全文获取类型
收费全文 | 1693篇 |
免费 | 24篇 |
国内免费 | 2篇 |
专业分类
化学 | 1109篇 |
晶体学 | 11篇 |
力学 | 24篇 |
数学 | 306篇 |
物理学 | 269篇 |
出版年
2022年 | 20篇 |
2021年 | 17篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 19篇 |
2017年 | 28篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 36篇 |
2013年 | 86篇 |
2012年 | 84篇 |
2011年 | 78篇 |
2010年 | 51篇 |
2009年 | 57篇 |
2008年 | 112篇 |
2007年 | 90篇 |
2006年 | 81篇 |
2005年 | 72篇 |
2004年 | 69篇 |
2003年 | 46篇 |
2002年 | 55篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1997年 | 12篇 |
1996年 | 26篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 30篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 38篇 |
1981年 | 29篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 28篇 |
1977年 | 18篇 |
1976年 | 21篇 |
1974年 | 15篇 |
1973年 | 30篇 |
1972年 | 13篇 |
1971年 | 12篇 |
排序方式: 共有1719条查询结果,搜索用时 15 毫秒
101.
Mahran Daif Konda Reddy Kunduru Natalia Laout Stanislav Ratner Nurit Beyth Abraham J. Domb 《Journal of polymer science. Part A, Polymer chemistry》2016,54(5):596-610
N‐bromo‐hydantoin and N‐bromo‐5,5′‐dimethylhydantoin conjugated polystyrene beads were synthesized from chloromethyl polystyrene beads which differ in their particles size, crosslinking, nano‐micro porosity, and tunnels size on the surface, in order to study the effect of these parameters on oxidative halogen release and resultant activity, for water purification applications. The synthesized beads were characterized using elemental analysis, FT‐IR, solid state 13C‐NMR, and scanning electron microscope (SEM). The conjugation yield and kinetics in different solvents and bromine loading capacity were studied. The N‐bromoamine polystyrene beads were tested for water decontamination according to NSF 231 protocol. The release of active bromine was analyzed by spectrophotometer using a DPD‐1 kit and also studied the antimicrobial activity against Escherichia coli and MS2 phages. Bead's nano‐micro characteristics were found critical for oxidative halogen release control: rate stabilization and modulation, extension and also influences antimicrobial activity. The synthesized beads exhibited extended and stable release of bromine, 6 and 4 log reduction for E. coli and MS2, respectively for 250 L of passing contaminated water. Thus, N‐halamine hydantoins conjugated polystyrenes, chemically or kinetically release modified should have applications as disinfectants in water purification systems as well as medical field. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 596–610 相似文献
102.
103.
Dielectrophoresis switching with vertical sidewall electrodes for microfluidic flow cytometry 总被引:5,自引:0,他引:5
A novel dielectrophoresis switching with vertical electrodes in the sidewall of microchannels for multiplexed switching of objects has been designed, fabricated and tested. With appropriate electrode design, lateral DEP force can be generated so that one can dynamically position particulates along the width of the channel. A set of interdigitated electrodes in the sidewall of the microchannels is used for the generation of non-uniform electrical fields to generate negative DEP forces that repel beads/cells from the sidewalls. A countering DEP force is generated from another set of electrodes patterned on the opposing sidewall. These lateral negative DEP forces can be adjusted by the voltage and frequency applied. By manipulating the coupled DEP forces, the particles flowing through the microchannel can be positioned at different equilibrium points along the width direction and continue to flow into different outlet channels. Experimental results for switching biological cells and polystyrene microbeads to multiple outlets (up to 5) have been achieved. This novel particle switching technique can be integrated with other particle detection components to enable microfluidic flow cytometry systems. 相似文献
104.
Competitive solubilization of cholesterol and phytosterols in nonionic microemulsions 总被引:1,自引:0,他引:1
It is well documented that phytosterols inhibit the uptake of exogenic cholesterol and do not interfere with cholesterol synthesis or cause side effects. The mechanism by which phytosterols interfere with cholesterol absorption is not completely clear and there are at least three hypotheses for their beneficial activity. Among these is that of competitive solubilization of phytosterols and cholesterol in dietary mixed micelles. In the present study we investigated the competitive solubilization of phytosterols (approximately 50% beta-sitosterol) and cholesterol in a nonionic microemulsion system constructed as a model for the dietary mixed micelles. We studied the effect of the competitive solubilization of cholesterol and phytosterols on the structural transformations and physical properties of the microemulsion and evaluated the locus of the solubilizates within the nanodroplets of each sterol separately and when they are loaded together at different weight ratios along one dilution line. Our results show that chemical and structural differences between cholesterol and phytosterols significantly influence the solubilization capacity of the nonionic microemulsion. Cholesterol, being more amphiphilic, is solubilized more efficiently at the W/O microemulsion interface, while in the O/W microemulsion phytosterols are dissolved somewhat more efficiently in the droplet core. 相似文献
105.
