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971.
Masanori Fujinami Satoshi Jinno Masafumi Fukuzumi Takumi Kawaguchi Koichi Oguma Takashi Akahane 《Analytical sciences》2008,24(1):73-79
A production method for a positron microprobe using a beta+-decay radioisotope (22Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was mounted at the focal point of the magnetic lens and was used as a remoderator for brightness enhancement in a transmission geometry. The remoderated positrons were accelerated by an electrostatic lens and focused on the target by an objective magnetic lens. As a result, a 4-mm-diameter positron beam could be transformed into a microprobe of 60 microm or less with 4.2% total efficiency. The S parameter profile obtained by a single-line scan of a test specimen coincided well with the defect distribution. This technique for a positron microprobe is available to an accelerator-based high-intensity positron source and allows 3-dimensional vacancy-type defect analysis and a positron source for a transmission positron microscope. 相似文献
972.
Sumio Kato Takuya Yoshizawa Nobuhiro Kakuta Shinya Akiyama Masataka Ogasawara Takashi Wakabayashi Yuunosuke Nakahara Shinichi Nakata 《Research on Chemical Intermediates》2008,34(8-9):703-708
Apatite-type silicate supported precious metal catalysts were prepared and investigated for their catalytic activity in selective catalytic NO reduction. Single-phase La9.33Si6O26 and La8.33ASi6O25.5 (A=Ca, Sr, Ba) were obtained by a sol-gel method. Pd/La9.33Si6O26 catalyst exhibited high activity for oxidation of C3H6, comparable to Pd/Al2O3 catalyst, although the specific surface area of La9.33Si6O26 was lower than that of Al2O3. In addition, Pt/La9.33Si6O26 catalyst exhibited higher activity for selective catalytic reduction of NO than Pt/Al2O3 catalyst. Substitution of Ba2+ for La3+ of La9.33Si6O26 led to increased catalytic activity at low temperature. 相似文献
973.
Mitsutaka Okumura Satoshi Sakane Yasutaka Kitagawa Takashi Kawakami Naoki Toshima Kizashi Yamaguchi 《Research on Chemical Intermediates》2008,34(8-9):737-742
It is reported that Pd?Pt core-shell type nanoclusters in which the inner atoms of the Pd cluster are substituted by Pt significantly enhance the catalytic activity for cycloocatdiene hydrogenation. In order to discuss the electronic states of core-shell clusters, DFT calculations were carried out for Pd13, Pt13, Pt/Pd12, Pd/Pt12 Pd38 and Pd6/Pt32 clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role for the modification of the electronic state of the surface atoms in them. 相似文献
974.
Himeda Y Onozawa-Komatsuzaki N Miyazawa S Sugihara H Hirose T Kasuga K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(35):11076-11081
Transfer hydrogenation catalyzed by an iridium catalyst with 4,4'-dihydroxy-2,2'-bipyridine (DHBP) in an aqueous formate solution exhibits highly pH-dependent catalytic activity and chemoselectivity. The substantial change in the activity is due to the electronic effect based on the acid-base equilibrium of the phenolic hydroxyl group of DHBP. Under basic conditions, high turnover frequency values of the DHBP complex, which can be more than 1000 times the value of the unsubstituted analogue, are obtained (up to 81 000 h(-1) at 80 degrees C). In addition, the DHBP catalyst exhibits pH-dependent chemoselectivity for alpha,beta-unsaturated carbonyl compounds. Selective reduction of the C=C bond of enone with high activity are observed under basic conditions. The ketone moieties can be reduced with satisfactory activity under acidic conditions. In particular, pH-selective chemoselectivity of the C=O versus C=C bond reduction was observed in the transfer hydrogenation of cinnamaldehyde. 相似文献
975.
Preparation and mechanical properties of bacterial cellulose nanocomposites loaded with silica nanoparticles 总被引:3,自引:0,他引:3
Shoichiro Yano Hideaki Maeda Megumi Nakajima Toshiki Hagiwara Takashi Sawaguchi 《Cellulose (London, England)》2008,15(1):111-120
Bacterial cellulose (BC), which is produced by Gluconacetobacter xylinus (Ga. xylinus) in culture, is made up of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. In the current
studies, we used two processes to prepare nanocomposites of BC filled with silica particles. In Process I, Ga. xylinus was incubated in medium containing silica sol Snowtex 0 (ST 0, pH 2–4) or Snowtex 20 (ST 20, pH 9.5–10.0). The elastic modulus
at 20 °C was improved by keeping the amount of silica in the nanocomposites below 4% when ST 20 was used and below 8.7% when
ST 0 was used. This process allowed incorporation of 50% silica in BC. Inclusion of higher amounts of silica reduced the modulus
at 20 °C and the strength of the nanocomposites below that of BC. X-ray diffraction measurements revealed that the silica
particles disturb the formation of ribbon-shaped fibrils and affect the preferential orientation of the (
) plane. We also produced BC-silica nanocomposites by Process II, wherein the BC hydrogel was immersed in different concentrations
of silica sols, allowing silica particles to diffuse into the BC hydrogel and lodge in the spaces between the ribbon-shaped
fibrils. This method increased the modulus at 20°C and the strength compared to the BC matrix, but it was difficult to load
the BC with more than 10% silica in this way. 相似文献
976.
