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941.
Michael Böhme Dirk Schuch Axel Buchholz Helmar Görls Winfried Plass 《无机化学与普通化学杂志》2020,646(3):166-174
The trinuclear nickel(II) complex [Ni3(saltagtBu)(bpy)3(H2O)3]Cl (H5saltagtBu = 1,2,3-tris[(5-tert-butylsalicylidene)amino]guanidine) was synthesized and characterized by experimental as well as theoretical methods. The complex salt crystallizes with three molecules of dimethylformamide (dmf) and water as [Ni3(saltagtBu)(bpy)3(H2O)3]Cl · 3dmf · 3H2O ( 1 ) in the trigonal space group P3 , with the complex located on a threefold rotation axis, which is consistent with the molecular C3 symmetry of the complex cation. Magnetic measurements reveal an antiferromagnetic coupling (J = –35.9 cm–1) between the nickel(II) ions leading to a diamagnetic ground state for the trinuclear complex cation. Theoretical investigations based on broken-symmetry DFT confirm the antiferromagnetic exchange within the complex cation of 1 . Additional single-ion CASSCF ab initio studies reveal that magnetic anisotropy is present in the system. The experimental and theoretical results for 1 are compared with those of a structurally similar nickel(II) complex that is based on the bromo-substituted derivative of the triaminoguanidine ligand. The differences in their magnetic properties can be attributed to the stronger elongation of the pseudo-octahedral coordination sphere at the nickel(II) centers in case of 1 . The analysis of the magnetic properties of 1 clearly shows that for such exchange coupled systems reliable parameters for the magnetic anisotropy cannot be extracted from experimental data alone. 相似文献
942.
An Operando FTIR Spectroscopic and Kinetic Study of Carbon Monoxide Pressure Influence on Rhodium‐Catalyzed Olefin Hydroformylation 下载免费PDF全文
Dr. Christoph Kubis Dr. Mathias Sawall Axel Block Prof. Dr. Klaus Neymeyr Prof. Ralf Ludwig Prof. Dr. Armin Börner Dr. Detlef Selent 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11921-11931
The influence of carbon monoxide concentration on the kinetics of the hydroformylation of 3,3‐dimethyl‐1‐butene with a phosphite‐modified rhodium catalyst has been studied for the pressure range p(CO)=0.20–3.83 MPa. Highly resolved time‐dependent concentration profiles of the organometallic intermediates were derived from IR spectroscopic data collected in situ for the entire olefin‐conversion range. The dynamics of the catalyst and organic components are described by enzyme‐type kinetics with competitive and uncompetitive inhibition reactions involving carbon monoxide taken into account. Saturation of the alkyl–rhodium intermediates with carbon monoxide as a cosubstrate occurs between 1.5 and 2 MPa of carbon monoxide pressure, which brings about a convergence of aldehyde regioselectivity. Hydrogenolysis of the acyl intermediate is fast at 30 °C and low pressure of p(CO)=0.2 MPa, but is of minus first order with respect to the solution concentration of carbon monoxide. Resting 18‐electron hydrido and acyl complexes that correspond to early and late rate‐determining states, respectively, coexist as long as the conversion of the substrate is not complete. 相似文献
943.
Alexander Hinz Dr. Rene Kuzora Prof.Dr. Uwe Rosenthal Prof.Dr. Axel Schulz Dr. Alexander Villinger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14659-14673
The reactivity of biradicaloid [P(μ‐NTer)]2 was employed to activate small molecules bearing single, double, and triple bonds. Addition of chalcogens (O2, S8, Sex and Tex) led to the formation of dichalcogen‐bridged P2N2 heterocycles, except from the reaction with molecular oxygen, which gave a P2N2 ring featuring a dicoordinated PIII and a four‐coordinated PV center. In formal [2πe+2πe] addition reactions, small unsaturated compounds such as ethylene, acetylene, acetone, acetonitrile, tolane, diphenylcarbodiimide, and bis(trimethylsilyl)sulfurdiimide are readily added to the P2N2 heterocycle of the biradicaloid [P(μ‐NTer)]2, yielding novel heteroatom cage compounds. The synthesis, reactivity, and bonding of the biradicaloid [P(μ‐NTer)]2 were studied in detail as well as the synthesis, properties, and structural features of all addition products. 相似文献
944.
