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991.
Acclimation of photosynthesis, H2 O2 content and antioxidants in maize (Zea mays) grown at sub-optimal temperatures 总被引:2,自引:1,他引:1
Maize plants were grown at 14, 18 and 20 °C until the fourth leaf had emerged. Leaves from plants grown at 14 and 18 °C had less chlorophyll than those grown at 20 °C. Maximal extractable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity was decreased at 14 °C compared with 20 °C, but the activation state was highest at 14 °C. Growth at 14 °C increased the abundance (but not the number) of Rubisco breakdown products. Phosphoenolpyruvate carboxylase (PEPC) activity was decreased at 14 °C compared with 20 °C but no chilling-dependent effects on the abundance of the PEPC protein were observed. Maximal extractable NADP-malate dehydrogenase activity increased at 14 °C compared with 20 °C whereas the glutathione pool was similar in leaves from plants grown at both temperatures. Foliar ascorbate and hydrogen peroxide were increased at 14 °C compared with 20 °C. The foliar hydrogen peroxide content was independent of irradiance at both growth temperatures. Plants grown at 14 °C had decreased rates of CO2 fixation together with decreased quantum efficiencies of photosystem (PS) II in the light, although there was no photo-inhibition. Growth at 14 °C decreased the abundance of the D1 protein of PSII and the PSI psaB gene product but the psaA gene product was largely unaffected by growth at low temperatures. The relationships between the photosystems and the co-ordinate regulation of electron transport and CO2 assimilation were maintained in plants grown at 14 °C. 相似文献
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993.
We have recently constructed hyperactive human deoxyribonuclease I (DNase I) variants that digest double-stranded DNA more efficiently under physiological saline conditions by introducing positively charged amino acids at eight positions that can interact favorably with the negatively charged DNA phosphates. In this study, we present data from supercoiled DNA nicking, linear DNA digestion, and hyperchromicity assays that distinguish two classes of DNase I hyperactive variants based upon their activity dependence on Ca2+. Class A variants are highly dependent upon Ca2+, having up to 300-fold lower activity in the presence of Mg2+ alone compared to that in the presence of Mg2+ and Ca2+, and include Q9R, H44K, and T205K, in addition to wild-type DNase I. In contrast, the catalytic activity of Class B variants, which comprise the E13R, T14K, N74K, S75K, and N110R hyperactive variants, is relatively Ca2+ independent. A significant proportion of this difference in Ca2+-dependent activity can be attributed to one of the two structural calcium binding sites in DNase I. Compared to wild-type, the removal of Ca2+ binding site 2 by alanine replacements at Asp99, Asp107, and Glu112 decreased activity up to 26-fold in the presence of Mg2+ and Ca2+, but had no effect in the presence of Mg2+ alone. We propose that the rate-enhancing effect of Ca2+ binding at site 2 can be replaced by favorable electrostatic interactions created by proximal positively charged amino acid substitutions such as those found in the Class B variants, thus reducing the dependence on Ca2+. 相似文献
994.
高压力对限制性内切酶活性的影响 总被引:1,自引:0,他引:1
以质粒pSPORT1为底物研究了高压力对Ⅱ型限制性内切酶HindⅢ和XbaⅠ反应的影响。高压力未引起两酶底物碱基特异性的改变,但二者反应活力均随压力升高而逐渐下降,XbaⅠ对高压力更敏感。引起HindⅢ和XbaⅠ限制性内切酶活性完全丧失的压力分别为200和180MPa,半失活压力分别为130和75MPa。 相似文献
995.
996.
Bryophytes are the transitional forms from water habitants to
terrestrials, however, there have been only a few works on their photosynthesis.
It was the first time to study on photosynthetic fluorescence spectra and
fluorescence kinetics of primitive and advanced species comparatively. Both the
primitive and advanced ones had the same fluorescence spectra at room
temperature, which contained two maximum emissions: F686-690 from the
Photosystem II and F736-740 from the Photosystem I. And then, there were three
maximum emissions in the fluorescence spectra at 77K :F687-689 and F697-699 from
Photosystem II, and F723-734 from Photosystem I. The first two maximum
emissions were the same for both the primitive and advanced species. According
to the third maximum emission the bryophytes under study fell into two
categories: The first one possessing the maximum emission around 725 nm,
including Ditrichum flexicaule , Didymodon icmadophyllum , Didymodon
rigidicaulis, Aloina obliquifolia, Plagiomnium confertidens and Marchantia
polymorpha, which were primitive mosses and advanced liverwort. The second
one possessing the maximum emission around 732nm, including Thuidium
delicatulum , Pylaisia brotheri , Myuroclada maximowiczii , Taxiphyllum
taxirameum, Gollania neckerella, Eurohypnum leptothallum, which were advanced
mosses, and the primitive one Plagiomnium rostratum. The characteristics of
fluorescence spectra implied that the Photosystem II was conservative and
Photosystem I was changeable during bryophyte evolution. The primitive mosses
possess mainly the PSI core complex (CPI) and then the advanced species contain
both CPI and LHC-I. In analysis of photosynthetic fluorescence kinetics,
Fv/(Fc+Fv) is a measure of the activity of the Photosystem II; Fv/Fm is dependent
on efficiency of primary photoconversion in the Photosystem II; Fm/(Fo+Fv) is
related to photosynthetic carbon assimilation; and Fd/Fs is a measure of the
potential photosynthetic quantum conversion. The fluorescence kinetics of the
bryophyte photosynthesis showed that the Photosystem II activity, the efficieiency of
primary photoconversion in Photosystem II, the photosynthetic carbon assimilation and the efficiency of the potential photosynthetic quantum conversion in
primitive species, such as Ditrichum flexicaule, Didymodon icmadophyllus, D.
rigidicaulis, Plagiomnium rostratum and the liverwort Marchantia polymorpha,
were lower than those in the advanced species, Myuroclada maximowiczii,
Pylaisia brotheri , Gollania neckerella Taxiphyllum taxirameum , Thuidium
delicatulum. However, the primitive Plagiomnium confertidens was of the high
activities and efficiencies and the advanced Eurohypnum leptothallum was of low
ones. It seemed that P. confertidens and E. leptothallum were an intermediatefrom the primitive to the advanced. 相似文献
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