全文获取类型
收费全文 | 2422篇 |
免费 | 331篇 |
国内免费 | 343篇 |
专业分类
化学 | 1857篇 |
晶体学 | 40篇 |
力学 | 90篇 |
综合类 | 57篇 |
数学 | 382篇 |
物理学 | 670篇 |
出版年
2023年 | 45篇 |
2022年 | 56篇 |
2021年 | 92篇 |
2020年 | 95篇 |
2019年 | 117篇 |
2018年 | 98篇 |
2017年 | 105篇 |
2016年 | 130篇 |
2015年 | 135篇 |
2014年 | 150篇 |
2013年 | 232篇 |
2012年 | 194篇 |
2011年 | 230篇 |
2010年 | 163篇 |
2009年 | 148篇 |
2008年 | 163篇 |
2007年 | 141篇 |
2006年 | 113篇 |
2005年 | 111篇 |
2004年 | 82篇 |
2003年 | 54篇 |
2002年 | 50篇 |
2001年 | 33篇 |
2000年 | 40篇 |
1999年 | 38篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 28篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有3096条查询结果,搜索用时 93 毫秒
941.
Liliang Wang Jian Xu Mitsuo Kira Liping Yan Xu‐Qiong Xiao Zhifang Li 《Angewandte Chemie (International ed. in English)》2020,59(5):1980-1984
A cyclic (R2SnAu)3 anion ( 3? , R2Sn=2,2,5,5‐tetrakis(trimethylsilyl)‐1‐stannacyclopentane‐1,1‐diyl) has been synthesized as a stable blue salt with K+(THF)6 through the reaction of stable dialkylstannylene 1 with R′3PAuCl (R′=Et, Ph) followed by the reduction with KC8. Crystallographic and NMR analysis shows that the six‐membered (SnAu)3 ring of 3? is planar and highly symmetric with an equal distance of six Au?Sn bonds. A UV/Vis spectrum of 3? in hexane reveals an intense absorption maximum at 598 nm. While cyclic Au3? with four valence electrons is known as unstable anti‐aromatic anion, 3? with three divalent tin ligands is stable σ aromatic anion with an unprecedented Möbius orbital array as predicted by the perturbation MO and CCSD analysis of 3? . 相似文献
942.
Jie Wei Huimin Wang Qiong Wu Xue Gong Kang Ma Xiaoqing Liu Fuan Wang 《Angewandte Chemie (International ed. in English)》2020,59(15):5965-5971
DNAzymes have been recognized as promising transducing agents for visualizing endogenous biomarkers, but their inefficient intracellular delivery and limited amplification capacity (including insufficient cofactor supply) preclude their extensive biological application. Herein, an autocatalytic DNAzyme (ACD) biocircuit is constructed for amplified microRNA imaging in vivo based on a hybridization chain reaction (HCR) and DNAzyme biocatalysis, sustained by a honeycomb MnO2 nanosponge (hMNS). The hMNS not only delivers DNA probes, but also supplies Mn2+ as a DNAzyme cofactor and magnetic resonance imaging (MRI) agent. Through the subsequent cross‐activation of HCR and DNAzyme amplicons, the ACD amplifies the limited signal resulting from miRNA recognition. The hMNS/ACD system was used to image microRNA in vivo, thus demonstrating its great promise in cancer diagnosis. 相似文献
943.
Vu T. Nguyen Viet D. Nguyen Graham C. Haug Ngan T. H. Vuong Hang T. Dang Hadi D. Arman Oleg V. Larionov 《Angewandte Chemie (International ed. in English)》2020,59(20):7921-7927
The development of efficient and selective C?N bond‐forming reactions from abundant feedstock chemicals remains a central theme in organic chemistry owing to the key roles of amines in synthesis, drug discovery, and materials science. Herein, we present a dual catalytic system for the N‐alkylation of diverse aromatic carbocyclic and heterocyclic amines directly with carboxylic acids, by‐passing their preactivation as redox‐active esters. The reaction, which is enabled by visible‐light‐driven, acridine‐catalyzed decarboxylation, provides access to N‐alkylated secondary and tertiary anilines and N‐heterocycles. Additional examples, including double alkylation, the installation of metabolically robust deuterated methyl groups, and tandem ring formation, further demonstrate the potential of the direct decarboxylative alkylation (DDA) reaction. 相似文献
944.
