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21.
Vallurupalli P Scott L Hennig M Williamson JR Kay LE 《Journal of the American Chemical Society》2006,128(29):9346-9347
A new labeling strategy is presented that greatly facilitates the measurement of 2H spin relaxation rates in RNA molecules as a probe of pico- to nanosecond time scale dynamics. In this labeling scheme the sugar positions are uniformly 13C-labeled, with position 2' protonated and all other sites on the sugar deuterated. Pulse sequences are presented for measurement of 2H R1 and R2 relaxation rates at positions 1', 3', and 4' with sensitivity gains that are on the order of 5-fold relative to previous methods that employed random fractional deuteration. The improved sensitivity is transformative and facilitates the study of motion in moderately sized RNA molecules with good sensitivity. The utility of the approach is demonstrated with an application to HIV-2 TAR, where the site-specific measures of molecular dynamics at sugar positions obtained here complement previous studies of dynamics at aromatic sites in the molecule. 相似文献
22.
Hennig M Munzarova ML Bermel W Scott LG Sklenar V Williamson JR 《Journal of the American Chemical Society》2006,128(17):5851-5858
Long-range scalar 5J(H1',F) couplings were observed in 5-fluoropyrimidine-substituted RNA. We developed a novel S3E-19F-alpha,beta-edited NOESY experiment for quantitation of these long-range scalar 5J(H1',F) couplings, where the J-couplings can be extracted from inspection of intraresidual (H1',H6) NOE cross-peaks. Quantum chemical calculations were exploited to investigate the relation between scalar couplings and conformations around the glycosidic bond in oligonucleotides. The theoretical dependence of the observed 5J(H1',F) couplings on the torsion angle chi can be described by a generalized Karplus relationship. The corresponding density functional theory (DFT) analysis is outlined. Additional NMR experiments facilitating the resonance assignments of 5-fluoropyrimidine-substituted RNAs are described, and chemical shift changes due to altered shielding in the presence of fluorine-19 (19F) are presented. 相似文献
23.
Giancarlo Marconi Sandra Monti Francesco Manoli Alessandra DegliEsposti Andrea Guerrini 《Helvetica chimica acta》2004,87(9):2368-2377
The circular dichroism (CD) spectra of the powerful antimalarian active principle artemisinin (ART; 1 ) from Artemisia annua, and of epiartemisinin (EPI, 2), its C(7) epimer, were studied in solution in the presence and absence of β‐cyclodextrin (β‐cd). A significant inversion of sign in the region of the second electronic transition was detected. The rotational strengths were successfully calculated within the time‐dependent density functional theory (DFT), which enabled us to establish a correlation between the molecular recognition and the biological acitivities of the two isomers. 相似文献
24.
25.
Shashank Vummidi Lakshman Edward L. Dreizin Mirko Schoenitz 《Journal of Thermal Analysis and Calorimetry》2014,116(1):141-149
The scope of this work was the assessment of thermo-oxidative deterioration, hydrothermal stability, and crystalline zone deterioration of some bookbinding leathers from some religious books published in XVIII century stored in Romanian libraries. In this purpose, the following thermal analysis methods were employed: thermogravimetry/derivative thermogravimetry (TG/DTG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The thermo-oxidative damage of investigated leathers was characterized by the rate of the first thermo-oxidation process put in evidence in TG/DTG curves recorded in static air atmosphere. The hydrothermal stability was characterized by shrinkage temperature determined by DSC analysis of leathers in water excess. The damage of the crystalline zone of leathers was determined by DSC in nitrogen flow and DMA analyses. The qualitative damage for each leather and each kind of degradation was evaluated using the criteria resulted by thermal analysis of a large number of collagen-based materials (pure collagens, new and old parchments and leathers). The obtained results could be used for finding the best possible methods for preservation and/or restoration of the investigated bookbinding leathers. 相似文献
26.
Minko S Müller M Motornov M Nitschke M Grundke K Stamm M 《Journal of the American Chemical Society》2003,125(13):3896-3900
We report a route to fabricate two-level structured self-adaptive surfaces (SAS) of polymer materials. The first level of structure is built by a rough polymer film that consists of needlelike structures of micrometer size. The second level of structure is formed by the nanoscopic self-assembled domains of a demixed polymer brush irreversibly grafted onto the needles. By exposing the surface to solvents that are selective to one of the components of the brush, we reversibly tune the surface properties. The large-scale surface structure amplifies the response and enables us to control wettability, adhesion, and chemical composition of the surface over a wide range. 相似文献
27.
A Highly Luminescent Tetramer from a Weakly Emitting Monomer: Acid‐ and Redox‐Controlled Multiple Complexation by Cucurbit[7]uril 下载免费PDF全文
Dr. Giacomo Bergamini Andrea Fermi Marianna Marchini Mirko Locritani Prof. Alberto Credi Prof. Margherita Venturi Prof. Fabrizia Negri Prof. Paola Ceroni Dr. Massimo Baroncini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):7054-7060
The tetrahedral, shape‐persistent molecule 1 4+, containing four pyridylpyridinium units connected through a central carbon atom, exhibits unexpected photophysical properties including a substantially redshifted absorption (2350 cm?1) and a very strong fluorescence (Φem=40 %), compared with the monomer 2 + (Φem=0.4 %). Density functional theory calculations on the structure and spectroscopic properties of 1 4+ and 2 + show that exciton interactions, homoconjugation, and orbital nature account for the observed differences in their photophysical properties. The protonated tetramer binds four cucurbit[7]uril molecules and the host/guest interactions can be controlled by chemical (acid/base) as well as redox stimuli. 相似文献
28.
