全文获取类型
收费全文 | 14480篇 |
免费 | 2971篇 |
国内免费 | 2268篇 |
专业分类
化学 | 7809篇 |
晶体学 | 182篇 |
力学 | 1469篇 |
综合类 | 149篇 |
数学 | 1001篇 |
物理学 | 9109篇 |
出版年
2024年 | 26篇 |
2023年 | 137篇 |
2022年 | 420篇 |
2021年 | 498篇 |
2020年 | 556篇 |
2019年 | 466篇 |
2018年 | 464篇 |
2017年 | 599篇 |
2016年 | 683篇 |
2015年 | 528篇 |
2014年 | 818篇 |
2013年 | 1262篇 |
2012年 | 947篇 |
2011年 | 1017篇 |
2010年 | 863篇 |
2009年 | 966篇 |
2008年 | 1012篇 |
2007年 | 908篇 |
2006年 | 943篇 |
2005年 | 747篇 |
2004年 | 736篇 |
2003年 | 631篇 |
2002年 | 544篇 |
2001年 | 522篇 |
2000年 | 467篇 |
1999年 | 339篇 |
1998年 | 383篇 |
1997年 | 307篇 |
1996年 | 289篇 |
1995年 | 240篇 |
1994年 | 223篇 |
1993年 | 193篇 |
1992年 | 181篇 |
1991年 | 129篇 |
1990年 | 112篇 |
1989年 | 95篇 |
1988年 | 106篇 |
1987年 | 71篇 |
1986年 | 50篇 |
1985年 | 39篇 |
1984年 | 46篇 |
1983年 | 17篇 |
1982年 | 32篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 18篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
911.
Dr. Jonathan Baram Dr. Haim Weissman Dr. Yaron Tidhar Dr. Iddo Pinkas Prof. Boris Rybtchinski 《Angewandte Chemie (International ed. in English)》2014,53(16):4123-4126
In covalent polymerization, a single monomer can result in different polymer structures due to positional, geometric, or stereoisomerism. We demonstrate that strong hydrophobic interactions result in stable noncovalent polymer isomers that are based on the same covalent unit (amphiphilic perylene diimide). These isomers have different structures and electronic/photonic properties, and are stable in water, even upon prolonged heating at 100 °C. Such combination of covalent‐like stability together with structural/functional variation is unique for noncovalent polymers, substantially advancing their potential as functional materials. 相似文献
912.
Molecular Salt Effects in the Gas Phase: Tuning the Kinetic Basicity of [HCCLiCl]− and [HCCMgCl2]− by LiCl and MgCl2 下载免费PDF全文
Dr. George N. Khairallah Dr. Gabriel da Silva Prof. Richard A. J. O'Hair 《Angewandte Chemie (International ed. in English)》2014,53(41):10979-10983
A combination of gas‐phase ion–molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC?CLiCl]? reacts with water more rapidly than [HC?CMgCl2]?, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC?CLiCl]? or [HC?CMgCl2]? enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC?CMgCl2]? enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. 相似文献
913.
Bixue Xu Luca Unione Dr. Joao Sardinha Shaoping Wu Prof. Mélanie Ethève‐Quelquejeu Prof. Amelia Pilar Rauter Prof. Yves Blériot Dr. Yongmin Zhang Dr. Sonsoles Martín‐Santamaría Dr. Dolores Díaz Prof. Jesus Jiménez‐Barbero Prof. Matthieu Sollogoub 《Angewandte Chemie (International ed. in English)》2014,53(36):9597-9602
Molecular mimicry is an essential part of the development of drugs and molecular probes. In the chemical glycobiology field, although many glycomimetics have been developed in the past years, it has been considered that many failures in their use are related to the lack of the anomeric effects in these analogues. Additionally, the origin of the anomeric effects is still the subject of virulent scientific debates. Herein, by combining chemical synthesis, NMR methods, and theoretical calculations, we show that it is possible to restore the anomeric effect for an acetal when replacing one of the oxygen atoms by a CF2 group. This result provides key findings in chemical sciences. On the one hand, it strongly suggests the key relevance of the stereoelectronic component of the anomeric effect. On the other hand, the CF2 analogue adopts the natural glycoside conformation, which might provide new avenues for sugar‐based drug design. 相似文献
914.
A Carbene‐Rich but Carbonyl‐Poor [Ir6(IMe)8(CO)2H14]2+ Polyhydride Cluster as a Deactivation Product from Catalytic Glycerol Dehydrogenation 下载免费PDF全文
Jesús Campos Liam S. Sharninghausen Prof. Robert H. Crabtree Dr. David Balcells 《Angewandte Chemie (International ed. in English)》2014,53(47):12808-12811
The title cluster, a deactivation product in the catalytic dehydrogenation of glycerol, was characterized by XRD, DFT calculations, HRMS, FTIR spectroscopy, and NMR spectroscopy. Experimental/computational studies located the 14 H ligands, and all 1H and 13C{1H} NMR resonances were assigned. The structure contains an unprecedented Ir6H14 core with two CO and eight IMe ligands. 相似文献
915.
