全文获取类型
收费全文 | 61418篇 |
免费 | 2811篇 |
国内免费 | 2544篇 |
专业分类
66773篇 |
出版年
2023年 | 713篇 |
2022年 | 1117篇 |
2021年 | 1242篇 |
2020年 | 1400篇 |
2019年 | 1758篇 |
2018年 | 1768篇 |
2017年 | 1371篇 |
2016年 | 1386篇 |
2015年 | 1451篇 |
2014年 | 3013篇 |
2013年 | 4750篇 |
2012年 | 2209篇 |
2011年 | 3125篇 |
2010年 | 2257篇 |
2009年 | 2849篇 |
2008年 | 3002篇 |
2007年 | 3016篇 |
2006年 | 2612篇 |
2005年 | 2410篇 |
2004年 | 2011篇 |
2003年 | 1880篇 |
2002年 | 1554篇 |
2001年 | 1170篇 |
2000年 | 1056篇 |
1999年 | 999篇 |
1998年 | 1002篇 |
1997年 | 913篇 |
1996年 | 900篇 |
1995年 | 827篇 |
1994年 | 837篇 |
1993年 | 784篇 |
1992年 | 718篇 |
1991年 | 644篇 |
1990年 | 584篇 |
1989年 | 550篇 |
1988年 | 494篇 |
1987年 | 504篇 |
1986年 | 373篇 |
1985年 | 772篇 |
1984年 | 1097篇 |
1983年 | 806篇 |
1982年 | 886篇 |
1981年 | 701篇 |
1980年 | 630篇 |
1979年 | 558篇 |
1978年 | 385篇 |
1977年 | 378篇 |
1976年 | 319篇 |
1975年 | 265篇 |
1973年 | 271篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A possibly physiologically significant inhibition of yeast enolase by fluoride occurs in the absence of inorganic phosphate. The inhibition increases with time, is strongly dependent on fluoride concentration and requires substrate and “catalytic” Mg2+. The inhibition increases more slowly in the presence of product (phosphoenolpyruvate) than substrate (2-phosphoglycerate). The dependence on fluoride concentration and the spans of substrate analogue displacement titrations suggest the inhibition is produced by two moles of fluoride per active site. 相似文献
62.
63.
64.
Robert J. Pryce 《Phytochemistry》1973,12(7):1745-1754
Allogibberic acid (I) has been identified as the compound responsible for the inhibition of flowering, increase in frond multiplication rate and decrease in frond size produced in Lemna perpusilla 6746 by autoclaved, unbuffered aqueous solutions of gibberellic acid (VII). 13-Deoxyallogibberic acid (IV), a product of autoclaving aq. GA7 (VIII) solutions, also inhibits flowering in L. perpusilla and is about 10 times more active than allogibberic acid. 相似文献
65.
66.
67.
The effect of buffers and chelators on the reaction of luminol with Fenton's reagent near neutral pH
G. Bottu 《Luminescence》1991,6(3):147-151
The chemiluminescence of the system luminol +Fe2+ + H2O2 was measured in aqueous buffer at pH 7.2. In veronal (5,5-diethybarbiturate) buffer, the luminescence is strongly quenched by ethanol and mannitol, but only weakly by t-butanol, benzoate and superoxide dismutase (SOD); complexing Fe2+ with 1,10-phenanthroline or 2,2′-dipyridyl causes a decrease of light production that can be partially obviated by the simultaneous addition of SOD. In phosphate buffer, the luminescence is higher than in veronal and it is efficiently quenched by all four OH · quenchers and by SOD. In Tris buffer, no light production is observed as long as the Fe2+ is not complexed. When Fe2+ is complexed by pyrophosphate or phytate, there is a strong chemiluminescence in all three buffers, which is quenched by all four OH · quenchers and by SOD. When Fe2+ is complexed by EDTA or DTPA, very little luminescence is observed. The luminol analogue phthalhydrazide, which was suggested by Merényi and Lind as a reliable OH · detector, can replace luminol only in phosphate buffer, and thus turns out to be very specific indeed for free OH ·. 相似文献
68.
We investigated the synthesis and translocation of amino compounds in Parasponia, a genus of the Ulmaceae that represents the only non-legumes known to form a root nodule symbiosis with rhizohia. In the xylem sap of P. andersonii we identified asparagine. aspartate. glutamine, glutamated significant quantities of a non-protein amino acid. 4-methylglutamte(2-amino-4-methylpentanedioic acid). This identification was confirmed by two methods, capillary gas chromatography (GC) electron ionization (El) mass spectrometry (MS) and reverse phase high pressure liquid chromatography (HPLC) analysis of derivatized compounds. In leaf, root and nodule samples from P. andersonii and P. parviflora we also identified the related compounds 4-methyleneglutamate and 4-methyleneglulamine. Using 15N2 labelling and GC-Ms analysis of root nodule extracts we followed N2 fixation and ammonia assimilation in P. andersonii root nodules and observed Label initially in glutamine and subsequently in glutamate, suggesting operation of the glutamine synthetase/glutamine:2-oxoglutarate aminotransferase (GS/GOGAT) pathway. Importantly, we observed the incorporation of significant quantities of 15N into 4-methylglutamate in nodules, demonstrating the de nova synthesis of this non protein amino acid and suggesting a role in the translation of N in symbioticParasponia. 相似文献
69.
An insect larval toxin designated CryII is produced by several subspecies of Bacillus thuringiensis and differs from the other major delta-endotoxins in these bacteria in its size, toxicity profile and presence as part of an operon with three open reading frames (ORF). Such an operon from a novel B. thuringiensis isolate has been cloned and differs from one previously characterized in the following ways: (a) the size and number of amino acid repeats in one of the ORFs; (b) the smaller size of the CryII protoxin and the presence of a unique 110-kDa CryII-related antigen; and (c) high larvicidal activity for a particular Lepidopteran but low activity for a Dipteran. Various subclones of this operon were introduced into a plasmid-free B. thuringiensis strain and only the cryII gene was found to be necessary for protoxin accumulation. 相似文献
70.
Strategies for signal amplification in nucleic acid detection 总被引:3,自引:0,他引:3
S. Calin Andras J. Brian Power Edward C. Cocking Michael R. Davey 《Molecular biotechnology》2001,19(1):29-44
Many aspects of molecular genetics necessitate the detection of nucleic acid sequences. Current approaches involving target
amplification (in situ PCR, Primed in situ Labeling, Self-Sustained Sequence Replication, Strand Displacement Amplification), probe amplification (Ligase Chain Reaction,
Padlock Probes, Rolling Circle Amplification) and signal amplification (Tyramide Signal Amplification, Branched DNA Amplification)
are summarized in the present review, together with their advantages and limitations. 相似文献