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81.
82.
Ed Cleator Carl A. Baxter Michael O’Hagan Timothy J.C. O’Riordan Faye J. Sheen Gavin W. Stewart 《Tetrahedron letters》2010,51(7):1079-4493
A simple one-pot synthesis of benzoxathiazepine-1,1-dioxides is described. Increased yields are afforded when suitable substituents are present in one of the starting materials. These additional substituents also provide a handle for further functionalization. 相似文献
83.
Bayley H 《Physics of life reviews》2012,9(2):161-3; discussion 174-6
84.
Bhaskar A Ramakrishna G Lu Z Twieg R Hales JM Hagan DJ Van Stryland E Goodson T 《Journal of the American Chemical Society》2006,128(36):11840-11849
Novel alkene and alkyne branched structures have been synthesized, and their two-photon absorption (2PA) properties are reported. This series of alkene and alkyne trimer systems tests the mechanistic approach for enhancing the 2PA process which is usually dictated by the pi-bridging, delocalization length, and corresponding charge transfer on the 2PA cross sections. The results suggest that alkene branched systems have higher 2PA cross sections. While steady-state absorption and emission measurements were not successful in predicting the observed trend of 2PA cross sections, time-resolved measurements have explained the trends observed. It was found that, upon photoexcitation, there is an ultrafast charge localization to an intramolecular charge-transfer (ICT) state, followed by the presence of a solvent and conformationally relaxed ICT state in these branched systems. 相似文献
85.
Individual nucleic acid molecules might be sequenced by the identification of nucleoside 5'-monophosphates as they are released by processive exonucleases. Here, we show that single molecule detection with a modified protein nanopore can be used to identify ribonucleoside and 2'-deoxyribonucleoside 5'-monophosphates, thereby taking a step along this path. Distinct levels of current block are observed for each of the four members of a set of nucleoside 5'-monophosphates when the molecules bind within a mutant alpha-hemolysin pore, (M113R)(7), equipped with the molecular adapter heptakis-(6-deoxy-6-amino)-beta-cyclodextrin. While our results compare favorably with alternative approaches, further work will be required to improve the accuracy of identification of the nucleic acid bases, to feed each released nucleotide into the pore, and to ensure that every nucleotide is captured by the adapter. 相似文献
86.
It is now more than 50 years since the first fluorinated natural product was identified. In that time only about a dozen fluorinated natural products have been isolated, the last one over a decade ago. Very little is known about the mechanism of biological fluorination although significant progress has been made in elucidating the pathway by which biosynthesis of fluoroacetate and 4-fluorothreonine occurs in the bacterium Streptomyces cattleya. In this article we review the fluorinated natural products and the current status of our understanding of fluorometabolite biosynthesis. 相似文献
87.
88.
Nanette A. Madigan Carolynne R.S. Hagan Honghua Zhang Louis A. Coury Jr. 《Ultrasonics sonochemistry》1996,3(3):69-S247
Ultrasonic irradiation at a frequency of 20 kHz has varying effects on electrode surfaces. Non-metals such as glassy carbon and Ebonex™ are severely pitted after only a few minutes of sonication in aqueous media. By contrast, metals such as Pt, Au, W and Pd remain largely undamaged after 120 s, as observed by scanning electron microscopy. The extent of damage does not appear to be related to the melting point of the material. By contrast, when electrodes are sonicated in suspensions of metal powders, particles are deposited onto electrode surfaces. The deposits were subsequently observed by scanning electron microscopy and by voltammetry. It is concluded that the ability to deposit particles on an electrode depends on both the melting point of the particles and the electrode, whereas surface damage is more closely related to the hardness of the material. 相似文献
89.
Li WW Claridge TD Li Q Wormald MR Davis BG Bayley H 《Journal of the American Chemical Society》2011,133(6):1987-2001
Cyclodextrins (CDs) have been widely used in host-guest molecular recognition because of their chiral and hydrophobic cavities. For example, β-cyclodextrin (βCD) lodged as a molecular adaptor in protein pores such as α-hemolysin (αHL) is used for stochastic sensing. Here, we have tuned the cavity and overall size of βCD by replacing a single oxygen atom in its ring skeleton by a disulfide unit in two different configurations to both expand our ability to detect analytes and understand the interactions of βCD with protein pores. The three-dimensional structures of the two stereoisomeric CDs have been determined by the combined application of NMR spectroscopy and molecular simulation and show distorted conformations as compared to natural βCD. The interactions of these synthetic βCD analogues with mutant αHL protein pores and guest molecules were studied by single-channel electrical recording. The dissociation rate constants for both disulfide CDs from the mutant pores show ~1000-fold increase as compared to those of unaltered βCD, but are ~10-fold lower than the dissociation rate constants for βCD from wild-type αHL. Both of the skeleton-modified CDs show altered selectivity toward guest molecules. Our approach expands the breadth in sensitivity and diversity of sensing with protein pores and suggests structural parameters useful for CD design, particularly in the creation of asymmetric cavities. 相似文献
90.
Reedy CR Hagan KA Marchiarullo DJ Dewald AH Barron A Bienvenue JM Landers JP 《Analytica chimica acta》2011,(2):2790-158
Microfluidic technology has been utilized in the development of a modular system for DNA identification through STR (short tandem repeat) analysis, reducing the total analysis time from the ∼6 h required with conventional approaches to less than 3 h. Results demonstrate the utilization of microfluidic devices for the purification, amplification, separation and detection of 9 loci associated with a commercially-available miniSTR amplification kit commonly used in the forensic community. First, DNA from buccal swabs purified in a microdevice was proven amplifiable for the 9 miniSTR loci via infrared (IR)-mediated PCR (polymerase chain reaction) on a microdevice. Microchip electrophoresis (ME) was then demonstrated as an effective method for the separation and detection of the chip-purified and chip-amplified DNA with results equivalent to those obtained using conventional separation methods on an ABI 310 Genetic Analyzer. The 3-chip system presented here demonstrates development of a modular, microfluidic system for STR analysis, allowing for user-discretion as to how to proceed after each process during the analysis of forensic casework samples. 相似文献