全文获取类型
收费全文 | 1125篇 |
免费 | 31篇 |
国内免费 | 6篇 |
专业分类
化学 | 710篇 |
晶体学 | 7篇 |
力学 | 23篇 |
数学 | 125篇 |
物理学 | 297篇 |
出版年
2022年 | 9篇 |
2020年 | 24篇 |
2019年 | 20篇 |
2016年 | 21篇 |
2015年 | 29篇 |
2014年 | 24篇 |
2013年 | 30篇 |
2012年 | 43篇 |
2011年 | 49篇 |
2010年 | 38篇 |
2009年 | 33篇 |
2008年 | 45篇 |
2007年 | 49篇 |
2006年 | 47篇 |
2005年 | 50篇 |
2004年 | 38篇 |
2003年 | 24篇 |
2002年 | 21篇 |
2001年 | 24篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1989年 | 11篇 |
1987年 | 9篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1978年 | 10篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1943年 | 12篇 |
1933年 | 11篇 |
1931年 | 8篇 |
1930年 | 9篇 |
1924年 | 8篇 |
1923年 | 10篇 |
1902年 | 7篇 |
1881年 | 7篇 |
排序方式: 共有1162条查询结果,搜索用时 15 毫秒
201.
202.
Dausend J Musyanovych A Dass M Walther P Schrezenmeier H Landfester K Mailänder V 《Macromolecular bioscience》2008,8(12):1135-1143
The endocytotic mechanisms involved in the uptake of charged polystyrene nanoparticles into HeLa cells were investigated. Uptake experiments were done in the presence or absence of drugs known to inhibit various factors in endocytosis. Independent of the particle charge, endocytosis is highly dependent on dynamin, F-actin, and tyrosine-specific protein kinases, which suggests a dynamin-dependent and lipid raft-dependent mechanism. However, cholesterol depletion did not hinder particle uptake. Regarding positively charged particles, macropinocytosis, the microtubule network, and cyclooxygenases are also involved. The clathrin-dependent pathway plays a minor role. 相似文献
203.
Time-resolved fluorescence spectroscopy was used to characterize water-soluble organic matter (WSOM) which plays an important
role in soil ecosystem processes. WSOM was extracted from plant biomass, animal manures, and soils from controlled cropping
systems studies with known histories of organic amendments. Lifetime constants were derived using the multi-way PowerSlicing
method which provides a non-iterative, multi-exponential fitting of decay profiles. The lifetimes obtained by PowerSlicing
were not significantly different from those obtained using the traditional discrete components analysis. The three components
attributed to WSOM had lifetimes of 0.38 ± 0.14, 2.11 ± 0.72, and 7.08 ± 1.18 ns which are in agreement with previous lifetimes
reported for humic substances. This study provides further support for the new paradigm for the structure of soil organic
matter where the organic matter is composed of low-molecular-weight components held together by hydrogen bonding and hydrophobic
interactions. 相似文献
204.
The synthesis and photophysical properties of a series of chromophore-quencher complexes are reported. They are all comprised of a luminescent rhenium(I) tricarbonyl diimine complex that is covalently attached to anthracene or phenanthrene moieties via rigid rod-like p-xylene bridges of variable lengths. Rhenium-to-anthracene energy transfer is strongly exergonic (-DeltaG0 approximately 0.9 eV) and causes very efficient rhenium MLCT luminescence quenching. By contrast, rhenium-to-phenanthrene energy transfer is only observed when complexes with sufficiently high MLCT energies are used because for these dyads, the driving force for energy transfer is low (-DeltaG0 approximately 0.1 eV). For a approximately 15 angstroms donor-acceptor distance, the rate constants of the weakly and the strongly exergonic energy transfer processes differ by more than 3 orders of magnitude. 相似文献
205.
We have conducted wave packet simulations of excited-state dynamics of 1,3-dibromopropane (DBP) with the aim of reproducing the experimental results of the gas-phase pump-probe experiment by Kotting et al. [ Kotting, C. ; Diau, E. W.-G. ; S?lling, T. I. ; Zewail, A. H. J. Phys. Chem. A 2002, 106, 7530 ]. In the experiment, DBP is excited to a Rydberg state 8 eV above the ground state. The interpretation of the results is that a torsional motion of the bromomethylene groups with a vibrational period of 680 fs is activated upon excitation. The Rydberg state decays to a valence state, causing a dissociation of one of the carbon bromine bonds on a time scale of 2.5 ps. Building the theoretical framework for the wave packet propagation around this model of the reaction dynamics, the simulations reproduce, to a good extent, the time scales observed in the experiment. Furthermore, the simulations provide insight into how the torsion motion influences the bond breakage, and we can conclude that the mechanism that delays the dissociation is solely the electronic transition from the Rydberg state to the valence state and does not involve, for example, intramolecular vibrational energy redistribution (IVR). 相似文献
206.
