全文获取类型
收费全文 | 1162篇 |
免费 | 41篇 |
国内免费 | 1篇 |
专业分类
化学 | 687篇 |
晶体学 | 7篇 |
力学 | 43篇 |
数学 | 88篇 |
物理学 | 379篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 27篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 38篇 |
2015年 | 32篇 |
2014年 | 31篇 |
2013年 | 74篇 |
2012年 | 58篇 |
2011年 | 82篇 |
2010年 | 47篇 |
2009年 | 34篇 |
2008年 | 55篇 |
2007年 | 44篇 |
2006年 | 53篇 |
2005年 | 40篇 |
2004年 | 33篇 |
2003年 | 30篇 |
2002年 | 28篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1973年 | 6篇 |
1971年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有1204条查询结果,搜索用时 375 毫秒
11.
We have initiated a search for a new type of nuclear matter, theη-mesic nucleus, using beams from the multi-GeV hadron facility, COSY at Juelich, Germany. A large acceptance scintillator detector, ENSTAR has been designed and built at BARC, Mumbai and fully assembled and tested at COSY. A test run for calibration and evaluation has been completed. In this contribution we present the design and technical details of the ENSTAR detector and how it will be used to detect protons and pions (the decay products ofη-mesic bound state). The detector is made of plastic scintillators arranged in three concentric cylindrical layers. The readout of the detectors is by means of optical fibres. The layers are used to generate ΔE –E spectra for particle identification and total energy information of stopped particles. The granularity of the detector allows for position (θ and ?ø determination making the event reconstruction kinematically complete 相似文献
12.
13.
14.
Hexacoordinate complexes of vanadium(III) containing tridentate ONS chelating substituted salicylaldehyde thiosemicarbazones have been prepared and characterised by elemental analysis, i.r. and u.v.–vis. spectroscopy and cyclic voltammetry. 相似文献
15.
Chatterjee A 《Talanta》2000,51(2):303-314
A microwave-assisted digestion procedure was developed in presence of concentrated nitric acid (2.0 ml) and 30% hydrogen peroxide (0.20 ml) using a closed pressurized microwave digestion system for the determination of total anionic and total cationic arsenic compounds reside in oyster tissue. At 450 W for 15 min digestion, 74% of anionic arsenic, and 31% of cationic arsenic (105% total arsenic) were retrieved. At 300 W microwave power, 68% of anionic and 30.5% of cationic arsenic (98.5% total arsenic), and 100 W, 63% of anionic and 31% of cationic arsenic (94% total arsenic) were extracted out. The methanol water mixture (9:1) was cull out, exclusively 31.6% of anionic and 29% of cationic arsenic compounds (60.6% total). The dimethylarsinoylriboside (phosphate-arsenosugar) was the predominant arsenic species, along with arsenobetaine (AB), dimethylarsinic acid (DMA), inorganic arsenic, methylarsonic acid (MA), arsenocholine (AC), trimethylarsineoxide (TMAO) and tetramethylarsonium ion (TMI). Some other arsenic compounds, those were not matched with the retention time of the available standards, were also detected. Arsenosugar was fragile and adequately transmuted to DMA (100%), AB and AC to TMAO (100%) when 450 W microwave power was applied for 15 min. The separation and quantification of arsenic compounds in the microwave digests and extracts, were carried out in anion (PRP-X100) and cation (LC-SCX) exchange columns using ICP-MS as arsenic specific detector. The procedure was also validated by determining the total cationic and total anionic arsenic compounds present in DORM 1. 相似文献
16.
