全文获取类型
收费全文 | 3757篇 |
免费 | 138篇 |
国内免费 | 45篇 |
专业分类
化学 | 2065篇 |
晶体学 | 53篇 |
力学 | 163篇 |
综合类 | 16篇 |
数学 | 898篇 |
物理学 | 745篇 |
出版年
2023年 | 24篇 |
2022年 | 46篇 |
2021年 | 57篇 |
2020年 | 80篇 |
2019年 | 88篇 |
2018年 | 128篇 |
2017年 | 136篇 |
2016年 | 170篇 |
2015年 | 133篇 |
2014年 | 181篇 |
2013年 | 439篇 |
2012年 | 219篇 |
2011年 | 236篇 |
2010年 | 259篇 |
2009年 | 170篇 |
2008年 | 207篇 |
2007年 | 190篇 |
2006年 | 143篇 |
2005年 | 110篇 |
2004年 | 88篇 |
2003年 | 66篇 |
2002年 | 105篇 |
2001年 | 77篇 |
2000年 | 60篇 |
1999年 | 44篇 |
1998年 | 44篇 |
1997年 | 32篇 |
1996年 | 35篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1986年 | 13篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 25篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1975年 | 10篇 |
1974年 | 13篇 |
1973年 | 10篇 |
排序方式: 共有3940条查询结果,搜索用时 328 毫秒
961.
Gökhan Alpaslan Hasan Tanak Ayşen Alaman Ağar Ahmet Erdönmez Şamil Işık 《Structural chemistry》2010,21(5):1027-1036
The Schiff base compound (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate has been synthesised and characterized
by IR, UV–Vis, and X-ray single-crystal determination. Ab initio calculations have been carried out for the title compound
using the density functional theory (DFT) and Hartree–Fock (HF) methods at 6-31G(d) basis set. The calculated results show
that the DFT/B3LYP and HF can well reproduce the structure of the title compound. Using the TD-DFT and TD-HF methods, electronic
absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental
ones is determined. Molecular orbital coefficient analyses reveal that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. To investigate the tautomeric stability, optimization calculations at B3LYP/6-31G(d)
level were performed for the NH and OH forms of the title compound. Calculated results reveal that the OH form is more stable
than NH form. In addition, molecular electrostatic potential and NBO analysis of the title compound were performed at B3LYP/6-31G(d)
level of theory. 相似文献
962.
Tingting Tu Mihaela Drăgu§anu Brînduşa-Alina Petre Don L. Rempel Michael Przybylski Michael L. Gross 《Journal of the American Society for Mass Spectrometry》2010,21(10):1660-1667
A new methodology using hydrogen/deuterium amide exchange (HDX) to determine the binding affinity of protein-peptide interactions
is reported. The method, based on our previously established approach, protein ligand interaction by mass spectrometry, titration,
and H/D exchange (PLIMSTEX) [J. Am. Chem. Soc.
2003, 125, 5252–5253], makes use of a dilution strategy (dPLIMSTEX) for HDX, using the mass of the peptide ligand as readout. We employed
dPLIMSTEX to study the interaction of calcium-saturated calmodulin with the opioid peptide β-endorphin as a model system;
the affinity results are in good agreement with those from traditional PLIMSTEX and with literature values obtained by using
other methods. We show that the dPLIMSTEX method is feasible to quantify an antigen-antibody interaction involving a 3-nitrotyrosine
modified peptide in complex with a monoclonal anti-nitrotyrosine antibody. A dissociation constant in the low nanomolar range
was determined, and a binding stoichiometry of antibody/peptide of 1:2 was confirmed. In addition, we determined that the
epitope in the binding interface contains a minimum of five amino acids. The dPLIMSTEX approach is a sensitive and powerful
tool for the quantitative determination of peptide affinities with antibodies, complementary to conventional immuno-analytical
techniques. 相似文献
963.
Berek D 《Journal of separation science》2010,33(22):3476-3493
Liquid chromatography under limiting conditions of desorption (LC LCD) enables fast, base-line discrimination of both parent homopolymers from various diblock copolymers in one single step. The low molecular admixtures are fully separated, as well. General rules are discussed in detail for selection of mobile phases and temperature applied in LC LCD of block copolymers. Typical practical separation examples are presented. It is shown that both the composition of the well-selected LC LCD mobile phase and the temperature of experiment may vary in a broad range without affecting the basics of method. This implies that the method is robust and user friendly. 相似文献
964.
Renato Fedele Dušan Jovanovi? Bengt Eliasson Padma K. Shukla 《Physics letters. A》2010,374(5):788-795
The possibility of the decomposition of the three-dimensional (3D) Gross-Pitaevskii equation (GPE) into a pair of coupled Schrödinger-type equations, is investigated. It is shown that, under suitable mathematical conditions, it is possible to construct the exact controlled solutions of the 3D GPE from the solutions of a linear 2D Schrödinger equation coupled with a 1D nonlinear Schrödinger equation (the transverse and longitudinal components of the GPE, respectively). The coupling between these two equations is the functional of the transverse and the longitudinal profiles. The applied method of nonlinear decomposition, called the controlling potential method (CPM), yields the full 3D solution in the form of the product of the solutions of the transverse and longitudinal components of the GPE. It is shown that the CPM constitutes a variational principle and sets up a condition on the controlling potential well. Its physical interpretation is given in terms of the minimization of the (energy) effects introduced by the control. The method is applied to the case of a parabolic external potential to construct analytically an exact BEC state in the form of a bright soliton, for which the quantitative comparison between the external and controlling potentials is presented. 相似文献
965.
