全文获取类型
收费全文 | 1401篇 |
免费 | 49篇 |
国内免费 | 1篇 |
专业分类
1451篇 |
出版年
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 24篇 |
2014年 | 48篇 |
2013年 | 59篇 |
2012年 | 66篇 |
2011年 | 66篇 |
2010年 | 51篇 |
2009年 | 34篇 |
2008年 | 69篇 |
2007年 | 72篇 |
2006年 | 63篇 |
2005年 | 55篇 |
2004年 | 72篇 |
2003年 | 47篇 |
2002年 | 67篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 8篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 16篇 |
1981年 | 28篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 28篇 |
1977年 | 13篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 21篇 |
1973年 | 16篇 |
1970年 | 7篇 |
1969年 | 7篇 |
1968年 | 11篇 |
1964年 | 8篇 |
排序方式: 共有1451条查询结果,搜索用时 15 毫秒
21.
22.
Free Fatty Acids in the Rat Brain in Moderate and Severe Hypoxia 总被引:20,自引:16,他引:4
Mark Gardiner Bengt Nilsson Stig Rehncrona Bo K. Siesjö 《Journal of neurochemistry》1981,36(4):1500-1505
Abstract: The effects of mild, moderate, and severe hypoxia on cerebral cortical concentrations of free fatty acids (FFAs) were investigated in artificially ventilated rats under nitrous oxide anaesthesia. No change occurred during either mild (arterial Po2 35–40 mm Hg) or moderate (Po2 25–30 mm Hg) hypoxia. The effects of severe hypoxia (Po2 about 20 mm Hg) combined with hypotension (mean arterial blood pressure 80–85 mm Hg) varied with the EEG pattern and the tissue energy state. Thus, a major increase in total as well as in individual FFAs occurred first when EEG was severely depressed (almost isoelectric) and energy homeostasis disrupted. On a relative basis the greatest change occurred in free arachidonic acid. It is concluded that hypoxia is associated with an increase in the concentrations of FFAs in brain tissue, provided that tissue oxygen deficiency is severe enough to cause tissue energy failure. However, an increase in FFAs does not invariably accompany minor reductions in the adenylate energy charge (EC) of the tissue. 相似文献
23.
The anterio-posterior distribution of cholinergic receptor binding sites in human hippocampus (five parts) as well as the effect of age (age range 3 days - 85 years) on receptor properties has been studied. Muscarinic binding sites was measured using labelled quinuclidinyl benzilate (3H-QNB) as ligand and labelled tubocurarine (3H-TC) was used for measurement of nicotine-like binding sites.The highest number of 3H-QNB binding sites in human hippocampus was measured at 3 days and 3 weeks of age and the lowest at 82 years of age. The proportion of high and low affinity muscarinic binding sites respectively was about the same at all ages investigated.A decrease in 3H-QNB binding sites with age was found in the anterior parts of the hippocampus (age range 55–84 years). When individual data for number of 3H-TC binding sites were plotted against corresponding number of 3H-QNB binding sites a strong correlation was observed in most of the different regions of the hippocampus. 相似文献
24.
Bengt Danielsson Fredrik Winqvist Jean Yves Malpote Klaus Mosbach 《Biotechnology letters》1982,4(10):673-678
Summary An alternative approach to the regeneration of coenzymes using immobilized hydrogen dehydrogenase (hydrogenase) is described. Hydrogenase isolated from Alcaligenes Eutrophus was immobilized to porous glass particles and used in combination with alanine dehydrogenase for formation of alanine, while the NADH consumed was regenerated by molecular hydrogen. Different physical arrangements of the two enzymes were compared. Alanine was conveniently assayed with a specially designed enzyme thermistor method. 相似文献
25.
26.
Paula Branefors-Helander Björn Classon Lennart Kenne Bengt Lindberg 《Carbohydrate research》1979,76(1):197-202
The structure of the capsular antigen from Haemophilus influenza type c has been investigated, n.m.r. spectroscopy being the principal method used. It is concluded that the antigen is composed of repeating-units having the following structure: O-Acetyl groups are present in ~90% of the repeating-units. 相似文献
27.
The structure of the polysaccharide antigen produced by Eubacterium saburreum, strain L 32, has been investigated. The principal methods used were methylation analysis, graded hydrolysis with acid, and n.m.r. spectroscopy. The polysaccharide, which contains the unusual sugar 3,6-dideoxy-D-arabino-hexose (tyvelose, Tyv), is composed of trisaccharide repeating-units having the following structure: 相似文献
28.
Summary The purpose of this study was to try to differentiate histochemically between the various enzymes which may catalyze the hydrolysis of ATP in developing rat dental tissues. Freeze cut and freeze dried sections of molar and incisor teeth were incubated in lead capture-based media at pH 5.0, 7.2 or 9.4 with one of the following substrates: -glycerophosphate, AMP, ADP, ATP, AMP-PNP and tetrasodium pyrophosphate. To establish the enzymatic nature of the hydrolysis parallel sections were incubated after prior fixation in either formaldehyde or glutaraldehyde.By comparing the enzymatic stainings obtained with the various substrates and at the different pH: s, it was concluded that ATP can be visibly hydrolyzed in rat dental tissues by alkaline phosphatase (stratum intermedium, apical part of maturation ameloblasts, basal part of all ameloblasts, odontoblasts and subodontoblastic layer), specific ATPase (apical and basal parts of secretory ameloblasts) and ATP pyrophosphatase and/or adenylate cyclase (stratum intermedium, odontoblasts). Acid phosphatase, specific ADPase, 5-nucleotidase, inorganic pyrophosphatase, 3:5-cyclic-AMP-phosphodiesterase and adenylate kinase on the other hand, seem not to be engaged in the ATP hydrolysis to such a degree as to complicate the interpretation of the histochemical staining. The alkaline phosphatase part of the ATP hydrolysis appeared to be rather insensitive to aldehyde fixation, while the hydrolysis effected by specific ATPase and ATP pyrophosphatase and/or adenylate cyclase was extinguished after fixation with formaldehyde for 4 h or glutaraldehyde for 10 min. 相似文献
29.
Cerebral arterio-venous differences of homovanillic acid (HVA) and cerebral blood flow were measured in 24 patients, 6 adults and 18 children, anaesthetized by different techniques. A statistically significant release of HVA from the brain (p < 0.001) was demonstrated in five children anaesthetized by barbiturate, nitrous oxide and droperidol/fentanyl. The release rate was 509 pmoles HVA/100 g brain tissue/minute - corresponding to approximately 1.3 mg HVA/24 hours from the whole brain. 相似文献
30.
Bo Mattiasson Bengt Danielsson Fredrik Winquist Hans Nilsson Klaus Mosbach 《Applied microbiology》1981,41(4):903-908
Immobilized penicillinase was applied in an enzyme thermistor for calorimetric analysis of samples containing penicillin G. Standard solutions as well as extracts from fermentation broth were analyzed. The enzyme was applied bound either to porous glass or, when dealing with crude preparations, to the inner surface of nylon tubing. In the fermentation system studied, high concentrations of penicillin were present, thus allowing dilution to reduce the influence of the composition of the medium on the analysis. The useful linear concentration range was from 0.1 to 100 mM. The coefficient of correlation between analytical results obtained with the present method and those from conventional assays was 0.997. 相似文献