全文获取类型
收费全文 | 2590篇 |
免费 | 48篇 |
国内免费 | 5篇 |
专业分类
化学 | 1670篇 |
晶体学 | 10篇 |
力学 | 28篇 |
数学 | 502篇 |
物理学 | 433篇 |
出版年
2020年 | 27篇 |
2019年 | 27篇 |
2016年 | 40篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 78篇 |
2012年 | 55篇 |
2011年 | 77篇 |
2010年 | 57篇 |
2009年 | 41篇 |
2008年 | 69篇 |
2007年 | 74篇 |
2006年 | 55篇 |
2005年 | 88篇 |
2004年 | 72篇 |
2003年 | 52篇 |
2002年 | 35篇 |
2001年 | 37篇 |
2000年 | 39篇 |
1999年 | 38篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 32篇 |
1994年 | 35篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 34篇 |
1990年 | 20篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 31篇 |
1986年 | 40篇 |
1985年 | 40篇 |
1984年 | 39篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1981年 | 50篇 |
1980年 | 45篇 |
1979年 | 32篇 |
1978年 | 45篇 |
1977年 | 41篇 |
1976年 | 34篇 |
1975年 | 24篇 |
1974年 | 30篇 |
1973年 | 23篇 |
1972年 | 27篇 |
1971年 | 34篇 |
1970年 | 31篇 |
1968年 | 24篇 |
1967年 | 37篇 |
排序方式: 共有2643条查询结果,搜索用时 15 毫秒
991.
Deng X Hahne T Schröder S Redweik S Nebija D Schmidt H Janssen O Lachmann B Wätzig H 《Electrophoresis》2012,33(2):263-269
Single proteins separated by 2-DE often show multiple spots spreading along the first dimension. In many cases, such charge trains are explained by isoform differences or by putative post-translational modifications including phosphorylation, glycosylation and others. We now report that individual spots of such charge trains on 2-D gels in fact often represent the same protein, but, apparently due to conformational changes, segregate to different isoelectric points. If MS analysis reveals protein identity, we therefore suggest integrating all individual spots within a charge train for quantification. Especially in quality control of pharmaceutical proteins, the integration of the spot groups of all active contents is preferable in order to obtain reproducible and reasonable quantitative results. However, most commercial software packages for gel analysis integrate the signals spot-wise. We provide an improved quantification tool for proteins with charge train groups. This calculation can be implemented using the MATLAB software and the self-developed "Correct Integration Software System" or the commercial software package Delta2D. 相似文献
992.
Feldmann V Engelmann J Gottschalk S Mayer HA 《Journal of colloid and interface science》2012,366(1):70-79
Spherical, nonporous and monodisperse silica nanoparticles (NPs) with a diameter of about 100 nm were synthesized and covalently functionalized with lanthanoid(III) (Ln=Gd or Y) chelate complexes, which serve as contrast agents (CAs) for magnetic resonance imaging (MRI). The materials were fully characterized after each synthetic step by different analytical methods, such as dynamic light scattering, scanning electron microscopy, DRIFT and NMR spectroscopy, thermogravimetry and elemental analysis, as well as zetapotential measurements. High surface concentrations of Gd(III) complexes (up to 50 μmol g(-1)) were determined by ICP-AES and T(1)-measurements, respectively. MRI experiments show the typical concentration-dependent increase of the longitudinal relaxation rate. T(1)-weighted images of samples with more than 25 μg NPs per 100 μL agar display a clear contrast enhancement in the agar layer. The transverse relaxivities r(2) of the materials are significantly higher than r(2) of the corresponding free Gd(III) complexes in water and medium, whereas the longitudinal relaxivities r(1) are slightly increased. Due to the high loading of Gd(III) complexes, the relaxivities per particle are remarkably high (up to 2.78×10(5) mM(-1) s(-1) for r(1)). Thus, new hybrid materials, based on nonporous silica NPs with high local relaxivity values were synthesized, which can serve as very effective CAs for MRI. 相似文献
993.
Molecule-by-molecule arrangement of proteins, for example, in enzymatic networks of predefined composition and proximity, is a major goal that may be accomplished by the single-molecule cut-and-paste technique (SMC&P). For this purpose, co-expressed anchors and handles as protein tags should be employed. As a first step in this direction, the authors develop an SMC&P design which exploits an antibody-peptide complex as a molecular handle. 相似文献
994.
