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71.
Monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) were determined in natural water samples by aqueous phase ethylation with sodium tetraethylborate (STEB), room temperature trapping of the resulting volatile derivatives on Tenax TA®, followed by gas chromatography-quartz furnace atomic absorption spectrometry (GC-QFAAS). Recoveries of butyltin spikes from natural water samples were 90-109% at concentrations of ∼100 ng Sn/l. The method precision at ∼100 ng Sn/l was ≤6% RSD for butyltins spiked into natural waters. The detection limits for 1 l water samples were <1 ng Sn/l for all butyltin species. Sample throughput of the method is high (greater than three samples per hour) due to the two-stage nature of the procedure, which allows derivatisation/trapping and GC-QFAAS quantitation to be performed separately. Off-line trapping is also advantageous as it extends the life of the GC column and quartz furnace to at least 12 months due to minimisation of carry-over of co-purged material. 相似文献
72.
Chen Z Cui H Hales K Li Z Qi K Pochan DJ Wooley KL 《Journal of the American Chemical Society》2005,127(24):8592-8593
The mechanism by which the unique toroidal supramolecular assemblies were formed for triblock copolymers of acrylic acid (AA), methyl acrylate (MA), and styrene (S), PAA99-b-PMA73-b-PS66, was probed in this study by investigating the influences of the block copolymer compositions and sequences. Two triblock copolymers, PAA99-b-PMA73-b-PS66 and PAA99-b-PS76-b-PMA62, and two diblock copolymers, PAA99-b-PMA155 and PAA99-b-PS133, were studied under experimental solution-state conditions that involved a range of solvent/nonsolvent (tetrahydrofuran/water) compositions, each in the presence of 2,2'-(ethylenedioxy)bis(ethylamine). The resulting morphologies were determined by transmission electron microscopy. The failures to afford toroidal supramolecular assemblies from both diblock copolymers having comparable lengths of the total hydrophobic chain segment, either entirely PMA or entirely PS, and from the triblock copolymer having a reversed connection sequence for the hydrophobic (PMA and PS) segments demonstrate the unique self-assembly behaviors of triblock copolymers and the importance of the block copolymer sequence. 相似文献
73.
Jonathan D. Matichak Joel M. Hales Dr. Shino Ohira Dr. Stephen Barlow Dr. Sei‐Hum Jang Dr. Alex K.‐Y. Jen Dr. Jean‐Luc Brédas Dr. Joseph W. Perry Dr. Seth R. Marder Dr. 《Chemphyschem》2010,11(1):130-138
Six anionic pentamethine dyes with different 2,2‐difluoro‐4‐aryl‐1,3,2(2 H)‐dioxaborin‐6‐yl termini were synthesized and isolated as tetra‐n‐octylammonium salts with a variety of aryl groups appended to increase conjugation beyond the dioxaborine termini. The increased conjugation was expected to decrease the energy of the lowest‐lying excited state, and increase the transition dipole moment linking this state to the ground state, which would be anticipated to result in an increase in the real part of the third‐order polarizability, Re(γ). UV/Vis‐NIR absorption spectroscopy indicates that the absorption maxima in DMSO vary from 691 to 761 nm, with the longest wavelength transitions observed for a derivative where the aryl group is 4‐nitrophenyl. Closed‐aperture Z‐scan measurements at 1.3 μm in DMSO indicate that Re(γ) varies from ?2.9×10?33 to ?5.4×10?33 esu in these systems. The largest magnitude of Re(γ) was observed for a dye with E‐4‐styrylphenyl aryl groups. This result can be rationalized using a two‐state expression which relates Re(γ) to the energy and transition dipole moment of the transition from the ground state to the lowest‐lying excited state. A nonamethine analogue of this compound was also synthesized and exhibits a slightly larger Re(γ) with respect to a previously reported bis(dioxaborine)‐terminated nonamethine. The extension of conjugation beyond the dioxaborine termini seems to result in an overall increase in Re(γ). However, the effects are smaller than those found by increasing conjugation in the polymethine bridge due to reduced participation of terminal groups in the HOMO. 相似文献
74.
