全文获取类型
收费全文 | 4217篇 |
免费 | 140篇 |
国内免费 | 25篇 |
专业分类
化学 | 2868篇 |
晶体学 | 34篇 |
力学 | 156篇 |
数学 | 400篇 |
物理学 | 924篇 |
出版年
2024年 | 18篇 |
2023年 | 36篇 |
2022年 | 256篇 |
2021年 | 199篇 |
2020年 | 146篇 |
2019年 | 133篇 |
2018年 | 162篇 |
2017年 | 116篇 |
2016年 | 161篇 |
2015年 | 156篇 |
2014年 | 160篇 |
2013年 | 308篇 |
2012年 | 254篇 |
2011年 | 285篇 |
2010年 | 157篇 |
2009年 | 140篇 |
2008年 | 150篇 |
2007年 | 170篇 |
2006年 | 128篇 |
2005年 | 133篇 |
2004年 | 84篇 |
2003年 | 78篇 |
2002年 | 70篇 |
2001年 | 71篇 |
2000年 | 52篇 |
1999年 | 58篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 28篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 40篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 38篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 27篇 |
1977年 | 28篇 |
1976年 | 18篇 |
1968年 | 10篇 |
排序方式: 共有4382条查询结果,搜索用时 15 毫秒
991.
M. S. Khan D. J. Schwartz N. A. Pasha A. K. Kakkar B. Lin P. R. Raithby J. Lewis 《无机化学与普通化学杂志》1992,616(10):121-124
Reaction of Pt(PnBu3)2Cl2 (1) or Pt(AsnBu32Cl2 (2) with stoichiometric amounts of 1,3,5-triethynylbenzene, [1,3,5-(H? C?C? )3C6H3] (3)yields monomeric, [1,3,5-Cl(PnBu3)2(Pt? C? C? )3C6H3] (4), [1,3,5-(C1)(AsnBu3)2Pt? C? C? 3C6H3] (5) or polymeric, {1,3,5-[(PnBu3)2Pt? C?C? ]3C6H3? )n (6), {1,3,5-[(AsnBu3)2Pt? C? C? ]3C6H3? }n (7) complexes. Treatment of (1) with (3) and 2,5-diethynyl-p-xylene,H? C? C? C6H2(CH3)2? C? C? H (8) in varying molar ratios yields a series of high molecular weight cross linked platinum metal containing polyyne copolymers. 相似文献
992.
R. K. Agarwal B. Prakash V. Kumar A. Aslam Khan 《Journal of the Iranian Chemical Society》2007,4(1):114-125
In present studies a new series of twenty four complexes of seven and ten coordinated compounds derived from 4[Ncinnamalidene) amino]antipyrine semicarbazone (CAAPS) as primary ligand and diphenyl sulfoxide (DPSO) as secondary ligand has been reported. All the complexes have the general composition LnX3.n(CAAPS).DPSO (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho, X = NCS or ClO4, n = 2, X = NO3, n = 1). The compounds have been characterized by elemental analysis, molar conductance, magnetic susceptibility, infrared and electronic spectra. Thermal characteristics were also reported. Based on the data appropriate structures are assigned for these complexes. 相似文献
993.
T. A. Khan W. D. Lauppe H. A. Selič H. Lawin G. Sadler M. Shaanan K. Sistemich 《Zeitschrift für Physik A Hadrons and Nuclei》1975,275(3):289-296
A windowless Si(Li) electron detector has been used in conjunction with the gas filled fission product separator JOSEF to study totally converted transitions in Zr and Mo isotopes. The existence of twoβ-decay modes in96Y,98Y and100Nb is confirmed. The half-lives of theβ-decaying levels feeding O 2 + states in96Zr and98Zr are 6.0 ± 0.4 sec and 0.60±0.05 sec respectively. A search for other first excited O 2 + states shows that no such states are apparent in100Zr and104Mo. 相似文献
994.
M. Niyaz Khan 《国际化学动力学杂志》2002,34(2):95-103
The kinetics of the aqueous cleavage of N‐ethoxycarbonylphthalimide (NCPH) in CH3NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC A B , where ENMBC, A , and B represent ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoyl]carbamate, N‐hydroxyl group cyclized product of ENMBC, and o ‐(N‐methyl‐N‐hydroxycarbamoyl)benzoic acid, respectively. The rate constant k1 obs at a constant pH, obeys the relationship k1 obs = kw + knapp [Am]T + kb[Am]T2, where [Am]T is the total concentration of CH3NHOH buffer and kw is first‐order rate constant for pH‐independent hydrolysis of NCPH. Buffer‐dependent rate constant kb shows the presence of both general base and general acid catalysis. Both the rate constants k2 obs and k3 obs are independent of [Am]T (within the [Am]T range of present study) at a constant pH and increase linearly with the increase in aOH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95–103, 2002 相似文献
995.
