全文获取类型
收费全文 | 61061篇 |
免费 | 4751篇 |
国内免费 | 2268篇 |
专业分类
68080篇 |
出版年
2023年 | 833篇 |
2022年 | 1225篇 |
2021年 | 1531篇 |
2020年 | 1896篇 |
2019年 | 2458篇 |
2018年 | 2260篇 |
2017年 | 1653篇 |
2016年 | 1648篇 |
2015年 | 1841篇 |
2014年 | 3562篇 |
2013年 | 4265篇 |
2012年 | 2783篇 |
2011年 | 3537篇 |
2010年 | 2670篇 |
2009年 | 2981篇 |
2008年 | 3260篇 |
2007年 | 3183篇 |
2006年 | 2666篇 |
2005年 | 2465篇 |
2004年 | 2203篇 |
2003年 | 1962篇 |
2002年 | 1687篇 |
2001年 | 1167篇 |
2000年 | 972篇 |
1999年 | 1030篇 |
1998年 | 986篇 |
1997年 | 847篇 |
1996年 | 781篇 |
1995年 | 779篇 |
1994年 | 755篇 |
1993年 | 625篇 |
1992年 | 567篇 |
1991年 | 504篇 |
1990年 | 400篇 |
1989年 | 394篇 |
1988年 | 306篇 |
1987年 | 327篇 |
1986年 | 248篇 |
1985年 | 429篇 |
1984年 | 603篇 |
1983年 | 492篇 |
1982年 | 507篇 |
1981年 | 444篇 |
1980年 | 413篇 |
1979年 | 342篇 |
1978年 | 276篇 |
1977年 | 243篇 |
1976年 | 250篇 |
1975年 | 205篇 |
1974年 | 203篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The development of a sensitive and specific enzyme immunoassay for GA3 is reported. This method was based on the use of peroxidase labelled GA3 and immobilized antibodies. In order to obtain a rapid immunoassay, several steps of purification were analyzed to show their necessity. Barley seed extracts were assayed at different steps of purification to exhibit the effect of extract components on the assay. It was demonstrated that HPLC had to be performed when a selective quantitation of GA3 was required. This assay allowed GA3 to be measured with reproducibility as its unmethylated form and the quantitation of GA3 in barley seeds with this enzyme immunoassay was correlated to a GC-MS method.Abbreviations GA3
gibberellin A3
- EIA
enzyme immunoassay
- DMF
dimethylformamide
- TEA
tri(n)ethylamine
- BSA
bovine serum albumin
- OVA
ovalbumine
- ECF
ethylchloroformate
- PB
phosphate buffer 相似文献
62.
Reversible binding of DIDS [4,4'-diisothiocyanato-2,2'-stilbenedisulphonate] to Band 3 protein, the anion exchanger located in erythrocyte plasma membrane, was studied in human erythrocytes. For this purpose, the tritiated form of DIDS ([3H]DIDS) has been synthesized and the filtering technique has been used to follow the kinetics of DIDS binding to the sites on Band 3 protein. The obtained results showed monophasic kinetics both for dissociation and association of the 'DIDS-Band 3' complex at 0° C in the presence of 165 mM KCl outside the cell (pH 7.3). A pseudo-first order association rate constant k+1 相似文献
63.
Band 3 protein extracted from human erythrocyte membranes by Triton X-100 was recombined with the major classes of phospholipid occurring in the erythrocyte membrane. The resulting vesicle systems were characterized with respect to recoveries, phospholipid composition, protein content and vesicle size as well as capacity and activation energy of sulfate transport. Transport was classified into band-3-specific fluxes and unspecific permeability by inhibitors. Transport numbers (sulfate ions per band 3 per minute) served as a measure of functional recovery after reconstitution. The transport properties of band 3 proved to be insensitive to replacement of phosphatidylcholine by phosphatidylethanolamine, while sphingomyelin and phosphatidylserine gradually inactivated band-3-specific anion transport when present at mole fractions exceeding 30 mol%. The activation energy of transport remained unaltered in spite of the decrease in transport numbers. The results, which are discussed in terms of requirements of band 3 protein function with respect to the fluidity and surface charge of its lipid environment, provide a new piece of evidence that the transport function of band 3 protein depends on the properties of its lipid environment just as the catalytic properties of some other membrane enzymes. The well-established species differences in anion transport (Gruber, W. and Deuticke, B. (1973) J. Membrane Biol. 13, 19–36) may to some extent reflect this lipid dependence. 相似文献
64.
65.
66.
Enhanced Noradrenergic Neuronal Activity Increases Homovanillic Acid Levels in Cerebrospinal Fluid 总被引:2,自引:2,他引:0
Harry Scheinin 《Journal of neurochemistry》1986,47(3):665-667
Idazoxan, a highly specific and selective alpha 2-adrenoceptor antagonist, caused a dose-dependent increase in the concentration of homovanillic acid (HVA) a metabolite of 3,4-dihydroxyphenylethylamine, in cisternal CSF of freely moving rats. This increase in HVA level could be antagonized by the alpha 2-adrenoceptor agonist medetomidine. The increase was directly proportional to the concurrent elevation in level of 3-methoxy-4-hydroxyphenylglycol, a metabolite of noradrenaline, in the CSF of individual rats and followed a similar time course. It is suggested that the HVA level in CSF may be increased under conditions of enhanced noradrenergic activity and that, in such situations, it reflects noradrenergic rather than dopaminergic neuronal activity. Care should be taken, therefore, when changes in central dopaminergic activity are assessed by measurements of HVA level in CSF. 相似文献
67.
Andrew Leask 《Journal of cell communication and signaling》2010,4(2):109-110
The role of CCN proteins in vivo is only just becoming understood. A prototypical member of the CCN family, CCN3 suppresses proliferation. In a study in press, Shimoyama and colleagues show that mice lacking CCN3 have a hyperproliferative response to vascular injury. These data, along with other recent observations, suggest that CCN3 may represent a novel therapy for hyperproliferative diseases. 相似文献
68.
The reactivity of sonicated phosphatidylcholine-cholesterol liposomes with cholesterol : oxygene oxydoreductase, an enzyme which catalyses the oxidation of the 3 beta hydroxyl group of cholesterol to a ketone group, is compared with that of ternary system phosphatidylcholine-cholesterol-Thesit. Regardless to the phosphatidylcholines nature and the phosphatidylcholine/cholesterol molar ratio (R), the enzymatic oxidation rate of liposomal cholesterol is slower than when the reaction is developed in the present of Thesit, a surfactif agent which destroyes the lamellar particles. This is true whether Thesit is added during preparation of dispersions or during incubation with cholesterol oxydase. The enzymatic oxydation rate of cholesterol of ternary systems phosphatidylcholine-cholesterol-Thesit is independent of the (R) value and the phosphatidylcholine fatty acid unsaturation, whereas that of phosphatidylcholine-cholesterol dispersions depends on these two parameters. The reaction rate increases in the order: dipalmitoylphosphatidylcholine to yolk egg phosphatidylcholines, and dioleylphosphatidylcholine. The optimal conditions for cholesterol oxidation were found to be R = 0.5. This result is not affected by the phosphatidylcholines nature. In order to explain these data, various hypotheses are considered. In particular, the weak liposomal cholesterol reactivity with cholesterol oxidase could result from an inhibitory effect on the enzyme-substrate combination due to the polar phosphorylcholine groups. 相似文献
69.
70.