全文获取类型
收费全文 | 2575篇 |
免费 | 115篇 |
国内免费 | 12篇 |
专业分类
化学 | 1616篇 |
晶体学 | 4篇 |
力学 | 57篇 |
数学 | 509篇 |
物理学 | 516篇 |
出版年
2023年 | 55篇 |
2022年 | 45篇 |
2021年 | 70篇 |
2020年 | 110篇 |
2019年 | 89篇 |
2018年 | 30篇 |
2017年 | 55篇 |
2016年 | 106篇 |
2015年 | 86篇 |
2014年 | 86篇 |
2013年 | 109篇 |
2012年 | 139篇 |
2011年 | 164篇 |
2010年 | 87篇 |
2009年 | 62篇 |
2008年 | 139篇 |
2007年 | 102篇 |
2006年 | 104篇 |
2005年 | 86篇 |
2004年 | 69篇 |
2003年 | 57篇 |
2002年 | 63篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1999年 | 18篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 25篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1989年 | 15篇 |
1987年 | 10篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 22篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 11篇 |
1968年 | 9篇 |
1934年 | 11篇 |
1933年 | 11篇 |
1881年 | 10篇 |
排序方式: 共有2702条查询结果,搜索用时 15 毫秒
31.
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
32.
33.
Mikhail D. Borisover Felix D. Baitalov Boris N. Solomonov 《Journal of solution chemistry》1995,24(6):579-586
A new method was suggested for estimating the hydrophobic effect of contributions to the Gibbs energies and enthalpies of hydration of hydrocarbons, inorganic gases and rare gases. In accordance with this method the hydrophobic effect contribution to the Gibbs energy was evaluated from the difference between the hydration Gibbs energy of a solute and the non hydrophobic contribution. To estimate the latter value, the known dependence connecting the Gibbs energies of solvation of a solute in a number of aprotic solvents to the Hildebrand solubility parameter for these solvents was used. The non hydrophobic contribution to the Gibbs energy of hydration was calculated for various solutes from such dependences extended to water as solvent. The Hildebrand solubility parameter for water used in the calculation was corrected for the effect of association through hydrogen bonding. This correction was made by subtraction of the water self-association enthalpy from the enthalpy of vaporization of water. The evaluated Gibbs energies of the hydrophobic effect are positive for saturated hydrocarbons, inorganic gases and rare gases and linearly depend on the solute molecular refraction. The hydrophobic contribution to the hydration enthalpies of the solutes was calculated in the same manner as was made to calculate the hydrophobic contribution to Gibbs energies of hydration. Enthalpies of the hydrophobic effect for the solutes under study are negative. 相似文献
34.
Background
In the barley malting process, partial hydrolysis of β-glucans begins with seed germination. However, the endogenous 1,3-1,4-β-glucanases are heat inactivated, and the remaining high molecular weight β-glucans may cause severe problems such as increased brewer mash viscosity and turbidity. Increased viscosity impairs pumping and filtration, resulting in lower efficiency, reduced yields of extracts, and lower filtration rates, as well as the appearance of gelatinous precipitates in the finished beer. Therefore, the use of exogenous β-glucanases to reduce the β-glucans already present in the malt barley is highly desirable. 相似文献35.
Summary The native enantioselectivity in binding of human serum albumin (HSA) towards 2-aryl propionic acid non-steroidal anti-inflammatory drugs (2-APA-NSAIDs, the profens) was found to be preserved when the protein was immobilized within a commercially available diol high-performance liquid chromatographic column. High capacity factors were obtained, reflecting the previously observed extensive binding of the 2-APA-NSAIDs to free HSA. The capacity factors were modified by the addition of octanoic acid to the mobile phase. Chiral resolution of the enantiomers of all nine 2-APA-NSAIDs studied was achieved. Preliminary studies show that in addition to being a useful chiral analytical tool for this therapeutically important series of compounds, the HSA chiral stationary phase may provide useful information on the affinity and binding mechanism of small molecules to HSA. 相似文献
36.
Two new Ru(II) diimine chromophores, each containing a single photochromic dianthryl unit, have been prepared and characterized. The photoluminescence from the Ru(II) complexes is modulated by the photochromic action of the dianthryl species, which serves as a triplet energy transfer quencher in one photochromic state. The coupling of the dianthryl photochromic action to the Ru(II) complex emission permits nondestructive photoluminescence readout of binary information photochemically recorded on the molecular level. Luminescent images stored on polystyrene films that contain these molecules maintained their integrity for periods of months with no apparent degradation or variation in the image resolution, suggesting their durability for long-term storage in read-only memory applications. 相似文献
37.
38.
39.
The synthesis, structural characterization, photoluminescence properties, and density functional theory analysis of three Pt(II) diimine complexes, Pt(dbbpy)(C triple bond CR)2 [dbbpy = 4,4'-di(tert-butyl-2,2'-bipyridine; R = -SiMe3, -CC-SiMe3, or -t-Bu], are presented. The Pt(dbbpy)(C triple bond C-tBu)2 complex serves as a carbon-based ligand structure for which the photophysical properties of the two silicon-bearing complexes are compared in dichloromethane. Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-C triple bond C-SiMe3)2 display visible absorptions with strong green emission (lambda(emmax) = 526 and 524 nm, respectively) while Pt(dbbpy)(C triple bond C-t-Bu)2 displays efficient, long-lived yellow emission (lambda(emmax) = 557 nm). Direct side by side comparisons of Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-t-Bu)2 suggest that the difference in excited state energy results from the relative sigma-donor strength of the acetylide ligands. 相似文献
40.
A large set of charged species arising mainly from protonation or deprotonation of hydrocarbons, alcohols, ethers, carboxylic acids, amines, imines, and nitriles has been studied by means of the semiempirical self-consistent-field (SCF ) molecular orbital (MO ) MNDO method. From the calculated heats of formation of such charged species and those of neutral molecules, MNDO -estimated proton affinities have been obtained and the results compared with experimental gas-phase proton affinities. If the small size anions and acetylides, for which the method predicts heats of formation too large, are ruled out, the mean absolute error in calculated proton affinities is ca. 7 kcal/mol for hydrocarbons (22 acid-base pairs) and ca. 8 kcal/mol for oxygen-containing compounds (25 acid-base pairs). For nitrogen-containing molecules it is necessary to discard, in addition, the values corresponding to the protonation of alkylamines and imines in order to achieve a reasonable mean absolute error of 7–8 kcal/mol. 相似文献