全文获取类型
收费全文 | 3439篇 |
免费 | 649篇 |
国内免费 | 408篇 |
专业分类
化学 | 2645篇 |
晶体学 | 37篇 |
力学 | 395篇 |
综合类 | 40篇 |
数学 | 475篇 |
物理学 | 904篇 |
出版年
2024年 | 3篇 |
2023年 | 58篇 |
2022年 | 109篇 |
2021年 | 145篇 |
2020年 | 198篇 |
2019年 | 175篇 |
2018年 | 140篇 |
2017年 | 161篇 |
2016年 | 214篇 |
2015年 | 164篇 |
2014年 | 216篇 |
2013年 | 312篇 |
2012年 | 256篇 |
2011年 | 259篇 |
2010年 | 215篇 |
2009年 | 210篇 |
2008年 | 198篇 |
2007年 | 200篇 |
2006年 | 184篇 |
2005年 | 166篇 |
2004年 | 155篇 |
2003年 | 179篇 |
2002年 | 116篇 |
2001年 | 79篇 |
2000年 | 53篇 |
1999年 | 46篇 |
1998年 | 40篇 |
1997年 | 40篇 |
1996年 | 23篇 |
1995年 | 38篇 |
1994年 | 29篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有4496条查询结果,搜索用时 16 毫秒
51.
Kiho Lee Ji-Yoon Lee Kyeong Lee Cho-Rock Jung Min-Ju Kim Jung-Ah Kim Dong-Gu Yoo Eun-Jin Shin Soo-Jin Oh 《Molecules (Basel, Switzerland)》2021,26(7)
A novel HIF (hypoxia-inducible factor)-1α inhibitor, the (aryloxyacetylamino)benzoic acid derivative LW6, is an anticancer agent that inhibits the accumulation of HIF-1α. The aim of this study was to characterize and determine the structures of the metabolites of LW6 in ICR mice. Metabolite identification was performed using a predictive multiple reaction monitoring-information dependent acquisition-enhanced product ion (pMRM-IDA-EPI) method in negative ion mode on a hybrid triple quadrupole-linear ion trap mass spectrometer (QTRAP). A total of 12 metabolites were characterized based on their MS/MS spectra, and the retention times were compared with those of the parent compound. The metabolites were divided into five structural classes based on biotransformation reactions: amide hydrolysis, ester hydrolysis, mono-oxidation, glucuronidation, and a combination of these reactions. From this study, 2-(4-((3r,5r,7r)-adamantan-1-yl)phenoxy)acetic acid (APA, M7), the metabolite produced via amide hydrolysis, was found to be a major circulating metabolite of LW6 in mice. The results of this study can be used to improve the pharmacokinetic profile by lowering the clearance and increasing the exposure relative to LW6. 相似文献
52.
Jinhua Wang Dr. Barbara Wicher Dr. Victor Maurizot Prof. Ivan Huc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):1031-1038
Quinoline based aromatic amide foldamers are known to adopt stable folded conformations. We have developed a synthetic approach to produce similar oligomers where all amide bonds, or part of them, have been replaced by an isosteric vinylene group. The results of solution and solid state structural studies show that oligomers exclusively containing vinylene linkages are not well folded, and adopt predominantly flat conformations. In contrast, a vinylene segment flanked by helical oligoamides also folds in a helix, albeit with a slightly lower curvature. The presence of vinylene functions also result in an extension of π-conjugation across the oligomer that may change charge transport properties. Altogether, these results pave the way to foldamers in which both structural control and specific electronic properties may be engineered. 相似文献
53.
