全文获取类型
收费全文 | 193865篇 |
免费 | 3025篇 |
国内免费 | 442篇 |
专业分类
化学 | 107572篇 |
晶体学 | 2668篇 |
力学 | 7004篇 |
综合类 | 3篇 |
数学 | 21816篇 |
物理学 | 58269篇 |
出版年
2021年 | 1450篇 |
2020年 | 1818篇 |
2019年 | 1737篇 |
2018年 | 2261篇 |
2017年 | 2284篇 |
2016年 | 3818篇 |
2015年 | 2693篇 |
2014年 | 3593篇 |
2013年 | 8611篇 |
2012年 | 6991篇 |
2011年 | 8450篇 |
2010年 | 5663篇 |
2009年 | 5460篇 |
2008年 | 8015篇 |
2007年 | 7689篇 |
2006年 | 7394篇 |
2005年 | 6673篇 |
2004年 | 5868篇 |
2003年 | 5284篇 |
2002年 | 5135篇 |
2001年 | 6356篇 |
2000年 | 4747篇 |
1999年 | 3648篇 |
1998年 | 2629篇 |
1997年 | 2688篇 |
1996年 | 2702篇 |
1995年 | 2444篇 |
1994年 | 2479篇 |
1993年 | 2382篇 |
1992年 | 2767篇 |
1991年 | 2717篇 |
1990年 | 2585篇 |
1989年 | 2502篇 |
1988年 | 2460篇 |
1987年 | 2477篇 |
1986年 | 2255篇 |
1985年 | 2909篇 |
1984年 | 2909篇 |
1983年 | 2392篇 |
1982年 | 2399篇 |
1981年 | 2258篇 |
1980年 | 2193篇 |
1979年 | 2453篇 |
1978年 | 2567篇 |
1977年 | 2483篇 |
1976年 | 2393篇 |
1975年 | 2242篇 |
1974年 | 2198篇 |
1973年 | 2245篇 |
1972年 | 1424篇 |
排序方式: 共有10000条查询结果,搜索用时 930 毫秒
81.
82.
Lotfi Boudjema Dr. Jérôme Long Dr. Fabrice Salles Prof. Joulia Larionova Dr. Yannick Guari Prof. Philippe Trens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(2):479-484
Porous coordination polymers are molecule-based materials presenting a high degree of tunability, which offer many advantages for targeted applications over conventional inorganic materials. This work demonstrates that the hydrophilic/hydrophobic character of Prussian blue analogues having a lipophilic feature may be tuned to optimize the gas adsorption properties. The role of the coordinatively unsaturated metal sites is emphasized through a combination of theoretical and experimental study of water, ethanol, and n-hexane adsorption. 相似文献
83.
Peter T. Smith Younghoon Kim Dr. Bahiru Punja Benke Prof. Kimoon Kim Prof. Christopher J. Chang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(12):4932-4937
We report a supramolecular strategy for promoting the selective reduction of O2 for direct electrosynthesis of H2O2. We utilized cobalt tetraphenylporphyrin (Co-TPP), an oxygen reduction reaction (ORR) catalyst with highly variable product selectivity, as a building block to assemble the permanently porous supramolecular cage Co-PB-1(6) bearing six Co-TPP subunits connected through twenty-four imine bonds. Reduction of these imine linkers to amines yields the more flexible cage Co-rPB-1(6). Both Co-PB-1(6) and Co-rPB-1(6) cages produce 90–100 % H2O2 from electrochemical ORR catalysis in neutral pH water, whereas the Co-TPP monomer gives a 50 % mixture of H2O2 and H2O. Bimolecular pathways have been implicated in facilitating H2O formation, therefore, we attribute this high H2O2 selectivity to site isolation of the discrete molecular units in each supramolecule. The ability to control reaction selectivity in supramolecular structures beyond traditional host–guest interactions offers new opportunities for designing such architectures for a broader range of catalytic applications. 相似文献
84.
Daniel Heinz Annette Meister Hazrat Hussain Karsten Busse Jörg Kressler 《Journal of polymer science. Part A, Polymer chemistry》2020,58(23):3322-3335
Adding perfluoroalkyl (PF) segments to amphiphilic copolymers yields triphilic copolymers with new application profiles. Usually, PF segments are attached as terminal blocks via Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC). The purpose of the current study is to design new triphilic architectures with a PF segment in central position. The PF segment bearing bifunctional atom transfer radical polymerization (ATRP) initiator is employed for the fabrication of triphilic poly(propylene oxide)-b-poly(glycerol monomethacrylate)-b-PF-b-poly(glycerol monomethacrylate)-b-poly(propylene oxide) PPO-b-PGMA-b-PF-b-PGMA-b-PPO pentablock copolymers by a combined ATRP and CuAAC reaction approach. Differential scanning calorimetry indicates the PF-initiator to undergo a solid–solid phase transition at 63°C before the final crystal melting at 95°C. This is further corroborated by polarized optical microscopy and X-ray diffraction studies. The PF-initiator could successfully polymerize solketal methacrylate (SMA) under typical ATRP conditions producing well-defined Br-PSMA-b-PF-b-PSMA-Br triblock copolymers that are then converted into PPO-b-PSMA-b-PF-b-PSMA-b-PPO pentablock copolymer via CuAAC reaction. Subsequently, acid hydrolysis of the PSMA blocks afforded water soluble well-defined triphilic pentablock copolymers PPO-b-PGMA-b-PF-b-PGMA-b-PPO with fluorophilic central segment, hydrophilic middle blocks, and lipophilic outer blocks. The triphilic block copolymers could self-assemble, depending upon the preparatory protocol, into spherical and filament-like phase-separated nanostructures as revealed by transmission electron microscopy. 相似文献
85.
Mathematical Notes - An algorithm is presented which determines in a finite number of steps whether an initial finite binary automaton is spherically transitive. Since the class of deterministic... 相似文献
86.
Markus Bödenler Ludovic de Rochefort P. James Ross Nicolas Chanet Geneviève Guillot Gareth R. Davies 《Molecular physics》2019,117(7-8):832-848
ABSTRACTFast field-cycling (FFC) nuclear magnetic resonance relaxometry is a well-established method to determine the relaxation rates as a function of magnetic field strength. This so-called nuclear magnetic relaxation dispersion gives insight into the underlying molecular dynamics of a wide range of complex systems and has gained interest especially in the characterisation of biological tissues and diseases. The combination of FFC techniques with magnetic resonance imaging (MRI) offers a high potential for new types of image contrast more specific to pathological molecular dynamics. This article reviews the progress in FFC-MRI over the last decade and gives an overview of the hardware systems currently in operation. We discuss limitations and error correction strategies specific to FFC-MRI such as field stability and homogeneity, signal-to-noise ratio, eddy currents and acquisition time. We also report potential applications with impact in biology and medicine. Finally, we discuss the challenges and future applications in transferring the underlying molecular dynamics into novel types of image contrast by exploiting the dispersive properties of biological tissue or MRI contrast agents. 相似文献
87.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
88.
89.
Lebedev V. T. Serebrov A. P. 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2020,14(1):1-5
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques - A method for studying the magnetic dynamics of endofullerenes M@C2n (2n = 60, 70, …) and their derivatives,... 相似文献
90.