全文获取类型
收费全文 | 1693篇 |
免费 | 71篇 |
国内免费 | 4篇 |
专业分类
化学 | 1171篇 |
晶体学 | 6篇 |
力学 | 21篇 |
数学 | 234篇 |
物理学 | 336篇 |
出版年
2023年 | 14篇 |
2022年 | 54篇 |
2021年 | 50篇 |
2020年 | 40篇 |
2019年 | 44篇 |
2018年 | 31篇 |
2017年 | 32篇 |
2016年 | 82篇 |
2015年 | 54篇 |
2014年 | 67篇 |
2013年 | 78篇 |
2012年 | 131篇 |
2011年 | 148篇 |
2010年 | 112篇 |
2009年 | 69篇 |
2008年 | 103篇 |
2007年 | 136篇 |
2006年 | 79篇 |
2005年 | 67篇 |
2004年 | 53篇 |
2003年 | 39篇 |
2002年 | 28篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 20篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1985年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1969年 | 3篇 |
1968年 | 22篇 |
1967年 | 19篇 |
1966年 | 13篇 |
1941年 | 2篇 |
1905年 | 3篇 |
1904年 | 2篇 |
排序方式: 共有1768条查询结果,搜索用时 15 毫秒
81.
Metalation of CH2OH-substituted triazolium salts with CoCl2 under basic conditions affords C,O-bidentate chelating carbene Co(III) complexes ( 3a , 3b ), while analogous phenyl-substituted triazolium salts produce monodentate carbene Co(II) complexes ( 3c , 3d ). The distinct substituent-induced properties of the metal centers were demonstrated by electrochemical measurements and catalytic activities in two specific processes. The complexes showed appreciable activity in the reduction of C=O bonds through hydrosilylation, with methoxybenzene-functionalized triazolylidene Co(III) complex 3a achieving a high selectivity towards aldehydes vs. ketones with turnover frequencies (TOFs) up to 200 h−1. The C,O-chelate systems were also active catalysts in the Biginelli process, a one-step three-component reaction for efficient dihydropyrimidinone synthesis. Optimization of reaction conditions provides high activity with complex 3a , reaching TOFs of 800 h−1, the highest activity known for cobalt NHC complexes to date. 相似文献
82.
Simone Pilon Steen Ingemann Jørgensen Prof. Dr. Jan H. van Maarseveen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(7):2310-2314
After earlier unsuccessful attempts, this work reports the application of covalent templating for the synthesis of mechanically interlocked molecules (MiMs) bearing no supramolecular recognition sites. Two linear strands were covalently connected in a perpendicular fashion by a central ketal linkage. After subsequent attachment of the first strand to a template via temporary benzylic linkages, the second was linked to the template in a backfolding macrocyclization. The resulting pseudo[1]rotaxane structure was successfully converted to a [2]catenane via a second macrocyclization and cleavage of the ketal and temporary linkages. 相似文献
83.
Annali di Matematica Pura ed Applicata (1923 -) - Let $$\mathcal X $$ be a flat analytic groupoid $$R_X\stackrel{s}{\underset{t}{\rightrightarrows }}X$$ such that the holomorphic map... 相似文献
84.
Folding of Synthetic Homogeneous Glycoproteins in the Presence of a Glycoprotein Folding Sensor Enzyme 下载免费PDF全文
Dr. Simone Dedola Dr. Masayuki Izumi Dr. Yutaka Makimura Dr. Akira Seko Dr. Akiko Kanamori Dr. Masafumi Sakono Prof. Dr. Yukishige Ito Prof. Dr. Yasuhiro Kajihara 《Angewandte Chemie (International ed. in English)》2014,53(11):2883-2887
UDP‐glucose:glycoprotein glucosyltransferase (UGGT) plays a key role in recognizing folded and misfolded glycoproteins in the glycoprotein quality control system of the endoplasmic reticulum. UGGT detects misfolded glycoproteins and re‐glucosylates them as a tag for misfolded glycoproteins. A flexible model to reproduce in vitro folding of a glycoprotein in the presence of UGGT in a mixture containing correctly folded, folding intermediates, and misfolded glycoproteins is described. The data demonstrates that UGGT can re‐glucosylate all intermediates in the in vitro folding experiments, thus indicating that UGGT inspects not only final folded products, but also the glycoprotein folding intermediates. 相似文献
85.
Inherently Chiral Macrocyclic Oligothiophenes: Easily Accessible Electrosensitive Cavities with Outstanding Enantioselection Performances 下载免费PDF全文
Prof. Francesco Sannicolò Prof. Patrizia R. Mussini Prof. Tiziana Benincori Dr. Roberto Cirilli Prof. Sergio Abbate Serena Arnaboldi Simone Casolo Dr. Ettore Castiglioni Prof. Giovanna Longhi Dr. Rocco Martinazzo Dr. Monica Panigati Dr. Marco Pappini Dr. Elsa Quartapelle Procopio Dr. Simona Rizzo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15298-15302
Linear conjugated oligothiophenes of variable length and different substitution pattern are ubiquitous in technologically advanced optoelectronic devices, though limitations in application derive from insolubility, scarce processability and chain‐end effects. This study describes an easy access to chiral cyclic oligothiophenes constituted by 12 and 18 fully conjugated thiophene units. Chemical oxidation of an “inherently chiral” sexithiophene monomer, synthesized in two steps from commercially available materials, induces the formation of an elliptical dimer and a triangular trimer endowed with electrosensitive cavities of different tunable sizes. Combination of chirality with electroactivity makes these molecules unique in the current oligothiophenes literature. These macrocycles, which are stable and soluble in most organic solvents, show outstanding chiroptical properties, high circularly polarized luminescence effects and an exceptional enantiorecognition ability. 相似文献
86.
