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101.
[reaction: see text] Spirocyclic C-arylribosides were synthesized from the known gamma-ribonolactone derivative. Lithium acetylide addition followed by glycosylation with 3-(trimethylsilyl)propargyl alcohol converted the ribonolactone to silylated diynes. After desilylation or iodination, subsequent ruthenium-catalyzed cycloaddition of resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C-arylribosides. 相似文献
102.
Masaya Kobayashi Takeo Tomita Kazuo Shin‐ya Makoto Nishiyama Tomohisa Kuzuyama 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13483-13487
Carquinostatin A (CQS), a potent neuroprotective substance, is a unique carbazole alkaloid with both an ortho‐quinone function and an isoprenoid moiety. We identified the entire gene cluster responsible for CQS biosynthesis in Streptomyces exfoliatus through heterologous production of CQS and gene deletion. Biochemical characterization of seven CQS biosynthetic gene products (CqsB1–7) established the total biosynthetic pathway of CQS. Reconstitution of CqsB1 and CqsB2 showed that the synthesis of the carbazole skeleton involves CqsB1‐catalyzed decarboxylative condensation of an α‐hydroxyl‐β‐keto acid intermediate with 3‐hydroxybutyryl‐ACP followed by CqsB2‐catalyzed oxidative cyclization. Based on crystal structures and mutagenesis‐based biochemical assays, a detailed mechanism for the unique deprotonation‐initiated cyclization catalyzed by CqsB2 is proposed. Finally, analysis of the substrate specificity of the biosynthetic enzymes led to the production of novel carbazoles. 相似文献
103.
Keiichi Murai Lukas Lauterbach Kazuya Teramoto Zhiyang Quan Lena Barra Tsuyoshi Yamamoto Kenichi Nonaka Kazuro Shiomi Makoto Nishiyama Tomohisa Kuzuyama Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2019,58(42):15046-15050
The skeletons of some classes of terpenoids are unusual in that they contain a larger number of Me groups (or their biosynthetic equivalents such as olefinic methylene groups, hydroxymethyl groups, aldehydes, or carboxylic acids and their derivatives) than provided by their oligoprenyl diphosphate precursor. This is sometimes the result of an oxidative ring‐opening reaction at a terpene‐cyclase‐derived molecule containing the regular number of Me group equivalents, as observed for picrotoxan sesquiterpenes. In this study a sesquiterpene cyclase from Trichoderma spp. is described that can convert farnesyl diphosphate (FPP) directly via a remarkable skeletal rearrangement into trichobrasilenol, a new brasilane sesquiterpene with one additional Me group equivalent compared to FPP. A mechanistic hypothesis for the formation of the brasilane skeleton is supported by extensive isotopic labelling studies. 相似文献
104.
105.
AbstractWe fabricated aggregates of cholesteric cylinders coexisting with the isotropic phase and investigated their dynamics under a temperature gradient. Each constituent cylinder possessed the double-twist (DT) structure, and when a heat flux was applied, the whole aggregates rotated as a rigid-body without changing the DT orientation. The angular velocity was proportional to the heat flux and the rotational direction was determined by the molecular chirality and the flux direction. The result suggests that the rigid-body rotation was driven by the thermomechanical cross-correlation in chiral LCs. We also succeeded in switching the rotation by changing the illumination onto the sample. 相似文献
106.
Stereoselective synthesis of triply isotope-labeled Ser, Cys, and Ala: amino acids for stereoarray isotope labeling technology 总被引:1,自引:0,他引:1
Efficient access to highly enantioselective isotope-labeled serine, cysteine, and alanine for stereoarray isotope labeling (SAIL) is described. 相似文献
107.
