全文获取类型
收费全文 | 802篇 |
免费 | 22篇 |
国内免费 | 6篇 |
专业分类
化学 | 508篇 |
晶体学 | 7篇 |
力学 | 38篇 |
数学 | 165篇 |
物理学 | 112篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 23篇 |
2021年 | 33篇 |
2020年 | 29篇 |
2019年 | 25篇 |
2018年 | 22篇 |
2017年 | 14篇 |
2016年 | 46篇 |
2015年 | 22篇 |
2014年 | 37篇 |
2013年 | 65篇 |
2012年 | 48篇 |
2011年 | 49篇 |
2010年 | 29篇 |
2009年 | 31篇 |
2008年 | 32篇 |
2007年 | 26篇 |
2006年 | 39篇 |
2005年 | 35篇 |
2004年 | 20篇 |
2003年 | 26篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有830条查询结果,搜索用时 15 毫秒
61.
Poli MA Rivera VR Neal DD Baden DG Messer SA Plakas SM Dickey RW Said KE Flewelling L Green D White J 《Journal of AOAC International》2007,90(1):173-178
A new competitive electrochemiluminescence-based immunoassay for the type-2 brevetoxins in oyster extracts was developed. The assay was verified by spiking known amounts of PbTx-3 into 80% methanol extracts of Gulf Coast oysters. We also provide preliminary data demonstrating that 100% acetone extracts, aqueous homogenates, and the clinical matrixes urine and serum can also be analyzed without significant matrix interferences. The assay offers the advantages of speed ( 2 h analysis time); simplicity (only 2 additions, one incubation period, and no wash steps before analysis); low limit of quantitation (conservatively, 50 pg/mL = 1 ng/g tissue equivalents); and a stable, nonradioactive label. Due to the variety of brevetoxin metabolites present and the lack of certified reference standards for liquid chromatography-mass spectrometry confirmation, a true validation of brevetoxins in shellfish extracts is not possible at this time. However, our assay correlated well with another brevetoxin immunoassay currently in use in the United States. We believe this assay could be useful as a regulatory screening tool and could support pharmacokinetic studies in animals and clinical evaluation of neurotoxic shellfish poisoning victims. 相似文献
62.
Existence and uniqueness results for a fractional two‐times evolution problem with constraints of purely integral type 下载免费PDF全文
Said Mesloub 《Mathematical Methods in the Applied Sciences》2016,39(6):1558-1567
This paper deals with a fractional two‐times evolution equation associated with initial and purely boundary integral conditions. The existence and uniqueness of generalized solution are proved. The classical functional method based on a priori estimates and density used by many authors in the case of nonfractional differential equations is applied for the time fractional case. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
63.
Elvira M. Bauer Marcello Colapietro Said A. Ibrahim Gustavo Portalone 《Journal of solid state chemistry》2006,179(2):389-397
Co[(CH3PO3)(H2O)] (1) and Co[(C2H5PO3)(H2O)] (2) were prepared by the hydrothermal method and isolated as blue-violet platelet crystals. They were characterized by X-ray diffraction, FT-IR, TGA-DSC techniques and their magnetic properties studied by a dc-SQUID magnetometer. Compound (1) shows an hybrid layered structure, made of alternating inorganic and organic layers along the a-direction of the unit cell. The inorganic layers contain Co(II) ions six-coordinated by five phosphonate oxygen atoms and one from the water molecule. These layers are separated by bi-layers of methyl groups and van der Waals contacts are established between them. In compound (2), the layered hybrid structure is rather similar to that described for compound (1), but the alternation of the inorganic and organic layers is along the b-direction of the unit cell. The magnetic behavior of (1) and (2) as function of temperature and magnetic field was studied. The compounds obey the Curie-Weiss law at temperatures above 100 K, the Curie C, and Weiss θ constants for the methyl derivative being and and for the ethyl derivative and , respectively. The observed magnetic moments for Co atom at room temperature (i.e. μeff=5.18 and 5.38 BM, respectively) are higher than those expected for a spin-only value for high spin Co(II) (S=3/2), revealing a substantial orbital contribution to the magnetic moment. The negative values of θ are an indication of the presence of antiferromagnetic exchange couplings between the near-neighbors Co(II) ions, within the layers. [Co(CnH2n+1PO3)(H2O)] (n=1,2) are 2D Ising antiferromagnets at low temperatures. 相似文献
64.
Said M. Bayomi 《中国化学会会志》1992,39(1):101-104
A convenient route is reported for the synthesis of fused pyrrolo[2,3-d][1,3]oxazine and pyrrolo[2,3-d]-pyrimidine derivatives from 2-amino-1-benzyl-3-t-butoxycarbonyl]-4,5-dimethylpyrrole. 相似文献
65.
