全文获取类型
收费全文 | 1821篇 |
免费 | 30篇 |
专业分类
化学 | 957篇 |
晶体学 | 4篇 |
力学 | 98篇 |
数学 | 331篇 |
物理学 | 461篇 |
出版年
2023年 | 9篇 |
2021年 | 16篇 |
2020年 | 15篇 |
2018年 | 13篇 |
2017年 | 24篇 |
2016年 | 44篇 |
2015年 | 46篇 |
2014年 | 40篇 |
2013年 | 57篇 |
2012年 | 84篇 |
2011年 | 116篇 |
2010年 | 65篇 |
2009年 | 45篇 |
2008年 | 97篇 |
2007年 | 84篇 |
2006年 | 97篇 |
2005年 | 89篇 |
2004年 | 51篇 |
2003年 | 59篇 |
2002年 | 47篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 15篇 |
1998年 | 23篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 23篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 27篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 17篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 28篇 |
1976年 | 20篇 |
1975年 | 15篇 |
1974年 | 16篇 |
1973年 | 19篇 |
1913年 | 7篇 |
排序方式: 共有1851条查询结果,搜索用时 15 毫秒
11.
"Bare" CeO(2)(+) ions can be prepared in the gas phase by consecutive oxidation of Ce(+) with O(2) and NO(2). The ability to activate saturated and unsaturated hydrocarbons is investigated by use of Fourier-transform ion cyclotron resonance mass spectrometry. In the reactions of CeO(2)(+) with linear and branched alkanes C-H bond activation is observed almost exclusively. In contrast, both oxygen-atom transfer and C-H bond activation processes occur when thermalized CeO(2)(+) cations react with simple alkenes and aromatic compounds. C-C bond activation is not observed at all. Insight into the structural and electronic properties of neutral CeO(2) and cationic CeO(2)(+) is provided by means of quasirelativistic density-functional and ab initio pseudopotential calculations. They reveal a (2)Sigma(u)(+) ground state for CeO(2)(+) which is best described as a linear cerium dioxide with a resonating pi bond. Finally, we discuss the influence of oxo ligands on the chemistry of the cationic CeO(n)()(+) (n = 0-2) species toward hydrocarbons. 相似文献
12.
Harry J. Whitlow Margaretha Andersson Mikael Hult Leif Persson Mohamed El Bouanani Mikael Östling Carina Zaring Nils Lundberg David D. Cohen Nick Dytlewski Peter N. Johnston Ian F. Bubb Scott R. Walker Erik Johanson Sture Hogmark P. Anders Ingemarsson 《Mikrochimica acta》1995,120(1-4):171-181
Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications. 相似文献
13.
Albrecht H Binder U Harder G Lembke-Koppitz I Philipp A Schmidt-Parzefall W Schröder H Schulz HD Wurth R Donker JP Drescher A Matthiesen U Scheck H Spaan B Spengler J Wegener aD Gabriel JC Schubert KR Stiewe J Waldi R Weseler S Brown NN Edwards KW Frisken WR Fukunaga C Gilkinson DJ Gingrich DM Goddard M Kapitza H Kim PC Kutschke R MacFarlane DB McKenna JA McLean KW Nilsson AW Orr RS Padley P Patel PM Prentice JD Seywerd HC Stacey BJ Yoon T Yun JC Ammar R Coppage D Davis R Kanekal S Kwak N 《Physical review letters》1986,56(6):549-552
14.
