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921.
Jouzi M Kerby MB Tripathi A Xu J 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):10786-10790
We describe a new method for measuring the activity of protein in miniscule quantities using a carbon nanotube nanoneedle. The unique features of this new method are (a) the immobilization of a few molecules; (b) subsequent translocation and isolation of them near the tip of a position-actuated nanoneedle; and (c) a fixed, defined, and unhindered molecular position to allow rapid real-time sensing and monitoring. The kinetic bioactivity of immobilized alkaline phosphatase (AP) molecules was measured as test model. Results show no decrease in enzymatic activity compared to that of the solution-phase enzyme reaction, suggesting that the immobilization provided unhindered access for ligand binding and minimal conformational modulation caused by undesired surface interactions. 相似文献
922.
Schneider C Jusufi A Farina R Li F Pincus P Tirrell M Ballauff M 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):10612-10615
We propose a new way to determine weak repulsive forces operative between colloidal particles by measuring the rate of slow coagulation. The rate of slow coagulation is directly related to the competition of the repulsion with thermal motion. Since the thermal forces are weak, measurements of the coagulation rate can lead to precise information on repulsive potentials having a magnitude of just a few kT. We demonstrate this novel way by studying colloidal spherical polyelectrolyte brush (SPB) particles in aqueous solution containing trivalent La3+ counterions. The particles consist of a monodisperse polystyrene core of 121 nm radius from which linear sodium poly(styrenesulfonate) (PSS) chains are densely grafted (contour length 48 nm). We determine the rate of coagulation by time-resolved simultaneous static and dynamic light scattering in the presence of LaCl3 (0.2 to 150 mM). Direct measurements of the repulsive force between macroscopic brush layers demonstrate that the potential is decaying exponentially with distance. This is in good agreement with a simple theoretical treatment that furthermore leads to the effective surface potential Psi0. The good agreement of data obtained by the novel microscopic method with direct macroscopic measurements underscores the general validity of our approach. 相似文献
923.
Kurkuri MD Nussio MR Deslandes A Voelcker NH 《Langmuir : the ACS journal of surfaces and colloids》2008,24(8):4238-4244
Expanded cross-linked copolymers of poly(N-isopropylacrylamide) (PNiPAAm) and poly(acrylic acid) (PAAc) of varying monomer ratios were grafted from a crystalline silicon surface. Surface-tethered polymerization was performed at a slightly basic pH, where electrostatic repulsion among acrylic acid monomer units forces the network into an expanded polymer conformation. The influence of this expanded conformation on switchability between a hydrophilic and a hydrophobic state was investigated. Characterization of the copolymer coating was carried out by means of X-ray photoelectron spectroscopy (XPS) ellipsometry, and diffuse reflectance IR. Lower critical solution temperatures (LCSTs) of the copolymer grafts on the silicon surfaces were determined by spectrophotometry. Temperature-induced wettability changes were studied using sessile drop contact angle measurements. The surface topography was investigated by atomic force microscopy (AFM) in Milli-Q water at 25 and 40 degrees C. The reversible attachment of a fluorescently labeled model protein was studied as a function of temperature using a fluorescence microscope and a fluorescence spectrometer. Maximum switching in terms of the contact angle change around the LCST was observed at a ratio of 36:1 PNiPAAm to PAAc. The enhanced control of biointerfaces achieved by these coatings may find applications in biomaterials, biochips, drug delivery, and microfluidics. 相似文献
924.
Alex S. Ionkin William J. Marshall Douglas J. Adelman Barbara Bobik Fones Brian M. Fish Matthew F. Schiffhauer Paul D. Soper Robert L. Waterland Rupert E. Spence Tuyu Xie 《Journal of polymer science. Part A, Polymer chemistry》2008,46(2):585-611
Series of Fe(II) and Fe(III) tridentate bis(imino)pyridine complexes without nitrilo groups 2–6 and with nitrilo groups 7–13 were synthesized. According to X‐ray analysis, the introduction of nitrilo groups in para‐ and ortho‐positions tends to result in shorter axial Fe? N bonds. Both types of complexes, 2–6 and 9–13 , afforded very productive catalysts for the production of α‐olefins with higher K values and better linearity of Schultz–Flory distribution α‐olefins than the parent methyl substituted Fe(II) complex 1 . Noticeably, the complexes functionalized with a para‐nitrilo group 9–13 tend to make α‐olefins with higher K values of the Schultz–Flory distribution, more ideal distributions, and less of the heavier insoluble fractions of α‐olefins than corresponding nonsymmetrically substituted complexes without para‐nitrilo groups 2–6 . Statistically significant correlations were obtained between % solids of total α‐olefins and the blocked solid angle fraction in the +z hemisphere ( = 51.3%, p = 0.012) and between catalyst productivity and total blocked solid angle fraction ( = 43.5%, p = 0.023). The modest values of show that, while steric effects are significant, they are not the sole factor determining catalyst performance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 585–611, 2008 相似文献
925.
