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991.
Remarkable Enhancement of Enantioselectivity in the Asymmetric Conjugate Addition of Dimethylzinc to (Z)‐Nitroalkenes with a Catalytic [(MeCN)4Cu]PF6–Hoveyda Ligand Complex 下载免费PDF全文
Dr. Xingzhong Zeng Joe J. Gao Dr. Jinhua J. Song Dr. Shengli Ma Dr. Jean‐Nicolas Desrosiers Dr. Jason A. Mulder Dr. Sonia Rodriguez Dr. Melissa A. Herbage Dr. Nizar Haddad Dr. Bo Qu Dr. Keith R. Fandrick Dr. Nelu Grinberg Dr. Heewon Lee Dr. Xudong Wei Dr. Nathan K. Yee Dr. Chris H. Senanayake 《Angewandte Chemie (International ed. in English)》2014,53(45):12153-12157
An enantioselective copper‐catalyzed asymmetric conjugate addition of Me2Zn to (Z)‐nitroalkenes led to the formation of all‐carbon quaternary stereogenic centers with high stereoselectivity. The key features of the new method are the unprecedented use of [(MeCN)4Cu]PF6 in conjunction with the Hoveyda ligand L1 and the use of (Z)‐nitroalkene substrates so that undesired nitroalkene isomerization is minimized and enantioselectivity is enhanced dramatically. We also describe a novel, practical, and highly (Z)‐selective nitroalkene synthesis. 相似文献
992.
Tuning the Guest‐Binding Ability of a Helically Folded Capsule by In Situ Modification of the Aromatic Oligoamide Backbone 下载免费PDF全文
Dr. Guillaume Lautrette Dr. Christophe Aube Dr. Yann Ferrand Dr. Muriel Pipelier Dr. Virginie Blot Dr. Christine Thobie Dr. Brice Kauffmann Prof. Didier Dubreuil Dr. Ivan Huc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1547-1553
Starting from a previously described aromatic oligoamide helically folded capsule that binds tartaric acid with high affinity and diastereoselectivity, we demonstrate the feasibility of the direct in situ modification of the helix backbone, which results in a conformational change that reduces its affinity for guests by two orders of magnitude. Specifically, ring contraction of the central pyridazine unit into a pyrrole in the full helical sequence was investigated by using electrochemical and chemical processes. The sequence containing the pyrrole was synthesized independently in a convergent manner to ascertain its structure. The conformation of the pyrrolic folded capsule was elucidated in the solid state by X‐ray crystallography and in solution by using 1H and 13C NMR spectroscopy. Solution studies revealed an unanticipated solvent‐dependent equilibrium between the anti–anti and syn–syn conformations of the pyrrole ring with respect to its two adjacent pyridine units. Titrations of the pyrrole‐containing sequence monitored by 1H NMR spectroscopy confirmed the expected drop in affinity for tartaric acid and malic acid that arises from the conformation change in the backbone that follows the replacement of the pyridazine by a pyrrole. The reduction of the pyridazine to a pyrrole was characterized by cyclic voltammetry both on the entire sequence and on a shorter precursor. The lower cathodic potential of the precursor made its preparative‐scale electroreduction possible. Direct in situ modification of the pyridazine within the entire capsule sequence was achieved chemically by using zinc in acetic acid. 相似文献
993.
Ming Liu Sandrine Peyrat Nicolas Illy Véronique Wintgens Blandine Brissault Jacques Penelle Valessa Barbier 《Journal of polymer science. Part A, Polymer chemistry》2014,52(16):2337-2345
We report the synthesis and ion‐binding properties of four poly(crown‐ethers) displaying either one or two crown‐ethers (15‐crown‐5 or 18‐crown‐6) on every third carbon alongside the backbone. The polymers were synthesized by living anionic ring‐opening polymerization of disubstituted cyclopropane‐1,1‐dicarboxylates monomers. Cation binding of the polychelating polymers and corresponding monomers to Na+ and K+ was evaluated by picrate extraction and isothermal calorimetry titration. This novel family of poly(crown‐ethers) demonstrated excellent initial binding of the alkali ions to the polymers, with a higher selectivity for potassium. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2337–2345 相似文献
994.