H. W. Gronert D. M. Herlach A. Schröder R. van den Berg H. von Löhneysen 《Zeitschrift für Physik B Condensed Matter》1986,63(2):173-178
Low-temperature measurements of the thermal conductivity (0.3KT5K) and of the specific heatC (0.07KT3.5K) of splat-cooled amorphous superconducting Zr0.67Ni0.33(T
c
2.7K) after different annealing stages are reported. increases progressively (up to 55%) after annealing. An analysis of with the help of normal-state measurements belowT
c
in an overcritical field shows that the phonon-electron scattering remains unaltered after annealing. Hence the increase in must be entirely attributed to structure-induced (intrinsic) scattering, i.e. by two-level tunneling states (TLS) at low temperatures (T1K). The specific heat shows a small decrease aboveT
c
(by 8%) which is attributed to a small diminution of the electronic density of states at the Fermi level and to a small increase in the Debye temperature. ForTT
c
where TLS dominate, the specific heatC decreases less upon annealing than expected from the increase of in the standard tunneling model. This points to a change in the TLS relaxation time spectrum upon annealing, as observed previously for Zr
x
Cu1–x
glasses. 相似文献
15.
Md Sharif Ullah Vladimir V. Zhivonitko Anatoliy Samoylenko Artem Zhyvolozhnyi Sirja Viitala Santeri Kankaanp Sanna Komulainen Leif Schrder Seppo J. Vainio Ville-Veikko Telkki 《Chemical science》2021,12(24):8311
Exosomes are a subset of secreted lipid envelope-encapsulated extracellular vesicles (EVs) of 50–150 nm diameter that can transfer cargo from donor to acceptor cells. In the current purification protocols of exosomes, many smaller and larger nanoparticles such as lipoproteins, exomers and microvesicles are typically co-isolated as well. Particle size distribution is one important characteristics of EV samples, as it reflects the cellular origin of EVs and the purity of the isolation. However, most of the physicochemical analytical methods today cannot illustrate the smallest exosomes and other small particles like the exomers. Here, we demonstrate that diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) method enables the determination of a very broad distribution of extracellular nanoparticles, ranging from 1 to 500 nm. The range covers sizes of all particles included in EV samples after isolation. The method is non-invasive, as it does not require any labelling or other chemical modification. We investigated EVs secreted from milk as well as embryonic kidney and renal carcinoma cells. Western blot analysis and immuno-electron microscopy confirmed expression of exosomal markers such as ALIX, TSG101, CD81, CD9, and CD63 in the EV samples. In addition to the larger particles observed by nanoparticle tracking analysis (NTA) in the range of 70–500 nm, the DOSY distributions include a significant number of smaller particles in the range of 10–70 nm, which are visible also in transmission electron microscopy images but invisible in NTA. Furthermore, we demonstrate that hyperpolarized chemical exchange saturation transfer (Hyper-CEST) with 129Xe NMR indicates also the existence of smaller and larger nanoparticles in the EV samples, providing also additional support for DOSY results. The method implies also that the Xe exchange is significantly faster in the EV pool than in the lipoprotein/exomer pool.Diffusion and xenon NMR based methods to determine a very broad range of sizes and sub-sets of extracellular vesicles. 相似文献
16.
H. Frunder D. Illig H. Finsterhölzl H.W. Schrōtter B. Lavorel G. Roussel J.C. Hilico J.P. Champion G. Pierre G. Poussigue E. Pascaud 《Chemical physics letters》1983,100(1):110-114
The CARS spectrum of the v1 band of 12CH4 at a pressure of 14 mbar was recorded using cw excitation in the cavity of a ring argon ion laser. The analysis of the intensity profile of the obarred spectrum led to the detection of inconsistencies with the hitherto proposed calculated positions of transitions with J = 7 to J = 10 and to a relocation of the corresponding lines. 相似文献
17.
A potentiometric method for the determination of organophosphorus insecticides based on the inhibition of cholinesterase is presented. The acetic acid formed by hydrolysis of acetylcholine is sensed by a glass electrode in a weakly buffered system. The insecticide is incubated with cholinesterase for 1 h at 25°C or 37°C before addition to the substrate. The effects of incubation time and temperature are discussed. The method is applied to the insecticides bromophos and dichlorvos. The detection limits are 2 × 10-5 M (7 ppb) for bromophos and 1 × 10-7 M (22 ppb) for dichlorvos. The initial rates of hydrolysis decrease linearly up to 2 × 10-7 M and 1 × 10-6 M, respectively. 相似文献
18.