Inside Back Cover: Molecular Salt Effects in the Gas Phase: Tuning the Kinetic Basicity of [HCCLiCl]− and [HCCMgCl2]− by LiCl and MgCl2 (Angew. Chem. Int. Ed. 41/2014) 下载免费PDF全文
916.
Mechanically Adaptive and Shape‐Memory Behaviour of Chitosan‐Modified Cellulose Whisker/Elastomer Composites in Different pH Environments 下载免费PDF全文
Biomimetic polymer composites with water‐active mechanically adaptive and shape‐memory behaviour in different pH environments are synthesised by using chitosan‐modified cellulose whiskers (CS‐CWs) as the stimulus‐responsive phase and thermoplastic polyurethane (TPU) as the resilient matrix. The effect of surface modification on the mechanically adaptive behaviour of CS‐CW/TPU composites is investigated by using three representative solutions with various pH values. The results show that surface modification significantly enhances the modulus contrast under wet and dry conditions with the acidic solution as the stimulus, while maintaining the high modulus contrast with the basic solution as the stimulus. CS‐CW/TPU composites also exhibit excellent shape‐memory effects in all three solutions that are comparable to those pristine CW/TPU composites. Furthermore, activation of force generation in the stretched CS‐CW/TPU composites by water absorption/desorption was observed. 相似文献
917.
The stabilities of [M12Ag32(SR)30]4- (M = Ag, Au and SR = SPhF2, SPhCF3, SPhF) clusters having the same structure but different surface ligands or counter cations were systematically studied. It was clearly revealed that a subtle structural change in the surface ligands or counter cations could significantly alter the overall stability of [M12Ag32(SR)30]4 although they all had an electronic structure of 18-electron superatom shell closure. SPhF2 was found as a better surface ligand than SPhCF3 or SPhF to stabilize [M12Ag32(SR)30]4-. And the use of more bulky [(PPhj)2N]+ as the counter cations was revealed to be more deleterious to the overall stability of [M12Ag32(SR)30]4- clusters than PPh4+. [Au12Ag32(SR)30]4- was much more stable than [Ag44(SR)30]4 with the same surface ligands and counter cations. An exceptional stability was observed on (PPh4)4[Au12Ag32(SPhF2)30] which was stable in DMF for more than 8 days in air at 80 ℃. More research efforts are still needed to deeply understand why a small structural change could result in a significant change in the stability of noble metal nanoclusters. 相似文献
918.
甲烷是一种在自然界中大量存在的原材料,在取代原油和合成重要化工产品等许多领域具有潜在的应用价值. 然而,由于CH4中C-H键的键能特别大(约~4.5 eV),如何实现甲烷的绿色有效转化在化学化工领域仍然是一个挑战. 本文采用密度泛函理论对Co3O4(001)和(011)晶面活化甲烷C-H键的机理进行了理论研究,得到了如下结论:(1) CH4的C-H键在Co3O4晶面的解离具有很高的活性,只需要克服大约1 eV的能垒;(2)与Co2+相连的Co-O离子对是CH4活化的活性位点,其中两个带正负电荷的离子对C-H解离起着协同作用,帮助产生Co-CH3和O-H物种;(3)(011)面的反应活性明显大于(001)面,与实验的观察一致. 本文的计算结果表明,Co3O4纳米晶面对CH4中C-H键的活化表现出明显的晶面效应和结构敏感效应,Co-O离子对活性中心对于活化惰性的C-H键发挥了关键作用. 相似文献
919.
采用水热法合成了小粒径、具有介孔结构的SAPO-11分子筛.采用浸渍法制备了不同Ni负载量的Ni/SAPO-11催化剂.并采用X射线衍射,扫描电镜,N2物理吸附-脱附,NH3程序升温脱附,热重和H2化学吸附技术对该类催化剂的物理化学性质进行了详细表征.结果表明,SAPO-11较大表面积和介孔结构可分散Ni,使得Ni粒子尺寸较小.在棕榈油加氢脱氧制备液体烃类燃料反应中,液体烷烃产物由相关脂肪酸中间产物的直接加氢脱氧和脱羰-加氢脱氧两种途径产生.Ni/SAPO-11催化剂的弱/中强酸性质及其匹配的金属-酸双功能可显著抑制积炭反应,提高催化剂的寿命,液体烷烃收率高达70%,异构烷烃选择性超过80%. 相似文献
920.
Shotaro Hayashi Fumitaka Ishiwari Takanori Fukushima Shohei Mikage Yutaka Imamura Motomichi Tashiro Michio Katouda 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(37):16329-16335
Elastic organic crystals have attracted considerable attention as next-generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10-dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c-axes) of the crystal are contracted upon elongation along the long axis (a-axis). Moreover, we found that the Poisson's ratios along the b-axis and c-axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c-axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other. 相似文献