Simulating periodic trends in the structure and catalytic activity of coinage metal nanoribbons 下载免费PDF全文
John J. Determan Salvador Moncho Edward N. Brothers Benjamin G. Janesko 《International journal of quantum chemistry》2015,115(24):1718-1725
We present a systematic density functional theory (DFT) study of the structure and catalytic activity of group 10 (Ni, Pd, Pt) and group 11 (Cu, Ag, Au) coinage metal nanoribbons. These infinite, periodic, quasi‐one‐dimensional structures are conceptually important as intermediates between small metal clusters and close‐packed metal surfaces, and have been shown experimentally to be practical catalysts. We find that nanoribbons have significantly higher predicted H2 dissociation activity than close‐packed metal surfaces consistent with their lower coordination numbers. Computed periodic trends are reasonable, with late transition states and low barriers for H2 dissociation over late group 10 nanoribbons, suggesting their promise as practical catalysts. These trends are consistent with the isolated nanoribbons' computed molecular electrostatic potentials. Calculations also predict nearly linear Brønsted–Evans–Polanyi relationships between the nanoribbons' H2 dissociation energies and dissociation barriers. We also test new meta‐generalized gradient approximation (GGA) and hybrid DFT approximations for H2 dissociation over these nanoribbons. These new functionals increase the (generally underestimated) dissociation barriers predicted by standard GGAs, motivating their continued application in surface chemistry. © 2015 Wiley Periodicals, Inc. 相似文献
54.
Selective Template Removal by Thermal Depolymerization to Obtain Mesostructured Molybdenum Oxycarbide
下载免费PDF全文
Martin Schieder Thomas Lunkenbein Carina Bojer Martin Dulle Julia vom Stein Gudrun Auffermann Tina Löbling Judith Schöbel Holger Schmalz Josef Breu 《无机化学与普通化学杂志》2015,641(10):1829-1834
The carbon content of mesostructured organic‐inorganic hybrid material of a cylindrical block copolymer template of poly(2‐vinylpyridine)‐block‐poly(allyl methacrylate) (P2VP‐b‐PAMA) and ammonium paramolybdate (APM) could be reduced by thermal depolymerization. By calcination in vacuo at 320 °C the PAMA core can be completely removed while the remaining P2VP brush preserves the mesostructure. The P2VP‐APM composite can then be carburized in‐situ to MoOxCy in a second pyrolysis step without any additional carbon source but P2VP. The molybdenum oxycarbide nanotubes obtained, form hierarchically porous non‐woven structures, which were tested as catalyst in the decomposition of NH3. They proved to be catalytically active at temperatures above 450 °C. The activation energy was estimated from an Arrhenius Plot to be 127 kJ · mol–1. 相似文献
55.
56.
Can Helical Peptides Unwind One Turn at a Time? ‐ Controlled Conformational Transitions in α,β2,3‐Hybrid Peptides 下载免费PDF全文
Dr. Dhayalan Balamurugan Dr. Kannoth M. Muraleedharan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9332-9338
Unfolding of helical trans‐β2,3‐hybrid peptides with (α–β)nα composition, when executed by increasing solvent polarity or temperature, proceeded in a systematic manner with the turns unwinding sequentially; C‐terminal region of these peptides were first to unwind and the process propagated towards N terminus with more and more β residues equilibrating from the gauche to the anti rotameric state across Cα?Cβ. This is evidenced by clear change in their CβH signal splitting, 3JCαH–CβH values, and sequential disappearance of i,i+2 NOEs. 相似文献
57.
Dr. Christiane Lang Sebastian Bestgen Dr. Alexander Welle Rouven Müller Prof. Peter W. Roesky Prof. Christopher Barner‐Kowollik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(42):14728-14731
A platform technology for the creation of spatially resolved surfaces encoded with a monolayer consisting of different metal complexes was developed. The concept entails the light‐triggered activation of a self‐ assembled monolayer (SAM) of UV‐labile anchors, that is, phenacylsulfides, and the subsequent cycloaddition of selected diene‐functionalized metal complexes at defined areas on the surface. The synthesis and characterization of the metal complexes for the UV‐light assisted anchoring on the surface and a detailed study of a short‐chain oligomer model system in solution confirm the high efficiency of the photoreaction. The hybrid materials obtained by this concept can potentially be utilized for the design of highly valuable catalytic or (opto‐)electronic devices. 相似文献
58.
