全文获取类型
收费全文 | 7189篇 |
免费 | 325篇 |
国内免费 | 34篇 |
专业分类
化学 | 5799篇 |
晶体学 | 53篇 |
力学 | 99篇 |
数学 | 909篇 |
物理学 | 688篇 |
出版年
2023年 | 79篇 |
2022年 | 65篇 |
2021年 | 312篇 |
2020年 | 236篇 |
2019年 | 236篇 |
2018年 | 198篇 |
2017年 | 164篇 |
2016年 | 316篇 |
2015年 | 229篇 |
2014年 | 318篇 |
2013年 | 487篇 |
2012年 | 533篇 |
2011年 | 581篇 |
2010年 | 392篇 |
2009年 | 295篇 |
2008年 | 472篇 |
2007年 | 440篇 |
2006年 | 414篇 |
2005年 | 316篇 |
2004年 | 268篇 |
2003年 | 193篇 |
2002年 | 157篇 |
2001年 | 76篇 |
2000年 | 54篇 |
1999年 | 32篇 |
1998年 | 36篇 |
1997年 | 31篇 |
1996年 | 48篇 |
1995年 | 35篇 |
1994年 | 32篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 32篇 |
1990年 | 25篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 44篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 22篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1935年 | 5篇 |
1932年 | 5篇 |
排序方式: 共有7548条查询结果,搜索用时 15 毫秒
1.
2.
Dr. Waleed Alsalahi Dr. Adam W. Augustyniak Dr. Włodzimierz Tylus Prof. Dr. Anna M. Trzeciak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(6):e202103538
The new nanocomposites, Pd/C/ZrO2, PdO/ZrO2, and Pd/PdO/ZrO2, were prepared by thermal conversion of Pd@UiO-66-Zr−NH2 (MOF) in nitrogen or air atmosphere. The presence of Pd nanoparticles, uniformly distributed on the ZrO2 or C/ZrO2 matrix, was evidenced by transmission electron microscopy, scanning electron microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS) methods. All pyrolysed composites retained the shape of the MOF template. They catalyze carbonylative Suzuki coupling under 1 atm CO with an efficiency significantly higher than the original Pd@UiO-66-Zr−NH2. The most active PdO/ZrO2 composite, formed benzophenone with TOF up to 1600 h−1, while by using Pd@UiO-66-Zr−NH2, much lower TOF values, 51–95 h−1, were achieved. After the reaction, PdO/ZrO2 was recovered with the same composition and catalytic activity. Very good results were also obtained in the transfer hydrogenation of benzophenones to alcohols with Pd/C/ZrO2 and PdO/ZrO2 catalysts under microwave irradiation. 相似文献
3.
Michnik Anna Kiełboń Agnieszka Duch Klaudia Sadowska-Krępa Ewa Pokora Ilona 《Journal of Thermal Analysis and Calorimetry》2022,147(12):6739-6743
Journal of Thermal Analysis and Calorimetry - The results of studies of physiological fluids by differential scanning calorimetry (DSC) for the purpose of diagnosis and monitoring of diseases are... 相似文献
4.
Daria Larowska Dr. Aleksandra Wojcik Dr. Marta Mazurkiewicz-Pawlicka Dr. Artur Malolepszy Dr. Leszek Stobiński Prof. Bronislaw Marciniak Dr. Anna Lewandowska-Andralojc 《Chemphyschem》2019,20(8):1054-1066
Non-covalent nanohybrids composed of cationic 5,10,15,20-tetra(4-trimethylammoniophenyl)porphyrin tetra(p-toluenesulfonate) (TMAP) and the graphene oxide sheets were prepared under two pH values (6.2 vs. 1.8). The TMAP molecule was positively charged, regardless of the pH value during preparation. However, protonation of the imino nitrogens increased the overall charge of the porphyrin molecule from +4 to +6 (TMAP4+ and TMAP6+). It was found that at acidic pH, interaction of TMAP6+ with GO was largely suppressed. On the other hand, results of FTIR, Raman spectroscopy, thermogravimetric analysis, atomic force microscopy (AFM) and elemental analysis confirmed effective non-covalent functionalization of graphene oxide with cationic porphyrin at pH 6.2. The TMAP4+-GO hybrids exhibited well defined structure with a monolayer of TMAP4+ on the GO sheets as confirmed by AFM. Formation of the ground-state TMAP4+-GO complex in solution was monitored by the red-shift of the porphyrin Soret absorption band. This ground-state interaction between TMAP4+ and GO is responsible for the static quenching of the porphyrin emission. Fluorescence was not detected for the nanohybrid which indicated that a very fast deactivation process had to take place. Ultrafast time-resolved transient absorption spectroscopy clearly demonstrated the occurrence of electron transfer from the photoexcited TMAP4+ singlet state to GO sheets, as proven by the formation of a porphyrin radical cation. 相似文献
5.
