全文获取类型
收费全文 | 5943篇 |
免费 | 144篇 |
国内免费 | 49篇 |
专业分类
化学 | 4073篇 |
晶体学 | 99篇 |
力学 | 141篇 |
数学 | 1000篇 |
物理学 | 823篇 |
出版年
2021年 | 39篇 |
2020年 | 42篇 |
2019年 | 68篇 |
2018年 | 58篇 |
2017年 | 47篇 |
2016年 | 118篇 |
2015年 | 118篇 |
2014年 | 115篇 |
2013年 | 324篇 |
2012年 | 277篇 |
2011年 | 340篇 |
2010年 | 158篇 |
2009年 | 156篇 |
2008年 | 301篇 |
2007年 | 329篇 |
2006年 | 292篇 |
2005年 | 319篇 |
2004年 | 267篇 |
2003年 | 274篇 |
2002年 | 219篇 |
2001年 | 91篇 |
2000年 | 80篇 |
1999年 | 64篇 |
1998年 | 50篇 |
1997年 | 71篇 |
1996年 | 93篇 |
1995年 | 101篇 |
1994年 | 87篇 |
1993年 | 67篇 |
1992年 | 63篇 |
1991年 | 61篇 |
1990年 | 50篇 |
1989年 | 67篇 |
1988年 | 72篇 |
1987年 | 55篇 |
1986年 | 54篇 |
1985年 | 85篇 |
1984年 | 106篇 |
1983年 | 70篇 |
1982年 | 90篇 |
1981年 | 96篇 |
1980年 | 93篇 |
1979年 | 77篇 |
1978年 | 80篇 |
1977年 | 75篇 |
1976年 | 72篇 |
1975年 | 59篇 |
1974年 | 49篇 |
1973年 | 38篇 |
1972年 | 21篇 |
排序方式: 共有6136条查询结果,搜索用时 15 毫秒
991.
Improved high-efficiency organic solar cells via incorporation of a conjugated polyelectrolyte interlayer 总被引:1,自引:0,他引:1
Seo JH Gutacker A Sun Y Wu H Huang F Cao Y Scherf U Heeger AJ Bazan GC 《Journal of the American Chemical Society》2011,133(22):8416-8419
The power conversion efficiencies of bulk heterojunction (BHJ) solar cells can be increased from 5 to 6.5% by incorporating an ultrathin conjugated polyelectrolyte (CPE) layer between the active layer and the metal cathode. Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C(71) butyric acid methyl ester (PC(71)BM) were chosen for the photoactive layer. CPEs with cationic polythiophenes, in both homopolymer and block copolymer configurations, were used to improve the electronic characteristics. The significant improvement in device performance and the simplicity of fabrication by solution processing suggest a promising and practical pathway for improving polymer solar cells with high efficiencies. 相似文献
992.
Rosanna Toniolo Alan Valentino G. Bontempelli Gilberto Schiavon 《Fresenius' Journal of Analytical Chemistry》1998,360(2):260-262
A simple method for the analysis of nanoliter droplets is proposed, which is profitable when larger samples cannot be collected
as, for instance, in the case of several biological fluids and particularly in clinical chemistry. A glass capillary associated
to a micromanipulator is used to collect submicroliter volumes which are partially transferred into transparent polymeric
tubings with known internal diameters (120–178 μm), where the volumes sampled are measured by meniscus collimations with a
collimator microscope at suitable magnification. Both ends of these tubings are preliminarily equipped with ferrules and fittings,
so as to make them suitable for connection as the loop to a conventional high-pressure injection valve. The reliability of
this procedure has been tested for the analysis of Na+, K+ and Ca2+ present in minute synthetic standard samples (10–200 nL) by a conventional ion-chromatographic instrumentation. Relative
standard deviations in peak area measurements (5–6%) are discussed in terms of the whole approximation affecting volume measurements,
which depends on both the inconstancy of the inner diameter of the polymeric tubings employed and the uncertainty characterizing
meniscus collimations. The proposed procedure can be easily extended to the determination of any organic or inorganic species
present in very small samples, provided that their detection can be achieved by any chromatographic approach or, more generally,
by flow injection analysis.
Received: 16 June 1997 / Revised: 12 August 1997 / Accepted: 14 August 1997 相似文献
993.
Alan L. Mackay 《Journal of mathematical chemistry》1997,21(2):197-209
The geometry of rings with 5, 6, 7, 8 and 9 links, particularly those with seven links such as occur in cyclo‐heptane and
analogous molecules* is re‐considered with the aid of distance geometry, now more practicable with modern mathematical software.
Use is made of a quadric surface which may be fitted to nine points.
*In admiration for the author I have ventured to appropriate the title of Archimedes’ work “On the regular heptagon”, which
came to light only in 1926 [C. Schoy, Graeco‐Arabische Studien, Isis 8 (1926) 21–40]. “Regular”, as applied to rings in space
admits of various definitions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
994.
