全文获取类型
收费全文 | 528篇 |
免费 | 40篇 |
专业分类
化学 | 440篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 24篇 |
物理学 | 92篇 |
出版年
2023年 | 15篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 25篇 |
2019年 | 13篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 27篇 |
2013年 | 31篇 |
2012年 | 56篇 |
2011年 | 59篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 29篇 |
2007年 | 32篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 23篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有568条查询结果,搜索用时 31 毫秒
31.
Monomeric Chini‐Type Triplatinum Clusters Featuring Dianionic and Radical‐Anionic π*‐Systems
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Brandon R. Barnett Prof. Arnold L. Rheingold Prof. Joshua S. Figueroa 《Angewandte Chemie (International ed. in English)》2016,55(32):9253-9258
Owing to their unique topologies and abilities to self‐assemble into a variety of extended and aggregated structures, the binary platinum carbonyl clusters [Pt3(CO)6]n2? (“Chini clusters”) continue to draw significant interest. Herein, we report the isolation and structural characterization of the trinuclear electron‐transfer series [Pt3(μ‐CO)3(CNArDipp2)3]n? (n=0, 1, 2), which represents a unique set of monomeric Pt3 clusters supported by π‐acidic ligands. Spectroscopic, computational, and synthetic investigations demonstrate that the highest‐occupied molecular orbitals of the mono‐ and dianionic clusters consist of a combined π*‐framework of the CO and CNArDipp2 ligands, with negligible Pt character. Accordingly, this study provides precedent for an ensemble of carbonyl and isocyanide ligands to function in a redox non‐innocent manner. 相似文献
32.
We describe the first example of Rh-catalyzed intermolecular C-alkylation of cyclic 1,2-diketones using simple terminal olefins as alkylating agents. Aminopyridine is employed as a recyclable directing group. First, it reacts with ketones to give enamines and delivers Rh to activate the vinyl C-H bonds in the same pot; second, it can be cleaved off and recovered via hydrolysis. A broad range of olefins can be utilized as substrates, including aliphatic, aromatic olefins and vinyl esters. The efficiency of this method is also demonstrated in the synthesis of a natural flavoring compound, 3-ethyl-5-methyl-1,2-cyclopentadione (one-pot 53% yield vs a previous four-step route 16% yield from the same starting material). This work is expected to serve as a seminal study toward catalytic ketone α-alkylation with unactivated olefins. 相似文献
33.
Copper(I)-catalyzed 1,3-dipolar cycloaddition reaction of nonfluorescent 3-azidocoumarins and terminal alkynes afforded intense fluorescent 1,2,3-triazole products. The mild condition of this reaction allowed us to construct a large library of pure fluorescent coumarin dyes. Since both azide and alkyne are quite inert to biological systems, this reaction has potential in bioconjugation and bioimaging applications. [reaction: see text] 相似文献
34.
Back Cover: Multifunctional Tricarbazolo Triazolophane Macrocycles: One‐Pot Preparation,Anion Binding,and Hierarchical Self‐Organization of Multilayers (Chem. Eur. J. 2/2016)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
35.
36.
Refraction indices at room temperature and the temperature dependence of the spontaneous birefringence have been measured in ferroelastic lead orthophosphate. The 180°C phase transition in this material has been determined as a thermodynamic first order transition. 相似文献
37.
Parallel synthesis and high throughput dissolution testing of biodegradable polyanhydride copolymers
Vogel BM Cabral JT Eidelman N Narasimhan B Mallapragada SK 《Journal of combinatorial chemistry》2005,7(6):921-928
We have demonstrated that polycondensation reactions can be carried out in a combinatorial fashion and that the polymer library can be screened at high throughput using a rapid prototyping technique to fabricate multiwell substrates. A linearly varying compositional library of 100 different biodegradable polyanhydride random copolymers that are promising carriers for controlled drug delivery was designed, fabricated, and characterized by IR microscopy within a few hours. The polyanhydride copolymer library was based on 1,6-bis(p-carboxyphenoxy)hexane (CPH) and sebacic anhydride (SA) and was characterized with infrared microspectroscopy to determine the composition within each well. Since degradation and release rates depend on copolymer composition, we also developed new high-throughput methods to investigate drug release from this library of copolymers by designing specific wells for each task. A subset of this library was chosen, and a substrate was designed and fabricated to enable the synthesis and monitoring of dye dissolution from a range of polyanhydride copolymers in a parallel fashion using a CCD camera. Multisample substrates were fabricated with a novel rapid prototyping method that consists of an organic solvent-resistant array of 10 x 10 microwells of 2-muL volume each. The libraries were deposited with a custom-built liquid dispensing system consisting of a series of computer-controlled volume-dispensing pumps and XYZ motion stages. The parallel dye dissolution study displayed a decreasing rate of release with increasing CPH content. This result agrees with previously published data for dye release from poly(CPH-co-SA) copolymers. The methodology described in this work is amenable to numerous applications in the arenas of high-throughput polymer synthesis and characterization. 相似文献
38.
Estimation of frequency-averaged loss factors by the power injection and the impulse response decay methods 总被引:2,自引:0,他引:2
This paper describes a comparison, both analytically and experimentally, between two widely used loss factor estimation techniques frequently used in statistical energy analysis. Analytical models of simple spring/mass/damper systems were created to compare frequency-averaged loss factor values from the single subsystem power injection method and the impulse response decay method. The parameters of the analytical models were varied to study the effects of the total number of modes, amount of damping, location of modes within frequency bands, and the width of the frequency bands on loss factor estimation. The analytical study shows that both methods give accurate loss factor values as long as the damping values remain realistic for linear systems and at least one modal resonance is present in each frequency band. These analytical results were verified experimentally by measuring the loss factors of simple steel plates, with and without damping treatments applied. 相似文献
39.
Kastak D Southall BL Schusterman RJ Kastak CR 《The Journal of the Acoustical Society of America》2005,118(5):3154-3163
Behavioral psychophysical techniques were used to evaluate the residual effects of underwater noise on the hearing sensitivity of three pinnipeds: a California sea lion (Zalophus californianus), a harbor seal (Phoca vitulina), and a northern elephant seal (Mirounga angustirostris). Temporary threshold shift (TTS), defined as the difference between auditory thresholds obtained before and after noise exposure, was assessed. The subjects were exposed to octave-band noise centered at 2500 Hz at two sound pressure levels: 80 and 95 dB SL (re: auditory threshold at 2500 Hz). Noise exposure durations were 22, 25, and 50 min. Threshold shifts were assessed at 2500 and 3530 Hz. Mean threshold shifts ranged from 2.9-12.2 dB. Full recovery of auditory sensitivity occurred within 24 h of noise exposure. Control sequences, comprising sham noise exposures, did not result in significant mean threshold shifts for any subject. Threshold shift magnitudes increased with increasing noise sound exposure level (SEL) for two of the three subjects. The results underscore the importance of including sound exposure metrics (incorporating sound pressure level and exposure duration) in order to fully assess the effects of noise on marine mammal hearing. 相似文献
40.
Bifunctional, conjugated oligomers for orthogonal self-assembly: selectivity varies from planar substrates to nanoparticles 总被引:1,自引:0,他引:1
Walker BR Wassel RA Stefanescu DM Gorman CB 《Journal of the American Chemical Society》2004,126(50):16330-16331
A diphenylacetylene containing two different end groups (isonitrile and thioacetate) was synthesized, showing that the chemistry used to install each end group is compatible with that of the others. The isonitrile group binds preferentially to platinum, and the thiol group binds preferentially to gold. However, the selectivity was different when nanoparticles were compared to planar substrates. 相似文献