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71.
The equilibrium and kinetics of thermal unfolding of yeast 5S ribosomal RNA have been studied by optical methods, in a low ionic strength environment without Mg2+, to follow the disruption of the secondary structure base pairs in the molecule. The equilibrium results demonstrated that all of the helical regions melted simultaneously, and the kinetics of the thermal unfolding were first order. These findings suggest the validity of the two-state approximation for the unfolding reaction under the present conditions. The total number of secondary structure base pairs estimated from our experiment was consistent with that contained in the conformational model based on the Raman spectrum rather than that in the one derived by the enzymic digestion method. Taking our results on the kinetic behavior of the thermal unfolding overall, we propose that the 5S RNA has a partly melted secondary structure under the solvent conditions used. 相似文献
72.
During a recent Antarctic research cruise (December 1994/February 1995), dissection of fresh Antarctic krill (Euphausia superba) on board ship revealed live motile ciliates in the gut of krill. Further observation of gut samples by scanning electron
microscopy indicated that the ciliates were symbionts located within the gut. We inferred that the ciliates may have enabled
the krill to digest a wider range of food items, and as a consequence, this had became an important strategy for Antarctic
krill's survival in the Antarctic ecosystem.
Received: 1 August 1996 / Accepted: 1 December 1996 相似文献
73.
Kentaro Kato Atsushi Sudo Kyousuke Kobayashi Tatsuki Sugi Yukinobu Tohya Hiroomi Akashi 《Parasitology international》2009,58(4):394-400
In Plasmodium berghei, the orthologous gene of P. falciparum calcium-dependent protein kinase 4 (PfCDPK4) was reported to be essential for the exflagellation of male gametocytes. To elucidate the role of PfCDPK4 in P. falciparum gametogenesis, we characterized the biological function of PfCDPK4 in vitro. PfCDPK4 was purified as a fusion protein that was labeled with [γ-32P]ATP; this labeling was then eliminated by phosphatase. Phosphorylation activity of PfCDPK4 was eliminated when its putative catalytic lysine residue was replaced with alanine. In biochemical analyses, PfCDPK4 was found to have characteristics that were similar to those of homologous proteins from plants. PfCDPK4 phosphorylation was activated when experimental conditions were changed from those characteristic of human blood (37 °C, pH 7.4) to those of the mosquito bloodmeal (at least 5 °C below 37 °C, pH 7.6, with xanthurenic acid (XA)). PfCDPK4 was overexpressed in day 15 gametocytes exposed to XA or human serum. Thus, PfCDPK4 phosphorylation is activated by an increase in Ca2+ concentration or pH and by a decrease in temperature, and is associated with the Ca2+ signals that facilitate P. falciparum gametogenesis. 相似文献
74.
Cheng-Hao Tang Wen-Yi Wu Shu-Chuan Tsai Tatsuki Yoshinaga Tsung-Han Lee 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(6):813-824
The milkfish (Chanos chanos) is an economic species in Southeast Asia. In Taiwan, the milkfish are commercially cultured in environments of various salinities.
Na+/K+-ATPase (NKA) is a key enzyme for fish iono- and osmoregulation. When compared with gills, NKA and its potential role were
less examined by different approaches in the other osmoregulatory organs (e.g., kidney) of euryhaline teleosts. The objective
of this study was to investigate the correlation between osmoregulatory plasticity and renal NKA in this euryhaline species.
Muscle water contents (MWC), plasma, and urine osmolality, kidney histology, as well as distribution, expression (mRNA and
protein), and specific activity of renal NKA were examined in juvenile milkfish acclimated to fresh water (FW), seawater (SW
35‰), and hypersaline water (HSW 60‰) for at least two weeks before experiments. MWC showed no significant difference among
all groups. Plasma osmolality was maintained within the range of physiological homeostasis in milkfish acclimated to different
salinities, while, urine osmolality of FW-acclimated fish was evidently lower than SW- and HSW-acclimated individuals. The
renal tubules were identified by staining with periodic acid Schiff’s reagent and hematoxylin. Moreover, immunohistochemical
staining showed that NKA was distributed in the epithelial cells of proximal tubules, distal tubules, and collecting tubules,
but not in glomeruli, of milkfish exposed to different ambient salinities. The highest abundance of relative NKA α subunit
mRNA was found in FW-acclimated milkfish rather than SW- and HSW-acclimated individuals. Furthermore, relative protein amounts
of renal NKA α and β subunits as well as NKA-specific activity were also found to be higher in the FW group than SW and the
HSW groups. This study integrated diverse levels (i.e., histological distribution, gene, protein, and specific activity) of
renal NKA expression and illustrated the potential role of NKA in triggering ion reabsorption in kidneys of the marine euryhaline
milkfish when acclimated to a hypotonic FW environment. 相似文献
75.
76.
