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921.
922.
The successful integration of living cells into synthetic devices requires precise control over cell patterning. Here we describe a versatile platform that can accomplish this goal through DNA hybridization. Living cells functionalized with exogenous cell-surface DNA strands bind to cognate sequences of DNA printed on glass slides. Attachment via these "cell-adhesion barcodes" is rapid and specific, with close-packed arrays of cells forming within minutes. The biophysical properties of the system are characterized, and the technique is used to form complex cellular patterns with single-cell line widths and self-assembled cellular microarrays. Key advantages of DNA-directed cell binding include the ability to immobilize both adherent and non-adherent cells, to capture cells selectively from a mixed population, to tune the binding properties of the cells, and to reuse substrates prepared with widely available DNA printing technologies. 相似文献
923.
Bonneau AL Robert N Hoarau C Baudoin O Marsais F 《Organic & biomolecular chemistry》2007,5(1):175-183
The synthesis of three novel racemic phenylpyridine-carbamate analogues of rhazinilam and their biological evaluation as inhibitors of microtubule assembly and disassembly by interaction with tubulin are described. The sterically hindered ortho-disubstituted biaryl unit as the challenging key structural element is first obtained by a sequential regiocontrolled nucleophilic addition of a lithium ortho-lithiohomobenzylic alkoxide species to 3-bromo-5-oxazolyl pyridine as the electrophile and a subsequent oxidation step. The incorporation of the amino group by replacement of the bromide has been achieved using a Buchwald-Hartwig amination coupling. Ultimate deprotection steps furnished free-amino and free-hydroxyl appendages which were connected by phosgenation to furnish the nine-membered median carbamate ring. 相似文献
924.
This article studies the problem of minimizing ∫ΩF(Du)+G(x,u) over the functions uW1,1(Ω) that assume given boundary values on ∂Ω. The function F and the domain Ω are assumed convex. In considering the same problem with G=0, and in the spirit of the classical Hilbert–Haar theory, Clarke has introduced a new type of hypothesis on the boundary function : the lower (or upper) bounded slope condition. This condition, which is less restrictive than the classical bounded slope condition of Hartman, Nirenberg and Stampacchia, is satisfied if is the restriction to ∂Ω of a convex (or concave) function. We show that for a class of problems in which G(x,u) is locally Lipschitz (but not necessarily convex) in u, the lower bounded slope condition implies the local Lipschitz regularity of solutions. 相似文献
925.
Foote KG Francis DT Atkins PR 《The Journal of the Acoustical Society of America》2007,121(3):1482-1490
The problem of calibrating parametric sonar systems at low difference frequencies used in backscattering applications is addressed. A particular parametric sonar is considered: the Simrad TOPAS PS18 Parametric Sub-bottom Profiler. This generates difference-frequency signals in the band 0.5-6 kHz. A standard target is specified according to optimization conditions based on maximizing the target strength consistent with the target strength being independent of orientation and the target being physically manageable. The second condition is expressed as the target having an immersion weight less than 200 N. The result is a 280-mm-diam sphere of aluminum. Its target strength varies from -43.4 dB at 0.5 kHz to -20.2 dB at 6 kHz. Maximum excursions in target strength over the frequency band due to uncertainty in material properties of the sphere are of order +/-0.1 dB. Maximum excursions in target strength due to variations in mass density and sound speed of the immersion medium are larger, but can be eliminated by attention to the hydrographic conditions. The results are also applicable to the standard-target calibration of conventional sonars operating at low-kilohertz frequencies. 相似文献
926.
Ultrafast Photoinduced Charge Separation in Wide‐Band‐Capturing Self‐Assembled Supramolecular Bis(donor styryl)BODIPY–Fullerene Conjugates 下载免费PDF全文
Shuai Shao Habtom B. Gobeze Prof. Dr. Paul A. Karr Prof. Dr. Francis D'Souza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):16005-16016
A new series of self‐assembled supramolecular donor–acceptor conjugates capable of wide‐band capture, and exhibiting photoinduced charge separation have been designed, synthesized and characterized using various techniques as artificial photosynthetic mimics. The donor host systems comprise of a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) containing a crown ether entity at the meso‐position and two styryl entities on the pyrrole rings. The styryl end groups also carried additional donor (triphenylamine or phenothiazine) entities. The acceptor host system was a fulleropyrrolidine comprised of an ethylammonium cation. Owing to the presence of extended conjugation and multiple chromophore entities, the BODIPY host revealed absorbance and emission well into the near‐IR region covering the 300–850 nm spectral range. The donor–acceptor conjugates formed by crown ether–alkyl ammonium cation binding of the host–guest system was characterized by optical absorbance and emission, computational, and electrochemical techniques. Experimentally determined binding constants were in the range of 1–2×105 M ?1. An energy‐level diagram to visualize different photochemical events was established using redox, computational, absorbance, and emission data. Spectral evidence for the occurrence of photoinduced charge separation in these conjugates was established from femtosecond transient absorption studies. The measured rates indicated ultrafast charge separation and relatively slow charge recombination revealing their usefulness in light‐energy harvesting and optoelectronic device applications. The bis(donor styryl)BODIPY‐derived conjugates populated their triplet excited states during charge recombination. 相似文献
927.
