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排序方式: 共有805条查询结果,搜索用时 234 毫秒
801.
Jiao Zhao Dr. Menglin Wang Yu Peng Jie Ni Sunpei Hu Prof. Dr. Jie Zeng Prof. Dr. Qianjin Chen 《Angewandte Chemie (International ed. in English)》2023,62(30):e202304424
Tuning the surface strain of heterogeneous catalysts is recognized as a powerful strategy for tailoring their catalytic activity. However, a clear understanding of the strain effect in electrocatalysis at single-particle resolution is still lacking. Here, we explore the electrochemical hydrogen evolution reaction (HER) of single Pd octahedra and icosahedra with the same surface bounded {111} crystal facet and similar sizes using scanning electrochemical cell microscopy (SECCM). It is revealed that tensilely strained Pd icosahedra display significantly superior HER electrocatalytic activity. The estimated turnover frequency at −0.87 V vs RHE on Pd icosahedra is about two times higher than that on Pd octahedra. Our single-particle electrochemistry study using SECCM at Pd nanocrystals unambiguously highlights the importance of tensile strain on electrocatalytic activity and may offer new strategy for understanding the fundamental relationship between surface strain and reactivity. 相似文献
802.
Photocatalytic C−C Cleavage of Methylenecyclobutanes for γ,δ-Unsaturated Aldehydes by Strain Release
Prof. Dr. Yan Zhang Chunhang Zhao Chanchan Ma Zhenzhi Cai Sven Trienes Prof. Dr. Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2023,62(22):e202300166
Radical additions onto olefins have surfaced as an increasingly powerful strategy for the synthesis of difunctionalized scaffolds. However, despite of major advances, known approaches continue to be largely limited to two manifolds, namely 1,2-difunctionalization of alkenes and remote difunctionalization via hydrogen atom transfer (HAT). Herein, we describe a mechanistically distinct approach by photoinduced carbon-carbon (C−C) activation/ring-opening to access γ,δ-unsaturated aldehydes from methylenecyclobutanols and sulfonyl chlorides by strain release. Remarkably, the sulfonyl motif on the products was easily removed by another photocatalytic process, which enabled the concise assembly of the natural product alatanone A. The synthetic utility of our approach was reflected by versatile functional group tolerance, ample substrate scope, and scalability. The photocatalysis represents a conceptually distinct alternative to existing approaches for remote 1,4-diversifications, with a double bond remaining in the thus obtained products. 相似文献
803.
According to the structural connection form of cord reinforced rubber composite,structural test samples with different lapping process parameters were designed and prepared. The dynamic and static tensile properties were studied by using two-dimensional digital image technology. The test results were as follows:The stiffness and tensile strength of double lap composites joints increased as the strain rate increasing,while the elongation at break unchanged. Compared with the no-lap samples,the tensile strength of the double lap composites sample was reduced by nearly 50%,and with the increase of the lap width,the elongation at break gradually decreased. The samples with lap width of 65 mm decreased by 24% compared with the no-lap ones. Compared with the elastic modulus of stage II,the elastic modulus of stage III increased significantly,that of the no-lap samples increased by 3 times,that of the lap samples were doubled,and the amplification of elastic modulus decreased with the increase of strain rate. © 2023, Youke Publishing Co.,Ltd. All rights reserved. 相似文献
804.
Vandana Jaiswal Soumik Mondal Bandana Singh Prof. Vinod. P. Singh Prof. Dr. Jaideep Saha 《Angewandte Chemie (International ed. in English)》2023,62(30):e202304471
Access to 1,3-functionalized azetidines through a diversity-oriented approach is highly sought-after for finding new applications in drug-discovery. To this goal, strain-release-driven functionalization of azabicyclo[1.1.0]-butane (ABB) has generated significant interest. Through appropriate N-activation, C3-substituted ABBs are shown to render tandem N/C3-fucntionalization/rearrangement, furnishing azetidines; although, modalities of such N-activation vis-à-vis N-functionalization remain limited to selected electrophiles. This work showcases a versatile cation-driven activation strategy of ABBs. And capitalizes on the use of Csp3 precursors amenable to forming reactive (aza)oxyallyl cations in situ. Herein, N-activation leads to formation of a congested C−N bond, and effective C3 activation. The concept was extended to formal [3+2] annulations involving (aza)oxyallyl cations and ABBs, leading to bridged bicyclic azetidines. Besides the fundamental appeal of this new activation paradigm, operational simplicity and remarkable diversity should engender its prompt use in synthetic and medicinal chemistry. 相似文献
805.
利用基于密度泛函理论的第一性原理计算方法, 研究了应变和C原子掺杂对单层BN纳米片的电子结构和磁学性质的影响. 计算结果表明未掺杂的单层BN纳米片具有宽的直接带隙, 在压缩和拉伸应变的作用下, 带隙会分别增大和减小, 但应变对带隙的调制整体效果不太明显. 单个C原子掺入BN纳米片的态密度揭示体系呈现出半金属性(Half-metallicity), 磁矩主要源于C 2p态, 而B 2p和N 2p态在极化作用下也能提供部分磁矩. 两个C原子掺入BN纳米片时, 磁性基态会随着C原子的间距发生变化: 当两C原子为最近邻(nn)和次近邻(nnn)时, 反铁磁态为磁性基态; 而当两C原子为次次近邻(nnnn)时, 铁磁态为基态, 并且其态密度也显示出半金属性. 相似文献