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681.
Alvaro S. de Sousa Zanele Hlam Manuel A. Fernandes Helder M. Marques 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(11):o553-o556
The achiral meso form of the title compound, C18H38N2O42+·2Cl−, crystallizes to form undulating layers consisting of chains linked via weak hydroxyalkyl C—H...Cl contacts. The chains are characterized by centrosymmetric hydrogen‐bonded dimers generated via N—H...Cl and hydroxycycloalkyl O—H...Cl interactions. trans‐N‐Alkyl bridges subdivide the chains into hydrophilic segments flanked by hydrophobic cycloalkyl stacks along [001]. 相似文献
682.
Alvaro Tejado Wei Chung Chen Md Nur Alam Theo G. M. van de Ven 《Cellulose (London, England)》2014,21(3):1735-1743
Wood (kraft) pulp was first dried into a low-density foam-like material by solvent-exchange with anhydrous ethanol. X-Ray tomography showed that, while pulp fibres are flat and resemble ribbons when dried from water, those dried from ethanol are quasi-tubular, inferring that capillary forces derived from a low surface tension solvent are not strong enough to promote fibre lumen collapse, contrary to what happens in water. When the resulting foam-like pulp was then subjected to a vapour phase reaction with trichloromethylsilane (TCMS) a silicon based polymeric coating was created on the surface of the fibres, and the totality of the hydroxyl groups (–OH) on the external surface of cellulose fibres and the internal surface of micropores in the fibre wall became silylated, whereas the surface of the nanopores was inaccessible to TCMS. The novelty lies in the ability to modify both the external surface and the internal micropore structure of cellulose fibres from 50 to 100 % silane coverage, which results in a novel superhydrophobic material, with a contact angle of approximately 150°. This is the first time cellulose is hydrophobized both internally and externally. We refer to the resulting foam as Cellufoam. 相似文献
683.
Dr. M. Carmen Ortega-Liebana Dr. M. Mar Encabo-Berzosa Dr. Alvaro Casanova Dr. M. Desiree Pereboom Prof. J. Octavio Alda Dr. Jose L. Hueso Prof. Jesus Santamaria 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(21):5539-5546
This work describes the synthesis of nitrogen-doped carbon nanodots (CNDs) synthesized from ethylenediaminetetraacetic acid (EDTA) as a precursor and their application as luminescent agents with a dual-mode theranostic role as near-infrared (NIR) triggered imaging and photodynamic therapy agents. Interestingly, these fluorescent CNDs are more rapidly and selectively internalized by tumor cells and exhibit very limited cytotoxicity until remotely activated with a NIR illumination source. These CNDs are excellent candidates for phototheranostic purposes, for example, simultaneous imaging and therapy can be carried out on cancer cells by using their luminescent properties and the in situ generation of reactive oxidative species (ROS) upon excitation in the NIR range. In the presence of CNDs, NIR remote activation induces the in vitro killing of U251MG cells. Through the use of flow imaging cytometry, we have been able to successfully map and quantify the different types of cell deaths induced by the presence of intracellular superoxide anions ( . O2−) and hydrogen peroxide (H2O2) ROS generated in situ upon NIR irradiation. 相似文献
684.
Ana Gimeno Sandra Delgado Pablo Valverde Sara Bertuzzi Manuel Alvaro Berbís Javier Echavarren Alessandra Lacetera Sonsoles Martín‐Santamaría Avadhesha Surolia Francisco Javier Caada Jesus Jimnez‐Barbero Ana Ard 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7346-7350
Ligand conformational entropy plays an important role in carbohydrate recognition events. Glycans are characterized by intrinsic flexibility around the glycosidic linkages, thus in most cases, loss of conformational entropy of the sugar upon complex formation strongly affects the entropy of the binding process. By employing a multidisciplinary approach combining structural, conformational, binding energy, and kinetic information, we investigated the role of conformational entropy in the recognition of the histo blood‐group antigens A and B by human galectin‐3, a lectin of biomedical interest. We show that these rigid natural antigens are pre‐organized ligands for hGal‐3, and that restriction of the conformational flexibility by the branched fucose (Fuc) residue modulates the thermodynamics and kinetics of the binding process. These results highlight the importance of glycan flexibility and provide inspiration for the design of high‐affinity ligands as antagonists for lectins. 相似文献
685.
Peroxygenase‐Catalyzed Oxyfunctionalization Reactions Promoted by the Complete Oxidation of Methanol 下载免费PDF全文
Dr. Yan Ni Dr. Elena Fernández‐Fueyo Dr. Alvaro Gomez Baraibar Dr. René Ullrich Prof. Dr. Martin Hofrichter Prof. Dr. Hideshi Yanase Prof. Dr. Miguel Alcalde Prof. Dr. Willem J. H. van Berkel Dr. Frank Hollmann 《Angewandte Chemie (International ed. in English)》2016,55(2):798-801
Peroxygenases catalyze a broad range of (stereo)selective oxyfunctionalization reactions. However, to access their full catalytic potential, peroxygenases need a balanced provision of hydrogen peroxide to achieve high catalytic activity while minimizing oxidative inactivation. Herein, we report an enzymatic cascade process that employs methanol as a sacrificial electron donor for the reductive activation of molecular oxygen. Full oxidation of methanol is achieved, generating three equivalents of hydrogen peroxide that can be used completely for the stereoselective hydroxylation of ethylbenzene as a model reaction. Overall we propose and demonstrate an atom‐efficient and easily applicable alternative to established hydrogen peroxide generation methods, which enables the efficient use of peroxygenases for oxyfunctionalization reactions. 相似文献
686.
