations. 相似文献
23.
Inmaculada Beloso Paulo Prez‐Lourido Jesús Castro Jos A. García‐Vzquez Jaime Romero 《无机化学与普通化学杂志》2005,631(11):2101-2106
Heteroleptic nickel(II) complexes [NiL2L′] of a series of monoanionic and potentially bidentate N‐2‐pyridyl‐sulfonamide ligands [HL] and 2,2′‐bipyridine or 1,10‐Phenanthroline (L′) have been prepared by electrochemical oxidation of a nickel anode in an acetonitrile solution of the ligands. The complexes have been characterized by microanalysis, IR and electronic spectroscopy, magnetic measurements and LSI mass spectrometry. The crystal structure of [Ni(Ms6mepy)2(bipy)] has been determined by x‐ray diffraction and shows the metal in an octahedral NiN6 environment. Octahedral structures are also proposed for the other complexes with the N‐2‐pyridyl‐sulfonamide ligands acting as N,N′ or N, O bidentate systems, depending on the position of the methyl substituent on the pyridine ring. 相似文献
24.
Vadillo JM Palanco S Romero MD Laserna JJ 《Analytical and bioanalytical chemistry》1996,355(7-8):909-912
The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N(2) laser at 337.1 nm (3.65 J/cm(2)) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 microm is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells. 相似文献
25.
Cinabro D Henderson S Kinoshita K Liu T Saulnier M Wilson R Yamamoto H Sadoff AJ Ammar R Ball S Baringer P Coppage D Copty N Davis R Hancock N Kelly M Kwak N Lam H Kubota Y Lattery M Nelson JK Patton S Perticone D Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Nemati B O'Neill JJ Romero V Severini H Sun CR Zoeller MM Crawford G Fulton R Fujino D Gan KK Kagan H Kass R Lee J Malchow R Morrow F Skovpen Y Sung M White C Whitmore J Wilson P Butler F Fu X Kalbfleisch G Lambrecht M Ross WR 《Physical review letters》1993,70(24):3700-3704
26.
J. Sanmartín M. R. Bermejo J. A. García-Vázquez J. Romero A. Sousa J. Strähle A. Brodbeck 《Transition Metal Chemistry》1993,18(2):187-190
Summary The electrochemical oxidation of anodic metal (nickel or cobalt) in MeCN solutions of 1-hydroxy-2-pyridinethione (HPT) gives [Ni(PT)2], [Co(PT)2] or [Co(PT)3]. When 1,10-phenanthroline (phen) or 2,2-bipyridine (bipy) are added to the electrolytic phase the product is a complex, [Ni(PT)2L] or [Co(PT)2L] (L = bipy or phen). The i.r., u.v. and 1H- and 13C-n.m.r. spectra of the complexes are discussed.This paper was presented at the 5th Inorganic Chemistry Meeting of the Royal Spanish Chemical Society, Tossa de Mar, Girona, Spain, September 1991. 相似文献
27.
The fluorimetric determination of adrenaline is carried out in a continuous-flow assembly and by means of the molecular dissolved oxygen. The sample solution merges with an NaOH stream, then the resulting mixture is heated at 73 °C and led to the flow-cell of the fluorimeter. The flow-assembly is very simple and the procedure is quick (107 samples h–1) reproducible (R.S.D. 0.6%), selective and suitable to be applied to determination of adrenaline in formulations. Calibrations graph are linear over the ranges 0.05–15 and 20–40 mgl–1. 相似文献
28.
F. J. Romero M. C. Gallardo A. Czarnecka M. Koralewski J. del Cerro 《Journal of Thermal Analysis and Calorimetry》2007,87(2):357-363
The specific heat
and the enthalpy variation of a highly deuterated crystal of ferroelectric
triglycine selenate have been measured around its first-order phase transition
using the technique square modulated differential thermal analysis (SMDTA).
The low temperature variation rate has allowed analyzing the kinetics of the
phase transition. Due to an internal crack in the sample, the transition is
carried out in two steps and an intermediate region where the transition is
blocked and both phases coexist without transformation has been found. The
latent heat on cooling (L
c=1.32±0.02
J g–1) is higher than on heating (L
h=1.08±0.02 J g–1)
due to the thermal hysteresis and the great difference between the specific
heat in both phases. Nevertheless, the enthalpy balance is fulfilled on heating
and on cooling. 相似文献
29.
Romero R Bagur MG Sánchez-Viñas M Gázquez D 《Analytical and bioanalytical chemistry》2003,376(2):162-167
Biogenic amines, as dabsyl derivatives, were determined in beer samples, intermediate products, and raw materials (malt and maize) by HPLC. A procedure for the extraction of the amines from malt and maize with diluted hydrochloric acid was optimised by combining a Response Surface Methodology with a Simultaneous Decision Making Approach. The results of the analysis indicate that, in brewing, technology and hygiene are the decisive factors that determine the amine concentrations in the final product. 相似文献
30.
Benniston AC Harriman A Romero FM Ziessel R 《Dalton transactions (Cambridge, England : 2003)》2004,(8):1233-1238
The photophysical properties of closely-coupled, binuclear complexes formed by connecting two ruthenium(II) tris(2,2'-bipyridine) complexes via an alkynylene group differ significantly from those of the relevant mononuclear complex. In particular, the energy of the first triplet excited state is lowered relative to the parent complex, because of the presence of the alkynylene substituent, while the triplet lifetime is prolonged, in part, because of extended electron delocalization. We now report that the triplet lifetime is also affected by the nature of the spectator 2,2'-bipyridyl ligands. Thus, replacing the parent 2,2'-bipyridine ligands with the corresponding 4,4'-dinitro-substituted ligands serves to decrease the luminescence yield and lifetime. With the corresponding carboxylate ester, the luminescence yield and lifetime are increased. Perdeuteration of the parent 2,2'-bipyridine ligands also leads to a modest increase in the luminescence yield. Such observations are indicative of electronic coupling between the various metal-to-ligand, charge-transfer excited triplet states. Temperature dependence studies confirm that these excited states are closely spaced and thermally accessible at ambient temperature. For some of the binuclear complexes, the quantum yield for formation of the lowest-energy triplet state is significantly less than unity. 相似文献