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排序方式: 共有649条查询结果,搜索用时 62 毫秒
621.
We designed and implemented an ultra low power CORDIC processor which targets the implementation of advanced wireless communications algorithms based on Givens rotations and Householder reflections. We propose a modified CORDIC algorithm and architecture, and we elaborate on the low power architectural and algorithmic techniques for minimizing its power consumption. Our CORDIC implementation consumes, in rotate mode, on average 50 W @ 10 MHz under 1 V supply voltage in a .25 m technology. 相似文献
622.
Iasemidis LD Tsakalis K Sackellares JC Pardalos PM 《Physical review letters》2005,94(1):019801; author reply 019802
623.
Beis K Allard ST Hegeman AD Murshudov G Philp D Naismith JH 《Journal of the American Chemical Society》2003,125(39):11872-11878
The structure of Streptococcus suis serotype type 2 dTDP-d-glucose 4,6-dehydratase (RmlB) has been determined to 1.5 A resolution with its nicotinamide coenzyme and substrate analogue dTDP-xylose bound in an abortive complex. During enzyme turnover, NAD(+) abstracts a hydride from the C4' atom of dTDP-glucose-forming NADH. After elimination of water, hydride is then transferred back to the C6' atom of dTDP-4-keto-5,6-glucosene-regenerating NAD(+). Single-crystal spectroscopic studies unambiguously show that the coenzyme has been trapped as NADH in the crystal. Electron density clearly demonstrates that in contrast to native structures of RmlB where a flat nicotinamide ring is observed, the dihydropyridine ring of the reduced cofactor in this complex is found as a boat. The si face, from which the pro-S hydride is transferred, has a concave surface. Ab initio electronic structure calculations demonstrate that the presence of an internal hydrogen bond, between the amide NH on the nicotinamide ring and one of the oxygen atoms on a phosphate group, stabilizes this distorted conformation. Additionally, calculations show that the hydride donor ability of NADH is influenced by the degree of bending in the ring and may be influenced by an active-site tyrosine residue (Tyr 161). These results demonstrate the ability of dehydratase enzymes to fine-tune the redox potential of NADH through conformational changes in the nicotinamide ring. 相似文献
624.
Carano M Da Ros T Fanti M Kordatos K Marcaccio M Paolucci F Prato M Roffia S Zerbetto F 《Journal of the American Chemical Society》2003,125(23):7139-7144
The cyclic voltammetric (CV) study of a series of novel bisfulleropyrrolidines (3) and bisfulleropyrrolidinium ions (4) is reported. The eight possible stereoisomers of each series were systematically investigated under strictly aprotic conditions that allowed the observation of up to four and five subsequent reversible reductions in 3 and 4, respectively. Because of the stabilizing effect of positive charges, a significant enhancement of the electronegative properties was observed in 4. In fact, 4-trans-2 and 4-trans-1 result among the strongest reversible electron-accepting C(60) oligoadducts. Furthermore, the study evidenced that, in both 3 and 4, the CV pattern, and in particular the potential separation between the second and third reductions, changes significantly with the addition pattern. A sequential pi-electron model that simulates the effect of subsequent reductions of C(60) bis-adducts gives a good correlation (r > 0.96) with the cyclic voltammetry data when the molecules are divided in two sets dependent on the location of the addends in the same or in opposite hemispheres. 相似文献
625.
Konstantinos P. Giapis Klavs F. Jensen John E. Potts Steven J. Pachuta 《Journal of Electronic Materials》1990,19(5):453-462
Observations of carbon incorporation in epitaxial ZnSe films grown by metalorganic chemical vapor deposition are presented.
Carbon is detected by secondary ion mass spectroscopy (SIMS) measurements in all ZnSe films grown from methylallylselenide
and dimethylzinc. The presence of carbon in the films is correlated with a new bound excitonic emission appearing at 2.7920
eV which dominates the near-band-edge low-temperature photoluminescence spectra of all carbon contaminated films. This peak
is also observed when growth is commenced from diethylselenide, under certain growth conditions, but not from hydrogen selenide.
The effect of the carbon contamination is discussed in terms of variations in surface morphology, electrical and luminescence
properties of as-grown films. Control of the carbon concentration is demonstrated by alternating between hydrogen selenide
and methylallylselenide during growth. Strategies to avoid carbon contamination in ZnSe are also proposed.
Author to whom correspondence should be addressed 相似文献
626.
627.
628.
Cassandra T. Eagle Konstantinos Kavallieratos Jeffrey C. Bryan 《Journal of chemical crystallography》2002,32(7):165-170
The structure of N,N-diphenyl-1,3-benzenedisulfonamide (1) was determined by single crystal X-ray diffraction. It crystallizes in P21/n with cell dimensions: a = 11.8390(6) Å, b = 12.3950(10) Å, c = 12.1184(10) Å, = 94.388(6)°, and V = 1773.1(2) Å3. Its di-t-butyl derivative, N,N-bis(4-t-butylphenyl)-1,3-benzenedisulfonamide (2), was prepared and structurally characterized as two solvated structures. Both crystallize in P
with cell dimensions: 2 CF3CH2OH, a = 9.469(2) Å, b = 10.0039(18) Å, c = 16.385(3) Å, = 85.561(16)°, = 83.035(18)°, = 72.459(16), and V = 1467.7(5) Å3; 2 ClCH2CH2Cl, a = 9.559(2) Å, b = 9.8125(12) Å, c = 17.100(6) Å, = 82.495(19)°, = 83.47(2)°, = 70.100(15), and V = 1491.1(6) Å3. The structures exhibit hydrogen-bonding, and are evaluated in terms of preorganization for anion binding. 相似文献
629.
Dr. Senthil Subramaniam Dr. Mond F. Guo Tanmayi Bathena Michel Gray Dr. Xiao Zhang Abraham Martinez Dr. Libor Kovarik Dr. Konstantinos A. Goulas Dr. Karthikeyan K. Ramasamy 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14658-14665
Ethanol can be used as a platform molecule for synthesizing valuable chemicals and fuel precursors. Direct synthesis of C5+ ketones, building blocks for lubricants and hydrocarbon fuels, from ethanol was achieved over a stable Pd-promoted ZnO-ZrO2 catalyst. The sequence of reaction steps involved in the C5+ ketone formation from ethanol was determined. The key reaction steps were found to be the in situ generation of the acetone intermediate and the cross-aldol condensation between the reaction intermediates acetaldehyde and acetone. The formation of a Pd–Zn alloy in situ was identified to be the critical factor in maintaining high yield to the C5+ ketones and the stability of the catalyst. A yield of >70 % to C5+ ketones was achieved over a 0.1 % Pd-ZnO-ZrO2 mixed oxide catalyst, and the catalyst was demonstrated to be stable beyond 2000 hours on stream without any catalyst deactivation. 相似文献
630.
Konstantinos Christodoulopoulos Emmanouel Varvarigos Kyriakos Vlachos 《Optical Switching and Networking》2007,4(3-4):200-212
We propose and evaluate a new burst assembly algorithm based on the average delay of the packets comprising a burst. This method fixes the average delay of the packets belonging to an assembled burst to a desired value that may be different for each forwarding equivalence class (FEC). We show that the proposed method significantly improves the delay jitter experienced by the packets during the burst assembly process, when compared to that of timer-based and burst length-based assembly policies. Minimizing packet delay jitter is important in a number of applications, such as real-audio and streaming-video applications. We also find that the improvement in the packet delay jitter yields a corresponding significant improvement in the performance of TCP, whose operation depends critically on the ability to obtain accurate estimates of the round-trip times (RTT). 相似文献