全文获取类型
收费全文 | 175篇 |
免费 | 11篇 |
专业分类
186篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 5篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 6篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 2篇 |
排序方式: 共有186条查询结果,搜索用时 15 毫秒
21.
The third-order nonlinear optical responses of β-carotene and its homologue having a conjugation-double bond n = 15 have been investigated using sub-20 fs ultra-short optical pulses in order to clarify the dissipation processes of excess
energy. Using the four-wave mixing spectroscopy, we observed a clear coherent oscillation with a period of a few tens of femtoseconds.
The spectral density of these molecules was estimated that allowed the theoretical linear and nonlinear optical signals to
be directly compared with the experimental data. Calculations based on the Brownian oscillator model were performed under
the impulsive excitation limit. We show that the memory of the vibronic coherence generated upon the excitation into the S2 state is lost via the relaxation process including the S1 state. The vibronic decoherence lifetime of the system was estimated to be 1 ps, which is about 5 times larger than the life
time of the S2 state (∼150 fs) determined in previous studies. The role of coherence and the efficient energy transfer in the light-harvesting
antenna complexes are discussed. 相似文献
22.
Masazumi Mitani 《Ecological Research》1999,14(4):371-383
Fruit syndrome found in zoochorous plants is regarded as a result of hypothetical coevolution with a seed disperser/predator. Fruiting phenology was compared among two representative syndromes, such as bird–monkey syndrome (BM) and ruminant–rodent–elephant syndrome (RRE), plus the gravity dispersal species for comparison, in south-western Cameroon in order to examine which biotic or abiotic factors educed syndrome variation. The individual size of selected plants (> 1.6 m in height) was recorded in a 16.95-ha area for recruitment estimation and their fruiting behaviour was checked for 9 months from June 1985 to February 1986. The BM species, a suggested successful group, fruited in a less synchronous manner within species and had fruiting peaks just before and during the rainy season. The RRE species, a suggested failing group, showed greater variation within syndrome in fruiting timing, duration and synchronization. Results obtained supported no clear phenological response to corresponding vertebrates except for the case of Sacoglottis gabonensis in the RRE. The reason for concealing potential responses is probably a result of conflicting requirements for seed dispersal and offspring survival. Periodical fruiting of the BM is likely to reflect ecological constraint, such as water stress on seedlings, caused from syndrome-specific morphological limitation. In this case, the animals have indirect effects on fruiting phenology through selecting syndrome-specific fruit morphology. The greater variation of the RRE suggests a broad spectrum of dispersal tactics from faithful zoochory to alternatives, with a trade off between agent restriction and seed size and another trade off between parental investment and seed-predation risk. 相似文献
23.
Hashimoto M Morimoto M Saimoto H Shigemasa Y Yanagie H Eriguchi M Sato T 《Biotechnology letters》2006,28(11):815-821
Chitosan is a biodegradable and biocompatible polymer and is useful as a non-viral vector for gene delivery. In order to deliver
pDNA/chitosan complex into macrophages expressing a mannose receptor, mannose-modified chitosan (man-chitosan) was employed.
The cellular uptake of pDNA/man-chitosan complexes through mannose recognition was then observed. The pDNA/man-chitosan complexes
showed no significant cytotoxicity in mouse peritoneal macrophages, while pDNA/man-PEI complexes showed strong cytotoxicity.
The pDNA/man-chitosan complexes showed much higher transfection efficiency than pDNA/chitosan complexes in mouse peritoneal
macrophages. Observation with a confocal laser microscope suggested differences in the cellular uptake mechanism between pDNA/chitosan
complexes and pDNA/man-chitosan complexes. Mannose receptor-mediated gene transfer thus enhances the transfection efficiency
of pDNA/chitosan complexes. 相似文献
24.
