全文获取类型
收费全文 | 10678篇 |
免费 | 902篇 |
出版年
2023年 | 37篇 |
2022年 | 89篇 |
2021年 | 158篇 |
2020年 | 115篇 |
2019年 | 156篇 |
2018年 | 200篇 |
2017年 | 170篇 |
2016年 | 266篇 |
2015年 | 433篇 |
2014年 | 446篇 |
2013年 | 637篇 |
2012年 | 729篇 |
2011年 | 682篇 |
2010年 | 473篇 |
2009年 | 430篇 |
2008年 | 587篇 |
2007年 | 634篇 |
2006年 | 553篇 |
2005年 | 562篇 |
2004年 | 562篇 |
2003年 | 555篇 |
2002年 | 632篇 |
2001年 | 133篇 |
2000年 | 93篇 |
1999年 | 140篇 |
1998年 | 156篇 |
1997年 | 144篇 |
1996年 | 128篇 |
1995年 | 110篇 |
1994年 | 100篇 |
1993年 | 101篇 |
1992年 | 106篇 |
1991年 | 81篇 |
1990年 | 70篇 |
1989年 | 66篇 |
1988年 | 51篇 |
1987年 | 51篇 |
1986年 | 40篇 |
1985年 | 53篇 |
1984年 | 67篇 |
1983年 | 60篇 |
1982年 | 95篇 |
1981年 | 84篇 |
1980年 | 64篇 |
1979年 | 55篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 51篇 |
1975年 | 39篇 |
1973年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Sylviane Olschwang Richard Fabre Pierre Laurent-Puig Anne Vassal Bernard Hamelin Yusuke Nakamura Gilles Thomas 《Human genetics》1992,88(6):658-660
Summary The EF5.44 locus is in close proximity to the chromosome 5 region to which the genetic defect responsible for familial adenomatous polyposis has been mapped. We have devised two oligonucleotides that promote the specific polymerase chain reaction (PCR) amplificiation of a 365-bp sequence in this region. Analysis by denaturing gradient gel electrophoresis of the resulting fragment has unravelled individual differences that could be identified as a single base pair change in aMnlI restriction site. This PCR assayable polymorphism increases the informativeness at this locus, and should be useful in the presymptomatic diagnosis of familial adenomatous polyposis. 相似文献
62.
Cadmium (Cd) is a non-essential, highly toxic heavy metal and a ubiquitous environmental contaminant. Evidence exists that Cd can affect parameters which are of great importance in the response towards xenobiotics. However, there is a lack of information about the mechanisms that take place at the cellular and molecular levels upon dual exposure to Cd and other toxins. The purpose of the present work was therefore to examine the biochemical interactions between Cd and a well-known genotoxic hepatocarcinogen, 2-acetylaminofluorene (AAF) in isolated rat hepatocytes. The cells were incubated for 10 hr with a sub-cytotoxic concentration (0.22 M) of 109Cd. This was followed by a 10 hr exposure to 1 M [3H]AAF. Cellular distribution of Cd and 3H was determined. Sephadex G-75 elution profiles of the cytosol showed that Cd was almost entirely associated with the intermediate molecular weight (IMW) fractions containing metallothionein (MT) (>80%), and with high molecular weight proteins. In parallel, the highest proportion of 3H was found in the low molecular weight components. Further analysis of IMW fractions by DEAE A-25 anion-exchange chromatography revealed that, in addition to Cd, there was some 3H which coeluted along with MT-I and MT-II isoforms, but preferentially with MT-I. Moreover, Cd pretreatment caused a 1.6-fold increase in MT level, as measured by the silver-saturation assay. Under these conditions, there was a 17% lower binding of 3H to the DNA. This reduced binding was neither accompanied by diminished AAF uptake nor by inhibition of cytochrome P-450 activity. Taken together, these results suggest that Cd exposure has a protective effect against the genotoxicity of AAF. MT, whose synthesis is induced, could play a role in the Cd-AAF interaction through scavenging of reactive metabolites.Abbreviations AAF
2-acetylaminofluorene
- Cd
cadmium
- DMSO
dimethyl sulfoxide
- HBSS
Hank's balanced salt solution
- LDH
lactate dehydrogenase
- MT
metallothionein
- UDS
unscheduled DNA synthesis 相似文献
63.
