全文获取类型
收费全文 | 3952篇 |
免费 | 112篇 |
国内免费 | 23篇 |
专业分类
化学 | 3277篇 |
晶体学 | 42篇 |
力学 | 42篇 |
数学 | 182篇 |
物理学 | 544篇 |
出版年
2023年 | 22篇 |
2022年 | 33篇 |
2021年 | 43篇 |
2020年 | 56篇 |
2019年 | 52篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 70篇 |
2015年 | 76篇 |
2014年 | 90篇 |
2013年 | 203篇 |
2012年 | 217篇 |
2011年 | 284篇 |
2010年 | 147篇 |
2009年 | 145篇 |
2008年 | 311篇 |
2007年 | 235篇 |
2006年 | 297篇 |
2005年 | 259篇 |
2004年 | 226篇 |
2003年 | 205篇 |
2002年 | 195篇 |
2001年 | 53篇 |
2000年 | 64篇 |
1999年 | 54篇 |
1998年 | 36篇 |
1997年 | 39篇 |
1996年 | 41篇 |
1995年 | 43篇 |
1994年 | 35篇 |
1993年 | 35篇 |
1992年 | 33篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 33篇 |
1984年 | 37篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 16篇 |
1974年 | 13篇 |
排序方式: 共有4087条查询结果,搜索用时 15 毫秒
991.
Structural characterization of glycoproteins remains among the most challenging areas of glycomics due to the requirement of large quantities of samples and laborious biochemical steps involved in the analytical procedure. Here we report the structural characterization of glycoproteins separated on a 2-D gel by using a MALDI-QIT-TOF MS where QIT is quadrupole IT. The combination of MALDI-ion source and QIT appears to generate a unique tendency to cause fragmentation of glycopeptides without collision-induced dissociation. The majority of such fragmentations observed in our study result from the cleavage of sugar linkages, but not of peptide-peptide or peptide-sugar linkages. This unique feature allows us to perform pseudo-MS3 analysis of a fragmented glycopeptide. A small gel spot of a glycoprotein in the abundance range of low picomoles was enough for the mass spectrometer to analyze fragmentation pathway of the sugar linkage and peptide backbone. In this study, we demonstrate direct determination of glycosylation sites and N-linked glycan-sequences of the tryptic glycopeptides of Drosophila glycoproteins. Glycopeptides with various MWs up to approximately 4000 Da were suitable for structural analysis, including its attachment site and the amino acid sequence, of the glycopeptide through multistage mass spectrometric analysis. 相似文献
992.
Electronic mechanism of the reversible O(2) binding by heme was studied by using Density Functional Theory calculations. The ground state of oxyheme was calculated to be open singlet state [Fe(S =1/2) + O(2)(S = 1/2)]. The potential energy surface for singlet state is associative, while that for triplet state is dissociative. Because the ground state of the O(2)+ deoxyheme system is triplet in the dissociation limit [Fe(S = 2) + O(2)(S = 1)], the O(2) binding process requires relativistic spin-orbit interaction to accomplish the intersystem crossing from triplet to singlet states. Owing to the singlet-triplet crossing, the activation energies for both O(2) binding and dissociation become moderate, and hence reversible. We also found that the deviation of the Fe atom from the porphyrin plane is also important reaction coordinate for O(2) binding. The potential surface is associative/dissociative when the Fe atom locates in-plane/out-of-plane. 相似文献
993.
Uehara H Asakawa T Kakiage M Yamanobe T Komoto T 《Langmuir : the ACS journal of surfaces and colloids》2006,22(11):4985-4991
The surface-deformation characteristics of uniaxially drawn poly(ethylene terephthalate) (PET) film were successfully evaluated with multiline scratch tests using scanning probe microscopy (SPM) on a nanometer scale. The PET film was prepared by compression molding from the melt, followed by quenching in ice water. The obtained amorphous film was drawn uniaxially below its glass-transition temperature, and the resultant surface roughness could be reduced to within 5 nm. A multiline scratch with the Si(3)N(4) tip of an SPM on the oriented PET surface was made parallel and perpendicular to the drawing axis under applied loads of 5-30 nN. The perpendicular scratching generated a characteristic periodic pattern on the film surface, but the parallel scratching induced a tearing of the surface. These results suggest that surface-deformation mechanisms were dominated by molecular anisotropy. The surface-deformation properties, as evaluated from scratch-angle dependences on morphological changes on a nanometer scale, were similar to the mechanical properties of the bulk. 相似文献
994.
