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91.
Sklenicka HM Hsung RP McLaughlin MJ Wei LL Gerasyuto AI Brennessel WB 《Journal of the American Chemical Society》2002,124(35):10435-10442
Evidence is described here to support that a highly stereoselective 6pi-electron electrocyclic ring closure of 1-azatrienes is a key step in formal [3 + 3] cycloaddition or annulation reactions of chiral vinylogous amides with alpha,beta-unsaturated iminium salts. This would represent the first highly stereoselective 6pi-electron electrocyclic ring closure of 1-azatrienes. We have also unambiguously demonstrated that these specific ring closures are reversible, leading to the major diastereomer that is also thermodynamically more stable, and that a rotation preference likely also plays a role. A synthetic application is illustrated here to stereoselectively transform the resulting dihydropyridines to cis-1-azadecalins with unique anti relative stereochemistry at C2 and C2a, leading to synthesis of epi isomers of (-)-pumiliotoxin C. 相似文献
92.
John McLaughlin 《Journal of statistical physics》1978,19(6):587-591
It is shown how to add dissipation to the resonant nonlinear oscillators studied by Ford and Lunsford in such a way that the system remains on the energy surface. In the dissipative system, the energy surface is stable in some directions and neutrally stable in other directions. The dissipative oscillators are special cases of the general type investigated by Sherman and McLaughlin. The connection between resonant conservative nonlinear oscillators and dissipative oscillators may make it easier to extend the theorem of Arnol'd to dissipative systems. 相似文献
93.
Matthew J. Rieser Xing-Ping Fang Jon E. Anderson Laura R. Miesbauer David L. Smith Jerry L. McLaughlin 《Helvetica chimica acta》1993,76(7):2433-2444
Extracts from the seeds of Annona muricata yielded three new Annonaceous acetogenins: muricatetrocin A (= (5S)-3-{(2R)-2-hydroxy-9-{(2R,5S)-tetrahydro-5-[(1S,4S,5S)-1,4,5-trihydroxyheptadecyl]furan-2-yl}nonyl}-5-methylfuran-2(5H)-one; 1 ), muricatetrocin B (= (5S)-{(2R)-2-hydroxy-9-{(2S,5S)-tetrahydro-5-[(1S,4S,5S)-1,4,5-trihydroxyheptadecyl]furan-2-yl}nonyl}-5-methylfuran-2(5H)-one; 2 ), and gigantetrocin B (= (5S)-3-{(2R)-2-hydroxy-7-{(2S,5S)-tetrahydro-5-[(1S,4R,5R)-1,4,5-trihydroxynonadecyl]furan-2-yl}heptyl}-5-methyl-furan-2(5H)-one; 3 ). Their C-skeletons were deduced by mass spectrometry. Configurations were determined by 1H-NMR of ketal derivatives and 2D-NMR experiments utilizing Mosher esters. A previously described compound, gigantetrocin A (= (5S)-3-{(2R)-2-hydroxy-7-{(2S,5S)-tetrahydro-5-[(1S,4S,5S)-1,4,5-trihydroxynonadecyl]furan-2-yl}heptyl}-5-methylfuran-2-(5H)one; 4 ), was also isolated and is new to this species. Compounds 1–4 were all selectively cytotoxic for the HT-29 human colon-tumor cell line with potencies at least 10 times that of adriamycin. 相似文献
94.
D. J. McLaughlin W. Lamb A. C. McBride 《Mathematical Methods in the Applied Sciences》1997,20(15):1313-1323
We investigate an initial-value problem modelling fragmentation processes where particles split into two or more pieces at a rate, γ, that not only depends on the sizes of the particles involved but also on time. The existence of non-negative, mass-conserving solutions is established by considering a truncated version of an associated non-autonomous abstract Cauchy problem. The latter has solutions of the form u(t)=Un(t,t0)f, t⩾t0, where f is the known data at some fixed time t0⩾0 and {Un(t,s)} is a uniformly continuous evolution system. A limit evolution system {U(t,s)} is shown to exist. Depending on the form of the known data f at time t0, the scalar-valued function u, obtained from the limit evolution system via u(x, t)=[U(t, t0)f](x) for a.e. x>0, t⩾t0, is a solution of either the original initial-value problem or an integral version of this problem. © 1997 B. G. Teubner Stuttgart–John Wiley & Sons Ltd. 相似文献
95.