Helen L. May-Simera Masatake Kai Victor Hernandez Masazumi Tada 《Developmental biology》2010,345(2):215-225
Laterality defects such as situs inversus are not uncommonly encountered in humans, either in isolation or as part of another syndrome, but can have devastating developmental consequences. The events that break symmetry during early embryogenesis are highly conserved amongst vertebrates and involve the establishment of unidirectional flow by cilia within an organising centre such as the node in mammals or Kupffer's vesicle (KV) in teleosts. Disruption of this flow can lead to the failure to successfully establish left-right asymmetry. The correct apical-posterior cellular position of each node/KV cilium is critical for its optimal radial movement which serves to sweep fluid (and morphogens) in the same direction as its neighbours. Planar cell polarity (PCP) is an important conserved process that governs ciliary position and posterior tilt; however the underlying mechanism by which this occurs remains unclear. Here we show that Bbs8, a ciliary/basal body protein important for intraciliary/flagellar transport and the core PCP protein Vangl2 interact and are required for establishment and maintenance of left-right asymmetry during early embryogenesis in zebrafish. We discovered that loss of bbs8 and vangl2 results in laterality defects due to cilia disruption at the KV. We showed that perturbation of cell polarity following abrogation of vangl2 causes nuclear mislocalisation, implying defective centrosome/basal body migration and apical docking. Moreover, upon loss of bbs8 and vangl2, we observed defective actin organisation. These data suggest that bbs8 and vangl2 act synergistically on cell polarization to establish and maintain the appropriate length and number of cilia in the KV and thereby facilitate correct LR asymmetry. 相似文献
25.
Masazumi Ando Hideaki Amayasu Takahiro Itai Hisahiro Yoshida 《BioPsychoSocial medicine》2017,11(1):19
Background
Administration of valproic acid (VPA) is complicated with approximately 0.9% of patients developing hyperammonemia, but the pathogenesis of this adverse effect remains to be clarified. The aim of the present study was to search for mechanisms associated with VPA-induced hyperammonemia in the light of changes in serum amino acids concentrations associated with the urea cycle of schizophrenic patients.Method
Blood samples (10 mL) were obtained from 37 schizophrenic patients receiving VPA for the prevention of violent behaviors in the morning after overnight fast. Blood concentrations of ammonia, VPA, free carnitine, acyl-carnitine, and 40 amino acids including glutamate and citrulline were measured for each patient. Univariate and multivariate regression analyses were performed to identify amino acids or concomitantly administered drugs that were associated with variability in the blood concentrations of ammonia.Result
The blood ammonia level was positively correlated with the serum glutamate concentration (r = 0.44, p < 0.01) but negatively correlated with glutamine (r = ?0.41, p = 0.01), citrulline (r = ?0.42, p = 0.01), and glycine concentrations (r = ?0.54, p < 0.01). It was also revealed that the concomitant administration of the mood stabilizers (p = 0.04) risperidone (p = 0.03) and blonanserin (p < 0.01) was positively associated with the elevation of the blood ammonia level.Conclusion
We hypothisized that VPA would elevate the blood ammonia level of schizophrenic patients. The observed changes in serum amino acids are compatible with urea cycle dysfunction, possibly due to reduced carbamoyl-phosphate synthase 1 (CPS1) activity. We conclude that VPA should be prudently prescribed to schizophrenic patients, particularly those receiving mood stabilizers or certain antipsychotics.26.
Takatoshi Soga Takahide Ohishi Tetsuo Matsui Tetsu Saito Mitsuyuki Matsumoto Jun Takasaki Shun-ichiro Matsumoto Masazumi Kamohara Hideki Hiyama Shigeru Yoshida Kazuhiro Momose Yoshitaka Ueda Hitoshi Matsushime Masato Kobori Kiyoshi Furuichi 《Biochemical and biophysical research communications》2005,329(1):417
27.
Phospholipase A1 is a hydrolytic enzyme that catalyzes the removal of the acyl group from position 1 of glycerophospholipids to form 2-acyl lysophospholipids. Lysophospholipids are used in foods, cosmetics, and pharmaceuticals as surfactants. Novel forms of phospholipase A1 that function at low temperatures are desirable for use in lipophilic systems in food processing. However, there is currently little variety in the available sources of phospholipase A1. Given this situation, we screened the intestinal contents of marine animals for phospholipase A1-producing bacteria. Colonies that formed a halo on K28CP screening medium and that grew in K28 medium were cultured in liquid K28 medium, and the supernatant was retrieved for analysis. Phosphatidylcholine was added to the culture supernatant, and the product of the reaction was analyzed by using TLC. For culture supernatants that were able to generate lysophosphatidylcholine, synthetic phosphatidylcholines were added, and the site of the reaction was determined by analyzing the fatty acid compositions of the lysophosphatidylcholines generated by GLC. A bacterial isolate from a flatfish, which we named HFKI0020, was found to have phospholipase A1 activity at low temperatures. We determined that the isolate HFKI0020 is closely related to Pseudomonas by using 16S rDNA sequence analysis and by characterizing the isolate with respect to its physiologic and biochemical properties. From the intestinal contents of a marine fish, we successfully isolated a bacterium that secretes phospholipase A1 that is active at low temperatures. 相似文献
28.
