全文获取类型
收费全文 | 103711篇 |
免费 | 3531篇 |
国内免费 | 1710篇 |
专业分类
108952篇 |
出版年
2022年 | 667篇 |
2021年 | 1175篇 |
2020年 | 816篇 |
2019年 | 954篇 |
2018年 | 1792篇 |
2017年 | 1738篇 |
2016年 | 3712篇 |
2015年 | 7407篇 |
2014年 | 7265篇 |
2013年 | 7140篇 |
2012年 | 6502篇 |
2011年 | 3635篇 |
2010年 | 3094篇 |
2009年 | 2966篇 |
2008年 | 1615篇 |
2007年 | 1426篇 |
2006年 | 1330篇 |
2005年 | 7273篇 |
2004年 | 5812篇 |
2003年 | 4008篇 |
2002年 | 1491篇 |
2001年 | 1394篇 |
2000年 | 629篇 |
1999年 | 1779篇 |
1998年 | 506篇 |
1992年 | 2074篇 |
1991年 | 2120篇 |
1990年 | 2177篇 |
1989年 | 2073篇 |
1988年 | 2005篇 |
1987年 | 1856篇 |
1986年 | 1658篇 |
1985年 | 1686篇 |
1984年 | 1103篇 |
1983年 | 848篇 |
1982年 | 473篇 |
1979年 | 1075篇 |
1978年 | 760篇 |
1977年 | 606篇 |
1976年 | 629篇 |
1975年 | 874篇 |
1974年 | 994篇 |
1973年 | 1005篇 |
1972年 | 953篇 |
1971年 | 928篇 |
1970年 | 820篇 |
1969年 | 830篇 |
1968年 | 734篇 |
1967年 | 751篇 |
1966年 | 585篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
92.
93.
94.
95.
96.
97.
98.
The use of the artificial antigen abequosylmannoside copolymer with acrylamide in the enzyme immunoassay for the determination of antibodies in the sera of salmonellosis patients has enhanced the specificity of the serological diagnosis of group B salmonellosis in comparison with the use of the natural antiren, S. typhimurium lipopolysaccharide. 相似文献
99.
Y. Jiang 《Biochimica et Biophysica Acta (BBA)/General Subjects》1994,1201(1):76-84
Proteolysis of the hydroxylase component of soluble methane monooxygenase (MMO) with trypsin yielded a protein which retained 50% activity in a standard MMO assay. In an H2O2-driven assay, in which H2O2 replaced two of the protein components, NADH and O2 used in the standard assay, the proteolysed hydroxylase retained full activity for ethane, propane and propene, but had a 2–3 fold increase with methane as substrate. Several crosslinking reagents have been tested for their ability to stabilise the proteolysed form of the hydroxylase. Using polyoxyethylene bis(imidazolyl carbonyl) (Mr 3350) as the crosslinking agent, increased thermostability of the hydroxylase was observed. Activated methoxypolyethylene glycol (Mr 5000) was used to modify the hydroxylase which was now soluble in organic solvents as well as water and could be activated by H2O2. The glycol-modified hydroxylase functioned well in organic solvents in the catalysis of propene oxidation. 相似文献
100.
Sulfur bacteria such as Beggiatoa or Thiomargarita have a particularly high capacity for storage because of their large size. In addition to sulfur and nitrate, these bacteria also store phosphorus in the form of polyphosphate. Thiomargarita namibiensis has been shown to release phosphate from internally stored polyphosphate in pulses creating steep peaks of phosphate in the sediment and thereby inducing the precipitation of phosphorus-rich minerals. Large sulfur bacteria populate sediments at the sites of recent phosphorite formation and are found as fossils in ancient phosphorite deposits. Therefore, it can be assumed that this physiology contributes to the removal of bioavailable phosphorus from the marine system and thus is important for the global phosphorus cycle. We investigated under defined laboratory conditions which parameters stimulate the decomposition of polyphosphate and the release of phosphate in a marine Beggiatoa strain. Initially, we tested phosphate release in response to anoxia and high concentrations of acetate, because acetate is described as the relevant stimulus for phosphate release in activated sludge. To our surprise, the Beggiatoa strain did not release phosphate in response to this treatment. Instead, we could clearly show that increasing sulfide concentrations and anoxia resulted in a decomposition of polyphosphate. This physiological reaction is a yet unknown mode of bacterial polyphosphate usage and provides a new explanation for high phosphate concentrations in sulfidic marine sediments. 相似文献