Substrate-based design of the first class of angiotensin-converting enzyme-related carboxypeptidase (ACE2) inhibitors 总被引:9,自引:0,他引:9
Dales NA Gould AE Brown JA Calderwood EF Guan B Minor CA Gavin JM Hales P Kaushik VK Stewart M Tummino PJ Vickers CS Ocain TD Patane MA 《Journal of the American Chemical Society》2002,124(40):11852-11853
Angiotensin-converting enzyme-related carboxypeptidase (ACE2) is a recently identified zinc metalloprotease with carboxypeptidase activity that was identified using our genomics platform. We implemented a rational design approach to identify potent and selective ACE2 inhibitors. To this end, picomolar inhibitors of ACE2 were designed and synthesized. 相似文献
75.
Chung SJ Zheng S Odani T Beverina L Fu J Padilha LA Biesso A Hales JM Zhan X Schmidt K Ye A Zojer E Barlow S Hagan DJ Van Stryland EW Yi Y Shuai Z Pagani GA Brédas JL Perry JW Marder SR 《Journal of the American Chemical Society》2006,128(45):14444-14445
Extended bis(donor)-substituted squaraine chromophores exhibit very high two-photon cross-sections (as high as 33 000 GM) in the near-IR; these can be attributed to the combination of large transition dipoles with small detuning energies. The modulus of the third-order nonlinear optical susceptibility at 1.3 mum has been found to be 7.0 x 10-11 esu for one of these chromophores. 相似文献
76.
Thomas C. Hales John Harrison Sean McLaughlin Tobias Nipkow Steven Obua Roland Zumkeller 《Discrete and Computational Geometry》2010,44(1):1-34
The Kepler conjecture asserts that no packing of congruent balls in three-dimensional Euclidean space has density greater
than that of the face-centered cubic packing. The original proof, announced in 1998 and published in 2006, is long and complex.
The process of revision and review did not end with the publication of the proof. This article summarizes the current status
of a long-term initiative to reorganize the original proof into a more transparent form and to provide a greater level of
certification of the correctness of the computer code and other details of the proof. A final part of this article lists errata
in the original proof of the Kepler conjecture. 相似文献
77.
78.
Dr. Karl J. Thorley Dr. Joel M. Hales Hyeongeu Kim Dr. Shino Ohira Prof. Jean‐Luc Brédas Prof. Joseph W. Perry Prof. Harry L. Anderson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10370-10377
Herein, the synthesis and properties of alkyne‐bridged carbocations, which are analogous in structure to cyanine dyes, are reported. An alkene‐bridged dye, linked at the third position of the indole, was also synthesized as a reference compound. These new carbocations are stable under ambient conditions, allowing characterization by UV/Vis and NMR (1H and 13C) spectroscopies. These techniques revealed a large degree of delocalization of the positive charge, similar to a previously reported porphyrin carbocation. The linear and nonlinear optical properties are compared with cyanine dyes and triarylmethyl cations, to investigate the effects of the bond‐length alternation and the overall molecular geometry. The value of Re(γ), the real part of the third‐order microscopic polarizability, of ?1.3×10?33 esu for the alkyne‐linked cation is comparable to that of a cyanine dye of similar length. Nondegenerate two‐photon absorption spectra showed that the alkene‐bridged dye exhibited characteristics of cyanines, whereas the alkyne‐bridged dye is reminiscent of octupolar chromophores, such as the triarylmethyl carbocation brilliant green. Such attributes were confirmed and rationalized by quantum chemical calculations. 相似文献
79.
Lin HC Kim H Barlow S Hales JM Perry JW Marder SR 《Chemical communications (Cambridge, England)》2011,47(2):782-784
Rh(III) and Ir(III) can be complexed to bipyridine groups attached to the termini of bis(dioxaborine)-capped heptamethines; these chromophores exhibit large third-order polarisabilities at 1.55 μm, while retaining good film-forming properties and linear optical transparency in the near infrared. 相似文献
80.