全文获取类型
| 收费全文 | 8811篇 |
| 免费 | 697篇 |
| 国内免费 | 1814篇 |
专业分类
| 化学 | 10222篇 |
| 晶体学 | 46篇 |
| 力学 | 57篇 |
| 综合类 | 59篇 |
| 数学 | 7篇 |
| 物理学 | 931篇 |
出版年
| 2025年 | 8篇 |
| 2024年 | 73篇 |
| 2023年 | 147篇 |
| 2022年 | 357篇 |
| 2021年 | 468篇 |
| 2020年 | 555篇 |
| 2019年 | 476篇 |
| 2018年 | 317篇 |
| 2017年 | 291篇 |
| 2016年 | 387篇 |
| 2015年 | 388篇 |
| 2014年 | 495篇 |
| 2013年 | 815篇 |
| 2012年 | 545篇 |
| 2011年 | 492篇 |
| 2010年 | 441篇 |
| 2009年 | 427篇 |
| 2008年 | 510篇 |
| 2007年 | 526篇 |
| 2006年 | 451篇 |
| 2005年 | 397篇 |
| 2004年 | 395篇 |
| 2003年 | 431篇 |
| 2002年 | 359篇 |
| 2001年 | 233篇 |
| 2000年 | 219篇 |
| 1999年 | 183篇 |
| 1998年 | 144篇 |
| 1997年 | 149篇 |
| 1996年 | 136篇 |
| 1995年 | 116篇 |
| 1994年 | 88篇 |
| 1993年 | 68篇 |
| 1992年 | 69篇 |
| 1991年 | 40篇 |
| 1990年 | 39篇 |
| 1989年 | 24篇 |
| 1988年 | 19篇 |
| 1987年 | 9篇 |
| 1986年 | 7篇 |
| 1985年 | 10篇 |
| 1984年 | 5篇 |
| 1983年 | 3篇 |
| 1982年 | 1篇 |
| 1981年 | 3篇 |
| 1980年 | 2篇 |
| 1977年 | 1篇 |
| 1973年 | 1篇 |
| 1969年 | 1篇 |
| 1959年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 0 毫秒
101.
Mechanism of the gas-phase oxidation of carbon disulfide at elevated temperatures (the C-S-O system)
A. V. Chernysheva V. Ya. Basevich V. I. Vedeneev V. S. Arutyunov 《Russian Chemical Bulletin》1992,41(4):629-637
Machine modeling was used to investigate the kinetic mechanism of the gas-phase oxidation of carbon disulfide at elevated temperatures. The scheme of the process examined includes 70 elementary reactions. On the basis of the kinetic data on these reactions available in the literature the rates of the oxidation process, the concentrations of end products and intermediate particles were calculated as a function of the time under various conditions (composition, pressure, temperature). Comparison of the results obtained with the experimental data showed satisfactory agreement and also revealed some important elementary reactions.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow 117977. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 812–822, April, 1992. 相似文献
102.
Lulu Wang Jinmiao Wang Chuanbin Fan Caifeng Bi Xia Zhang Dongmei Zhang Mei Wang Yuhua Fan 《应用有机金属化学》2020,34(9):e5767
Two novel Co (II)- coordination polymers (CPs) based on 2,5-bis(4-carboxylpheny)-1,3,4-oxadiazole (bcpo), namely [Co/(bcpo)0.5(tib)(H2O)2]n (1) and [Co (bcpo)0.5(bidpe)(H2O)2]n (2) (tib = 1,3,5-tirs(1-imidazolyl)benzene, bidpe = 4,4′-bis (imidazolyl)diphenyl ether) have been synthesized under solvothermal conditions and characterized by powder X-ray diffraction (PXRD), single crystal X-ray diffraction, photochemistry as well as electrochemistry. The investigation of the photo-degradation methyl blue and methyl violet (MB, MV) properties of CPs 1–2 demonstrates that CP 1 shows great performance for the degradation of MB, and CP 2 could efficiently degrade MB/MV. Meanwhile, the possible photo-degradation mechanism has been proposed and explored. Simultaneously, electrochemistry studies show that both CPs 1 and 2 can catalyze water oxidation under an alkaline condition at the potential around 1.20 V vs. NHE with relatively low overpotential of 330–510 mV vs. NHE. 相似文献
103.