A lot of methods were created in last decade for the spatio-temporal analysis of multi-electrode array (MEA) neuronal data
sets. In this paper we show how a new simple analysis approach that considers the total network activity, is able to show
interesting neuronal network system dynamical features. In particular, we perform two different analyses: a neuronal connectivity
examination studying networks at different days in vitro (div) and an analysis of the long per- iod effects of the administration of two common neuroactive drugs, Tetrodotoxin (TTX)
and D-2-amino-5-phosphonovalerate (AP5), to spontaneously spiking mature neuronal networks. Our analysis is performed considering
burst topology, i.e., cataloguing network bursts as Global (if they involve more than the 25% of the MEA channels) or Local
(if less that 25%). In the first analysis, this division allows to understand the network connectivity developments. The networking
increases from div 1 to 6 building up an undifferentiated highly connected network. From div 6 to 10 the networking decreases
(pruning) till reaching a plateau in a small-world like organization. The second analysis highlights substantial differences
between long period effects of TTX and AP5. Results show that AP5, selectively blocking NMDA receptors and inhibiting long
term potentiation, is unable to produce activity twisting in a network that already reached a developmental plateau, but it
is able to desynchronize sub-network (Local) activity. TTX, on the other side, blocking any type of electrical communication
among neurons, acts on the whole network synchronization. The important activity increment in the post-TTX epoch (+66%), together
with the Global activity explosion, suggests the possibility of a long-term inhibitory-synapse depression mechanism. 相似文献
29.
Mirko Lepović 《Journal of Applied Mathematics and Computing》2003,11(1-2):109-122
A tree is called starlike if it has exactly one vertex of degree greater than two. In [4] it was proved that two starlike treesG andH are cospectral if and only if they are isomorphic. We prove here that there exist no two non-isomorphic Laplacian cospectral starlike trees. Further, letG be a simple graph of ordern with vertex setV(G)={1,2, …,n} and letH={H 1,H 2, ...H n } be a family of rooted graphs. According to [2], the rooted productG(H) is the graph obtained by identifying the root ofH i with thei-th vertex ofG. In particular, ifH is the family of the paths $P_{k_1 } , P_{k_2 } , ..., P_{k_n } $ with the rooted vertices of degree one, in this paper the corresponding graphG(H) is called the sunlike graph and is denoted byG(k 1,k 2, …,k n ). For any (x 1,x 2, …,x n ) ∈I * n , whereI *={0,1}, letG(x 1,x 2, …,x n ) be the subgraph ofG which is obtained by deleting the verticesi 1, i2, …,i j ∈ V(G) (0≤j≤n), provided that $x_{i_1 } = x_{i_2 } = ... = x_{i_j } = 0$ . LetG(x 1,x 2,…, x n] be the characteristic polynomial ofG(x 1,x 2,…, x n ), understanding thatG[0, 0, …, 0] ≡ 1. We prove that $$G[k_1 , k_2 ,..., k_n ] = \Sigma _{x \in ^{I_ * ^n } } \left[ {\Pi _{i = 1}^n P_{k_i + x_i - 2} (\lambda )} \right]( - 1)^{n - (\mathop \Sigma \limits_{i = 1}^n x_i )} G[x_1 , x_2 , ..., x_n ]$$ where x=(x 1,x 2,…,x n );G[k 1,k 2,…,k n ] andP n (γ) denote the characteristic polynomial ofG(k 1,k 2,…,k n ) andP n , respectively. Besides, ifG is a graph with λ1(G)≥1 we show that λ1(G)≤λ1(G(k 1,k 2, ...,k n )) < for all positive integersk 1,k 2,…,k n , where λ1 denotes the largest eigenvalue. 相似文献
30.
C.?Degli Esposti Boschi E.?Ercolessi F.?Ortolani M.?RoncagliaEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,35(4):465-473
Quantum spin-1 chains may develop massless phases in presence of Ising-like and single-ion anisotropies. We have studied c = 1 critical phases by means of both analytical techniques, including a mapping of the lattice Hamiltonian onto an O(2) NL
M, and a multi-target DMRG algorithm which allows for accurate calculation of excited states. We find excellent quantitative agreement with the theoretical predictions and conclude that a pure Gaussian model, without any orbifold construction, describes correctly the low-energy physics of these critical phases. This combined analysis indicates that the multicritical point at large single-ion anisotropy does not belong to the same universality class as the Takhtajan-Babujian Hamiltonian as claimed in the past. A link between string-order correlation functions and twisting vertex operators, along the c = 1 line that ends at this point, is also suggested.Received: 16 July 2003, Published online: 24 October 2003PACS:
75.40.-s Critical-point effects, specific heats, short-range order - 75.10.Jm Quantized spin models - 02.70.-c Computational techniques 相似文献