全文获取类型
| 收费全文 | 3116篇 |
| 免费 | 47篇 |
| 国内免费 | 9篇 |
专业分类
| 化学 | 1752篇 |
| 晶体学 | 18篇 |
| 力学 | 82篇 |
| 数学 | 453篇 |
| 物理学 | 867篇 |
出版年
| 2022年 | 38篇 |
| 2021年 | 45篇 |
| 2020年 | 48篇 |
| 2019年 | 51篇 |
| 2018年 | 31篇 |
| 2016年 | 53篇 |
| 2015年 | 56篇 |
| 2014年 | 58篇 |
| 2013年 | 128篇 |
| 2012年 | 135篇 |
| 2011年 | 177篇 |
| 2010年 | 104篇 |
| 2009年 | 93篇 |
| 2008年 | 149篇 |
| 2007年 | 168篇 |
| 2006年 | 145篇 |
| 2005年 | 148篇 |
| 2004年 | 120篇 |
| 2003年 | 105篇 |
| 2002年 | 102篇 |
| 2001年 | 50篇 |
| 2000年 | 49篇 |
| 1999年 | 40篇 |
| 1998年 | 28篇 |
| 1997年 | 31篇 |
| 1996年 | 60篇 |
| 1995年 | 47篇 |
| 1994年 | 46篇 |
| 1993年 | 41篇 |
| 1992年 | 41篇 |
| 1991年 | 35篇 |
| 1990年 | 31篇 |
| 1989年 | 31篇 |
| 1988年 | 27篇 |
| 1987年 | 28篇 |
| 1986年 | 39篇 |
| 1985年 | 24篇 |
| 1984年 | 44篇 |
| 1983年 | 28篇 |
| 1982年 | 23篇 |
| 1981年 | 39篇 |
| 1980年 | 30篇 |
| 1979年 | 26篇 |
| 1978年 | 23篇 |
| 1977年 | 38篇 |
| 1976年 | 23篇 |
| 1975年 | 36篇 |
| 1974年 | 36篇 |
| 1973年 | 25篇 |
| 1972年 | 20篇 |
排序方式： 共有3172条查询结果，搜索用时 46 毫秒
991.
Dr. Bruno Mattia Bizzarri Dr. Paola Manini Dr. Valeria Lino Prof. Marco d'Ischia Dr. Michail Kapralov Prof. Eugene Krasavin Klaudia Mráziková Prof. Jiří Šponer Dr. Judit E. Šponer Prof. Ernesto Di Mauro Prof. Raffaele Saladino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14919-14928
Formation and structural modification of oxygenated polycyclic aromatic hydrocarbons (oxyPAHs) by UV irradiation on minerals have recently been proposed as a possible channel of PAH transformation in astrochemical and prebiotic scenarios of possible relevance for the origin of life. Herein, it is demonstrated that high-energy proton-beam irradiation in the presence of various meteorites, including stony iron, achondrite, and chondrite types, promotes the conversion of two representative oxyPAH compounds, 1-naphthol and 1,8-dihydroxynaphthalene, to complex mixtures of oxygenated and oligomeric derivatives. The main identified products include polyhydroxy derivatives, isomeric dimers encompassing benzofuran and benzopyran scaffolds, and, notably, a range of quinones and perylene derivatives. Addition of urea, a prebiotically relevant chemical precursor, expanded the range of identified species to include, among others, quinone diimines. Proton-beam irradiation of oxyPAH modulated by nitrogen-containing compounds such as urea is proposed as a possible contributory mechanism for the formation and processing of insoluble organic matter in meteorites and in prebiotic processes. 相似文献
992.
