全文获取类型
收费全文 | 2726篇 |
免费 | 296篇 |
国内免费 | 169篇 |
学科分类
数理化 | 3191篇 |
出版年
2024年 | 15篇 |
2023年 | 107篇 |
2022年 | 204篇 |
2021年 | 164篇 |
2020年 | 172篇 |
2019年 | 176篇 |
2018年 | 162篇 |
2017年 | 121篇 |
2016年 | 187篇 |
2015年 | 181篇 |
2014年 | 195篇 |
2013年 | 244篇 |
2012年 | 269篇 |
2011年 | 256篇 |
2010年 | 164篇 |
2009年 | 128篇 |
2008年 | 134篇 |
2007年 | 109篇 |
2006年 | 63篇 |
2005年 | 37篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1986年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有3191条查询结果,搜索用时 0 毫秒
31.
An N-heterocyclic carbene(NHC)-catalyzed enantioselective Mannich reaction of the remote γ-carbon of cyclopropylcarbaldehydes is disclosed for the first time. Diastereo-and enantiomerically enriched multicyclic δ-lactam compound is afforded as the main product from 8 possible stereo-specific isomers through dynamic kinetic asymmetric transformation(DYKAT) processes. Multiple chiral functional molecules can be afforded from the lactam products through simple protocols with retentions of the optical purities. 相似文献
32.
33.
Ying Lv Bofeng Zhang Guobing Zou Xiaodong Yue Zhikang Xu Haiyan Li 《Entropy (Basel, Switzerland)》2022,24(7)
Domain adaptation aims to learn a classifier for a target domain task by using related labeled data from the source domain. Because source domain data and target domain task may be mismatched, there is an uncertainty of source domain data with respect to the target domain task. Ignoring the uncertainty may lead to models with unreliable and suboptimal classification results for the target domain task. However, most previous works focus on reducing the gap in data distribution between the source and target domains. They do not consider the uncertainty of source domain data about the target domain task and cannot apply the uncertainty to learn an adaptive classifier. Aimed at this problem, we revisit the domain adaptation from source domain data uncertainty based on evidence theory and thereby devise an adaptive classifier with the uncertainty measure. Based on evidence theory, we first design an evidence net to estimate the uncertainty of source domain data about the target domain task. Second, we design a general loss function with the uncertainty measure for the adaptive classifier and extend the loss function to support vector machine. Finally, numerical experiments on simulation datasets and real-world applications are given to comprehensively demonstrate the effectiveness of the adaptive classifier with the uncertainty measure. 相似文献
34.
A convenient and regioselective sulfonylation/cyclization of 1,6-enynes with arylazo sulfones has been developed to access a series of sulfonylated γ-butyrolactams.The present reaction could be efficiently conducted under catalyst-and additive-free conditions,in which C-S and C-C bonds were selectively constructed in one-pot procedure. 相似文献
35.
Xiuxiu Wang Zong-Chang Han Wei Wei Hanshi Hu Pengfei Li Peiqing Sun Xiangzhi Liu Zhijia Lv Feng Wang Yi Cao Zijian Guo Jun Li Jing Zhao 《Chemical science》2022,13(24):7269
Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins. Herein we report the formation and crystal structure of a planar square tetranuclear silver cluster when silver ions were mixed with human copper chaperone Atox1. Quantum chemical studies reveal that two Ag 5s1 electrons in the tetranuclear silver cluster fully occupy the one bonding molecular orbital, with the assumption that this Ag4 cluster is Ag42+, leading to extensive electron delocalization over the planar square and significant stabilization. This bonding pattern of the tetranuclear silver cluster represents an aromatic all-metal structure that follows a 4n + 2 electron counting rule (n = 0). This is the first time an all-metal aromatic silver cluster was observed in a protein.Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins. 相似文献
36.
