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141.
Back Cover: Imaging Glycosylation In Vivo by Metabolic Labeling and Magnetic Resonance Imaging (Angew. Chem. Int. Ed. 4/2016) 下载免费PDF全文
Dr. André A. Neves Dr. Yéléna A. Wainman Dr. Alan Wright Dr. Mikko I. Kettunen Dr. Tiago B. Rodrigues Sarah McGuire Dr. De‐En Hu Flaviu Bulat Dr. Simonetta Geninatti Crich Dr. Henning Stöckmann Dr. Finian J. Leeper Prof. Kevin M. Brindle 《Angewandte Chemie (International ed. in English)》2016,55(4):1566-1566
142.
Mechanistic Characterisation of Two Sesquiterpene Cyclases from the Plant Pathogenic Fungus Fusarium fujikuroi 下载免费PDF全文
Immo Burkhardt Thomas Siemon Dr. Matthias Henrot Dr. Lena Studt Sarah Rösler Prof. Dr. Bettina Tudzynski Prof. Dr. Mathias Christmann Prof. Dr. Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2016,55(30):8748-8751
Two sesquiterpene cyclases from Fusarium fujikuroi were expressed in Escherichia coli and purified. The first enzyme was inactive because of a critical mutation, but activity was restored by sequence correction through site‐directed mutagenesis. The mutated enzyme and two naturally functional homologues from other fusaria converted farnesyl diphosphate into guaia‐6,10(14)‐diene. The second enzyme produced eremophilene. The absolute configuration of guaia‐6,10(14)‐diene was elucidated by enantioselective synthesis, while that of eremophilene was evident from the sign of its optical rotation and is opposite to that in plants but the same as in Sorangium cellulosum. The mechanisms of both terpene cyclases were studied with various 13C‐ and 2H‐labelled FPP isotopomers. 相似文献
143.
Ferrous Iron Binding Key to Mms6 Magnetite Biomineralisation: A Mechanistic Study to Understand Magnetite Formation Using pH Titration and NMR Spectroscopy 下载免费PDF全文
Dr. Andrea E. Rawlings Dr. Jonathan P. Bramble Andrea M. Hounslow Prof. Michael P. Williamson Dr. Amy E. Monnington Dr. David J. Cooke Dr. Sarah S. Staniland 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7885-7894
Formation of magnetite nanocrystals by magnetotactic bacteria is controlled by specific proteins which regulate the particles’ nucleation and growth. One such protein is Mms6. This small, amphiphilic protein can self‐assemble and bind ferric ions to aid in magnetite formation. To understand the role of Mms6 during in vitro iron oxide precipitation we have performed in situ pH titrations. We find Mms6 has little effect during ferric salt precipitation, but exerts greatest influence during the incorporation of ferrous ions and conversion of this salt to mixed‐valence iron minerals, suggesting Mms6 has a hitherto unrecorded ferrous iron interacting property which promotes the formation of magnetite in ferrous‐rich solutions. We show ferrous binding to the DEEVE motif within the C‐terminal region of Mms6 by NMR spectroscopy, and model these binding events using molecular simulations. We conclude that Mms6 functions as a magnetite nucleating protein under conditions where ferrous ions predominate. 相似文献
144.
Liana Hie Emma L. Baker Sarah M. Anthony Dr. Jean‐Nicolas Desrosiers Dr. Chris Senanayake Prof. Dr. Neil K. Garg 《Angewandte Chemie (International ed. in English)》2016,55(48):15129-15132
Recent studies have demonstrated that amides can be used in nickel‐catalyzed reactions that lead to cleavage of the amide C?N bond, with formation of a C?C or C?heteroatom bond. However, the general scope of these methodologies has been restricted to amides where the carbonyl is directly attached to an arene or heteroarene. We now report the nickel‐catalyzed esterification of amides derived from aliphatic carboxylic acids. The transformation requires only a slight excess of the alcohol nucleophile and is tolerant of heterocycles, substrates with epimerizable stereocenters, and sterically congested coupling partners. Moreover, a series of amide competition experiments establish selectivity principles that will aid future synthetic design. These studies overcome a critical limitation of current Ni‐catalyzed amide couplings and are expected to further stimulate the use of amides as synthetic building blocks in C?N bond cleavage processes. 相似文献
145.