C. Malherbe I. B. Hutchinson M. McHugh H. Lerman L. V. Harris R. Ingley H.M.G. Edwards J. Parnell G. Eppe 《Journal of Raman spectroscopy : JRS》2020,51(9):1613-1623
Two rovers will be launched in 2020 for robotic exploration missions on Mars: the ESA/Roscosmos ExoMars and the NASA Mars 2020 missions. Both missions will include Raman instruments to characterize the habitable of Mars and to search for molecular evidence of past and present life. In preparation for these missions and to characterize the scientific information that will eventually return from Mars, terrestrial analogue samples of rock formations on Mars are studied in detail. During this study, we compared Raman spectra obtained from different samples of geological matrixes, including specimens of silicate, sulfate, carbonates, and sulfurs, with two Raman instruments. Raman data were obtained in the field with a portable instrument operating with a 785-nm laser. Based on fast data analyses in the field, a selection of samples were collected and were further analyzed using a benchtop confocal instrument operated in the laboratory and with two excitation lasers at 532 and 785 nm. We illustrate the possible interference from sharp fluorescence associated with rare earth element present in trace amount in minerals. In addition, carbonaceous compounds and β-carotene, a highly Raman-active biomarker, were also detected by Raman spectroscopy in association with specific minerals. In the context of planetary exploration, we discuss the capacity for specific mineral matrixes to sustain life under extreme conditions. We also discuss that Raman imaging, although not ready yet for space application with miniaturized spectroscopy, could significantly help in discussing the possible biotic origin of carbonaceous residues, especially by the association of molecular signatures with the localized microstructure. 相似文献
993.
Dr. Koushik Barman Prof. Martin A. Edwards Prof. David P. Hickey Dr. Christopher Sandford Prof. Yinghua Qiu Dr. Rui Gao Prof. Shelley D. Minteer Prof. Henry S. White 《ChemElectroChem》2020,7(6):1473-1479
Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here, the electroreduction of [Ni(Mebpy)3]2+ (Mebpy=4,4′-dimethyl-2,2′-bipyridine) in dimethylformamide is reported, with the aim of determining the redox mechanism and oxidation states of products formed under well-controlled electrochemical conditions. Results from cyclic voltammetry, steady-state voltammetry (SSV) and chronoamperometry demonstrate that [Ni(Mebpy)3]2+ undergoes two sequential 1e reductions at closely separated potentials (E10’=−1.06±0.01 V and E20’=−1.15±0.01 V vs Ag/AgCl (3.4 M KCl)). Homogeneous comproportionation to generate [Ni(Mebpy)3]+ is demonstrated in SSV experiments in low ionic strength solutions. The comproportionation rate constant is determined to be >106 M−1 s−1, consistent with rapid outer-sphere electron transfer. Consequentially, on voltammetric time scales, the 2e reduction of [Ni(Mebpy)3]2+ results in formation of [Ni(Mebpy)3]+ as the predominant species released into bulk solution. We also demonstrate that [Ni(Mebpy)3]0 slowly loses a Mebpy ligand (∼10 s−1). 相似文献
994.
995.
Dr. Ramadoss Govindarajan Shubham Deolka Dr. Eugene Khaskin Dr. Robert R. Fayzullin Dr. Shrinwantu Pal Dr. Serhii Vasylevskyi Prof. Julia R. Khusnutdinova 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(44):e202201639
We report a series of heterobimetallic Pt/Zn and Pt/Ca complexes to study the effect of proximity of a dicationic base metal on the organometallic Pt species. Varying degrees of Pt⋅⋅⋅Zn and Zn interaction with the bridging Me group are achieved, showcasing snapshots of a hypothetical process of retrotransmetalation from Pt to Zn. In contrast, only weak interactions were observed for Ca with a Pt-bound Me group. Activation of H2, B−H and Si−H bonds leads to the formation of hydride-bridged Pt−H−Zn complexes, which is not observed in the absence of Zn, pointing out the importance of metal-metal cooperation. Reactivity of PtMe2/M2+ with terminal acetylene, water and methanol is also studied, leading to facile protonation of one of the Me groups at the Pt center only when Zn is present. This study sheds light on various ways in which the presence of a 2+ metal cation significantly affects the reactivity of a common organoplatinum complex. 相似文献
996.
