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991.
Engineered L‐Serine Hydroxymethyltransferase from Streptococcus thermophilus for the Synthesis of α,α‐Dialkyl‐α‐Amino Acids 下载免费PDF全文
Karel Hernandez Igor Zelen Giovanna Petrillo Prof. Dr. Isabel Usón Claudia M. Wandtke Dr. Jordi Bujons Dr. Jesús Joglar Dr. Teodor Parella Prof. Dr. Pere Clapés 《Angewandte Chemie (International ed. in English)》2015,54(10):3013-3017
α,α‐Disubstituted α‐amino acids are central to biotechnological and biomedical chemical processes for their own sake and as substructures of biologically active molecules for diverse biomedical applications. Structurally, these compounds contain a quaternary stereocenter, which is particularly challenging for stereoselective synthesis. The pyridoxal‐5′‐phosphate (PLP)‐dependent L ‐serine hydroxymethyltransferase from Streptococcus thermophilus (SHMTSth; EC 2.1.2.1) was engineered to achieve the stereoselective synthesis of a broad structural variety of α,α‐dialkyl‐α‐amino acids. This was accomplished by the formation of quaternary stereocenters through aldol addition of the amino acids D ‐Ala and D ‐Ser to a wide acceptor scope catalyzed by the minimalist SHMTSth Y55T variant overcoming the limitation of the native enzyme for Gly. The SHMTSth Y55T variant tolerates aromatic and aliphatic aldehydes as well as hydroxy‐ and nitrogen‐containing aldehydes as acceptors. 相似文献
992.
Na4IrO4: Square‐Planar Coordination of a Transition Metal in d5 Configuration due to Weak On‐Site Coulomb Interactions 下载免费PDF全文
Dr. Sudipta Kanungo Dr. Binghai Yan Patrick Merz Prof. Dr. Claudia Felser Prof. Dr. Martin Jansen 《Angewandte Chemie (International ed. in English)》2015,54(18):5417-5420
Local environments and valence electron counts primarily determine the electronic states and physical properties of transition‐metal complexes. For example, square‐planar coordination geometries found in transition‐metal oxometalates such as cuprates are usually associated with the d8 or d9 electron configuration. In this work, we address an unusual square‐planar single oxoanionic [IrO4]4? species, as observed in Na4IrO4 in which IrIV has a d5 configuration, and characterize the chemical bonding through experiments and by ab initio calculations. We find that the IrIV center in ground‐state Na4IrO4 has square‐planar coordination geometry because of the weak Coulomb repulsion of the Ir‐5d electrons. In contrast, in its 3d counterpart Na4CoO4, the CoIV center is tetrahedrally coordinated because of strong electron correlation. Na4IrO4 may thus serve as a simple yet important example to study the ramifications of Hubbard‐type Coulomb interactions on local geometries. 相似文献
993.
Spectroscopic and Crystal Field Consequences of Fluoride Binding by [Yb⋅DTMA]3+ in Aqueous Solution 下载免费PDF全文
Dr. Octavia A. Blackburn Dr. Nicholas F. Chilton Katharina Keller Dr. Claudia E. Tait Dr. William K. Myers Prof. Eric J. L. McInnes Dr. Alan M. Kenwright Prof. Paul D. Beer Prof. Christiane R. Timmel Prof. Stephen Faulkner 《Angewandte Chemie (International ed. in English)》2015,54(37):10783-10786
Yb?DTMA forms a ternary complex with fluoride in aqueous solution by displacement of a bound solvent molecule from the lanthanide ion. [Yb?DTMA?F]2+ and [Yb?DTMA?OH2]3+ are in slow exchange on the relevant NMR timescale (<2000 s?1), and profound differences are observed in their respective NMR and EPR spectra of these species. The observed differences can be explained by drastic modification of the ligand field states due to the fluoride binding. This changes the magnetic anisotropy of the YbIII ground state from easy‐axis to easy‐plane type, and this change is easily detected in the observed magnetic anisotropy despite thermal population of more than just the ground state. The spectroscopic consequences of such drastic changes to the ligand field represent important new opportunities in developing fluoride‐responsive complexes and contrast agents. 相似文献
994.
Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid 下载免费PDF全文
Dr. Nathan Hollingsworth Dr. S. F. Rebecca Taylor Miguel T. Galante Dr. Johan Jacquemin Dr. Claudia Longo Dr. Katherine B. Holt Prof. Nora H. de Leeuw Prof. Christopher Hardacre 《Angewandte Chemie (International ed. in English)》2015,54(47):14164-14168
A new low‐energy pathway is reported for the electrochemical reduction of CO2 to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P66614][124Triz] is able to chemisorb CO2 through equimolar binding of CO2 with the 1,2,4‐triazole anion. This chemisorbed CO2 can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO2 within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P66614][NTf2]) undergoes reduction at significantly increased overpotentials, producing only CO as the product. 相似文献
995.