An asymmetrically substituted viologen (V) has been covalently anchored to single wall carbon nanotube (SWNT) through an ester linkage by reacting chlorinated purified SWNT with N-methyl-N'-(6-hydroxyhexyl)-4,4'-bipyridine. Spectroscopic evidence for the covalent bond of viologen in V-SWNT comes from the chemical shift of the -CH2-O-CO- methylene group in 1H NMR and from the variations of the 1590 and 1380 cm(-1) bands in the Raman spectrum of the V-SWNT with respect to SWNT. The fact that the estimated quenching constant of the SWNT emission by viologen is about 2 orders of magnitude higher than the diffusion coefficient indicates the occurrence of a static quenching arising from the formation of a nonemissive viologen-SWNT complex. Laser flash photolysis shows the formation of viologen radical cation upon direct excitation of V-SWNT. The viologen moiety of V-SWNT is able to form a charge-transfer complex with 2,6-dimethoxynaphthalene (DMN) as evidenced by optical spectroscopy and, upon selective photoexcitation in the charge-transfer band, this V-DMN complex anchored to SWNT gives rise to the corresponding charge separated state decaying in the submillisecond time scales. 相似文献
687.
Gomes Constantino M da Silva Filho LC Neto AC Gomes Heleno VC da Silva GV Callegari Lopes JL 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(1-2):171-176
A detailed NMR analysis with total assignment of (1)H and (13)C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by (1)H and (13)C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311 + g(2d, p) from optimized structures at the B3LYP/6-31g(d) level. 相似文献
688.
Lucía Otero Julio Benítez Dinorah Gambino Eduardo Kremer Enrique
J. Baran Alvaro Mombrú Leopoldo Suescun Raúl Mariezcurrena 《无机化学与普通化学杂志》1999,625(11):1866-1872
Capability of [ReIII(tu-S)6]Cl3, where tu = thiourea, as a precursor to other ReIII complexes by ligand substitution in aqueous medium is studied. For the decomposition of [Re(tu-S)6]Cl3, experiments suggest pseudo first order kinetics and observed rate constants vary from 1.3 × 10–2 to 9.6 × 10–2 min–1 in the pH range 2.80–5.04. Experiments in presence of incoming ligand (ethylendiaminetetraacetic acid or diethylentriaminepentaacetic acid) show that ligand substitution is significantly slower than decomposition of the precursor, even when pH and temperature are modified. Similar results were obtained working with [ReIII(Metu-S)6]Cl3, where Metu = N-methylthiourea. Molecular structure of [ReIII(Metu-S)6](PF6)3 · H2O was determined by single crystal X-ray diffractometry. The coordination polyhedron around the Re ion is a distorted octahedron. The six methylthiourea ligands are bonded to the metal through the sulfur atoms [bond lengths range from 2.409(2) to 2.451(2) Å]. 相似文献
689.
Dinorah Gambino Eduardo Kremer Enrique J.
Baran Alvaro Mombrú Leopoldo Suescun Raúl Mariezcurrena Martina Kieninger Oscar N.
Ventura 《无机化学与普通化学杂志》1999,625(5):813-819
A new ReV oxo complex with tetramethylthiourea, [ReO(Me4tu)4](PF6)3, has been synthesized by reduction of perrhenate with tin(II) chloride in strongly acidic solution in the presence of excess tetramethylthiourea. The complex has been characterized by elemental analysis and electronic and FTIR spectroscopy. The molecular structure of the compound was determined by X‐ray diffraction methods. The coordination polyhedron is a regular square pyramid with the substituted thiourea sulfur atoms in the equatorial positions [d(Re–S) = 2.339(3) Å] and the oxo ligand located in the summit [d(Re–O) = 1.63(2) Å]. Computational methods were employed to analyze the geometric and electronic structures of tetramethylthiourea and thiourea. Quantum mechanical studies suggest steric hindrance as the reason for the stabilization of the ReO3+ center instead of the ReIII one. 相似文献
690.
L. B. L. S. Lara E. A. N. Fernandes H. Oliveira M. A. Bacchi E. S. B. Ferraz 《Journal of Radioanalytical and Nuclear Chemistry》1997,216(2):279-284
The interactive processes operating on the continental shelf adjacent to the river mouth control the amount and the characteristics of the Amazon discharge reaching the Atlantic Ocean. In this study, the distribution of trace elemental concentrations, with emphasis to the rare-earth elements, in sediment cores collected at several stations from the Amazon continental shelf during the falling water period was investigated by instrumental neutron activation analysis. Cores from the terrigenous and blue water zones have relatively uniform REE concentrations throughout the profile. Cerium anomalies for samples of the upper section of the eight stations are consistently positive and of high values (normally >2). Similar variation in the elemental concentration ratios between the seabed sediments and Amazon River suspended sediments was seen for stations located in the biogenic and blue water zones, with an enrichment for Ce, Sm, Fe, Th, and Sc and a depletion for the La, Eu, Tb, Yb, Co, Cr, Cs, Hf, Ta, and Zn. The shale-normalized REE patterns from shelf sediments are enriched in LREE relative to HREE, with enrichment factors varying from 1.5 for stations near the river mouth (terrigenous zone) to 1.9 for stations located far in the blue water zone. Published data for the Amazon River suspended sediment agree remarkably well with this observation of LREE-enrichment. 相似文献