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991.
A gas chromatography-tandem mass spectrometry method for detection of diazepam, nordazepam and oxazepam is presented. The method associates electron capture ionization and multiple reaction monitoring (MRM). No derivatization is performed; oxazepam undergoes thermal degradation during chromatographic injection and is thus quantified via its decomposition product. The negative molecular ions are so stable that they do not dissociate when collision is performed under "classical" conditions (i.e. with argon as collision gas). With xenon as collision gas, the energy transfer is sufficient to provide two product ions for diazepam and nordazepam and one product ion for the decomposition product of oxazepam. The sample preparation part involves liquid/liquid extraction with TOXI-TUBES A extraction tubes; it provides recovery yields between 68 and 95%, depending of the benzodiazepine considered, with coefficients of variation below 6% for 10 samples. The applicability of the method was demonstrated on urine extracts. From 1 mL of urine, the method provides quantitation limits of 0.15 ng/mL for diazepam, 1.0 ng/mL for nordazepam and 1.5 ng/mL for oxazepam. Mechanisms of dissociation of M*(-) ions of benzodiazepines are suggested. 相似文献
992.
Ivan Zemskov Heike M. Kropp Prof. Dr. Valentin Wittmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10990-10997
Microcystins are cyanobacterial toxins that can be found in fresh and coastal waters during algal blooms. Microcystin contamination of water can cause severe poisoning of animals and humans. Quantification of these toxins in biological samples is complicated because a major proportion of microcystins is covalently linked to proteins through thioether bonds formed through a Michael‐type addition of cysteine residues of proteins to an N‐methyldehydroalanine residue in the microcystins. We investigated chemical methods that can be used to cleave such thioether bonds by means of an elimination reaction that leaves the microcystin backbone intact for subsequent analysis. The known reagent O‐mesitylenesulfonylhydroxylamine (MSH) led to regioselective thioether cleavage, but a large excess of reagent was needed, thus making purification challenging. An unexpected side reaction observed during the investigation of the base‐induced elimination inspired us to develop a new thioether‐cleavage methodology based on the addition of propargylamine as a nucleophile that can trap the elimination product. This methodology could be successfully applied to the quantitative cleavage of a microcystin‐LF–glutathione conjugate. The alkyne moiety introduced by this procedure offers the possibility for further reactions with azides by using click chemistry, which might be useful for the derivatization or isolation of microcystins. 相似文献
993.
Dr. Biancamaria Farina Dr. Ivan de Paola Dr. Luigi Russo Dr. Domenica Capasso Dr. Annamaria Liguoro Dr. Annarita Del Gatto Dr. Michele Saviano Prof. Paolo V. Pedone Dr. Sonia Di Gaetano Dr. Gaetano Malgieri Dr. Laura Zaccaro Prof. Roberto Fattorusso 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):681-693
The critical role of integrins in tumor progression and metastasis has stimulated intense efforts to identify pharmacological agents that can modulate integrin function. In recent years, αvβ3 and αvβ5 integrin antagonists were demonstrated to be effective in blocking tumor progression. RGDechi‐hCit, a chimeric peptide containing a cyclic RGD motif linked to an echistatin C‐terminal fragment, is able to recognize selectively αvβ3 integrin both in vitro and in vivo. High‐resolution molecular details of the selective αvβ3 recognition of the peptide are certainly required, nonetheless RGDechi‐hCit internalization limited the use of classical in cell NMR experiments. To overcome such limitations, we used WM266 isolated cellular membranes to accomplish a detailed NMR interaction study that, combined with a computational analysis, provides significant structural insights into αvβ3 molecular recognition by RGDechi‐hCit. Remarkably, on the basis of the identified molecular determinants, we design a RGDechi‐hCit mutant that is selective for αvβ5 integrin. 相似文献
994.
