全文获取类型
收费全文 | 6626篇 |
免费 | 316篇 |
国内免费 | 29篇 |
专业分类
化学 | 4816篇 |
晶体学 | 29篇 |
力学 | 111篇 |
数学 | 592篇 |
物理学 | 933篇 |
无线电 | 490篇 |
出版年
2023年 | 70篇 |
2022年 | 154篇 |
2021年 | 227篇 |
2020年 | 182篇 |
2019年 | 167篇 |
2018年 | 97篇 |
2017年 | 90篇 |
2016年 | 250篇 |
2015年 | 252篇 |
2014年 | 249篇 |
2013年 | 374篇 |
2012年 | 460篇 |
2011年 | 517篇 |
2010年 | 299篇 |
2009年 | 271篇 |
2008年 | 423篇 |
2007年 | 387篇 |
2006年 | 364篇 |
2005年 | 269篇 |
2004年 | 288篇 |
2003年 | 214篇 |
2002年 | 210篇 |
2001年 | 84篇 |
2000年 | 101篇 |
1999年 | 63篇 |
1998年 | 62篇 |
1997年 | 51篇 |
1996年 | 55篇 |
1995年 | 60篇 |
1994年 | 52篇 |
1993年 | 39篇 |
1992年 | 38篇 |
1991年 | 43篇 |
1990年 | 41篇 |
1989年 | 31篇 |
1988年 | 32篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 45篇 |
1984年 | 45篇 |
1983年 | 33篇 |
1982年 | 33篇 |
1981年 | 36篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 24篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1974年 | 13篇 |
排序方式: 共有6971条查询结果,搜索用时 0 毫秒
81.
A major challenge in the area of DNA detection is the development of rapid methods that do not require polymerase chain reaction
(PCR) amplification of the genetic sample. The PCR amplification step increases the cost of the assay, the complexity of the
detection, and the quantity of DNA required for the assay. In this context, methods that are able to perform DNA analyses
with ultrasensitivity have recently been investigated with the aim of developing new PCR-free detection protocols. Functionalized
gold nanoparticles have played a central role in the development of such methods. Here, possibilities offered by functionalized
gold nanoparticle in the ultrasensitive detection of DNA are discussed. The different functionalization protocols available
for gold nanoparticles and the principal DNA detection methods that are able to detect DNA at the femtomolar to attomolar
level are presented. 相似文献
82.
Smith EF Garcia IJ Briggs D Licence P 《Chemical communications (Cambridge, England)》2005,(45):5633-5635
The in situ monitoring of catalysis in Room Temperature Ionic Liquids (RTILs) is fundamental to the understanding of catalytic processes and the role of RTILs in catalytic turnover; we describe how XPS can be used to give information on both pure RTILs and catalytically-active RTIL-based solutions. 相似文献
83.
Engineering Homochiral Metal–Organic Frameworks by Spatially Separating 1D Chiral Metal–Peptide Ladders: Tuning the Pore Size for Enantioselective Adsorption 下载免费PDF全文
Dr. Kyriakos C. Stylianou Dr. Laura Gómez Dr. Inhar Imaz Dr. Cristóbal Verdugo‐Escamilla Dr. Xavi Ribas Prof. Daniel Maspoch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):9964-9969
The reaction of the chiral dipeptide glycyl‐L(S)‐glutamate with CoII ions produces chiral ladders that can be used as rigid 1D building units. Spatial separation of these building units with linkers of different lengths allows the engineering of homochiral porous MOFs with enhanced pore sizes, pore volumes, and surface areas. This strategy enables the synthesis of a family of isoreticular MOFs, in which the pore size dictates the enantioselective adsorption of chiral molecules (in terms of their size and enantiomeric excess). 相似文献
84.
The diffusion of liposomes and PL/DNA complexes in mucin and collagen solutions, considered to model ‘in vivo’ colloidal gene delivery vector transport, is studied with FCS. The diffusion of defined liposomes is investigated as a function of particle size, surface charge, and the deviation from the Stokes‐Einstein behavior. In all cases the self‐diffusion coefficient decreases exponentially with polymer concentration. The same surface charge dependence of diffusion is observed in mucin for PL/DNA complexes with either positive or negative excess charge. Incubation of positively‐charged PL/DNA complexes in a natural lung surfactant lipid increases the diffusion coefficients to almost the same as for the negatively‐charged PL/DNA complexes.
85.
Suero MG De la Campa R Torre-Fernández L García-Granda S Flórez J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7287-7295
The successive coupling of an alkoxy(aryl/heteroaryl)carbene complex of chromium with either a ketone or an imide lithium enolate and then a 3-substituted (H, TMS, PhCH(2), PhCH(2)CH(2), Me) propargylic organomagnesium reagent has afforded novel hydroxy-substituted bicyclic [4.3.0]-γ-alkylidene-2-butenolides with three modular points that has allowed the efficient introduction of molecular complexity, including a homopropargylic alcohol core. The selective formation of these five- or six-component heterobicyclisation products is the result of the regioselective integration of the Grignard reagent as a propargyl fragment followed by a cascade CO/alkyne/CO insertion, ketene trapping and elimination sequence. By using lithium enolates of chiral N-acetyl-2-oxazolidinones and the corresponding propargylic organocerium reagents, both enantiomers of these bicyclic heterocycles were efficiently prepared with very high enantiomeric purity. Architecturally, these fused bicyclic butenolides are characterised by a highly unsaturated and oxygenated core and they exhibit strong blue fluorescence in solution. 相似文献
86.
