全文获取类型
收费全文 | 1301篇 |
免费 | 32篇 |
国内免费 | 5篇 |
专业分类
化学 | 994篇 |
晶体学 | 5篇 |
力学 | 16篇 |
数学 | 163篇 |
物理学 | 160篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 49篇 |
2021年 | 56篇 |
2020年 | 34篇 |
2019年 | 29篇 |
2018年 | 22篇 |
2017年 | 16篇 |
2016年 | 41篇 |
2015年 | 35篇 |
2014年 | 46篇 |
2013年 | 60篇 |
2012年 | 67篇 |
2011年 | 97篇 |
2010年 | 69篇 |
2009年 | 54篇 |
2008年 | 70篇 |
2007年 | 86篇 |
2006年 | 65篇 |
2005年 | 59篇 |
2004年 | 48篇 |
2003年 | 53篇 |
2002年 | 61篇 |
2001年 | 18篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1939年 | 2篇 |
1938年 | 2篇 |
1937年 | 2篇 |
1921年 | 2篇 |
排序方式: 共有1338条查询结果,搜索用时 15 毫秒
101.
Lucia De Rosa Rossella Di Stasi Alessandra Romanelli Luca Domenico DAndrea 《Molecules (Basel, Switzerland)》2021,26(12)
Although a plethora of chemistries have been developed to selectively decorate protein molecules, novel strategies continue to be reported with the final aim of improving selectivity and mildness of the reaction conditions, preserve protein integrity, and fulfill all the increasing requirements of the modern applications of protein conjugates. The targeting of the protein N-terminal alpha-amine group appears a convenient solution to the issue, emerging as a useful and unique reactive site universally present in each protein molecule. Herein, we provide an updated overview of the methodologies developed until today to afford the selective modification of proteins through the targeting of the N-terminal alpha-amine. Chemical and enzymatic strategies enabling the selective labeling of the protein N-terminal alpha-amine group are described. 相似文献
102.
Nsevolo Samba Radhia Aitfella-Lahlou Mpazu Nelo Lucia Silva Rui Coca. Pedro Rocha Jesus Miguel Lpez Rodilla 《Molecules (Basel, Switzerland)》2021,26(1)
The purpose of the study was to determine the chemical composition and antibacterial activity of Lippia multiflora Moldenke essential oils (EOs) collected in different regions of Angola. Antibacterial activity was evaluated using the agar wells technique and vapour phase test. Analysis of the oils by GC/MS identified thirty-five components representing 67.5 to 100% of the total oils. Monoterpene hydrocarbons were the most prevalent compounds, followed by oxygenated monoterpenes. The content of the compounds varied according to the samples. The main components were Limonene, Piperitenone, Neral, Citral, Elemol, p-cymene, Transtagetone, and Artemisia ketone. Only one of the eleven samples contained Verbenone as the majority compound. In the vapour phase test, a single oil was the most effective against all the pathogens studied. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) of components of the selected EOs and inhibition zone diameter values of agar wells technique allowed us to identify a variability between the plants from the two provinces, but also intraspecific variability between sub-groups within a population. Each group of essential oils constituted a chemotype responsible for their bacterial inhibition capacity. The results presented here suggest that Angolan Lippia multiflora Moldenke has antibacterial properties and could be a potential source of antimicrobial agents for the pharmaceutical and food industry. 相似文献
103.
Dr. Elisa Bonandi Dr. Mattia Mori Dr. Paola Infante Dr. Irene Basili Prof. Dr. Lucia Di Marcotullio Dr. Andrea Calcaterra Dr. Federica Catti Prof. Dr. Bruno Botta Prof. Dr. Daniele Passarella 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(32):8350-8357
Withanolides constitute a well-known family of plant-based alkaloids characterised by widespread biological properties, including the ability of interfering with Hedgehog (Hh) signalling pathway. Following our interest in natural products and in anticancer compounds, we report here the synthesis of a new class of Hh signalling pathway inhibitors, inspired by withaferin A, the first isolated member of withanolides. The decoration of our scaffolds was rationally supported by in silico studies, while functional evaluation revealed promising candidates, confirming once again the importance of natural products as inspiration source for the discovery of novel bioactive compounds. A stereoselective approach, based on Brown chemistry, allowed the obtainment and the functional evaluation of the enantiopure hit compounds. 相似文献
104.
