全文获取类型
收费全文 | 3452篇 |
免费 | 569篇 |
国内免费 | 366篇 |
专业分类
化学 | 2567篇 |
晶体学 | 41篇 |
力学 | 148篇 |
综合类 | 5篇 |
数学 | 346篇 |
物理学 | 1280篇 |
出版年
2024年 | 7篇 |
2023年 | 68篇 |
2022年 | 115篇 |
2021年 | 155篇 |
2020年 | 145篇 |
2019年 | 134篇 |
2018年 | 122篇 |
2017年 | 108篇 |
2016年 | 166篇 |
2015年 | 182篇 |
2014年 | 194篇 |
2013年 | 274篇 |
2012年 | 353篇 |
2011年 | 340篇 |
2010年 | 196篇 |
2009年 | 237篇 |
2008年 | 192篇 |
2007年 | 203篇 |
2006年 | 188篇 |
2005年 | 127篇 |
2004年 | 124篇 |
2003年 | 89篇 |
2002年 | 76篇 |
2001年 | 47篇 |
2000年 | 57篇 |
1999年 | 67篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 65篇 |
1995年 | 27篇 |
1994年 | 30篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4387条查询结果,搜索用时 15 毫秒
101.
Highly Enantioselective Ring‐Opening Reactions of Aziridines with Indole and Its Application in the Building of C3‐Halogenated Pyrroloindolines 下载免费PDF全文
Fengxia Han Dan Li Dr. Depeng Zhao Dr. Yiming Cao Yunxia Ma Weidong Kong Quantao Sun Prof. Dr. Rui Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16478-16483
A magnesium‐catalyzed asymmetric ring‐opening reaction of aziridine with indole has been realized by employing commercially available chiral ligands. Both of the enantiomers of the ring‐opening product could be obtained with good yields and a high level of enantioselectivity. The corresponding ring‐opening product could be further transformed to various types of enantioenriched C3‐halogenated‐pyrroloindolines. 相似文献
102.
Dr. Wangqing Kong Dr. Estíbaliz Merino Prof. Dr. Cristina Nevado 《Angewandte Chemie (International ed. in English)》2014,53(20):5078-5082
Two radical‐mediated processes of activated alkenes, namely arylphosphonylation and arylazidation, are described. The difunctionalization of alkenes by a tandem process that involves radical addition, 1,4‐aryl migration, and desulfonylation generates α‐aryl‐β‐heterofunctionalized amides bearing a quaternary stereocenter when the substituent on the nitrogen atom is an aryl group. Alternatively, heterooxindoles or spirobicycles can be obtained with excellent regioselectivity in the presence of an alkyl substituent on the nitrogen atom. 相似文献
103.
Yue Sun Dr. Tiandu Dong Dr. Chunxin Lu Weiwen Xin Linsen Yang Pei Liu Yongchao Qian Yuanyuan Zhao Dr. Xiang-Yu Kong Prof. Liping Wen Prof. Lei Jiang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(40):17576-17581
Osmotic energy, obtained through different concentrations of salt solutions, is recognized as a form of a sustainable energy source. In the past years, membranes derived from asymmetric aromatic compounds have attracted attention because of their low cost and high performance in osmotic energy conversion. The membrane formation process, charging state, functional groups, membrane thickness, and the ion-exchange capacity of the membrane could affect the power generation performance. Among asymmetric membranes, a bipolar membrane could largely promote the ion transport. Here, two polymers with the same poly(ether sulfone) main chain but opposite charges were synthesized to prepare bipolar membranes by a nonsolvent-induced phase separation (NIPS) and spin-coating (SC) method. The maximum power density of the bipolar membrane reaches about 6.2 W m−2 under a 50-fold salinity gradient, and this result can serve as a reference for the design of bipolar membranes for osmotic energy conversion systems. 相似文献
104.
Metal-reinforced sulfonic-acid-modified zirconia catalysts were successfully prepared and used to remove trace olefins from aromatics in a fixed-bed reactor. Catalysts were characterized by ICP-OES, N2 adsorption–desorption, X-ray diffraction, thermogravimetric analysis (TGA), and pyridine-FTIR spectroscopy. Different metals and calcination temperatures had great influence on the catalytic activity. Alumina-reinforced sulfated zirconia exhibited outstanding catalytic performance, stable regeneration activity, and giant surface area, and are promising in industrial catalysis. TGA showed that the decomposition of methyl could be attributed to Brønsted acid sites, and pyridine-FTIR spectroscopy proved the weak Brønsted sites on these synthesized metal-reinforced sulfated zirconia. Also, a relation between the reaction rate and weak Brønsted acid density is proposed. 相似文献
105.
Dr. Xi-Sha Zhang Yan-Ying Huang Jing Zhang Dr. Wei Meng Dr. Qian Peng Ruirui Kong Zhenwei Xiao Dr. Jie Liu Miaofei Huang Dr. Yuanping Yi Liangliang Chen Qingrui Fan Dr. Gaobo Lin Dr. Zitong Liu Dr. Guanxin Zhang Dr. Lang Jiang Prof. Dr. Deqing Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3557-3561
Polycyclic aromatic hydrocarbons with hexagons/pentagons or hexagons/heptagons have been intensively investigated in recent years, but those with simultaneous presence of hexagons, pentagons and heptagons remain rare. In this paper, we report dicyclohepta[ijkl,uvwx]rubicene ( DHR ), a non-benzenoid isomer of dibenzo[bc,kl]coronene with two pentagons and two heptagons. We developed an efficient and scalable synthetic method for DHR by using Scholl reaction and dehydrogenation. Crystal structure of DHR shows that the benzenoid rings, two pentagons and two heptagons are coplanar. The bond lengths analysis and the ICSS(1)zz and LOL-π calculations indicate that the incorporation of two formal azulene moieties has an effect on the conjugated structure. The π-electrons of benzenoid and pentagon rings are more delocalized. Cyclic voltammetry studies indicate that DHR shows multiple oxidation and reduction potentials. Interestingly, DHR exhibits unusual S0 to S2 absorption and abnormal anti-Kasha S2 to S0 emission. Moreover, crystals of DHR exhibit semiconducting behaviour with hole mobility up to 0.082 cm2 V−1 s−1. 相似文献
106.
