全文获取类型
收费全文 | 327篇 |
免费 | 10篇 |
专业分类
化学 | 169篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 16篇 |
物理学 | 140篇 |
出版年
2023年 | 2篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2018年 | 4篇 |
2016年 | 5篇 |
2015年 | 11篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 20篇 |
2011年 | 14篇 |
2010年 | 14篇 |
2009年 | 6篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1986年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1964年 | 1篇 |
1963年 | 2篇 |
1961年 | 1篇 |
1932年 | 1篇 |
1931年 | 3篇 |
1930年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有337条查询结果,搜索用时 0 毫秒
21.
Using deeply virtual Compton scattering as a tool to study the structure of hadrons in an exclusive process, one expresses the amplitudes in terms of invariant quantities: the Compton form factors. In this paper the sensitivity of the hadronic part of the cross section to the Compton form factors is determined. 相似文献
22.
We have used femtosecond midinfrared spectroscopy to study the orientational mobility of water molecules in the hydration shells of hydrophobic groups. Our results show that hydrophobic groups are surrounded by a number of water molecules that display much slower orientational dynamics than the bulk liquid and that are therefore effectively immobilized. It turns out that each methyl group is surrounded by four immobilized water OH groups. 相似文献
23.
24.
Chueng-Ryong Ji Bernard L. G. Bakker Ziyue Li Alfredo T. Suzuki 《Few-Body Systems》2014,55(5-7):425-434
Among the three forms of relativistic Hamiltonian dynamics proposed by Dirac in 1949, the front form has the largest number of kinematic generators. This distinction provides useful consequences in the analysis of physical observables in hadron physics. Using the method of interpolation between the instant form and the front form, we introduce the interpolating scattering amplitude that links the corresponding time-ordered amplitudes between the two forms of dynamics and provide the physical meaning of the kinematic transformations as they allow the invariance of each individual time-ordered amplitude for an arbitrary interpolation angle. We discuss the rationale for using front form dynamics, nowadays known as light-front dynamics (LFD), and present a few explicit examples of hadron phenomenology that LFD uniquely can offer from first-principles quantum chromodynamics. In particular, model-independent constraints are provided for the analyses of deuteron form factors and the N Δ transition form factors at large momentum transfer squared Q 2. The swap of helicity amplitudes between the collinear and non-collinear kinematics is also discussed in deeply virtual Compton scattering. 相似文献
25.
It is shown that, in the relativistic case, the fine-structure splittings of the excited 23 P J and 33 P J states in charmonium are as large as those of the 13 P J state if the same value of αs(μ)≈0.36 is used. The predicted mass of M(23 P 0)=3.84 GeV appears to be 120 MeV lower than the center of gravity of the 23 P J multiplet and lies below the D $\bar D$ * threshold. Our value of M(23 P 0) is nearly 80 MeV lower than that from the Godfrey and Isgur article [Phys. Rev. D 32, 189 (1985)], while the differences in other masses are not greater than 20 MeV. 相似文献
26.
Magnetic resonance images are prone to artifacts caused by metallic objects. Such artifacts may not only hamper image interpretation, but also have been shown to provide information about the magnetic properties of the substances involved. In this work, we aim to explore the potential of MRI to detect, localize and characterize changes in magnetic properties that may occur when certain alloys have been exposed to a thermomechanical stress. For this purpose, stainless steel 304 L wires were drawn to induce a change from paramagnetic austenitic into ferromagnetic martensitic microstructure. The changes in magnetic behavior were quantified by analyzing the geometric distortion in spin echo and the geometric distortion and intravoxel dephasing in gradient echo images at 0.5, 1.5 and 3 T. The results of both imaging strategies were in agreement and in accordance with independent measurements with a vibrating sample magnetometer. Drawing wire to 2% of its cross-sectional area was found to increase the volume fraction of the ferromagnetic martensite from 0.3% to 80% and to enhance the magnetization up to two or three orders of magnitude. The results demonstrate the potential of MRI to locate and quantify stress-induced changes in the magnetic properties of alloys in a completely noninvasive and nondestructive way. 相似文献
27.
