全文获取类型
收费全文 | 1006篇 |
免费 | 40篇 |
国内免费 | 4篇 |
专业分类
化学 | 771篇 |
晶体学 | 5篇 |
力学 | 21篇 |
数学 | 91篇 |
物理学 | 162篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 26篇 |
2015年 | 22篇 |
2014年 | 27篇 |
2013年 | 53篇 |
2012年 | 63篇 |
2011年 | 90篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 73篇 |
2007年 | 66篇 |
2006年 | 73篇 |
2005年 | 42篇 |
2004年 | 32篇 |
2003年 | 34篇 |
2002年 | 36篇 |
2001年 | 21篇 |
2000年 | 12篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有1050条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
The performance of single-drop microextraction (SDME), coupled with gas chromatography/mass spectrometry, was assessed for the determination of tributyltin compounds in water and solid samples. Experimental parameters impacting the performance of SDME, such as microextraction solvent and sampling and stirring time, were investigated. Analytical results obtained by SDME were compared with those generated by conventional solid phase microextraction (SPME) and liquid-liquid extraction (LLE) for the determination of TBT in PACS-2 sediment certified reference material (CRM). 相似文献
5.
Michael P. Hartshorn Richard G. Jensen A. Grant Waller Graeme J. Wright 《Tetrahedron letters》1987,28(52):6701-6704
Reaction of the 15N-4-nitrodienone (1) with excess nitrogen dioxide in benzene for 16 h gives the 4,5,6-trinitro ketone (2), labelled (15NO2) at C6 but not at C4, and recovered 4-nitrodienone (1) in which extensive loss of 15NO2 has occurred. The mechanistic implications of these and related results are discussed. 相似文献
6.
A. Sionkowska M. Wisniewski G.F. Poggi C.A. Maxwell 《Polymer Degradation and Stability》2006,91(12):3026-3032
The thermal and mechanical properties of collagen/chitosan blends before and after UV irradiation have been investigated using thermal analysis and mechanical (Instron) techniques. Comparisons were made with the thermal and mechanical properties of both collagen and chitosan films. Air-dried collagen, chitosan and collagen/chitosan films were exposed to UV irradiation (wavelength 254 nm) for different time intervals. Thermal properties of collagen/chitosan blends depend on the composition of the blend and are not significantly altered by UV irradiation.Mechanical properties such as ultimate tensile strength and ultimate percentage of elongation were much better for collagen films than for collagen/chitosan films. The results have shown that the mechanical properties of the blends were greatly affected by the duration of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the blend. Increasing UV irradiation leads to an increase in Young's modulus of the collagen/chitosan blend. 相似文献
7.
The complexes CoH(PF3)4?n (PPh3)n (n = 1–3) have been prepared by low from the reaction between CoH(PF3)(PPh3)3 and butadiene. The hydrido complexes are active catalysts for the isomerisation of 1-octene to 2-octene under hydrogen or nitrogen. 相似文献
8.
A series of neutral porphyrin-containing catenanes has been synthesised, consisting of a zinc porphyrin strapped by a polyethylene glycol chain containing four or six ethylenoxy-units and incorporating a central naphthoquinol unit, interlinked with a naphthalene diimide macrocycle. The napthalene diimide precursor units exhibit only weak binding with the strapped porphyrins (Ka between 8 and 0.02 M(-1)), but good yields of the catenanes were obtained by Glaser coupling of the alkynyl napthalene diimide precursors in the presence of the porphyrins. Structures and solution conformations were determined by mass spectral and detailed 1H NMR studies. For the longer strapped porphyrins, the diimide macrocycle rotates around the central naphthoquinol unit at 420-450 times per second, while rotation is virtually prevented in the tighter strapped derivatives. A second dynamic process occurring in both sets of catenanes and described as 'yawing' leads to inequivalence in the naphthalene moieties. UV-Visible spectra indicate charge transfer interactions and electronic communication between the two components of the catenane. 相似文献
9.
Hogarth G Holman KT Pateman A Sella A Steed JW Richards I 《Dalton transactions (Cambridge, England : 2003)》2005,(16):2688-2695
The iodine(III) reagent, PhI[double bond, length as m-dash]NTs, acts as a source of the nitrene fragment NTs, which undergoes facile insertion into the metal-sulfur bonds of a range of dithiocarbamate complexes. Addition of two equivalents of PhI=NTs to [M(S(2)CNR2)2] affords sulfido-amido complexes [M{SC(NR2)SNTs}2](M=Ni, Cu), which insert two further nitrene fragments to afford zwitterionic tetraamido complexes [M{TsNSC(NR2)SNTs}2](M=Co, Ni, Cu). Crystallographic studies have been carried out on both types of complex allowing possible resonance hydrids of the new ligand types to be assessed. 相似文献
10.
The development of sample extraction techniques in conjunction with application of a modified version of an established HPLC technique allowed the rapid estimation of concentrations of long chain fatty acids (LCFA) produced by the lipolytic activity of bacteria in anaerobic digestor sludges or experiments using the sludges as inocula. It was established that free long chain fatty acids will preferentially partition into certain phases in the sludge or experimental cultures. These data, and application of the developed techniques for monitoring of LCFA, may lead to the avoidance of toxicity and failure of full-scale anaerobic digestors treating high lipid content waste in the future. 相似文献