Qi-Jun Li Ya-Jie Ren Qin Xie Min Wu Hua-Xing Feng Li-Mei Zheng Hua-Xin Zhang Jin-Qiao Long Tian-Shun Wang 《应用有机金属化学》2020,34(10):e5813
Two nickel complexes, [Ni(tpen)](ClO4)2.0.5CH3COCH3 ( 1 ) and [Ni(tpbn)](ClO4)2 ( 2 ), of tetrapyridyl ligands N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,2-ethanediamine (tpen) and N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiOx composite (nickel oxide with general formula NixOyHz) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiOx composite active for WOR. The NiOx composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2 . This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center. 相似文献
104.
Shuping Zhang Dr. Hongpan Rong Tianyi Yang Bing Bai Prof. Jiatao Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(18):4025-4031
Dilute alloy nanostructures have been demonstrated to possess distinct catalytic properties. Noble-metal-induced reduction is one effective synthesis strategy to construct dilute alloys and modify the catalytic performance of the host metal. Herein, we report the synthesis of ultrafine PtRu dilute alloy nanodendrites (PtRu NDs, molar ratio Ru/Pt is 1:199) by the reduction of RuIII ions induced by Pt metal. For the methanol oxidation reaction, PtRu NDs showed the highest forward peak current density (2.66 mA cm−2, 1.14 A/mgPt) and the best stability compared to those of pure-Pt nanodendrites (pure-Pt NDs), commercial PtRu/C and commercial Pt/C catalysts. 相似文献
105.
Prof. Dr. Jevgenij A. Raskatov Dr. Scott Virgil Dr. Hsiau-Wei Lee Dr. Lawrence M. Henling Ka Chan Ariel J. Kuhn Alejandro R. Foley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4467-4470
Methionine (Met) oxidation is an important biological redox node, with hundreds if not thousands of protein targets. The process yields methionine oxide (MetO). It renders the sulfur chiral, producing two distinct, diastereomerically related products. Despite the biological significance of Met oxidation, a reliable protocol to separate the resultant MetO diastereomers is currently lacking. This hampers our ability to make peptides and proteins that contain stereochemically defined MetO to then study their structural and functional properties. We have developed a facile method that uses supercritical CO2 chromatography and allows obtaining both diastereomers in purities exceeding 99 %. 1H NMR spectra were correlated with X-ray structural information. The stereochemical interconversion barrier at sulfur was calculated as 45.2 kcal mol−1, highlighting the remarkable stereochemical stability of MetO sulfur chirality. Our protocol should open the road to synthesis and study of a wide variety of stereochemically defined MetO-containing proteins and peptides. 相似文献
106.
Delfino Chamorro-Arenas Alejandro A. Nolasco-Hernández Dr. Lilia Fuentes Dr. Leticia Quintero Prof. Dr. Fernando Sartillo-Piscil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(21):4671-4676
Remote and multiple functionalization of piperidines without the use of transition-metal catalysts and elaborate directing groups is one of the major challenges in organic synthesis. Herein is reported an unprecedented two-step protocol that enables the multiple functionalization of piperidines to either 4-substituted or trans-3,4-disubstituted 2-piperidones. First, by exploiting the duality of TEMPO reactivity, which under oxidative and thermal conditions fluctuates between cationic and persistent-radical form, a novel multiple C(sp3)-H oxidation of piperidines to α,β-unsaturated 2-piperidones was developed. Second, the intrinsic low reactivity of the unsaturated piperidones toward conjugated Grignard additions was overcome by using trimethylsilyl chloride (TMSCl) as Lewis acid. Subsequently, conjugated Grignard addition/electrophilic trapping protocol provided substituted 2-piperidone intermediates, some of which were then transformed into pharmaceutical alkaloids. 相似文献
107.