Charge Separation in Graphene‐Decorated Multimodular Tris(pyrene)–Subphthalocyanine–Fullerene Donor–Acceptor Hybrids 下载免费PDF全文
Chandra B. KC Gary N. Lim Prof. Dr. Francis D'Souza 《Angewandte Chemie (International ed. in English)》2015,54(17):5088-5092
A new approach to probe the effect of graphene on photochemical charge separation in donor–acceptor conjugates is devised. For this, multimodular donor–acceptor conjugates, composed of three molecules of pyrene, a subphthalocyanine, and a fullerene C60 ((Pyr)3SubPc‐C60), have been synthesized and characterized. These systems were hybridized on few‐layer graphene through π–π stacking interactions of the three pyrene moieties. The hybrids were characterized using Raman, HRTEM, and spectroscopic and electrochemical techniques. The energy levels of the donor–acceptor conjugates were fine‐tuned upon interaction with graphene and photoinduced charge separation in the absence and presence of graphene was studied by femtosecond transient absorption spectroscopy. Accelerated charge separation and recombination was detected in these graphene‐decorated conjugates suggesting that they could be used as materials for fast‐responding optoelectronic devices and in light energy harvesting applications. 相似文献
928.
Dr. Yi Hu Dr. Michael B. Thomas Dr. Whitney A. Webre Austen Moss Dr. R. G. Waruna Jinadasa Dr. Vladimir N. Nesterov Prof. Dr. Francis D'Souza Prof. Dr. Hong Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20250-20257
A series of largely π-extended multichromophoric molecules including cross-conjugated, half cross-conjugated, conjugation-interrupted and linearly conjugated systems were synthesized and characterized. These multichromophoric molecular systems revealed interesting structural-property relationships. Bisporphyrin-fused pentacenes Pen-1 b and Pen-2 a showed rich redox chemistry with 7 and 8 observable redox states, respectively. The linearly-conjugated bisporphyrin-fused pentacenes ( Pen-1 b and Pen-2 a ) possess much narrower HOMO–LUMO gaps (1.65 and 1.42 eV redox, respectively) and higher HOMO energy levels than those of their pentacene analogues (2.23 and 2.01 eV redox, respectively), similar to those of much less stable hexacenes and heptacenes. An estimated half-life of >945 h was obtained for bisporphyrin-fused pentacene Pen-2 a , which is much longer than that of its pentacene analogue ( BPE-P , half-life, 33 h). 相似文献
929.
Huijun Guo Wenting Sun Francis M. Haas Tanvir Farouk Frederick L. Dryer Yiguang Ju 《Proceedings of the Combustion Institute》2013,34(1):573-581
H2O2 is one of the most important species in dimethyl ether (DME) oxidation, acting not only as a marker for low temperature kinetic activity but also responsible for the “hot ignition” transition. This study reports, for the first time, direct measurements of H2O2 and CH3OCHO, among other intermediate species concentrations in helium-diluted DME oxidation in an atmospheric pressure flow reactor from 490 to 750 K, using molecular beam electron-ionization mass spectrometry (MBMS). H2O2 measurements were directly calibrated, while a number of other species were quantified by both MBMS and micro gas chromatography to achieve cross-validation of the measurements. Experimental results were compared to two different DME kinetic models with an updated rate coefficient for the H + DME reaction, under both zero-dimensional and two-dimensional physical model assumptions. The results confirm that low and intermediate temperature DME oxidation produces significant amounts of H2O2. Peroxide, as well as O2, DME, CO, and CH3OCHO profiles are reasonably well predicted, though profile predictions for H2/CO2 and CH2O are poor above and below ~625 K, respectively. The effect of the collisional efficiencies for the H + O2 + M = HO2 + M reaction on DME oxidation was investigated by replacing 20% He with 20% CO2. Observed changes in measured H2O2 concentrations agree well with model predictions. The new experimental characterizations of important intermediate species including H2O2, CH2O and CH3OCHO, and a path flux analysis of the oxidation pathways of DME support that kinetic parameters for decomposition reactions of HOCH2OCO and HCOOH directly to CO2 may be responsible for model under-prediction of CO2. The H abstraction reactions for DME and/or CH2O and the unimolecular decomposition of HOCH2O merit further scrutiny towards improving the prediction of H2 formation. 相似文献
930.
Francis E. H. Tay Yung C. Liang V. J. Logeeswaran 《International Journal of Electronics》2013,100(10):1179-1191
The micromachined gyroscope is rapidly gaining popularity as a rate sensor for application in areas such as automotive and aerospace systems, where low power consumption, high sensitivity, low temperature drift and good stability are prerequisites. In this paper, the overall design and fabrication process of a reactive ion-etched inertial resonant gyroscope based on the capacitive sensing principle is reported. The experimental results are also discussed. 相似文献