Analysis of Cu segregation to oxide–metal interface of Ni‐based alloy in a metal‐dusting environment
Takashi Doi Kazuyuki Kitamura Yoshitaka Nishiyama Nobuo Otsuka Takeo Kudo Masugu Sato Eiji Ikenaga Shigenori Ueda Keisuke Kobayashi 《Surface and interface analysis : SIA》2008,40(10):1374-1381
Hard X‐ray photoelectron spectroscopy (HX‐PES) has been realized using high‐brilliance synchrotron radiation. High‐energy photon excitation enables us to probe photoelectrons with larger escape depth compared to conventional PES. This allows us to conduct, without destruction, a study of the embedded interface of materials as the oxide‐ metal interface. We apply HX‐PES to investigate for Cu segregation in the oxide–metal interface during metal‐dusting corrosion. The effective concentration of Cu in the segregation was estimated a few times higher than the bulk concentration. These results on the interface layer can explain the variation in the corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
108.
K. Tanoi H. Matsue H. Iikura T. Saito Y. Hayashi Y. Hamada H. Nishiyama N. I. Kobayashi T. M. Nakanishi 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(2):375-379
We carried out instrumental neutron activation analysis (INAA) as well as k
0-based prompt gamma-ray analysis (k
0-PGA) to measure the amount of the elements in onions and studied whether the onions collected from different sites can be
categorized based on the elemental concentration profile. Six elements (Na, Mg, Cl, K, Ca, Mn) and 3 elements (B, S, Cl) were
measured by INAA and PGA in the onions grown in two districts, Hokkaido and Saga, in Japan, respectively. After principal
component analysis, it was found that Cl was an important element to feature the producing districts of onions. 相似文献
109.
Dr. Ziqian Xue Dr. Jia-Jia Zheng Dr. Yusuke Nishiyama Dr. Ming-Shui Yao Dr. Yoshitaka Aoyama Zeyu Fan Dr. Ping Wang Prof. Takashi Kajiwara Prof. Yoshiki Kubota Prof. Satoshi Horike Prof. Ken-ichi Otake Prof. Susumu Kitagawa 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(2):e202215234
Exploring new porous coordination polymers (PCPs) that have tunable structure and conductivity is attractive but remains challenging. Herein, fine pore structure engineering by ligand conformation control of naphthalene diimide (NDI)-based semiconducting PCPs with π stacking-dependent conductivity tunability is achieved. The π stacking distances and ligand conformation in these isoreticular PCPs were modulated by employing metal centers with different coordination geometries. As a result, three conjugated PCPs (Co−pyNDI, Ni−pyNDI, and Zn−pyNDI) with varying pore structure and conductivity were obtained. Their crystal structures were determined by three-dimensional electron diffraction. The through-space charge transfer and tunable pore structure in these PCPs result in modulated selectivity and sensitivity in gas sensing. Zn−pyNDI can serve as a room-temperature operable chemiresistive sensor selective to acetone. 相似文献
110.
Siquan Zhang Loris Lombardo Masahiko Tsujimoto Zeyu Fan Ellan K. Berdichevsky Yong-Sheng Wei Kotoha Kageyama Yusuke Nishiyama Satoshi Horike 《Angewandte Chemie (International ed. in English)》2023,62(47):e202312095
Crystalline triazine-based covalent organic frameworks (COFs) are aromatic nitrogen-rich porous materials. COFs typically show high thermal/chemical stability, and are promising for energy applications, but often require harsh synthesis conditions and suffer from low crystallinity. In this work, we propose an environmentally friendly route for the synthesis of crystalline COFs from CO2 molecules as a precursor. The mass ratio of CO2 conversion into COFs formula unit reaches 46.3 %. The synthesis consists of two steps; preparation of 1,4-piperazinedicarboxaldehyde from CO2 and piperazine, and condensation of the dicarboxaldehyde and melamine to construct the framework. The CO2-derived COF has a 3-fold interpenetrated structure of 2D layers determined by powder X-ray diffraction, high-resolution transmission electron microscopy, and select-area electron diffraction. The structure shows a high Brunauer–Emmett–Teller surface area of 945 m2 g−1 and high stability against strong acid (6 M HCl), base (6 M NaOH), and boiling water over 24 hours. Post-modification of the framework with oxone has been demonstrated to modulate hydrophilicity, and it exhibits proton conductivity of 2.5×10−2 S cm−1 at 85 °C, 95 % of relative humidity. 相似文献