全文获取类型
收费全文 | 1361篇 |
免费 | 30篇 |
国内免费 | 14篇 |
专业分类
化学 | 796篇 |
晶体学 | 10篇 |
力学 | 40篇 |
数学 | 328篇 |
物理学 | 231篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 14篇 |
2020年 | 23篇 |
2019年 | 12篇 |
2018年 | 28篇 |
2017年 | 24篇 |
2016年 | 48篇 |
2015年 | 54篇 |
2014年 | 42篇 |
2013年 | 92篇 |
2012年 | 78篇 |
2011年 | 100篇 |
2010年 | 80篇 |
2009年 | 49篇 |
2008年 | 79篇 |
2007年 | 81篇 |
2006年 | 51篇 |
2005年 | 54篇 |
2004年 | 60篇 |
2003年 | 35篇 |
2002年 | 43篇 |
2001年 | 21篇 |
2000年 | 31篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1966年 | 6篇 |
1965年 | 4篇 |
1962年 | 6篇 |
1959年 | 7篇 |
1958年 | 7篇 |
1957年 | 22篇 |
1956年 | 13篇 |
1955年 | 15篇 |
排序方式: 共有1405条查询结果,搜索用时 15 毫秒
921.
922.
Macíčková-Cahová H Pohl R Horáková P Havran L Špaček J Fojta M Hocek M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(21):5833-5841
Aqueous Suzuki–Miyaura cross‐coupling reactions of halogenated nucleosides, nucleotides and nucleoside triphosphates derived from 5‐iodocytosine and 7‐iodo‐7‐deazaadenine with methyl‐, benzyl‐ and tritylsufanylphenylboronic acids gave the corresponding alkylsulfanylphenyl derivatives of nucleosides and nucleotides. The modified nucleoside triphosphates were incorporated into DNA by primer extension by using Vent(exo‐) polymerase. The electrochemical behaviour of the alkylsulfanylphenyl nucleosides indicated formation of compact layers on the electrode. Modified nucleotides and DNA with incorporated benzyl‐ or tritylsulfanylphenyl moieties produced signals in [Co(NH3)6]3+ ammonium buffer, attributed to the Brdi?ka catalytic response, depending on the negative potential applied. Repeated constant current chronopotentiometric scans in this medium showed increased Brdi?ka catalytic response, which suggests the deprotection of the alkylsulfanyl derivatives to free thiols under the conditions. 相似文献
923.
Macwan JS Ionita IA Dostalek M Akhlaghi F 《Analytical and bioanalytical chemistry》2011,400(2):423-433
The aim of the proposed work was to develop and validate a simple and sensitive assay for the analysis of atorvastatin (ATV)
acid, ortho- and para-hydroxy-ATV, ATV lactone, and ortho- and para-hydroxy-ATV lactone in human plasma using liquid chromatography-tandem mass spectrometry. All six analytes and corresponding
deuterium (d5)-labeled internal standards were extracted from 50 μL of human plasma by protein precipitation. The chromatographic
separation of analytes was achieved using a Zorbax-SB Phenyl column (2.1 mm × 100 mm, 3.5 μm). The mobile phase consisted
of a gradient mixture of 0.1% v/v glacial acetic acid in 10% v/v methanol in water (solvent A) and 40% v/v methanol in acetonitrile (solvent B). All analytes including ortho- and para-hydroxy metabolites were baseline-separated within 7.0 min using a flow rate of 0.35 mL/min. Mass spectrometry detection was
carried out in positive electrospray ionization mode, with multiple-reaction monitoring scan. The calibration curves for all
analytes were linear (R
2 ≥ 0.9975, n = 3) over the concentration range of 0.05–100 ng/mL and with lower limit of quantitation of 0.05 ng/mL. Mean extraction recoveries
ranged between 88.6–111%. Intra- and inter-run mean percent accuracy were between 85–115% and percent imprecision was ≤ 15%.
Stability studies revealed that ATV acid and lactone forms were stable in plasma during bench top (6 h on ice-water slurry),
at the end of three successive freeze and thaw cycles and at −80 °C for 3 months. The method was successfully applied in a
clinical study to determine concentrations of ATV and its metabolites over 12 h post-dose in patients receiving atorvastatin. 相似文献
924.
Kostečka P Havran L Bittová M Pivoňková H Fojta M 《Analytical and bioanalytical chemistry》2011,400(1):197-204
A complex OsO4, 2,2′-bipyridine (Os,bipy), has been used for electroactive labeling of biopolymers as well as for probing of nucleic acids
and protein structure and interactions. In DNA, Os,bipy forms electrochemically active adducts with pyrimidine nucleobases,
exhibiting highly selective modification of thymine residues in single-stranded DNA. Here, we show that modification of rare
thymine residues (one thymine among several tens of unreactive purine bases) can easily be detected by means of a simple ex
situ voltammetric analysis using carbon electrodes. Based on this remarkable sensitivity of detection, Os,bipy has been used
as an electroactive probe for unpaired and/or mismatched thymine residues within DNA heteroduplexes. Site-specific chemical
modification of the DNA with the Os,bipy has allowed a clear distinction between perfectly base-paired DNA homoduplexes and
mismatched heteroduplexes, as well as discrimination among heteroduplexes containing one or two mispaired thymines, a single
thymine insertion, or combination of a mispair and an insertion. 相似文献
925.