Axel Mie Kristian Holst Laursen K. Magnus Åberg Jenny Forshed Anna Lindahl Kristian Thorup-Kristensen Marie Olsson Pia Knuthsen Erik Huusfeldt Larsen Søren Husted 《Analytical and bioanalytical chemistry》2014,406(12):2885-2897
The influence of organic and conventional farming practices on the content of single nutrients in plants is disputed in the scientific literature. Here, large-scale untargeted LC-MS-based metabolomics was used to compare the composition of white cabbage from organic and conventional agriculture, measuring 1,600 compounds. Cabbage was sampled in 2 years from one conventional and two organic farming systems in a rigidly controlled long-term field trial in Denmark. Using Orthogonal Projection to Latent Structures–Discriminant Analysis (OPLS-DA), we found that the production system leaves a significant (p?=?0.013) imprint in the white cabbage metabolome that is retained between production years. We externally validated this finding by predicting the production system of samples from one year using a classification model built on samples from the other year, with a correct classification in 83 % of cases. Thus, it was concluded that the investigated conventional and organic management practices have a systematic impact on the metabolome of white cabbage. This emphasizes the potential of untargeted metabolomics for authenticity testing of organic plant products. 相似文献
945.
Hassan A. Azab Axel Duerkop Z.M. Anwar Belal H.M. Hussein Moustafa A. Rizk Tarek Amin 《Analytica chimica acta》2013
Luminescence quenching of a novel long lived Eu(III)–pyridine-2,6-dicarboxylic acid probe of 1:2 stoichiometric ratio has been studied in 0.10 volume fraction ethanol–water mixture at pH 7.5 (HEPES buffer) in the presence of the organophosphorus pesticides chlorfenvinphos (P1), malathion (P2), azinphos (P3), and paraxon ethyl (P4). The luminescence intensity of Eu(III)–(PDCA)2 probe decreases as the concentration of the pesticide increases. It was observed that the quenching due to P3 and P4 proceeds via both diffusional and static quenching processes. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence quenching of Eu(III)–pyridine-2,6-dicarboxylic acid probe in solution. The linear range for determination of the selected pesticides is 1.0–35.0 μM. The detection limits were 0.24–0.55 μM for P3, P4, and P1 and 2.5 μM for P2, respectively. The binding constants (K), and thermodynamic parameters of the OPs with Eu(III)–(PDCA)2 were evaluated. Positive and negative values of entropy (ΔS) and enthalpy (ΔH) changes for Eu(III)–(PDCA)2–P1 ternary complex were calculated. As the waters in this study do not contain the above mentioned OPs over the limit detectable by the method, a recovery study was carried out after the addition of the adequate amounts of the organophosphorus pesticides under investigation. 相似文献
946.
We present multireference calculations for the characterization of ring inversion and double bond shifting in cyclooctatetraene. The results show that it is necessary to treat the dynamical correlation very accurately to obtain correct values for the barrier heights. This can be done, for example, with multireference configuration interaction or with perturbation theory of third order. However, detailed analysis also shows that already a complete active space self‐consistent field treatment describes the processes surprisingly well. Thus, this method could be used as a computationally cheap method, for example, for dynamics simulations. © 2013 Wiley Periodicals, Inc. 相似文献
947.
Felix D. Sokolov Maria G. Babashkina Damir A. Safin Axel Klein 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):1815-1822
The complexation and extraction properties of RC(S)NHP(X)(OiPr)2 [X = S, R = PhNH (HLI); X = O, R = PhNH (HLII), Ph (HLIII)] towards cobalt cations were studied. The nitrocellulose membrane was used as a carrier for HLI?III. The maximal degree of extraction of cobalt cations from an aqueous solution is observed at pH = 7.8–8.4. It was established that complexes formed are kept in a water solution on a surface of the carrier and washed away in 96% aqueous ethanol. The membrane modified by HLI allows extraction and concentration of Co(II) selectively, while the modification by HLIII leads to the selective extraction of Co(III). 相似文献
948.
