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排序方式: 共有924条查询结果,搜索用时 15 毫秒
1.
Aida Contreras-Ramirez Dr. Bryan E. Tomlin Gregory S. Day Prof. Dr. Abraham Clearfield Prof. Dr. Hong-Cai Zhou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(28):6185-6194
Nanosized α-zirconium phenylphosphonate particles were successfully prepared by the reaction between different zirconium sources and molten phenylphosphonic acid in the absence of solvent. The resultant nanoplates exhibit particle sizes in the range of 15 to 30 nm. The use of a topotactic anion exchange method starting from α-zirconium phosphate instead resulted in the generation of 15 to 180 nm plates, while also resulting in nanoparticles with a higher degree of crystallinity. The topotactic anion exchange of the phosphate groups by phenylphosphonate groups could be performed to completion when performed in molten phenylphosphonic acid. Characterization of both the final products as well as the individual steps in the anion exchange were performed by powder XRD, fast neutron activation analysis, TGA, FTIR spectroscopy, TEM, solid-state NMR and XPS. 相似文献
2.
Caitlin E. Shields Dr. Xue Wang Dr. Thomas Fellowes Rob Clowes Dr. Linjiang Chen Prof. Graeme M. Day Prof. Anna G. Slater Dr. John W. Ward Dr. Marc A. Little Prof. Andrew I. Cooper 《Angewandte Chemie (International ed. in English)》2023,62(34):e202303167
Hydrogen-bonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structure-property predictions to generate energy-structure-function (ESF) maps for a series of triptycene-based molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown low-energy HOF (TH5-A) with a remarkably low density of 0.374 g cm−3 and three-dimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5-A polymorph experimentally. This material has a high accessible surface area of 3,284 m2 g−1, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date. 相似文献
3.
Donglin He Chengxi Zhao Dr. Linjiang Chen Dr. Marc A. Little Dr. Samantha Y. Chong Rob Clowes Katherine McKie Mark G. Roper Graeme M. Day Dr. Ming Liu Prof. Andrew I. Cooper 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(41):10589-10594
Ethyl acetate is an important chemical raw material and solvent. It is also a key volatile organic compound in the brewing industry and a marker for lung cancer. Materials that are highly selective toward ethyl acetate are needed for its separation and detection. Here, we report a trianglimine macrocycle ( TAMC ) that selectively adsorbs ethyl acetate by forming a solvate. Crystal structure prediction showed this to be the lowest energy solvate structure available. This solvate leaves a metastable, “templated” cavity after solvent removal. Adsorption and breakthrough experiments confirmed that TAMC has adequate adsorption kinetics to separate ethyl acetate from azeotropic mixtures with ethanol, which is a challenging and energy-intensive industrial separation. 相似文献
4.
Martin V. Day 《Journal of Dynamics and Differential Equations》1996,8(4):573-601
We discuss the phenomenon of cycling for noise induced escape to a unstable periodic orbit. The presence of cycling is shown to follow from qualitative properties of two quasipotential functions. A method of numerically evaluating these quasipotential functions is described, and applied to the Van der Pol oscillator as an example. Figures resulting from these calculations reveal that nonconvergent cycling of exit measures does occur for the Van der Pol example. 相似文献
5.
The majority of aquatic vertebrates are suction feeders: by rapidly expanding the mouth cavity they generate a fluid flow
outside of their head in order to draw prey into their mouth. In addition to the biological relevance, the generated flow
field is interesting fluid mechanically as it incorporates high velocities, is localized in front of the mouth, and is unsteady,
typically lasting between 10 and 50 ms. Using manometry and high-speed particle image velocimetry, this is the first study
to quantify pressure within and outside the mouth of a feeding fish while simultaneously measuring the velocity field outside
the mouth. Measurements with a high temporal (2 ms) and spatial (<1 mm) resolution were made for several feeding events of
a single largemouth bass (Micropterus salmoides). General properties of the flow were evaluated, including the transient velocity field, its relationship to pressure within
the mouth and pressure at the prey. We find that throughout the feeding event a relationship exists for the magnitude of fluid
speed as a function of distance from the predator mouth that is based on scaling the velocity field according to the size
of the mouth opening and the magnitude of fluid speed at the mouth. The velocity field is concentrated within an area extending
approximately one mouth diameter from the fish and the generated pressure field is even more local to the mouth aperture.
Although peak suction pressures measured inside the mouth were slightly larger than those that were predicted using the equations
of motion, we find that these equations give a very accurate prediction of the timing of peak pressure, so long as the unsteady
nature of the flow is included. 相似文献
6.
