全文获取类型
收费全文 | 6308篇 |
免费 | 512篇 |
国内免费 | 2篇 |
出版年
2022年 | 40篇 |
2021年 | 71篇 |
2020年 | 35篇 |
2019年 | 69篇 |
2018年 | 62篇 |
2017年 | 85篇 |
2016年 | 145篇 |
2015年 | 198篇 |
2014年 | 243篇 |
2013年 | 370篇 |
2012年 | 394篇 |
2011年 | 403篇 |
2010年 | 283篇 |
2009年 | 300篇 |
2008年 | 396篇 |
2007年 | 411篇 |
2006年 | 398篇 |
2005年 | 389篇 |
2004年 | 390篇 |
2003年 | 414篇 |
2002年 | 385篇 |
2001年 | 72篇 |
2000年 | 53篇 |
1999年 | 86篇 |
1998年 | 130篇 |
1997年 | 86篇 |
1996年 | 72篇 |
1995年 | 86篇 |
1994年 | 64篇 |
1993年 | 58篇 |
1992年 | 68篇 |
1991年 | 51篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 37篇 |
1983年 | 16篇 |
1982年 | 32篇 |
1981年 | 29篇 |
1980年 | 33篇 |
1979年 | 32篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1972年 | 15篇 |
排序方式: 共有6822条查询结果,搜索用时 15 毫秒
991.
Carmen Lapadatescu Gilles Feron Catherine Vergoignan Aleth Djian Alain Durand Pascal Bonnarme 《Applied microbiology and biotechnology》1997,47(6):708-714
Three white-rot basidiomycetes, Bjerkandera adusta, Ischnoderma benzoinum and Dichomitus squalens, were cultivated on a liquid medium supplemented with l-phenylalanine, a precursor for benzaldehyde (bitter almond aroma) and benzyl alcohol. Remarkable amounts of benzaldehyde
(587 mg l−1) were found in cultures of B. adusta. Immobilization of this fungus on polyurethane foam cubes allowed an 8.3-fold increase of the production of benzaldehyde
and a 15-fold increase of the productivity as compared with non-immobilized cells. Aryl-alcohol oxidase activity was only
detected in B. adusta. This activity was also significantly enhanced in immobilized cells, suggesting that it plays an important role in benzaldehyde
biosynthesis. Conversely, consistent amounts of benzyl alcohol (340 mg l−1 for B. adusta and I. benzoinum and 100 mg l−1 for D. squalens) were produced by the three fungi when immobilized. Laccase activity was found only in the strains I. benzoinum and D. squalens. This activity was markedly enhanced in free cells cultures. Immobilization of the fungi did not promote benzyl alcohol production
by comparison with free cell cultures (500 mg l−1).
Received: 10 December 1996 / Received revision: 17 February 1997 / Accepted: 22 February 1997 相似文献
992.
François-Yves Dupradeau Guillaume Le Flem Jean-Michel Wieruszeski Manuel Dauchez Alain Alix Véronique Larreta-Garde Jean-Pierre Monti 《International journal of peptide research and therapeutics》1997,4(4-6):489-495
Summary
1H-NMR studies of the bovine insulin S-sulfonated B-chain are reported in H2O/D2O (9/1) and in glycerol-d
5 (5 M) using two-dimensional NMR spectroscopy. The first results show that the oxidized insulin B-chain secondary structure
differs from that of native insulin by a loss of the α-helix between the two disulfide bridges and that the glycerol favours
the structuring of the peptide. 相似文献
993.
Mathieu Marc Lehmann Christian Razaname Alain Tuchscherer Gabriele 《International journal of peptide research and therapeutics》1997,4(2):95-100
Summary The assembly of helical and β-sheet peptide blocks containing reactive chain ends results in highly branched chain architectures
(‘locked-in folds’) mimicking native tertiary structures. This molecular kit strategy allows to bypass the protein folding
problem in protein de novo design and gives access to protein mimetics of high thermodynamic stability. The validity of this
concept is exemplified for the design and synthesis of locked-in folds mimicking the zinc finger and MHC folding motifs. 相似文献
994.
