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971.
972.
Stereoselective Csp3–Csp2 Bond‐Forming Reactions by Transition‐Metal‐Free Reductive Coupling of Cyclic Tosylhydrazones with Boronic Acids
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Manuel Plaza Dr. M. Carmen Pérez‐Aguilar Dr. Carlos Valdés 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(18):6253-6257
The reactions between alkenylboronic acids and tosylhydrazones derived from substituted cyclohexanones lead to the construction of disubstituted cyclohexanes with total regio‐ and stereoselectivity. In these transition‐metal‐free processes, a Csp3?Csp2 and Csp3?H bond are formed on the same carbon atom. The stereoselective reaction is general for 2‐, 3‐, and 4‐substituted cyclohexanone tosylhydrazones, as well as for 2‐substituted cyclopentanones. However, no stereoselectivity is observed for acyclic derivatives. DFT computational modeling suggests that the stereoselectivity of the reaction is determined by the approach of the boronic acid to the diazocyclohexane on its most stable chair conformation through an equatorial trajectory. 相似文献
973.
Maria Caterina Fragnelli Pilar Hoyos Diego Romano Raffaela Gandolfi Andrés R. Alcántara Francesco Molinari 《Tetrahedron》2012,68(2):523-528
Water/organic solvent two-liquid-phase systems have been successfully applied in the synthesis of enantiomerically pure (S)-benzoin through two different methodologies catalysed by whole cells from the non-conventional yeast Pichia glucozyma: the stereoselective monoreduction of benzil and the deracemisation of benzoin. The presence of the organic solvent influences the redox systems implied in the reactions, avoiding the formation of the corresponding diols, increasing the enantioselectivity and allowing the easy isolation of the products in high yields and excellent enantiomeric excesses. The use of both strategies has been extended to the preparation of different chiral benzoin derivatives. 相似文献
974.
László Lázár Erika Mező Mihály Herczeg András Lipták Sándor Antus Anikó Borbás 《Tetrahedron》2012,68(36):7386-7399
A glucoronic acid-containing trisaccharide related to the antithrombin-binding DEFGH domain of heparin and its methanesulfonic acid analogues were synthesized. Trisaccharides without sulfonic acid content or possessing a sulfonatomethyl moiety at position 2 or 6 of unit F were prepared in high yields by [DE+F] couplings using the same disaccharide uronate donor, respectively. Synthesis of the trisaccharide with a 3-deoxy-3-sulfonatomethyl function was accomplished in three different pathways, from which a [D+EF] coupling and applying a non-oxidized precursor of the glucuronic acid afforded the trisaccharide in the highest yield. 相似文献
975.
Dr. Gui‐Chao Kuang Ming‐Jun Teng Prof. Xin‐Ru Jia Prof. Dr. Er‐Qiang Chen Prof. Dr. Yen Wei 《化学:亚洲杂志》2011,6(5):1163-1170
There is a delicate balance for a low‐weight molecule to behave as a gelator or crystal. The synthesis of two novel amino acid‐based naphthalene‐dendrons, Nap ‐ G1 and Nap ‐ G2 is described. Both dendrons display polymorphic properties in organic solvents. Nap ‐ G1 developed a fibrous network with β‐sheet architecture in cyclohexane but exhibited a spherulitic network in mixed solvents (chloroform/petroleum ether 1:5, v/v). On the other hand, Nap ‐ G2 acted as an efficient organogelator in chloroform but formed crystalline fibers in relatively high polarity solvents (such as acetone and methanol). Combinations of characterizations have been employed to study the polymorphism. 相似文献
976.
Elena Fernández Manuel Ortuño Andrés Márquez Rosa Fuentes Inmaculada Pascual 《Optik》2010,121(2):151-158
Holographic data pages were stored in a polyvinyl alcohol (PVA)/acrylamide (AA) photopolymer. This material is formed of AA photopolymers which are considered interesting materials for recording holographic memories. A liquid crystal device was used to modify the object beam and store the data pages in the material. During the storage process, some parameters like exposure time, beam ratio and reading beam intensity were controlled to obtain high image quality after the reconstruction process. The bit error rate (BER) was calculated fitting the histograms of the images to determine what parameters improve the quality of the images. 相似文献
977.
Youjun He Yi Zhou Guangjin Zhao Jie Min Xia Guo Bo Zhang Maojie Zhang Jing Zhang Yongfang Li Fengling Zhang Olle Inganäs 《Journal of polymer science. Part A, Polymer chemistry》2010,48(8):1822-1829
A new benzodithiophene (BDT)‐based polymer, poly(4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene vinylene) (PBDTV), was synthesized by Pd‐catalyzed Stille‐coupling method. The polymer is soluble in common organic solvents and possesses high thermal stability. PBDTV film shows a broad absorption band covering from 350 nm to 618 nm, strong photoluminescence peaked at 545 nm and high hole mobility of 4.84 × 10?3 cm2/Vs. Photovoltaic properties of PBDTV were studied by fabricating the polymer solar cells based on PBDTV as donor and PC70BM as acceptor. With the weight ratio of PBDTV: PC70BM of 1:4 and the active layer thickness of 65 nm, the power conversion efficiency of the device reached 2.63% with Voc = 0.71 V, Isc = 6.46 mA/cm2, and FF = 0.57 under the illumination of AM1.5, 100 mW/cm2. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1822–1829, 2010 相似文献
978.
Inês R. Ramos Fiona M. Lyng Ihtesham Ur Rehman Basil Sharrack M. Nicola Woodroofe 《应用光谱学评论》2017,52(10):868-882
Spectroscopy techniques are valuable tools in biomedical research and have been used extensively in the study of disease. However, neurological conditions such as multiple sclerosis (MS) have received little attention and the available spectroscopy studies are limited, both in overall numbers of patients studied and the disease samples considered. MS is a complex immune-mediated disease, with variable clinical courses and limited therapeutic options. This review aims to summarize current literature in the area, demonstrating how spectroscopy techniques can provide valuable information to inform and advance research into the most common neurological condition affecting young adults. 相似文献
979.
Attila G. Császár Tamás Szidarovszky Nikolai F. Zobov Oleg L. Polyansky Jonathan Tennyson 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(9):1043-1106
A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron mass-velocity and Darwin corrections. For H216O, the PES has a dissociation energy of D0 = 41 109 cm−1 and supports 1150 vibrational energy levels up to 41 083 cm−1. The deviation between the computed and the experimentally measured energy levels is below 15 cm−1 for all the states with energies less than 39 000 cm−1. Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26 500 cm−1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed. 相似文献
980.