Anna S. Savchenkova Alexander S. Semenikhin Ivan V. Chechet Sergey G. Matveev Alexander A. Konnov Alexander M. Mebel 《Journal of computational chemistry》2019,40(2):387-399
Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH2 with ketene CH2CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH3 and C2H4 + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C2H4 + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH2COCH2 intermediate or along the pathway of CO elimination from the initial CH2CH2CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C2H4 + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH3CHCO and cyclic CH2COCH2 intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion. © 2018 Wiley Periodicals, Inc. 相似文献
6.
Numerous biological processes are connected with the efficient electron transfer reactions in proteins and peptides. In this review, we discuss briefly the relevance and current challenges associated with the voltammetric analysis of peptides and proteins with and without a metal redox center. Special attention is paid to the integration of electrochemical methods with new nanomaterials which offers amplification of multiplexing capabilities for simultaneous and very sensitive examination of various proteins. After critically discussing the most interesting approaches in the proteins/peptides voltammetric analysis reported so far, for the single or multiplexed examination of such biomolecules with demonstrated applicability in the real-sample analysis, existing challenges still need to be addressed and future directions in this field will be pointed out. 相似文献
7.
Raoul Walther Anna K. Winther Anne Sofie Fruergaard Wouter vandenAkker Lise Srensen Signe Maria Nielsen Morten T. JarlstadOlesen Yitao Dai Henrik S. Jeppesen Paolo Lamagni Aleksandr Savateev Sren Lykke Pedersen Camilla Kaas Frich Ccile Vigier‐Carrire Nina Lock Mandeep Singh Vipul Bansal Rikke L. Meyer Alexander N. Zelikin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(1):284-288
Nanozymes, nanoparticles that mimic the natural activity of enzymes, are intriguing academically and are important in the context of the Origin of Life. However, current nanozymes offer mimicry of a narrow range of mammalian enzymes, near‐exclusively performing redox reactions. We present an unexpected discovery of non‐proteinaceous enzymes based on metals, metal oxides, 1D/2D‐materials, and non‐metallic nanomaterials. The specific novelty of these findings lies in the identification of nanozymes with apparent mimicry of diverse mammalian enzymes, including unique pan‐glycosidases. Further novelty lies in the identification of the substrate scope for the lead candidates, specifically in the context of bioconversion of glucuronides, that is, human metabolites and privileged prodrugs in the field of enzyme‐prodrug therapies. Lastly, nanozymes are employed for conversion of glucuronide prodrugs into marketed anti‐inflammatory and antibacterial agents, as well as “nanozyme prodrug therapy” to mediate antibacterial measures. 相似文献
8.
Magorzata Katarzyna Cabaj Roman Gajda Anna Hoser Anna Makal Paulina Maria Dominiak 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(8):1036-1044
Crystals of hypoxanthinium (6‐oxo‐1H,7H‐purin‐9‐ium) nitrate hydrates were investigated by means of X‐ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C5H5N4O+·NO3?·H2O, Hx1 ) were collected at 20, 105 and 285 K. The room‐temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C 46 , 340–342] and the low‐temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P21/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H3O+·C5H5N4O+·2NO3?·2H2O, Hx2 ) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H3O+·H2O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C5H5N4O+·NO3?·H2O, and oxonium nitrate monohydrate, H3O+(H2O)·NO3?. 相似文献
9.
Gabrielle A. Leith Allison M. Rice Brandon J. Yarbrough Anna A. Berseneva Richard T. Ly Charles N. Buck III Dr. Denis Chusov Amy J. Brandt Prof. Dr. Donna A. Chen Benjamin W. Lamm Prof. Dr. Morgan Stefik Kenneth S. Stephenson Dr. Mark D. Smith Prof. Dr. Aaron K. Vannucci Dr. Perry J. Pellechia Prof. Dr. Sophya Garashchuk Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6056-6062
The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two- and three-dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight-fold conductivity enhancement. The first evaluation of redox behavior of buckyball- or tetracyanoquinodimethane-integrated crystalline was conducted. In parallel with tailoring the D-A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli-controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials. 相似文献
10.
Monia Vadrucci Anna Mazzinghi Beatrice Sorrentino Stella Falzone Claudia Gioia Patrizia Gioia Ersilia M. Loreti Massimo Chiari 《X射线光谱测定》2020,49(6):668-678
Scientific investigation is very important in studies addressing issues of archaeological and historical objects. Ion beam analysis (IBA) and macro X-ray fluorescence (MA-XRF) spectroscopy are remarkable tools to obtain information about elemental composition and imaging of historical artefacts with a non-invasive character. These investigation techniques were employed in the framework of a project aimed at supporting the characterization of materials and techniques related with the Roman wall painting. The archaeological excavations at Villa della Piscina in Rome have revealed a luxury building with a large pool (about 50 m long) and thermal baths and numerous fragments of plaster, coming from intentional demolitions referable to two distinct architectural contexts of the Villa during the imperial age, have been found. This work deals with studying the interesting wall pictorial apparatus of great cultural value of the heritage inherited from the Roman age in the area of the ancient city of Rome. The colour palette of the pigments investigated, in particular, by MA-XRF and particle-induced X-ray emission (PIXE) and has revealed Fe, Cu, Pb, Si and Hg as main elements. Traces of other constituents uncover the choice of the different colours chosen by the artists who had embellished the rooms of the Villa. 相似文献