Yutaka Morita Manfred Hesse Hans Schmid Avijit Banerji Julie Banerji Asima Chatterjee Willi E. Oberhnsli 《Helvetica chimica acta》1977,60(4):1419-1434
Alstonia scholaris: The structure of the indole alkaloid nareline Besides the known akuammidine, picralinal, picrinine and pseudoakuammigine a new indole alkaloid called nareline (M=352) was isolated from Alstonia scholaris R. BR. , which belongs to the plant family of Apocynaceae. Its structure 2 was deduced by single crystal X-ray diffraction. 2 represents the absolute configuration. The spectroscopic data of 2 and its derivatives (Scheme 1) as well as their chemical behavior support this structure. In biogenetic sense nareline is related to the bases akuammiline ( 4 ) and picraline ( 5 ) (Scheme 2). In contrast to those the C-atom 5 is exocyclic and represents an aldehyde group which forms together with the oxygen atom of the N (4)-hydroxylamine group a cyclic half acetale. - By oxidation (CrO3/CH3COOH) of 2 the oxindol derivative 19 (oxonareline) is formed which contains a cyclic acetal as a partial structure element (Scheme 4). 相似文献
17.
S. Bhattacharya A.N. Mandal S.R. Ray Chaudhuri A. Chatterjee 《Tetrahedron letters》1984,25(28):3007-3010
An efficient ring contraction of stereoisomeric 1,2-benzo-4-bromo-3-hydroxycyclohept-1-ene and their derivatives (1a-e) to (2a-c) is reported, and a probable mechanism for this ring contraction has been suggested. 相似文献
18.
The charge transfer (CT) band maximum of N-alkyl pyridinium iodide (NAPI) has been studied as a function of the composition of binary mixed dipolar aprotic solvents. The deviation from linearity of the energy maximum (E12) and the mole fraction (of a component solvent) plot is explained as due to a preferential solvation by the more polar cosolvent in the binary mixture. The extent of preferential solvation has been observed to vary with the composition, the maximum being towards the less-polar end. The role of hydrogen bond donating ability of a solvent in preferential solvation is discussed. 相似文献
19.
S. K. Chatterjee A. Malhotra D. Yadav 《Journal of polymer science. Part A, Polymer chemistry》1986,24(10):2591-2597
Interpolymer complex formation has been studied between methacrylic acid–methacrylamide copolymer and poly(vinyl pyrrolidone) in acetone–water mixtures of different compositions. At a specific composition of the solvent (e.g., 70% water + 30% acetone by volume), the intrinsic viscosity of the copolymer and the reduced viscosity of 1:1 interpolymer complex had minimum values. Preferential solvation coefficients (λ/C) have been calculated for the various compositions of the solvent mixtures. An excellent coincidence could be obtained between the maximum (λ/C) and the minimum in the viscosity of the polymer solutions. Interpretations have been sought in terms of conformational change of the copolymer at the specific composition of the solvent mixture. 相似文献
20.
Craviso GL Chatterjee I Publicover NG 《Bioelectrochemistry (Amsterdam, Netherlands)》2003,60(1-2):57-64
Effects of powerline frequency (50/60 Hz) electric and magnetic fields on the central nervous system may involve altered neurotransmitter release. This possibility was addressed by determining whether 60-Hz linearly polarized sinusoidal magnetic fields (MFs) alter the release of catecholamines from cultured bovine adrenal chromaffin cells, a well-characterized model of neural-type cells. Dishes of cells were placed in the center of each of two four-coil Merritt exposure systems that were enclosed within mu-metal chambers in matched incubators for simultaneous sham and MF exposure. Following 15-min MF exposure of the cells to flux densities of 0.01, 0.1, 1.0 or 2 mT, norepinephrine and epinephrine release were quantified by high-performance liquid chromatography (HPLC) coupled with electrochemical detection. No significant differences in the release of either norepinephrine or epinephrine were detected between sham-exposed cells and cells exposed to MFs in either the absence or presence of Bay K-8644 (2 microM) or dimethylphenylpiperazinium (DMPP, 10 microM). Consistent with these null findings is the lack of effect of MF exposure on calcium influx. We conclude that catecholamine release from chromaffin cells is not sensitive to 60-Hz MFs at magnetic flux densities in the 0.01-2 mT range. 相似文献