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排序方式: 共有883条查询结果,搜索用时 15 毫秒
141.
Dr. Cristian Pezzato Dr. Minh T. Nguyen Dr. Dong Jun Kim Dr. Ommid Anamimoghadam Dr. Lorenzo Mosca Prof. Dr. J. Fraser Stoddart 《Angewandte Chemie (International ed. in English)》2018,57(30):9325-9329
Artificial molecular machines can be operated using either physical or chemical inputs. Light‐powered motors display clean and autonomous operations, whereas chemically driven machines generate waste products and are intermittent in their motions. Herein, we show that controlled changes in applied electrochemical potentials can drive the operation of artificial molecular pumps in a semi‐autonomous manner—that is, without the need for consecutive additions of chemical fuel(s). The electroanalytical approach described in this Communication promotes the assembly of cyclobis(paraquat‐p‐phenylene) rings along a positively charged oligomeric chain, providing easy access to the formation of multiple mechanical bonds by means of a controlled supply of electricity. 相似文献
142.
Charged donor-acceptor [3]catenanes comprising the pi-accepting cyclobis(paraquat-4,4'-biphenylene) and pi-donating aromatic crown ether macrocycles have been prepared in high yields using thermodynamically controlled dynamic nucleophilic substitution. 相似文献
143.
Rio-Echevarria IM White FJ Brechin EK Tasker PA Harris SG 《Chemical communications (Cambridge, England)》2008,(38):4570-4572
Benzohydroxamic acid is shown to be an unexpectedly good ligand for iron(iii) oxides, favouring surface attachment to the formation of trisbenzohydroxamato complexes, which are known to have very high thermodynamic stability in solution. 相似文献
144.
Xiao-Yang Chen Hongliang Chen J. Fraser Stoddart 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202211387
The tetracationic cyclophane, cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a modular receptor that has facilitated the discovery of many host–guest complexes and mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as forming trisradical tricationic complexes with viologen radical cations in its doubly reduced bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials. Since the first reports in 1988, the little blue box has been featured in over 500 publications in the literature. All this research activity would not have been possible without the seminal contributions carried out by Siegfried Hünig, who not only pioneered the syntheses of viologen-containing cyclophanes, but also revealed their rich redox chemistry in addition to their ability to undergo intramolecular π-dimerization. This Review describes how his pioneering research led to the design and synthesis of the little blue box, and how this redox-active host evolved into the key component of molecular shuttles, switches, and machines. 相似文献
145.
Ronconi CM Stoddart JF Balzani V Baroncini M Ceroni P Giansante C Venturi M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(27):8365-8373
Two dendrimers were designed and synthesized that contain a 1,3,5-trisubstituted benzenoid core and incorporate 9 and 21 viologen (4,4'-bipyridinium) units in their branches in addition to hydrophilic (aryloxy) terminal groups. For comparison purposes, model compounds containing one and two viologen units were also studied. These polycationic dendrimers form strong host-guest complexes with the dianionic form of the red dye eosin in dilute CH(2)Cl(2) solutions. Titration experiments, based on fluorescence measurements, showed that each viologen unit in the dendritic structures becomes associated with an eosin dianion. Electrochemical (in MeCN) and photosensitization (in CH(2)Cl(2)) experiments revealed that only a fraction of the viologen units present in the dendritic structures can be reduced. This fraction corresponds to the number of viologen units present in the outer shells of the dendrimers. The reasons for incomplete charge pooling are discussed. Comparison with the behavior of polyviologen dendrimers that are terminated with bulky tetraarylmethane groups and were studied previously enabled the role played by the terminal groups in the redox and hosting properties to be elucidated. 相似文献
146.
