全文获取类型
收费全文 | 2598篇 |
免费 | 87篇 |
国内免费 | 23篇 |
专业分类
化学 | 1596篇 |
晶体学 | 9篇 |
力学 | 49篇 |
数学 | 429篇 |
物理学 | 625篇 |
出版年
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 29篇 |
2020年 | 38篇 |
2019年 | 31篇 |
2018年 | 35篇 |
2017年 | 39篇 |
2016年 | 62篇 |
2015年 | 62篇 |
2014年 | 62篇 |
2013年 | 128篇 |
2012年 | 195篇 |
2011年 | 188篇 |
2010年 | 131篇 |
2009年 | 117篇 |
2008年 | 167篇 |
2007年 | 175篇 |
2006年 | 175篇 |
2005年 | 215篇 |
2004年 | 154篇 |
2003年 | 135篇 |
2002年 | 123篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 21篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 35篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1973年 | 9篇 |
1972年 | 3篇 |
1970年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有2708条查询结果,搜索用时 0 毫秒
51.
Star-shaped azo-based dipolar chromophores: design, synthesis, matrix compatibility, and electro-optic activity 总被引:1,自引:0,他引:1
Gopalan P Katz HE McGee DJ Erben C Zielinski T Bousquet D Muller D Grazul J Olsson Y 《Journal of the American Chemical Society》2004,126(6):1741-1747
Three new azo-benzene-based push-pull chromophores with dendritic architecture were synthesized as active materials for electro-optic applications. These chromophores were synthesized in six or seven synthetic steps with an overall yield of around 80% per step and high purity. UV-vis spectroscopy showed significant influence of the transient dipole moment on the observed r(33) values. The chromophores were stable to photochemical oxidation in ambient light and air. The electrical poling conditions were optimized for each chromophore as the T(g) of the composite material varied significantly. The highest EO coefficient achieved was 22-25 pm/V at 1550 nm wavelength. STEM analysis of the blends enabled the correlation of the activity of these large chromophores with the blend morphology. An amorphous polycarbonate host effectively disperses the chromophores in 2-20 nm aggregates in the active materials. However, macrophase separation into 200-500 nm aggregates was observed in a methacrylate host matrix. 相似文献
52.
Bruckbauer A Ying L Rothery AM Zhou D Shevchuk AI Abell C Korchev YE Klenerman D 《Journal of the American Chemical Society》2002,124(30):8810-8811
We present a new, general method for the controlled deposition of biological molecules on surfaces, based on a nanopipet operating in ionic solution. The potential applied to the pipet tip controls the flux of biological molecules from the pipet, allowing fine control of the delivery rate. We used the ion current to control the distance of the pipet from the surface of a glass slide and deposited the fluorescently labeled DNA or protein G at a defined location onto the surface. Features of 830 nm size were obtained by depositing the biotinylated DNA onto a streptavidin surface; 1.3 mum size spots were obtained by depositing protein G onto a positively charged glass surface. 相似文献
53.
Zhdankin VV Kuehl CJ Krasutsky AP Bolz JT Simonsen AJ 《The Journal of organic chemistry》1996,61(19):6547-6551
Organosulfonyloxy derivatives of 1,2-benziodoxol-3(1H)-one (3a-c) and 3,3-bis(trifluoromethyl)-3(1H)-1,2-benziodoxole (5a-c) can be prepared in high yield by the reaction of 1-hydroxybenziodoxoles 1 or 4 and the corresponding sulfonic acids or Me(3)SiOTf in the form of stable, but moderately hygroscopic, microcrystalline solids. Reaction of the triflate derivatives 3a and 5a with alkynyltrimethylsilanes affords either alkynyliodonium triflates 6, or (E)-beta-(trifluoromethanesulfonyloxy)alkenyliodonium triflates 7, while the same reaction in the presence of pyridine selectively gives the respective 1-alkynylbenziodoxoles 8 and 9 in 82-90% yield. 相似文献
54.
The objective of this study was to develop and evaluate a supported capillary membrane sampling-gas chromatography method for the analysis of trihalomethanes (THMs) in drinking water. The effects of experimental parameters, such as flow rate of carrier gas, water temperature, ionic strengths of solutions and transfer line temperature on the system performance were investigated. The results of method detection limit and accuracy and precision studies are reported. 相似文献
55.
Wong KL Bitter M Hammett GW Heidbrink W Hendel H Kaita R Scott S Strachan JD Tait G Bell MG Budny R Bush C Chan A Coonrod J Efthimion PC England AC Eubank HP Fredrickson E Furth HP Goldston RJ Grek B Grisham L Hawryluk RJ Hill KW Johnson D Kamperschroer J Kugel H Ma C Mansfield D Manos D McCune DC McGuire K Medley SS Mueller D Nieschmidt E Owens DK Paré VK Park H Ramsey A Rasmussen D Roquemore AL Schivell J Sesnic S Taylor G Williams MD Zarnstorff MC 《Physical review letters》1985,55(23):2587-2590
56.