Nicole Benhamou Pierre J. Lafontaine Dominique Mazau Marie-Thérèse Esquerré-Tugayé 《Planta》1991,184(4):457-467
An antiserum raised against deglycosylated hydroxyproline-rich glycoproteins (HPGPs) from melon (Cucumis melo L.) was used to study the relationship between Rhizobium infection and induction of HRGPs in bean (Phaseolus vulgaris L.) root nodule cells infected with either the wild-type or a C4-dicarboxylic acid mutant strain of Rhizobium leguminosarum bv. phaseoli. In effective nodules, where fixation of atmospheric dinitrogen is taking place, HRGPs were found to accumulate mainly in the walls of infected cells and in peribacteroid membranes surrounding groups of bacteroids. Internal ramifications of the peribacteroid membrane were also enriched in HRGPs whereas the peribacteroid space as well as the bacteroids themselves were free of these glycoproteins. In mutant-induced root nodules, HRGPs were specifically associated with the electron-dense, laminated structures formed in plastids as a reaction to infection by this mutant. The presence of HRGPs was also detected in the host cytoplasm. The aberrant distribution of HRGPs in infected cells of mutant-induced nodules likely reflects one aspect of the altered host metabolism in relation to peribacteroid-membrane breakdown. The possibility that the antiserum used for HRGP localization may have cross-reacted with ENOD 2 gene products is discussed in relation to amino-acid sequences and sites of accumulation. 相似文献
64.
Marie-Hélène Avelange Jean M. Thiéry Frédéric Sarrey Pierre Gans Fabrice Rébeillé 《Planta》1991,183(2):150-157
In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO2 and O2 gas exchange were performed using 18O2, 13CO2 and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O2 and CO2. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO2), the rate of CO2 influx represented 75±5% of the rate of gross O2 evolution. After a dark-to-light transition, the rate of CO2 efflux was inhibited by 50% whereas the O2-uptake rate was little affected. The effect of a recycling of respiratory CO2 through photosynthesis on the exchange of CO2 gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO2 recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO2 efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO2 efflux and O2 uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO2-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation.Abbreviations Chl
chlorophyll
- Kd
permeability coefficient
The authors thank Drs A. Vermeglio and P. Thibault, Dépt. de Biologie, CEN-Cadarache, St. Paul Lez Durance, France, for helpful discussions. 相似文献
65.
Universal primers for amplification of three non-coding regions of chloroplast DNA 总被引:90,自引:0,他引:90
Six primers for the amplification of three non-coding regions of chloroplast DNA via the polymerase chain reaction (PCR) have been designed. In order to find out whether these primers were universal, we used them in an attempt to amplify DNA from various plant species. The primers worked for most species tested including algae, bryophytes, pteridophytes, gymnosperms and angiosperms. The fact that they amplify chloroplast DNA non-coding regions over a wide taxonomic range means that these primers may be used to study the population biology (in supplying markers) and evolution (inter- and probably intraspecific phylogenies) of plants. 相似文献
66.
67.
Molecular analysis of the avirulence gene avr9 of the fungal tomato pathogen Cladosporium fulvum fully supports the gene-for-gene hypothesis 总被引:12,自引:0,他引:12
Guido F.J.M. Van den Ackerveken Jan A.L. Van Kan Pierre J.G.M. De Wit 《The Plant journal : for cell and molecular biology》1992,2(3):359-366
The interaction between the fungal pathogen Cladosporium fulvum and tomato is supposed to have a gene-for-gene basis. Races of C. fulvum which have 'overcome' the resistance gene Cf9 of tomato, lack the avirulence gene avr9 which encodes a race-specific peptide elicitor. Races avirulent on tomato genotypes carrying the resistance gene Cf9 produce the race-specific peptide elicitor, which induces the hypersensitive response (HR) on those genotypes. The causal relationship between the presence of a functional avr9 gene and avirulence on tomato genotype Cf9 was demonstrated by cloning of the avr9 gene and subsequent transformation of C. fulvum. A race virulent on tomato genotype Cf9 was shown to become avirulent by transformation with the cloned avr9 gene. These results clearly demonstrate that the avr9 gene is responsible for cultivar specificity on tomato genotype Cf9 and fully support the gene-for-gene hypothesis. The avr9 gene is the first fungal avirulence gene to be cloned. 相似文献
68.
