全文获取类型
收费全文 | 2769篇 |
免费 | 94篇 |
国内免费 | 13篇 |
专业分类
化学 | 1944篇 |
晶体学 | 118篇 |
力学 | 58篇 |
数学 | 209篇 |
物理学 | 547篇 |
出版年
2023年 | 26篇 |
2022年 | 56篇 |
2021年 | 53篇 |
2020年 | 51篇 |
2019年 | 66篇 |
2018年 | 47篇 |
2017年 | 65篇 |
2016年 | 109篇 |
2015年 | 54篇 |
2014年 | 75篇 |
2013年 | 227篇 |
2012年 | 145篇 |
2011年 | 173篇 |
2010年 | 109篇 |
2009年 | 83篇 |
2008年 | 154篇 |
2007年 | 136篇 |
2006年 | 134篇 |
2005年 | 113篇 |
2004年 | 85篇 |
2003年 | 75篇 |
2002年 | 63篇 |
2001年 | 32篇 |
2000年 | 49篇 |
1999年 | 27篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 22篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 23篇 |
1992年 | 29篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 31篇 |
1985年 | 25篇 |
1984年 | 31篇 |
1983年 | 23篇 |
1982年 | 31篇 |
1981年 | 35篇 |
1980年 | 25篇 |
1979年 | 25篇 |
1978年 | 23篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1975年 | 22篇 |
1973年 | 19篇 |
排序方式: 共有2876条查询结果,搜索用时 15 毫秒
941.
Summary The chromatographic separation and resolution of the enantiomers of flurbiprofen and its two major metabolites, 4′-hydroxyflurbiprofen
and 3′-hydroxy-4′-methoxyflurbiprofen was investigated using four different approaches: reversed-phase HPLC after pre-column
derivatization with (R)-1-(naphthen-1-yl)ethylamine; reversed-phase HPLC using hydroxypropyl-β-cyclodextrin as a chiral mobile phase additive; chiral-phase
HPLC using either an α1-acid glycoprotein CSP (Chiral-AGP) or an amylose tris(3,5-dimethylphenylcarbamate) CSP (Chiralpak AD). Of all the approaches,
only the direct method using the Chiralpak AD CSP demonstrated separation and enantiomeric resolution of all three analytes
within an acceptable run time of 45 minutes. Enantiomeric resolution values of 1.67,3.67 and 3.44 were obtained for flurbiprofen,
4′-hydroxyflurbiprofen and 3′-hydroxy-4′-methoxyflurbiprofen respectively. Semi-preparative isolation of the individual enantiomers
of both metabolites, followed by CD analysis, revealed that the elution order on the AD CSP wasR-beforeS-enantiomer for both metabolites and the same as that observed for flurbiprofen. The metabolite elution order was subsequently
confirmed on the analysis of urine samples obtained from a healthy volunteer following oral administration of the individual
drug enantiomers. 相似文献
942.
All Mendelsohn designs containing a Frobenius group with cyclic complement of orderv – 1 as a subgroup of the automorphism are found. Furthermore, the automorphism group of each of the designs is constructed. These designs generalize Mendelsohn's construction of Mendelsohn designs containing a certain doubly transitive automorphism group.The research on this paper was partially supported by North Texas State Faculty Research Grant #35524. 相似文献
943.
S Chopra N S Pawar M P Singh Rakesh Kumar J Prasad V P Patel Raj Pal B Kumar S Ojha K Devarani T Nandi M Sota P Barua S Gargari R Joshi D Kanjilal SK Datta 《Pramana》2002,59(5):753-759
The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications
performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor
network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper
system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter
etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken
and other activities for the system are being reported in the present paper. 相似文献
944.
