全文获取类型
收费全文 | 988篇 |
免费 | 45篇 |
国内免费 | 1篇 |
专业分类
化学 | 626篇 |
晶体学 | 2篇 |
力学 | 17篇 |
数学 | 155篇 |
物理学 | 234篇 |
出版年
2023年 | 14篇 |
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 28篇 |
2018年 | 23篇 |
2017年 | 11篇 |
2016年 | 35篇 |
2015年 | 31篇 |
2014年 | 30篇 |
2013年 | 30篇 |
2012年 | 60篇 |
2011年 | 56篇 |
2010年 | 47篇 |
2009年 | 36篇 |
2008年 | 41篇 |
2007年 | 38篇 |
2006年 | 40篇 |
2005年 | 35篇 |
2004年 | 28篇 |
2003年 | 24篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1931年 | 7篇 |
1928年 | 6篇 |
排序方式: 共有1034条查询结果,搜索用时 31 毫秒
991.
This paper analyzes several aspects of the Markov-modulated infinite-server queue. In the system considered (i) particles arrive according to a Poisson process with rate $\lambda _i$ when an external Markov process (“background process”) is in state $i$ , (ii) service times are drawn from a distribution with distribution function $F_i(\cdot )$ when the state of the background process (as seen at arrival) is $i$ , (iii) there are infinitely many servers. We start by setting up explicit formulas for the mean and variance of the number of particles in the system at time $t\ge 0$ , given the system started empty. The special case of exponential service times is studied in detail, resulting in a recursive scheme to compute the moments of the number of particles at an exponentially distributed time, as well as their steady-state counterparts. Then we consider an asymptotic regime in which the arrival rates are sped up by a factor $N$ , and the transition times by a factor $N^{1+\varepsilon }$ (for some $\varepsilon >0$ ). Under this scaling it turns out that the number of customers at time $t\ge 0$ obeys a central limit theorem; the convergence of the finite-dimensional distributions is proven. 相似文献
992.
Electrocatalysis of Water Oxidation by H2O‐Capped Iridium‐Oxide Nanoparticles Electrodeposited on Spectroscopic Graphite 下载免费PDF全文
Naghmehalsadat Mirbagheri Dr. Jacques Chevallier Dr. Jakob Kibsgaard Prof. Flemming Besenbacher Prof. Elena E. Ferapontova 《Chemphyschem》2014,15(13):2844-2850
Electrocatalysis of water oxidation by 1.54 nm IrOx nanoparticles (NPs) immobilized on spectroscopic graphite electrodes was demonstrated to proceed with a higher efficiency than on all other, hitherto reported, electrode supports. IrOx NPs were electrodeposited on the graphite surface, and their electrocatalytic activity for water oxidation was correlated with the surface concentrations of different redox states of IrOx as a function of the deposition time and potential. Under optimal conditions, the overpotential of the reaction was reduced to 0.21 V and the electrocatalytic current density was 43 mA cm?2 at 1 V versus Ag/AgCl (3 M KCl) and pH 7. These results beneficially compete with previously reported electrocatalytic oxidations of water by IrOx NPs electrodeposited onto glassy carbon and indium tin oxide electrodes and provide the basis for the further development of efficient IrOx NP‐based electrocatalysts immobilized on high‐surface‐area carbon electrode materials. 相似文献
993.