Gerui Pei Dr. Pei Zhao Song Xu Xintian Zhao Prof. Chuncai Kong Prof. Zhimao Yang Prof. Masahiro Ehara Prof. Tao Yang 《ChemistryOpen》2020,9(11):1195-1201
The coordination of 10-electron diatomic ligands (BF, CO N2) to iron complexes Fe(CO)2(CNArTripp2)2 [ArTripp2=2,6-(2,4,6-(iso-propyl)3C6H2)2C6H3] have been realized in experiments very recently (Science, 2019 , 363, 1203–1205). Herein, the stability, electronic structures, and bonding properties of (E1E2)Fe-(CO)2(CNArTripp2)2 (E1E2=BF, CO, N2, CN−, NO+) were studied using density functional (DFT) calculations. The ground state of all those molecules is singlet and the calculated geometries are in excellent agreement with the experimental values. The natural bond orbital analysis revealed that Fe is negatively charged while E1 possesses positive charges. By employing the energy decomposition analysis, the bonding nature of the E2E1–Fe(CO)2(CNArTripp2)2 bond was disclosed to be the classic dative bond E2E1→Fe(CO)2(CNArTripp2)2 rather than the electron-sharing double bond. More interestingly, the bonding strength between BF and Fe(CO)2(CNArTripp2)2 is much stronger than that between CO (or N2) and Fe(CO)2(CNArTripp2)2, which is ascribed to the better σ-donation and π back-donations. However, the orbital interactions in CN−→Fe(CO)2(CNArTripp2)2 and NO+→Fe(CO)2(CNArTripp2)2 mainly come from σ-donation and π back-donation, respectively. The different contributions from σ donation and π donation for different ligands can be well explained by using the energy levels of E1E2 and Fe(CO)2(CNArTripp2)2 fragments. 相似文献
107.
Yan Meng Ziyin Kong James P. Morken 《Angewandte Chemie (International ed. in English)》2020,59(22):8456-8459
Chiral 1,2‐bimetallic reagents are useful motifs in synthetic chemistry. Although syn‐1,2‐bimetallic compounds can be prepared by alkene dimetallation, anti‐1,2‐bimetallics are still rare. The stereospecific 1,2‐metallate shift that occurs during conjunctive cross‐coupling is shown to enable a practical and modular approach to the catalytic synthesis of enantioenriched anti‐1,2‐borosilanes. In addition to reaction development, the synthetic utility of anti‐1,2‐borosilanes was investigated, including applications to the synthesis of anti‐1,2‐diols and anti‐1,2‐amino alcohols 相似文献
108.
Shijie Ding Lingyu Kong Yanjuan Jin Jinbao Lin Chao Chang Huaying Li Erqiang Liu Haitao Liu 《先进技术聚合物》2020,31(4):873-884
Fused deposition molding (FDM) is one of the most widely used three‐dimensional (3D) printing technologies. This paper explores the influence of the forming angle on the tensile properties of FDM specimens. Orthogonal layering details were studied through experiments, theory, and finite element simulations. The stiffness and strength of the specimens were analyzed using the classical laminated plate theory and the Tsai–Wu failure criterion. The experimental process was simulated using finite element simulations. Results show that it is feasible to predict the stiffness and strength of FDM specimens using classical laminated plate theory and the Tsai–Wu failure criterion. A molding angle of 45° leads to specimens with maximized tensile properties. Numerical simulations show that changing the molding angle changes the internal stress and deformation fields inside samples, leading to FDM samples with different mechanical properties due to the orthogonal layers at different molding angles. 相似文献
109.
A novel fluorinated chain extender, (1‐(ethyl(2‐hydroxyethyl)amino)‐3‐ ((3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl)oxy)propan‐2‐ol) (FPO), was synthesized and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and elemental analysis. Poly (ether urethane)s containing various amounts of the chain extender with fluorinated side chains (FPUs) were prepared by isophorone diisocyanate (IPDI), polytetra‐methylene‐ether‐glycol (PTMG), 3‐aminopropyltriethoxysilane (KH‐550), and 1,4‐butandiol (BDO). Films of FPUs were investigated by water absorption, contact angle, pencil hardness, adhesive force, and thermal analysis. Coating FPUs on micro‐nano concave‐convex structure plate realizes superhydrophobic performance. Scanning electron microscope (SEM) and atomic force microscopy (AFM) demonstrated that there is a lot of irregular concave‐convex structure, which forms a typical air cushion model. X‐ray photoelectron spectroscopy (XPS) analysis showed that surface fluorine content is 165% more than that of film average fluorine content. The superhydrophobic plate with 10% or higher F‐containing FPUs coating is of outstanding chemical corrosion resistance, excellent solvent resistance, and wear resistance. 相似文献
110.
A new type of catalyst for the hydrosilylation of unsaturated monomers with dichloromethylsilane (DCMS) was prepared, which consisted of thiolmethylene-substituted styrene–divinyl benzene copolymer and platinum. When using DCMS as a hydrosilylation agent, these catalysts showed a high activity in the hydrosilylation of vinyl and acetylene monomers as styrene, alkyl vinyl silanes, acetylene, phenyl acetylene, butyl acrylate. The activities of catalysts were not significantly reduced even after 20 reuse cycles. 相似文献