Jing Yang Ran Wang Lin Huang Mengji Zhang Jingyang Niu Chunde Bao Nan Shen Min Dai Qiang Guo Qian Wang Qin Wang Qiong Fu Kun Qian 《Angewandte Chemie (International ed. in English)》2020,59(4):1703-1710
Metabolic fingerprints of biofluids encode diverse diseases and particularly urine detection offers complete non‐invasiveness for diagnostics of the future. Present urine detection affords unsatisfactory performance and requires advanced materials to extract molecular information, due to the limited biomarkers and high sample complexity. Herein, we report plasmonic polymer@Ag for laser desorption/ionization mass spectrometry (LDI‐MS) and sparse‐learning‐based metabolic diagnosis of kidney diseases. Using only 1 μL of urine without enrichment or purification, polymer@Ag afforded urine metabolic fingerprints (UMFs) by LDI‐MS in seconds. Analysis by sparse learning discriminated lupus nephritis from various other non‐lupus nephropathies and controls. We combined UMFs with urine protein levels (UPLs) and constructed a new diagnostic model to characterize subtypes of kidney diseases. Our work guides urine‐based diagnosis and leads to new personalized analytical tools for other diseases. 相似文献
945.
Jeishla L. M. Matos Samantha A. Green Yuge Chun Vuong Q. Dang Russell G. Dushin Paul Richardson Jason S. Chen David W. Piotrowski Brian M. Paegel Ryan A. Shenvi 《Angewandte Chemie (International ed. in English)》2020,59(31):12998-13003
Preparative reactions that occur efficiently under dilute, buffered, aqueous conditions in the presence of biomolecules find application in ligation, peptide synthesis, and polynucleotide synthesis and sequencing. However, the identification of functional groups or reagents that are mutually reactive with one another, but unreactive with biopolymers and water, is challenging. Shown here are cobalt catalysts that react with alkenes under dilute, aqueous, buffered conditions and promote efficient cycloisomerization and formal Friedel–Crafts reactions. The constraining conditions of bioorthogonal chemistry are beneficial for reaction efficiency as superior conversion at low catalyst concentration is obtained and competent rates in dilute conditions are maintained. Efficiency at high dilution in the presence of buffer and nucleobases suggests that these reaction conditions may find broad application. 相似文献
946.
Nguyen Tien Cong Huynh Thi Xuan Trang Pham Duc Dung Tran Hoang Phuong Vu Quoc Trung Nguyen Dang Dat Dang Thi Tuyet Anh Nguyen Van Tuyen Luc Van Meervelt 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(9):874-882
Five 2‐aroyl‐5‐bromobenzo[b]furan‐3‐ol compounds (two of which are new) and four new 2‐aroyl‐5‐iodobenzo[b]furan‐3‐ol compounds were synthesized starting from salicylic acid. The compounds were characterized by mass spectrometry and 1H NMR and 13C NMR spectroscopy. Single‐crystal X‐ray diffraction studies of four compounds, namely, (5‐bromo‐3‐hydroxybenzofuran‐2‐yl)(4‐fluorophenyl)methanone, C15H8BrFO3, (5‐bromo‐3‐hydroxybenzofuran‐2‐yl)(4‐chlorophenyl)methanone, C15H8BrClO3, (5‐bromo‐3‐hydroxybenzofuran‐2‐yl)(4‐bromophenyl)methanone, C15H8Br2O3, and (4‐bromophenyl)(3‐hydroxy‐5‐iodobenzofuran‐2‐yl)methanone, C15H8BrIO3, were also carried out. The compounds were tested for their in vitro cytotoxicity on the four human cancer cell lines KB, Hep‐G2, Lu‐1 and MCF7. Six compounds show good inhibiting abilities on Hep‐G2 cells, with IC50 values of 1.39–8.03 µM. 相似文献
947.