Isabel Guerrero Dr. Zsolt Kelemen Prof. Dr. Clara Viñas Dr. Isabel Romero Prof. Dr. Francesc Teixidor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):5027-5036
Metallacarboranes with the shape of the Greek letter θ, such as [Co(C2B9H11)2]−, were tested, for the first time, as efficient photoredox catalysts in the oxidation of aromatic and aliphatic alcohols in water. Their efficiency is linked to their high solubility in water, their high oxidizing power (Co4+/3+), and their absence of fluorescence on excitation, among others. In most of the studied examples, using a catalyst load of 0.4 mol % gave high yields of 90–95 % with selectivity greater than 99 %. By reducing the catalyst load to 0.01 mol %, quantitative conversion of reactants to products was achieved, in some cases with greater than 99 % yield, high catalyst efficiency reaching a turnover number of 10 000, and a higher yield with a 45 times lower concentration of catalyst. The metallacarboranes can be recovered easily by precipitation on addition of [NMe4]Cl. A pathway for the photoredox-catalyzed oxidation of alcohols is proposed. 相似文献
108.
Lukas Lohmeyer Dr. Elisabeth Kaifer Prof. Hubert Wadepohl Prof. Hans-Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(26):5834-5845
New redox-active 1,2,5,6-tetrakis(guanidino)-naphthalene compounds, isolable and storable in the neutral and deep-green dicationic redox states and oxidisable further in two one-electron steps to the tetracations, are reported. Protonation switches on blue fluorescence, with the fluorescence intensity (quantum yield) increasing with the degree of protonation. Reactions with N-halogenosuccinimides or N-halogenophthalimides led to a series of new redox-active halogeno- and succinimido-/phthalimido-substituted derivatives. These highly selective reactions are proposed to proceed via the tri- or tetracationic state as the intermediate. The derivatives are oxidised reversibly at slightly higher potentials than that of the unsubstituted compounds to dications and further to tri- and tetracations. The integration of redox-active ligands in the transition-metal complexes shifts the redox potentials to higher values and also allows reversible oxidation in two potentially separated one-electron steps. 相似文献
109.
Ganyuan Xiao Dr. James R. D. Montgomery Dr. Christopher S. Lancefield Dr. Isabella Panovic Prof. Dr. Nicholas J. Westwood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(54):12397-12402
Selective processing of the β-O-4 unit in lignin is essential for the efficient depolymerisation of this biopolymer and therefore its successful integration into a biorefinery set-up. An approach is described in which this unit is modified to incorporate a carboxylic ester with the goal of enabling the use of mild depolymerisation conditions. Inspired by preliminary results using a Cu/TEMPO/O2 system, a protocol was developed that gave the desired β-O-4-containing ester in high yield using certain dimeric model compounds. The optimised reaction conditions were then applied to an oligomeric lignin model system. Extensive 2D NMR analysis demonstrated that analogous chemistry could be achieved with the oligomeric substrate. Mild depolymerisation of the ester-containing oligomer delivered the expected aryl acid monomer. 相似文献
110.
Ömer Taspinar Tobias Wilczek Julian Erver Dr. Martin Breugst Dr. Jörg-Martin Neudörfl Prof. Dr. Hans-Günther Schmalz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(19):4256-4260
We report the first chemical synthesis of eurysterol A, a cytotoxic and antifungal marine steroidal sulfate with a unique C8−C19 oxy-bridged cholestane skeleton. After C19 hydroxylation of cholesteryl acetate, used as an inexpensive commercial starting material, the challenging oxidative functionalization of ring B was achieved by two different routes to set up a 5α-hydroxy-7-en-6-one moiety. As a key step, an intramolecular oxa-Michael addition was exploited to close the oxy-bridge (8β,19-epoxy unit). DFT calculations show this reversible transformation being exergonic by about −30 kJ mol−1. Along the optimized (scalable) synthetic sequence, the target natural product was obtained in only 11 steps in 5 % overall yield. In addition, an access to (isomeric) 7β,19-epoxy steroids with a previously unknown pentacyclic ring system was discovered. 相似文献