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21.
Arthur J. Banister Anthony W. Luke 《Journal of polymer science. Part A, Polymer chemistry》1992,30(12):2653-2656
Mono-, bis- and tris-(1,3,2,4-dithiadiazolium) salts [R-(CNSNS +)n]n+[AsF-6]n (R = aryl, n = 1, 2, 3) were found to initiate the cationic ring-opening polymerization of tetrahydrofuran (THF) at room temperature to give clear gels from which the pure polymer was precipitated. 1,3,2,4-Dithiadiazolium cations associated with the hard [AsF6]- anion thus constitute a new class of cationic polymerization initiators. The poly(THF) formed by initiation with 1,3,2,4-dithiadiazolium cation was characterized by gel permeation chromatography, infrared spectrophotometry, and 13C-NMR spectroscopy. Number-average molecular weights of 198 700 g mol-1 (polydispersity 1.96) and 190 000 g mol-1 (polydispersity 1.61) were obtained using [PhCNSNS ] [AsF6] and [C6H3-1,3,5-(CNSNS )3][AsF6]3, respectively, as initiators. The use of multifunctional dithiadiazolium salts as initiators suggests that they may be useful in the preparation of starburst and dendritic polymers. © 1992 John Wiley & Sons, Inc. 相似文献
22.
T. L. Luke H. Mohan V. M. Manoj P. Manoj J. P. Mittal C. T. Aravindakumar 《Research on Chemical Intermediates》2003,29(4):379-391
Reactions of sulphate radical anion (SO·4
-) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 6-methyl uracil (MU) and 5,6-dimethyl uracil (DMU) have been studied by pulse radiolysis at pH 3 and at pH 10. The transient intermediate spectra were compared with those from the reaction of hydroxyl radical (·OH). It is proposed that SO·4
- produces radical cations of these pyrimidines in the initial stage. These radical cations are short-lived except in the case of DMHP where a relatively longer lived radical cation is proposed to be formed. When there is a hydrogen atom attached to the N(1) or N(3) position, a deprotonation from these sites is highly favored. When there is no hydrogen attached to these sites, deprotonation from a substituted methyl group is favored. At acidic pH, deprotonation from nitrogen is observed for DHMP, MU and DMU. At basic pH, the radical cation reacts with OH- leading to the formation of OH adducts. 相似文献
23.
The low-lying singlet and triplet states of H2CBe and HCBeH are examined using ab inito molecular orbital theory. In agreement with earlier results, the lowest-lying structure of H2CBe has C2v symmetry and is a triplet with one π electron (3 B1). The results presented here suggest that the lowest-energy singlet structure is the (1B1) open-shell singlet, also with C2v symmetry, at least 2.5 kcal/mol higher in energy. The singlet C2v structure with two π electrons (1A1) is 15.9 kcal/mol higher than 3B1. All of these structures are bound with respect to the ground state of methylene and the beryllium atom. In HCBeH, linear equilibrium geometries are found for the triplet (3Σ) and singlet (1Δ) states. The triplet is more stable than the singlet (1Δ) by 35.4 kcal/mol, and is only 2.9 kcal/mol higher in energy than triplet H2 CBe. Since the transition structure connecting these two triplet molecules is found to be 50.2 kcal/mol higher in energy than H2 CBe, both triplet equilibrium species might exist independently. The harmonic vibrational frequencies of all structures are also reported. 相似文献
24.
In this paper an approximative procedure to determine of the most probable model of oxide film originating at thermal oxidation of GaAs single-crystal samples within the temperature range 480–530 °C is proposed. It is shown that the system presented is more complicated if compare with that presumed previously. 相似文献
25.
M. A. Hartl D. J. Williams A. I. Acatrinei A. Stowe Luke L. Daemen Dr. 《无机化学与普通化学杂志》2007,633(1):120-126
The crystal structure of one of the simplest organoboron compounds, trimethyl borate does not appear to have been determined hitherto. The compound is of interest for the study of π‐donor ligands and their interaction with the π‐acceptor behavior of trigonal boron and the consequences of such interactions on molecular structure. We used powder neutron (with isotopically labeled material) and X‐ray diffraction to determine the crystal structure of trimethyl borate at 15 K and 200 K (neutron) and 200 K (X‐ray). The material is hexagonal (Z = 2) with a = b = 6.950(8) Å and c = 6.501(3) Å at 15 K. The unit cell volume is 272.00(1) Å3. The space group is P63/m (SG 176) at 15 K and 200 K. This is the first crystal structure solved on the Neutron Powder Diffractometer (NPDF) at the Lujan Center. 相似文献
26.
Adams LA Aggarwal VK Bonnert RV Bressel B Cox RJ Shepherd J de Vicente J Walter M Whittingham WG Winn CL 《The Journal of organic chemistry》2003,68(24):9433-9440
A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3]. 相似文献
27.
28.
29.
B.T. Luke 《SAR and QSAR in environmental research》2013,24(1):41-57
While quantitative structure-activity relationships attempt to predict the numerical value of the activities, it is found that statistically good predictors do not always do a good job of qualitatively determining the activity. This study shows how Fuzzy classifiers can be used to generate Fuzzy structure-activity relationships which can more accurately determine whether or not a compound will be highly inactive, moderately inactive or active, or highly active. Four examples of these classifiers are presented and applied to a well-studied activity dataset. 相似文献
30.
Unraveling σ and π Effects on Magnetic Anisotropy in cis‐NiA4B2 Complexes: Magnetization,HF‐HFEPR Studies,First‐Principles Calculations,and Orbital Modeling
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Dr. Gaëlle Charron Dr. Elena Malkin Dr. Guillaume Rogez Dr. Luke J. Batchelor Dr. Sandra Mazerat Dr. Régis Guillot Dr. Nathalie Guihéry Dr. Anne‐Laure Barra Dr. Talal Mallah Dr. Hélène Bolvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16850-16862
By using complementary experimental techniques and first‐principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2v, has been investigated. Four complexes have the general formula [Ni(bpy)X2]n+ (bpy=2,2′‐bipyridine; X2=bpy ( 1 ), (NCS?)2 ( 2 ), C2O42? ( 3 ), NO3? ( 4 )). In the fifth complex, [Ni(HIM2‐py)2(NO3)]+ ( 5 ; HIM2‐py=2‐(2‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2‐py. Analysis of the high‐field, high‐frequency electronic paramagnetic resonance (HF‐HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from ?1 to ?10 cm?1. First‐principles SO‐CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3 , on one hand, and 4 and 5 , on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters (D (axial), E (rhombic), and gi) are rationalized in terms of ordering of the 3 d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the eg‐like orbitals and is due to the difference in the σ‐donor strength of NO3? and bpy or HIM2‐py, whereas the difference in anisotropy between the two compounds is due to splitting of the t2g‐like orbitals; and 2) the anisotropy of complexes 1 – 3 arises from the small splitting of the t2g‐like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model. 相似文献