Huayna Terraschke Matthias Franzreb Claudia Wickleder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(30):6833-6838
Afterglow–magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core–shell strategy is presented, uniting co-precipitation with combustion synthesis routes to combine an Fe3O4 magnetic core (≈15 nm) with an afterglow SrAl2O4:Eu2+,Dy3+ outer coat (≈10 nm), and applying a SiO2 protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe3O4@SiO2@SrAl2O4:Eu2+,Dy3+ NPs emit green light attributed to the 4f65d1→4f7(8S7/2) transition of Eu2+ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules. 相似文献
996.
Lisa-Lou Gracia Luisa Luci Cecilia Bruschi Prof. Dr. Letizia Sambri Dr. Patrick Weis Dr. Olaf Fuhr Dr. Claudia Bizzarri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):9929-9937
Earth-abundant metal complexes have been attracting increasing attention in the field of photo(redox)catalysis. In this work, the synthesis and full characterisation of four new heteroleptic CuI complexes are reported, which can work as photosensitizers. The complexes bear a bulky diphosphine (DPEPhos=bis[(2-diphenylphosphino)phenyl] ether) and a diimine chelating ligand based on 1-benzyl-4-(quinol-2′yl)-1,2,3-triazole. Their absorption has a relative maximum in the visible-light region, up to 450 nm. Thus, their use in photocatalytic systems for the reduction of CO2 with blue light in combination with the known catalyst [NiII(cyclam)]Cl2 was tested. This system produced CO as the main product through visible light (λ=420 nm) with a TON up to 8 after 4 hours. This value is in line with other photocatalytic systems using the same catalyst. Nevertheless, this system is entirely noble-metal free. 相似文献
997.
Berencie Yahuaca-Juárez Gerardo González Marco A. Ramírez-Morales Calara Alba-Betancourt Martha A. Deveze-Álvarez Claudia L. Mendoza-Macías 《合成通讯》2020,50(4):539-548
AbstractThe first iodine(III)-based procedure for the benzylic oxidation of different arenes is described by using the (PhIO)n/Al(NO3)3 system under catalytic conditions leading to the formation of the corresponding carbonyl derivatives. The method proceeds under mild, operationally simple, room temperature, short reaction times, and open flask conditions. In light of the organocatalysis relevance and the novelty of our protocol, we wish to communicate our initial results of this novel oxidation. 相似文献
998.
Wonmin Choi Dr. Hao Sun Dr. Claudia Battistella Dr. Or Berger Maria A. Vratsanos Max M. Wang Prof. Dr. Nathan C. Gianneschi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):19930-19940
In this Minireview, we describe synthetic polymers densely functionalized with sequence-defined biomolecular sidechains. We focus on synthetic brush polymers of oligonucleotides, oligosaccharides, and oligopeptides, prepared via graft-through polymerization from biomolecule functionalized monomers. The resulting structures are brush polymers wherein a biomolecular graft is positioned at each monomer backbone unit. We describe key synthetic milestones, identify synthetic opportunities, and highlight recent advances in the field, including biological applications. 相似文献
999.
M.C. Arenas L. Fernando Rodríguez-Núnez Domingo Rangel Omar Martínez-Álvarez Claudia Martínez-Alonso V.M. Castaño 《Ultrasonics sonochemistry》2013,20(2):777-784
In this work, hybrid nanocomposites based on anatase titania:polypyrrole (TiO2:PPy) were directly obtained from a simple, one-step, ultrasonic (UT)-assisted synthesis. The properties of these crystalline nanocomposites were compared with those of others fabricated using cold (Cold)-assisted synthesis without any UT assistance, which required a hydrothermal treatment (HT) to yield crystalline anatase titania in the nanocomposite (TiO2:PPy) at low temperature (130 °C) and in a short time (3 h). The SEM results demonstrated that the UT-assisted synthesis is a feasible method to obtain anatase TiO2:PPy nanocomposites with controlled morphology using low energy. The Fourier transform infrared (FT-IR) bands of the crystalline nanocomposites exhibited a shift with respect to neat components, which was attributed to the strong interaction between the secondary amine groups (N–H) of PPy and the oxygen from TiO2. The acceptable absorption in the visible region (λmax = 670 nm) indicates that these nanocomposites are good candidates for harvesting energy in solar cells. Devices based on these nanocomposites were built to evaluate their electrical properties. An increase in the photocurrent was observed for the devices prepared with the nanocomposites from the UT-assisted synthesis. 相似文献
1000.