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81.
Excimer laser ablation at 308 nm has been used to texture the surfaces of a variety of materials of interest for optoelectronic and biotechnological applications. Using a range of pre- and post-processing methods, we are able to produce nano-, micro- and meso-scale features over large areas rapidly in materials such as crystalline Si, porous silicon and TiO2. Texturing of porous silicon leads to the growth of crystalline dendritic structures, which distinguishes them dramatically from the conical pillars formed from crystalline silicon. Regular arrays of Si microdots are formed by irradiating a Si surface pre-covered with a Cr thin film grating. Nano-crystalline porous TiO2 films are easily ablated or compacted with laser irradiation. However, at low enough laser fluence, surface roughening without complete loss of porosity is possible. 相似文献
82.
Shaun Bullett 《Communications in Mathematical Physics》1986,107(2):241-262
We investigate invariant circles for a one-parameter family of piecewise linear twist homeomorphisms of the annulus. We show that invariant circles of all types and rotation numbers occur and we classify them into families. We compute parameter ranges in which there are no invariant circles. 相似文献
83.
Wolfgang Oppolzer Robert J. Mills Werner Pachinger Thomas Stevenson 《Helvetica chimica acta》1986,69(7):1542-1545
EtAlCl2-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic β-silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si-C bond cleavage furnished enantiomerically pure acetate-derived aldols and propionate-derived ‘anti’ -aldols (via silyl-directed α-methylation). 相似文献
84.
The extension of a new, low dose, Mössbauer spectroscopy approach to cancer radiation therapy to “easy” isotopes other than Iron-57 is outlined. New in vitro studies using a number of cancer cell lines are reported. 相似文献
85.
A. Sulfrian M. Kapp Margaret D. Foster und E. V. Mills 《Fresenius' Journal of Analytical Chemistry》1933,95(1-3):105-107
Ohne Zusammenfassung 相似文献
86.
A J Klein J H Mills W Y Adkins 《The Journal of the Acoustical Society of America》1990,87(3):1266-1271
Upward spreading of masking, measured in terms of absolute masked threshold, is greater in hearing-impaired listeners than in listeners with normal hearing. The purpose of this study was to make further observations on upward-masked thresholds and speech recognition in noise in elderly listeners. Two age groups were used: One group consisted of listeners who were more than 60 years old, and the second group consisted of listeners who were less than 36 years old. Both groups had listeners with normal hearing as well as listeners with mild to moderate sensorineural loss. The masking paradigm consisted of a continuous low-pass-filtered (1000-Hz) noise, which was mixed with the output of a self-tracking, sweep-frequency Bekesy audiometer. Thresholds were measured in quiet and with maskers at 70 and 90 dB SPL. The upward-masked thresholds were similar for young and elderly hearing-impaired listeners. A few elderly listeners had lower upward-masked thresholds compared with the young control group; however, their on-frequency masked thresholds were nearly identical to the control group. A significant correlation was found between upward-masked thresholds and the Speech Perception in Noise (SPIN) test in elderly listeners. 相似文献
87.
The remarkable ability of nematic elastomers to exhibit large deformations under small applied forces is known as soft elasticity.
The recently proposed neo-classical free-energy density for nematic elastomers, derived by molecular-statistical arguments,
has been used to model soft elasticity. In particular, the neo-classical free-energy density allows for a continuous spectrum
of equilibria, which implies that deformations may occur in the complete absence of force and energy cost. Here we study the
notion of force-free states in the context of a continuum theory of nematic elastomers that allows for isotropy, uniaxiality,
and biaxiality of the polymer microstructure. Within that theory, the neo-classical free-energy density is an example of a
free-energy density function that depends on the deformation gradient only through a nonlinear strain measure associated with
the deformation of the polymer microstructure relative to the macroscopic continuum. Among the force-free states for a nematic
elastomer described by the neo-classical free energy density, there is, in particular, a continuous spectrum of states parameterized
by a pair of tensors that allows for soft deformations. In these force-free states the polymer microstructure is material
in the sense that it stretches and rotates with the macroscopic continuum. Limitations of and possible improvements upon the
neo-classical model are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
88.
Lippow SM Moon TS Basu S Yoon SH Li X Chapman BA Robison K Lipovšek D Prather KL 《Chemistry & biology》2010,17(12):1306-1315
Engineered biosynthetic pathways have the potential to produce high-value molecules from inexpensive feedstocks, but a key limitation is engineering enzymes with high activity and specificity for new reactions. Here, we developed a method for combining structure-based computational protein design with library-based enzyme screening, in which inter-residue correlations favored by the design are encoded into a defined-sequence library. We validated this approach by engineering a glucose 6-oxidase enzyme for use in a proposed pathway to convert D-glucose into D-glucaric acid. The most active variant, identified after only one round of diversification and screening of only 10,000 wells, is approximately 400-fold more active on glucose than is the wild-type enzyme. We anticipate that this strategy will be broadly applicable to the discovery of new enzymes for engineered biological pathways. 相似文献
89.
Cassidy DB Bromley MW Cota LC Hisakado TH Tom HW Mills AP 《Physical review letters》2011,106(2):023401
We report experiments in which the line shape of the Lyman-alpha (1S-2P) transition was measured for positronium (Ps) atoms both inside and outside a porous silica target. The energy interval ΔE for confined atoms was observed to be larger than that of free Ps by 1.26±0.06 meV. A configuration interaction calculation yields results that are consistent with our ~5 nm sample, and suggests that ΔE decreases dramatically for larger cavity diameters. The linewidth of the transition, (0.066±0.004) nm (FWHM), is about half of what one would expect for free Ps at room temperature due to the Dicke line narrowing effect of confinement. Such measurements can be used to determine void sizes in porous films and Ps dynamics therein, and elimination of the Doppler spread of atoms in a porous film could be useful for the efficient excitation of a Ps gas. 相似文献
90.
Zeeman mixing of singlet and triplet 2P states of positronium (Ps) atoms, followed by decay back to the ground state, can effectively turn a long-lived triplet atom into a short-lived singlet state, which would seem to preclude laser cooling of Ps in a magnetic field. Here we report experiments which show that, in fact, because of the large splitting of the n=2 states in a high magnetic field (the Paschen-Back regime), the amount of such mixing diminishes approximately exponentially with an increasing magnetic field >0.01 T and is essentially eliminated above ~2 T. Thus, laser cooling of Ps should be feasible at high fields, which will facilitate the production of a Ps Bose-Einstein condensate. 相似文献