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21.
Regioselectivity and stereoselectivity of nucleophilic addition to glycal and imino‐glycal vinyl epoxides and their carba analogs: a rationalization based on HSAB theory and MEP 下载免费PDF全文
22.
Access to the Aeruginosin Serine Protease Inhibitors through the Nucleophilic Opening of an Oxabicyclo[2.2.1]heptane: Total Synthesis of Microcin SF608 下载免费PDF全文
Stefan Diethelm Corinna S. Schindler Prof. Dr. Erick M. Carreira 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):6071-6080
Serine proteases play key roles in many biological processes and are associated with several human diseases such as thrombosis or cancer. During the search for selective inhibitors of serine proteases, a family of linear peptides named the aeruginosins was discovered in marine cyanobacteria. We herein report an entry route into the synthetically challenging core fragment of these natural products. Starting from the common oxabicyclic building block 11 , we accessed the octahydroindole core of the aeruginosins, exemplified by the total synthesis of microcin SF608 ( 2 ). Key to the synthetic strategy is a highly efficient nucleophilic opening of an oxabicyclo[2.2.1]heptane producing the hydroindole motif of microcin SF608. Moreover, during the synthetic efforts we have observed an unusual regioselective epoxide reduction. Detailed experimental studies of this reaction led us to propose a mechanistic rationale involving intramolecular hydrogen atom delivery by a carbamate NH group to control the regioselectivity of the homolytic epoxide cleavage. 相似文献
23.
Development of a Halide‐Free Aluminium‐Based Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide 下载免费PDF全文
Dr. Jose A. Castro‐Osma Prof. Michael North Dr. Xiao Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):15005-15008
Kinetic studies of the synthesis of glycerol carbonate from glycidol and carbon dioxide have been carried out. These showed that under suitable reaction conditions, bimetallic aluminium(salen) complex 4 is able to catalyse the conversion of epoxides into the corresponding cyclic carbonates without the need for a co‐catalyst. 相似文献
24.
Helen R. Thomas Alexander J. Marsden Dr. Marc Walker Dr. Neil R. Wilson Dr. Jonathan P. Rourke 《Angewandte Chemie (International ed. in English)》2014,53(29):7613-7618
The treatment of graphene oxide (GO) with potassium thioacetate followed by an aqueous work‐up yields a new material via the ring‐opening of the epoxide groups. The new material is a thiol‐functionalized GO (GO‐SH) which is able to undergo further functionalization. Reaction with butyl bromide gives another new material, GO‐SBu, which shows significantly enhanced thermal stability compared to both GO and GO‐SH. The thiol‐functionalized GO material showed a high affinity for gold, as demonstrated by the selective deposition of a high density of gold nanoparticles. 相似文献
25.
Caleb R. Schlachter Andrea OMalley Linda L. Grimes John J. Tomashek Maksymilian Chruszcz L. Andrew Lee 《Molecules (Basel, Switzerland)》2022,27(1)
Sulfatases are ubiquitous enzymes that hydrolyze sulfate from sulfated organic substrates such as carbohydrates, steroids, and flavones. These enzymes can be exploited in the field of biotechnology to analyze sulfated metabolites in humans, such as steroids and drugs of abuse. Because genomic data far outstrip biochemical characterization, the analysis of sulfatases from published sequences can lead to the discovery of new and unique activities advantageous for biotechnological applications. We expressed and characterized a putative sulfatase (PyuS) from the bacterium Pedobacter yulinensis. PyuS contains the (C/S)XPXR sulfatase motif, where the Cys or Ser is post-translationally converted into a formylglycine residue (FGly). His-tagged PyuS was co-expressed in Escherichia coli with a formylglycine-generating enzyme (FGE) from Mycobacterium tuberculosis and purified. We obtained several crystal structures of PyuS, and the FGly modification was detected at the active site. The enzyme has sulfatase activity on aromatic sulfated substrates as well as phosphatase activity on some aromatic phosphates; however, PyuS did not have detectable activity on 17α-estradiol sulfate, cortisol 21-sulfate, or boldenone sulfate. 相似文献
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研究了阳离子光引发剂[CpFe(η6-tol)]BF4引发脂环族环氧树脂ERL-4221阳离子光聚合的活性.其响应峰在 374nm和 450nm处,大于二甲苯基碘盐的240nm,具有更高的感度.同时,研究了一些不同种类的过氧化物对[CpFe(η6-tol)]BF4的增感作用,敏化效果与其氧化性一致:过氧化羟基异丙苯(CHP)≈过氧化苯甲酰 (BPO) >过氧化二异丙苯 (DCP),研究了光敏体系的紫外吸收光谱和荧光发射光谱,对增感机理作出初步解释. 相似文献
29.
Julia Ertl Dr. Maria Elena Ortiz-Soto Thien Anh Le Julian Bechold Junwen Shan Dr. Jörg Teßmar Prof. Bernd Engels Prof. Jürgen Seibel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(26):6533-6541
Selective chemical modification of proteins plays a pivotal role for the rational design of enzymes with novel and specific functionalities. In this study, a strategic combination of genetic and chemical engineering paves the way for systematic construction of biocatalysts by tuning the product spectrum of a levansucrase from Bacillus megaterium (Bm-LS), which typically produces small levan-like oligosaccharides. The implementation of site-directed mutagenesis followed by a tyrosine-specific modification enabled control of the product synthesis: depending on the position, the modification provoked either enrichment of short oligosaccharides (up to 800 % in some cases) or triggered the formation of high molecular weight polymer. The chemical modification can recover polymerization ability in variants with defective oligosaccharide binding motifs. Molecular dynamic (MD) simulations provided insights into the effect of modifying non-native tyrosine residues on product specificity. 相似文献
30.
Dr. Shuangyan Hu Lijun Liu Dr. Heng Li Dr. David Pahovnik Prof. Dr. Nikos Hadjichristidis Prof. Dr. Xuechang Zhou Prof. Dr. Junpeng Zhao 《化学:亚洲杂志》2023,18(1):e202201097
A series of ester-ether copolymers were obtained via the reaction between α,ω-dihydroxyl poly(ϵ-caprolactone) (PCL) and ethylene oxide (EO) or monosubstituted epoxides catalyzed by strong phosphazene bases. The two types of monomeric units were distributed in highly random manners due to the concurrence of epoxide ring-opening and fast transesterification reactions. The substituent of epoxide showed an interesting bidirectional effect on the enzymatic degradability of the copolymer. Compared with PCL, copolymers derived from EO exhibited enhanced hydrophilicity and decreased crystallinity which then resulted in higher degradability. For the copolymers derived from propylene oxide and 1,2-butylene oxide, the hydrophobic alkyl pendant groups also allowed lower crystallinity of the copolymers thus higher degradation rates. However, further enlarging the pendant groups by using styrene oxide or 2-ethylhexyl glycidyl ether caused a decrease in the degradation rate, which might be ascribed to the higher bulkiness hindering the contact of ester groups with lipase. 相似文献