Selective addition to iridium of aryl C-H bonds ortho to coordinating groups. Not chelation-assisted
Zhang X Kanzelberger M Emge TJ Goldman AS 《Journal of the American Chemical Society》2004,126(41):13192-13193
Precursors of the pincer-ligated iridium species, (PCP)Ir, react with nitrobenzene or acetophenone at ambient temperature to give O,C-chelated complexes resulting from addition of an aryl C-H bond and coordination of a nitro or acetyl oxygen. The C-H additions appear to be completely regioselective for the position ortho to the functional group; however, structural characterization and low-temperature NMR studies demonstrate that the reaction does not proceed via coordination of the functional group followed by C-H addition. In the case of nitrobenzene, kinetic preference for the para and meta positions is demonstrated at low temperature. Addition occurs more slowly at the ortho position, without assistance by the functional group; the ortho-C-H addition product is then trapped by chelation. 相似文献
995.
The first general approach to enantioselective catalysis of the Diels-Alder reaction with simple ketone dienophiles has been accomplished. The use of iminium catalysis has enabled enantioselective access to a fundamental Diels-Alder reaction variant that has previously been unavailable using chiral Lewis acid catalysis. A new chiral amine catalyst has been developed that allows a variety of monodentate cyclic and acyclic ketones to successfully participate in enantioselective [4 + 2] cycloadditions. A wide spectrum of cyclic and acyclic diene substrates can also be accommodated in this new organocatalytic transformation. A computational model is provided that is in accord with the sense of enantioinduction observed for all reactions conducted during the course of this study. 相似文献
996.
Wang X Yu JC Yip HY Wu L Wong PK Lai SY 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):2997-3004
A novel metal/semiconductor nanocomposite with catalytic and photocatalytic functions has been prepared. The new material consists of highly dispersed platinum (Pt) nanoparticles embedded in a cubic mesoporous nanocrystalline anatase (meso-nc-TiO2) thin film. The porous thin film possesses a narrow pore-size distribution and a large surface area. The diameter of the Pt cluster can be controlled to below 5 nm, and the high dispersion of these clusters gives rise to catalytic activity for the oxidation of carbon monoxide, an important reaction for automobile exhaust treatment. This novel ordered mesoporous Pt/TiO2 nanoarchitecture is also a promising photochemical material, as demonstrated by the photo-driven killing of Micrococcus lylae cells on the film. 相似文献
997.
Transfection mediated by gemini surfactants: engineered escape from the endosomal compartment 总被引:8,自引:0,他引:8
Bell PC Bergsma M Dolbnya IP Bras W Stuart MC Rowan AE Feiters MC Engberts JB 《Journal of the American Chemical Society》2003,125(6):1551-1558
The structure of the lipoplex formed from DNA and the sugar-based cationic gemini surfactant 1, which exhibits excellent transfection efficiency, has been investigated in the pH range 8.8-3.0 utilizing small-angle X-ray scattering (SAXS) and cryo-electron microscopy (cryo-TEM). Uniquely, three well-defined morphologies of the lipoplex were observed upon gradual acidification: a lamellar phase, a condensed lamellar phase, and an inverted hexagonal (H(II)) columnar phase. Using molecular modeling, we link the observed lipoplex morphologies and physical behavior to specific structural features in the individual surfactant, illuminating key factors in future surfactant design, viz., a spacer of six methylene groups, the presence of two nitrogens that can be protonated in the physiological pH range, two unsaturated alkyl tails, and hydrophilic sugar headgroups. Assuming that the mechanism of transfection by synthetic cationic surfactants involves endocytosis, we contend that the efficacy of gemini surfactant 1 as a gene delivery vehicle can be explained by the unprecedented observation of a pH-induced formation of the inverted hexagonal phase of the lipoplex in the endosomal pH range. This change in morphology leads to destabilization of the endosome through fusion of the lipoplex with the endosomal wall, resulting in release of DNA into the cytoplasm. 相似文献
998.
999.
This paper presents a new method for calculating accurate masses of isotopic peaks. It is based on breaking the calculation into a binary series of calculations. The molecule is built up by a series of such calculations. At each step the accurate masses are calculated as a probability weighted sum of the masses of the contributing peaks. The method is computationally efficient and accurate for both mass and relative abundance. 相似文献
1000.
Anions formed from the lithiation of 1-(1-benzotriazolylalkyl)benzotriazoles (1, 6) and 1-(1-methylthioalkyl)benzotriazoles (10 and 10a) with n-BuLi underwent additions to cyclic and acyclic ketones giving intermediates 3a-f, 7b-f, and 11b-d, respectively, in excellent yields. Thermal rearrangements of intermediates 3a,b,d-f and 7b-d,f in the presence of zinc bromide provided one-carbon chain-extended or ring-expanded alpha-benzotriazolyl ketones 4a,b,d-f and 8b-d,f in moderate yields with excellent regioselectivity. By contrast, intermediates 11b-d on treatment with zinc bromide loose a molecule of benzotriazole followed by intramolecular cyclization of the resulting intermediates 12b-d to provide the 2,3- and 1,2,3-substituted indenes 13b-d in good yields. 相似文献