全文获取类型
收费全文 | 1291篇 |
免费 | 53篇 |
国内免费 | 13篇 |
专业分类
化学 | 767篇 |
晶体学 | 12篇 |
力学 | 29篇 |
数学 | 351篇 |
物理学 | 198篇 |
出版年
2023年 | 12篇 |
2022年 | 43篇 |
2021年 | 74篇 |
2020年 | 52篇 |
2019年 | 68篇 |
2018年 | 63篇 |
2017年 | 57篇 |
2016年 | 79篇 |
2015年 | 63篇 |
2014年 | 71篇 |
2013年 | 86篇 |
2012年 | 93篇 |
2011年 | 93篇 |
2010年 | 51篇 |
2009年 | 46篇 |
2008年 | 48篇 |
2007年 | 49篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1972年 | 3篇 |
1935年 | 2篇 |
排序方式: 共有1357条查询结果,搜索用时 15 毫秒
31.
Proton affinities of a series of triphenyl Group Va compounds have been determined by bracketing using reactant ion monitoring: (C6H5)3N = 904 ± 8 kJ mol?1, (C6H5)3P = 968 ± 5 kJ mol?1, (C6H5)3As = 904 ± 8 kJ mol?1 and (C6H5)3Sb = 846 ± 8 kJ mol?1. The large difference in substituent effect of phenyl for hydrogen between As or P and N may result from overlap of the 2p orbitals of N with the sp2 orbitals on the ring carbons and lack of overlap for P or As. Proton affinities of phenylalkylphosphine oxides are essentially the same, 904 ± 8 kJ mol?1, independent of alkyl group. 相似文献
32.
Nguyen Van Do Tran Duc Thiep Truong Thi An Tran Minh Duc Han Ngoc Cuong 《Journal of Radioanalytical and Nuclear Chemistry》1986,107(1):29-37
Photon activation analysis has been success-fully applied to the fast and non-destructive analysis of tin in cassiterite ores
based on the 159.7 keV gamma line of123mSn produced in the124Sn/γ, n/123mSn reaction. In order to improve the accuracy of analytical results, corrections for self-absorption and pile-up effects were
performed. Under typical conditions /15 μA electron beam current, 15 MeV bremsstrahlung energy, 5 min irradiation time and
10 min measurement/ the sensitivity of the analysis is 10 ppm. The proposed method can be used for routine analysis of tin
in geological samples. 相似文献
33.
Analysis of organotin compounds by grignard derivatization and gas chromatography-ion trap tandem mass spectrometry 总被引:1,自引:0,他引:1
Tsunoi S Matoba T Shioji H Giang le TH Harino H Tanaka M 《Journal of chromatography. A》2002,962(1-2):197-206
The determination of organotin compounds in water using gas chromatography-tandem mass spectrometry (GC-MS-MS) is described. Several organotin derivatives were synthesized by the reaction of organotin chlorides with Grignard reagents such as methyl-, propyl- and pentylmagnesium halides. After the optimization of the GC-MS-MS conditions, several derivatizations with the Grignard reagents were compared by evaluating the molar responses and volatilities of the derivatives and derivatization yields. As a result, the derivatizing reagent of choice is pentylmagnesium bromide. Calibration curves for the mono-, di- and tributyltins and mono-, di- and triphenyltins with pentylmagnesium bromide were linear in the range of 0.5-100 pg of Sn. The instrumental detection limits of six organotins ranged from 0.20 to 0.35 pg of Sn. The recovery tests from water samples (500 ml) were performed by using sodium diethyldithiocarbamate (DDTC) as a complexing reagent. Except for monophenyltin, the absolute recoveries of organotins from pure water at 200 ng of Sn/l were satisfactory. The recoveries calibrated by surrogate compounds (perdeuterated organotin chlorides) ranged from 71 to 109%. The method detection limits ranged from 0.26 to 0.84 pg of Sn (500-ml sample). This method was applied to the recovery of organotins from river water and seawater. The calibrated recoveries were between 90 and 122%. 相似文献
34.