Broadband Sheet Parametric Oscillator for x~((2)) Optical Frequency Comb Generation via Cavity Phase Matching 下载免费PDF全文
Xin Ni Kunpeng Jia Xiaohan Wang Huaying Liu Jian Guo Shu-Wei Huang Baicheng Yao Nicolò Sernicola Zhenlin Wang Xinjie Lv Gang Zhao Zhenda Xie Shi-Ning Zhu 《中国物理快报》2021,(6):37-49
We demonstrate a broadband optical parametric oscillation, using a sheet cavity, via cavity phase-matching. A21.2 THz broad comb-like spectrum is achieved, with a uniform line spacing of 133.0 GHz, despite a relatively large dispersion of 275.4 fs~2/mm around 1064 nm. With 22.6% high slope efficiency, and 14.9 kW peak power handling, this sheet optical parametric oscillator can be further developed for x~((2)) comb. 相似文献
37.
Dr. Naixia Lv Jie Yin Wendi Fu Jinrui Zhang Yujun Li Dr. Ding Jiang Dr. Hongping Li Prof. Wenshuai Zhu 《Chemphyschem》2021,22(2):168-177
The rational design of highly active hexagonal boron nitride (h-BN) catalysts at the atomic level is urgent for aerobic reactions. Herein, a doping impurity atom strategy is adopted to increase its catalytic activities. A series of doping systems involving O, C impurities and B, N antisites are constructed and their catalytic activities for molecular O2 have been studied by density functional theory (DFT) calculations. It is demonstrated that O2 is highly activated on ON and BN defects, and moderately activated on CB and CN defects, however, it is not stable on NB and OB defects. The subsequent application in oxidative desulfurization (ODS) reactions proves the ON and C-doped (CB, CN) systems to be good choice for sulfocompounds oxidization, especially for dibenzothiophene (DBT). While the BN antisite is not suitable for such aerobic reaction due to the extremely stable B−O*−B species formed during the oxidation process. 相似文献
38.
Lv Xinrong Wang Yanfang Wang Ying-ao Lin Xiaoyun Ni Yongnian 《Journal of Solid State Electrochemistry》2021,25(6):1871-1880
Journal of Solid State Electrochemistry - In this work, the binary nanocomposite of crosslinked polyaniline nanorods (CPANINRs) and molybdenum disulfide (MoS2) is first synthesized by in situ... 相似文献
39.
Ping Lv Xin Shen Zhiliyu Cui Bo Li Qiangqiang Xu Zhuo Yu Weijie Lu Haonan Shao Yan Ge Zhenhui Qi 《Journal of polymer science. Part A, Polymer chemistry》2021,59(23):3001-3008
Fiber-reinforced-concrete (FRC) mechanism refers short discrete fibers that are uniformly distributed and randomly oriented, which offers an effective way to improve the mechanical performance of concrete. In the design of supramolecular polymers, an analogous concept of FRC appears to have been considered very rarely-although fibrous structure has been frequently observed/generated during the supramolecular polymerization. In this work, we apply the alkane thermosets, octadecane (C18H38) and tetracosane (C24H50), taking the role of “concrete”, and the low-molecular-weight monomer with long alkyl chains as the essential “fiber” component, to fabricate the “fiber reinforced supramolecular polymer”. Very much like FRC mechanism in material science, the resulting fiber reinforced supramolecular polymer thus exhibit unusually high mechanical strength and stiffness, which is unprecedented in the conventional supramolecular strategy. 相似文献
40.
Wei Lv Chun Wang Xing-Chi Lin Xiao-Fei Mei Wen Wang E Yang Qi-Dan Ling Zheng-Huan Lin 《高分子科学》2021,39(9):1177-1184
Solid-stated smart polymers responsive to external stimuli have attracted much attention for potential application in the field of photoelectron devices, logic gates, sensor, data storage and security. However, it is a bigger challenge for polymers than that for small molecules in solid state to acquire stimuli-responsive properties, because polymers with high molecular weight are not as easy to change the packing structure as small molecules under external stimulation. Here, a D-A type alternat... 相似文献