Suzuki H Tabata KV Noji H Takeuchi S 《Langmuir : the ACS journal of surfaces and colloids》2006,22(4):1937-1942
We developed a highly reproducible method for planar lipid bilayer reconstitution using a microfluidic system made of a polymethyl methacrylate (PMMA) plastic substrate. Planar lipid bilayers are formed at apertures, 100 microm in diameter, by flowing lipid solution and buffer alternately into an integrated microfluidic channel. Since the amount and distribution of the lipid solution at the aperture determines the state of the lipid bilayer, controlling them precisely is crucial. We designed the geometry of the fluidic system so that a constant amount of lipid solution is distributed at the aperture. Then, the layer of lipid solution was thinned by applying an external pressure and finally became a bilayer when a pressure of 200-400 Pa was applied. The formation process can be simultaneously monitored with optical and electrical recordings. The maximum yield for bilayer formation was 90%. Using this technique, four lipid bilayers are formed simultaneously in a single chip. Finally, a channel current through gramicidin peptide ion channels was recorded to prove the compatibility of the chip with single molecule electrophysiology. 相似文献
995.
Shinto H Komiyama D Higashitani K 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2058-2064
When two solid bodies are placed on the surface of a dense liquid under gravitation, they deform the liquid surface to experience a lateral capillary force between themselves that can be attractive and repulsive, depending on the wettabilities and weights of the bodies. In the present study, the lateral capillary force between two square bodies at a liquid-vapor interface has been examined using numerical simulations based on a two-dimensional two-phase lattice Boltzmann (LB) method. The particular situations were simulated, where every body was vertically constrained and had the fixed triple points at its upper or lower corners. Here, the triple point indicates the place at which vapor, liquid, and solid phases meet. The interaction force between these two bodies was calculated as a function of the separation distance, the interfacial tension, and the gravitational acceleration. The simulation results agree well with the analytical expression of the lateral capillary interaction, indicating that our LB method can reproduce the interaction force between two bodies of various wettabilities at a liquid-vapor interface in mechanical equilibrium. 相似文献
996.
Suzuki M Yoon MC Kim DY Kwon JH Furuta H Kim D Osuka A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(6):1754-1759
Treatment of hexakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1) (1) with CuCl in the presence of pyridine and molecular oxygen led to formation of doubly N-confused [26]hexaphyrin(1.1.1.1.1.1) 2 in a moderate yield through an unprecedented double pyrrolic rearrangement. Macrocycle 2 has been shown to serve as an effective bis-metal-coordinating ligand and exhibits attractive optical properties such as a sharp Soret-like band at 566 nm and low-energy fluorescence at 1058 nm. 相似文献
997.
Tolis EI Engelhardt LP Mason PV Rajaraman G Kindo K Luban M Matsuo A Nojiri H Raftery J Schröder C Timco GA Tuna F Wernsdorfer W Winpenny RE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(35):8961-8968
The synthesis and structural characterization of a nonanuclear FeIII cage complex is reported. The nine iron centers in [Fe9(mu3-O)4(O3PPh)3(O2CCMe3)13] lie on the vertices of an incomplete icosahedron, with the P atoms of triphenylphosphonate at the other three vertices. The paramagnetic core therefore describes a tridiminished icosahedron. Magnetic studies suggest an S=1/2 ground state for the molecule. Analysis of exchange paths and the susceptibility data point to the interpretation that the cluster can be divided into two nearly decoupled sections: an {Fe6O3} section, with an S=0 ground state, in which three oxo-centered triangles bound a central triangle that is not oxo-centered; and an {Fe3O} triangle with S=1/2. The analysis of the susceptibility data leads to a Heisenberg model based on three significant antiferromagnetic exchange interactions, with values of 173.7 cm-1 in the {Fe3O} triangle, and 30.9 and 19.1 cm-1 within the {Fe6O3} section, while the exchange between them is <1 cm-1. With these assignments, the theoretical low-temperature differential susceptibility is also in very good agreement with measurements up to 50 T. Magnetic measurements in the milli-kelvin range reveal striking hysteresis loops and magnetization reversals associated with a Landau-Zener-Stückelberg (LZS) transition as enhanced by the occurrence of a phonon bottleneck. 相似文献
998.
Nakata S Morishima S Ichino T Kitahata H 《The journal of physical chemistry. A》2006,110(50):13475-13478
The photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated on a circular ring, which was drawn using computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. Under the initial conditions, a chemical wave propagated with a constant velocity on the black ring under a bright background. When the background was rapidly changed to dark, coexistence of the oscillation on part of the ring and propagation of the chemical wave on the other part was observed. These experimental results are discussed in relation to the nature of the photosensitive BZ reaction and theoretically reproduced based on a reaction-diffusion system using the modified Oregonator model. 相似文献
999.
The propagation of chemical waves in the photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated using an excitable field composed of two rings in slight contact, which were drawn using computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. When the initial phase difference between the two chemical waves in the individual rings was smaller than a critical value, this initial value was maintained after collision of the chemical waves. However, when the initial phase difference was larger than this critical value, the phase difference converged to the same value after the second collision. The critical value increased with an increase in the thickness of the rings. These experimental results on the geometry of the excitable field are discussed in relation to the nature of chemical wave propagation. These results suggest that the photosensitive BZ reaction may be useful for creating spatiotemporal patterns that depend on the geometric arrangement of excitable fields. 相似文献
1000.
Several types of organic reactions were accelerated by immediate evaporation of solvents because of remarkable enhancement of molecule-to-molecule contacts between reactants. 相似文献