Zander W Irschik H Augustiniak H Herrmann M Jansen R Steinmetz H Gerth K Kessler W Kalesse M Höfle G Müller R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(20):6264-6271
Sulfangolids are the first sulfate ester containing secondary metabolites from myxobacteria. The metabolites 1-4 and the structurally related kulkenon (5) were isolated from different strains of the species Sorangium cellulosum. In the course of isolation all metabolites proved to be rather sensitive due to their conjugated double bond systems and the strong acidic nature of the sulfate ester in sulfangolids. The relative configuration of sulfangolid C (3) was assigned by extensive 1D and 2D NMR analysis and molecular modelling. In addition, the biosynthesis of 3 was studied by feeding experiments. 相似文献
995.
996.
Andreas W. W. Ludwig Hermann Schulz-Baldes Michael Stolz 《Journal of statistical physics》2013,152(2):275-304
A random phase property is proposed for products of random matrices drawn from any one of the classical groups associated with the ten Cartan symmetry classes of non-interacting disordered Fermion systems. It allows to calculate the Lyapunov spectrum explicitly in a perturbative regime. These results apply to quasi-one-dimensional random Dirac operators which can be constructed as representatives for each of the ten symmetry classes. For those symmetry classes that correspond to two-dimensional topological insulators or superconductors, the random Dirac operators describing the one-dimensional boundaries have vanishing Lyapunov exponents and almost surely an absolutely continuous spectrum, reflecting the gapless and conducting nature of the boundary degrees of freedom. 相似文献
997.
Kirk A. Peterson Christine Krause Hermann Stoll J. Grant Hill 《Molecular physics》2013,111(22):2607-2623
A benchmark of explicitly correlated CCSD(T)-F12 methods for the dimers Ga2, As2, Br2 and diatomic molecules AsN, BrO, HBr, GaF, GaCl, GaBr, AsF, AsCl, BrF, and BrCl is presented. Equilibrium distances, harmonic vibrational frequencies, and dissociation energies are compared with extensive conventional CCSD(T) calculations using a variety of orbital basis sets and different ansätze for the explicitly correlated wavefunctions. Correlation of the 3d electrons has a strong effect, in particular on the equilibrium distances, and it is shown that this can be recovered very efficiently by the explicit correlation treatment. It is found that CCSD(T)-F12 calculations with new F12-specific cc-pVnZ-F12 basis sets give comparable accuracy to standard CCSD(T) calculations with very much larger aug-cc-pwCV(n+2)Z basis sets. The effects of higher order valence electron correlation (up to CCSDTQP) are also investigated in conventional calculations and are found to be significant in some cases. 相似文献
998.
Hermann Schulz-Baldes 《Communications in Mathematical Physics》2013,324(2):589-600
For a disordered two-dimensional model of a topological insulator (such as a Kane-Mele model with disordered potential) with small coupling of spin invariance and time-reversal symmetry breaking terms (such as a Rashba spin-orbit coupling and a Zeeman term), it is proved that the spin edge currents persist provided there is a spectral gap and the spin Chern numbers are well-defined and non-trivial. These are sufficient conditions for being in the quantum spin Hall phase. The result materializes the general philosophy that topological insulators are topologically non-trivial bulk systems with persistent edge or surface currents. 相似文献
999.
Motivated by a recent experimental observation of a nodal liquid on both single crystals and thin films of Bi2Sr2CaCu2O8 + δ by Chatterjee et al. [Nature Phys. 6 (2010) 99], we perform a field-theoretical renormalization group (RG) analysis of a two-dimensional model such that only eight points located near the “hot spots” on the Fermi surface are retained, which are directly connected by spin density wave ordering wavevector. We derive RG equations up to two-loop order describing the flow of renormalized couplings, quasiparticle weight, several order-parameter response functions, and uniform spin and charge susceptibilities of the model. We find that while the order-parameter susceptibilities investigated here become non-divergent at two loops, the quasiparticle weight vanishes in the low-energy limit, indicating a breakdown of Fermi liquid behavior at this RG level. Moreover, both uniform spin and charge susceptibilities become suppressed in the scaling limit which indicate gap openings in both spin and charge excitation spectra of the model. 相似文献
1000.
Angelamaria Cardone Ida Del Prete Hermann Brunner 《Journal of Difference Equations and Applications》2013,19(9):1531-1543
Sufficient conditions for the asymptotic periodicity of solutions of nonlinear discrete Volterra equations of Hammerstein type are obtained. Such results are applied to analyze the property of a class of numerical methods to preserve the asymptotic periodicity of the analytical solution of Volterra integral equations. 相似文献