Bulloch EM Jones MA Parker EJ Osborne AP Stephens E Davies GM Coggins JR Abell C 《Journal of the American Chemical Society》2004,126(32):9912-9913
(6S)-6-Fluoroshikimate has antimicrobial activity. The molecular basis of this effect had not been identified, but there was speculation that (6S)-6-fluoroshikimate is first converted in vivo into 2-fluorochorismate, which then could inhibit 4-amino-4-deoxychorismate synthase (ADCS). 2-Fluorochorismate was prepared from E-fluorophosphoenolpyruvate and erythose-4-phosphate by the sequential reactions of DAHP synthase, dehydroquinate synthase, dehydroquinase, shikimate dehydrogenase, EPSP synthase, and chorismate synthase. Inhibition studies on ADCS showed that it was inhibited rapidly and irreversibly by 2-fluorochorismate. Electrospray mass spectrometry of the inactivated enzyme showed an additional mass of 198 +/- 10 Da. A novel peptide of 1087.6 Da was identified in the HPLC trace for the tryptic digest of 2-fluorochorismate-inactivated ADCS. Sequencing of this peptide by MS/MS showed that the peptide corresponded to residues 272-279 with a modification of 206.1 Da on Lys-274. This observation is particularly exciting in the context of a recent proposal for the catalytic mechanism of ADCS. 相似文献
57.
Smith AB Doughty VA Sfouggatakis C Bennett CS Koyanagi J Takeuchi M 《Organic letters》2002,4(5):783-786
[reaction: see text] A short, efficient, and stereocontrolled synthesis of (-)-4, an advanced ABCD subunit of the spongistatins, has been achieved. Central to the synthetic strategy is the multicomponent linchpin union of silyl dithianes with epoxides to access both the AB and CD fragments. Fragment coupling was then achieved via an efficient stereoselective aldol reaction. The linear sequence required 22 steps and proceeded in 4.0% overall yield. 相似文献
58.
Liu C Walter D Neuhauser D Baer R 《Journal of the American Chemical Society》2003,125(46):13936-13937
Crown ethers have the remarkable property of recognizing and binding specific metal cations in complex mixtures. We propose to combine molecular recognition with molecular electric conductance. The question we address is: can the event of binding a cation be sensed by a change in conductance? Specifically, we study a short molecular wire (MW) containing a crown-6 molecule connected via sulfur atoms to two gold atomic wires acting as metallic leads. Upon binding a cation, the density of states of the system is only slightly affected. This reflects the fact that the cation binding is largely electrostatic in nature and is accompanied by little electronic reorganization. Yet, the cationic binding does significantly lower conductance. We also identify strong interference affecting the conductance. A striking feature is the insensitivity of conductance to the type of ligand with the exception of the proton. 相似文献
59.
Chambers C Smith F Williams C Marcos S Liu ZH Hayter P Ciaramella G Keighley W Gribbon P Sewing A 《Combinatorial chemistry & high throughput screening》2003,6(4):355-362
The measurement of intracellular calcium fluxes in real time is widely applied within the pharmaceutical industry to measure the activation of G-protein coupled receptors (GPCRhyp;s), either for pharmacological characterisation or to screen for new surrogate ligands. Initially restricted to G(q) coupled GPCRs, the introduction of promiscuous and chimeric G-proteins has further widened the application of these assays. The development of new calcium sensitive dyes and assays has provided sensitive, homogeneous assays which can be readily applied to high throughput screening (HTS). In this paper we describe the full automation of this assay type using a fluorometric imaging plate reader (FLIPR ) integrated into a Beckman/Sagian system to establish a simple robotic system that is well suited for the current medium throughput screening in this area of lead discovery. Using a recently completed HTS we discuss important determinants for FLIPR based screening, highlight some limitations of the current approach, and look at the requirements for future automated systems capable of keeping up with expanding compound files. 相似文献
60.
Winter B Ivanco J Netzer FP Ramsey MG Salzmann I Resel R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7512-7516
A combination of in situ surface sensitive-techniques, UV photoemission and low energy electron diffraction, with ex situ bulk sensitive X-ray diffraction reveals the formation of epitaxial thin films of sexiphenyl on Al(111) starting from the first monolayer. For room temperature growth, highly ordered films are formed with a unique alignment of the sexiphenyl molecules with the long axes of all molecules aligned parallel to both the surface and the <10> azimuthal directions of Al(111). This is related to a densely packed highly commensurate first monolayer, which acts as a template for the unique (21) crystallite orientation observed. 相似文献