E. I. Klimova E. A. Vazquez Lopez T. Klimova M. Martinez Garcia Ortega S. Hernandez L. Ruiz Ramirez 《Russian Journal of General Chemistry》2004,74(11):1757-1762
Ferrocenyltetrahydropyrimidin-2-ones were prepared by reactions of linear and cyclic ,-unsaturated ketones of the ferrocene series with urea in i-PrOH in the presence of t-BuOK. The structures of the compounds prepared were studied by 1H and 13C NMR and IR spectroscopy, and also by single crystal X-ray diffraction.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1887–1893.Original Russian Text Copyright © 2004 by E. Klimova, Lorez, T. Klimova, Garcia, Hernandez, Ramirez.This revised version was published online in April 2005 with a corrected cover date. 相似文献
87.
Armentano D De Munno G Di Donna L Sindona G Giorgi G Salvini L Napoli A 《Journal of the American Society for Mass Spectrometry》2004,15(2):268-279
Electrospray tandem mass spectrometry (ESI-MS/MS) is used to evaluate the assembling of cytosine and thymine nucleosides in the gas phase, through the formation of hydrogen bonded supermolecules. Mixtures of cytidine analogues and homologues deliver in the gas phase proton-bound heterodimers stabilized by multiple interactions, as proven by the kinetics of their dissociation into the corresponding protonated monomers. Theoretical calculations, performed on initial structures of methylcytosine homodimers available in the literature, converged to a minimized structure whereby the two pyrimidine rings interact through the formation of three hydrogen bonds of similar energy. The crystallographic data here reported show the equivalency of the two interacting pyrimidines which is attributable to the presence of an inversion center. Thymine and uracil pyrimidyl nucleosides form, by ESI, gaseous proton-bound dimers. The kinetic of their dissociation into the related protonated monomers shows that the nucleobases are weekly interacting through a single hydrogen bond. The minimized structure of the protonated heterodimer formed by thymine and N-1-methylthymine confirmed the existence of mainly one hydrogen bond which links the two nucleobases through the O4 oxygens. No crystallographic data exists on thymine proton-bound species, nor have we been able to obtain these aggregates in the solid phase. The gaseous phase, under high vacuum conditions, seems therefore a suitable environment where vanishing structures produced by ESI can be studied with a good degree of approximation. 相似文献
88.
el Hajjouji H Belmonte E García-López J Fernández I Iglesias MJ Roces L García-Granda S El Laghdach A López Ortiz F 《Organic & biomolecular chemistry》2012,10(29):5647-5658
ortho-Lithiation of N,N-diisopropyl-P,P-diphenylphosphinothioic amide using n-BuLi in the presence of TMEDA in diethyl ether followed by electrophilic trapping is described as an efficient method for the synthesis of ortho-functionalised derivatives in high yields. The structural modification of the phosphinothioic amide includes C-X (X = P, S, Si, Sn, I) and C-C bond forming reactions with a large variety of electrophiles. Additional applications based on functional group transformations are also reported. They include imine formation, desulfurization and Suzuki cross-coupling reactions on selected compounds. 相似文献
89.
Anaïs Geny Dr. Nicolas Agenet Dr. Laura Iannazzo Max Malacria Prof. Dr. Corinne Aubert Dr. Vincent Gandon Dr. 《Angewandte Chemie (International ed. in English)》2009,48(10):1810-1813
Cobalt cyclopentadienyl complexes incorporating a fumarate and a CO ligand (see picture) efficiently catalyze inter‐ and intramolecular [2+2+2] cycloadditions of alkynes, nitriles, and/or alkenes to give benzenes, pyridines, or 1,3‐cyclohexadienes. Unlike catalysts such as [CpCo(CO)2] or [CpCo(C2H4)2] (Cp=C5H5), they are air‐stable, easy to handle, compatible with microwave conditions, and do not necessarily require irradiation to be active.
90.
Jovita Mendoza-Barrón Araceli Jacobo-Azuara Roberto Leyva-Ramos Ma. Selene Berber-Mendoza Rosa Ma. Guerrero-Coronado Laura Fuentes-Rubio J. Merced Martínez-Rosales 《Adsorption》2011,17(3):489-496
In this study a surfactant-modified zeolite (SMZ) was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium
(HDTMA) bromide on a clinoptilolite. The adsorption of the surfactant modified the surface properties of the clinoptilolite
and enhanced the anionic capacity of the SMZ. The adsorption equilibrium data of As(V) from the water solution on the SMZ
were obtained in a batch adsorber, and the Langmuir isotherm matched the data reasonably well. The As(V) adsorption capacity
of the SMZ was 12.5 times greater than that of the clinoptilolite. The adsorption of As(V) on SMZ was mainly due to the interactions
between the anionic sites of the SMZ and the As(V) anions in water solution. The adsorption capacity of the SMZ was dependent
on the solution pH. The adsorption capacity was increased and decreased by augmenting the pH from 5 to 7 and from 7 to 12,
respectively. This unusual behavior was due to the fact that the affinity of the As(V) for the SMZ was dependent on the As(V)
species that were present in solution. The adsorption capacity of the SMZ was slightly favored by decreasing the temperature
from 25 to 15 °C. The heat of adsorption was estimated to be ΔH
ads=−46.82 KJ/mol, indicating that the adsorption was exothermic and the As(V) was chemisorbed on the SMZ. 相似文献