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151.
152.
Jonathan A. Sherratt 《Journal of mathematical biology》1995,33(3):295-308
This paper is concerned with the possibility of Turing bifurcations in a reaction-diffusion system in which the diffusion coefficient of one species varies periodically in time. This problem was introduced and investigated numerically by Timm and Okubo (J. Math. Biol. 30, 307, 1992) in the context of predator-prey interactions in plankton populations. Here, I consider the simple case in which the temporal variation in diffusivity has a square-tooth form, alternating between two constant values, with a period that is long compared with the time scale of the kinetics. The analysis is valid for any set of reaction kinetics. I derive explicit expressions for the Floquet multipliers that determine the stability of the steady state, and thereby obtain the conditions for diffusion driven instability to occur. These conditions imply that, depending on the kinetics, the homogeneous equilibrium may be either more or less stable than when the diffusion coefficient is a constant equal to the mean of the variable diffusivity. I go on to consider the form of the solution when diffusion driven instability does occur, and I use perturbation theory to determine the effect of a small temporal variation in the diffusion coefficient on the spatial wavelength of the pattern that results from diffusion driven instability. 相似文献
153.
In a previous study, nonlinear autoregressive (NLAR) models applied to ictal electroencephalogram (EEG) recordings in six
patients revealed nonlinear signal interactions that correlated with seizure type and clinical diagnosis. Here we interpret
these models from a theoretical viewpoint. Extended models with multiple nonlinear terms are employed to demonstrate the independence
of nonlinear dynamical interactions identified in the ‘NLAR fingerprint’ of patients with 3/s seizure discharges. Analysis
of the role of periodicity in the EEG signal reveals that the fingerprints reflect the dynamics not only of the periodic discharge
itself, but also of the fluctuations of each cycle about an average waveform. A stability analysis is used to make qualitative
inferences concerning the network properties of the ictal generators. Finally, the NLAR fingerprint is analyzed in the context
of Volterra-Weiner theory.
Received: 6 April 1994/Accepted in revised form: 18 November 1994 相似文献
154.
Maninder K. Sohi Tommy Wan Brian J. Sutton Tony Atkinson Max A. Atkinson Jonathan P. Murphy Stephen P. Bottomley Michael G. Gore 《Proteins》1995,23(4):610-612
Protein L is a multi domain cell wall constituent of certain strains of Peptostreptococcus magnus which binds to the variable domain of immunoglobulin κ-light chains. A single immunoglobulin-binding domain of Mr = 9000 from this protein has been isolated and crystallized. The crystals are of space group P42212, with cell dimensions a = b = 66.9 Å, c = 68.3 Å, and diffract to at least 2.2 Å resolution. The asymmetric unit of the crystal contains two molecules of the protein L domain, related by a noncrystallographic 2-fold axis, as revealed by a self-rotation function calculated with native diffraction data. © 1995 Wiley-Liss, Inc. 相似文献
155.
Jonathan H. Davis 《Journal of biomolecular NMR》1995,5(4):433-437
Summary 2D 15N-1H correlation spectra are ideal for measuring backbone amide populations to determine amide exchange protection factors in studies of protein folding or other structural features. Most protein NMR spectroscopists use HSQC, which has been shown to be generally superior to HMQC in both resolution and sensitivity. The refocused HSQC experiment is intrinsically less sensitive than the regular HSQC, due to T2 relaxation during the refocusing delays. However, we show here that, when high 15N resolution is needed, an optimized refocused HSQC sequence that utilizes a semi-constant time evolution period and pulsed field gradients has better signal-to-noise ratio and resolution, and integrates more accurately, than a similar HSQC. The differences are demonstrated on a 20 kDa protein. The technique can also be applied to 3D NOESY experiments to eliminate strong NH2 geminal peaks and their truncation artefacts at a modest cost in sensitivity. 相似文献
156.
Alexander Matschiner Jonathan S. Dordick David W. Murhammer 《Biotechnology Techniques》1995,9(12):897-900
A method was developed that can be used to isolate virally-infected insect cells from a mixed population containing infected and uninfected cells. Specifically, Spodoptera frugiperda Sf-9 cells infected with the Autographa californica multiple nuclear polyhedrosis virus were treated with a primary antibody specific for the gp64 protein present on the surface of virally-infected cells and a secondary antibody labeled with a fluorochrome. The resulting labeled cells were isolated by using fluorescence-activated cell sorting. 相似文献
157.
158.
Acetylation of rat testis histones H2B and TH2B 总被引:3,自引:1,他引:2
The in vivo acetylation of rat testis histones H3 and H4 has been demonstrated in previous studies. In this study, analysis of purified histone fractions revealed the in vivo acetylation of histone H2B, the testis histone variant designated TH2B, and two or more of the histone H2A variants. These findings are quite significant, because it is possible that all of the core histones are acetylated in elongating spermatids at the time of removal of the entire histone complement for replacement by basic spermatidal transition proteins (S.R. Grimes and N. Henderson, 1983, Arch. Biochem. Biophys. 221, 108-116). 相似文献
159.
Identification of two molecular-mass forms of phenylalanine hydroxylase that segregate independently in rats. Specific association of each form with certain rat strains 总被引:1,自引:1,他引:0 下载免费PDF全文
The nature of the different molecular-mass forms of phenylalanine hydroxylase in rat livers was examined by immunoprecipitation of the enzyme from crude liver extracts that had been radiolabelled by reductive methylation. The two forms of the enzyme were resolved by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and detected by fluorography. Segregation of the two forms of the enzyme was demonstrated in Sprague-Dawley rats, as would be expected if the two forms were products of allelic genes. In addition, hooded and albino Wistar rat livers contained only the slower-migrating form and Lewis rat livers contained only the faster-migrating form, and hence we suggest that the forms be referred to as W (for Wistar) and L (for Lewis). Peptide mapping showed that the W and L forms are closely related, and the difference between them appears to reside at one or other end of the polypeptide chain. The kidney contained the same forms as the liver in one-tenth the quantity, providing further evidence that the same phenylalanine hydroxylase gene is expressed in liver and kidney. 相似文献
160.
In barley seedling extracts, p-coumaroyl-CoA is rapidly hydrolysed to p-coumaroyl-dephospho-CoA, p-coumaroyl-4′-phosphopantetheine and p-coumaroyl-pantetheine. p-Coumaroyl-4′-phosphopantetheine is active as a substrate of agmatine coumaroyl transferase in the formation of p-coumaroyl-agmatine, but p-coumaroyl-pantetheine is inactive. The phosphohydrolysis can be partly inhibited by inorganic pyrophosphate, sodium fluoride and purine nucleotides. A simplified method for the synthesis of N-hydroxysuccinimide esters of hydroxycinnamic acids, used in the synthesis of CoA thioesters, is also described. 相似文献