Uemura T Sano H Katoh T Nishitani C Mitsuzawa H Shimizu T Kuroki Y 《Biochemistry》2006,45(48):14543-14551
Pulmonary surfactant protein A (SP-A) belongs to the collectin subgroup of the C-type lectin superfamily. SP-A oligomerizes as an octadecamer, which forms a flower bouquet-like structure. A collagen-like domain of human SP-A consists of 23 Gly-X-Y repeats with an interruption near the midpoint of this domain. This interruption causes a kink, but its role remains unknown. To define the importance of the kink region of SP-A, two mutated proteins were constructed to disrupt the interruption of Gly-X-Y repeats: SP-ADEL, which lacks the Pro47-Cys48-Pro49-Pro50 sequence at the interruption, and SP-AINS, in which two glycines were introduced to insert Gly-X-Y repeats (Gly-Pro47-Cys48-Gly-Pro49-Pro50). Electron microscopy using rotary shadowing revealed that both mutants form octadecamers that lack a bend in the collagenous domain. Electrophoretic analysis under nondenaturing conditions and gel filtration chromatography demonstrated that SP-AINS consisted of a large assembly of oligomers whereas SP-ADEL formed mainly octadecamers. Both SP-ADEL and SP-AINS mutants as well as wild-type SP-A bound to liposomes containing dipalmitoylphosphatidylcholine and galactosylceramide at equivalent levels, but the abilities of the mutants to induce phospholipid liposome aggregation were significantly less developed than that of the wild type. The mutants SP-ADEL and SP-AINS augmented liposome uptake by alveolar type II cells and inhibited secretion of phospholipids from type II cells at a level comparable to that of wild-type SP-A. These results indicate that the interruption of Gly-X-Y repeats in the SP-A molecule is critical for the formation of a flower bouquet-like octadecamer and contributes to SP-A's capacity to aggregate phospholipid liposomes. 相似文献
77.
Ai-Rong Liu Dong-Jin Qian Meng Chen Tatsuki Wakayama Chikashi Nakamura Nikolay A. Zorin Jun Miyake 《NanoBioTechnology》2006,2(3-4):135-141
Hydrogenase (H2 ase) purified from phototropic bacteriumThiocapsa roseopersicina was coassembled with carbon nanotubes (CNTs) on glass carbon electrodes. Both oxidized CNTs and Nafion-CNT composites were
used to modify the electrodes. The pure H2 are formed dot-like domains, while the oxidized CNT-H2 ase and Nafion-CNT-H2 ase composites formed wire-like and large closely packed aggregates, respectively. The reductive potentials for the [4Fe-4S]2+/1+ clusters of H2ase were at about −500, −650, and −700 mV (vs Ag/AgCl) for the electrodes modified with pure H2ase, Nafion-SWNT-H2ase, and Nafion-MWNT-H2ase composites, respectively. Potential step chronocoulometry measurements indicated a larger charge-transfer diffusion coefficient
between the H2ase and electrodes when the CNTs were co-assembled with H2ase, suggesting that the CNTs can not only act as a supporting layer to immobilize enzymes, but also act as a highly conductive
wire throughout the films. 相似文献
78.
Tatsuki Itoh Takao Satou Shozo Nishida Masahiro Tsubaki Motohiro Imano Shigeo Hashimoto Hiroyuki Ito 《Neurochemical research》2010,35(2):348-355
Edaravone is a novel free radical scavenger used clinically in patients with acute cerebral infarction; however, it has not
been assessed in traumatic brain injury (TBI). We investigated the effects of edaravone on cerebral function and morphology
following TBI. Rats received TBI with a pneumatic controlled injury device. Edaravone (3 mg/kg) or physiological saline was
administered intravenously following TBI. Numbers of 8-OHdG-, 4-HNE-, and ssDNA-positive cells around the damaged area after
TBI were significantly decreased in the edaravone group compared with the saline group (P < 0.01). There was a significant increase in neuronal cell number and improvement in cerebral dysfunction after TBI in the
edaravone group compared with the saline group (P < 0.01). Edaravone administration following TBI inhibited free radical-induced neuronal degeneration and apoptotic cell death
around the damaged area. In summary, edaravone treatment improved cerebral dysfunction following TBI, suggesting its potential
as an effective clinical therapy. 相似文献
79.
80.
Jotaro?UrabeEmail author Takehito?Yoshida Tek?Bahadur?Gurung Tatsuki?Sekino Narumi?Tsugeki Kentaro?Nozaki Masahiro?Maruo Eiichioro?Nakayama Masami?Nakanishi 《Ecological Research》2005,20(3):367-375
Production-to-respiration (P:R) ratio was estimated at an offshore site of Lake Biwa in order to examine whether the plankton and benthic community is subsidized with allochthonous organic carbon, and to clarify the role of this lake as potential source or sink of carbon dioxide. The respiration rate of protozoan and metazoan plankton was calculated from their biomass and empirical equations of oxygen consumption rates, and that of bacterioplankton was derived from their production rate and growth efficiency. In addition, the carbon mineralization rate in the lake sediments was estimated from the accumulation rate of organic carbon, which was determined using a 210Pb dating technique. On an annual basis, the sum of respiration rates of heterotrophic plankton was comparable to net primary production rate measured by the 13C method. However, when the mineralization rate in the lake sediments was included, the areal P:R ratio was 0.89, suggesting that Lake Biwa is net heterotrophic at the offshore site with the community being subsidized with allochthonous organic carbon. Such a view was supported by the surface water pCO2 that was on average higher than that of the atmosphere. However, the estimate of net CO2 release rate was close to that of carbon burial rate in the sediments. The result suggests that the role of Lake Biwa in relation to atmospheric carbon is almost null at the offshore site, although the community is supported partially by organic carbon released from the surrounding areas. 相似文献