Multi-walled carbon nanotubes (MWCNTs) were modified by corona discharge and then heat treated in the air. The influences of corona discharge parameters such as treatment time and processing power were investigated. The results of energy dispersive X-ray analysis (EDX) and thermogravimetric analysis (TGA) indicated the introduction of oxygen-containing functional groups onto the surface of the MWCNTs after heat treatment. The water contact angle tests showed that the hydrophobicity of the MWCNTs was decreased to some extent. The static water contact angle was reduced from 146° to 122° when the time of the corona discharge treatment reached 3 min at the processing power of 200 W. The enhanced thermomechanical and mechanical properties of epoxy nanocomposites filled with the corona discharge treated MWCNTs were observed. The modified MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between the treated MWCNTs and epoxy. 相似文献
966.
Miroslav Stanković Margarita Gabrovska Jugoslav Krstić Peter Tzvetkov Maya Shopska Tsenka Tsacheva Predrag Banković Rumeana Edreva-Kardjieva Dušan Jovanović 《Journal of molecular catalysis. A, Chemical》2009,297(1):54-62
Silver modified Mg-Ni/diatomite materials with ratios of SiO2/Ni = 1.07 and Mg/Ni = 0.1, differing in Ag content (Ag/Ni = 0.025 and 0.1) were prepared by the precipitation–deposition method. The effects of silver presence and content on the structure, morphology, texture and H2-adsorption capacity of the obtained precursors were studied by X-ray diffraction, scanning electron microscopy, Hg-porosimetry and H2-chemisorption techniques. The catalytic performance of the corresponding catalysts in the soybean oil hydrogenation was investigated. The increase of the silver loading resulted in the development of macroporosity and increase in the total sample porosity. The decrease of both H2-adsorption capacity and hydrogenation activity are related to the metallic silver covering and blocking effects on the Ni2+ species, thus hampering the access of hydrogen. The decrease of hydrogenation activity and favorable limiting of cis–trans isomerization on the silver modified catalyst are explained by Horiuti–Polanyi mechanism based on the assumption that hydrogenation and isomerization proceed at the same active metallic nickel sites via half-hydrogenated intermediates.It was shown that the adjustment of the catalyst composition by changing the content of silver modifier offers the possibility to control the total amount of solid fat content, stearic acid and detrimental trans fatty acids in the hydrogenated derivatives. The catalyst with higher silver content is proposed as a promising candidate for selective edible oil hydrogenation catalyst. 相似文献
967.
F. Doğan M. Ulusoy Ö. F. Öztürk İ. Kaya B. Salih 《Journal of Thermal Analysis and Calorimetry》2009,96(1):267-276
The thermal decomposition kinetics of sterically hindered salen type ligand (L) and its metal complexes [M=Co(II), Ni(II), Cu(II)] were investigated by thermogravimetric analysis. A direct insertion probe-mass spectrometer (DIP-MS)
was used for the characterization of metal complexes of L and all fragmentations and stable ions were characterized. The thermogravimetry and differential thermogravimetry (TG-DTG)
plots of salen type salicylaldimine ligand and complexes showed a single step.
The kinetic analysis of thermogravimetric data was performed by using the invariant kinetic parameter method (IKP). The values
of the invariant activation energy, E
inv and the invariant pre-exponential factor, A
inv, were calculated by using Coats-Redfern (CR) method. The thermal stabilities and activation energies of metal complexes of
sterically hindered salen type ligand (L) were found as Co(II)>Cu(II)>Ni(II)>L and E
Cu>E
Ni>E
Co>L. Also, the probabilities of decomposition functions were investigated. The diffusion functions (D
n) are most probable for the thermal decomposition of all complexes. 相似文献
968.
Tania A. Lazăr Adrian Petruşel Naseer Shahzad 《Nonlinear Analysis: Theory, Methods & Applications》2009
The purpose of this paper is to discuss some basic problems of the fixed point theory for non-self (single-valued and multivalued) generalized contractions. As consequences, new open operator principles and domain invariance theorems are obtained. The results complement and extend some known results in the literature. 相似文献
969.
We prove that Dranishnikov's k-dimensional resolution is a UVn − 1-divider of Chigogidze's k-dimensional resolution ck. This fact implies that preserves Z-sets. A further development of the concept of UVn − 1-dividers permits us to find sufficient conditions for to be homeomorphic to the Nöbeling space νk or the universal pseudoboundary σk. We also obtain some other applications. 相似文献
970.
We prove recognition theorems for codimension one manifold factors of dimension n?4. In particular, we formalize topographical methods and introduce three ribbons properties: the crinkled ribbons property, the twisted crinkled ribbons property, and the fuzzy ribbons property. We show that X×R is a manifold in the cases when X is a resolvable generalized manifold of finite dimension n?3 with either: (1) the crinkled ribbons property; (2) the twisted crinkled ribbons property and the disjoint point disk property; or (3) the fuzzy ribbons property. 相似文献