Damir A. Safin Maria G. Babashkina Michael Bolte Łukasz Szyrwiel Axel Klein Henryk Kozlowski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1739-1745
The reaction of the potassium salt of the N-(thio)phosphorylated thioureas AdNHC(S)NHP(O)(OiPr)2 (HLI , Ad = Adamantyl) and MeNHC(S)NHP(S)(OiPr)2 (HLII ) with Co(II) and Zn(II) in aqueous EtOH leads to [MLI,II 2] chelate complexes. They were investigated by UV-vis, 1H and 31P NMR spectroscopy, and microanalysis. The molecular structures of [MLI 2] were elucidated by single crystal X-ray diffraction analysis. The metal centers in both complexes are found to be in a distorted-tetrahedral O2S2 environment formed by the C=S sulfur atoms and the P=O oxygen atoms of two deprotonated LI ligands. The photoluminescence properties of [ZnLII 2] are also reported. 相似文献
949.
Yannick Linne Axel Schönwald Sebastian Weißbach Prof. Dr. Markus Kalesse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(36):7998-8002
anti-Configured 1,3-dimethyl deoxypropionate motifs are important sub structures in natural products. Herein, we describe a bidirectional approach for the rapid construction of natural products featuring such motifs by using C2-symmetrical 1,3-bis(boronic esters). As for its application in convergent syntheses it was important to establish a selective mono-Zweifel olefination we describe the scope and limitations by using different 1,3-bis(boronic esters) and nucleophiles. This protocol takes advantage of the combination of the Hoppe–Matteson–Zweifel chemistry, which was elegantly put into practice by Aggarwal et al. In order to show its applicability the total syntheses of two natural products, serricornin and (+)-invictolide, were performed. 相似文献
950.
On Silylated Oxonium and Sulfonium Ions and Their Interaction with Weakly Coordinating Borate Anions
Kevin Bläsing Dr. Rene Labbow Dr. Dirk Michalik Dr. Fabian Reiß Prof. Dr. Axel Schulz Dr. Alexander Villinger Svenja Walker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(7):1640-1652
Attempts have been made to prepare salts with the labile tris(trimethylsilyl)chalconium ions, [(Me3Si)3E]+ (E=O, S), by reacting [Me3Si-H-SiMe3][B(C6F5)4] and Me3Si[CB] (CB−=carborate=[CHB11H5Cl6]−, [CHB11Cl11]−) with Me3Si-E-SiMe3. In the reaction of Me3Si-O-SiMe3 with [Me3Si-H-SiMe3][B(C6F5)4], a ligand exchange was observed in the [Me3Si-H-SiMe3]+ cation leading to the surprising formation of the persilylated [(Me3Si)2(Me2(H)Si)O]+ oxonium ion in a formal [Me2(H)Si]+ instead of the desired [Me3Si]+ transfer reaction. In contrast, the expected homoleptic persilylated [(Me3Si)3S]+ ion was formed and isolated as [B(C6F5)4]− and [CB]− salt, when Me3Si-S-SiMe3 was treated with either [Me3Si-H-SiMe3][B(C6F5)4] or Me3Si[CB]. However, the addition of Me3Si[CB] to Me3Si-O-SiMe3 unexpectedly led to the release of Me4Si with simultaneous formation of a cyclic dioxonium dication of the type [Me3Si-μO-SiMe2]2[CB]2 in an anion-mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me3Si)3E]+ and [(Me3Si)2(Me2(H)Si)E]+ ion formation are presented as well as mechanistic investigations on the template-driven transformation of the [(Me3Si)3E]+ ion into a cyclic dichalconium dication [Me3Si-μE-SiMe2]22+. 相似文献