Haggenmueller R Rahatekar SS Fagan JA Chun J Becker ML Naik RR Krauss T Carlson L Kadla JF Trulove PC Fox DF Delong HC Fang Z Kelley SO Gilman JW 《Langmuir : the ACS journal of surfaces and colloids》2008,24(9):5070-5078
The use of single wall carbon nanotubes (SWCNTs) in current and future applications depends on the ability to process SWCNTs in a solvent to yield high-quality dispersions characterized by individual SWCNTs and possessing a minimum of SWCNT bundles. Many approaches for the dispersion of SWCNTs have been reported. However, there is no general assessment which compares the relative quality and dispersion efficiency of the respective methods. Herein we report a quantitative comparison of the relative ability of "wrapping polymers" including oligonucleotides, peptides, lignin, chitosan, and cellulose and surfactants such as cholates, ionic liquids, and organosulfates to disperse SWCNTs in water. Optical absorption and fluorescence spectroscopy provide quantitative characterization (amount of SWCNTs that can be suspended by a given surfactant and its ability to debundle SWCNTs) of these suspensions. Sodium deoxy cholate (SDOCO), oligonucleotides (GT)(15), (GT)(10), (AC)(15), (AC)(10), C(10-30), and carboxymethylcellulose (CBMC-250K) exhibited the highest quality suspensions of the various systems studied in this work. The information presented here provides a good framework for further study of SWCNT purification and applications. 相似文献
926.
Labrosse MR Shi W Johnson JK 《Langmuir : the ACS journal of surfaces and colloids》2008,24(17):9430-9439
Molecular simulations are used to shed light on an ongoing controversy over where gases adsorb on single walled carbon nanotube bundles. We have performed simulations using models of carbon nanotube bundles composed of tubes of all the same diameter (homogeneous) and tubes of different diameters (heterogeneous). Simulation data are compared with experimental data in an effort to identify the best model for describing experimental data. Adsorption isotherms, isosteric heats of adsorption, and specific surface areas have been computed for Ar, CH 4, and Xe on closed, open, and partially opened homogeneous and heterogeneous nanotube bundles. Experimental data from nanotubes prepared from two different methods, electric arc and HiPco, were examined. Experimental adsorption isotherms and isosteric heats for nanotubes prepared by the electric arc method are in best agreement with simulations for heterogeneous bundles of closed nanotubes. Models including adsorption in defect interstitial channels are required to achieve good agreement with experiments. Experimental isosteric heats and specific surface areas on HiPco nanotubes are best described by a model consisting of heterogeneous bundles with approximately 11% of the nanotubes opened. 相似文献
927.
Perez Barrio J Rebilly JN Carter B Bradshaw D Bacsa J Ganin AY Park H Trewin A Vaidhyanathan R Cooper AI Warren JE Rosseinsky MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(15):4521-4532
Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework. 相似文献
928.
Sai KK Tokarz MJ Malunchuk AP Zheng C Gilbert TM Klumpp DA 《Journal of the American Chemical Society》2008,130(44):14388-14389
In reactions with benzene and related substrates, an oxazole-based superelectrophile is found to be significantly more reactive than a related monocationic species. Theoretical calculations estimate that the lowest unoccupied molecular orbital (LUMO) for the superelectrophile is about 4 eV lower in energy than the LUMOs of comparable monocations. When the oxazole-based superelectrophile is reacted with ferrocene, a dimeric product is formed in high yield. The dimerization occurs by a single electron transfer reaction between the dicationic superelectrophile and ferrocene, followed by coupling of the radical cations. 相似文献
929.
Popescu DL Chanda A Stadler MJ Mondal S Tehranchi J Ryabov AD Collins TJ 《Journal of the American Chemical Society》2008,130(37):12260-12261
Recent broad-ranging mechanistic studies of FeIII-TAML peroxide activators enable a strategy for designing catalysts with improved (i) hydrolytic and (ii) operational stabilities, (iii) faster activation of H2O2 and other peroxides, and (iv) a pH of highest activity closer to 7. Combining all items of insight leads to [Fe{1-NO2C6H3-3,4-(NCOCMe2NCO)2CF2}(OH2)]- (1a) which exhibits the most desirable technical performance in its class. 相似文献
930.
Keck GE Kraft MB Truong AP Li W Sanchez CC Kedei N Lewin NE Blumberg PM 《Journal of the American Chemical Society》2008,130(21):6660-6661
Highly potent bryostatin analogues which contain the complete bryostatin core structure have been synthesized using a pyran annulation approach as a key strategic element. The A ring pyran was assembled using a pyran annulation reaction between a C1-C8 hydroxy allylsilane and an aldehyde comprising C9-C13. This pyran was transformed to a new hydroxy allylsilane and then coupled with a preformed C ring aldehyde subunit in a second pyran annulation, with concomitant formation of the B ring. This tricyclic intermediate was elaborated to bryostatin analogues which displayed nanomolar to subnanomolar affinity for PKC, but displayed properties indistinguishable from a phorbol ester in a proliferation/attachment assay. 相似文献