Ahmed A. Abdel-Khalek Said M. Sayyah Fadia F. Abdel-Hameed 《Transition Metal Chemistry》1994,19(1):108-110
A novel chromium(III) complex of tetraoxalylurea was prepared. In aqueous solutions, [CrIII(H2L)(H2O)]+ (H2L = diprotonated tetraoxalylurea) is oxidized by IO
4
–
according to the rate law
相似文献
66.
In this paper, we calculate the band gap and the band discontinuities of a GaN
y
AsBi
x
structure lattice matched to GaAs substrate using the conduction and the valence band anticrossing models at the same time.
The results obtained show a good agreement with experiment. The nitrogen and the bismuth concentrations leading to a wavelength
emission of 1.55 μm have been determined (x = 3.5%, y = 2%). This structure shows a good electron confinement resulting in a high characteristic temperature. 相似文献
67.
Said Mesloub 《Journal of Mathematical Analysis and Applications》2006,316(1):189-209
We study a nonlocal mixed problem for a nonlinear pseudoparabolic equation, which can, for example, model the heat conduction involving a certain thermodynamic temperature and a conductive temperature. We prove the existence, uniqueness and continuous dependence of a strong solution of the posed problem. We first establish for the associated linear problem a priori estimate and prove that the range of the operator generated by the considered problem is dense. The technique of deriving the a priori estimate is based on constructing a suitable multiplicator. From the resulted energy estimate, it is possible to establish the solvability of the linear problem. Then, by applying an iterative process based on the obtained results for the linear problem, we establish the existence, uniqueness and continuous dependence of the weak solution of the nonlinear problem. 相似文献
68.
Syed Najmul Hejaz Azmi Bashir Iqbal Muna Ahmed Mohad Jaboob Warda Ali Said Al Shahari Nafisur Rahman 《中国化学会会志》2009,56(6):1083-1091
The objective of this work is to develop and validate spectrophotometric method for the determination of piroxicam in commercial dosage forms. The method is based on the chelation of the drug with Fe(III) to form pink coloured metal chelate at room temperature which absorbs maximally at 504 nm. Beer's law is obeyed over the concentration range of 8–160 μg mL?1 (A = 1.07 × 10?3 + 7.75 × 10?3 C). Under the optimized experimental conditions, proposed method is validated as per the International Conference on Harmonisation guidelines. The limits of detection and quantitation for the proposed method are 0.775 and 2.348 μg mL?1, respectively. The proposed method has been successfully applied to the determination of piroxicam in commercial dosage forms. The results are compared with the reference El‐Ries et al. spectrophotometric method. 相似文献
69.
Liu D Chu XQ Lagi M Zhang Y Fratini E Baglioni P Alatas A Said A Alp E Chen SH 《Physical review letters》2008,101(13):135501
Molecular dynamics simulations and neutron scattering experiments have shown that many hydrated globular proteins exhibit a universal dynamic transition at TD = 220 K, below which the biological activity of a protein sharply diminishes. We studied the phononlike low-energy excitations of two structurally very different proteins, lysozyme and bovine serum albumin, using inelastic x-ray scattering above and below TD. We found that the excitation energies of the high-Q phonons show a marked softening above TD. This suggests that the large amplitude motions of wavelengths corresponding to this specific Q range are intimately correlated with the increase of biological activities of the proteins. 相似文献
70.
Determination of flumequine in channel catfish by liquid chromatography with fluorescence detection.
S M Plakas K R el Said F A Bencsath S M Musser C C Walker 《Journal of AOAC International》1999,82(3):614-619
Rapid methods are described for determination of flumequine (FLU) residues in muscle and plasma of farm-raised channel catfish (Ictalurus punctatus). FLU residues were extracted from tissues with an acidified methanol solution, and extracts were cleaned up on C18 solid-phase extraction cartridges. FLU concentrations were determined by liquid chromatography (LC) using a C18 analytical column and fluorescence detection (excitation, 325 nm; emission, 360 nm). Mean recoveries of FLU from fortified muscle were 87-94% at 5 levels ranging from 10 to 160 ppb (5 replicates per level). FLU recoveries from fortified plasma were 92-97% at 5 levels ranging from 20 to 320 ppb. Limits of detection (signal-to-noise ratio, 3:1) for the method as described were 3 and 6 ppb for muscle and plasma, respectively. Relative standard deviations (RSDs) for recoveries were < or = 12%. Live catfish were dosed with 14C-labeled or unlabeled FLU to generate incurred residues. Recoveries of 14C residues throughout extraction and cleanup were 90 and 94% for muscle and plasma, respectively. RSDs for incurred FLU at 2 levels in muscle and plasma ranged from 2 to 6%. The identity of FLU in incurred tissues was confirmed by LC/mass spectrometry. 相似文献
|