以硫酸镉、叠氮化钠和4-氰基吡啶或3-氰基吡啶为反应物,在水热条件下,通过原位反应分别得到了2个基于硫酸根离子和5-(4-吡啶基)四氮唑(4-Hptz)或5-(3-吡啶基)四氮唑(3-Hptz)配体的,具有三维层-柱状框架结构的无机-有机杂化材料,即[Cd2(H2O)(OH)(SO4)(4-ptz)]n(1)和[Cd2(OH)(SO4)(3-ptz)]n(2)。通过元素分析、红外光谱、热重分析以及单晶和粉末X-射线衍射分析对它们的组成和结构进行了表征。在配合物1和2的结构中,每个镉(Ⅱ)离子的配位数均为6,处于扭曲的八面体配位环境中,SO42-和OH-阴离子连接镉(Ⅱ)离子扩展形成碱式硫酸镉的二维无机阳离子层结构[Cd2(H2O)(OH)(SO4)]nn+(1)或[Cd2(OH)(SO4)]nn+(2),相邻的二维无机阳离子层间再通过4-ptz-(1)或3-ptz-(2)进一步柱连接,形成三维层-柱状结构的无机-有机杂化框架结构。室温下的固体荧光实验表明,在350nm的光激发下,配合物1和2分别在481和489nm处出现强烈的荧光发射。 相似文献
59.
Encapsulation of Functional Organic Compounds in Nanoglass for Optically Anisotropic Coatings 下载免费PDF全文
Matthias Stöter Dr. Bernhard Biersack Dr. Sabine Rosenfeldt Markus J. Leitl Dr. Hussein Kalo Prof. Dr. Rainer Schobert Prof. Dr. Hartmut Yersin Prof. Geoffrey A. Ozin Prof. Dr. Stephan Förster Prof. Dr. Josef Breu 《Angewandte Chemie (International ed. in English)》2015,54(16):4963-4967
A novel approach is presented for the encapsulation of organic functional molecules between two sheets of 1 nm thin silicate layers, which like glass are transparent and chemically stable. An ordered heterostructure with organic interlayers strictly alternating with osmotically swelling sodium interlayers can be spontaneously delaminated into double stacks with the organic interlayers sandwiched between two silicate layers. The double stacks show high aspect ratios of >1000 (typical lateral extension 5000 nm, thickness 4.5 nm). This newly developed technique can be used to mask hydrophobic functional molecules and render them completely dispersible in water. The combination of the structural anisotropy of the silicate layers and a preferred orientation of molecules confined in the interlayer space allows polymer nanocomposite films to be cast with a well‐defined orientation of the encapsulated molecules, thus rendering the optical properties of the nanocoatings anisotropic. 相似文献
60.
Chun‐Feng Wang Dr. Ren‐Fu Li Prof. Dr. Xue‐Yuan Chen Dr. Rong‐Jia Wei Prof. Dr. Lan‐Sun Zheng Prof. Dr. Jun Tao 《Angewandte Chemie (International ed. in English)》2015,54(5):1574-1577
Hybrid materials integrated with a variety of physical properties, such as spin crossover (SCO) and fluorescence, may show synergetic effects that find applications in many fields. Herein we demonstrate a promising post‐synthetic approach to achieve such materials by grafting fluorophores (1‐pyrenecarboxaldehyde and Rhodamine B) on one‐dimensional SCO FeII structures. The resulting hybrid materials display expected one‐step SCO behavior and fluorescent properties, in particular showing a coupling between the transition temperature of SCO and the temperature where the fluorescent intensity reverses. Consequently, synergetic effect between SCO and fluorescence is incorporated into materials despite different fluorophores. This study provides an effective strategy for the design and development of novel magnetic and optical materials. 相似文献