全文获取类型
收费全文 | 1805篇 |
免费 | 163篇 |
出版年
2022年 | 12篇 |
2021年 | 30篇 |
2020年 | 10篇 |
2019年 | 27篇 |
2018年 | 30篇 |
2017年 | 12篇 |
2016年 | 37篇 |
2015年 | 55篇 |
2014年 | 60篇 |
2013年 | 96篇 |
2012年 | 126篇 |
2011年 | 111篇 |
2010年 | 79篇 |
2009年 | 82篇 |
2008年 | 104篇 |
2007年 | 93篇 |
2006年 | 70篇 |
2005年 | 102篇 |
2004年 | 72篇 |
2003年 | 104篇 |
2002年 | 102篇 |
2001年 | 38篇 |
2000年 | 59篇 |
1999年 | 54篇 |
1998年 | 16篇 |
1997年 | 26篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1972年 | 7篇 |
1971年 | 16篇 |
1970年 | 9篇 |
1969年 | 9篇 |
1968年 | 12篇 |
1967年 | 10篇 |
排序方式: 共有1968条查询结果,搜索用时 406 毫秒
21.
Petit DW 《California medicine》1967,107(2):184-185
22.
23.
Two malformed newborns with the typical Wolf-Hirschhorn syndrome (WHS) resulting from familial balanced translocations t(4;11)(p153;p154) and t(4;18)(p152;q23) respectively, are presented. A third child with the Cri du Chat syndrome and der(5), t(2;5)(q333;p141) is reported. These three cases give further support to the epistatic hypothesis at the chromosomal level of the Bp monosomies over other partial autosomal trisomic syndromes. 相似文献
24.
Roberto Bacilieri Alexis Ducousso Rmy J. Petit Antoine Kremer 《Evolution; international journal of organic evolution》1996,50(2):900-908
The sessile (Quercus petraea [Matt.] Liebl.) and pedunculate (Quercus robur L.) oaks are two closely related species having a wide sympatric distribution over Europe. Under natural conditions, they frequently form mixed forests, where hybridization is suspected to occur. In this paper, two different approaches have been applied to the study of the mating system and the interspecific gene flow in a mixed stand formed by the two species. The mating systems of both species have been studied separately by means of the mixed-mating model. The relative contribution of the parental species to the progenies have been estimated with two different methods. The first uses the admixture model. The second is an extension of the mixed-mating model and subdivides the outcrossing rate into intra- and interspecific components. The two species were almost completely outcrossing. This high level of outcrossing and interspecific gene flow could play an important role in the maintenance of the genetic diversity in these long-lived forest tree species. The contribution of the sessile oak to the pedunculate oak progenies varied from 17% to 48%. In contrast, ovules of sessile oak trees appear to be preferentially fertilized by other extreme sessile genotypes. We suggest that interspecific and directional gene flow was responsible for such patterns. Pedunculate oak is considered as a pioneer species and is progressively replaced by sessile oak. Our present findings add a further genetic component to this succession scheme, suggesting that unidirectional gene flow reinforces succession between the two species. 相似文献
25.
Living yeast cells can be selectively stained with the lipophilic cationic cyanine dye DiOC6(3) in a mitochondrial membrane potential-dependent manner. Our study extends the use of flow cytometric analysis and sorting to DiOC6(3)-stained yeast cells. Experimental conditions were developed that prevented the toxic side effect of the probe and gave a quantitative correlation between fluorescence and mitochondrial membrane potential, without any staining of other membranes. The localization of the fluorochrome was checked by confocal microscopy and image cytometry. The mitochondrial membrane alterations were also tested through cardiolipin staining with nonyl acridine orange. Differences in light scattering and in fluorescence were detected in mutants (rho-, rho degrees, mit-, or pet-) and wild-type (rho+mit+) populations of yeast. The dye uptake of respiratory-deficient yeast strains was significantly reduced as compared to that of the wild-type. Application of an uncoupler (mCICCP), which collapsed the mitochondrial membrane potential (alphapsi(m)), led to a drastic reduction of the dye uptake. It was observed that a decrease in deltapsi(m), was usually correlated with a decrease in cardiolipin stainability by nonyl acridine orange (NAO). Quantitative flow cytometry is a fast and reproducible technique for rapid screening of yeast strains that might be suspected of respiratory dysfunction and/or mitochondrial structural changes. We give evidence that it is an adequate method to characterize and isolate respiratory mutants through sorting procedure, with selective enrichment of the population studied in respiring or non-respiring yeast cells. Confocal microscopy and image cytometry corroborate the flow cytometry results. 相似文献
26.