Denis Roy Pierre Chevalier Pierre Ward Luc Savoie 《Applied microbiology and biotechnology》1991,34(5):653-655
Summary The ability of Bifidobacterium infantis ATCC 27 920 to ferment glucose, galactose, lactose, melibiose and raffinose was investigated with respect to -galactosidase (-d-galactoside galactohydrolase, E.C. 3.2.1.22). The sugars were tested at three concentrations: 0.5, 1.0 and 2.0%. The growth of B. infantis was slower on glucose compared with the other sugars. The highest specific growth rate was observed on melibiose followed by lactose. High cell numbers could be rapidly obtained on galactose-containing sugars. For each carbohydrate, enzyme activity was maximal at the end of the exponential phase and the highest specific -galactosidase activities were recorded on the two -1,6 galactosaccharides (melibiose and raffinose: 3.0 and 4.5 nkat · 109 colony-forming units, respectively).Contribution no. 186 from the Food Research and Development Centre
Offprint requests to: D. Roy 相似文献
69.
The role of malic acid in the metabolism of Schizosaccharomyces pombe: substrate consumption and cell growth 总被引:2,自引:0,他引:2
Summary The effect of initial concentrations of malate varying from 0 to 28.6 g/l was studied. The acid was found to be inhibitory for growth of Schizosaccharomyces pombe but not for its deacidification activity. Malate was never integrated into biomass but partly transformed into ethanol if the aeration rate was weak (oxygen limitation). In the absence of glucose, resting cells of S. pombe were able to degrade malic acid if their concentration was sufficient, but their viability gradually decreased. However, for 0.15 g/l of growing cells (inoculum) 6 g/l of glucose was necessary to consume 8 g/l of malate. When the medium did not contain sugar no growth was observed despite the partial consumption of malate, showing that the acid was neither a carbon source nor an energy source.
Offprint requests to: P. Strehaiano 相似文献
70.
Paul Salers L'Houcine Ouafik Pierre Giraud Anne Dutour Jean-Yves Maltese Charles Oliver 《Molecular and cellular biochemistry》1991,106(1):15-24
Thyrotropin-R eleasing hormone (TRH)-degrading pyroglutamyl peptidase I(PGP I) and prolyl endopeptidase (PE) activities have been demonstrated in rat insulinoma RINm 5F cell line. These two enzymes catalyze the conversion of TRH to Histydyl-Proline-Diketopiperazine and to acid TRH respectively.After cell fractionation, we found all the PGP I and PE activities in the cytosolic fraction. The membranebound PGP II activity is not detectable in the RINm 5F cells. Further investigations on these two cytosolic enzymes show that pyroglutamyl- and proline-containing peptides are inhibitors of each TRH-degrading enzyme.Gelfiltration chromatography on Sephadex G100 shows that PGP I and PE activity have an apparent molecular mass of about 18 kDa and 57 kDa, respectively. Kinetic analysis with TRH as substrate, gives a Km of 44 µM and 235 µM, and a Vmax of 1.49 and 8.80 pmoUmin/µg protein for PGP I and PE, respectively. Immunoreactive TRH, His-Pro-Diketopiperazine and acid TRH levels in the cell line extracts are 2.2 ± 0.9, 22.5 ± 11.1 and 28.7 ± 14.6pg/106 cells, respectively. When cells have been incubated for 2 to 72 hours with a P. E. inhibitor (Z-Gly-Pro-CHN2) at 5 × 10–7M, both cell PGP I and PE activities are inhibited. No change in the cellular content of immunoreactive TRH, His-Pro-Diketopiperazine and acid TRH have been observed in treated cells.These data suggest that TRH is not degraded by cytosolic, unspecific PGP I and PE enzymes in RINm 5F. The finding that these cells contain 10 and 13 times more His-Pro-Diketopiperazine and acid TRH than TRH may be an indirect evidence for the existence of another precursor than TRH for these two peptides or of the possibility that TRH can be degraded by other peptidases.Abbreviations TRH
Thyrotropin-Releasing Hormone or Thyroliberin
- His-Pro-DKP
Histidyl-ProlineDiketopiperazine
- TRH-OH
acid TRH or deamidated TRH
- LH-RH
Luteinizing Hormone-Releasing Hormone
- Z-Gly-Pro-CHN2
N-benzyloxycarboxyl-Gly-Pro-diazomethylketone
- PGP
Pyroglutamyl Peptidase, PGP I (EC 3.4.19.3) and PGP II (EC 3.4.19.-)
- PE
Prolyl Endopeptidase or post-proline cleaving enzyme (EC 3.4.21.26) 相似文献