Khan F 《Macromolecular bioscience》2005,5(1):78-89
Gamma-radiation-induced graft copolymerization of methyl methacrylate onto natural lignocellulose (jute) fiber was carried out by the preirradiation method in an aqueous medium by using octylphenoxy-polyethoxyethanol as an emulsifier. The different factors that influenced the graft copolymer reaction process were investigated. In the case of radiation-dose-dependent grafting, samples irradiated in the presence of air produced up to 73% graft weight compared to 53% obtained in the case of irradiation in a nitrogen environment. By assuming Arrhenius reaction kinetics, the activation energy (E(a)) of the grafting reaction process was evaluated for different reaction temperatures. Moreover, the graft copolymer reaction was controlled by incorporating a homopolymer-inhibiting agent and three different chain-transfer agents in the reaction medium. The mechanical and thermal properties of jute fiber 'as received' and jute-graft-poly(methyl methacrylate) were also investigated. The results showed that the percentage of grafting with jute fiber has a significant effect on the properties. The kinetic parameters were evaluated from TGA thermograms by using Broido's method in the temperature range 240-350 degrees C. Scanning electron micrographs show that the structural changes on the surface of jute fibers were induced by graft copolymerization of methyl methacrylate monomer. Fiber-fiber surface friction was measured in terms of the average maximum load and the kinetic friction. SEM of jute-graft-poly(methyl methacrylate). 相似文献
996.
A simple and rapid spectrophotometric method has been investigated for the determination of furosemide. The method is based upon simple diazotization reaction. The absorbance was measured at 480 nm. The method is optimized for acidity, amount of reagents required and heating time. The range of linearity was 0.4–10 μg mL?1 of furosemide with molar absorptivity of 1.0 × 104 l mol?1 cm?1. Standard deviation, coefficient of variance, limit of detection and limit of quantification were calculated using authentic standard of furosemide and were found to ± 0.0013,12.7%, 0.16 ppm and 0.52 ppm, respectively. The method was applied to various pharmaceutical preparations containing furosemide. The results of the investigated method for furosemide were compared with available official literature method. The results obtained by the proposed method agree well with the standard established method. 相似文献
997.
Heather Davis Walter Skrzypek Arshad Khan 《Journal of polymer science. Part A, Polymer chemistry》1994,32(12):2267-2274
The iodine binding capacity (IBC) of amylopectin (AP, from potatoes) is determined to be around 0.38% (w/w) of the total AP in the solution. The mass of iodine bound comprises about 13.6% of the mass of AP involved with the complex, suggesting that with every four iodine atoms bound there are 23 anhydroglucose residues (AGU). Since our previous study indicates that four iodine atoms within the helix of 11 AGUs form a chromophore unit in the API complex, only 48% of the AGUs (11 out of 23) in the AP molecule are directly involved with the iodine. The heat of reaction for the API complex formation is determined to be around ?47 kJ/mol of I–I units bound and is significantly lower in magnitude than that of the amylose-iodine (AI) complex [Biopolymers, 31 , 57 (1991)]. A possible mechanism has been proposed for the formation of AI and API complexes with fixed compositions. © 1994 John Wiley & Sons, Inc. 相似文献
998.
A highly oxygenated, novel pentacyclic bis-oxa-bridged compound 8 was synthesized with remarkable efficiency starting from readily available tetrachloro-5,5-dimethoxyclopentadiene and 1,4-cyclohexadiene in three steps. The ruthenium-catalyzed oxidation of 2:1 bis-adduct 1 followed by a one-pot transformation of the resulting bis-alpha-diketone 3 furnished (after esterification) the title compound in an overall yield of 29.1%. The versatility of this simple method was further demonstrated with other norbornyl alpha-diketones to obtain the corresponding strained oxa-bridged derivatives. 相似文献
999.
The role of anion-exchange resin beads in the initiation of reactions of tertiary amines with 2,4-dinitrophenylhydrazine has been explored. This reagent has been used for the selective detection and determination of aliphatic amines. Radiochemical studies have been performed to show that the coloured species is adsorbed but not exchanged on ion-exchange beads. A model for the interaction is proposed. 相似文献
1000.
V. Lange M. A. Khan U. Eichmann W. Sandner 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,18(4):319-324
We report on the spectroscopy of highly excited strontium ions after resonant multistep laser excitation. The states observed belonged to then s (26≦n≦79),n d (25≦n≦83),n f (28≦n≦86) andn g (30≦n≦81) series of Sr+. A least squares fit has been applied to determine the quantum defects and their linear energy dependence in each series, together with the ionisation limit of Sr+. The analysis of our data lead to a revised value for this ionisation limit of 88 965.18±0.02 cm?1, with respect to the ground state of the Sr+ ion. Analysis of the non core-penetratingn g states yielded experimental values for the dipole and quadrupole polarizability of Sr++, which are in satisfactory agreement with previous calculations. 相似文献