全文获取类型
收费全文 | 3414篇 |
免费 | 154篇 |
国内免费 | 1篇 |
专业分类
3569篇 |
出版年
2023年 | 37篇 |
2022年 | 63篇 |
2021年 | 80篇 |
2020年 | 58篇 |
2019年 | 63篇 |
2018年 | 103篇 |
2017年 | 80篇 |
2016年 | 136篇 |
2015年 | 161篇 |
2014年 | 169篇 |
2013年 | 268篇 |
2012年 | 312篇 |
2011年 | 254篇 |
2010年 | 170篇 |
2009年 | 164篇 |
2008年 | 179篇 |
2007年 | 168篇 |
2006年 | 133篇 |
2005年 | 112篇 |
2004年 | 101篇 |
2003年 | 93篇 |
2002年 | 62篇 |
2001年 | 51篇 |
2000年 | 41篇 |
1999年 | 32篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 26篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 24篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1974年 | 14篇 |
1972年 | 18篇 |
1971年 | 12篇 |
1969年 | 10篇 |
排序方式: 共有3569条查询结果,搜索用时 15 毫秒
11.
12.
13.
Improved synthesis of oligodeoxyribonucleotide using 3-methoxy-4-phenoxybenzoyl group for amino protection. 总被引:1,自引:1,他引:0 下载免费PDF全文
3-Methoxy-4-phenoxybenzoyl group has been used for the protection of exocyclic amino group of nucleosides. In case of 2'-deoxycytidine it has been found to be highly selective under controlled conditions. The N-protected derivatives of 2'-deoxyadenosine and 2'-deoxyguanosine have been found to be sufficiently stable towards acids minimising depurination under conditions of synthesis of oligodeoxyribonucleotide on solid support via phosphotriester approach. The high lipophilicity of the group and milder deprotection conditions are additional advantages. 相似文献
14.
It is clear that C. albicans lipids have gained tremendous importance in recent years. In addition to being a barrier for entrance of various metabolites, it also provides the site of action for the synthesis of enzyme(s) involved in cell wall morphogenesis and antifungal action. While alterations in lipid composition during a yeast to mycelia transition have been observed, in most of the studies, lipid fluctuations reported could have been due to various environmental factors involved in the induction of morphogenesis [4,5]. A clear understanding of lipid biosynthesis and metabolic blocks due to antifungal action is likely to shed further light on selective interactions of antifungals. Despite the multifacet role of lipids in various functions of this pathogenic yeast, their exact involvement is poorly understood. The situation is little better with regard to ergosterol and its metabolism. Ergosterol is, indeed, important for anti-candidal activity and appears to be involved in the morphogenesis of C. albicans. The fluctuation in phospholipid composition have led to altered properties of plasma membrane namely, membrane fluidity, transport activities and drug sensitivity, which suggest that-a critical level of individual phospholipid is important for proper functioning of the plasma membrane. What the exact role is of individual phospholipid is far from clear. Many unanswered questions relating to the role of PI and sphingomyelin in signal transduction, involvement of phospholipases in the maintenance of phospholipid composition, and role of lipid transfer proteins in assembly and asymmetry of lipids are some aspects which merit further work. 相似文献
15.
Ian T. Forrester Anthony C. Grabski Chittra Mishra Brian D. Kelley W. Nick Strickland Gary F. Leatham Richard R. Burgess 《Applied microbiology and biotechnology》1990,33(3):359-365
Summary Extracellular culture filtrates from ligninolytic cultures of the lignin-degrading basidiomycete Lentinula (syn. Lentinus) edodes (Berk.) Pegler contained one major peroxidase when grown on a commercial oak-wood substrate. The peroxidase was purified by polyethylenimine clarification, anion-exchange chromatography, and hydrophobic-interaction HPLC. The enzyme (MnP1) was a heme-iron protein with an apparent molecular weight of 44 600 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels and an isoelectric point of pH 3.2. The native enzyme had an absorption maximum at 407 nm, which shifted to 420 nm upon H2O2 addition. The pyridine-hemochrome-absorption spectrum indicated that one heme group was present per enzyme as protoporphyrin IX. N-terminal amino acid sequencing showed that MnP1 had higher sequence homology with manganese peroxidases than with lignin peroxidases reported from Phanerochaete chrysosporium. L. edodes MnP1 was capable of oxidizing lignin and lignin-model compounds in the presence of manganese and H2O2.On leave from the Department of Biochemistry, University of Otago, P. O. Box 56, Dunedin, New Zealand.Research carried out while a visiting scientist at the USDA Forest Products Laboratory from the National Chemistry Laboratory, Pune, India 41 1008
Offprint requests to: I. T. Forrester 相似文献
16.
The effect of Ca2+ and Mg2+ on relative fluidity of phosphatidylcholine liposomes was studied by measuring the degree of chlorophyll fluorescence polarization.
An increase in the degree of fluorescence polarization was observed on incubation of liposomes with different concentrations
of Ca2+ or Mg2+. The results have been interpreted on the basis of increase in the size of liposomes which could be brought about by calcium
or magnesium induced fusion of small unilamellar liposomes to form larger vesicles. Fusion of liposomes has also been confirmed
by the experiments on efficiency of energy transfer from chlorophyll b to chlorophyll a, and transmission electron microscopy
of liposomes before and after incubation with Ca2+ and Mg2+. 相似文献
17.
Airborne fungi were monitored at five sample sites with the Burkard portable, the RCS Plus, and the SAS Super 90 air samplers; the Andersen 2-stage impactor was used for comparison. All samplers were calibrated before being used simultaneously to collect 100-liter samples at each site. The Andersen and Burkard samplers retrieved equivalent volumes of airborne fungi; the SAS Super 90 and RCS Plus measurements did not differ from each other but were significantly lower than those obtained with the Andersen or Burkard samplers. Total fungal counts correlated linearly with Cladosporium and Penicillium counts. Alternaria species, although present at all sites, did not correlate with total count or with amounts of any other fungal genera. Sampler and location significantly influenced fungal counts, but no interactions between samplers and locations were found. 相似文献
18.
D. G. Ahearn R. B. Simmons D. L. Price L. Ajello S. A. Crow S. K. Mishra D. L. Pierson 《Journal of industrial microbiology & biotechnology》1995,14(1):26-30
Summary Materials being used or considered for use in space flight were examined for their susceptibility to fungal colonization. The materials included soft goods (clothing) and insulation and fabrication products such as Velcro® attachments and elastic cord binders. Materials were exposed for at least 28 days in a highhumidity chamber colonized with over 50 species of fungi, including those species recommended for determining recalcitrance of materials to fungal biodegradation. At least nine of 25 products demonstrated extensive microscopic colonization by fungi, mostly byAcremonium obclavatum. Challenge procedures that rely on observations with the unaided eye, or 40×magnification of growth by a restricted number of fungal species with a cellulosic substrate as a positive control, are insufficient for determining the resistance of synthetic substrates to fungal colonization. 相似文献
19.
20.
Hydrogen sulphide is a common toxic contaminant in natural gas and oil. In this study, the strictly autotrophic bacterium Thiobacillus ferrooxidans , which oxidizes reduced sulphur compounds, was used to desulphur petroleum oil and gas. The reaction was carried out in a closed vessel containing substrate mixed with a bacterial suspension. The significance of the hydrogen sulphide oxidizing activity of T. ferrooxidans is discussed. 相似文献