Parkin A Goldet G Cavazza C Fontecilla-Camps JC Armstrong FA 《Journal of the American Chemical Society》2008,130(40):13410-13416
Protein film voltammetry studies of the [NiFeSe]-hydrogenase from Desulfomicrobium baculatum show it to be a highly efficient H2 cycling catalyst. In the presence of 100% H2, the ratio of H2 production to H2 oxidation activity is higher than for any conventional [NiFe]-hydrogenases (lacking a selenocysteine ligand) that have been investigated to date. Although traces of O2 (< 1%) rapidly and completely remove H2 oxidation activity, the enzyme sustains partial activity for H2 production even in the presence of 1% O2 in the atmosphere. That H2 production should be partly allowed, whereas H2 oxidation is not, is explained because the inactive product of O2 attack is reductively reactivated very rapidly, but this requires a potential that is almost as negative as the thermodynamic potential for the 2H(+)/H2 couple. The study provides further encouragement and clues regarding the feasibility of microbial/enzymatic H2 production free from restrictions of anaerobicity. 相似文献
147.
Benitez D Tkatchouk E Yoon I Stoddart JF Goddard WA 《Journal of the American Chemical Society》2008,130(45):14928-14929
Mechanically interlocked molecules (rotaxanes and catenanes) have already revolutionized molecular electronics and have the promise of a similar impact in other areas of nanotechnology, ranging from nanoactuators to in vivo drug nanocarriers. However, it would be most useful to have quantitative criteria for predicting structures, binding, and excitation energies for use in designing molecules with mechanical bonds. We assess here the use of density functional theory (DFT) to a noncovalently bound complex and find that no density functional is fully satisfactory. However, we find that the new M06-suite of density functionals, which include attractive medium-range interactions, leads to dramatic improvements in the structures (error of 0.04 A in the interplanar distances for M06-L compared to 0.42 A for B3LYP) and excitation energies (within 0.08 eV for TD-M06-HF without empirical correction compared to 2.2 eV error for TD-B3LYP). However, M06 predicts the complex to be too strongly bound by 22.6 kcal mol(-1) (B3LYP leads to too weak a bond by 29 kcal mol(-1)), while current empirical FF DREIDING is too weakly bound by only 15 kcal mol(-1). 相似文献
148.
Synchrotron X‐ray CT characterization of titanium parts fabricated by additive manufacturing. Part I. Morphology 下载免费PDF全文
Nicola Vivienne Yorke Scarlett Peter Tyson Darren Fraser Sheridan Mayo Anton Maksimenko 《Journal of synchrotron radiation》2016,23(4):1006-1014
Synchrotron X‐ray tomography has been applied to the study of titanium parts fabricated by additive manufacturing (AM). The AM method employed here was the Arcam EBM® (electron beam melting) process which uses powdered titanium alloy, Ti64 (Ti alloy with approximately 6%Al and 4%V), as the feed and an electron beam for the sintering/welding. The experiment was conducted on the Imaging and Medical Beamline of the Australian Synchrotron. Samples were chosen to examine the effect of build direction and complexity of design on the surface morphology and final dimensions of the piece. 相似文献
149.
[reaction: see text] A guest molecule-a bis-N-tetraethyleneglycol-substituted 3,3'-difluorobenzidine derivative-has been synthesized, and its complexation with the host, cyclobis(paraquat-p-phenylene), has been investigated. This host-guest complex was then employed in the template-directed synthesis of a blue-colored [2]rotaxane. The color of this [2]rotaxane arises from the charge-transfer absorption band between the HOMO of the guest and the LUMO of the host. This host-guest complex, and the derived [2]rotaxane, completes the donor-acceptor-based RGB (red/green/blue) color complex set. 相似文献
150.
In this critical review, we discuss switching of the light-powered bistable rotaxanes and catenanes and highlight the practical applications of some of these systems. Photoactive molecular and supramolecular machines are comprised of two parts-1) a switching element, based on noncovalent interactions within the recognition units, which is responsible for executing mechanical movement, and 2) a light-harvesting unit which utilizes light to control the competitive interactions between the recognition sites. We also survey another class of molecular devices, namely molecular rotary motors--i.e., those that behave like their macroscopic counterparts--in which photochemically and thermally induced mechanical movement relies on isomerizations of a pivotal C=C bond, leading to a rotation of the top propeller part with respect to the stationary bottom part of the helical shaped chiral molecule. (146 references.). 相似文献