全文获取类型
收费全文 | 161篇 |
免费 | 19篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2015年 | 5篇 |
2013年 | 10篇 |
2012年 | 1篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 3篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1961年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 15 毫秒
1.
2.
Most current photosynthesis models, and interpretations of many wholeleaf CO2 gas exchange measurements, are based on the often unstated assumption that the partial pressure of CO2 is nearly uniform throughout the airspaces of the leaf mesophyll. Here we present measurements of CO2 gradients across amphistomatous leaves allowed to assimilate CO2 through only one surface, thus simulating hypostomatous leaves. We studied five species: Eucalyptus pauciflora Sieb. ex Spreng., Brassica chinensis L., Gossypium hirsutum L., Phaseolus vulgaris L., and Spinacia oleracea L. For Eucalyptus, maximum CO2 pressure differences across the leaf mesophyll were 73 and 160 microbar when the pressures outside the lower leaf surface were 310 and 590 microbar, respectively. Using an approximate theoretical calculation, we infer that if the CO2 had been supplied equally at both surfaces then the respective mean intercellular CO2 pressures would have been roughly 12 and 27 microbar less than the pressures in the substomatal cavities in these cases. For ambient CO2 pressures near 320 microbar, the average and minimum pressure differences across the mesophyll were 45 and 13 microbar. The corresponding mean intercellular CO2 pressures would then be roughly 8 and 2 microbar less than those in the substomatal cavities. Pressure differences were generally smaller for the four agricultural species than for Eucalyptus, but they were nevertheless larger than previously reported values. 相似文献
3.
M R Chance L J Parkhurst L S Powers B Chance 《The Journal of biological chemistry》1986,261(13):5689-5692
Carp Hb undergoes a well known change in kinetics over the pH range 6-9. X-ray absorption spectroscopy, in conjunction with refined data analysis procedures, shows no difference in iron-ligand distances when carp HbCO is switched from R (high affinity) to T (low affinity) states. These distances are 2.015 +/- 0.015 A for the average iron-pyrrole nitrogen distance, 2.14 +/- 0.04 A for the iron-nitrogen (of histidine) distance, and 1.89 +/- 0.05 A for the Fe-C (of CO) distance. Examination of the region from 30 to 100 eV above the threshold, called the ligand field indicator region, reveals spectral differences, which when compared to model compounds suggest that the iron and the heme are less coplanar in the T-like forms. These results are consistent with the iron being 0.1 A more out of the mean heme plane in both carp HbCO and carp Hb T states, relative to the R forms, and that the change in iron position on ligation to either T or R state is four times larger than that occurring with the quaternary switch. 相似文献
4.
Different modes of ligand binding to the hepatic galactose/N-acetylgalactosamine lectin on the surface of rabbit hepatocytes 总被引:6,自引:0,他引:6
A study of the binding of three different 125I-labeled, galactose-terminated ligands to the hepatic galactose/N-acetylgalactosamine-specific lectin found on the surface of rabbit hepatocytes revealed that the different ligands manifest different physical parameters of binding. Asialoorosomucoid (125I-ASOR) binding was best described as involving two independent classes of binding sites on rabbit hepatocytes, with 161 000 sites/cell with a dissociation constant of 0.44 nM and 292 000 sites/cell with a Kd of 9.7 nM. Asialotriantennary glycopeptide purified from human alpha-1 protease inhibitor and modified with tyrosine at the N-terminus to permit radioiodination (TRI) [Lee, Y. C., Townsend, R. R., Hardy, M. R., L?nngren, J., Arnarp, J., Haraldsson, M., & L?nn, H. (1983) J. Biol. Chem. 258, 199-202] was also found to bind to two apparent classes of binding sites but with different binding parameters: 292 000 sites/cell of Kd = 1.47 nM and 982 000 sites/cell of Kd = 25.3 nM. A synthetic ligand, alpha,beta-diaspartamide of tris[(beta-lactosyloxy)methyl](6-aminohexanamido)methane (di-tris-lac) containing six nonreducing galactose residues [Lee, R. T., Lin, P., & Lee, Y. C. (1984) Biochemistry 23, 4255-4261], was found to bind to 817 000 sites/cell of Kd = 0.63 nM and 1.23 X 10(6) sites/cell of Kd = 25.3 nM. Thus, there were many more total binding sites for TRI or di-tris-lac on the surface of rabbit hepatocytes than there were for asialoorosomucoid, although the dissociation constants were similar for all three ligands.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
5.
