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排序方式: 共有744条查询结果,搜索用时 15 毫秒
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Thitivat Suebsaeng Charles A. Wilkie Vern T. Burger Janet Carter Charles Eric Brown 《Journal of polymer science. Part A, Polymer chemistry》1984,22(4):945-957
The solid reaction products from pyrolysis of polyethylene terephthalate in the presence and absence of red phosphorus were characterized by CP/MAS 13C-NMR, FR-IR, and MAS 31P-NMR spectroscopy. Over the temperature range of 300–400°C, polyethylene terephthalate was converted in a sealed vial to a highly crosslinked polymer of terephthalic acid. Pyrolysis in the presence of red phosphorus, which functions as a flame retardant by increasing the amount of char, yielded an intractible polyaromatic phosphate ester. After thermal cleavage of polyethylene terephthalate with formation of free carboxyl and vinyl ester groups, there are two competing reaction pathways. The smaller molecular weight fragments may enter the vapor phase where they undergo further degradation primarily to CO2, CO, and acetaldehyde, as described by others. However, if volatilization of the oligomeric fragments is inhibited, an alternate reaction pathway gives rise to the formation of highly crosslinked char. Red phosphorus decreases the volatility of the oligomeric fragments by converting them to phosphates and thereby enhances char formation. 相似文献
3.
Sportsman JR Daijo J Gaudet EA 《Combinatorial chemistry & high throughput screening》2003,6(3):195-200
Fluorescence polarization (FP) has become widely employed for high throughput screening used in pharmaceutical drug discovery. Assays of important signal transduction targets are now adapted to FP. In this review we examine assays for cyclic adenosine monophosphate, phosphodiesterases, and protein kinases and phosphatases using FP competitive immunoassays and a direct enzymatic method called IMAP. 相似文献
4.
Haiwen Zhang David W. Norman Tracey M. Wentzell Alison M. Irving Janet P. Edwards Susan L. Wheaton Christopher M. Vogels Stephen A. Westcott Felix J. Baerlocher Andreas Decken 《Transition Metal Chemistry》2005,30(1):63-68
Reactions of salicylaldehydes with boronate ester derivatives of aniline have been examined. Addition of these Schiff base ligands to palladium acetate or Na2PdCl4 afforded novel boron-containing trans-bis(N-arylsalicylaldiminato) palladium complexes.Condensation of salicylaldehyde (2-HOC6H4C(O)H) with H2NC6H4Bpin (pin=1,2-O2C2Me4) afforded the boron-containing Schiff bases, 2-HOC6H4C(H)=NC6H4Bpin (1–3a). Similar reactivity with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde gave the corresponding Schiff bases (1-3b) and (1-3c), respectively. Reaction of Schiff bases (2) and (3) with palladium acetate or Na2PdCl4 afforded complexes of the type PdL2
(4,5), where L=deprotonated Schiff base. The molecular structure of the nitro-salicylaldehyde 4-Bpin palladium complex (5b) was characterized by an X-ray diffraction study. All new palladium compounds have been characterized fully and tested for their antifungal activity against Aspergillus niger and Aspergillus flavus. 相似文献
5.
Janet E. Del Bene 《Journal of computational chemistry》1987,8(6):810-815
Basis set expansion and correlation effects on computed hydrogen bond energies of the positive ion complexes AHn · AHn + 1+1, for AHn = NH3, OH2 and FH, have been evaluated. The addition of diffuse functions on nonhydrogen atoms is the single most important enhancement of split-valence plus polarization basis sets for computing hydrogen bond energies. Basis set enhancement effects appear to be additive in these systems. The correlation energy contribution to the stabilization energies of these complexes is significant, with the second order term being the largest term and having a stabilizing effect. The third order term is smaller and of opposite sign, while the fourth order term is smaller yet and stabilizing. As a result, computed MP4 stabilization energies are bracketed by the MP2 and MP3 energies. The overall effect of basis set enhancement is to decrease hydrogen bond energies, whereas the addition of electron correlation increases stabilization energies. 相似文献
6.
Dafnis Aguilar-Farrera Jocksan I. Morales-Camacho Edgar Espinosa-Hernndez Claudia G. Benítez-Cardoza G. Janet Jara-Romero Silvia Luna-Surez 《Molecules (Basel, Switzerland)》2022,27(11)
Some studies aimed at revealing the relationship between protein structure and their functional properties. However, the majority of these reports have been carried out using protein isolates. There are limited reports on the possible relationship between the functional properties and the structure of a purified protein. In this work the amaranth 11S globulin acidic subunit (AAC) and five mutations of the same protein that were modified in their variable regions with antihypertensive peptides (VYVYVYVY and RIPP), were analyzed at two ionic strength (2.9 and 17.6 g/L NaCl) and pH (3.0–7.0). Results revealed better solubility for the proteins mutated at the terminal ends (AACM.1 and AACM.4) and lower solubility for the protein inserted with RIPP peptide. Spectroscopy studies revealed an increase of β-sheet structure at high salt concentration for all proteins. It was also observed that salt concentration acted as a modulator, which allowed a better foam features for all modified proteins limiting movement of side chains and reducing red-shifted displacement of λmax. All proteins showed foam capacity ranging from 76 to 93% although foam stability was twofold better for modified proteins than for AAC at high salt concentration. This study allowed better understanding about the structural changes that influence the foaming properties of engineered proteins. 相似文献
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A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non‐linear Hammett 下载免费PDF全文
Perumal Subramaniam Jebamoney Janet Sylvia Jaba Rose Rajasingh Jeevi Esther Rathinakumari 《Journal of Physical Organic Chemistry》2016,29(10):496-504
Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)3]3+ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)3]3+ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron‐withdrawing and electron‐releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron‐releasing to electron‐withdrawing groups. Electron‐releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron‐withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H2O which leading to low magnitude of ρ+ compared to high ρ? values of electron‐releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
9.
Janet E. Jones 《Annals of Physics》1976,101(2):380-393
It is shown for the case of a conformally flat vacuum that the curvature of space-time may be viewed as the observable consequence of particle interactions involving a scalar field φ, rather than the independent agency of the gravitational field by itself. The quantum nature of gravity comes in as a consequence of the quantum properties of the φ-field (“vacuum fluctuation”), and a direct analogy is drawn between the renormalizations of charge and mass. Cosmological solutions are derived: These being just the conventional Friedmann solutions, or the de Sitter solution. It is pointed out that a totally empty universe must be Minkowskian. 相似文献
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