全文获取类型
收费全文 | 6510篇 |
免费 | 442篇 |
国内免费 | 2篇 |
出版年
2023年 | 66篇 |
2022年 | 46篇 |
2021年 | 104篇 |
2020年 | 85篇 |
2019年 | 96篇 |
2018年 | 308篇 |
2017年 | 260篇 |
2016年 | 304篇 |
2015年 | 229篇 |
2014年 | 305篇 |
2013年 | 497篇 |
2012年 | 539篇 |
2011年 | 584篇 |
2010年 | 361篇 |
2009年 | 250篇 |
2008年 | 213篇 |
2007年 | 192篇 |
2006年 | 198篇 |
2005年 | 94篇 |
2004年 | 90篇 |
2003年 | 93篇 |
2002年 | 66篇 |
2001年 | 77篇 |
2000年 | 85篇 |
1999年 | 94篇 |
1998年 | 73篇 |
1997年 | 71篇 |
1996年 | 68篇 |
1995年 | 86篇 |
1994年 | 63篇 |
1993年 | 49篇 |
1992年 | 58篇 |
1991年 | 54篇 |
1990年 | 35篇 |
1989年 | 53篇 |
1988年 | 37篇 |
1987年 | 51篇 |
1986年 | 38篇 |
1985年 | 55篇 |
1984年 | 45篇 |
1983年 | 52篇 |
1982年 | 49篇 |
1981年 | 57篇 |
1980年 | 47篇 |
1979年 | 54篇 |
1978年 | 43篇 |
1977年 | 52篇 |
1974年 | 36篇 |
1973年 | 39篇 |
1969年 | 40篇 |
排序方式: 共有6954条查询结果,搜索用时 31 毫秒
991.
Z. Řeháček J. Kozová A. Řičicová J. Kašlík P. Sajdl S. Švarc S. C. Basappa 《Folia microbiologica》1971,16(1):35-40
Shake flask cultures ofClaviceps paspali (Stev. et Hall) andClaviceps purpurea (Fr.) Tul. on simple synthetic medium have been studied. Both strains grown in the absence of added tryptophan accumulate
extra endogenous tryptophan. A certain concentration of cell-pool tryptophan is needed to promote alkaloid synthesis. Alkaloid
production commences while tryptophan synthetase activity is increasing. In the alkloid-producing phase cell-pool tryptophan
shows a single minimum while the change in level of cell-protein tryptophan is negligible. Alkaloid formation is suggested
to reflect a regulatory device to keep endogenous tryptophan balanced. By adding amitrole the alkaloid spectrum is changed.
The tryptophan-histidine cross-pathway probably serves a useful function inthe biosynthesis of ergot alkaloids. 相似文献
992.
993.
Selection of a large number of different strains of hyphal fungi of the genusAspergillus, capable of production of extracellular mannosidase and mannanase type enzymes, was carried out. Before cultivating the strains
on liquid synthetic medium containing 0.5%Saccharomyces cerevisiae mannan as the carbon source, they were adapted by multiple passage on solid synthetic media containingd-mannose,d-mannose and α-mannan and lastly only α-mannan. The extracellular enzymatic preparations of the mould fungi were tested for
their ability to hydrolyse three different substrates—Saccharomyces cerevisiae, Torulopsis ingeniosa andTorulopsis colliculosa mannan. The production of α-mannosidase was found to be specifically dependent on the character of the substrate used for
cultivation of the fungus. 相似文献
994.
Purified phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) fromStreptomyces aureofaciens shows kinetics resembling those of known allosteric enzymes. It is inhibited by ATP, GTP, CTP succinate, aspartate and citrate.
ATP, GTP and CTP are the most powerful inhibitors. On the basis of kinetic data three categories of inhibitors are distinguished.
Succinic acid is a true noncompetitive inhibitor, other inhibitors affect the steric configuration of the enzyme: aspartic
and citric acids are negative effectors, while ATP acts as a substrate analogue. A possible physical basis for the observed
kinetics and the metabolic significance of the system are discussed.
Previous paper of the series: J. Voříšek, A. J. Powell and Z. Vaněk, Fol. microbiol. 14: 398, 1969. 相似文献
995.
Summary Distribution of cholinesterase-containing nerve fibres was studied in 15 human dental pulps by the thiocholine method. Falk's fluorescent method was used to demonstrate catecholamines (8 dental pulps).Cholinesterases were localized partly in the subodontoblastic plexus sending out fine branches towards odontoblasts, and partly in the nerve fibres attached to the blood vessel walls. These fibres in contrast to those of the subodontoblastic plexus were finer and showed fine varicosities.Monoaminergic terminals were localized mainly along blood vessel walls, however, some fibres having no relation to the blood vessels were also found.Cholinesterase-containing nerve fibres in the periphery of the pulp are considered to be sensitive nerve fibres originating from n.V. Distribution of cholinesterase-containing nerve fibres and monoaminergic terminals along the blood vessel walls indicates that the blood vessels in the human dental pulp might be under both parasympathetic and sympathetic control. 相似文献
996.
