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排序方式: 共有223条查询结果,搜索用时 46 毫秒
41.
In this paper we present multi-channel chirp measurements of wide-band sources, using a programmable Fourier-domain optical processor (FDOP) as a near-perfect linear frequency discriminator element followed by a fast photodiode and electrical sampling oscilloscope. The electric field of a 10.7 Gbit/s phase-encoded data source and a directly modulated laser diode are simultaneously interrogated with this measurement system. The constellation diagram of the phase-encoded data source is demonstrated, and a comparison with another phase-sensitive measurement technique is performed. Additionally, an extension to this technique is demonstrated in which the time-resolved chirp of a picosecond-duration mode-locked laser diode with a 260 GHz spectral bandwidth is characterised using the FDOP and a high-bandwidth optical sampling oscilloscope. This measurement ensemble has sufficient temporal resolution to characterise random or repetitive data signals up to 100GBaud. 相似文献
42.
Aggarwal VK Ball LT Carobene S Connelly RL Hesse MJ Partridge BM Roth P Thomas SP Webster MP 《Chemical communications (Cambridge, England)》2012,48(74):9230-9232
The expedient enantioselective synthesis of 5 bisabolane sesquiterpenes has been achieved using a common, one-pot lithiation-borylation reaction of secondary benzylic carbamates and either protodeboronation or oxidation to give the natural products in fewer than 5 steps, with high yield and >94?:?6 er. 相似文献
43.
Liam McElroy Mark Nieuwenhuyzen Graham C. Saunders 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):678-679
The title molecule, [Mo{P(C6H5)2(C6H4F)}(HNC5H10)(CO)4] or [Mo(C18H14FP)(C5H11N)(CO)4], has irregular octahedral geometry about the Mo atom. The molecules form a complicated hydrogen‐bonded network comprising C—H?O, C—H?F and C—H?π hydrogen bonds and π–π interactions. The C—H?π and π–π interactions form chains containing C—H?π/π–π dimers linked via C—H?π interactions and the chains are linked into a three‐dimensional network via C—H?O and C—H?F hydrogen bonds. 相似文献
44.
The residual-stress distribution of through-the-wall thickness in the roller-expanded region of thin-walled incoloy-800 Fe–Ni–Cr alloy tubing was determined. Such tubes are commonly used in the fabrication of steam generators for nuclear-power stations. For the present study, the test specimens consisted of short lengths of tubing which were roller-expanded into tubesheet simulation blocks. Some of the specimens were then heat treated. The measurement method involved the installation of strain-gage rosette strips on the inner tube wall. Strain measurements were first taken after the removal of the tubesheet simulation block. Residual stresses were then released by progressive chemical etching of the outer tube wall. In some cases the inner tube wall was etched instead and this required the removal of the inner strain-gage strip and its replacement by one attached to the outer wall. A calculation procedure based on the Sachs approach, first proposed for straight unrolled tubes, was used for determining the residual-stress distribution in the vicinity of the roller-expanded zone and through-the-wall thickness. Surface residual stresses of the order of 250 MPa were determined in the as-received specimens. Residual stresses in the stress-relieved heat-treated specimens were generally lower by about 40 percent. Contact stresses were nearly eliminated by the heat-treating process. The residual stresses in the various specimens of the same type compared to within a standard deviation of 35 MPa. 相似文献
45.
Baldwin RK Pettigrew KA Ratai E Augustine MP Kauzlarich SM 《Chemical communications (Cambridge, England)》2002,(17):1822-1823
This paper describes the preparation of air and moisture stable octanol derivatized crystalline silicon nanoparticles by room temperature sodium naphthalenide reduction of silicon halides. 相似文献
46.
We report a highly diastereoselective approach for the synthesis of the pentacyclic indole core of the manadomanzamine alkaloid skeleton, with complete control over the relative and absolute stereochemistries at the three contiguous stereocentres at ring positions 1, 10, and 24, from a readily available chiral template. 相似文献
47.
Steven M. Allin Liam J. Duffy Vickie McKee Michael J. McKenzie Oriol Bassas Joan Bosch 《Tetrahedron letters》2006,47(32):5713-5716
We report new and complementary routes for the highly stereoselective construction of functionalized benzoquinolizidine targets from readily available, non-racemic chiral templates. The methods developed allow us to predetermine relative product stereochemistries by judicious choice of substrate sub-structure, and provide ready access to alternative stereoisomers. 相似文献
48.
A.F. Maarten Altelaar Ioana M. Taban Liam A. McDonnell Peter D.E.M. Verhaert Robert P.J. de Lange Roger A.H. Adan Wolter J. Mooi Ron M.A. Heeren Sander R. Piersma 《International journal of mass spectrometry》2007,260(2-3):203
Matrix assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) has been used to determine peptide distributions directly from rat, mouse and human pituitary tissue sections. Since these organs are small (102–103 μm) the spatial resolution of IMS is a key issue in molecular imaging of pituitary tissue sections. Here we show that high-resolution IMS allows localization of neuropeptide distributions within different cell clusters of a single organ of a pituitary tissue section. The sample preparation protocol does not result in analyte redistribution and is therefore applicable to IMS experiments at cellular length scales. The stigmatic imaging mass spectrometer used in this study produces selected-ion-count images with pixel sizes of 500 nm and a resolving power of 4 μm, yielding superior spatial detail compared to images obtained in microprobe imaging experiments. Furthermore, we show that with imaging mass spectrometry a distinction can be made between different mammalian tissue sections based on differences in the amino acid sequence of neuropeptides with the same function. This example demonstrates the power of IMS for label-free molecular imaging at relevant biological length scales. 相似文献
49.
50.
Dr. Valentin Magné Dr. Liam T. Ball 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(37):8903-8910
Thiophenols are versatile synthetic intermediates whose practical appeal is marred by their air sensitivity, toxicity and extreme malodor. Herein we report an efficient catalytic method for the preparation of S-aryl isothiouronium salts, and demonstrate that these air-stable, odorless solids serve as user-friendly sources of thiophenols in synthesis. Diverse isothiouronium salts featuring synthetically useful functionality are readily accessible by nickel-catalyzed C−S cross-coupling of (hetero)aryl iodides and thiourea. Convenient, chromatography-free isolation of these salts is achieved by precipitation, allowing the methodology to be applied directly to large scales. Thiophenols are liberated from the corresponding isothiouronium salts upon treatment with a weak base, enabling an in situ release/S-functionalization strategy that entirely negates the need to isolate, purify or manipulate these noxious reagents. 相似文献