Speciation analysis of orthophosphate and myo‐inositol hexakisphosphate in soil‐ and plant‐related samples by high‐performance ion chromatography combined with inductively coupled plasma mass spectrometry 下载免费PDF全文
Ariana Rugova Markus Puschenreiter Jakob Santner Lisa Fischer Stefan Neubauer Gunda Koellensperger Stephan Hann 《Journal of separation science》2014,37(14):1711-1719
A novel method based on high‐performance ion chromatography inductively coupled plasma mass spectrometry employing strong anion exchange chromatography with HNO3 gradient elution for simultaneous analysis of orthophosphate and myo‐inositol hexakisphosphate (IP6) in soil solution and plant extracts is presented. As inductively coupled plasma mass spectrometry analysis of phosphorus at m/z 31 is hampered by N‐based interferences, 31P was measured as 31P16O+ at m/z 47 employing dynamic reaction cell technique with O2 as reaction gas. Orthophosphate and IP6 were separated within a total chromatographic run‐time of 12 min revealing a limit of detection of 0.3 μmol/L. The coefficients of determination obtained in a working range of 1–100 and 1–30 μmol/L were 0.9991 for orthophosphate and 0.9968 for IP6, respectively. The method was successfully applied to extracts from three different soils as well as root and shoot extracts of Brassica napus L. The precision of three independently prepared soil extracts was in the range of 4–10% relative standard deviation for PO43? and 3–8% relative standard deviation for IP6. Soil adsorption/desorption kinetics for IP6/orthophosphate were performed for investigating the sorption behavior of the two P species in the experimental soils. 相似文献
994.
995.
Martin CA Ding D Sørensen JK Bjørnholm T van Ruitenbeek JM van der Zant HS 《Journal of the American Chemical Society》2008,130(40):13198-13199
We present results on a new fullerene-based anchoring group for molecular electronics. Using lithographic mechanically controllable break junctions in vacuum we have determined the conductance and stability of single-molecule junctions of 1,4-bis(fullero[c]pyrrolidin-1-yl)benzene. The compound can be self-assembled from solution and has a low-bias conductance of 3 x 10(-4) G0. Compared to 1,4-benzenedithiol the fullerene-anchored molecule exhibits a considerably lower conductance spread. In addition, the signature of the new compound in histograms is more significant than that of 1,4-benzenediamine, probably owing to a more stable adsorption motif. Statistical analyses of the breaking of the junctions confirm the stability of the fullerene-gold bond. 相似文献
996.
Protein-surfactant interactions at hydrophobic interfaces studied with total internal reflection fluorescence correlation spectroscopy (TIR-FCS) 总被引:1,自引:0,他引:1
Sonesson AW Blom H Hassler K Elofsson UM Callisen TH Widengren J Brismar H 《Journal of colloid and interface science》2008,317(2):449-457
The aim of this work was to study the dynamics of proteins near solid surfaces in the presence or absence of competing surfactants by means of total internal reflection fluorescence correlation spectroscopy (TIR-FCS). Two different proteins were studied, bovine serum albumin (BSA) and Thermomyces lanuginosus lipase (TLL). A nonionic/anionic (C12E6/LAS) surfactant composition was used to mimic a detergent formulation and the surfaces used were C18 terminated glass. It was found that with increasing surfactant concentrations the term in the autocorrelation function (ACF) representing surface binding decreased. This suggested that the proteins were competed off the hydrophobic surface by the surfactant. When fitting the measured ACF to a model for surface kinetics, it was seen that with raised C12E6/LAS concentration, the surface interaction rate increased for both proteins. Under these experimental conditions this meant that the time the protein was bound to the surface decreased. At 10 microM C12E6/LAS the surface interaction was not visible for BSA, whereas it was still distinguishable in the ACF for TLL. This indicated that TLL had a higher affinity than BSA for the C18 surface. The study showed that TIR-FCS provides a useful tool to quantify the surfactant effect on proteins adsorption. 相似文献
997.
Dr. Jakob Thyr Prof. Tomas Edvinsson 《Angewandte Chemie (International ed. in English)》2023,62(43):e202219047
Micro-Raman spectroscopy is an important analytical tool in a large variety of science disciplines. The technique is suitable for both identification of chemical bonds and studying more detailed phenomena like molecular interactions, material strain, crystallinity, defects, and bond formations. Raman scattering has one major weakness however: it is a very low probability process. The weak signals require very sensitive detection systems, which leads to a high probability of picking up signals from origins other than the sample. This complicates the analysis of the results and increases the risk of misinterpreting data. This work provides an overview of the sources of spurious signals occurring in Raman spectra, including photoluminescence, cosmic rays, stray light, artefacts caused by spectrometer components, and signals from other compounds in or surrounding the sample. The origins of these false Raman peaks are explained and means to identify and counteract them are provided. 相似文献
998.
