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191.
We report the formation of a new class of supported membranes consisting of a fluid phospholipid bilayer coupled directly to a broadly tunable colloidal crystal with a well-defined photonic band gap. For nanoscale colloidal crystals exhibiting a band gap at the optical frequencies, substrate-induced vesicle fusion gives rise to a surface bilayer riding onto the crystal surface. The bilayer is two-dimensionally continuous, spanning multiple beads with lateral mobilities which reflect the coupling between the bilayer topography and the curvature of the supporting colloidal surface. In contrast, the spreading of vesicles on micrometer scale colloidal crystals results in the formation of bilayers wrapping individual colloidal beads. We show that simple UV photolithography of colloidal crystals produces binary patterns of crystal wettabilities, photonic stopbands, and corresponding patterns of lipid mono- and bilayer morphologies. We envisage that these approaches will be exploitable for the development of optical transduction assays and microarrays for many membrane-mediated processes, including transport and receptor-ligand interactions. 相似文献
192.
Smith SD Hamersky MW Bowman MK Rasmussen KØ Spontak RJ 《Langmuir : the ACS journal of surfaces and colloids》2006,22(15):6465-6468
The conditions signaling the formation of bidisperse brushes in ordered block copolymers are investigated as an A(2) block is progressively grown onto an A(1)B diblock copolymer to form a series of molecularly asymmetric, isomorphic A(1)BA(2) triblock copolymers. Small-angle scattering and self-consistent field theory confirm that the microphase-ordered period decreases when the A(2) block is short relative to the A(1) block, but then increases as A(1)+A(2) bidisperse brushes develop. The mechanical properties systematically follow the spatial distribution of the A(2) block. 相似文献
193.
Carlson JC Jena SS Flenniken M Chou TF Siegel RA Wagner CR 《Journal of the American Chemical Society》2006,128(23):7630-7638
The exploitation of biological macromolecules, such as nucleic acids, for the fabrication of advanced materials is a promising area of research. Although a greater variety of structural and functional uses can be envisioned for protein-based materials, systematic approaches for their construction have yet to emerge. Consistent with theoretical models of polymer macrocyclization, we have demonstrated that, in the presence of dimeric methotrexate (bisMTX), wild-type Escherichia coli dihydrofolate reductase (DHFR) molecules tethered together by a flexible peptide linker (ecDHFR(2)) are capable of spontaneously forming highly stable cyclic structures with diameters ranging from 8 to 20 nm. The nanoring size is dependent on the length and composition of the peptide linker, on the affinity and conformational state of the dimerizer, and on induced protein-protein interactions. Delineation of these and other rules for the control of protein oligomer assembly by chemical induction provides an avenue to the future design of protein-based materials and nanostructures. 相似文献
194.
The following novel solvatochromic probes were synthesized: 2,6-dibromo-4-[(E)-2-(1-alkylpyridinium-4-yl)ethenyl] phenolate, where the alkyl groups are methyl, n-butyl, n-hexyl, and n-octyl, respectively. Solvatochromism of three of these probes (C(1), C(4), and C(8)) was studied in 36 protic and aprotic solvents. A modified linear solvation energy relationship has been applied to the data obtained at 25 degrees C. Correlation of (empirical) polarities with other solvent properties showed more dependence on lipophilicity than on basicity. A similar conclusion has been reached for a series of other solvatochromic indicators. Exceptions are those that carry acidic hydrogens, being biased toward solvent basicity. Thermosolvatochromism has been studied in mixtures of water with methanol, 1-propanol, acetonitrile, and DMSO. Thermosolvatochromic data have been treated according to a model that explicitly considers the presence in bulk solution of three "species": water, organic component, and solvent-water hydrogen-bonded aggregate. Solvation by the latter is favored over solvation by either of the two precursor solvents (aqueous DMSO is an exception). Temperature increase resulted in desolvation of the probes, due to concomitant decrease of the structures of the component solvents. The above-mentioned modified solvation equation has been successfully applied to solvatochromism in aqueous methanol and aqueous 1-propanol. 相似文献
195.
High-level ab initio calculations demonstrate that alkoxy-thiocarbonyl radicals (ROC*=S) undergo beta-scission significantly faster than alkoxycarbonyl radicals (ROC*=O) despite having similar exothermicities. The relatively low reactivity of the ROC*=O radicals is reduced further by electron-donating R groups and arises from the large polarization of the C*-O bonds of the reactant radicals. The results suggest that the generation of alkyl radicals from ROC*=S should be particularly efficient when the R group bears radical-stabilizing and/or electron-accepting groups, such as CN. 相似文献
196.