The depository effects that occur in slowly metabolized proteins (typically glycation) are very difficult to assess, owing to their extremely low concentration in the protein matrix. Collagen accumulates reactive metabolites through reactions that are not regulated by enzymes. A typical example of these non-enzymatic changes is glycation (the Maillard reaction, the formation of advanced glycation end products), resulting from the reaction of the oxo-group of sugars with the epsilon-amino group of lysine and arginine. Collagen samples (type I) as a test protein were incubated separately with glucose, ribose and malondialdehyde. Collagen was fragmented with cyanogen bromide and then digested with trypsin. This peptide digest was separated by CE, CE-MS/MS, and HPLC-MS/MS. An ion trap MS was used and MS conditions were optimized for both methods. These on-line CE-MS/MS and HPLC-MS/MS couplings made it possible to discover specific modifications such as (N(epsilon)-(carboxymethyl)-lysine) in the precise location in the structure of collagen corresponding to posttranslational non-enzymatic modifications. A new CE-MS/MS technique for peptide analysis was developed, and applied in the identification of posttranslational modifications in slowly metabolized test proteins. 相似文献
995.
Taichi Ikeda Dr. Sourav Saha Dr. Ivan Aprahamian Dr. Ken C.‐F. Leung Dr. Adides Williams Wei‐Qiao Deng Dr. Amar H. Flood Dr. William A. Goddard III Prof. J. Fraser Stoddart Prof. 《化学:亚洲杂志》2007,2(1):76-93
Encouraged by the prospect of producing an electrochemical, color‐switchable red–green–blue (RGB) dye compound, we have designed, synthesized, and characterized two three‐station [2]catenanes. Both are composed of macrocyclic polyethers containing three π‐electron‐rich stations, which act as recognition sites for a π‐electron‐deficient tetracationic cyclophane. The molecular structures of the two three‐station [2]catenanes were characterized fully by mass spectrometry and 1H NMR spectroscopy. To anticipate the relative occupancies of the three stations in each [2]catenane by the cyclophane, model compounds with the same constitutions in the vicinity of the stations were synthesized. The relative ground‐state populations of the three stations occupied in both [2]catenanes were estimated from the thermodynamic parameters for 1:1 complexes between all these model compounds and the cyclophane, obtained from isothermal titration calorimetry (ITC). The electrochemical and electromechanical properties of the three‐station [2]catenanes were analyzed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry (SEC). The first three‐station [2]catenane was found to behave like a bistable system, whereas the second can be described as a quasi‐tristable system. 相似文献
996.
Vukadin M. Leovac Ljiljana S. Jovanović Vladimir Divjaković Andrej Pevec Ivan Leban Thomas Armbruster 《Polyhedron》2007
This paper describes the synthesis of the first Ni(II) complexes with pyridoxal semicarbazone (PLSC), viz. Ni(PLSC)Cl2 · 3.5H2O (1), [Ni(PLSC)(H2O)3](NO3)2 (2), Ni(PLSC)(NCS)2 · 4H2O (3), [Ni(PLSC-2H)NH3] · 1.5H2O (4), as well as two new complexes with pyridoxal thiosemicarbazone (PLTSC), [Ni(PLTSC-H)py]NO3 (5) and [Ni(PLTSC-H)NCS] (6). Complexes 1–3 are paramagnetic and have most probably an octahedral structure, for complex 2 this was proved by X-ray diffraction analysis. In contrast, complexes 4–6 are diamagnetic and have a square-planar structure, and in the case of complex 5 this was also confirmed by X-ray structural analysis. In all cases the Schiff bases are coordinated as tridentate ligands with an ONX (X = O, PLSC; X = S, PLTSC) set of donor atoms. With the complexes involving the neutral form of PLSC and the monoanionic form of PLTSC, the PL moiety is in the form of a zwitterion. In addition to the above-mentioned techniques, all the complexes were characterized by measuring their molar conductivities, UV–Vis and partial IR spectra. 相似文献
997.
