全文获取类型
收费全文 | 976篇 |
免费 | 89篇 |
国内免费 | 1篇 |
专业分类
1066篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 22篇 |
2016年 | 29篇 |
2015年 | 39篇 |
2014年 | 33篇 |
2013年 | 54篇 |
2012年 | 72篇 |
2011年 | 62篇 |
2010年 | 36篇 |
2009年 | 29篇 |
2008年 | 44篇 |
2007年 | 42篇 |
2006年 | 35篇 |
2005年 | 40篇 |
2004年 | 54篇 |
2003年 | 32篇 |
2002年 | 51篇 |
2001年 | 24篇 |
2000年 | 27篇 |
1999年 | 30篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 18篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 6篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有1066条查询结果,搜索用时 15 毫秒
11.
12.
C. Benito M. P. Romero N. Henriques-Gil F. Llorente A. M. Figueiras 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(5-6):926-931
The variation in recombination frequency (rf) is important to plant breeders since their major objective is to obtain favorable recombinants of linked genes. One source of variation in rf is sex. Sex differences for recombination frequencies were studied in four of the seven chromosomes of Secale cereale L. cv Ailés using isozyme and storage protein loci and were determined on the basis of reciprocal crosses between heterozygous plants of cv. Ailés and homozygous plants of the inbred line Riodeva. The differences were found to be strongly segmentspecific. In some cases the level of crossing-over in male and female meiosis was about the same (between Pgm1 and Ndh1 loci on chromosome arm 4RS). However, for most of the chromosome segments in 1R, 3RL and 6RL the male rf was significantly higher than the female rf. Different hypotheses about the mechanisms of plant sex differences for recombination are discussed. 相似文献
13.
Sequence similarity of putative transposases links the maize Mutator autonomous element and a group of bacterial insertion sequences. 总被引:10,自引:0,他引:10 下载免费PDF全文
The Mutator transposable element system of maize is the most active transposable element system characterized in higher plants. While Mutator has been used to generate and tag thousands of new maize mutants, the mechanism and regulation of its transposition are poorly understood. The Mutator autonomous element, MuDR, encodes two proteins: MURA and MURB. We have detected an amino acid sequence motif shared by MURA and the putative transposases of a group of bacterial insertion sequences. Based on this similarity we believe that MURA is the transposase of the Mutator system. In addition we have detected two rice cDNAs in genbank with extensive similarity to MURA. This sequence similarity suggests that a Mutator-like element is present in rice. We believe that Mutator, a group of bacterial insertion sequences, and an uncharacterized rice transposon represent members of a family of transposable elements. 相似文献
14.
Characterization of Monoclonal Antibodies Specific for Erwinia carotovora subsp. atroseptica and Comparison of Serological Methods for Its Sensitive Detection on Potato Tubers 总被引:1,自引:0,他引:1 下载免费PDF全文
María Teresa Gorris Benito Alarcon María M. Lopez Mariano Cambra 《Applied microbiology》1994,60(6):2076-2085
Seven monoclonal antibodies (MAbs) to Erwinia carotovora subsp. atroseptica have been produced. One, called 4G4, reacted with high specificity for serogroup I of E. carotovora subsp. atroseptica, the most common serogroup on potato tubers in different serological assays. Eighty-six strains belonging to different E. carotovora subsp. atroseptica serogroups were assayed. Some strains of serogroup XXII also reacted positively. No cross-reactions were observed against other species of plant pathogenic bacteria or 162 saprophytic bacteria from potato tubers. Only one strain of E. chrysanthemi from potato cross-reacted. A comparison of several serological techniques to detect E. carotovora subsp. atroseptica on potato tubers was performed with MAb 4G4 or polyclonal antibodies. The organism was extracted directly from potato peels of artificially inoculated tubers by soaking or selective enrichment under anaerobiosis in a medium with polypectate. MAb 4G4 was able to detect specifically 240 E. carotovora subsp. atroseptica cells per ml by indirect immunofluorescence and immunofluorescence colony staining and after soaking by ELISA-DAS (double-antibody sandwich enzyme-linked immunosorbent assay) after enrichment. The same amount of cells was detected by using immunolectrotransfer with polyclonal antibodies, and E. carotovora subsp. atroseptica and subsp. carotovora were distinguished by the latter technique. ELISA-DAS using MAb 4G4 with an enrichment step also efficiently detected E. carotovora subsp. atroseptica in naturally infected tubers and plants. 相似文献
15.
