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931.
Why can enzymes provide different products from only slightly different substrates? While the reaction of 2-hydroxyethylphosphonate (2-HEP) catalyzed by 2-hydroxyethylphosphonate dioxygenase (HEPD) yields hydroxymethylphosphonate and formic acid, the HEPD-catalyzed reaction of 1-HEP gives acetylphosphate. ONIOM(DFT:MM) was used to uncover the distinct reaction mechanisms for the different substrates. Calculations show that, in both reactions, similar radical intermediates are generated by the same process. After the formation of common radical intermediates, proton-coupled electron transfer (PCET) operates in the 1-HEP reaction, whereas in the 2-HEP reaction, it cannot occur and an alternative pathway sets in. Thus, the PCET plays a critical role in defining the fates of the substrates. 相似文献
932.
Takashi Kuchiyama Kenji YamamotoShigehiko Hasegawa Hajime Asahi 《Applied Surface Science》2011,258(4):1488-1490
Surface morphology and crystalline structure of high-stable zinc oxide films were evaluated by atomic force microscopy, scanning electron microscopy and X-ray diffraction (XRD) measurements. AFM measurement revealed that the higher stable samples have smaller roughness (average roughness and root mean square) parameters than the lower stable samples. Furthermore, in-plane XRD measurement showed that the crystallite size of high stable samples is smaller than that of the low stable samples. These results indicate that the larger surface area and lower film density deteriorates the stability of zinc oxide films through the adsorption and reaction of water or oxygen molecules. They also suggest that we can prepare the high stable zinc oxide transparent electrode films by controlling the surface morphology. 相似文献
933.
A General Palladium‐Catalyzed Method for Alkylation of Heteroarenes Using Secondary and Tertiary Alkyl Halides
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Xiaojin Wu Jessica Wei Ting See Kai Xu Hajime Hirao Julien Roger Jean‐Cyrille Hierso Jianrong Zhou 《Angewandte Chemie (International ed. in English)》2014,53(49):13573-13577
A general alkylation of heterocycles using a simple palladium catalyst is reported. Most classes of heterocycles, including indoles and pyridines, efficiently coupled with unactivated secondary and tertiary alkyl halides. An alkyl radical addition to neutral heteroarenes is most likely involved. 相似文献
934.
Multicolour Fluorescent Memory Based on the Interaction of Hydroxy Terphenyls with Fluoride Anions
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Masaaki Akamatsu Dr. Taizo Mori Dr. Ken Okamoto Prof. Dr. Hideki Sakai Prof. Dr. Masahiko Abe Dr. Jonathan P. Hill Prof. Dr. Katsuhiko Ariga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16293-16300
Memory operations based on variation of a molecule’s properties are important because they may lead to device miniaturization to the molecular scale or increasingly complex information processing protocols beyond the binary level. Molecular memory also introduces possibilities related to information‐storage security where chemical information (or reagents) might be used as an encryption key, in this case, acidic/basic reagents. Chemical memory that possesses both volatile and non‐volatile functionality requires reversible conversion between at least two chemically different stable or quasi‐stable states. Here we have developed the phenol–phenoxide equilibrium of phenol fluorophores as a data storage element, which can be used to write or modulate data using chemical reagents. The properties of this system allow data to be stored and erased either in non‐volatile or volatile modes. We also demonstrate non‐binary switching of states made possible by preparation of a composite containing the molecular memory elements. 相似文献
935.
Universal Reaction Mechanism of Boronic Acids with Diols in Aqueous Solution: Kinetics and the Basic Concept of a Conditional Formation Constant
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Yuki Furikado Tomomi Nagahata Takuya Okamoto Dr. Tomoaki Sugaya Prof. Dr. Satoshi Iwatsuki Prof. Dr. Masahiko Inamo Prof. Dr. Hideo D. Takagi Prof. Dr. Akira Odani Prof. Dr. Koji Ishihara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13194-13202
To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (${K{{{\rm BL}\hfill \atop {\rm a}\hfill}}}$ ) of boronic acid diol esters (HBLs) were determined based on the well‐established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4‐difluorophenylboronic acid and chromotropic acid, 3‐nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K′, based on the main reaction: RB(OH)2+H2L ${{\mathop \leftrightarrow \limits ^{K{_{1}}}_{}}}$ RB(L)(OH)?+H3O+ instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B′) with uncomplexed diol species (L′) to form boronic acid diol complex species (esters, BL′) in aqueous solution at pH 5–11: B′+L′ ${{\mathop \leftrightarrow \limits ^{K{^\prime}}_{}}}$ BL′. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution. 相似文献
936.
This work introduces a novel method of recovery of iron hydroxide using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were co-precipitated with iron hydroxide, and this precipitate was sent to chelating resin column. Ferric ions in the iron hydroxide were bonded to functional groups of the chelating resin directly, resulting in a pH increase of the effluent by release of hydroxide ion from the iron hydroxide. The co-precipitated thorium isotopes were quantitatively collected within the column, which indicated that thorium was retained on the iron hydroxide remaining on the chelating column. The chelating column quantitatively collected 232Th with iron hydroxide in seawater at flow rates of 20–25 mL min−1. Based on this flow rate, a 5 L sample was processed within 3–4 h. The >20 h aging of iron hydroxide tends to reduce the recovery of 232Th. The rapid collection method was successfully applied to the determination of 230Th and 232Th in open-ocean seawater samples. 相似文献
937.
Kouji Chiba Toshiyuki Hirano Fumitoshi Sato Masahiro Okamoto 《International journal of quantum chemistry》2013,113(21):2345-2354
This article reports the proton tautomerization effects of distal histidine residues in carbonmonoxy myoglobin according to the density functional calculations of the whole protein. The electron eigenstates and electrostatic potential (ESP) distributed around heme and its pocket vary significantly depending on the protonation positions of the distal histidine residues. To investigate the range over which the electronic structures are affected by the proton tautomerization, the quantum mechanics/molecular mechanics (QM/MM) method is applied to probe the QM size to reproduce the atomic partial charges and ESP around the active center. Consequently, we show that these properties converged for the 300 pm QM/MM system in this study. During the analysis, we also find that amino residues such as Phe43, Val68, and Phe138 interact strongly with heme through orbital mixing, indicating that the protein is a medium not only interacting with the reaction center, but also buffering on electrons. © 2013 Wiley Periodicals, Inc. 相似文献
938.
939.
Hideto Tsuji Hajime Kabashima Hideaki Kita Hideshi Hattori 《Reaction Kinetics and Catalysis Letters》1995,56(2):363-369
KF/alumina catalyst exhibits activity for double bond isomerization of 1-pentene at 273 K when pretreatedin vacuo in the temperature range 573–673 K, while the activity for Michael addition of nitromethane to butene-2-one does not change much with the pretreatment temperature. 相似文献
940.
We have developed a highly sensitive analytical technique for detecting the distribution of surfactants existing on a polymer surface. We studied the chemical modification of surfactants with the hydroxyl group by using amine-containing compounds in the gaseous phase at 23 °C; then, we performed measurements by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). We found that 4-(dimethylamino) phenyl isocyanate as a modification reagent is capable of modifying the hydroxyl group when 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) is used as a catalytic agent. We demonstrated this modification with stearyl alcohol on a polymer material surface. The signal sensitivity of stearyl alcohol after the modification increased considerably in comparison with that of the unmodified stearyl alcohol. Moreover, we confirmed that this modification method can be used for the distribution analysis of surfactants. The distribution conditions of traces of surfactants with the hydroxyl group can be observed clearly by using this modification method. 相似文献