Mariya A. Shamraeva Denis S. Bormotov Ekaterina V. Shamarina Konstantin V. Bocharov Olga V. Peregudova Stanislav I. Pekov Eugene N. Nikolaev Igor A. Popov 《Molecules (Basel, Switzerland)》2022,27(3)
Ambient ionization mass spectrometry has become one of the most promising approaches for rapid and high-throughput screening of small molecules in complex biological matrices for emergency medicine, forensics, and food and agriculture applications. The simple procedures for sample collection and ionization without additional pretreatment are vital in these fields. Many efforts have been devoted to modifying various ambient ionization techniques to simplify the procedures and improve the robustness and sensitivity of the methods. Here, we demonstrate the implementation of rigid spherical sampler probes to improve the robustness of touch spray ionization mass spectrometry. The sphericity of the probes increases the stability of the cone-jet mode of electrospray, reduces the requirements for fine positioning of a sampler in the ion source, and decreases the possibility of corona discharge occurrence. The utilization of spherical sampler probes allows fast, non-invasive sampling, followed by rapid analysis for various drugs of different chemical classes in complex biological matrices, such as the whole blood or sebum collected from the skin surface. The linearity of the analytical signal response from drug concentration confirms the possibility of creating a simple semiquantitative method for small molecules monitoring using spherical sampler probes. 相似文献
997.
Iakov S. Fomenko Medhanie Afewerki Marko I. Gongola Eugene S. Vasilyev Lidia S. Shul&#x;pina Nikolay S. Ikonnikov Georgiy B. Shul&#x;pin Denis G. Samsonenko Vadim V. Yanshole Vladimir A. Nadolinny Alexander N. Lavrov Alexey V. Tkachev Artem L. Gushchin 《Molecules (Basel, Switzerland)》2022,27(13)
The reactions of CuX2 (X = Cl, Br) with dipinodiazafluorenes yielded four new complexes [CuX2L1]2 (X = Cl (1), Br (2), L1 = (1R,3R,8R,10R)-2,2,9,9-Tetramethyl-3,4,7,8,9,10-hexahydro-1H-1,3:8,10-dimethanocyclopenta [1,2-b:5,4-b’]diquinolin-12(2H)-one) and [(CuX2)2L2]n (X = Cl (3), Br (4), L2 = (1R,3R,8R,10R,1’R,3’R,8’R,10’R)-2,2,2’,2’,9,9,9’,9’-Octamethyl-1,1’,2,2’,3,3’,4,4’,7,7’,8,8’,9,9’,10,10’-hexadecahydro-1,3:1’,3’:8,10:8’,10’-tetramethano-12,12’-bi(cyclopenta [1,2-b:5,4-b’]diquinolinylidene). The complexes were characterized by IR and EPR spectroscopy, HR-ESI-MS and elemental analysis. The crystal structures of compounds 1, 2 and 4 were determined by X-ray diffraction (XRD) analysis. Complexes 1–2 have a monomeric structure, while complex 4 has a polymeric structure due to additional coordinating N,N sites in L2. All complexes contain a binuclear fragment {Cu2(μ-X)2×2} (X = Cl, Br) in their structures. Each copper atom has a distorted square-pyramidal coordination environment formed by two nitrogen atoms and three halogen atoms. The Cu-Nax distance is elongated compared to Cu-Neq. The EPR spectra of compounds 1–4 in CH3CN confirm their paramagnetic nature due to the d9 electronic configuration of the copper(II) ion. The magnetic properties of all compounds were studied by the method of static magnetic susceptibility. For complexes 1 and 2, the effective magnetic moments are µeff ≈ 1.87 and 1.83 µB (per each Cu2+ ion), respectively, in the temperature range 50–300 K, which are close to the theoretical spin value (1.73 µB). Ferromagnetic exchange interactions between Cu(II) ions inside {Cu2(μ-X)2X2} (X = Cl, Br) dimers (J/kB ≈ 25 and 31 K for 1 and 2, respectively) or between dimers (θ′ ≈ 0.30 and 0.47 K for 1 and 2, respectively) were found at low temperatures. For compounds 3 and 4, the magnetic susceptibility is well described by the Curie–Weiss law in the temperature range 1.77–300 K with µeff ≈ 1.72 and 1.70 µB for 3 and 4, respectively, and weak antiferromagnetic interactions (θ ≈ −0.4 K for 3 and −0.65 K for 4). Complexes 1–4 exhibit high catalytic activity in the oxidation of alkanes and alcohols with peroxides. The maximum yield of cyclohexane oxidation products reached 50% (complex 3). Based on the data on the study of regio- and bond-selectivity, it was concluded that hydroxyl radicals play a decisive role in the oxidation reaction. The initial products in reactions with alkanes are alkyl hydroperoxides. 相似文献
998.
