全文获取类型
收费全文 | 686篇 |
免费 | 8篇 |
专业分类
化学 | 331篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 121篇 |
物理学 | 221篇 |
出版年
2021年 | 5篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 43篇 |
2012年 | 34篇 |
2011年 | 53篇 |
2010年 | 26篇 |
2009年 | 37篇 |
2008年 | 28篇 |
2007年 | 20篇 |
2006年 | 25篇 |
2005年 | 17篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 5篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 18篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1980年 | 4篇 |
1979年 | 18篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1973年 | 17篇 |
1971年 | 5篇 |
1968年 | 4篇 |
1962年 | 4篇 |
1959年 | 7篇 |
1958年 | 6篇 |
1954年 | 5篇 |
1935年 | 5篇 |
排序方式: 共有694条查询结果,搜索用时 15 毫秒
151.
Shubhankar Kumar Bose K. Geetharani V. Ramkumar Shaikh M. Mobin Sundargopal Ghosh Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(48):13483-13490
Reaction of [CpnMCl4?x] (M=V: n=x=2; M=Nb: n=1, x=0) or [Cp*TaCl4] (Cp=η5‐C5H5, Cp*=η5‐C5Me5), with [LiBH4?thf] at ?70 °C followed by thermolysis at 85 °C in the presence of [BH3?thf] yielded the hydrogen‐rich metallaboranes [(CpM)2(B2H6)2] ( 1 : M=V; 2 : M = Nb) and [(Cp*Ta)2(B2H6)2] ( 3 ) in modest to high yields. Complexes 1 and 3 are the first structurally characterized compounds with a metal–metal bond bridged by two hexahydroborate (B2H6) groups forming a symmetrical complex. Addition of [BH3?thf] to 3 results in formation of a metallaborane [(Cp*Ta)2B4H8(μ‐BH4)] ( 4 ) containing a tetrahydroborate ligand, [BH4]?, bound exo to the bicapped tetrahedral cage [(Cp*Ta)2B4H8] by two Ta‐H‐B bridge bonds. The interesting structural feature of 4 is the coordination of the bridging tetrahydroborate group, which has two B? H bonds coordinated to the tantalum atoms. All these new metallaboranes have been characterized by mass, 1H, 11B, and 13C NMR spectroscopy and elemental analysis and the structural types were established unequivocally by crystallographic analysis of 1 – 4 . 相似文献
152.
The catalytic effect of Dy2O3 on the isothermal decomposition of sodium bromate has been investigated at 613.0 K. The data are analyzed in the light of various topochemical models. Dy2O3, being a p-type semiconductor, accelerates the decomposition of bromate by favoring the electron transfer reaction involved in the process. The plausible mechanism of the catalytic activity on the decomposition process is discussed. 相似文献
153.
Micromechanical fast quasi‐static detection of α and β relaxations with nanograms of polymer 下载免费PDF全文
Sanjukta Bose Silvan Schmid Tom Larsen Stephan Sylvest Keller Anja Boisen Kristoffer Almdal 《Journal of Polymer Science.Polymer Physics》2015,53(15):1035-1039
Micromechanical string resonators are used as a highly sensitive tool for the detection of glass transition (Tg or α relaxation) and sub‐Tg (β relaxation) temperatures of polystyrene (PS) and poly (methyl methacrylate) (PMMA). The characterization technique allows for a fast detection of mechanical relaxations of polymers with only few nanograms of sample in a quasi‐static condition. The polymers are spray coated on one side of silicon nitride (SiN) microstrings. These are pre‐stressed suspended structures clamped on both ends to a silicon frame. The resonance frequency of the microstrings is then monitored as a function of increasing temperature. α and β relaxations in the polymer affect the net static tensile stress of the microstring and result in measureable local frequency slope maxima. Tg of PS and PMMA is detected at 91 ±2°C and 114 ±2°C, respectively. The results match well with the glass transition values of 93.6°C and 114.5°C obtained from differential scanning calorimetry of PS and PMMA, respectively. The β relaxation temperatures are detected at 30 ± 2°C and 33 ± 2°C for PS and PMMA which is in accordance with values reported in literature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1035–1039 相似文献
154.
Shubhankar Kumar Bose 《Journal of organometallic chemistry》2010,695(24):2567-2571
Reaction of [(CpV)2(B2H6)2], 1 (Cp = η5-C5H5) with four equivalents of [Co2(CO)8] or [Co4(CO)12] in hexane at 70 °C leads to the isolation of the tetranuclear carbonyl cluster, [(η6-C6H5OCo)Co3(CO)9], 2 in modest yield. The geometry of 2 is similar to that of [Co4(CO)12] where all the four Co atoms are arranged in a tetrahedral geometry. The apical cobalt atom in 2 is coordinated to C6H5O ring in a η6-fashion and the other three cobalt atoms are each coordinated to three carbonyl ligands. Compound 2 has been characterized in solution by IR, 1H, 13C NMR and mass spectrometry and the structural types were unequivocally established by crystallographic analysis. 相似文献
155.