W. Schr?n A. Detcheva B. Dre?ler K. Danzer 《Fresenius' Journal of Analytical Chemistry》1998,361(2):106-109
Direct solid sampling graphite furnace AAS (SS-GF-AAS) provides an advantageous alternative to the conventional AAS which
requires wet digestion of the samples. This method is suitable for trace element determination in calcium fluoride and other
fluoride-containing samples. Matrix effects were studied by using calibration standards, certified reference materials with
different matrices and by means of three-dimensional calibration. 3D calibration is suitable for selection of calibration
samples for more reliable analyses. Cu, Pb, Cd, Zn, and Fe were determined by means of calibration with variation of sample
weight using certified reference materials and suitable fluoride-containing calibration samples.
Received: 25 July 1997 / Revised: 15 December 1997 / Accepted: 20 December 1997 相似文献
19.
Khlobystov AN Brett MT Blake AJ Champness NR Gill PM O'Neill DP Teat SJ Wilson C Schröder M 《Journal of the American Chemical Society》2003,125(22):6753-6761
A series of structurally related binuclear metallacycles [Cd(NO(3))(2)L](2), where L is an angular exo-bidentate ligand, have been synthesized. Each metallacycle contains two coordinatively unsaturated, chiral metal centers within a single molecule, and the assembly of these metallacycles into polymeric framework structures has been studied systematically for the first time. Stereoselective homochiral association of [Cd(NO(3))(2)L](2) leads to the formation of helical coordination polymers, whereas meso type association results in nonhelical chain structures. The type of stereoselective aggregation depends on the conditions of self-assembly as well as on ligand functionality. Both helical and nonhelical polymeric complexes have been isolated for the metallacycle [Cd(NO(3))(2)(2,4'-pyacph)](2) (2,4'-pyacph = 2,4'-(4-ethynylphenyl)bipyridyl). Homochiral association results in the formation of helical [Cd(NO(3))]( infinity ) chains which link the binuclear [Cd(NO(3))(2)(2,4'-pyacph)](2) metallacycles into racemic two-dimensional sheets which contain both P and M [Cd(NO(3))]( infinity ) helices. In contrast, meso-association leads to the formation of nonhelical one-dimensional chains. It is shown that the product of homochiral association is predominately formed at room temperature and that of meso-association is generated at elevated temperatures. Thus, it may be concluded that the homochiral association appears to be energetically less favorable than the meso-association, a conclusion that has been confirmed by theoretical calculations of the crystal lattice energy. Several high-yield syntheses of bipyridyl-type ligands used for metallacyclic assembly are also reported. 相似文献
20.
Mikkelsen Ø Skogvold SM Schrøder KH Gjerde MI Aarhaug TA 《Analytical and bioanalytical chemistry》2003,377(2):322-326
Evaluation of different solid electrode systems for detection of zinc, lead, cobalt, and nickel in process water from metallurgical nickel industry with use of differential pulse stripping voltammetry has been performed. Zinc was detected by differential pulse anodic stripping voltammetry (DPASV) on a dental amalgam electrode as intermetallic Ni–Zn compound after dilution in ammonium buffer solution. The intermetallic compound was observed at –375 mV, and a linear response was found in the range 0.2–1.2 mg L–1 (r2=0.98) for 60 s deposition time. Simultaneous detection of nickel and cobalt in the low g L–1 range was successfully performed by use of adsorptive cathodic stripping voltammetry (AdCSV) of dimethylglyoxime complexes on a silver–bismuth alloy electrode, and a good correlation was found with corresponding AAS results (r2=0.999 for nickel and 0.965 for cobalt). Analyses of lead in the g L–1 range in nickel-plating solution were performed with good sensitivity and stability by DPASV, using a working electrode of silver together with a glassy carbon counter electrode in samples diluted 1:3 with distilled water and acidified with H2SO4 to pH 2. A new commercial automatic at-line system was tested, and the results were found to be in agreement with an older mercury drop system. The stability of the solid electrode systems was found to be from one to several days without any maintenance needed. 相似文献