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81.
T. R. Carron M. P. Robbins P. Morris 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,87(8):1006-1015
An antisense dihydroflavonol reductase (DFR) gene-construct made using the cDNA for DFR from Antirrhinum majus was introduced into the genome of a series of clonal genotypes of Lotus corniculatus via Agrobacterium rhizogenes. After initial screening, 17 antisense and 11 control transformation events were analysed and tannin levels found to be reduced in antisense root cultures. The effect of this antisense construct, (pMAJ2), which consisted of the 5 half of the DFR cDNA sequence, was compared in three different recipient Lotus genotypes. This construct effectively down-regulated tannin biosynthesis in two of the recepient genotypes (s33 and s50); however, this construct was relatively ineffective in a third genotype (s41) which accumulated high levels of condensed tannins in derived transgenic root cultures. Four pMAJ2 antisense and three control lines derived from clonal genotypes s33 and s50 were selected and studied in greater detail. The antisense DFR construct was found to be integrated into the genome of the antisense hairy root cultures, and the antisense RNA was shown to be expressed. Tannin levels were much lower in antisense roots compared to the controls and this reduction in tannin levels was accompanied by a change in condensed tannin subunit composition. 相似文献
82.
Multiple haplotypes from each of three nuclear loci were isolated and
sequenced from geographic populations of the American oyster, Crassostrea
virginica. In tests of alternative phylogeographic hypotheses for this
species, nuclear gene genealogies constructed for these haplotypes were
compared to one another, to a mitochondrial gene tree, and to patterns of
allele frequency variation in nuclear restriction site polymorphisms
(RFLPs) and allozymes. Oyster populations from the Atlantic versus the Gulf
of Mexico are not reciprocally monophyletic in any of the nuclear gene
trees, despite considerable genetic variation and despite large allele
frequency differences previously reported in several other genetic assays.
If these populations were separated vicariantly in the past, either
insufficient time has elapsed for neutral lineage sorting to have achieved
monophyly at most nuclear loci, or balancing selection may have inhibited
lineage extinction, or secondary gene flow may have moved haplotypes
between regions. These and other possibilities are examined in light of
available genetic evidence, and it is concluded that no simple explanation
can account for the great variety of population genetic patterns across
loci displayed by American oysters. Regardless of the source of this
heterogeneity, this study provides an empirical demonstration that
different sequences of DNA within the same organismal pedigree can have
quite different phylogeographic histories.
相似文献
83.
Experiments have been carried out to test the proposal that the pH increase at fertilization in sea urchin eggs promotes microvillar elongation. Results presented herein show that microvillar elongation and microfilament formation occurred when sea urchin eggs were incubated in sodium-free seawater containing the calcium ionophore A23187, a treatment which initiates activation, i.e., induces a transient increase in intracellular free calcium, but prevents subsequent cytoplasmic alkalinization. Within elongated microvilli and cortices of these eggs, microfilaments were arranged in a loose meshwork. However, if the pH of the egg cytoplasm was increased experimentally, microfilament bundles appeared within individual microvilli. These findings suggest that: (1) microvillar elongation and microfilament formation in the sea urchin egg at fertilization may occur when cytoplasmic alkalinization is inhibited, and (2) formation of the microvillus bundle of microfilaments at egg activation is pH sensitive. Additionally, if the cytoplasmic pH of unfertilized eggs was experimentally elevated by NH4Cl, microvilli failed to elongate. These data indicate that elevation of intracellular pH by this method is not sufficient to induce microvillar elongation. 相似文献
84.
The aim of this experiment was to evaluate the effects of an intracerebroventricular (icv) injection of prostaglandin E1 (PGE1) on the sympathetic activation and the thermogenic changes in rats with acute lesions of the ventromedial hypothalamus (VMH). Four groups of six Sprague-Dawley male rats were anesthetized with ethyl-urethane. The firing rate of the sympathetic nerves innervating the interscapular brown adipose tissue (IBAT) and the colonic and IBAT temperatures were monitored both before and after one of the following treatments: 1) VMH lesion plus icv injection of PGE1 (500 ng); 2) VMH lesion plus icv injection of saline; 3) sham lesion plus icv injection of PGE1; and 4) sham lesion plus icv injection of saline. PGE1 induced an increase in the firing rate of IBAT nerves and the colonic and IBAT temperatures. These effects were reduced by VMH lesion. The findings indicate that acute lesions of the VMH reduce the effects of PGE1 and seem to suggest a possible role played by the VMH in the control of the sympathetic activation and the thermogenic changes during PGE1 hyperthermia. 相似文献
85.
86.
TD Smith KP Bhatnagar CJ Bonar KL Shimp MP Mooney MI Siegel 《American journal of physical anthropology》2003,122(3):301-301
87.
This paper looked at the leaf architecture characteristics of Vachellia tortilis to determine if either there is or not an effect of the tropic line on plants. Vachellia tortilis leaves were sampled along a national road (N1) in Limpopo province. Sampling points were set 10 km apart away from the Tropic of Capricon in opposite directions. Leaf morphology revealed that leaves of V. tortilis are bipinnately compound with alternate arrangement. The venation pattern of the pinnules was eucamptodromus and brochidodromous with imperfect reticulation. Areoles were imperfect and pentagonal or irregular in shape. 相似文献
88.
A reliable cryopreservation technique was developed for friable embryogenic callus lines of Hevea brasiliensis. The study showed that reducing the CaCl2 concentration of the pre-culture medium from 9 mM to 1 or 0 mM CaCl2 before cryopreservation promoted post-thaw callus growth, 1 mM being the optimum CaCl2 concentration for embryo regeneration. Post-thaw callus proliferation decreased in line with the increase of plated callus
weight. The effect of cryopreservation was assessed on 39 independent lines showing that cryopreservation did not affect embryogenic
and plant regeneration for a majority of lines. The decrease in CaCl2 concentration of the pre-culture medium led to a drop in callus calcium content indicating a direct link between the CaCl2 concentration of the pre-culture medium and the endogenous calcium content of the calli. It also highlighted the implication
of tissue calcium content in cryotolerance. Callus water status and the different ways by which calcium could prevent cryoinjury
is also discussed. 相似文献
89.
Walter A. Henne Sumith A. Kularatne John Hakenjos Joshua D. Carron Kristene L. Henne 《Bioorganic & medicinal chemistry letters》2013,23(21):5810-5813
A folate targeted camptothecin small molecule drug conjugate (SMDC) was synthesized using a monodisperse PEG spacer linked to folate via a releasable disulfide carbonate linker. Cell cytotoxicity in human KB cells exhibited an IC50 of 6 nM. Importantly, activity of the prodrug was blocked by excess folate, demonstrating receptor-mediated celluar uptake of the PEG conjugate. 相似文献
90.