全文获取类型
收费全文 | 9228篇 |
免费 | 1489篇 |
国内免费 | 893篇 |
专业分类
化学 | 4120篇 |
晶体学 | 68篇 |
力学 | 842篇 |
综合类 | 49篇 |
数学 | 363篇 |
物理学 | 6168篇 |
出版年
2024年 | 15篇 |
2023年 | 83篇 |
2022年 | 243篇 |
2021年 | 237篇 |
2020年 | 261篇 |
2019年 | 261篇 |
2018年 | 246篇 |
2017年 | 270篇 |
2016年 | 345篇 |
2015年 | 332篇 |
2014年 | 458篇 |
2013年 | 757篇 |
2012年 | 547篇 |
2011年 | 688篇 |
2010年 | 489篇 |
2009年 | 613篇 |
2008年 | 625篇 |
2007年 | 690篇 |
2006年 | 593篇 |
2005年 | 469篇 |
2004年 | 402篇 |
2003年 | 364篇 |
2002年 | 396篇 |
2001年 | 294篇 |
2000年 | 296篇 |
1999年 | 212篇 |
1998年 | 203篇 |
1997年 | 154篇 |
1996年 | 125篇 |
1995年 | 144篇 |
1994年 | 107篇 |
1993年 | 132篇 |
1992年 | 87篇 |
1991年 | 69篇 |
1990年 | 59篇 |
1989年 | 38篇 |
1988年 | 38篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 37篇 |
1984年 | 43篇 |
1983年 | 16篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
211.
212.
213.
An overview is given on recent advances of density functional theory (DFT) as applied to the calculation of nuclear magnetic
resonance (NMR) chemical shifts and electron spin resonance (ESR) g-tensors. This is a new research area that has seen tremendous progress and success recently; we try to present some of these
developments. DFT accounts for correlation effects efficiently. Therefore, it is the only first-principle method that can
handle NMR calculations on large systems like transition-metal complexes. Relativistic effects become important for heavier
element compounds; here we show how they can be accounted for. The ESR g-tensor is related conceptually to the NMR shielding, and results of g-tensor calculations are presented. DFT has been very successful in its application to magnetic properties, for metal complexes
in particular. However, there are still certain shortcomings and limitations, e.g., in the exchange-correlation functional,
that are discussed as well.
Received: 24 October 1997 / Accepted: 19 December 1997 相似文献
214.
A novel method for the determination of proteins in aqueous solutions has been developed based on the enhancement of resonance light scattering (RLS) of Ag nanoparticles in the presence of proteins. Factors including acidity of the media, concentration of Ag hydrosol, reaction time, temperature, and interference of non-protein substances were investigated. Under the optimal conditions, with the enhanced RLS signals at 452nm, the linear ranges of calibration curves were 0–0.8µgmL–1 for bovine serum albumin (BSA), 0–1.2µgmL–1 for human serum albumin (HSA), and 0–2.5µgmL–1 for human -IgG (-IgG), respectively. The detection limits were 1.3ngmL–1 for BSA, 10ngmL–1 for HAS, and 5.7ngmL–1 for -IgG.This method has been applied to the analysis of synthetic samples and real human serum samples, and the results were in good agreement with those reported by the hospital, indicating that the method presented here is not only sensitive and simple, but also reliable and suitable for practical applications. 相似文献
215.
Qing Z Wen-Chen Z Xiao-Xuan W Yang M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):769-772
From the high-order perturbation formulas of EPR parameters (zero-field splitting D, g factors gparallel, gperpendicular and hyperfine structure constants Aparallel, Aperpendicular) based on the two spin-orbit coupling parameter model for 3d3 ions in trigonal symmetry, the EPR parameters of Cr3+ and V2+ ions in HfS2 crystals are calculated. From the calculations, it is found that the local trigonal distortion angle theta of impurity center in HfS2:Cr3+ is smaller than that in HfS2:V2+. The dominant cause of the small zero-field splitting |D| and g-anisotropy |Deltag|=|gparallel-gperpendicular| in HfS2:Cr3+ (compound to HfS2:V2+) is due to the small local trigonal distortion angle theta rather than to the small impurity-ligand distance R in HfS2:Cr3+. 相似文献
216.
A quantitative determination method of formic acid in apple juices is proposed by means of the proton nuclear magnetic resonance (1H NMR) technique. Formic acid gives a singlet signal at the 8.2-8.4 ppm interval of the spectrum, and its area is used to determine the concentration of the acid. 1,3,5-Benzenetricarboxylic acid is added to the juice as an internal standard. Since the chemical shift of both species varies with the pH, ascorbic acid is also added to adjust it at 2.74 and to avoid the overlapping of the signals. Recoveries between 95 and 109% are obtained when the standard addition method is applied to the juices of five different cider apple varieties. The coefficient of variation obtained is 3.9% for intra-day repeatability (n = 5), and 4.6% for inter-day repeatability (n = 10). The limit of detection is 1.49 mg/l, calculated from “3Sy/x + intercept”. The described method is direct and no previous derivatization is needed. 相似文献
217.
The mouse immunoglobulin G (mouse IgG) as a kind of bio-molecule was labeled with two different luminescent colloidal semiconductor quantum dots (QDs), green-emitting CdTe quantum dots and red-emitting CdTe quantum dots in this work. As a result of the fluorescence resonance energy transfer (FRET) between the two different sizes nanoparticles with mouse IgG as the binding bridge, a significant enhancement of the emission of the red-emitting CdTe quantum dots and the corresponding quenching of the emission of green-emitting CdTe quantum dots were observed. The relationship between the concentration of the mouse immunoglobulin G and the fluorescence intensity ratio (Ia/Id) of acceptors and donors was studied also. Under optimal conditions, the calibration graph is linear over the range of 0.1–20.0 mg/L mouse IgG. 相似文献
218.
Quantum equations of motion describing the energy transfer dynamics via intramolecular anharmonic coupling are presented and solved numerically. Dynamical features of the average excitations of a homogeneous system (SF6) and a heterogeneous system (H/W) are quantitatively discussed in terms of the intramolecular vibrational relaxation (IVR) rates. Possible mechanisms of surface-enhanced desorption via low-power laser radiation are proposed.This work was supported in part by the Office of Naval Research, the Air Force Office of Scientific Research (AFSC), United States Air Force, under Grant AFOSR-82-0046 and the National Science Foundation under Grant No. CHE-8022874Camille and Henry Dreyfus Teacher-Scholar (1975–82) 相似文献
219.
On Chalcogenolates. 206. N-Thioacetyl Dithiocarbamates and Esters of N-Thioacetyl Dithiocarbamic Acid Thioacetamide reacts with carbon disulfide in the presence of KH to form via the tetrabutyl ammonium salt dark yellow N-thioacetyl dithiocarbamates M[S2C? NH? CS? CH3], where M = K, Rb, Cs. The salts as well as the methyl and ethyl ester have been characterized by means of electron absorption, infrared, nuclear magnetic resonance (1H and 13C), and mass spectra. Attempts to synthesize N-thioacetyl dithiocarbamic acid were not successful. 相似文献
220.