全文获取类型
收费全文 | 5059篇 |
免费 | 630篇 |
国内免费 | 456篇 |
专业分类
化学 | 2325篇 |
晶体学 | 66篇 |
力学 | 1191篇 |
综合类 | 43篇 |
数学 | 276篇 |
物理学 | 2244篇 |
出版年
2024年 | 8篇 |
2023年 | 48篇 |
2022年 | 98篇 |
2021年 | 118篇 |
2020年 | 189篇 |
2019年 | 118篇 |
2018年 | 140篇 |
2017年 | 163篇 |
2016年 | 211篇 |
2015年 | 180篇 |
2014年 | 291篇 |
2013年 | 316篇 |
2012年 | 251篇 |
2011年 | 343篇 |
2010年 | 295篇 |
2009年 | 343篇 |
2008年 | 318篇 |
2007年 | 366篇 |
2006年 | 307篇 |
2005年 | 273篇 |
2004年 | 289篇 |
2003年 | 237篇 |
2002年 | 203篇 |
2001年 | 165篇 |
2000年 | 158篇 |
1999年 | 147篇 |
1998年 | 102篇 |
1997年 | 77篇 |
1996年 | 73篇 |
1995年 | 50篇 |
1994年 | 39篇 |
1993年 | 27篇 |
1992年 | 19篇 |
1991年 | 35篇 |
1990年 | 20篇 |
1989年 | 10篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1977年 | 3篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1957年 | 4篇 |
排序方式: 共有6145条查询结果,搜索用时 0 毫秒
871.
《International journal of quantum chemistry》2018,118(11)
Perturbed structures for QTAIM dual functional analysis (QTAIM‐DFA) are proposed to generate using the coordinates corresponding to the compliance force constants in internal vibrations (CIV). In QTAIM‐DFA, total electron energy densities Hb( r c) are plotted versus Hb( r c) – Vb( r c)/2 at bond critical points (BCPs) of interactions in question, where Vb( r c) are potential energy densities at BCPs. Each plot of an interaction based on the data from both perturbed structures and fully optimized one takes the form (θp, κp), where θp corresponds to the tangent line of the plot and κp is the curvature. The θp values evaluated with CIV are equal to those obtained by partial optimizations with the interaction distance in question being fixed suitably, within the calculation errors. Very high applicability of CIV is demonstrated to generate the perturbed structures for QTAIM‐DFA. Dynamic nature of interactions based on (θp, κp) with CIV is called “intrinsic dynamic nature of interactions.” 相似文献
872.
E. N. Kolesnikova Yu. A. Polovko V. S. Yuferev A. I. Zhmakin 《Journal of Crystal Growth》1997,180(3-4):578-586
In contrast with the generally accepted viewpoint, it is shown that the Coriolis force caused by rotation of an orbital station can appreciably affect natural convection and impurity distribution during the growth of crystals from a melt in orbital flight conditions. 2D and 3D steady and oscillatory convection in a rectangular enclosure is considered. The resonance phenomenon arising due to the interaction of the Coriolis force and harmonic oscillations of the gravity force is demonstrated. It is shown that for moderate values of the Ekman number the Coriolis force suppresses convection in one direction and amplifies it in the other, which in turn results in deformation of the impurity distribution over the cross-section of the crystal. 相似文献
873.
V. Deuster M. Schick Th. Kayser H. Dabringhaus H. Klapper K. Wandelt 《Journal of Crystal Growth》2003,250(3-4):313-323
The present paper deals with studies of the facetting of the polished (1 0 0) surface of CaF2 during annealing and growth in UHV using low energy electron diffraction (LEED), atomic force microscopy (AFM), and transmission electron microscopy (TEM). First morphological modifications of the polished surfaces become visible at temperatures of T=874 K. Surfaces annealed at T=974 K exhibit a micro-roughening with pyramidal protrusions and corresponding depressions. LEED studies indicate the evolution of {1 1 1} facets. Reflexes from the (1 0 0) surface are not seen. After growth of about 660 monolayers of CaF2 at T=1093 K and a saturation ratio S=33 from the vapor phase, larger pyramid-like or hip roof-like crystallites are developed. The results of AFM height profiles as well as of the LEED investigations indicate again the formation of {1 1 1} facets as proved by their angles of 54.7 o with the base (1 0 0) surface. This shows that the crystallites are homoepitaxially grown on the underlying CaF2 substrate. 相似文献
874.