Thep-Si/HF-electrolyte interface was characterized by capacitance–voltage (C–V) and current–voltage (I–V) studies. At low frequency, the measured capacitance exhibits two maxima: one in the weak accumulation regime (around 0.8 V
[SCE]) and the other in the strong accumulation regime (around 2.6 V [SCE]), both of which disappear at high frequency. The
disappearance of the two capacitance maxima is attributed to the slow response of interface traps to high frequencies. The
flat-band potential, VFB, is found to be frequency dependent. The surface state densities corresponding to the two capacitance maxima are estimated
to be 3.2×1011 cm-2 and 2.4×1011 cm-2, respectively. The in situ I–V characteristics distinguish pore formation, transition and electropolishing regions. Porous Si synthesized at 50 mA cm-2 gives a broad photoluminescence peak around 2.04 eV at 300 K.
Received: 4 September 2000 / Accepted: 9 February 2001 / Published online: 26 April 2001 相似文献
945.
We report the results of the computer simulation of a collection of particles interacting via an anisotropic potential proposed by Luckhurst and Romano and modified by scaling with part of the anisotropic well depth formalism employed by Gay-Berne. Using the molecular dynamics technique for 256 particles in the NVE ensemble, the system is shown to exhibit a variety of mesophases, as the temperature is lowered, and these are provisionally identified as isotropic, discotic nematic, a highly ordered fluid phase with some columnar features and a crystal. 相似文献
946.
Polyethers have been prepared by condensing the disodium salt of 5,5′-methylene-bis(8-hydroxyquinoline) (MBQ) with p-xylylene dichloride and dibromide, 4,4′-dichloromethyldiphenyl ether, 4,4′-dichloroacetyldiphenyl, 4,4′-dichloroacetyldiphenyl ether and methylene and ethylene dichlorides. All the polycondensations except those with the two aliphatic dihalides could be effected in dioxane and in DMF. The polycondensation of the disodium salt of MBQ with the two aliphatic dihalides could be effected in the absence of solvent in a sealed tube using Ullman catalysts. All the polyethers are insoluble in common organic solvents. I.R. spectra of the polyethers have been measured in KBr. The thermal and electrical properties of these polyethers have been studied. 相似文献
947.
Boron (<20 μg ml?1) in aqueous solutions gives no absorbance but addition of ascorbic acid, especially with titanium greatly enhances the signal, leading to a detection limit of 0.2 μg ml?1 boron. The presence of uranium (<10 mg ml?) only slightly decreases the boron signal. 相似文献
948.
949.
Using fits to the available data on the pion and deuteron electromagnetic form factors and the Chou-Yang model, the computed
values of differential cross-sections for high-energy pion-deuteron elastic scattering agree reasonably well with the available
experimental data. Whereas only a shoulder is expected to appear up to energies of several hundreds of GeV, a dip and a secondary
maximum are predicted to be conspicuous only forP
lab≫400 GeV/C. The position of the dip starts at a much lower value, |t
d| ≅ 0.5–0.6 GeV2, as compared to the corresponding position in thepp scattering. The positions of the first dip are plotted against total cross-section which can be verified by future high-energy
experiments. Limitations of the model predictions for ultrahigh energies are pointed out. 相似文献
950.
Albert H. Schroeder Frank B. Kaufman Vishnu Patel Edward M. Engler 《Journal of Electroanalytical Chemistry》1980,113(2):193-208
General methods are described for the synthesis of electroactive polymers and the preparation of uniform, stable, polymer-coated electrodes. The electrochemical behaviour of thin films of eight different functionalized polystyrenes, differing in the identity and amount of attached electroactive species, and polyvinylferrocene is presented. A wide range of electrochemical properties can be observed by varying parameters such as film thickness, nature of the bound redox couple, extent of polymer functionalization and oxidation state. The deviations from ideal surface behavior are investigated in detail. These are shown to be consequences of cooperative electronic interactions, structural reorganization or uncompensated resistance within the film, depending upon the material. The film resistance varies greatly among the polymer films studied and is shown, in some cases, to be a sensitive function of the extent of oxidation and prior treatment of the film. This variable resistance is shown to be a consequence of slow ion transport through the film. The mechanism of electron transport in such materials is considered and a model of the metal/polymer/electrolyte interface is proposed. 相似文献