Yi-Xiang Shi Huan-Huan Chen Prof. Wen-Hua Zhang Gregory S. Day Prof. Jian-Ping Lang Prof. Hong-Cai Zhou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(36):8543-8549
The photoinduced dynamic behavior of flexible materials has received considerable attention for potential applications, such as in data storage or as smart optical devices and molecular mechanical actuators. Until now, precisely controlling expansion and contraction with light has remained a challenge. Unraveling the detailed mechanisms of photoinduced structural transformations remains a critical step necessary to understand the molecular architecture necessary for the design of sensitive photomechanical actuators. Herein, a two-dimensional flexible metal–organic framework [Zn2(bdc)2(3-CH3-spy)2]⋅H2O ( Zn2-1 ; H2bdc=1,4-benzenedicaboxylic acid; 3-CH3-spy=3-methylstyrylpyridine) with a positive volumetric thermal expansion coefficient of +78.78×10−6 K−1 is reported. Upon light irradiation at different wavelengths, the MOF underwent a [2+2] cycloaddition, which afforded a family of isomeric, three-dimensional MOFs ( Zn2-2 n , n=a–d) in a single-crystal-to-single-crystal (SCSC) manner. An unprecedented phenomenon, that is, photoinduced nonlinear contraction (PINC), was observed during this conversion. The PINC is caused by conformational changes in the 3-CH3-spy and bdc2− ligands, the bending of metal–ligand bonds, and the local distortion of the paddle-wheel SBUs. The formation of a “wrinkle morphology” on the crystal surface after the photoreaction was observed by AFM. This PINC behavior can broaden the studies on materials expansion and offer a photodriven approach for the future design of supersensitive photomechanical actuators. 相似文献
7.
M. E. Keillor L. E. Erikson C. E. Aalseth A. R. Day E. S. Fuller B. D. Glasgow E. W. Hoppe T. W. Hossbach L. K. Mizouni A. W. Myers C. T. Overman A. Seifert T. J. Stavenger 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):683-687
The Pacific Northwest National Laboratory (PNNL) is currently developing a custom software suite capable of automating many of the tasks required to accurately analyze coincident signals within gamma spectrometer arrays. During the course of this work, significant crosstalk was identified in the energy determination for spectra collected with a new low-background intrinsic germanium (HPGe) array at PNNL. The HPGe array is designed for high detection efficiency, ultra-low-background performance, and sensitive γ–γ coincidence detection. The first half of the array, a single cryostat containing seven HPGe crystals, was recently installed into a new shallow underground laboratory facility. This update will present a brief review of the germanium array, describe the observed crosstalk, and present a straight-forward empirical correction that significantly reduces the impact of this crosstalk on the spectroscopic performance of the system. 相似文献
8.
9.
Guochuan Yin Suparna Baksi Roy Andrew M. Danby Victor Day John Carter William M. Scheper Daryle H. Busch 《Journal of inclusion phenomena and macrocyclic chemistry》2011,71(3-4):311-318
On the basis of mass spectral studies alone, the relatively new manganese complex, Mn(Et2EBC)Cl2 (Et2EBC = 4,11-diethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane), a homolog of the well proven, peroxide-based laundry bleach, Mn(Me2EBC)Cl2, has been reported to undergo a sequence of 2-electron oxidation steps, ultimately converting its ethyl groups into chelated ethoxo and methylene carboxylato groups, [MnIV{(?OCH2CH2)(?O2CCH2)}EBC)](PF6)2. We report here the isolation and characterization of that unusual product, and provide insight into the remarkable catalytic pathway to its formation. At temperatures above 0 °C, oxidation by aqueous H2O2 reliably transforms Mn(Et2EBC)Cl2 into [MnIV{(?OCH2CH2)(?O2CCH2)}EBC)]2+. The experimental data for this intramolecular ethyl group transformation is consistent with oxygen insertion into a methyl C?CH moiety of the ethyl group, ?CNCH2C(?CH)H2, by the MnIV?COOH functional group. 相似文献
10.
Alfred Schmidpeter Angela Willhalm Jürgen Kroner Roberta O. Day Joan M. Holmes Robert R. Holmes 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):495-498
Abstract Phosphamethincyanines prepared in 1964 by Dimroth and Hoffmann were among the first compounds with two-coordinate phosphorus. They are special cases of 2-phospha-allylic cations. Simple representatives of this type become available from the reaction of imidoyl chlorides with tris(trimethylsily1)phosphane. 相似文献