We present benchmark CCSD(T) calculations of the adiabatic electron affinities (AEA) and the vertical detachment energies (VDE) of the uracil molecule interacting with one to three water molecules. Calculations with rather large aug-cc-pVTZ basis set were only tractable when the space of virtual orbitals was reduced to about 60% of the full space employing the OVOS (Optimized Virtual Orbital Space) technique. Because of the microhydration, the valence-bound uracil anion is stabilized leading to gradually more positive values of both AEA and VDE with increasing number of participating water molecules. This agrees with experimental findings. Upon hydration by three water molecules, the electron affinity of uracil increased in comparison with AEA of the isolated molecule by about 250 up to 570 meV, depending on the geometry of the complex. CCSD(T) results confirm trends determined by DFT calculations of the microhydrated uracil and its anion, even if electron affinities of the free and hydrated uracil molecule are overestimated by DFT by up to 300 meV. 相似文献
926.
Miroslav Pavlović 《Archiv der Mathematik》2011,97(5):467-473
We improve a recent result of Yang and Xu (Arch. Math. 96 (2011), 151–160) by proving that if ψ is a normal function on [1, ∞) and \({f(z)=\sum_{n=0}^\infty a_n z^{k_n}}\) (|z| < 1) is an analytic function with Hadamard gaps, thenwhere C is a constant independent of ζ and {a n }.
相似文献
$\frac 1C \sup_{n\ge 0} \frac{|a_n|}{\psi(k_n)} \le \sup_{0 < r < 1} \frac{|f(r\zeta)|}{\psi(1/(1-r))} \le C\sup_{n\ge 0}\frac{|a_n|}{\psi(k_n)}, \quad |\zeta|=1,$
927.
Tom Urbnek Jií Trousil Dmytro Rak Kristýna Gunr Rafa Konefa Miroslav louf Marin Sedlk Olga ebestov Janoukov Martin Hrubý 《Macromolecular bioscience》2020,20(5)
Polymeric drug carriers exhibit excellent properties that advance drug delivery systems. In particular, carriers based on poly(ethylene oxide)‐block‐poly(ε‐caprolactone) are very useful in pharmacokinetics. In addition to their proven biocompatibility, there are several requirements for the efficacy of the polymeric drug carriers after internalization, e.g., nanoparticle behavior, cellular uptake, the rate of degradation, and cellular localization. The introduction of γ‐butyrolactone units into the hydrophobic block enables the tuning of the abovementioned properties over a wide range. In this study, a relatively high content of γ‐butyrolactone units with a reasonable yield of ≈60% is achieved by anionic ring‐opening copolymerization using 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene as a very efficient catalyst in the nonpolar environment of toluene with an incorporated γ‐butyrolactone content of ≈30%. The content of γ‐butyrolactone units can be easily modulated according to the feed ratio of the monomers. This method enables control over the rate of degradation so that when the content of γ‐butyrolactone increases, the rate of degradation increases. These findings broaden the application possibilities of polyester‐polyether‐based nanoparticles for biomedical applications, such as drug delivery systems. 相似文献
928.
Stanković Violeta V. Ristić Miroslav M. Vojnović Mirjana M. Aoneas Muna M. Poparić Goran B. 《Plasma Chemistry and Plasma Processing》2020,40(6):1621-1637
Plasma Chemistry and Plasma Processing - The rate coefficients for the electron impact ionization and electronic state excitation of the CO2 molecule are calculated in non-equilibrium conditions in... 相似文献
929.
Hafeesudeen Sahabudeen Dr. Haoyuan Qi Marco Ballabio Dr. Miroslav Položij Dr. Selina Olthof Rishi Shivhare Dr. Yu Jing SangWook Park Kejun Liu Dr. Tao Zhang Ji Ma Dr. Bernd Rellinghaus Prof. Dr. Stefan Mannsfeld Prof. Dr. Thomas Heine Prof. Dr. Mischa Bonn Prof. Dr. Enrique Cánovas Prof. Dr. Zhikun Zheng Prof. Dr. Ute Kaiser Dr. Renhao Dong Prof. Dr. Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6084-6092
Single-layer and multi-layer 2D polyimine films have been achieved through interfacial synthesis methods. However, it remains a great challenge to achieve the maximum degree of crystallinity in the 2D polyimines, which largely limits the long-range transport properties. Here we employ a surfactant-monolayer-assisted interfacial synthesis (SMAIS) method for the successful preparation of porphyrin and triazine containing polyimine-based 2D polymer (PI-2DP) films with square and hexagonal lattices, respectively. The synthetic PI-2DP films are featured with polycrystalline multilayers with tunable thickness from 6 to 200 nm and large crystalline domains (100–150 nm in size). Intrigued by high crystallinity and the presence of electroactive porphyrin moieties, the optoelectronic properties of PI-2DP are investigated by time-resolved terahertz spectroscopy. Typically, the porphyrin-based PI-2DP 1 film exhibits a p-type semiconductor behavior with a band gap of 1.38 eV and hole mobility as high as 0.01 cm2 V−1 s−1, superior to the previously reported polyimine based materials. 相似文献
930.
Abstract PVC-(n-propyl xanthate) macroinitiators (PVC-nPX) with different fractions of xanthate groups were synthesized in THF/acetone solutions from PVC and potassium n-propyl xanthate (nPX). Methyl methacrylate (MMA) was grafted onto PVC-nPX macroinitiators using UV light of 254, 302, and 366 nm at 20 and 40°C. Reaction time was 1, 3, or 5 hours. Graft copolymerization and UV homopolymerization took place at the same time. Grafting was the most effective at a wavelength of 302 nm with a weight gain of copolymerization of up to 45%. The grafted copolymers were separated from the mixture by selective precipitation of THF solutions with hot ethanol and extraction with hot ethanol. The mechanism of grafting is discussed on the basis of the molecular weight of copolymers, on the quantity of homopolymers, on the structure of copolymers, and on the UV absorption of end groups. 相似文献