Frdric Tournier Yves Bobinnec Alain Debec Pedro Santamaria Michel Bornens 《Biology of the cell / under the auspices of the European Cell Biology Organization》1999,91(2):99-108
Centrosomes are powerful and exclusive parthenogenetic agents in the Xenopus egg. We have previously shown that heterologous centrosomes from various vertebrate species were able to promote egg cleavage in Xenopus and that human centrosome activity was associated with an insoluble proteinacious structure that is not significantly simpler than the native centrosome. In this work, we have investigated the parthenogenetic capacity of more evolutionary distant centrosomes. We show that centrosomes devoid of centrioles, such as SPBs isolated from Saccharomyces cerevisiae, do not form asters of microtubules in cytoplasmic extracts from Xenopus eggs, and are inactive in the parthenogenetic test. We further show that Drosophila centrosomes which possess a typical centriole architecture, and are quite active to nucleate microtubules in Xenopus cytoplasmic extracts, are unable to trigger egg cleavage. This was observed both with centrosomes isolated from Drosophila syncytial embryos and nucleus-centrosome complexes from the Drosophila Kc23 cell line. We demonstrate that this inability could not be restored after pre-incubation of Drosophila centrosomes in the egg cytoplasm before injection. We conclude that the parthenogenetic activity of a centrosome is not directly linked to its capacity to nucleate microtubules from the egg tubulin, and that the evolutionary conserved nine-fold symmetrical structure of the centriole cannot be considered as sufficient for triggering procentriole assembly. 相似文献
995.
Detection of Anatoxin-a(s) in Environmental Samples of Cyanobacteria by Using a Biosensor with Engineered Acetylcholinesterases
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Eric Devic Dunhai Li Alain Dauta Peter Henriksen Geoffrey A. Codd Jean-Louis Marty Didier Fournier 《Applied microbiology》2002,68(8):4102-4106
Bioassays are little used to detect individual toxins in the environment because, compared to analytical methods, these assays are still limited by several problems, such as the sensitivity and specificity of detection. We tentatively solved these two drawbacks for detection of anatoxin-a(s) by engineering an acetylcholinesterase to increase its sensitivity and by using a combination of mutants to obtain increased analyte specificity. Anatoxin-a(s), a neurotoxin produced by some freshwater cyanobacteria, was detected by measuring the inhibition of acetylcholinesterase activity. By using mutated enzyme, the sensitivity of detection was brought to below the nanomole-per-liter level. However, anatoxin-a(s) is an organophosphorous compound, as are several synthetic molecules which are widely used as insecticides. The mode of action of these compounds is via inhibition of acetylcholinesterase, which makes the biotest nonspecific. The use of a four-mutant set of acetylcholinesterase variants, two mutants that are sensitive to anatoxin-a(s) and two mutants that are sensitive to the insecticides, allows specific detection of the cyanobacterial neurotoxin. 相似文献
996.
Alain Hamon Nicolas Gilles Pierre Sautière Arlette Martinage Charles Kopeyan Chris Ulens Jan Tytgat Jean-Marc Lancelin Dalia Gordon 《European journal of biochemistry》2002,269(16):3920-3933
Two novel toxins, Lqh6 and Lqh7, isolated from the venom of the scorpion Leiurus quinquestriatus hebraeus, have in their sequence a molecular signature (8Q/KPE10) associated with a recently defined group of alpha-toxins that target Na channels, namely the alpha-like toxins [reviewed in Gordon, D., Savarin, P., Gurevitz, M. & Zinn-Justin, S. (1998) J. Toxicol. Toxin Rev. 17, 131-159]. Lqh6 and Lqh7 are highly toxic to insects and mice, and inhibit the binding of alpha-toxins to cockroach neuronal membranes. Although they kill rodents by intracerebroventricular injection, they do not inhibit the binding of antimammal alpha-toxins (e.g. Lqh2) to rat brain synaptosomes, not even at high concentrations. Furthermore, in voltage-clamp experiments, rat brain Na channels IIA (rNav1.2A) expressed in Xenopus oocytes are not affected by Lqh6 nor by Lqh7 below 3 micro m. In contrast, muscular Na channels (rNav1.4 and hNav1.5) expressed in the same cells respond to nanomolar concentrations of Lqh6 and Lqh7 by slowing of Na current inactivation and a leftward shift of the peak conductance-voltage curve. The structural and pharmacological properties of the new toxins are compared to those of other scorpion alpha-toxins in order to re-examine the hallmarks previously set for the alpha-like toxin group. 相似文献
997.