Dang Ngoc Quang Chung Thanh Pham Linh Thi Khanh Le Quynh Ngoc Ta Ngoc Kim Dang Nhung Thi Hoang 《Natural product research》2020,34(4):585-589
AbstractPhytochemical study on the extract of Vietnamese medicinal plant Helicteres hirsuta Lour. has led to the isolation and structural elucidation of twelve secondary metabolites, 3-O-trans-caffeoylbetulinic acid (1), 3β-benzoylbetulinic acid (2), betulinic acid methyl ester (3), betulinic acid (4), lupeol (5), 4-hydroxybenzoic acid (6), 3,4-dihydroxybenzoic acid methyl ester (7), 4-hydroxy-3,5-dimethoxybenzoic acid (8), 5,8-dihydroxy-7,4′-dimethoxyflavone (9), isoscutellarein 4’-methyl ether 8-O-β-D-glucopyranoside (10), methyl caffeate (11) and stigmasterol (12). Especially, compound 2 was reported as a new natural product. Their structures were elucidated by a combination of 2D NMR and ESI-FT-ICR-MS spectroscopies. Furthermore, eight compounds were tested for their cytotoxicity against five cancer cell lines (Hela, HepG2, SK-LU-1, AGS and SK-MEL-2). The results showed that compounds (1, 3-5, 9) have moderate activities. This is the first study on the chemical constituents and their cytotoxicity of the Vietnamese Helicteres hirsuta L. 相似文献
948.
Phorate, an extremely hazardous organophosphorus insecticide, is still widely used in many countries and territories currently. It may be released in the atmosphere where it can undergo transport and chemical transformations. In this study, the reaction mechanism for the OH-initiated atmospheric oxidation of phorate was investigated. The geometrical parameters and vibrational frequencies of all the stationary points were calculated at the MPWB1K level with the 6-31G(d,p) basis set. Single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level. Canonical variational transition-state theory with small curvature tunneling contribution was used to calculate the rate constants over the temperature range of 200–370 K. The Arrhenius formulas were fitted. The results indicate that the channel of the formation of phorate oxon resulting from OH addition to phorate, and H abstractions from the –CH2– portion of the –CH2CH3 group in phorate are energetically favorable. The main degradation products include phorate oxon, SO2. 相似文献
949.
Unravelling the Structure of Electrocatalytically Active Fe–N Complexes in Carbon for the Oxygen Reduction Reaction 下载免费PDF全文
Yansong Zhu Bingsen Zhang Xin Liu Da‐Wei Wang Prof. Dang Sheng Su 《Angewandte Chemie (International ed. in English)》2014,53(40):10673-10677
Non‐precious Fe/N co‐modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron‐free N‐doped carbon electrocatalysts, Fe/N‐modified electrocatalysts show four‐electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe–N complexes, however, the Fe–N structure remains unknown. We used o,m,p‐phenylenediamine as nitrogen precursors to tailor the Fe–N structures in heterogeneous electrocatalysts which contain FeS and Fe3C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half‐wave potential. By combining advanced electron microscopy and Mössbauer spectroscopy, we have identified the electrocatalytically active Fe–N6 complexes (FeN6, [FeIII(porphyrin)(pyridine)2]). We expect the understanding of the FeN6 structure will pave the way towards new advanced Fe–N based electrocatalysts. 相似文献
950.
Back Cover: Visualizing an Ultra‐Weak Protein–Protein Interaction in Phosphorylation Signaling (Angew. Chem. Int. Ed. 43/2014) 下载免费PDF全文
Qiong Xing Peng Huang Ju Yang Jian‐Qiang Sun Dr. Zhou Gong Dr. Xu Dong Dr. Da‐Chuan Guo Shao‐Min Chen Yu‐Hong Yang Yan Wang Prof. Ming‐Hui Yang Dr. Ming Yi Prof. Yi‐Ming Ding Prof. Mai‐Li Liu Prof. Wei‐Ping Zhang Prof. Chun Tang 《Angewandte Chemie (International ed. in English)》2014,53(43):11666-11666