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801.
Perkins MC Bell G Briggs D Davies MC Friedman A Hart CA Roberts CJ Rutten FJ 《Colloids and surfaces. B, Biointerfaces》2008,67(1):1-13
Understanding the movement of the active ingredient in relation to the other formulation components following application is crucial to an overall understanding of herbicide performance. We describe the novel use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) as a tool for following the movement of herbicide formulation components into and across plant cuticles. This technique provides new insights since it provides both high (sub-micron) spatial resolution combined with the chemical specificity associated with organic mass spectrometry. The components studied include the oligomeric ethoxylate surfactants Synperonic A7 and A20 and active ingredient Sulfosate (trimesium glyphosate). The movement of these molecules, both separately and when combined in a simple formulation, into the surface of Prunus laurocerasus leaves and across the isolated plant cuticle was investigated and clear differences in penetration/diffusion behaviour were identified. ToF-SIMS was uniquely able to (simultaneously) spatially resolve all the species involved, including the anion and cation components of the active ingredient. Also, using spectral reconstructions from the imaging raw data streams, the behaviour of individual oligomers within the surfactant distributions, could be assessed. The observations are discussed with reference to the action of surfactants identified in parallel micro-structural studies and the current understanding of herbicide uptake. 相似文献
802.
Yongdong Jin Dr. Olga Girshevitz Dr. Noga Friedman Dr. Izhar Ron David Cahen Prof. Mordechai Sheves Prof. 《化学:亚洲杂志》2008,3(7):1146-1155
The interfacing of functional proteins with solid supports and the study of related protein‐adsorption behavior are promising and important for potential device applications. In this study, we describe the preparation of bacteriorhodopsin (bR) monolayers on Br‐terminated solid supports through covalent attachment. The bonding, by chemical reaction of the exposed free amine groups of bR with the pendant Br group of the chemically modified solid surface, was confirmed both by negative AFM results obtained when acetylated bR (instead of native bR) was used as a control and by weak bands observed at around 1610 cm?1 in the FTIR spectrum. The coverage of the resultant bR monolayer was significantly increased by changing the pH of the purple‐membrane suspension from 9.2 to 6.8. Although bR, which is an exceptionally stable protein, showed a pronounced loss of its photoactivity in these bR monolayers, it retained full photoactivity after covalent binding to Br‐terminated alkyls in solution. Several characterization methods, including atomic force microscopy (AFM), contact potential difference (CPD) measurements, and UV/Vis and Fourier transform infrared (FTIR) spectroscopy, verified that these bR monolayers behaved significantly different from native bR. Current–voltage (I–V) measurements (and optical absorption spectroscopy) suggest that the retinal chromophore is probably still present in the protein, whereas the UV/Vis spectrum suggests that it lacks the characteristic covalent protonated Schiff base linkage. This finding sheds light on the unique interactions of biomolecules with solid surfaces and may be significant for the design of protein‐containing device structures. 相似文献
803.
Unique intermolecular reaction of simple porphyrins at a metal surface gives covalent nanostructures
In't Veld M Iavicoli P Haq S Amabilino DB Raval R 《Chemical communications (Cambridge, England)》2008,(13):1536-1538
Deposition of a porphyrin onto metallic copper followed by heating leads to an unprecedented type of linking of the molecules giving a mixture of covalent multiporphyrin nanostructures at the surface. 相似文献
804.
We consider a free boundary problem for a system of partial differential equations, which arises in a model of tumor growth. For any positive number there exists a radially symmetric stationary solution with free boundary . The system depends on a positive parameter , and for a sequence of values there also exist branches of symmetric-breaking stationary solutions, parameterized by , small, which bifurcate from these values. In particular, for near the free boundary has the form where is the spherical harmonic of mode . It was recently proved by the authors that the stationary solution is asymptotically stable for any , but linearly unstable if , where if and if ; . In this paper we prove that for each of the stationary solutions which bifurcates from is linearly stable if and linearly unstable if . We also prove, for , that the point is a Hopf bifurcation, in the sense that the linearized time-dependent problem has a family of solutions which are asymptotically periodic in .
805.
SA Haughey TA Field J Langer NS Shuman TM Miller JF Friedman AA Viggiano 《The Journal of chemical physics》2012,137(5):054310
Dissociative electron attachment to the reactive C(2)F(5) molecular radical has been investigated with two complimentary experimental methods; a single collision beam experiment and a new flowing afterglow Langmuir probe technique. The beam results show that F(-) is formed close to zero electron energy in dissociative electron attachment to C(2)F(5). The afterglow measurements also show that F(-) is formed in collisions between electrons and C(2)F(5) molecules with rate constants of 3.7 × 10(-9) cm(3) s(-1) to 4.7 × 10(-9) cm(3) s(-1) at temperatures of 300-600 K. The rate constant increases slowly with increasing temperature, but the rise observed is smaller than the experimental uncertainty of 35%. 相似文献
806.
807.
Equilibria of binary neutron stars in close circular orbits are computed numerically in a waveless formulation: the full Einstein-relativistic-Euler system is solved on an initial hypersurface to obtain an asymptotically flat form of the 4-metric and an extrinsic curvature whose time derivative vanishes in a comoving frame. Two independent numerical codes are developed, and solution sequences that model inspiraling binary neutron stars during the final several orbits are successfully computed. The binding energy of the system near its final orbit deviates from earlier results of third post-Newtonian and of spatially conformally flat calculations. The new solutions may serve as initial data for merger simulations and as members of quasiequilibrium sequences to generate gravitational-wave templates, and may improve estimates of the gravitational-wave cutoff frequency set by the last inspiral orbit. 相似文献
808.
We analytically examine the time-dependent adsorption of analyte (solute) on a finite-sized adsorption region as a model for sensors utilizing patterned or heterogeneous surfaces. We account for both reversible adsorption (assuming first-order reaction) and saturation of the adsorption patch that may arise either from packing constraints (finite area) or because of a finite number of binding sites (ligands). Our main conclusions include the following: (1) Saturation effects, due to either finite patch size or finite number of binding sites, become significant at extremely short times. (2) Increasing the strength of binding between the analyte and the adsorption sites increases the adsorbed amount at short times, but, at long times, the mass adsorbed on a weakly binding patch is higher than that on a strongly binding one. (3) The sensitivity of detection, as defined by the adsorption of the minimal analyte mass required for signaling, over a fixed period of time, does not scale as 1/detection time. As a result, increasing the time over which adsorption occurs increases sensitivity, but not linearly. Sensitivity of detection also increases with increasing patch area and initial binding strength. 相似文献
809.
Acetylation of purple membranes (PM) significantly enhances the surface photovoltage that they exhibit, if adsorbed as a monolayer on a solid surface; we suggest that this increase is due to the improved orientation of the PM on the surface. 相似文献
810.
We consider a time-dependent free boundary problem with radially symmetric initial data: σt − Δσ + σ = 0 if and σ(r,0)=σ0(r) in {r < R(0)} where R(0) is given. This is a model for tumor growth, with nutrient concentration (or tumor cells density) σ(r,t) and proliferation rate then there exists a unique stationary solution (σS(r), RS), where RS depends only on the number . We prove that there exists a number μ*, such that if μ < μ* . . . then the stationary solution is stable with respect to non-radially symmetric perturbations, whereas if μ > μ* then the stationary solution is unstable. 相似文献