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排序方式: 共有137条查询结果,搜索用时 15 毫秒
61.
Valentin Rautenstrauch Mikael Lindstrm Bernadette Bourdin Jane Curie Esther Oliveros 《Helvetica chimica acta》1993,76(1):607-615
The commercially available camphor enantiomers are extensively used in several important areas of chemical research, and it seems that they are often considered to be enantiomerically pure (the meaning of the term is discussed); there are certainly no enantiomeric purities (e.p.) on record. By standard GLC on a modified cyclodextrin column, we have now found five commercial (R)-camphors to have the same high but imperfect e.p., (99.62 ± 0.02)% (R), a sixth a slightly higher e.p., (99.76 ± 0.06) % (R), and three (S)-camphors to have different and lower e.p. Nailing down these e.p. is useful by itself and puts into focus the sensitivity of present day GLC, and how little is know about high e.p. in general. 相似文献
62.
The interpretation of the spectra of free atoms and gaseous ions in the 4fN and 5fN periods became less active after critical compilations of energy levels appeared. However, several spectra are still under study and the application of the Racah-Slater and HFR methods to extended sets of configurations leads to revisions and additions. In doubly charged ions of lanthanides, the treatment of configuration interaction by means of effective parameters and by extension of the basis of states are both important. Concerning actinides, calculations of several observables (Landé factors and isotope shifts in Pu I, hyperfine constants, transition probabilities) prove the quality of eigenfunctions. The classification of Es I and Es II has been extended and radial parameters for fine and hyperfine structures have been derived. Level predictions for the next element fermium are supported by parameter extrapolations. 相似文献
63.
A general quantum theoretical approach of the nu(X-H) IR line shape of cyclic dimers of weakly H-bonded species in the gas phase is proposed. In this model, the adiabatic approximation (allowing to separate the high frequency motion from the slow one of the H-bond bridge), is performed for each separate H-bond bridge of the dimer and a strong nonadiabatic correction is introduced into the model via the resonant exchange between the fast mode excited states of the two moieties. The present model reduces satisfactorily to many models in the literature dealing with more special situations. It has been applied to the cyclic dimers (CD(3)CO(2)H)(2) and (CD(3)CO(2)D)(2) in the gas phase. It correctly fits the experimental line shape of the hydrogenated compound and predict satisfactorily the evolution in the line shapes, to the deuterated one by reducing simply the angular frequency of the H-bond bridge and the anharmonic coupling parameter by the factor 1/ square root of 2. 相似文献
64.
J. Rossat-Mignod P. Burlet S. Quezel A. Blaise J.M. Fournier D.A. Damien A. Wojakowski 《Journal of magnetism and magnetic materials》1982,30(1):122-126
A neutron diffraction study on a small NpAs2 single crystal is reported. NpAs2 orders at TN = 52 K with a pure sine wave modulation propagating along a ≤100≥ direction of the tetragonal unit cell. The value of the wave vector is incommensurate with the lattice (k = ≤0.141,0,0≥) and is temperature independent down to TIC = 18.5 K where a first-order transition towards a commensurate ferromagnetic state occurs. At all temperatures the magnetic moments are aligned along the c-axis with a value of (1.45±0.1)μB at T = 5 K. 相似文献
65.
A new analysis of the spectrum of neutral protactinium led to revise and to extend the earlier level list. The Slater-Condon method was used to interpret the low even group of configurations 5f 26d7s 2+5f 26d 27s with a root mean square deviation of 134cm?1 for 64 energy levels. 相似文献
66.
Thermal Transition of Bimetallic Metal–Phenolic Networks to Biomass‐Derived Hierarchically Porous Nanofibers 下载免费PDF全文
Dr. Gao Xiao Wei Chen Fan Tian Dr. Joseph J. Richardson Dr. Blaise L. Tardy Prof. Minghua Liu Prof. Neel S. Joshi Dr. Junling Guo 《化学:亚洲杂志》2018,13(8):972-976
The development and utilization of biomass resources could contribute to new materials for long‐term sustainable energy storage and environmental applications, reduce environmental impacts, and meet the urgent need for green and sustainable development strategies. Herein, a bimetallic metal–phenolic network (MPN) was applied to incorporate different metallic element species into cattle skin and fabricate collagen‐fiber‐derived complex oxide nanofibers using natural polyphenols (Myrica tannins). Direct thermal transition of these biomass–MPN composites generates hierarchically porous nanofibers possessing micro‐ and mesoporous architectures along with a well‐preserved macroscopic structure. The pore system and complex oxide composition provide excellent photocatalytic performance. This low‐cost, simple, and readily scalable MPN‐based approach provides a straightforward route to synthesize nanostructured materials directly from biomass, which could play important roles in a wide range of potential applications. 相似文献
67.
68.
J.M. Costantini D. Damien C.H. de Novion A. Blaise A. Cousson H. Abazli M. Pagès 《Journal of solid state chemistry》1983,47(2):219-224
We describe the preparation and some physical properties of Pu2O2Te. The plutonium oxide telluride is isostructural with the corresponding rare-earth oxide tellurides which crystallize in the tetragonal system of La2O2Te-type. Magnetic susceptibility data from 4 K to room temperature are reported together with resistivity measurements. Pu2O2Te is found to be an antiferromagnet below 56 K and a semiconductor with an intrinsic energy gap of 0.65 eV. The magnetic behavior is interpreted in terms of superexchange coupling interactions via nonmetal p orbitals, i.e., in terms of 5f-p overlaps. This conclusion is supported by crystal chemistry considerations by comparison of cell volumes of Pu2O2Te and Nd2O2Te. In Pu2O2Te, the Pu crystal radius is found to be much lower than that of Nd in Nd2O2Te, suggesting some 5f electron “delocalization” leading to a crystal radius shrinkage. As for the hexagonal Pu2O2X compounds, with X = O, S, Se, the measured gap may be considered as the energy separation between the chalcogen np band and the 6d-7s conduction band, the occupied 5f states lying just below the np band with some 5f-np overlap. 相似文献
69.
Xin Zhang Jason B. Cross Jan Romero Alexander Heifetz Eric Humphries Katie Hall Yuchuan Wu Sabrina Stucka Jing Zhang Haoqun Chandonnet Blaise Lippa M. Dominic Ryan J. Christian Baber 《Journal of computer-aided molecular design》2018,32(4):573-582
Antagonism of CCR9 is a promising mechanism for treatment of inflammatory bowel disease, including ulcerative colitis and Crohn’s disease. There is limited experimental data on CCR9 and its ligands, complicating efforts to identify new small molecule antagonists. We present here results of a successful virtual screening and rational hit-to-lead campaign that led to the discovery and initial optimization of novel CCR9 antagonists. This work uses a novel data fusion strategy to integrate the output of multiple computational tools, such as 2D similarity search, shape similarity, pharmacophore searching, and molecular docking, as well as the identification and incorporation of privileged chemokine fragments. The application of various ranking strategies, which combined consensus and parallel selection methods to achieve a balance of enrichment and novelty, resulted in 198 virtual screening hits in total, with an overall hit rate of 18%. Several hits were developed into early leads through targeted synthesis and purchase of analogs. 相似文献
70.
Mathematical Programming - In the present paper we derive a Pontryagin maximum principle for general nonlinear optimal sampled-data control problems in the presence of running inequality state... 相似文献