Self-assembling peptide nanofiber scaffolds are an excellent material for applications such as tissue repair, tissue regeneration, instant stopping of bleeding, and slow drug release. We report a new self-assembling peptide D-EAK16 consisting purely of D-amino acids. D-EAK16 and L-EAK16 display mirror-image CD spectra at 20 degrees C. Like L-EAK16, D-EAK16 self-assembles into nanofibers, thus demonstrating that chiral self-assembling peptide nanofiber scaffolds can be made from both L- and D-amino acids. We also show that D-peptide nanofibers are resistant to natural proteases and may thus be useful in biotechnology, nanobiotechnology, tissue repair and tissue regeneration as well as other medical applications. 相似文献
875.
Towards chemical analysis of nanostructures in biofilms II: tip-enhanced Raman spectroscopy of alginates 总被引:1,自引:1,他引:0
Schmid T Messmer A Yeo BS Zhang W Zenobi R 《Analytical and bioanalytical chemistry》2008,391(5):1907-1916
This study examines the feasibility of using tip-enhanced Raman spectroscopy (TERS) for label-free chemical characterization
of nanostructures in biological systems. For this purpose, a well-defined model system consisting of calcium alginate fibers
is studied. In a companion paper, calcium alginate fibers and their network structures were shown to be a good model for the
extracellular polysaccharides of biofilms at the nanoscale. TERS analysis of biological macromolecules, such as alginates,
is complicated by heterogeneity in their sequence, molecular weight, and conformations, their small Raman cross-section, and
the large number of functional groups, which can chemically interact with the silver surface of the tip and cause significant
band shifts. Due to these effects, Raman frequencies in TERS spectra of biopolymers do not necessarily resemble band positions
in the normal Raman spectrum of the bulk material, as is the case for less complex samples (e.g., dye molecules) studied so
far. Additionally, analyte decomposition due to laser heating can have a significant influence, and carbon contamination signals
can sometimes even overwhelm the weak analyte signals. Based on the investigation of alginates, strategies for spectra correction,
choice of appropriate reference samples, and data interpretation are presented. With this approach, characteristic frequency
ranges and specific marker bands can be found for biological macromolecules that can be employed for their identification
in complex environments.
Figure TERS spectrum of a calcium alginate fiber bundle 相似文献
876.
Schmid T Burkhard J Yeo BS Zhang W Zenobi R 《Analytical and bioanalytical chemistry》2008,391(5):1899-1905
Due to their direct influence on the stability of bacterial biofilms, a better insight into the nanoscopic spatial arrangement
of the different extracellular polymeric substances (EPS), e.g., polysaccharides and proteins, is important for the improvement
of biocides and for process optimization in wastewater treatment and biofiltration. Here, the first application of a combination
of confocal laser-scanning microscopy (CLSM) and atomic force microscopy (AFM) to the investigation of river-water biofilms
and related biopolymers is presented. AFM images collected at selected areas of CLS micrographs dramatically demonstrate the
heterogeneity of biofilms at the nanometer scale and the need for a chemical imaging method with nanoscale resolution. The
nanostructures (e.g., pili, flagella, hydrocolloids, and EPS) found in the extracellular matrix are classified according to
shape and size, which is typically 50–150 nm in width and 1–10 nm in thickness, and sets the demands regarding spatial resolution
of a potential chemical imaging method. Additionally, thin layers of the polysaccharide alginate were investigated. We demonstrate
that calcium alginate is a good model for the EPS architecture at the nanometer scale, because of its similar network-like
structure.
Figure CLSM-AFM allows imaging of nanometer-sized extracellular structures 相似文献
877.
