全文获取类型
收费全文 | 545篇 |
免费 | 29篇 |
专业分类
化学 | 396篇 |
晶体学 | 6篇 |
力学 | 24篇 |
数学 | 43篇 |
物理学 | 105篇 |
出版年
2023年 | 7篇 |
2022年 | 12篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 17篇 |
2012年 | 29篇 |
2011年 | 48篇 |
2010年 | 30篇 |
2009年 | 19篇 |
2008年 | 41篇 |
2007年 | 37篇 |
2006年 | 26篇 |
2005年 | 38篇 |
2004年 | 22篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 14篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有574条查询结果,搜索用时 250 毫秒
111.
112.
Elena I. Klimova Eduardo A. Vzquez Lpez Tatiana Klimova Cecilio Alvarez Toledano Ruben A. Toscano Marcos Martínez García 《Journal of heterocyclic chemistry》2005,42(2):265-271
Reactions of arene‐ and pyridinecarbaldehydes with ferrocenyl‐4,5‐dihydropyrazoles afforded 1‐arylmethyl‐ and 1‐pyridylmethyl‐3,5‐aryl(ferrocenyl)pyrazoles. Their structures were established based on spectroscopic methods and, for 4‐[(3,5‐diferrocenylpyrazol‐1‐yl)methyl]pyridine, based on X‐ray diffraction analysis. 相似文献
113.
Inspired by the current representation of the ligand-receptor binding process, a normal-mode-based methodology is presented to incorporate receptor flexibility in ligand docking and virtual screening. However, the systematic representation of the deformation space grows geometrically with the number of modes, and furthermore, midscale loop rearrangements like those found in protein kinase binding pockets cannot be accounted for with the first lowest-frequency modes. We thus introduced a measure of relevance of normal modes on a given region of interest and showed that only very few modes in the low-frequency range are necessary and sufficient to describe loop flexibility in cAMP-dependent protein kinase. We used this approach to generate an ensemble of representative receptor backbone conformations by perturbing the structure along a combination of relevant modes. Each ensemble conformation is complexed with known non-native binders to optimize the position of the binding-pocket side chains through a full flexible docking procedure. The multiple receptor conformations thus obtained are used in a small-scale virtual screening using receptor ensemble docking. We evaluated this algorithm on holo and apo structures of cAMP-dependent protein kinase that exhibit backbone rearrangements on two independent loop regions close to the binding pocket. Docking accuracy is improved, since the ligands considered in the virtual screening docked within 1.5 A to at least one of the structures. The discrimination between binders and nonbinders is also enhanced, as shown by the improvement of the enrichment factor. This constitutes a new step toward the systematic integration of flexible ligand-flexible receptor docking tools in structure-based drug discovery. 相似文献
114.
Tetrahedral n-type materials: efficient quenching of the excitation of p-type polymers in amorphous films 总被引:1,自引:0,他引:1
Ganesan P Yang X Loos J Savenije TJ Abellon RD Zuilhof H Sudhölter EJ 《Journal of the American Chemical Society》2005,127(42):14530-14531
Tetrahedral naphthalenediimide compound 1 has been synthesized as an example of a new class of amorphous n-type materials, in which the nondirectionality obtained by its shape is decoupled from its optoelectronic properties. 1 forms bicontinuous films with p-type polymers and effectively quenches the excited state, yielding long-lived mobile charge carriers on pulsed illumination. 相似文献
115.
Alipázaga MV Moreno RG Linares E Medeiros MH Coichev N 《Dalton transactions (Cambridge, England : 2003)》2005,(23):3738-3744
NiIIGGH (GGH = glycylglycylhistidine) reacts rapidly with S(IV), in air-saturated solution, to produce NiIIIGGH. A mechanism is proposed where initial NiIII oxidizes SO3(2-) to SO3*-, which reacts with dissolved oxygen to produce SO5*-, initiating radical chain reactions. DNA strand breaks and 8-oxo-7,8-dihydro-2'-deoxyguanosine formation were observed in air-saturated solutions containing micromolar concentrations of Ni(II) and S(IV). The extent of DNA damage showed dependence on the ratio of the NiIIGGH : S(IV) concentrations and the ionic strength. 相似文献
116.