Tatsukawa Y Nakashima E Yamada M Funamoto S Hida A Akahoshi M Sakata R Ross NP Kasagi F Fujiwara S Shore RE 《Radiation research》2008,170(3):269-274
Tatsukawa, Y., Nakashima, E., Yamada, M., Funamoto, S., Hida, A., Akahoshi, M., Sakata, R., Ross, N. P., Kasagi, F., Fujiwara, S. and Shore, R. E. Cardiovascular Disease Risk among Atomic Bomb Survivors Exposed In Utero, 1978-2003. Radiat. Res. 170, 269-274 (2008).Given the well-documented association of in utero radiation exposure with childhood cancer and developmental impairments, the possibility of effects on adult onset diseases is an important issue. The objectives of the present study were to examine the effects of atomic bomb radiation dose on the incidence of hypertension, hypercholesterolemia and cardiovascular disease (myocardial infarction and stroke) among survivors exposed in utero and to compare their risk estimates with those of survivors exposed in childhood (<10 years old) at the time of the bombing. A total of 506 participants exposed in utero and 1,053 participants exposed in childhood were followed during 1978-2003 with biennial clinical examinations. There were no significant radiation dose effects for any diseases in the entire in utero-exposed cohort or in trimester-of-exposure subgroups, though there was a suggestion of an increased risk when fatal and nonfatal cardiovascular disease cases were combined. Positive radiation dose effects were found for hypertension and cardiovascular disease in the childhood-exposure cohort, but there were no statistically significant differences in the relative risks when we compared the two cohorts. Since the in utero cohort was under age 60 at the latest examination, continued follow-up is needed to document cardiovascular disease risk more fully. 相似文献
29.
Novel synthetic collagen fibers, poly(PHG) made by polycondensation of Pro-Hyp-Gly, spontaneously assume polymeric structure with molecular weights greater than 105. Its application for biomaterials has been explored, but that for a platelet agonist has not been investigated. Poly(PHG)-induced platelet aggregation independently of thromboxane A2 and integrin α2β1. Poly(PHG)-induced tyrosine phosphorylation of glycoprotein VI (GPVI)-related molecules and failed to activate GPVI/FcRγ-deficient platelets. Binding of GPVI to poly(PHG) was confirmed by a surface plasmon resonance spectroscopy, suggesting that poly(PHG) activates platelets through GPVI. Poly(PHG) is an useful research tool to investigate GPVI-mediated signals and a substitute for collagen in platelet functional assays. 相似文献
30.
Raphaël Plasson Maika Tsuji Masazumi Kamata Kouichi Asakura 《Origins of life and evolution of the biosphere》2011,41(5):413-435
A good comprehension of the reactivity of peptides in aqueous solution is fundamental in prebiotic chemistry, namely for understanding
their stability and behavior in primitive oceans. Relying on the stereoselectivity of the involved reactions, there is a huge
interest in amino acid derivatives for explaining the spontaneous emergence of homochirality on primitive Earth. The corresponding
kinetic and thermodynamic parameters are however still poorly known in the literature. We studied the reactivity of alanylalanine
in acidic to neutral conditions as a model system. The hydrolysis into amino acids, the epimerization of the N-terminal residue,
and the cyclization into diketopiperazine could be successfully identified and studied. This kinetic investigation highlighted
interesting behaviors. Complex mechanisms were observed in very acidic conditions. The relative kinetic stability of the diastereoisomers
of the dipeptide is highly dependent of the pH, with the possibility to dynamically destabilize the thermodynamically more
stable diastereoisomers. The existence of the cyclization of dipeptides adds complexity to the system. On one hand it brings
additional stereoselectivities; on the other hand fast racemization of heterochiral dipeptides is obtained. 相似文献