Smoothing and passivation of special Si(111) substrates: studied by SPV,PL, AFM and SEM measurements
Angermann H Rappich J Sieber I Hübener K Hauschild J 《Analytical and bioanalytical chemistry》2008,390(6):1463-1470
Surface sensitive techniques, the field-modulated surface photovoltage, photoluminescence measurements, atomic force microscopy
and scanning electron microscopy, were employed to yield detailed information on the influence of wet-chemical treatments
on the preparation induced microroughness and electronic properties of wet-chemically passivated Si(111) substrates with special
surface morphology. Stepped substrates with evenly distributed atomically flat terraces were prepared and passivated by thin
oxide layers, which were used as a starting point for the subsequent H-termination after long storage in air. It was shown
that their surface morphology and electronic properties do not degrade. Applying this preparation method to solar cell substrates
with randomly distributed Si(111) pyramids, we achieved significantly lower densities of surface states and reduced recombination
loss at a-Si:H/c-Si interfaces, compared with conventional pretreatments. The surface microroughness, the density of rechargeable
states and the resulting recombination loss on a-Si:H/c-Si heterojunctions were found to be mainly influenced by two steps
of surface pretreatment: firstly, the wet-chemical smoothing procedure of structured substrates and, secondly, the removal
of native and wet-chemical oxides during the final etching in HF- or NH4F- containing solutions.
Figure After wet-chemical oxidation in H2SO4/H2O2 and storage in air 相似文献
878.
In this paper we report the first application of multivariate data analysis techniques to force spectrometry measurement sets
to enable the physicochemical assignment of spatially ordered multi-component systems. Principal component analysis (PCA)
and hierarchical clustering techniques were used to reveal hidden chemical information within force-distance curves generated
by high spatial resolution force microscopy. Two experimental samples were analyzed: (i) a two-component system of cytochrome
c proteins on a mica surface, and (ii) a three-component system of avidin protein islands positioned on a gold and glass surface.
PCA and hierarchical clustering techniques were used to discriminate the different components of the two-component system,
whereas hierarchical clustering was found to be superior for the three-component system. Results were in good agreement with
the topography and prior knowledge of the surface patterns. This research represents a formative step towards the combination
of force spectrometry with chemometric tools for the high resolution physicochemical investigation of complex biochemical
systems. 相似文献
879.
G. W. Chądzyński P. Staszczuk D. Sternik M. Błachnio 《Journal of Thermal Analysis and Calorimetry》2008,94(3):623-626
Properties relating to porosity of solids (fractal dimensions, surface roughness parameters) were evaluated from atomic force
microscopy (AFM) and nitrogen adsorption-desorption isotherms measured at 77 K for selected high-temperature [(RE) Ba2Cu3O7−x, RE=Y, Sm] superconductors. Adsorption capacity, specific surface area, fractal dimensions were determined from adsorption-desorption
isotherms. The adsorption isotherms of all samples were S-shaped and belong to type II according to the IUPAC classification.
A linear relationship was demonstrated between the fractal coefficients calculated by using the two methods and values of
adsorption capacity of monolayer. 相似文献
880.
Javier Sotres Anabel Lostao Dr. Linda Wildling Andreas Ebner Carlos Gómez‐Moreno Prof. Hermann J. Gruber Prof. Dr. Peter Hinterdorfer Prof. Dr. Arturo M. Baró Prof. 《Chemphyschem》2008,9(4):590-599
Atomic force microscopy is a technique capable to study biological recognition processes at the single‐molecule level. In this work we operate the AFM in a force‐scan based mode, the jumping mode, where simultaneous topographic and tip–sample adhesion maps are acquired. This approach obtains the unbinding force between a well‐defined receptor molecule and a ligand attached to the AFM tip. The method is applied to the avidin–biotin system. In contrast with previous data, we obtain laterally resolved adhesion maps of avidin–biotin unbinding forces highly correlated with single avidin molecules in the corresponding topographic map. The scanning rate 250 pixel s?1 (2 min for a 128×128 image) is limited by the hydrodynamic drag force. We are able to build a rupture‐force distribution histogram that corresponds to a single defined molecule. Furthermore, we find that due to the motility of the polymer used as spacer to anchor the ligand to the tip, its direction at rupture does not generally coincide with the normal to the tip–sample, this introduces an appreciable error in the measured force. 相似文献