Phan AT Kuryavyi V Burge S Neidle S Patel DJ 《Journal of the American Chemical Society》2007,129(14):4386-4392
The c-kit oncogene is an important target in the treatment of gastrointestinal tumors. A potential approach to inhibition of the expression of this gene involves selective stabilization of G-quadruplex structures that may be induced to form in the c-kit promoter region. Here we report on the structure of an unprecedented intramolecular G-quadruplex formed by a G-rich sequence in the c-kit promoter in K+ solution. The structure represents a new folding topology with several unique features. Most strikingly, an isolated guanine is involved in G-tetrad core formation, despite the presence of four three-guanine tracts. There are four loops: two single-residue double-chain-reversal loops, a two-residue loop, and a five-residue stem-loop, which contain base-pairing alignments. This unique structural scaffold provides a highly specific platform for the future design of ligands specifically targeted to the promoter DNA of c-kit. 相似文献
146.
Ketyl radicals produced by photolysis of ketones or di-tert-butyl peroxide (DTBP) in alcohol solvents react rapidly with tirapazamine (TPZ). The acetone ketyl radical (ACOH) reacts with TPZ with an absolute second-order rate constant of (9.7 +/- 0.4) x 108 M-1 s-1. The reaction kinetics can be followed by monitoring the bleaching of TPZ absorption at 475 nm or the formation of a reaction product which absorbs at 320 and 410 nm. The ACOD radical reacts with TPZ in 2-propanol-OD with an absolute rate constant of (6.7 +/- 0.5) x 108 M-1 s-1, corresponding to a kinetic isotope effect (KIE) of 1.4. Deuteration of the radical on carbon (ACOH-d6) retards the reaction of the radical with TPZ even further (absolute rate constant = (4.8 +/- 0.04) x 108 M-1 s-1). This result corresponds to a KIE of 2.0. Radicals derived from dioxane and diisopropyl ether by flash photolysis of DTBP in ethereal solvent react with TPZ more slowly than do ketyl radicals. It is concluded that ketyl radicals react, in part, with TPZ in organic solvents by transfer of a hydrogen atom from the OH and CH3 groups of the ketyl radical to the oxygen atom at the N4 position of TPZ to form acetone or acetone enol and a radical derivative of TPZ (TPZH). The latter species absorbs at 320 and 405 nm, has a lifetime of hundreds of microseconds in alcohol solvents, and decays by disproportionation to form TPZ and a reduced heterocycle. The reduced heterocycle eventually forms a desoxytirapazamine by a polar mechanism. The results are supported by density functional theory calculations. It is proposed that dioxanyl radical will also react, in part, with TPZ by transfer of a hydrogen atom from the carbon adjacent to the radical center to the oxygen atom at the N4 position of TPZ. This produces the enol ether and the previously mentioned TPZH radical. It is further posited that ether radicals react a bit more slowly than ketyl radicals because they lack the second mode of hydrogen transfer (from the OH group) that is present in the ACOH radical. Our data are permissive of the possibility that ether radicals add to TPZ at a rate that is competitive with beta-hydrogen atom transfer. 相似文献
147.
Ammonium is a toxic waste product that has been reported to negatively inhibit cell growth and recombinant glycosylation in
Chinese hamster ovary (CHO) cells; however, the effect of this toxicity on intracellular gene expression has received only
limited investigation. We used a differential display method to identify genes in CHO cells that were affected by ammonium
stress. Eight genes whose mRNA levels significantly changed in response to elevated ammonium were isolated and identified.