Basil I. Swanson Lucia M. Babcock David Schiferl David C. Moody Robert L. Mills Robert R. Ryan 《Chemical physics letters》1982,91(5):393-395
We report Raman measurements made on SO2 in a diamond cell up to 75 kbar showing two new phases, solid II and solid III, which differ from known, zero-pressure solid I. Spectra indicate that SO2 molecules aggregate in solid III to possibly form a cyclical trimer; solid III is shown to be photochemically active to blue radiation. 相似文献
105.
106.
Brezger B Hackermüller L Uttenthaler S Petschinka J Arndt M Zeilinger A 《Physical review letters》2002,88(10):100404
We demonstrate a near-field Talbot-Lau interferometer for C70 fullerene molecules. Such interferometers are particularly suitable for larger masses. Using three free-standing gold gratings of 1 microm period and a transversally incoherent but velocity-selected molecular beam, we achieve an interference fringe visibility of 40% with high count rate. Both the high visibility and its velocity dependence are in good agreement with a quantum simulation that takes into account the van der Waals interaction of the molecules with the gratings and are in striking contrast to a classical moiré model. 相似文献
107.
The static dielectric properties of (001)(GaAs)(p)/(AlAs)(p) superlattices have been calculated as a function of their period p for 1< or = p < or =12, starting from density-functional theory. The interplay between quantum confinement and local field effects is shown to be crucial. For light polarized in the growth direction it leads to the otherwise surprising justification of the use of a classical effective medium theory, even for the smallest periods. Only the inclusion of both contributions allows in ab initio and in semiempirical calculations to reproduce the experimentally observed birefringence. 相似文献
108.
A millimeter-wave molecular beam maser has been used to resolve the magnetic hyperfine structure of hydrogen cyanide. The spin-rotation interaction constants have been measured for the three nuclei 14N, 13C, and H. The paramagnetic nuclear shielding factors have been calculated for the three nuclear sites. The spin-rotation constants for 14N in H12C14N, for H in H12C14N and for 13C in D13C14N are + 10.4 kHz, −3.7 kHz, and +15.0 kHz, respectively. The respective paramagnetic shielding factors are −408.98 × 10−6, −73.40 × 10−6, and −249.52 × 10−6. 相似文献
109.
Banci L Bertini I Felli IC Sarrou J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,172(2):191-200
CH(alpha) residual dipolar couplings (Deltardc's) were measured for the oxidized cytochrome b562 from Escherichia coli as a result of its partial self-orientation in high magnetic fields due to the anisotropy of the overall magnetic susceptibility tensor. Both the low spin iron (III) heme and the four-helix bundle fold contribute to the magnetic anisotropy tensor. CH(alpha) Deltardc's, which span a larger range than the analogous NH values (already available in the literature) sample large space variations at variance with NH Deltardc's, which are largely isooriented within alpha helices. The whole structure is now significantly refined with the chemical shift index and CH(alpha) Deltardc's. The latter are particularly useful also in defining the molecular magnetic anisotropy parameters. It is shown here that the backbone folding can be conveniently and accurately determined using backbone restraints only, which include NOEs, hydrogen bonds, residual dipolar couplings, pseudocontact shifts, and chemical shift index. All these restraints are easily and quickly determined from the backbone assignment. The calculated backbone structure is comparable to that obtained by using also side chain restraint. Furthermore, the structure obtained with backbone only restraints is, in its whole, very similar to that obtained with the complete set of restraints. The paramagnetism based restraints are shown to be absolutely relevant, especially for Deltardc's. 相似文献
110.