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991.
Aleer M. Yol David E. Dabney Shih-Fan Wang Boyd A. Laurent Mark D. Foster Roderic P. Quirk Scott M. Grayson Chrys Wesdemiotis 《Journal of the American Society for Mass Spectrometry》2013,24(1):74-82
[M + Ag]+ ions from cyclic and linear polystyrenes and polybutadienes, formed by matrix-assisted laser desorption ionization (MALDI), give rise to significantly different fragmentation patterns in tandem mass spectrometry (MS2) experiments. In both cases, fragmentation starts with homolytic cleavage at the weakest bond, usually a C–C bond, to generate two radicals. From linear structures, the separated radicals depolymerize extensively by monomer losses and backbiting rearrangements, leading to low-mass radical ions and much less abundant medium- and high-mass closed-shell fragments that contain one of the original end groups, along with internal fragments. With cyclic structures, depolymerization is less efficient, as it can readily be terminated by intramolecular H-atom transfer between the still interconnected radical sites (disproportionation). These differences in fragmentation reactivity result in substantially different fragment ion distributions in the MS2 spectra. Simple inspection of the relative intensities of low- versus high-mass fragments permits conclusive determination of the macromolecular architecture, while full spectral interpretation reveals the individual end groups of linear polymers or the identity of the linker used to form the cyclic polymer. Figure
Macrocyclic and linear polystyrene and polydiene architectures are conclusively distinguished by the MS2 fragmentation patterns of Ag+-cationized oligomers. 相似文献
992.
Dr. Nicolas Popoff Dr. Jeff Espinas Dr. Jérémie Pelletier Benoît Macqueron Dr. Kai C. Szeto Olivier Boyron Dr. Christophe Boisson Dr. Iker Del Rosal Dr. Laurent Maron Dr. Aimery De Mallmann Dr. Régis M. Gauvin Dr. Mostafa Taoufik 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):964-973
Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi‐grafted and mono‐grafted single‐site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono‐ versus bi‐grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi‐grafted species displayed higher activity than their mono‐grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions. 相似文献
993.
Dr. Matthew P. Conley Ruben M. Drost Dr. Mathieu Baffert Dr. David Gajan Prof. Dr. Cornelis Elsevier Dr. W. Trent Franks Prof. Dr. Hartmut Oschkinat Laurent Veyre Alexandre Zagdoun Dr. Aaron Rossini Dr. Moreno Lelli Dr. Anne Lesage Dr. Gilles Casano Dr. Olivier Ouari Prof. Dr. Paul Tordo Prof. Dr. Lyndon Emsley Prof. Dr. Christophe Copéret Dr. Chloé Thieuleux 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12234-12238
994.
Benjamin Briois Tsuguyuki Saito Christian Pétrier Jean-Luc Putaux Yoshiharu Nishiyama Laurent Heux Sonia Molina-Boisseau 《Cellulose (London, England)》2013,20(2):597-603
Aqueous suspensions of dispersed Glaucocystis cellulose microfibrils were sonicated at 4 °C for 3 h, using 24 kHz ultrasonic waves. This treatment induced a variety of ultrastructural defects, as the microfibrils became not only shortened, but also presented substantial damage materialized by kinks and subfibrillation. Upon analysis by X-ray diffraction and 13C solid-state NMR spectroscopy, it was found that the initial sample that contained 90 % of cellulose Iα allomorph became, to a large extent, unexpectedly converted into the Iβ phase, while the loss of crystallinity was only moderate during the sonication treatment. 相似文献
995.
Mihaela Mândru Constantin Ciobanu Stelian Vlad Maria Butnaru Laurent Lebrun Marcel Popa 《Central European Journal of Chemistry》2013,11(4):542-553
This paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications. 相似文献
996.