Enzyme Design from the Bottom Up: An Active Nickel Electrocatalyst with a Structured Peptide Outer Coordination Sphere 下载免费PDF全文
Dr. Matthew L. Reback Dr. Garry W. Buchko Dr. Brandon L. Kier Bojana Ginovska‐Pangovska Dr. Yijia Xiong Dr. Sheri Lense Dr. Jianbo Hou Dr. John A. S. Roberts Dr. Christina M. Sorensen Dr. Simone Raugei Dr. Thomas C. Squier Dr. Wendy J. Shaw 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1510-1514
Catalytic, peptide‐containing metal complexes with a well‐defined peptide structure have the potential to enhance molecular catalysts through an enzyme‐like outer coordination sphere. Here, we report the synthesis and characterization of an active, peptide‐based metal complex built upon the well‐characterized hydrogen production catalyst [Ni(PPh2NPh)2]2+ (PPh2NPh=1,3,6‐triphenyl‐1‐aza‐3,6‐diphosphacycloheptane). The incorporated peptide maintains its β‐hairpin structure when appended to the metal core, and the electrocatalytic activity of the peptide‐based metal complex (≈100,000 s?1) is enhanced compared to the parent complex ([Ni(PPh2NAPPA)2]2+; ≈50,500 s‐1). The combination of an active molecular catalyst with a structured peptide provides a scaffold that permits the incorporation of features of an enzyme‐like outer‐coordination sphere necessary to create molecular electrocatalysts with enhanced functionality. 相似文献
87.
Simone Manzini Dr. Albert Poater Dr. David J. Nelson Prof. Dr. Luigi Cavallo Prof. Dr. Alexandra M. Z. Slawin Prof. Dr. Steven P. Nolan 《Angewandte Chemie (International ed. in English)》2014,53(34):8995-8999
The decomposition of a series of benzylidene, methylidene, and 3‐phenylindenylidene complexes has been probed in alcohol solution in the presence of base. Tricyclohexylphosphane‐containing precatalysts are shown to yield [RuCl(H)(H2)(PCy3)2] in isopropyl alcohol solutions, while 3‐phenylindenylidene complexes lead to η5‐(3‐phenyl)indenyl products. The potential‐energy surfaces for the formation of the latter species have been probed using density functional theory studies. 相似文献
88.
Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds 下载免费PDF全文
Hendrik Herrmann Alexandra Ziesak Ute Wild Simone Leingang David Schrempp Norbert Wagner Prof. Dr. Johannes Beck Dr. Elisabeth Kaifer Prof. Dr. Hubert Wadepohl Prof. Dr. Hans‐Jörg Himmel 《Chemphyschem》2014,15(2):351-365
In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity. 相似文献
89.
Sayonara Maria Calado Gonçalves Glória Najara Silva Ivan da Rocha Pitta Moacyr Jesus Barreto de Melo Rêgo Simone Cristina Baggio Gnoato 《Natural product research》2020,34(12):1702-1711
AbstractBetulin (BE) is a pentacyclic triterpenes, obtained from natural sources and with several biological activities described, such as anti-tumoral and anti-inflammatory activities. The BE esterification at hydroxyl group (C-3 and C-28) resulted in five new ester derivatives with different numbers of carbons or halogens (chlorine and fluorine). Among these BE derivatives, two (2a e 2c) were able to significantly decrease IFN-g (*p?=?0.0391; **p?=?0.0156) and 2c modulated the expression of COX-2 better than Dexamethasone (DEXA). Regarding to cytotoxic assay, the best results were obtained for BE without modifications, with emphasis on tumoral cell lines Raji and MCF-7. The derivatives 2a and 2c showed immunomodulation activity (for the cytokines IFN-g). The presence of chorine in BE seems to be important for the ability of modulate COX-2 expression, since the ester chloride derivative 2c at 100?μM is more powerful inhibitor of COX-2 than DEXA. 相似文献
90.
Andrea Macrelli Nicol Simone Villa Andrea Lucotti David Dellasega Paolo Maria Ossi Matteo Tommasini 《Molecules (Basel, Switzerland)》2022,27(1)
The applications of SERS in therapeutic drug monitoring, or other fields of analytical chemistry, require the availability of sensitive sensors and experimental approaches that can be implemented in affordable ways. In this contribution, we show the production of cost-effective SERS sensors obtained by depositing Lee-Meisel Ag colloids on filter paper either by natural sedimentation or centrifugation. We have characterized the morphological and plasmonic features of the sensors by optical microscopy, SEM, and UV-Vis spectroscopy. Such sensors can be used to quantify by SERS the anti-epileptic drug Perampanel (in the concentration range 1 × 10−4–5 × 10−6 M) by spinning them during the micro-Raman measurements on the top of a custom device obtained from spare part hard disk drives. This approach minimizes laser-induced heating effects and allows averaging over the spatial non-uniformity of the sensor. 相似文献