全文获取类型
收费全文 | 2507篇 |
免费 | 63篇 |
国内免费 | 7篇 |
专业分类
化学 | 1490篇 |
晶体学 | 34篇 |
力学 | 32篇 |
数学 | 439篇 |
物理学 | 582篇 |
出版年
2020年 | 28篇 |
2019年 | 24篇 |
2016年 | 38篇 |
2015年 | 48篇 |
2014年 | 47篇 |
2013年 | 101篇 |
2012年 | 95篇 |
2011年 | 96篇 |
2010年 | 76篇 |
2009年 | 55篇 |
2008年 | 97篇 |
2007年 | 118篇 |
2006年 | 108篇 |
2005年 | 81篇 |
2004年 | 112篇 |
2003年 | 73篇 |
2002年 | 57篇 |
2001年 | 55篇 |
2000年 | 46篇 |
1999年 | 37篇 |
1998年 | 29篇 |
1997年 | 44篇 |
1996年 | 39篇 |
1995年 | 35篇 |
1994年 | 40篇 |
1993年 | 52篇 |
1992年 | 46篇 |
1991年 | 33篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 31篇 |
1977年 | 28篇 |
1976年 | 25篇 |
1975年 | 32篇 |
1974年 | 32篇 |
1973年 | 26篇 |
1972年 | 33篇 |
1971年 | 25篇 |
1970年 | 29篇 |
1968年 | 20篇 |
排序方式: 共有2577条查询结果,搜索用时 15 毫秒
1.
Biomaterial scaffolds are the cornerstone to supporting 3D tissue growth. Optimized scaffold design is critical to successful regeneration, and this optimization requires accurate knowledge of the scaffold's interaction with living tissue in the dynamic in vivo milieu. Unfortunately, non‐invasive methods that can probe scaffolds in the intact living subject are largely underexplored, with imaging‐based assessment relying on either imaging cells seeded on the scaffold or imaging scaffolds that have been chemically altered. In this work, the authors develop a broadly applicable magnetic resonance imaging (MRI) method to image scaffolds directly. A positive‐contrast “bright” manganese porphyrin (MnP) agent for labeling scaffolds is used to achieve high sensitivity and specificity, and polydopamine, a biologically derived universal adhesive, is employed for adhering the MnP. The technique was optimized in vitro on a prototypic collagen gel, and in vivo assessment was performed in rats. The results demonstrate superior in vivo scaffold visualization and the potential for quantitative tracking of degradation over time. Designed with ease of synthesis in mind and general applicability for the continuing expansion of available biomaterials, the proposed method will allow tissue engineers to assess and fine‐tune the in vivo behavior of their scaffolds for optimal regeneration. 相似文献
2.
3.
4.
A Promiscuous De Novo Retro‐Aldolase Catalyzes Asymmetric Michael Additions via Schiff Base Intermediates 下载免费PDF全文
Dr. Xavier Garrabou Dr. Tobias Beck Prof. Dr. Donald Hilvert 《Angewandte Chemie (International ed. in English)》2015,54(19):5609-5612
Recent advances in computational design have enabled the development of primitive enzymes for a range of mechanistically distinct reactions. Here we show that the rudimentary active sites of these catalysts can give rise to useful chemical promiscuity. Specifically, RA95.5‐8, designed and evolved as a retro‐aldolase, also promotes asymmetric Michael additions of carbanions to unsaturated ketones with high rates and selectivities. The reactions proceed by amine catalysis, as indicated by mutagenesis and X‐ray data. The inherent flexibility and tunability of this catalyst should make it a versatile platform for further optimization and/or mechanistic diversification by directed evolution. 相似文献
5.
6.
Prof. Margaret A. Brimble Dr. Pat J. Edwards Dr. Paul W. R. Harris Dr. Gillian E. Norris Dr. Mark L. Patchett Tom H. Wright Dr. Sung‐Hyun Yang Dr. Sarah E. Carley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3556-3561
The first total synthesis of glycocin F, a uniquely diglycosylated antimicrobial peptide bearing a rare S‐linked N‐acetylglucosamine (GlcNAc) moiety in addition to an O‐linked GlcNAc, has been accomplished using a native chemical ligation strategy. The synthetic and naturally occurring peptides were compared by HPLC, mass spectrometry, NMR and CD spectroscopy, and their stability towards chymotrypsin digestion and antimicrobial activity were measured. This is the first comprehensive structural and functional comparison of a naturally occurring glycocin with an active synthetic analogue. 相似文献
7.
Determination of nicotine,glycerol, propylene glycol and water in electronic cigarette fluids using quantitative 1H NMR 下载免费PDF全文
8.
9.
Grace C. Thaggard Dr. Gabrielle A. Leith Daniil Sosnin Dr. Corey R. Martin Kyoung Chul Park Margaret K. McBride Dr. Jaewoong Lim Brandon J. Yarbrough Buddhima K. P. Maldeni Kankanamalage Gina R. Wilson Austin R. Hill Dr. Mark D. Smith Prof. Dr. Sophya Garashchuk Prof. Dr. Andrew B. Greytak Prof. Dr. Ivan Aprahamian Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(2):e202211776
Confinement-imposed photophysics was probed for novel stimuli-responsive hydrazone-based compounds demonstrating a conceptual difference in their behavior within 2D versus 3D porous matrices for the first time. The challenges associated with photoswitch isomerization arising from host interactions with photochromic compounds in 2D scaffolds could be overcome in 3D materials. Solution-like photoisomerization rate constants were realized for sterically demanding hydrazone derivatives in the solid state through their coordinative immobilization in 3D scaffolds. According to steady-state and time-resolved photophysical measurements and theoretical modeling, this approach provides access to hydrazone-based materials with fast photoisomerization kinetics in the solid state. Fast isomerization of integrated hydrazone derivatives allows for probing and tailoring resonance energy transfer (ET) processes as a function of excitation wavelength, providing a novel pathway for ET modulation. 相似文献
10.
Jürgen Beck Matthias Biechele Christoph Repik Petra Gruber Paul G. Furtmüller Rainer Hahn 《Journal of separation science》2023,46(8):2200943
Detailed studies on the sorption behavior of plasmids on anion exchangers are rare compared to proteins. In this study, we systematically compare the elution behavior of plasmid DNA on three common anion exchange resins using linear gradient and isocratic elution experiments. Two plasmids of different lengths, 8 and 20 kbp, were studied and their elution characteristics were compared to a green fluorescent protein. Using established methods for determining retention characteristics of biomolecules in ion exchange chromatography lead to remarkable results. In contrast to the green fluorescent protein, plasmid DNA consistently elutes at one characteristic salt concentration in linear gradient elution. This salt concentration was the same independent of plasmid size but differed slightly for different resins. The behavior is consistent also at preparative loadings of plasmid DNA. Thus, only a single linear gradient elution experiment is sufficient to design elution in a process scale capture step. At isocratic elution conditions, plasmid DNA elutes only above this characteristic concentration. Even at slightly lower concentrations most plasmids remain tightly bound. We hypothesize, that the desorption is accompanied by a conformational change leading to a reduced number of available negative charges for binding. This explanation is supported by structural analysis before and after elution. 相似文献