Charge calculations in molecular mechanics. Part 8 Partial atomic charges from classical calculations 总被引:1,自引:0,他引:1
Raymond J. Abraham Guy H. Grant Ian S. Haworth Paul E. Smith 《Journal of computer-aided molecular design》1991,5(1):21-39
Summary The CHARGE2 programme, which involves the classical calculation of both the inductive and resonance contributions to the partial atomic charges in molecules is described, and the charges and electrostatic potentials obtained presented for some illustrative examples.In substituted methanes (CH3X, CF3X, CCl3X) the effects of varying the electronegativity of the substituents and the - and -substituent contributions are clearly illustrated for a variety of substituent groups X.The problems involved in the inclusion of silicon into this scheme are detailed, together with the methods of overcoming them. The partial atomic charges ( and contributions) and electrostatic potentials for some silicon oxygen compounds are presented and discussed.The partial atomic charges from CHARGE2 for all the natural amino acids as their N-acetyl, N-methyl-amides are given and compared with those obtained from the AMBER and ECEPP/2 force fields. Considerable differences in these figures are observed, with the AMBER charges consistently much larger than those from the other two methods.The CHARGE2 partial atomic charges and electrostatic potentials for the four common nucleic acids, adenine, cytosine, guanine and thymine, are given and compared with those derived from other calculations. Again there is general similarity but also there are considerable differences, with those from the AMBER force field somewhat larger than the other methods.For previous parts in this series, see Refs. 1-7. 相似文献
106.
S. David Morley Raymond J. Abraham Ian S. Haworth David E. Jackson Martin R. Saunders Jeremy G. Vinter 《Journal of computer-aided molecular design》1991,5(5):475-496
Summary Four modifications to the COSMIC molecular mechanics force field are described, which greatly increase both its versatility and the accuracy of calculated conformational energies. The Hill non-bonded van der Waals potential function has been replaced by a two-parameter Morse curve and a new H-H potential, similar to that in MM3, incorporated. Hydrocarbon energies in particular are much improved.A simple iterative Hückel pi-electron molecular orbital calculation allows modelling of conjugated systems. Calculated bond lengths and rotational barriers for a series of conjugated hydrocarbons and nitrogen heterocycles are shown to be as accurate as those determined by the MM2 SCF method.Explicit hydrogen-bonding potentials for H-bond acceptor-donor atom pairs have been included to give better hydrogen bond energies and lengths. The van der Waals radii of protonic hydrogens are reduced to 0.5 Å and the energy well depth is increased to 1.0 kcal mol-1.Two new general atom types, N+
sp
2
and O-
sp
3
, have been introduced which allow a wide variety of charged conjugated systems to be studied. A minimum of parameterisation is required, as the new types are easily included in the Hückel scheme which automatically adjusts bond and torsional parameters according to the defined bond-order relationships. 相似文献
107.
The composition of cellulose, hemicellulose, starch, lignin, pectin, protein, and total lipid content in the selected cellulosic
wastes-tapioca (Manihot esculenta) stem, leaf, petiole, and water hyacinth (Eichhornia crassipes) were determined. The effectiveness of various physical and chemical pretreatments on the enzymatic digestibility of these
wastes were identified. In general, chemical pretreatments were more effective than physical pretreatments. The efficiency
of the pretreatment was checked by subjecting these wastes to enzymatic saccharification after the pretreatments. 相似文献
108.
Studies were carried out on saccharification of pretreated tapioca waste and water hyacinth under two different conditions:
using microbial enzymes (cellulase fromMyrothecium verrucaria, Coprinus comatus,Pleurotus florida, andCellulomonas sp.) and solid-state fermentation. The rate of saccharification was determined at different temperatures, pH, substrate concentration,
and incubation period. It was found that as the source of the enzyme varies, the optimal temperature and pH for the saccharification
varies. Among the two different treatments, enzymatic saccharification was found to be the most efficient. Among the various
cellulase sources tested, M.verrucaria cellulase was found to be the most efficient one followed byC. comatus, P. florida, and finallyCellulomonas sp. 相似文献
109.
Igor A. Sedov Timur I. Magsumov Erin Hart Elizabeth Higgins Damini Grover Heidi Zettl Minaz Zad William E. AcreeJr. Michael H. Abraham 《Journal of solution chemistry》2017,46(2):331-351
A gas chromatographic headspace analysis method was used to experimentally determine gas-to-liquid partition coefficients and infinite dilution activity dilution for 14 different aliphatic and cyclic hydrocarbons (alkanes, cycloalkanes, alkenes, alkynes), eight different aromatic compounds (benzene, alkylbenzenes, halobenzenes), five different chloroalkanes (dichloromethane, trichloromethane, 1-chlorobutane, 1,2-dichloropropane, isopropylbromide), tetrahydrofuran, butyl acetate, and acetonitrile dissolved in diethylene glycol at 298.15 K. Solubilities were also measured at 298.15 K for 31 crystalline nonelectrolyte organic solutes including several polycyclic aromatic hydrocarbons and substituted benzoic acid derivatives. The experimental results of the headspace chromatographic and spectroscopic solubility measurements were converted to gas-to-diethylene glycol and water-to-diethylene glycol partition coefficients, and molar solubility ratios using standard thermodynamic relationships. Expressions were derived for solute transfer into diethylene glycol from the calculated partition coefficients and solubility ratios. Mathematical correlations based on the Abraham model describe the observed partition coefficient and solubility data to within 0.14 log10 units (or less). 相似文献
110.
Ester Abtew Abraham J. Domb Arijit Basu 《Journal of polymer science. Part A, Polymer chemistry》2017,55(16):2657-2662
We report on the synthesis of polypeptides with saccharide side chains starting from d ‐glucosaminic acid. The hydroxyl groups were first protected by benzylation, followed by N‐carboxyanhydride formation, which was polymerized by ring opening to form a high molecular weight polyamide. De‐protection of the benzyl groups yields a polypeptide with fully de‐protected saccharide side chains. The resulting new non‐ionic, water soluble, and optically active polymers possessing the properties of both peptides and saccharides have potential use as scaffolds for tissue engineering and drug carriers. The method described here may be extended to any saccharide α‐amino acid. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2657–2662 相似文献