Prasanna A. Yakkala Samir R. Panda Syed Shafi V. G. M. Naidu M. Shahar Yar Philemon N. Ubanako Samson A. Adeyemi Pradeep Kumar Yahya E. Choonara Eugene V. Radchenko Vladimir A. Palyulin Ahmed Kamal 《Molecules (Basel, Switzerland)》2022,27(21)
A series of new 1,2,4-triazolo-linked bis-indolyl conjugates (15a–r) were prepared by multistep synthesis and evaluated for their cytotoxic activity against various human cancer cell lines. It was observed that they were more susceptible to colon and breast cancer cells. Conjugates 15o (IC50 = 2.04 μM) and 15r (IC50 = 0.85 μM) illustrated promising cytotoxicity compared to 5-fluorouracil (5-FU, IC50 = 5.31 μM) against the HT-29 cell line. Interestingly, 15o and 15r induced cell cycle arrest at the G0/G1 phase and disrupted the mitochondrial membrane potential. Moreover, these conjugates led to apoptosis in HT-29 at 2 μM and 1 μM, respectively, and also enhanced the total ROS production as well as the mitochondrial-generated ROS. Immunofluorescence and Western blot assays revealed that these conjugates reduced the expression levels of the PI3K-P85, β-catenin, TAB-182, β-actin, AXIN-2, and NF-κB markers that are involved in the β-catenin pathway of colorectal cancer. The results of the in silico docking studies of 15r and 15o further support their dual inhibitory behaviour against PI3K and tankyrase. Interestingly, the conjugates have adequate ADME-toxicity parameters based on the calculated results of the molecular dynamic simulations, as we found that these inhibitors (15r) influenced the conformational flexibility of the 4OA7 and 3L54 proteins. 相似文献
999.
Dr. João Ameixa Dr. Eugene Arthur-Baidoo João Pereira-da-Silva Júlio C. Ruivo Prof. Dr. Márcio T. do N. Varella Prof. Dr. Martin K. Beyer Dr. Milan Ončák Prof. Dr. Filipe Ferreira da Silva Prof. Dr. Stephan Denifl 《Chemphyschem》2022,23(5):e202100834
Ubiquinone molecules have a high biological relevance due to their action as electron carriers in the mitochondrial electron transport chain. Here, we studied the dissociative interaction of free electrons with CoQ0, the smallest ubiquinone derivative with no isoprenyl units, and its fully reduced form, 2,3-dimethoxy-5-methylhydroquinone (CoQ0H2), an ubiquinol derivative. The anionic products produced upon dissociative electron attachment (DEA) were detected by quadrupole mass spectrometry and studied theoretically through quantum chemical and electron scattering calculations. Despite the structural similarity of the two studied molecules, remarkably only a few DEA reactions are present for both compounds, such as abstraction of a neutral hydrogen atom or the release of a negatively charged methyl group. While the loss of a neutral methyl group represents the most abundant reaction observed in DEA to CoQ0, this pathway is not observed for CoQ0H2. Instead, the loss of a neutral OH radical from the CoQ0H2 temporary negative ion is observed as the most abundant reaction channel. Overall, this study gives insights into electron attachment properties of simple derivatives of more complex molecules found in biochemical pathways. 相似文献
1000.