Dr. Jakob Wörner M.Sc. Sabrina Panter Dr. Boris Illarionov Prof. Dr. Adelbert Bacher Prof. Dr. Markus Fischer Prof. Dr. Stefan Weber 《Angewandte Chemie (International ed. in English)》2023,62(43):e202309334
Deazaflavins are important analogues of the naturally occurring flavins: riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). The use of 5-deazaflavin as a replacement coenzyme in a number of flavoproteins has proven particularly valuable in unraveling and manipulating their reaction mechanisms. It was frequently reported that one-electron-transfer reactions in flavoproteins are impeded with 5-deazaflavin as the cofactor. Based on these findings, it was concluded that the 5-deazaflavin radical is significantly less stable compared to the respective flavin semiquinone and quickly re-oxidizes or undergoes disproportionation. The long-standing paradigm of 5-deazaflavin being solely a two-electron/hydride acceptor/donor—“a nicotinamide in flavin clothing”—needs to be re-evaluated now with the indirect observation of a one-electron-reduced (paramagnetic) species using photochemically induced dynamic nuclear polarization (photo-CIDNP) 1H nuclear magnetic resonance (NMR) under biologically relevant conditions. 相似文献
999.
Martin Frandsen Kassem El-Chami Johan Palmfeldt Jakob Melgaard Smidt Maja E. T. Langballe Dr. Alexander Sandahl Prof. Dr. Kurt V. Gothelf 《Angewandte Chemie (International ed. in English)》2023,62(23):e202303170
A method for automated solid-phase synthesis of oligo(disulfide)s was developed. It is based on a synthetic cycle comprising removal of a protecting group from a resin-bound thiol followed by treatment with monomers containing a thiosulfonate as an activated precursor. For ease of purification and characterization, the disulfide oligomers were synthesized as extensions of oligonucleotides on an automated oligonucleotide synthesizer. Six different dithiol monomer building blocks were synthesized. Sequence-defined oligomers of up to seven disulfide units were synthesized and purified. The sequence of the oligomer was confirmed by tandem MS/MS analysis. One of the monomers contains a coumarin cargo that can be released by a thiol-mediated release mechanism. When the monomer was incorporated into an oligo(disulfide) and subjected to reducing conditions, the cargo was released under near-physiological conditions, which underlines the potential use of these molecules in drug delivery systems. 相似文献
1000.
Dr. Anna J. Parker Dr. Arnab Dey Mohammad Usman Qureshi Jakob M. Steiner Dr. John W. Blanchard Dr. Jochen Scheuer Nikolas Tomek Dr. Stephan Knecht Felix Josten Dr. Christoph Müller Dr. Patrick Hautle Dr. Ilai Schwartz Prof. Patrick Giraudeau Dr. Tim R. Eichhorn Dr. Jean-Nicolas Dumez 《Angewandte Chemie (International ed. in English)》2023,62(50):e202312302
The HYPNOESYS method (Hyperpolarized NOE System), which relies on the dissolution of optically polarized crystals, has recently emerged as a promising approach to enhance the sensitivity of NMR spectroscopy in the solution state. However, HYPNOESYS is a single-shot method that is not generally compatible with multidimensional NMR. Here we show that 2D NMR spectra can be obtained from HYPNOESYS-polarized samples, using single-scan acquisition methods. The approach is illustrated with a mixture of terpene molecules and a benchtop NMR spectrometer, paving the way to a sensitive, information-rich and affordable analytical method. 相似文献