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181.
182.
Macdonald Critchley 《BMJ (Clinical research ed.)》1945,2(4413):145-148
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185.
Ferdinand Bohlmann Christa Zdero Robert M. King Harold Robinson 《Phytochemistry》1984,23(7):1509-1511
A reinvestigation of the aerial parts of Conocliniopsis prasiifolia afforded two furoheliangolides, conoprasiolide-9-O,5′-O-diacetate and 相似文献
186.
Ferdinand Bohlmann Christa Zdero Robert M. King Harold Robinson 《Phytochemistry》1984,23(5):1185-1187
Perymenium featherstonei afforded, in addition to the known ent-kaurene derivative 4α, 15-dihydroencelin, two closely related epimeric acids. 相似文献
187.
Generalization and categorization of spectral colors in goldfish I. Experiments with one training wavelength 总被引:1,自引:1,他引:0
Manuela?Kitschmann Christa?NeumeyerEmail author 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2005,191(11):1025-1036
Goldfish have a tetrachromatic color vision with a high discrimination ability for spectral colors as well as for object colors.
We investigate the question whether goldfish organize the high number of discriminable colors in terms of color categories,
i.e. in a few larger groups of colors independent of wavelength discrimination. Twenty-four goldfish were trained with food
reward, each fish on one out of 13 wavelengths between 371 nm and 630 nm. In transfer tests two different wavelengths were
presented, one shorter and one longer than the training wavelength, and the choice behavior was determined. Choice frequencies
of ≥50% were assumed to indicate similarity to the training color. The wavelength ranges ≥50% were about 100 nm and twice
as large as the just noticeable differences measured in wavelength discrimination tests (Fig. 7). The ranges were surprisingly
about the same for all training wavelengths, provided the data were plotted on a wavelength scale weighted according to discrimination
ability (Fig. 4). Thus, with the training method chosen goldfish showed a kind of categorization which, however, depends on
training wavelength and discrimination ability. Generalization tests in which training wavelength and test wavelengths were
shown separately for 2 min each gave the same results as wavelength discrimination tests (Figs. 5 and 6) and are, therefore,
not indicative for color categories. 相似文献
188.
In previous studies, we have shown that annual expression profiles of cambial and wood tissue with respect to the Shaker K+ channel PTORK correlate with cambial activity. To follow PTORK-gene activity on the cellular level, we isolated the respective promoter regions and generated transgenic Arabidopsis plants expressing the GUS gene under the control of the PTORK promoter. Cross-sections of petioles showed PTORK-driven signals predominantly in the xylem parenchyma surrounding the vessels and in the phloem. Antibodies raised against a unique N-terminal region of PTORK in histo-immunochemical analyses recognised this K+-release channel in growth-active poplar plants only. PTORK labelling was found in differentiating xylem cells (young fibres) and mature xylem (vessel-associated cells of the ray parenchyma). Patch-clamp measurements on fibre cell protoplasts, derived from young poplar twigs, identified outward-rectifying K+ channels as the major K+ conductance of this cell type, which resembled the biophysical properties of PTORK when expressed in Xenopus oocytes.Electronic Supplementary Material Supplementary material is available for this article at
Matthias Arend and Andrea Stinzing contributed equally to this work 相似文献
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190.
Jakopitsch C Ivancich A Schmuckenschlager F Wanasinghe A Pöltl G Furtmüller PG Rüker F Obinger C 《The Journal of biological chemistry》2004,279(44):46082-46095
Catalase-peroxidases (KatGs) are heme peroxidases with a catalatic activity comparable to monofunctional catalases. They contain an unusual covalent distal side adduct with the side chains of Trp(122), Tyr(249), and Met(275) (Synechocysis KatG numbering). The known crystal structures suggest that Tyr(249) and Met(275) could be within hydrogen-bonding distance to Arg(439). To investigate the role of this peculiar adduct, the variants Y249F, M275I, R439A, and R439N were investigated by electronic absorption, steady-state and transient-state kinetic techniques and EPR spectroscopy combined with deuterium labeling. Exchange of these conserved residues exhibited dramatic consequences on the bifunctional activity of this peroxidase. The turnover numbers of catalase activity of M275I, Y249F, R439A, and R439N are 0.6, 0.17, 4.9, and 3.14% of wild-type activity, respectively. By contrast, the peroxidase activity was unaffected or even enhanced, in particular for the M275I variant. As shown by mass spectrometry and EPR spectra, the KatG typical adduct is intact in both Arg(439) variants, as is the case of the wild-type enzyme, whereas in the M275I variant the covalent link exists only between Tyr(249) and Trp(122). In the Y249F variant, the link is absent. EPR studies showed that the radical species formed upon reaction of the Y249F and R439A/N variants with peroxoacetic acid are the oxoferryl-porphyrin radical, the tryptophanyl and the tyrosyl radicals, as in the wild-type enzyme. The dramatic loss in catalase activity of the Y249F variant allowed the comparison of the radical species formed with hydrogen peroxide and peroxoacetic acid. The EPR data strongly suggest that the sequence of intermediates formed in the absence of a one electron donor substrate, is por(.-)(+) --> Trp(.-) (or Trp(.-)(+)) --> Tyr(.-). The M275I variant did not form the Trp(.-) species because of the dramatic changes on the heme distal side, most probably induced by the repositioning of the remaining Trp(122)-Tyr(249) adduct. The results are discussed with respect to the bifunctional activity of catalase-peroxidases. 相似文献