M. Pawlak E. Grygolowicz‐Pawlak G. A. Crespo G. Mistlberger E. Bakker 《Electroanalysis》2013,25(8):1840-1846
We report here on plasticized ion‐selective poly(vinyl chloride) membranes with increased biocompatibility by means of a copper(I)‐catalyzed azide‐alkyne cycloaddition (‘click chemistry’) on the surface of finished membranes. We aimed for increasing the hydrophilicity of the surface and the application of NO releasing molecules. Employing the first principle, sodium selective membranes based on azide‐substituted PVC were modified with different length poly(ethylene glycol) (PEG) chains. For the second, cysteine groups were used as a nitrous oxide releasing substance. Surface modification was confirmed by Electrochemical Impedance Spectroscopy (EIS). Potentiometric measurements in undiluted whole blood showed an increased sensor stability in comparison to unmodified PVC. Membrane surfaces after 18 h contact with blood were analyzed with Scanning Electron Microscopy (SEM) and revealed a reduced level of blood cell adsorption on membranes modified with tetraethylene glycol (TEG) and PEGs. In contrast, cysteine modified membranes did not exhibit improved fouling resistance, suggesting that nitric oxide release by itself is not a sufficiently efficient mechanism. 相似文献
28.
Petersen C Bakulin AA Pavelyev VG Pshenichnikov MS Bakker HJ 《The Journal of chemical physics》2010,133(16):164514
We study the spectral and orientational dynamics of HDO molecules in aqueous solutions of different concentrations of tertiary butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO). The spectral dynamics is investigated with femtosecond two-dimensional infrared spectroscopy of the O-H stretch vibration of HDO:D(2)O, and the orientational dynamics is studied with femtosecond polarization-resolved pump-probe spectroscopy of the O-D stretch vibration of HDO:H(2)O. Both the spectral and orientational dynamics are observed to show bimodal behavior: part of the water molecules shows spectral and orientational dynamics similar to bulk liquid water and part of the water molecules displays a much slower dynamics. For low solute concentrations, the latter fraction of slow water increases linearly as a function of solute molality, indicating that the slow water is contained in the solvation shells of TBA and TMAO. At higher concentrations, the fraction of slow water saturates. The saturation behavior is much stronger for TBA solutions than for TMAO solutions, indicating the aggregation of the TBA molecules. 相似文献
29.
Bakker MJ Vergeer FW Hartl F Rosa P Ricard L Le Floch P Calhorda MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(7):1741-1752
Herein we describe in detail the bonding properties and electrochemical behavior of the first known triosmium carbonyl clusters with a coordinated redox-active ligand 4,4',5,5'-tetramethyl-2,2'-biphosphinine (tmbp), the phosphorus derivative of 2,2'-bipyridine. The clusters investigated were [Os(3)(CO)(10)(tmbp)] (1) and its derivative [Os(3)(CO)(9)(PPh(3))(tmbp)] (2). The crystal structures of both clusters are compared with those of relevant compounds; they served as the basis for density functional theory (DFT and time-dependent DFT) calculations. The experimental and theoretical data reveal an unexpected and unprecedented bridging coordination mode of tmbp, with each P atom bridging two metal atoms. The tmbp ligand is formally reduced by transfer of two electrons from the triangular cluster core that consequently lacks one of the metal-metal bonds. Both 1 and 2 therefore represent 50e(-) clusters with a coordinated 8e(-) donor, [tmbp](2-). The HOMO and LUMO of 1 and 2 possess a predominant contribution from different pi*(tmbp) orbitals, implying that the lowest energy excited state possesses a significant intraligand character. This is in agreement with the photostability of these clusters. DFT calculations also predict the experimentally observed structure of 1 to be the most stable one in a series of several plausible structural isomers. Stepwise two-electron electrochemical reduction of 1 and 2 results in dissociation of CO and PPh(3), respectively, and formation of the [Os(3)(CO)(9)(tmbp)](2-) ion. The initially produced radical anions of the parent clusters, in which the odd electron is predominantly localized on the tmbp ligand, are sufficiently stable at low temperatures and can be observed with IR spectroelectrochemistry. The electron-deficiency of the cluster core in 1 permits facile electrocatalytic substitution of a CO ligand by tertiary phosphane and phosphite donors. 相似文献
30.
Jockusch RA Kroemer RT Talbot FO Snoek LC Carçabal P Simons JP Havenith M Bakker JM Compagnon I Meijer G von Helden G 《Journal of the American Chemical Society》2004,126(18):5709-5714
The beta(1-->4) glycosidic linkage found in lactose is a prevalent structural motif in many carbohydrates and glycoconjugates. Using UV and IR ion-dip spectroscopies to probe benzyl lactoside isolated in the gas phase, we find that the disaccharide unit adopts only a single, rigid structure. Its fully resolved infrared ion-dip spectrum is in excellent agreement with that of the global minimum structure computed ab initio. This has glycosidic torsion angles of phi(H) (H1-C1-O-C4') approximately 180 degrees and psi(H) (C1-O-C4'-H4') approximately 0 degrees which correspond to a rotation of approximately 150 degrees about the glycosidic bond compared to the accepted solution-phase conformation. We discuss the biological implications of this discovery and the generality of the strategies employed in making it. 相似文献