Maris A Giuliano BM Bonazzi D Caminati W 《Journal of the American Chemical Society》2008,130(42):13860-13861
Two homochiral dimers of glycidol, deriving from two different conformers, have been characterized by rotational spectroscopy in a supersonic expansion. 相似文献
207.
More than one multi-informative analytical technique is often applied when describing the condition of a set of samples. Often a part of the information found in these data blocks is redundant and can be extracted from more blocks. This study puts forward a method (multiblock variance partitioning—MVP) to compare the information/variation in different data blocks using simple quantitative measures. These measures are the unique part of the variation only found in one data block and the common part that can be found in more data blocks. These different parts are found using PLS models between predictor blocks and a common response. MVP provides a different view on the information in different blocks than normal multiblock analysis. It will be shown that this has many applications in very diverse fields such as process control, assessor performance in sensory analysis, efficiency of preprocessing methods and as complementary information to an interval PLS analysis. Here the ideas of the MVP approach are presented in detail using a study of red wines from different regions measured with GC-MS and FT-IR instruments providing different kinds of data representations. 相似文献
208.
Giuliano BM Ottaviani P Favero LB Caminati W Grabow JU Giardini A Satta M 《Physical chemistry chemical physics : PCCP》2007,9(32):4460-4464
The rotational spectra of normal and O-d species of the two most stable conformers of chiral 1-phenyl-1-propanol, obtained by free jet millimetre-wave absorption spectroscopy reveal that both conformers are stabilized by a O-H[dot dot dot]pi interaction, and have the Calpha-Cbeta-bond oriented nearly perpendicular to the plane of the benzene ring. The methyl group is trans with respect to the phenyl group for the most stable conformer (T), while it is gauche with respect to the phenyl group and entgegen with respect to the hydroxyl group for the second most stable conformer (GE). The energy difference (E(GE)-E(T)) was estimated to be 50(50) cm(-1) from relative intensity measurements. 相似文献
209.
Blanco S Melandri S Ottaviani P Caminati W 《Journal of the American Chemical Society》2007,129(9):2700-2703
The trimer of difluoromethane, (CH2F2)3, has been characterized by supersonic jet Fourier transform microwave spectroscopy. The rotational spectrum displays all types (mu(a), mu(b), and mu(c)) of transitions, showing that the adduct does not possess any element of molecular symmetry. The investigation of the three 13C species in natural abundance indicates that the three carbon atoms form a triangle where the C-C distances are 3.648(2), 3.825(8), and 3.942(6) A, respectively. The three subunits are held together by nine CH...F weak hydrogen bonds. 相似文献
210.
Poulsen RD Jørgensen MR Overgaard J Larsen FK Morgenroth W Graber T Chen YS Iversen BB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(35):9775-9790
Three high-quality single-crystal X-ray diffraction data sets have been measured under very different conditions on a structurally simple, but magnetically complex, coordination polymer, [Mn(HCOO)(2)(H(2)O)(2)](infinity) (1). The first data set is a conventional 100(2) K Mo(Kalpha) data set, the second is a very high resolution 100(2) K data set measured on a second-generation synchrotron source, while the third data set was measured with a tiny crystal on a high brilliance third-generation synchrotron source at 16(2) K. Furthermore, the magnetic susceptibility (chi) and the heat capacity (C(p)) have been measured from 2 to 300 K on pressed powder. The charge density of 1 was determined from multipole modeling of the experimental structure factors, and overall there is good agreement between the densities obtained separately from the three data sets. When considering the fine density features, the two 100 K data sets agree well with each other, but show small differences to the 16 K data set. Comparison with ab initio theory suggests that the 16 K APS data set provides the most accurate density. Topological analysis of the metal-ligand bonding, experimental 3d orbital populations on the Mn atoms, and Bader atomic charges indicate quite ionic, high-spin metal atoms. This picture is supported by the effective moment estimated from the magnetization measurements (5.840(2) mu(B)), but it is at variance with earlier spin density measurements from polarized neutron diffraction. The magnetic ordering originates from superexchange involving covalent interactions with the ligands, and non-ionic effects are observed in the static deformation density maps as well as in plots of the valence shell charge concentrations. Overall, the present study provides a benchmark charge density that can be used in comparison with future metal formate dihydrate charge densities. 相似文献