The paper summarizes the results of the palaeoecological study of one profile of the Bláto mire, situated in southeastern Bohemia (Czechoslovakia). The authors evaluate their finds and endeavour to present a phytocenological picture of the composition and succession of peatforming communities from the Alleröd Period onwards. 相似文献
997.
Effect of some pre-treatments on UV-sensitivity and on the course of macromolecular synthesis inEscherichia coli 15 T−, U−, his− 总被引:1,自引:0,他引:1
The UV-sensitivity ofEscherichia coli 15 T−, U−, his− cells after a 45 minutes glucose, thymine uracil, or histidine pre-irradiation starvation, as well as the course of DNA,
RNA, and protein synthesis during starvation and during a 60 minute post-treatment in a complete medium were investigated.
An increased radioresistance was observed when starvation for some compounds resulted in a consequent inhibition of protein
synthesis, as it was observed in the case of glucose, histidine, or uracil starvation. During thymine starvation, which led
to a decreased resistance, no inhibition of protein synthesis was recorded. The postirradiation time-course of DNA synthesis
did not show any correlation with the increased rate of resistance. The DNA synthesis after U− pre-treatment was greatly delayed, however, after glucose pre-treatment no retardation was observed although both factors
increased the rate of surviving cells approximately to the same extent. We assume that the factors which increase the radio-resistance
could act by a similar mechanism which would take part in the inhibition of protein synthesis. This mechanism could consist
in a decrease of the m-RNA turnover. 相似文献
998.
A. Kocková-Kratochvílová A. Vojtková-Lepšíková J. Šandula M. Pokorná 《Folia microbiologica》1968,13(4):300-309
The speciesSaccharomyces heterogenicus Osterwalder,Saccharomyces steineri Lodder et Kreger-van Rij,Saccharomyces pastorianus Hansen,Saccharomyces bayanus Saccardo andSaccharomyces willianus Saccardo were compared. It was found that the biochemical characters used for the definition of these species were variable and the strains of the given species were therefore evaluated together. With reference to the present accepted criteria of species specificity, grouping on the basis of coefficients of similarity was not conclusive. One of the characters (the fermentation and assimilation of galactose) was therefore dispensed with, while a new characteristic (determination) of amylolytic activity was added. It was found that the speciesSaccharomyces pastorianus, Saccharomyces bayanus andSaccharomyces willianus were so similar that they could be grouped in one species.Saccharomyces heterogenicus retained its species specific characteristics, whileSaccharomyces steineri formed a transition between this species and the other three. The coefficients of similarity, S, calculated by the methods of Jaccard and of Sokal and Michener, were compared and some of the more problematical questions of the numerical method are discussed. 相似文献
999.
Properties of the sugar carrier in Baker's yeast 总被引:3,自引:0,他引:3
Incubation ofSaccharomyces cerevisiae cells withd-galactose induced the formation of galactose-utilizing enzymes, among them a monosaccharide carrier, apparently synthesized as a proteinde novo. The synthesis of the carrier preceded that of galactokinase by as much as 2 h. The inducible carrier shows a preference for monosaccharides with an axial hydroxyl group at carbon 4 of theC1 chair conformation or at carbon 2 of the1C chair conformation. Through its mediation, some sugars normally poorly transported (d-galactose,d-fucose,l-xylose,l-arabinose) can enter into the entire cell water, occupying then one more kinetic (and morphological ?) compartment than before induction. Some other monosaccharides, readily transported even by a constitutive carrier system (e.g.l-sorbose,d-xylose,d-arabinose) share the newly synthesized carrier. 相似文献
1000.
E. Seemanová I. Lesný J. Hyánek K. Brachfeld M. Rössler M. Prošková 《Human genetics》1973,20(2):113-117
Summary Two brothers (7 years of age and 8 months respectively) are reported. They both suffered from a combination of severe microcephaly,
spastic tetraplegia, clonic epileptic fits, absent abdominal cutaneous reflexes and severe mental retardation. This syndrome
shows an X-chromosomal mode of inheritance. Dermatoglyphic patterns were characteristic. There was no change in aminoacids
in CSF and the birth weight was high (4000g, in contrast to the cases described by Warkany et al.).
Zusammenfassung Es wird über zwei Brüder (7 Jahre bzw. 8 Monate alt) berichtet. Beide litten an einer Kombination von schwerer Mikrocephalie, spastischer Tetraplegie, klonischen epileptischen Anf?llen, fehlenden abdominalen Hautreflexen und schwerem Schwachsinn. Es fand sich ein X-chromosomaler Erbgang. Die Dermatoglyphen zeigten einen charakteristischen Befund. Die Aminos?uren waren im Liquor cerebrospinalis nicht ver?ndert, und das Geburtsgewicht war hoch im Gegensatz zu den F?llen von Warkany et al.相似文献