A Genetically Encoded β‐Lactamase Reporter for Ultrasensitive 129Xe NMR in Mammalian Cells 下载免费PDF全文
Yanfei Wang Benjamin W. Roose Eugene J. Palovcak Dr. Vincenzo Carnevale Prof. Ivan J. Dmochowski 《Angewandte Chemie (International ed. in English)》2016,55(31):8984-8987
Molecular imaging holds considerable promise for elucidating biological processes in normal physiology as well as disease states, but requires noninvasive methods for identifying analytes at sub‐micromolar concentrations. Particularly useful are genetically encoded, single‐protein reporters that harness the power of molecular biology to visualize specific molecular processes, but such reporters have been conspicuously lacking for in vivo magnetic resonance imaging (MRI). Herein, we report TEM‐1 β‐lactamase (bla) as a single‐protein reporter for hyperpolarized (HP) 129Xe NMR, with significant saturation contrast at 0.1 μm . Xenon chemical exchange saturation transfer (CEST) interactions with the primary allosteric site in bla give rise to a unique saturation peak at 255 ppm, well removed (≈60 ppm downfield) from the 129Xe‐H2O peak. Useful saturation contrast was also observed for bla expressed in bacterial cells and mammalian cells. 相似文献
998.
Yanfei Wang Benjamin W. Roose John P. Philbin Jordan L. Doman Prof. Ivan J. Dmochowski 《Angewandte Chemie (International ed. in English)》2016,55(5):1733-1736
A supramolecular strategy for detecting specific proteins in complex media by using hyperpolarized 129Xe NMR is reported. A cucurbit[6]uril (CB[6])‐based molecular relay was programmed for three sequential equilibrium conditions by designing a two‐faced guest (TFG) that initially binds CB[6] and blocks the CB[6]–Xe interaction. The protein analyte recruits the TFG and frees CB[6] for Xe binding. TFGs containing CB[6]‐ and carbonic anhydrase II (CAII)‐binding domains were synthesized in one or two steps. X‐ray crystallography confirmed TFG binding to Zn2+ in the deep CAII active‐site cleft, which precludes simultaneous CB[6] binding. The molecular relay was reprogrammed to detect avidin by using a different TFG. Finally, Xe binding by CB[6] was detected in buffer and in E. coli cultures expressing CAII through ultrasensitive 129Xe NMR spectroscopy. 相似文献
999.
We proposed EPR spectroscopy using spin-trap DEPMPO as a novel method for the detection of a hydrogen atom (*H) produced by chemical and biological systems. In complex EPR spectra of DEPMPO adducts in biological systems, spectral lines of unknown origin have been observed. We have assumed (Baci?, G.; Mojovi?, M. Ann. N. Y. Acad. Sci. 2005, 1048, 230-243) that those lines represent the spectrum of a hydrogen atom (*H) adduct i.e., DEPMPO/H. An electrochemical system known to produce only *H radicals was used here in order to obtain a separate spectrum of the DEPMPO/H adduct. An acquired spectrum as well as a computer spectral simulation of the DEPMPO/H adduct showed considerable resemblance with additional lines in the EPR spectra of DEPMPO adducts in biological systems-plant plasma membranes and cell walls. This shows that such a radical is produced by plants as well as that DEPMPO is suitable for detection in both electrochemical and biological systems. 相似文献
1000.
Liquid-liquid and liquid-vapor coexistence regions of various water models were determined by Monte Carlo (MC) simulations of isotherms of density fluctuation-restricted systems and by Gibbs ensemble MC simulations. All studied water models show multiple liquid-liquid phase transitions in the supercooled region: we observe two transitions of the TIP4P, TIP5P, and SPCE models and three transitions of the ST2 model. The location of these phase transitions with respect to the liquid-vapor coexistence curve and the glass temperature is highly sensitive to the water model and its implementation. We suggest that the apparent thermodynamic singularity of real liquid water in the supercooled region at about 228 K is caused by an approach to the spinodal of the first (lowest density) liquid-liquid phase transition. The well-known density maximum of liquid water at 277 K is related to the second liquid-liquid phase transition, which is located at positive pressures with a critical point close to the maximum. A possible order parameter and the universality class of liquid-liquid phase transitions in one-component fluids are discussed. 相似文献