The influence of chromium concentration on ethylene production in bean plants ( Phaseolus vulgaris L. cv. Contender) was investigated. A Cr ion-induced inhibition of ethylene synthesis from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) was observed within both leaf discs floated on 2 m M CrO2− 4 or Cr3+ and leaf discs from plants cultured in nutrient solutions containing 10, 20 or 40 μ M CrO2− 4 . However, Cr ions supplied either to plants with the nutrient solution or to discs with the incubation medium rather increased the conversion of exogenous ACC to ethylene. Primary leaves of plants exposed to CrO2− 4 -containing nutrient solutions showed a statistically insignificant decrease of ACC-synthase activity. In the trifoliolate leaves of plants exposed to 10 μ M CrO2− 4 , in which a significant decrease of ethylene production from endogenous ACC was observed, a substantial increase of ACC synthase was found. These results indicate that Cr ion-induced inhibition of ethylene production is not due to a breakdown of membrane integrity, which is necessary for ethylene forming enzyme activity, but caused by metabolic alterations leading to decreased ACC availability. Chromium ions may act by inhibiting ACC synthase activity or by diverting a metabolic step prior to the ACC synthase catalyzed reaction. 相似文献
16.
Rhodobacter capsulatus E1F1 showed high cytosolic urease activity when growing on urea, purines, and purine metabolites as nitrogen source. Molecular mass ofR. capsulatus enzyme is similar to that of other bacteria and greatly differs from that of jack bean. Kinetic parameters of partially purifiedR. capsulatus enzyme resemble those described in other bacterial ureases. The activity was inhibited by metal-chelating agents and by mercurials. Urease fromR. capsulatus E1F1 was negligible in nitrogen-starved cells or in cells cultured with nitrate, ammonium, or amino acids. Moreover, ammonium inhibited both the urea uptake and the urease activity expression inR. capsulatus cells. 相似文献
17.
The expression of malic enzyme and glucose-6-phosphate (Glc6P) dehydrogenase was investigated in primary cultures of fetal brown adipocytes after the prolonged presence (6 d or 10 d) of various hormones under non-proliferative conditions. The presence of triiodothyronine for 6 d and 10 d resulted in maturation of the triiodothyronine regulatory mechanism of malic-enzyme expression at the mRNA level. However, triiodothyronine had no effect on Glc6P dehydrogenase expression. Insulin increased malic-enzyme and Glc6P dehydrogenase expression at the mRNA and protein level after 6 d and 10 d of culture. The joint presence of triiodothyronine and insulin produced an additive effect on malic-enzyme expression at the mRNA and protein level after 6 d and 10 d of culture, by two independent mechanisms. Noradrenaline prevented the effect at the protein level after 6 d, but not after 10 d, probably due to loss of the beta-adrenergic response of brown adipocytes after prolonged culture. Triiodothyronine overexpressed the Glc6P dehydrogenase mRNA induced by the presence of insulin at 6 d and 10 d of culture. There was no adrenergic regulation of Glc6P dehydrogenase expression in cultured fetal brown adipocytes, regardless of the time of culture. 相似文献
18.
The epidermis of the tentacles of Phoronis australis consists of six cell types: supporting cells, choanocyte-like sensory cells, both types monociliated, secretory A-cells with a mucous secretion, and three kinds of B-cells with mucoprotein secretions. On cross-sections of the tentacle, one can distinguish four faces: the frontal one, heavily ciliated and located between the two frontolateral rows of sensory cells, the lateral and the abfrontal ones. The orientation of the basal structures of the cilia is related to the direction of their beat. The basiepidermal nervous system is grouped mainly at the frontal and abfrontal faces. The basement membrane is thickest on the frontal face and consists of circular collagen fibrils near the epidermis and longitudinal ones near the peritoneum. All peritoneal cells surrounding the mesocoel are provided with smooth longitudinal myofibrils, and isolated axons are situated between these cells and the basement membrane. The wall of the single blood capillary in each tentacle consists of epitheliomuscular cells with circular myofilaments, lying on a thin internal basal lamina; there is no endothelium. 相似文献
19.
R.M. de Figueroa I.L. Benito de Cárdenas F. Sesma F. Alvarez A. P. de Ruiz Holgado G. Oliver 《Journal of applied microbiology》1996,81(4):348-354
Lactobacillus rhamnosus ATCC 7469 exhibited diauxie when grown in a medium containing both glucose and citrate as energy source. Glucose was used as the primary energy source during the glucose-citrate diauxie. Uptake of citrate was carried out by an inducible citrate transport system. The induction of citrate uptake system was repressed in the presence of glucose. This repression was reversible and mediated by cAMP. 相似文献
20.
R. Pérez-Vicente M. I. Burón J. A. González-Reyes J. Cárdenas M. Pineda 《Protoplasma》1995,186(1-2):93-98
Summary Utilization of xanthine as the sole nitrogen source for growth byChlamydomonas reinhardtii cells involved the formation of a transient, intracellular pool of xanthine. Up to 20% of the total xanthine supplied to the medium was not assimilated after uptake but stored in the cells at concentrations that exceeded xanthine solubility in water. At the subcellular level, a massive accumulation of starch grains in the chloroplast and the appearance of many vacuoles in the cytoplasm distinguished xanthine-grown from ammonium-grown cells. Starch accumulation, but not development of vacuoles, was also observed in N-starved cells. Uptake experiments with radio-labelled xanthine showed that this accumulates only in the cytoplasm, most probably inside vacuoles. The electron-dense material observed in vacuoles of xanthine-grown cells suggests that the intracellular xanthine is in part solid xanthine. 相似文献