Five of the genes were identified as having lower expression under the ammonium stress, whereas three genes were identified
as having higher expression. Sequence homology with other mammalian organisms was used to attribute function to these newly
identified genes. The identified ammonium-sensitive genes were grouped into three broad functional groups: cellular processes,
energy metabolism, and genetic-information processing. The three cellular process-related genes had lower expression (anaphase-promoting
complex subunit 5, eukaryotic initiation factor 5A II, KIAA1091 protein). The two energy-related genes had higher expression
under ammonium stress (adenosine triphosphate synthase subunit C and mitofusin 1). Both of the genetic information-processing
genes (endoplasmic reticulum [ER]-resident protein ERdj5 and structure-specific recognition protein 1) had lower expression
under the ammonium stress, whereas the 26S proteasome subunit adenosine triphosphatase 3 gene had higher expression. These
preliminary results indicate that ammonium stress lowers expression of genes controlling cell cycle, protein folding, and
quality and raises genes that control energy metabolism and degradation. Our findings demonstrate the usefulness of mRNA differential-display
techniques for the detection of CHO cell genes affected by ammonium stress. 相似文献
148.
Kolosova AY De Saeger S Eremin SA Van Peteghem C 《Analytical and bioanalytical chemistry》2007,387(3):1095-1104
Rapid-response analytical tests that can be performed at the point of sampling are based on a visual detection system. The
influence of different factors on the signal generation in a membrane-based enzyme immunoassay was investigated. The research
was applied to a flow-through immunoassay for the detection of ochratoxin A (OTA). This assay format is a very convenient,
simple and fast qualitative screening tool. Conjugates of OTA with horseradish peroxidase (HRP) and alkaline phosphatase (AP)
were used as enzyme tracers. A new conjugate OTA-AP has been synthesized in our laboratory and its performance in the assay
was compared with that of OTA-HRP. Different substrate systems for HRP and AP were compared. Several reagents, including polymers
and surfactants, were tested for their possible effect on signal generation with the use of OTA-HRP conjugate. Polymers such
as poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) 6000 exerted a favourable effect on signal amplification, whereas
surfactants negatively affected assay performance. The highest signal amplification (30–70% compared to the standard assay
procedure) was achieved using 0.5% PVA in tetramethylbenzidine (TMB) Colorburst substrate solution and phosphate-buffered
saline (PBS) for the washing step. It allowed more reliable visual estimation of the results from OTA-HRP assay. Exclusion
of the detergent (Tween 20) from the washing solution exerted a favourable effect on assay performance using both enzyme tracers.
The assay using OTA-HRP was more susceptible to matrix interferences than the assay with OTA-AP. Signal development in the
matrix was better for the OTA-AP assay and visual estimation of the results was easier to perform in this case. For the analysis
of spiked wheat samples, OTA-AP conjugate gave a more sensitive, stable and reproducible assay with a cut-off level of 4 μg
kg−1 for OTA. The application of the new OTA-AP conjugate resulted in improved assay performance for the food samples. 相似文献
149.
The ionic liquid 1-N-butyl-3-methylimidazolium chloride ([C4mim]+Cl−) was investigated as reaction media for the homogeneous acylation of cellulose with 2-furoyl chloride in the presence of
pyridine. The preparation of cellulose furoate depending on the reaction conditions, the cellulose type and the pyridine content
was studied. Cellulose furoates with a degree of substitution in the range from 0.46 to 3.0 were accessible, i.e., under mild
conditions, with a low excess of reagent and in a short reaction time. The products were characterized by elemental analysis,
perpropionylation, 1H- and 13C NMR spectroscopy and FTIR spectroscopy.
Thomas Heinze is the member of the European Polysaccharide Network of Excellence (EPNOE), www.epnoe.eu 相似文献
150.
Sarah J.P. Yoon-Miller 《Tetrahedron letters》2007,48(5):827-830
A three step, convergent synthesis of 4-aryl-3-pyrrolin-2-ones from a tetramic acid has been developed. The key transformation utilized a Suzuki-Miyaura cross-coupling reaction between a 4-tosyloxy-3-pyrrolin-2-one and an arylboronic acid. This work also provides access to 4-arylpyrrolidin-2-ones, cyclic analogs of γ-aminobutyric acid (GABA). Hydrogenation of 4-(4′-chlorophenyl)-3-pyrrolin-2-one proceeded smoothly to give baclofen lactam. 相似文献