Veronique Billat Jean C. Renoux Jacques Pinoteau Bernard Petit Jean P. Koralsztein 《European journal of applied physiology and occupational physiology》1994,69(3):271-273
The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits
max
max in 38 elite male long - distance runners
max = 71.4 ± 5.5 ml.kg–1.min–1 and
max = 21.8 ± 1.2 km.h–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in
max. Tlim value was negatively correlated with
max (r = -0.362, p< 0.05) and
max (r = –0.347, p< 0.05) but positively with LT (%v
max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at
max in a homogeneous group of elite male long-distance runners was inversely related to
max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) . 相似文献
27.
Gerard Berger Guy Girault Jean-Michel Galmiche Stephane Pezennec 《Journal of bioenergetics and biomembranes》1994,26(3):335-346
The influences of total magnesium ion concentration at different total ATP concentrations, and of total ATP concentration, for different total magnesium ion concentrations, on the enzymatic rate of the isolated chloroplast F1 ATPase, have been followed by a chromatographic method consisting in the separation and determination of ADP. From the various series of curves, it is concluded that the experimental results (position of the maxima,K
m
values) are better fitted by a mechanism involving the activation of the enzyme by magnesium ion and hydrolysis of free ATP, rather than by the classical mechanism, for which the enzyme hydrolyzes the MgATP complex and is inhibited by Mg2+. Although the equations giving the reaction rate are similar in the two cases, the calculated values ofK
m
are widely different. The value obtained from the classical mechanism does not agree withK
D
, the dissociation constant of the enzyme-substrate complex, measured by the Hummel and Dreyer method. Moreover, when the total ATP concentration tends toward the total magnesium ion concentration, the nucleotide binding to the enzyme tends toward zero, although it should be maximum if MgATP were the true substrate. Finally, the inhibitory effect of Na+ is more easily explained as a competition between this ion and the activating Mg2+, than by the classical mechanism. 相似文献
28.
Zoran G. Cerovic Maurice Bergher Yves Goulas Stephane Tosti Ismael Moya 《Photosynthesis research》1993,36(3):193-204
A newly developed nitrogen laser fluorimeter insensitive to actinic illumination was used to follow simultaneously the light induced changes in red and blue fluorescence of intact isolated spinach chloroplasts and leaf pieces. The recorded variable blue fluorescence was linked to a water soluble component of intact isolated chloroplasts, depended on Photosystem I, and was related to changes in carbon metabolism. From the comparison of changes in intact and broken chloroplasts and from fluorescence spectra under different conditions, it was concluded that the variation in NADPH was the major cause for the changes in blue fluorescence. This study opens a path towards continuous and non-destructive monitoring of NADPH redox state in chloroplasts and leaves.Abbreviations Chl
chlorophyll
- DHAP
dihydroxyacetone phosphate
- DLGA
DL-glyceraldehyde
- FNR
ferredoxin-NADP reductase
- FWHM
full width at half maximum
- LED
light emitting diodes
- OAA
oxaloacetate
- qN
non-photochemical quenching
- PGA
3-phosphoglycerate
- Pi
inorganic orthophosphate
- qP
photochemical quenching
- PPFD
photosynthetic photon flux density
- QA
primary quinone acceptor of Photosystem II
Preliminary results of this work were presented at the First Conference on the Physiology and Biochemistry of high Mountain Plants, 2–3 July 1992, Villar d'Arene, France. 相似文献
29.
R. J. Petit A. Kremer D. B. Wagner 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,87(1-2):122-128
Chloroplast DNA polymorphisms have been detected by the conventional Southern-blotting hybridization method in four species of European oaks (Quercus petraea, Q. robur, Q. pubescens and Q. pyrenaica). Three polymorphisms, shared by at least three of these species, can be scored directly in ethidium bromidestained gels and were used in a broad survey of the level of differentiation of the oak species and of their pattern of genetic structure in western Europe. The highly significant geographic variation and the high genetic differentiation (Gst=0.895, SGst=0.025) indicate a low level of cytoplasmic gene flow. We conclude that cytoplasmic genomes are well suited for the reconstruction of past migrational routes of such a complex of species. 相似文献
30.
MTT reduction is usually analysed by colorimetric assay to study mitochondrial dehydrogenase activity as a test of cytotoxicity. This enzymatic reaction produces dark-blue granules of formazan, which increase cell refringency. In this work, we define the conditions for MTT use in quantitative flow cytometric analysis. MTT reduction provides a non-fluorescent dye usable by this technique to study an intracellular NADH-dependent dehydrogenase activity in vital cells. We observe that formazan production increases asymptotically with cell concentration and that this temperature-dependent Michaelis enzymatic reduction is produced essentially by mitochondrial dehydrogenases. In isolated mitochondria from rat hepatocytes and in whole L1210 murine leukemia cells, the Michaelis constants (KM) observed in the presence of respiratory substrates were, respectively, 10 microM and 500 microM. The inhibition of mitochondrial protein synthesis by chloramphenicol, which induces a rise of MTT reduction due to the correlative stimulation of glycolysis (Pasteur effect), is a limit of the MTT assay as a cytotoxicity test. 相似文献