Wright P Chassaing C Cussans N Gibson D Green C Gleave M Jones R Macrae P Saunders K 《Biomedical chromatography : BMC》2006,20(6-7):585-596
Increased demand for assays for compounds at the early stages of drug discovery within the pharmaceutical industry has led to the need for open-access mass spectrometry systems for performing quantitative analysis in a variety of biological matrices. The open-access mass spectrometers described here are LC/MS/MS systems operated in 'multiple reaction monitoring' (MRM) mode to obtain the sensitivity and specificity required to quantitate low levels of pharmaceutical compounds in an excess of biological matrix. Instigation of these open-access systems has resulted in mass spectrometers becoming the detectors of choice for non-expert users, drastically reducing analytical method development time and allowing drug discovery scientists to concentrate on their core expertise of pharmacokinetics and drug metabolism. Setting up an open-access facility that effectively allows a user with minimal mass spectral knowledge to exploit the MS/MS capability of triple quadrupole mass spectrometers presents a significantly different challenge from setting up qualitative single stage mass spectrometry systems. Evolution of quantitative open access mass spectrometry within a pharmaceutical drug metabolism and pharmacokinetics group, from its beginnings as a single generic system to a series of specialist fully integrated walk-up facilities, is described. 相似文献
197.
D. Michelle Motley Judith A. Walmsley Julio Zukerman-Schpector Edward R. T. Tiekink 《Journal of chemical crystallography》2009,39(5):364-367
Abstract The gold(III) atom in [Au(NH2CH2CH2NH2)Cl2]NO3 is chelated by the ethylenediamine (en) ligand and the approximately square planar geometry is completed by two chloride
atoms. Weak Au···O and Au···Cl contacts are noted above and below the square plane leading to a tetragonally distorted octahedron
for the gold(III) center. Extensive charge-assisted hydrogen bonding of the type N–H···O leads to the formation of a 2-D array
and layers are consolidated into a 3-D network via C–H···O and C–H···Cl contacts. The compound crystallizes in the orthorhombic
space group Pbca with a = 10.3380(11) ?, b = 8.2105(7) ?, c = 19.625(2) ?, and Z = 8.
Index Abstract Square planar complex cations form additional Au···O and Au···Cl interactions to form a tetragonally distorted octahedron
for gold. The ionic components are connected into a 2-D array via charge-assisted N–H···O hydrogen bonding interactions.
相似文献
198.
Phonation threshold pressure (PTP), effort for speaking, and vibratory closure pattern were assessed in 4 women with normal untrained voices after 2 hours of loud reading. PTP generally increased after this vocally fatiguing task at conversational pitch and 10%, 50%, and especially 80% of the pitch range. Increased systemic hydration by drinking water appeared to attenuate and/or delay the elevation of PTP for 3 subjects, at least at the highest pitch tested. Effort for speaking increased consistently throughout the loud reading task and subsequently decreased after 15 minutes of vocal silence. Upon videostroboscopic examination of the larynx, 3 subjects demonstrated spindle-shaped vibratory closure patterns on occasion after loud reading. The results provide preliminary support for increasing water consumption to reduce or delay some vocal-function changes after prolonged loud phonation in untrained speakers. 相似文献
199.
Hydrogels, three-dimensional hydrophilic polymer networks, are appealing candidate materials for study- ing the cellular microenvironment as their substantial water content helps to better mimic soft tissue. However, hydrogels can lack mechanical stiffness, strength, and tough- ness. Composite hydrogel systems have been shown to improve upon mechanical properties compared to their single- component counterparts. Poly (ethylene glycol) dimethacrylate (PEGDMA) and alginate are polymers that have been used to form hydrogels for biological applications. Single- component and composite PEGDMA and alginate systems were fabricated with a range of total polymer concentrations. Bulk gels were mechanically characterized using spherical indentation testing and a viscoelastic analysis framework. An increase in shear modulus with increasing polymer con- centration was demonstrated for all systems. Alginate hydro- gels were shown to have a smaller viscoelastic ratio than the PEGDMA gels, indicating more extensive relaxation over time. Composite alginate and PEGDMA hydrogels exhib- ited a combination of the mechanical properties of the con- stituents, as well as a qualitative increase in toughness. Additionally, multiple hydrogel systems were produced that had similar shear moduli, but different viscoelastic behaviors. Accurate measurement of the mechanical properties of hydrogels is necessary in order to determine what parameters are key in modeling the cellular microenvironment. 相似文献