Sharma Neeraj Bose B. Kaistha Atul Bhatt Sarvjeet S. Chaudhry Subhash C. 《Transition Metal Chemistry》2002,27(7):736-740
Niobium(V) chloride aryloxides [NbCl3(OAr)2] and [NbCl2(OAr)3] (Oar = —OC6H4Bu
t
-4 and —OC6H4OMe-4) have been prepared by reacting NbCl5 with two and three equivalents of the respective phenol in CCl4. The complexes have been characterized by elemental analysis, molecular weight determination, i.r., 1H-n.m.r., u.v.–vis. and MS techniques. Thermal behaviour (t.g.–d.t.) of the complexes has also been studied and decomposition schemes proposed. The kinetic and thermodynamic parameters namely, the activation energy 'E
*', the frequency factor 'A', entropy of activation 'S' and specific rate constant 'kr' etc. have been calculated employing the Coats–Redfern equation. The non-isothermal t.g. data has also been utilized to determine the most probable mechanism and corresponding activation energy for the decomposition of niobium(V) complexes by testing seven different theoretically possible decomposition mechanisms. 相似文献
156.
The [3+3] cyclization of 1,3-bis-silyl enol ethers with 1,1-diacylcyclopentanes allows a convenient synthesis of spiro[5.4]decenones. Treatment of these compounds with trifluoroacetic acid (TFA) afforded a great variety of bicyclo[4.4.0]deca-1,4-dien-3-ones containing an angular alkyl group. This core structure occurs in a number of pharmacologically relevant natural products. 相似文献
157.
The reaction of [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))] (1; Cp* = η(5)-C(5)Me(5)) with [Fe(2)(CO)(9)] in hexane yielded [(Cp*Ta)(2)B(5)H(7){Fe(CO)(3)}(2)] (2) and [(Cp*Ta)(2)B(5)H(9){Fe(CO)(3)}(4)] (3) in moderate yield. Cluster 2 represents the first example of a bicapped pentagonal-bipyramidal metallaborane with a deformed equatorial plane, and 3 can be described as a fused cluster in which two pentagonal-bipyramidal units are fused through a common 3-vertex triangular face. Compounds 2 and 3 have been characterized by mass spectrometry and IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis. 相似文献
158.
Debosreeta Bose Deboleena Sarkar Nitin Chattopadhyay 《Photochemistry and photobiology》2010,86(3):538-544
In the present investigation, an attempt has been made to study the interaction of phenosafranin (PSF), a cationic phenazinium dye with the transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA), employing steady-state and time-resolved fluorometric and circular dichroism (CD) techniques. The photophysical properties of the dye are altered on binding with the serum proteins. An explicit study with respect to the modification of the fluorescence and fluorescence anisotropy upon binding, effect of denaturant, fluorescence lifetime and CD measurements reveal that the dye binds to both BSA and HSA with almost the same affinity. Far-UV CD spectra indicate a decrease in the percentage of α-helicity only for BSA upon binding with the probe. Near-UV CD responses indicate an alteration in the tertiary structure of both the transport proteins because of binding. 相似文献
159.
A convenient access to substituted benzothiazole scaffolds via intramolecular cyclization of thioformanilides 总被引:1,自引:0,他引:1
A new and practical method has been developed for the synthesis of substituted benzothiazoles via the intramolecular cyclization of thioformanilides using DDQ in CH2Cl2 at ambient temperature. The reaction proceeds in high yields via the thiyl radical to give novel oxybis-benzothiazole, and offers a high degree of flexibility with regard to the functional groups that can be placed on the benzothiazole nucleus or 2-aryl moiety which in turn generates scaffolds for parallel synthesis. 相似文献
160.
Treatment of group 5 metal polychlorides such as, [CpnMCl4-x] (M = V: n, x = 2; M = Nb: n = 1, x = 0), or [Cp∗TaCl4] (Cp = η5-C5H5, Cp∗ = η5-C5Me5), with [LiBH4·THF] followed by thermolysis in the presence of diphenyl diselenide yielded metallaheteroborane clusters [{CpV(μ-SePh)}2(μ-Se)], 1 [(CpNb)2B4H9(μ-SePh)], 2 and [(Cp∗Ta)2B4H11(SePh)], 3 in modest yields. Compound 1 is an organovanadium selenolato cluster in which two (CpV) moieties bridged by (μ-Se) and two (μ-SePh) ligands. Compound 2 exhibits a bicapped tetrahedral core with one (μ-SePh) ligand. 3 is a tantalahexaborane cluster in which one of the terminal BH protons is substituted by SePh. Compounds 1-3 have been characterized by mass spectrometry, 1H, 11B, 13C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis of 1-3. 相似文献