Claire Berkaloff Bernard Rousseau Alain Cout Eliette Casadevall Pierre Metzger Christian Chirac 《Journal of phycology》1984,20(3):377-389
Different samples of Botryococcus braunii Kütz., freshly collected from nature or laboratory-grown from culture collection strains, were studied by electron microscopy and their hydrocarbon content analyzed. Although the general internal structure of the cells was rather constant, the organization of the outer walls forming the hydrocarbon-rich matrix of the colonies differed greatly from one sample to another. In the majority of cultivated strains, the colonies were rather small, the different successive external walls remained distinct and all strains contained dienic or trienic hydrocarbons. In contrast, most of the collected samples possessed large colonies with a rather compact matrix formed by the hydrocarbon-rich part of the successive closely appressed external wall layers. These samples contained polyunsaturated hydrocarbons, i.e. botryococcenes. Well defined cell caps which sheared off the cells were observed only in those strains with a compact matrix. The Austin strain and some collected samples, however, were intermediate with rather small colonies, dense matrix, definite cell caps and dienic hydrocarbons. Thus, the hydrocarbon composition did not correlate directly with the variations in wall structure; however, the occurence of dienic and botryococcene-like hydrocarbons together in one strain was never observed, although analyzed at various stages of growth. Thus, the existence of distinct strains of Botryococcus braunii, some synthesizing dienes, others botryococcenes, appears highly probable. 相似文献
998.
A complete, unambiguous assignment of all the 13C signals of cellobiose and maltose has been achieved using methods such as selective proton decoupling, 13C selective spin labeling, and isotopic chemical shift induced by deuterium. The chemical-shift variation of the 13C signals with the degree of polymerization in each α or β (1 → 4) series is discussed. The chemical-shift dependence on temperature and solvent in these two series is shown and interpreted in terms of modifications of the solvation and of the conformation. 相似文献
999.
1000.
Population cycles of many forest-defoliating insects often show synchronous fluctuations at both intra-specific (spatial synchrony) and inter-specific levels. However, population dynamics of different host-associated biotypes of the same species, such as those of the larch budmoth (LBM), Zeiraphera diniana (Lepidoptera: Tortricidae), have never been compared. This species causes extensive defoliation of larch forests every 8 to 9 years in the Alps, but it consists of two genetically-differentiated host races, the first one developing on European larch, Larix decidua , and the other one developing on Swiss stone pine, Pinus cembra . The dynamics of Zeiraphera populations have been extensively studied on larch, whereas little is known about larval density and possible population fluctuations on sympatric pines. A larval census on Swiss stone pine was conducted in the Swiss Alps intermittently between 1958 to 2004 and in the French Alps from 1992 to 2004. Population density of Zeiraphera on pine varied up to 5000-fold and showed periodic oscillations, with five peaks in Switzerland and one in France. Because the feeding activity of the pine race is restricted to the elongating shoot of the current year, no conspicuous defoliation of pine trees was noted during years of high larval densities. Zeiraphera populations on pine oscillated in significant synchrony with larch-associated populations, and peak densities were observed either the same year or shifted by±one year. Our results did not allow any explanation for cyclic fluctuations of LBM on pine, but the synchrony with the larch race's cycle suggests that studies on genetics as well as on parasitism should be intensified. 相似文献