Oxygen and CO ligand binding kinetics have been studied for the hybrid hemoglobin (Hb) alpha (human):beta (carp), hybrid II. Valency and half-saturated hybrids were used to aid in the assignment of the conformations of both chains. In hybrid II, an intermediate S state occurs, in which one chain has R- and the other T-state properties. In HbCO at pH 6 (plus 1 mM inositol hexaphosphate), the human alpha-chain is R state and the carp beta-chain is T state. We have no evidence at this pH that the carp beta-chain ever assumes the R conformation. At pH 6, the human alpha-chain shows human Hb R-state kinetics at low fractional photolysis and T-state rates for CO ligation by stopped flow. At pH 7, the human-chain R-state rate slows toward a carp hemoglobin rate. The carp beta-chains, on the other hand, react 50% more rapidly in the liganded conformation than in carp hemoglobin, and while the human alpha-chains are in the R state, the two beta-chains appear to function as a cooperative dimer. In this hemoglobin, the chains appear to be somewhat decoupled near pH 7, allowing a sequential conformational change from the R state in which the beta-chains first assume T-state properties, followed by the alpha-chains. The rate of the R-T conformational change for the carp beta-chains is at least 300 times greater than that for the human alpha-chains. At pH 9, the R----T conformational transition rate is at least 200 times slower than that for human hemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
6.
7.
The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds. 相似文献
8.
Hrushikesh S. Chaudhari Omkar S. Palkar KM Abha Mishra Kalyan K. Sethi 《Journal of biochemical and molecular toxicology》2023,37(9):e23417
During the period of COVID-19, the occurrences of mucormycosis in immunocompromised patients have increased significantly. Mucormycosis (black fungus) is a rare and rapidly progressing fungal infection associated with high mortality and morbidity in India as well as globally. The causative agents for this infection are collectively called mucoromycetes which are the members of the order Mucorales. The diagnosis of the infection needs to be performed as soon as the occurrence of clinical symptoms which differs with types of Mucorales infection. Imaging techniques magnetic resonance imaging or computed tomography scan, culture testing, and microscopy are the approaches for the diagnosis. After the diagnosis of the infection is confirmed, rapid action is needed for the treatment in the form of antifungal therapy or surgery depending upon the severity of the infection. Delaying in treatment declines the chances of survival. In antifungal therapy, there are two approaches first-line therapy (monotherapy) and combination therapy. Amphotericin B ( 1 ) and isavuconazole ( 2 ) are the drugs of choice for first-line therapy in the treatment of mucormycosis. Salvage therapy with posaconazole ( 3 ) and deferasirox ( 4 ) is another approach for patients who are not responsible for any other therapy. Adjunctive therapy is also used in the treatment of mucormycosis along with first-line therapy, which involves hyperbaric oxygen and cytokine therapy. There are some drugs like VT-1161 ( 5 ) and APX001A ( 6 ), Colistin, SCH 42427, and PC1244 that are under clinical trials. Despite all these approaches, none can be 100% successful in giving results. Therefore, new medications with favorable or little side effects are required for the treatment of mucormycosis. 相似文献
9.
Leukocytes must migrate through tissues to fulfill their role in the immune response, but direct methods for observing and quantifying cell motility have mostly been limited to migration on two-dimensional surfaces. We have now developed methods for examining neutrophil movement in a three-dimensional gel containing 0.1 to 0.7 mg/ml rat tail tendon collagen. Neutrophil-populated collagen gels were formed within flat glass capillary tubes, permitting direct observation with light microscopy. By following the tracks of individual cells over a 13.5-min observation period and comparing them to a stochastic model of cell movement, we quantified cell speed within a given gel by estimating a random motility coefficient (mu) and persistence time (P). The random motility coefficient changed significantly with collagen concentration in the gel, varying from 1.6 to 13.3 x 10(-9) cm2/s, with the maximum occurring at a collagen gel concentration of 0.3 mg/ml. The methods described may be useful for studying tissue dynamics and for evaluating the mechanism of cell movement in three-dimensional gels of extracellular matrix (ECM) molecules. 相似文献
10.
A small stopped-flow cuvette was built into a computer-controlled Cary 210 spectrophotometer. The enzymatic depletion of oxygen in solutions of hemoglobin and myoglobin was initiated by flowing the hemeproteins with the enzyme against a solution of the hemeproteins containing the appropriate substrate. The deoxygenation was homogeneous throughout the solution. Oxygen activity was calculated at each instant of time from the fractional saturation of Mb, determined from observations at the Hb/HbO2 isosbestic wavelength. Fractional saturation of Hb was determined from absorbances at the Mb/MbO2 isosbestic wavelength. The spectrophotometer cycled between these two wavelengths during the deoxygenation. The deoxygenation of HbO2 was largely complete in 20-25 min, whereas the deoxygenation of MbO2 was allowed to proceed for about 1 h. This procedure eliminates equilibration of Hb solutions with a gas phase and replaces oxygen electrode readings with spectrophotometric sensing by Mb, providing essentially instantaneous determinations of oxygen activity and hence 250-500 or more independent data points per run. The Mb and Hb data vectors require several manipulations to correct for small relative displacements in time and for small non-isosbestic effects. Detailed consideration of the enzyme kinetics allowed oxygen activities to be determined in regions where Mb is a poor sensor. Studies of HbO2 deoxygenation as a function of wavelength show that the determination of the four Adair constants requires in addition the determination of three spectroscopic parameters. Values of the apparent Adair constants, determined without these spectroscopic parameters, depend strongly on the monitoring wavelength. 相似文献