Mizuta M Banba J Kanamori T Tawarada R Ohkubo A Sekine M Seio K 《Journal of the American Chemical Society》2008,130(30):9622-9623
New nucleotide pairs applicable to formation of DNA triplexes were developed. We designed oligonucleotides incorporating 5-aryl deoxycytidine derivatives (dC5Ars) and cyclic deoxycytidine derivatives, dCPPP and dCPPI, having an expanded aromatic area, as the second strand. As pairing partners, two types of abasic residues (C3: propylene linker, phi: abasic base) were chosen. It was concluded that, when the 5-aryl-modified cytosine bases paired with the abasic sites in TFOs in a space-fitting manner, the stability of the resulting triplexes significantly increased. The recognition of C3 toward dC5Ars was selective because of the stacking interactions between their aromatic part and the nucleobases flanking the abasic site. These results indicate the potential utility of new nucleotide triplets for DNA triplex formation, which might expand the variety of structures and sequences and might be useful for biorelated fields such as DNA nanotechnologies. 相似文献
977.
Yorita H Otomo K Hiramatsu H Toyama A Miura T Takeuchi H 《Journal of the American Chemical Society》2008,130(46):15266-15267
The cation-pi interaction, a noncovalent interaction of electrostatic nature between a cation and an electron-rich pi system, is increasingly recognized as an important force that influences the structures and functions of molecules including proteins. Unlike other metal cations, the transition metal cation Cu2+ is not regarded to take part in a cation-pi interaction because Cu2+ tends to oxidize the pi electron system, in particular that of Trp, and to introduce covalency in the metal-pi electron interaction. This paper reports the first spectral evidence for the cation-pi interaction between Cu2+ and Trp. The Cu2+ ion bound to the amino N-terminal Cu2+/Ni2+ binding motif composed of three amino acid residues interacts with the indole ring of the fourth Trp residue in a noncovalent manner. The Cu2+-Trp interaction produces a distinct negative band at 223 nm in circular dichroism (CD), which disappears upon mutation or depletion of the Trp residue or upon replacement of the Cu2+ ion by Ni2+. In UV absorption, a pair of negative/positive intensity changes is generated at 222/231 nm by the Cu2+-Trp interaction, being consistent with the previous observations on the indole ring interacting with K+ or a cationic His imidazole ring. The negative CD band around 223 nm is characteristic of the Cu2+-Trp pair and may be useful as a marker of the Cu2+-Trp cation-pi interaction. Coordination of negatively charged ligands to Cu2+ is suggested to be important for the cation to be involved in a cation-pi interaction. 相似文献
978.
A chiral ammonium betaine, an intramolecular ion-pairing quaternary ammonium aryloxide 3, has been designed and its vast potential as an enantioselective organic base catalyst has been successfully demonstrated in the highly enantioselective direct Mannich-type reaction of alpha-substituted alpha-nitrocarboxylates 2 with various N-Boc imines 1. The present study provides a conceptually new approach toward the design of bifunctional, chiral quaternary ammonium salts and their utilizations as a homogeneous organic molecular catalyst. 相似文献
979.
980.
Context-dependent fluorescence detection of a phosphorylated tyrosine residue by a ribonucleopeptide
Hasegawa T Hagihara M Fukuda M Nakano S Fujieda N Morii T 《Journal of the American Chemical Society》2008,130(27):8804-8812
Tools for selective recognition and sensing of specific phosphorylated tyrosine residues on the protein surface are essential for understanding signal transduction cascades in the cell. A stable complex of RNA and peptide, a ribonucleopeptide (RNP), provides effective approaches to tailor RNP receptors and fluorescent RNP sensors for small molecules. In vitro selection of an RNA-derived pool of RNP afforded RNP receptors specific for a phosphotyrosine residue within a defined amino-acid sequence Gly-Tyr-Ser-Arg. The RNP receptor for the specific phosphotyrosine residue was successfully converted to a fluorescent RNP sensor for sequence-specific recognition of a phosphorylated tyrosine by screening a pool of fluorescent phosphotyrosine-binding RNPs generated by a combination of the RNA subunits of phosphotyrosine-binding RNPs and various fluorophore-modified peptide subunits. The phosphotyrosine-binding RNP receptor and fluorescent RNP sensor constructed from the RNP receptor not only discriminated phosphotyrosine against tyrosine, phosphoserine, or phosphothreonine, but also showed specific recognition of amino acid residues surrounding the phosphotyrosine residue. A fluorescent RNP sensor for one of the tyrosine phosphorylation sites of p100 coactivator showed a binding affinity to the target site ~95-fold higher than the other tyrosine phosphorylation site. The fluorescent RNP sensor has an ability to function as a specific fluorescent sensor for the phosphorylated tyrosine residue within a defined amino-acid sequence in HeLa cell extracts. 相似文献