Lutfi Arif Ngah Olivier Alibart Laurent Labont Virginia D'Auria Sbastien Tanzilli 《Laser \u0026amp; Photonics Reviews》2015,9(2):L1-L5
The realization of an ultra‐fast source of heralded single photons emitted at the wavelength of 1540 nm is reported. The presented strategy is based on state‐of‐the‐art telecom technology, combined with off‐the‐shelf fiber components and waveguide non‐linear stages pumped by a 10 GHz repetition rate laser. The single photons are heralded at a rate as high as 2.1 MHz with a heralding efficiency of 42%. Single‐photon character of the source is inferred by measuring the second‐order autocorrelation function. For the highest heralding rate, a value as low as 0.023 is found. This not only proves negligible multi‐photon contributions but also represents one of the best measured values reported to date for heralding rates in the MHz regime. These performances, associated with a device‐like configuration, are key ingredients for both fast and secure quantum communication protocols.
997.
Isabelle Martiel Laurent Sagalowicz Raffaele Mezzenga 《Advances in colloid and interface science》2014
Phospholipids are ubiquitous cell membrane components and relatively well-accepted ingredients due to their natural origin. Phosphatidylcholine (PC) in particular offers a promising alternative to monoglycerides for lyotropic liquid crystalline (LLC) delivery system applications in the food, cosmetics and pharmaceutical industries, provided its strong tendency to form zero-mean curvature lamellar mesophases in water can be overcome. Higher negative curvatures are usually reached through the addition of a third lipid component, forming a ternary diagram phospholipid/water/oil. 相似文献
998.
Adèle D. Laurent Vitaly N. Glushkov Thibaut Very Xavier Assfeld 《Journal of computational chemistry》2014,35(15):1131-1139
Experimental X‐ray absorption spectra are extensively used to determine electronic structure of small molecules but remain difficult to exploit for proteins due to the large number of peaks within their spectra. For such complex systems, theoretical tools like quantum mechanics/molecular mechanics methodology can greatly ease the assignment of the spectra. This study presents a systematic methodology to evaluate core‐ionization energies (Eion) in proteins with the help of the asymptotic projection approach (Glushkov and Tsaune, Z. Vichislit. Matem. Mat. Fiz. 1985, 25, 298; Glushkov, Chem. Phys. Lett. 1997, 273, 122; Glushkov, Chem. Phys. Lett. 1998, 287, 189; Glushkov, J. Math. Chem. 2002, 31, 91; Glushkov, Opt. Spectrosc. 2002, 93, 15). An in‐depth inspection of Eion of systems of increasing complexity is considered, going from amino acids to polyglycine and to glycine in human serum albumin (HSA). Computational analysis can help to better understand experimental data and to discriminate environmental effects by tracing them back to individual and collective electrostatic contributions. In the present work, it was found that Eion of alpha carbon of glycine residues in HSA ranges from 285 to 295 eV depending on their surroundings. © 2014 Wiley Periodicals, Inc. 相似文献
999.
Marie-Fran?oise Bidaut-V��ron Augusto C. Ponce Laurent V��ron 《Calculus of Variations and Partial Differential Equations》2011,40(1-2):183-221
Given a smooth domain ${\Omega\subset\mathbb{R}^N}$ such that ${0 \in \partial\Omega}$ and given a nonnegative smooth function ?? on ???, we study the behavior near 0 of positive solutions of ???u?=?u q in ?? such that u =? ?? on ???\{0}. We prove that if ${\frac{N+1}{N-1} < q < \frac{N+2}{N-2}}$ , then ${u(x)\leq C |x|^{-\frac{2}{q-1}}}$ and we compute the limit of ${|x|^{\frac{2}{q-1}} u(x)}$ as x ?? 0. We also investigate the case ${q= \frac{N+1}{N-1}}$ . The proofs rely on the existence and uniqueness of solutions of related equations on spherical domains. 相似文献
1000.
This paper presents a method for computing the solution to the time-dependent wave equation from the knowledge of a largely
incomplete set of eigenfunctions of the Helmholtz operator, chosen at random. While a linear superposition of eigenfunctions
can fail to properly synthesize the solution if a single term is missing, it is shown that solving a sparsity-promoting ℓ
1 minimization problem can vastly enhance the quality of recovery. This phenomenon may be seen as “compressive sampling in
the Helmholtz domain.” 相似文献