全文获取类型
收费全文 | 1144篇 |
免费 | 76篇 |
国内免费 | 23篇 |
专业分类
化学 | 833篇 |
晶体学 | 2篇 |
力学 | 73篇 |
数学 | 122篇 |
物理学 | 213篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 42篇 |
2021年 | 40篇 |
2020年 | 63篇 |
2019年 | 68篇 |
2018年 | 107篇 |
2017年 | 68篇 |
2016年 | 103篇 |
2015年 | 64篇 |
2014年 | 84篇 |
2013年 | 141篇 |
2012年 | 104篇 |
2011年 | 81篇 |
2010年 | 54篇 |
2009年 | 36篇 |
2008年 | 39篇 |
2007年 | 37篇 |
2006年 | 30篇 |
2005年 | 27篇 |
2004年 | 18篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有1243条查询结果,搜索用时 0 毫秒
91.
A new furnace system with an almost zero temperature gradient throughout the sample area was designed for multi-anvil high pressure experiments. Test experiments of the new design were performed using 18/11 and 25/15 cell assemblies at 4?GPa, 1400°C and 1500°C, respectively. The temperature field within the sample capsules appeared to be very homogenous as indicated by Mg2Si2O6–MgCaSi2O6 two-pyroxene thermometry, by direct temperature measurements using two thermocouples within the same assembly, and by distribution of solid and liquid phases in the sample capsule. The temperature gradient is estimated to be <2.4°C/mm over an area of 4?×?5?mm2 within the furnace. It is significantly lower than standard multi-anvil experiments with straight or stepped furnace systems, which are at the levels of 20–200°C/mm. 相似文献
92.
Hosseini M Ganjali MR Tavakoli M Norouzi P Faridbod F Goldooz H Badiei A 《Journal of fluorescence》2011,21(4):1509-1513
A novel and simple fluorescence enhancement method for selective pyrophosphate(PPi) sensing was proposed based on a 1:1 metal
complex formation between bis(8-hydroxy quinoline-5-solphonat) chloride aluminum(III) (Al(QS)2Cl), (L) and PPi in aqueous solution. The linear response range covers a concentration range of 1.6 × 10−7 to 1.0 × 10−5 mol/L of PPi and the detection limit of 2.3 × 10−8 mol/L. The association constant of L-PPi complex was calculated 2.6 × 105 L/mol. L was found to show selectively and sensitively fluorescence enhancement toward PPi over than I3-, NO3-, CN−, CO32−, Br−, Cl−, F−, H2PO4− and SO42−, which was attributed to higher stability of inorganic complex between pyrophosphate and L. 相似文献
93.
Hossein Anaraki-Ardakani Shirin Sadeghian Foroghossadat Rastegari Alireza Hassanabadi 《合成通讯》2013,43(12):1990-1999
The three-component reaction between dialkyl acetylenedicarboxylates and triphenylphosphine in the presence of arylsulfonyl hydrazides or aryl hydrazines produces highly functionalized, salt-free phosphorus ylides in excellent yields. 相似文献
94.
We propose a method for the approximation of solutions of PDEs with stochastic coefficients based on the direct, i.e., non-adapted, sampling of solutions. This sampling can be done by using any legacy code for the deterministic problem as a black box. The method converges in probability (with probabilistic error bounds) as a consequence of sparsity and a concentration of measure phenomenon on the empirical correlation between samples. We show that the method is well suited for truly high-dimensional problems. 相似文献
95.
Markus Langsdorf Alireza Ghassempour Andreas Römpp Bernhard Spengler 《Rapid communications in mass spectrometry : RCM》2010,24(19):2885-2899
A new tryptophyllin‐like peptide family was found in the skin secretion of the tree frog Hyla savignyi. Peptides were characterized by database‐independent sequencing strategies and specific ion fragmentation features were investigated. Skin secretions from specimens of Hyla savignyi were collected by mild electrical stimulation. Peptides were separated by reversed‐phase nano‐high‐performance liquid chromatography (nanoHPLC) and mass spectra were acquired online by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS). Peptides were characterized by manual de novo sequencing and by composition‐based sequencing (CBS), appearing mostly as C‐terminal free acids and as their acid amide analogs. Amide peptides yielded lower intensities of y‐type ions after collision‐induced dissociation (CID) than their acid analogs. A mechanism of internal b‐ion formation (positive ion mode) and of CO2 elimination (negative ion mode) is proposed. We also exemplified phenomena such as the proline effect and formation of non‐direct sequence ions after sequence rearrangements. The occurrence of rearrangement products, of internal ions and of the proline effect made the CID spectra highly complex. CBS analysis nevertheless resulted in successful and highly reliable sequence analysis. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
96.
Protonation of the reactive 1:1 intermediate produced in the reaction between dimethyl acetylenedicarboxylate and triphenylphosphine by benzoylhydrazones leads to vinylphosphonium salts, which undergo Michael addition with the conjugate base of the NH acid to produce highly fanctionalized, salt-free phosphorus ylides in excellent yields. 相似文献
97.
Using the Martin-Siggia-Rose method, we study propagation of acoustic waves in strongly heterogeneous media which are characterized by a broad distribution of the elastic constants. Gaussian-white distributed elastic constants, as well as those with long-range correlations with nondecaying power-law correlation functions, are considered. The study is motivated in part by a recent discovery that the elastic moduli of rock at large length scales may be characterized by long-range power-law correlation functions. Depending on the disorder, the renormalization group (RG) flows exhibit a transition to localized regime in any dimension. We have numerically checked the RG results using the transfer-matrix method and direct numerical simulations for one- and two-dimensional systems, respectively. 相似文献
98.
Shahla Masoudian Hassan Hosseini Monfared Alireza Aghaei 《Transition Metal Chemistry》2011,36(5):521-530
Various aerogels of silica gel doped with Fe2O3 were prepared by sol–gel method. They were calcined to produce nanoparticle solids. The nanosized mixed oxides were active
in the oxidation of alcohols and produced carbonyl compounds in very good to excellent yields using hydrogen peroxide. 相似文献
99.
100.
Alireza Banaei Afshin Saadat Mina Mohammad Goli Patrick McArdle Eslam Pourbasheer Parinaz Pargolghasemi 《Heteroatom Chemistry》2016,27(6):353-360
Two novel dithiophosphonate ligands, HS2P(p‐C6H4OMe)(OCH2CH2CH(CH3)2) ( 1 ) and HS2P(p‐C6H4OMe)(OCH(CH3)2) ( 2 ), were synthesized and characterized by multinuclear (1H, 31P, and 13C) NMR, infrared spectroscopy as well as elemental analysis. The reactions of 1 and 2 with NiCl2·6H2O and Cd(NO3)2·4H2O in methanol led to novel complexes 3 and 4 . The single crystal X‐ray structures of 3 and 4 showed tetracoordinated structure with square planar geometry for the nickel complex, while it showed pentacoordinated structure with distorted square‐pyramid environment for the cadmium complex. 相似文献