全文获取类型
收费全文 | 9560篇 |
免费 | 691篇 |
国内免费 | 2篇 |
出版年
2021年 | 103篇 |
2020年 | 68篇 |
2019年 | 87篇 |
2018年 | 108篇 |
2017年 | 99篇 |
2016年 | 201篇 |
2015年 | 311篇 |
2014年 | 370篇 |
2013年 | 523篇 |
2012年 | 551篇 |
2011年 | 564篇 |
2010年 | 410篇 |
2009年 | 339篇 |
2008年 | 491篇 |
2007年 | 550篇 |
2006年 | 497篇 |
2005年 | 535篇 |
2004年 | 493篇 |
2003年 | 481篇 |
2002年 | 487篇 |
2001年 | 133篇 |
2000年 | 100篇 |
1999年 | 121篇 |
1998年 | 167篇 |
1997年 | 108篇 |
1996年 | 116篇 |
1995年 | 128篇 |
1994年 | 122篇 |
1993年 | 122篇 |
1992年 | 94篇 |
1991年 | 81篇 |
1990年 | 101篇 |
1989年 | 99篇 |
1988年 | 73篇 |
1987年 | 78篇 |
1986年 | 74篇 |
1985年 | 76篇 |
1984年 | 81篇 |
1983年 | 83篇 |
1982年 | 67篇 |
1981年 | 78篇 |
1980年 | 62篇 |
1979年 | 59篇 |
1978年 | 54篇 |
1977年 | 54篇 |
1976年 | 51篇 |
1975年 | 47篇 |
1974年 | 45篇 |
1973年 | 40篇 |
1968年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
To control the environmentally detrimental impact of acid rock drainage, two different countermeasures, layers of acid-buffering
materials and sodium dodecyl sulphate addition, were tested for their efficiency in laboratory percolation experiments. In
the experiment with a layer of calcium bentonite, only the iron output was reduced. The experiments with layers of concrete
grains demonstrated a decrease of the microbial activity as well as a precipitation of heavy-metal ions, whereas the cell
numbers did not decrease. Furthermore, finely grained concrete (1–5 mm) formed a water-tight hardpan (self-sealing layer).
In the experiment with 1 mM sodium dodecyl sulphate, all the microorganisms were killed and hence metal sulphide dissolution
was stopped. With 0.1 mM sodium dodecyl sulphate only a short, transient inhibition of leaching was achieved. The bacteria
remained alive.
Received: 16 February 1998 / Accepted: 23 February 1998 相似文献
2.
3.
Abstract We have analyzed the sequence downstream of rpoN from Zcinetobacter calcoaceticus and identified an open reading frame encoding a protein with high similarity to UDP- N -acetylgucosamine 1-carboxyvinyl-transferase (MurZ). Multicopy plasmids encoding this enzyme conferred phosphomycin resistance to A. calcoaceticus . The polar effect of a rpoN mutation on the phosphomycin resistance level suggests that murZ is, in part, cotranscribed with rpoN . These observations confirm that A. calcoaceticus represents the first exceptin from a conserved genetic context of rpoN observed in several other Gram-negative bacteria. 相似文献
4.
G. Wolfgang Fuhs 《Archives of microbiology》1961,39(4):374-422
Ohne Zusammenfassung 相似文献
5.
6.
7.
8.
9.
The overproduction of specialized metabolites requires plants to manage the inherent burdens, including the risk of self-intoxication. We present a control mechanism that stops the expression of phytoalexin biosynthetic enzymes by blocking the antecedent signal transduction cascade. Cultured cells of Eschscholzia californica (Papaveraceae) and Catharanthus roseus (Apocynaceae) overproduce benzophenanthridine alkaloids and monoterpenoid indole alkaloids, respectively, in response to microbial elicitors. In both plants, an elicitor-responsive phospholipase A2 (PLA2) at the plasma membrane generates signal molecules that initiate the induction of biosynthetic enzymes. The final alkaloids produced in the respective plant inhibit the respective PLA, a negative feedback that prevents continuous overexpression. The selective inhibition by alkaloids from the class produced in the “self” plant could be transferred to leaves of Nicotiana benthamiana via recombinant expression of PLA2. The 3D homology model of each PLA2 displays a binding pocket that specifically accommodates alkaloids of the class produced by the same plant, but not of the other class; for example, C. roseus PLA2 only accommodates C. roseus alkaloids. The interaction energies of docked alkaloids correlate with their selective inhibition of PLA2 activity. The existence in two evolutionary distant plants of phospholipases A2 that discriminate “self-made” from “foreign” alkaloids reveals molecular fingerprints left in signal enzymes during the evolution of species-specific, cytotoxic phytoalexins. 相似文献
10.
Pyruvate kinase, purified from flounder liver, in two forms, i.e. PK I and PK II, is characterized by sigmoid kinetics with phosphoenolpyruvate as substrate at pH 6.3, 6.7 and 7.7. K0.5 for PEP increases with increasing pH. PK I and PK II show hyperbolic kinetics with ADP, but are inhibited by ADP concentrations above 1-2 mM. K0.5 for ADP decreases with increasing pH. PK I and PK II differ in their K0.5 values for PEP with a factor of at least 2, showing the highest figures for the latter. K0.5 for ADP is about the same for the two enzyme forms. Other nucleotide diphosphates can replace ADP as the substrate. When the nucleoside diphosphates are arranged in a rank order showing decreasing effectiveness as substrate, different rank orders are obtained for PK I and PK II. 相似文献