Ruben M Ziener U Lehn JM Ksenofontov V Gütlich P Vaughan GB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):94-100
Hierarchical self-assembly of complex supramolecular architectures allows for the emergence of novel properties at each level of complexity. The reaction of the ligand components A and B with Fe(II) cations generates the [2x2] grid-type functional building modules 1 and 2, presenting spin-transition properties and preorganizing an array of coordination sites that sets the stage for a second assembly step. Indeed, binding of La(III) ions to 1 and of Ag(I) ions to 2 leads to a 1D columnar superstructure 3 and to a wall-like 2D layer 4, respectively, with concomitant modulation of the magnetic properties of 1 and 2. Thus, to each of the two levels of structural complexity generated by the two sequential self-assembly steps corresponds the emergence of novel functional features. 相似文献
117.
Rita Baraldi Gianpaolo Bertazza Judit Bogino Virginia Luna Ruben Bottini 《Photochemistry and photobiology》1995,62(4):800-803
Abstract— The endogenous levels of indole-3-acetic acid (IAA), abscisic acid (ABA) and gibberellins (GA) were examined by gas chromatography-mass spectrometry in Prunus cerasus plantlets grown under different light conditions in relation to previous work on the photocontrol of stem elongation. The endogenous levels of free and conjugated IAA in the apical sections of red-grown shoots were about two-fold higher than those in the blue-treated plants, and these corresponded with maximum shoot elongation. By contrast, greater concentrations of ABA and GA were found in blue-grown plants compared to red with intermediate shoot growth. When blue was combined with red or far red, lower levels of IAA, ABA and GA correlated with less growth. These results suggest that the regulation of stem elongation by phytochrome and a blue-absorbing pigment may, at least in part, occur through a modulation of hormone levels. 相似文献
118.
Ysaura De Sanctis Alejandro J. Arce Ruben Machado Teresa González 《Journal of organometallic chemistry》2004,689(11):2025-2028
The cluster [Os3(CO)10(MeCN)2] reacts readily with azulene in refluxing cyclohexane to give the oxidative addition product [Os3(μ-H)(μ2-η1-C10H7)(CO)10] 1 which was shown by its X-ray crystal structure to contain the C5 ring of the azulenyl ligand bonded through a single carbon atom at the 1-position. We propose that the compound is zwitterionic, with the 7-membered ring a tropylium cation and the 5-membered ring coordinated as a μ-alkylidene to the metal cluster, which carries a formal negative charge. Thermal loss of one CO ligand leads by further oxidative addition to the known cluster [Os3(μ-H)2(μ3-η1:η1:η1-C10H6)(CO)9] 2. 相似文献
119.
An efficient algorithm for parallelization of a molecular mechanics program operating in the space of internal coordinates such as dihedral angles, bond angles, and bond lengths is described. The iterative procedure to calculate analytical energy derivatives with respect to the internal coordinates was modified to allow parallelization. Computationally intensive modules that calculate energy and its derivatives, solvent-accessible surface, electrostatic polarization energy and that update lists of interactions were parallelized with nearly 100% efficiency. The proposed strategy for the shared-memory computer architecture is easily scalable and requires minimum changes in a program code. The overall speedup for a realistic calculation minimizing the energy of a myoglobin reaches a factor of 3 for 4 processors. © 1994 by John Wiley & Sons, Inc. 相似文献
120.
Time-dependent diffusion studies have been done on hexadecane molecules confined inside core shell polystyrene capsules in
order to extract capsule-size distribution. The polymeric capsules were prepared by an emulsification–diffusion technique.
The nuclear magnetic resonance (NMR) diffusometry technique implemented in our investigations is the so-called pulse gradient
stimulated echo technique. With this technique, diffusion times between 20 and 500 ms could be probed. The distribution of
the apparent diffusion coefficients was extracted using a numerical Laplace inversion. These data allowed us to obtain dimension
distributions in good agreement with the direct observations from electron micrographs. 相似文献