全文获取类型
收费全文 | 664篇 |
免费 | 72篇 |
出版年
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 4篇 |
2017年 | 15篇 |
2016年 | 19篇 |
2015年 | 33篇 |
2014年 | 31篇 |
2013年 | 36篇 |
2012年 | 51篇 |
2011年 | 51篇 |
2010年 | 29篇 |
2009年 | 16篇 |
2008年 | 41篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 29篇 |
2002年 | 30篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1982年 | 3篇 |
1978年 | 4篇 |
1975年 | 7篇 |
1973年 | 3篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 4篇 |
1965年 | 3篇 |
1963年 | 4篇 |
1961年 | 4篇 |
1956年 | 2篇 |
排序方式: 共有736条查询结果,搜索用时 33 毫秒
1.
2.
Long chain acylamides of ethanolamine were previously found to increase in the infarcted canine myocardium. Subsequent in vitro experiments established a number of interesting biological and physiological properties of these compounds including alteration of rabbit skeletal sarcoplasmic reticulum function and inhibition of permeability dependent calcium release from heart mitochondria. These results suggested an interaction between the N-acylethanolamines and biological membranes. In the present work we show that the most potent species in previous studies, N-oleylethanolamine, forms stable complexes with phospholipid vesicles, lowers diphenylhexatriene polarization ratios in dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine uni- and multilamellar bilayer vesicles, and also produces a concentration dependent decrease in the phase transitions of these lipid structures. In addition studies with parinaric acids also suggested that N-oleylethanolamine partitions preferentially into more fluid areas of the bilayer. The results are discussed in terms of possible effects on biological membranes. 相似文献
3.
4.
The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention
in recent years. However, insufficient information exists on the coordination of transpiration and CO2 uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration
(E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and
first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas
exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and
fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed
for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf
age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial
leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO2 mmol−1 H2O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in
stomatal conductance (gs·H2O) since decreases in gs·H2O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along
the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these
findings are presented in relation to light competition within the plant canopy during development. 相似文献
5.
An amino acid analysis method using a commercially available analyzer that accurately quantitates protein-derived amino acids in the 10-100 pmol range is described. The method utilizes the robotic capability of the analyzer's autosampler to perform precolumn derivatization of both primary and secondary amino acids with o-phthalaldehyde and 9-fluorenylmethyl chloroformate, respectively. The derivatized amino acids are then separated on a C-18 reverse-phase amino acid column and quantitated in a single run by fluorescence detection. The characterization of beta-lactoglobulin and two tryptic peptides from the bacterial enzyme diaminopimelic acid epimerase is used to demonstrate the sensitivity and utility of this method. 相似文献
6.
The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge. 相似文献
7.
Summary The most widely used technique of leaf water potential measurements is with the Scholander pressure chamber. Representative leaf water potential values require many determinations on individual leaves and this can be time consuming in large fields or experiments with multiple treatments. This paper describes a method of obtaining a mean value more rapidly, by using two leaves in the pressure chamber at the same time, but recording the end point of each leaf separately. 相似文献
8.
Richard L. Jackson Lilian Socorro Geralyn M. Fletcher Alan D. Cardin 《FEBS letters》1985,190(2):297-300
Heparin was fractionated on an affinity column of bovine milk lipoprotein lipase (LpL) immobilized to Affi-Gel-15. The bound heparin, designated high-reactive heparin (HRH), enhanced LpL activity, presumably by stabilizing the enzyme against denaturation. The unbound heparin fraction had no observable effect on the initial rate of enzyme activity. However, at longer times of incubation there was inhibition of LpL activity. LpL-specific HRH also showed a high, Ca2+-dependent precipitating activity towards human plasma low density lipoproteins (LDL). Since LpL and LDL both bind to heparin-like molecules at the surface of the arterial wall, we suggest that their similar heparin-binding specificity may have physiological consequences as it relates to the development of atherosclerosis.
Heparin binding Lipoprotein lipase LDL Apolipoprotein Lipolysis 相似文献
9.
E. H. Derrick 《International journal of biometeorology》1966,10(1):91-99
A study has been made of the annual incidence of asthma in Brisbane for 7 years in relation to the weather. The element most closely associated with asthma was rainfall. There was a minor, independent association with temperature. The association of asthma with rain and warmth, which promote the growth of vegetation, supports the suggestion arising from the seasonal study of asthma that vegetation may be an important source of allergens.
Zusammenfassung Die Beziehung zwischen dem Wetter und der Häufigkeit von Asthma in Brisbane während 7 Jahren wurde untersucht. Unter den meteorologischen Elementen ergab sich die engste Beziehung zwischen Asthmahäufigkeit und Niederschlägen. Eine geringere, unabhängige Beziehung bestand mit der Temperatur. Die Verbindung von Asthma mit Niederschlägen und Wärme stützt die Vermutung, dass die Vegetation eine wichtige Allergenquelle ist.
Resume On a étudié durant 7 années la relation existant entre le temps et la fréquence des crises d'asthme à Brisbane. Parmi les éléments météorologiques examinés, celui qui donna la plus étroite relation est la précipitation.Une relation indépendante, moindre il est vrai, existe également avec la température.L'étroite relation entre les crises d'asthme d'une part, les précipitations et la chaleur d'autre part renforce l'hypothèse que la végétation est la principale source des principes allergènes.相似文献
10.
Chloramphenicol acetyltransferase (CAT) was used to assess the feasibility of study of specific proton resonances in an enzyme of overall molecular mass 75,000, [ring 2-13C]Histidine was selectively incorporated into the type III chloramphenicol acetyltransferase (CATIII) using a histidine auxotroph of E. coli. Heteronuclear multiple and single quantum experiments were used to select the C2 protons in the histidyl imidazole ring. One- and two-dimensional spectra revealed six signals out of a total of seven histidine residues in CATIII. pH titration, chemical modification and ligand binding were used to demonstrate that the signal from H195, the histidine at the active site, is not among those observed. Nevertheless, this work demonstrates that selective isotopic enrichment and multiple quantum coherence techniques can be used to distinguish proton resonances in a protein of high molecular mass. 相似文献