Assessment of DNA Binding to Human Rad51 Protein by using Quartz Crystal Microbalance and Atomic Force Microscopy: Effects of ADP and BRC4‐28 Peptide Inhibitor 下载免费PDF全文
Dr. Charles Esnault Dr. Axelle Renodon‐Cornière Dr. Masayuki Takahashi Dr. Nathalie Casse Dr. Nicolas Delorme Prof. Guy Louarn Prof. Fabrice Fleury Prof. Jean‐François Pilard Prof. Benoît Chénais 《Chemphyschem》2014,15(17):3753-3760
The interaction of human Rad51 protein (HsRad51) with single‐stranded deoxyribonucleic acid (ssDNA) was investigated by using quartz crystal microbalance (QCM) monitoring and atomic force microscopy (AFM) visualization. Gold surfaces for QCM and AFM were modified by electrografting of the in situ generated aryldiazonium salt from the sulfanilic acid to obtain the organic layer Au–ArSO3H. The Au–ArSO3H layer was activated by using a solution of PCl5 in CH2Cl2 to give a Au–ArSO2Cl layer. The modified surface was then used to immobilize long ssDNA molecules. The results obtained showed that the presence of adenosine diphosphate promotes the protein autoassociation rather than nucleation around DNA. In addition, when the BRC4‐28 peptide inhibitor was used, both QCM and AFM confirmed the inhibitory effect of BRC4‐28 toward HsRad51 autoassociation. Altogether these results show the suitability of this modified surface to investigate the kinetics and structure of DNA–protein interactions and for the screening of inhibitors. 相似文献
995.
Understanding Bacterial Bioluminescence: A Theoretical Study of the Entire Process,from Reduced Flavin to Light Emission 下载免费PDF全文
Cong Hou Prof. Dr. Ya‐Jun Liu Prof. Dr. Nicolas Ferré Prof. Dr. Wei‐Hai Fang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):7979-7986
Bacterial bioluminescence (BL) has been successfully applied in water‐quality monitoring and in vivo imaging. The attention of researchers has been attracted for several decades, but the mechanism of bacterial BL is still largely unknown due to the complexity of the multistep reaction process. Debates mainly focus on three key questions: How is the bioluminophore produced? What is the exact chemical form of the bioluminophore? How does the protein environment affect the light emission? Using quantum mechanics (QM), combined QM and molecular mechanics (QM/MM) and molecular dynamic (MD) calculations in gas‐phase, solvent and protein environments, the entire process of bacterial BL was investigated, from flavin reduction to light emission. This investigation revealed that: 1) the chemiluminescent decomposition of flavin peroxyhemiacetal does not occur through the intramolecular chemical initiated electron exchange luminescence (CIEEL) or the “dioxirane” mechanism, as suggested in the literature. Instead, the decomposition occurs according to the charge‐transfer initiated luminescence (CTIL) mechanism for the thermolysis of dioxetanone. 2) The first excited state of 4a‐hydroxy‐4a,5‐dihydroFMN (HFOH) was affirmed to be the bioluminophore of bacterial BL. This study provides details regarding the mechanism by which bacterial BL is produced and is helpful in understanding bacterial BL in general. 相似文献
996.
Thiazole‐Based γ‐Building Blocks as Reverse‐Turn Mimetic to Design a Gramicidin S Analogue: Conformational and Biological Evaluation 下载免费PDF全文
Dr. Baptiste Legrand Loïc Mathieu Aurélien Lebrun Soahary Andriamanarivo Prof. Vincent Lisowski Dr. Nicolas Masurier Dr. Séverine Zirah Prof. Young Kee Kang Prof. Jean Martinez Dr. Ludovic T. Maillard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6713-6720
This paper describes the ability of a new class of heterocyclic γ‐amino acids named ATCs (4‐amino(methyl)‐1,3‐thiazole‐5‐carboxylic acids) to induce turns when included in a tetrapeptide template. Both hybrid Ac‐Val‐(R or S)‐ATC‐Ile‐Ala‐NH2 sequences were synthesized and their conformations were studied by circular dichroism, NMR spectroscopy, MD simulations, and DFT calculations. It was demonstrated that the ATCs induced highly stable C9 pseudocycles in both compounds promoting a twist turn and a reverse turn conformation depending on their absolute configurations. As a proof of concept, a bioactive analogue of gramicidin S was successfully designed using an ATC building block as a turn inducer. The NMR solution structure of the analogue adopted an antiparallel β‐pleated sheet conformation similar to that of the natural compound. The hybrid α,γ‐cyclopeptide exhibited significant reduced haemotoxicity compared to gramicidin S, while maintaining strong antibacterial activity. 相似文献
997.