Jennifer Wytko Volker Berl Mark McLaughlin Rik R. Tykwinski Martin Schreiber Franois Diederich Corinne Boudon Jean-Paul Gisselbrecht Maurice Gross 《Helvetica chimica acta》1998,81(11):1964-1977
Two series of linearly conjugated hybrid materials, consisting of (E)-1,2-diethynylethene (DEE; hex-3-ene-1,5-diyne) and ZnII porphyrin components, were prepared by Pd0-catalyzed cross-coupling reactions. In one series, one or two DEE substituents were introduced into the meso-positions of the ZnII porphyrins, leading from 5 ⋅ Zn , to 9 and 1 (Scheme 1). The second series contains the linearly π-conjugated molecular rods 1 – 3 that span a length range from 23 Å ( 1 ) to 53 Å ( 3 ) (Fig. 1). The larger rods 2 and 3 consist of two or three porphyrin moieties, respectively, that are bridged at the meso-positions by trans-enediynediyl (hex-3-ene-1,5-diyne-1,6-diyl) linkers (Scheme 2). The UV/VIS spectra in the series 5 ⋅ Zn , 9 , and 1 (Fig. 2) showed a strong bathochromic shift of both Soret and Q bands of the ZnII porphyrin as a result of the addition of DEE substituents. Upon changing from 1 to 2 (Fig. 3), the Q band was further bathochromically shifted, whereas the Soret band remained nearly at the same position but became broadened and displayed a shoulder on the lower-wavelength edge as a result of excitonic coupling. The close resemblance between the UV/VIS spectra of 2 and 3 suggests that saturation of the optical properties in the oligomeric series already occurs at the stage of dimeric 2 . Stationary voltammetric investigations showed that the DEE substituents act as strong electron acceptors which induce large anodic shifts in the first reduction potential upon changing from 5 ⋅ Zn to 9 (ΔE=190 mV) and to 1 (ΔE=340 mV). Increasing the number of porphyrin moieties upon changing from 1 to 2 had no effect on the first reduction potential yet the first oxidation potential was substantially lowered (ΔE=110 mV). Large differences in the potentials for one-electron oxidation of the two porphyrin moieties in 2 (ΔE=200 mV) confirmed the existence of substantial electronic communication between the two macrocycles across the trans-enediynediyl bridge. 相似文献
96.
Frank R. Fronczek Jos Giralds Mark L. McLaughlin 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(5):m159-m161
The title compound, [Fe(C5H5)(C9H9O3)], has Fe–centroid distances of 1.6551 (11) and 1.6445 (11) Å to the cyclopentadienyl rings. The carboxyl group forms hydrogen bonds in the extremely rare syn–anti chain motif, with O⋯O distances of 2.667 (3) and 2.655 (3) Å. The carboxyl group and the hydrogen‐bonded chains are disordered. 相似文献
97.
A sensor with potential for the development of a “chemical barcode” for real-time monitoring of fish freshness is described. This on-package sensor contains a pH sensitive dye, bromocresol green, that responds through visible colour change to basic volatile spoilage compounds, such as trimethylamine (TMA), ammonia (NH3) and dimethylamine (DMA) collectively known as Total Volatile Basic Nitrogen (TVB-N). The sensor characteristics were studied as well as its response with standard ammonia gas. Trials on cod and under-utilised species have verified that the sensor response correlates with bacterial growth patterns in fish samples thus enabling the “real-time” monitoring of spoilage in various fish species. The sensor response can be interrogated with a simple, inexpensive reflectance colorimeter that we have developed based on two light emitting diodes (LEDs) and a photodetector. 相似文献
98.
99.
Thomas McLaughlin 《Mathematical Logic Quarterly》1993,39(1):431-435
By suitably adapting an argument of Hirschfeld (see [2, Chapter 9]), we show that there is a single Δ1 formula that defeats “bounded collection” for any model of II2 Arithmetic that is either a recursive ultrapower or an existentially complete model. Some related facts are noted. MSC: 03F30, 03C62. 相似文献
100.
N. M. Ercolani M. G. Forest D. W. McLaughlin A. Sinha 《Journal of Nonlinear Science》1993,3(1):393-426
Summary The purpose of this paper is the derivation of reduced, finite-dimensional dynamical systems that govern the near-integrable
modulations ofN-phase, spatially periodic, integrable wavetrains. The small parameter in this perturbation theory is the size of the nonintegrable
perturbation in the equation, rather than the amplitude of the solution, which is arbitrary. Therefore, these reduced equations
locally approximate strongly nonlinear behavior of the nearly integrable PDE. The derivation we present relies heavily on
the integrability of the underlying PDE and applies, in general, to anyN-phase periodic wavetrain. For specific applications, however, a numerical pretest is applied to fix the truncation orderN. We present one example of the reduction philosophy with the damped, driven sine-Gordon system and summarize our present
progress toward application of the modulation equations to this numerical study. 相似文献