C. Decker H. Le Xuan T. Nguyen Thi Viet 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2759-2772
Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc. 相似文献
35.
Z. Szeglowski L. I. Guseva Dinh Thi Lien V. P. Domanov B. Kubica G. S. Tikhomirowa O. Constantinescu M. Constantinescu A. B. Yakushev 《Journal of Radioanalytical and Nuclear Chemistry》1998,228(1-2):145-150
The short-lived isotopes of W and their descendants have been separated from nuclear reaction products arising in the bombardment of samarium target with24Mg ions at the U-400 cyclotron of JINR-Dubna. Chemical separations were performed using previously elaborated fast and continuous ion exchange. In similar way products of235U fission, obtained at the microtron MT-25 during irradiation of235U target with photoneutrons were separated. 相似文献
36.
37.
The adsorption of a basic dye (Methylene Blue; MB) and an acidic dye (Acid Orange; AO) has been studied on three activated carbons (ACs; FAS, SKD, and BAU) significantly differing in their porous structures and surface concentrations of ion-exchange groups and on graphitic thermal carbon black (GTCB). The effective specific surface area of FAS, SKD, and BAU determined by dye adsorption is, respectively, 60, 50, and 40% of the BET nitrogen adsorption surface area. The MB uptake on ACs and GTCB increases with rising pH, while the AO uptake decreases. Addition of an electrolyte (0.3 M NaCl) virtually does not effect the adsorption of dyes on ACs and GTCB. It is suggested that hydrophobic interactions, and not ionic ones, are the major contributors to the adsorption of dyes on ACs. 相似文献
38.
39.
We construct a quantum circuit to produce a task-oriented partially entangled state and use it as the quantum channel for controlled joint remote state preparation. Unlike most previous works, where the parameters of the quantum channel are given to the receiver who can accomplish the task only probabilistically by consuming auxiliary resource, operation and measurement, here we give them to the supervisor. Thanks to the knowledge of the task-oriented quantum channel parameters, the supervisor can carry out proper complete projective measurement, which, combined with the feed-forward technique adapted by the preparers, not only much economizes (simplifies) the receiver's resource (operation) but also yields unit total success probability. Notably, such apparent perfection does not depend on the entanglement degree of the shared quantum channel. Our protocol is within the reach of current quantum technologies. 相似文献
40.
Redox‐responsive core cross‐linked micelles of poly(ethylene oxide)‐b‐poly(furfuryl methacrylate) by Diels‐Alder reaction for doxorubicin release 下载免费PDF全文
Cuong M. Q. Le Hai Ha Pham Thi Xuan Thang Cao Gun‐Do Kim Chul‐Woong Oh Kwon Taek Lim 《Journal of polymer science. Part A, Polymer chemistry》2016,54(23):3741-3750
Redox‐responsive core cross‐linked (CCL) micelles of poly(ethylene oxide)‐b‐poly(furfuryl methacrylate) (PEO‐b‐PFMA) block copolymers were prepared by the Diels‐Alder click‐type reaction. First, the PEO‐b‐PFMA amphiphilic block copolymer was synthesized by the reversible addition‐fragmentation chain transfer polymerization. The hydrophobic blocks of PFMA were employed to encapsulate the doxorubicin (DOX) drug, and they were cross‐linked using dithiobismaleimidoethane at 60 °C without any catalyst. Under physiological circumstance, the CCL micelles demonstrated the enhanced structural stability of the micelles, whereas dissociation of the micelles took place rapidly through the breaking of disulfide bonds in the cross‐linking linkages under reduction environment. The core‐cross‐linked micelles showed fine spherical distribution with hydrodynamic diameter of 68 ± 2.9 nm. The in vitro drug release profiles presented a slight release of DOX at pH 7.4, while a significant release of DOX was observed at pH 5.0 in the presence of 1,4‐dithiothreitol. MTT assays demonstrated that the block copolymer did not have any practically cytotoxicity against the normal HEK293 cell line while DOX‐loaded CCL micelles exhibited a high antitumor activity towards HepG2 cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3741–3750 相似文献