Development of an Iron(II)‐Catalyzed Aerobic Catechol Cleavage and Biomimetic Synthesis of Betanidin 下载免费PDF全文
Dr. Nicolas Guimond Dr. Peter Mayer Prof. Dr. Dirk Trauner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9519-9523
An aerobic iron(II)‐catalyzed cleavage of catechols was developed. This reaction allows for the preparation of 2‐methoxy‐2 H‐pyrans that can be employed as versatile building blocks for synthesis. The utility of this biomimetic oxidative cleavage is featured in the synthesis of betanidin, a natural colorant with antioxidant properties. 相似文献
998.
Marek Koutny Martine Sancelme Nicolas Pichon Jacques Lemaire 《Polymer Degradation and Stability》2006,91(7):1495-1503
Biodegrability of high density polyethylene film (HDPE) and low density polyethylene film (LDPE) both containing a balance of antioxidants and pro-oxidants was studied with defined microbial strains particularly with Rhodococcus rhodochrous and Nocardia asteroides in mineral medium. After an abiotic pre-treatment consisting of photooxidation and thermo-oxidation corresponding to about 3 years of outdoor weathering the samples were inoculated, incubated up to 200 days and during the period their metabolic activities were followed by measuring adenosine triphosphate content. Simultaneously the cultures were also monitored by optical microscopy and FTIR spectroscopy. The first initial phase of fast growth caused by the presence of low molecular extractable compounds was followed by a long period of stabilized metabolic activity suggesting that microorganisms continued to gain energy from the substrate but evidently at a much slower rate. Complementary analysis performed at the end of incubation revealed that during the experiment time biodegradation processes probably affected surface layer of materials only. 相似文献
999.
Zhang T Tang XN Lau KC Ng CY Nicolas C Peterka DS Ahmed M Morton ML Ruscic B Yang R Wei LX Huang CQ Yang B Wang J Sheng LS Zhang YW Qi F 《The Journal of chemical physics》2006,124(7):74302
We have developed an effusive laser photodissociation radical source, aiming for the production of vibrationally relaxed radicals. Employing this radical source, we have measured the vacuum ultraviolet (VUV) photoionization efficiency (PIE) spectrum of the propargyl radical (C(3)H(3)) formed by the 193 nm excimer laser photodissociation of propargyl chloride in the energy range of 8.5-9.9 eV using high-resolution (energy bandwidth = 1 meV) multibunch synchrotron radiation. The VUV-PIE spectrum of C(3)H(3) thus obtained is found to exhibit pronounced autoionization features, which are tentatively assigned as members of two vibrational progressions of C(3)H(3) in excited autoionizing Rydberg states. The ionization energy (IE = 8.674 +/- 0.001 eV) of C(3)H(3) determined by a small steplike feature resolved at the photoionization onset of the VUV-PIE spectrum is in excellent agreement with the IE value reported in a previous pulsed field ionization-photoelectron study. We have also calculated the Franck-Condon factors (FCFs) for the photoionization transitions C(3)H(3) (+)(X;nu(i),i = 1-12)<--C(3)H(3)(X). The comparison between the pattern of FCFs and the autoionization peaks resolved in the VUV-PIE spectrum of C(3)H(3) points to the conclusion that the resonance-enhanced autoionization mechanism is most likely responsible for the observation of pronounced autoionization features. We also present here the VUV-PIE spectra for the mass 39 ions observed in the VUV synchrotron-based photoionization mass spectrometric sampling of several premixed flames. The excellent agreement of the IE value and the pattern of autoionizing features of the VUV-PIE spectra observed in the photodissociation and flames studies has provided an unambiguous identification of the propargyl radical as an important intermediate in the premixed combustion flames. The discrepancy found between the PIE spectra obtained in flames and photodissociation at energies above the IE(C(3)H(3)) suggests that the PIE spectra obtained in flames might have contributions from the photoionization of vibrationally excited C(3)H(3) and/or the dissociative photoionization processes involving larger hydrocarbon species formed in flames. 相似文献
1000.
Adkine P Cantat T Deschamps E Ricard L Mézailles N Le Floch P Geoffroy M 《Physical chemistry chemical physics : PCCP》2006,8(7):862-868
Cyclic voltammetry and EPR spectroscopy show that cationic phospholium groups are good electron acceptors whose reduction leads to a neutral radical where the unpaired electron is mainly delocalized on the carbon atoms of the five-membered ring. DFT calculations together with the crystal structure of phospholiums indicate that the electron addition causes a drastic diminution of the exocyclic CPC angle. The SOMO of reduced phospholium is compared to the SOMO of the phosphole radical anion. 相似文献