全文获取类型
收费全文 | 17307篇 |
免费 | 939篇 |
国内免费 | 972篇 |
出版年
2024年 | 19篇 |
2023年 | 131篇 |
2022年 | 189篇 |
2021年 | 327篇 |
2020年 | 321篇 |
2019年 | 393篇 |
2018年 | 344篇 |
2017年 | 356篇 |
2016年 | 354篇 |
2015年 | 580篇 |
2014年 | 715篇 |
2013年 | 972篇 |
2012年 | 714篇 |
2011年 | 743篇 |
2010年 | 552篇 |
2009年 | 870篇 |
2008年 | 929篇 |
2007年 | 976篇 |
2006年 | 1003篇 |
2005年 | 835篇 |
2004年 | 751篇 |
2003年 | 700篇 |
2002年 | 585篇 |
2001年 | 569篇 |
2000年 | 535篇 |
1999年 | 481篇 |
1998年 | 510篇 |
1997年 | 401篇 |
1996年 | 337篇 |
1995年 | 313篇 |
1994年 | 307篇 |
1993年 | 336篇 |
1992年 | 257篇 |
1991年 | 218篇 |
1990年 | 234篇 |
1989年 | 180篇 |
1988年 | 143篇 |
1987年 | 130篇 |
1986年 | 115篇 |
1985年 | 164篇 |
1984年 | 154篇 |
1983年 | 63篇 |
1982年 | 91篇 |
1981年 | 64篇 |
1980年 | 61篇 |
1979年 | 37篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 535 毫秒
991.
Increasing the zinc content of cereal grains will be important for improving human nutrition. Improved plant zinc efficiency will lead to increased yields when available zinc is limiting plant growth. The aim of our work was to test how the over-expression of zinc transporters in cereals affects plant growth, seed mineral content, and zinc transport rates. Known zinc transporters from Arabidopsis were over-expressed in Hordeum vulgare cv. Golden Promise by means of a ubiquitin promoter. Multiple transgenic lines were obtained, and the locus number and expression levels were verified. Transgenic lines were tested in long-term growth and short-term uptake experiments. Seeds from transgenic lines grown in soil had higher zinc and iron contents than controls. Short-term uptake rates were higher in the transgenic lines after zinc deprivation. Resupply of zinc after a period of deprivation resulted in the rapid decrease in zinc uptake even in transgenic lines in which a zinc transporter gene was constitutively expressed. Similar to processes in yeast and Arabidopsis, we hypothesize that this rapid decrease in zinc transport activity may be caused by the degradation of transporters in response to zinc-sufficient conditions. In the long-term growth experiments, there were no significant differences between transgenic and control lines in leaf zinc content or shoot biomass under zinc-sufficient or -deficient conditions. However, root-to-shoot ratios were higher in the transgenic plants grown under low-zinc conditions; this could impact zinc acquisition under field conditions. Increased seed zinc and iron content by over-expression of a zinc transporter provides a new strategy for increasing the micronutrient content of cereals. 相似文献
992.
Arabidopsis var1 and var2 mutants exhibit leaf variegation. VAR1 and VAR2 encode similar FtsH metalloproteases (FtsH5 and FtsH2, respectively). We have previously found many variegated mutants to be allelic to var2. Each mutant was shown to express a different degree of variegation, and the formation of white sectors was enhanced in severely variegated alleles when these alleles were grown at low temperature. VAR1/FtsH5 and VAR2/FtsH2 levels were mutually affected even in the weak alleles, confirming our previous observation that the two proteins form a hetero complex. In this study, the sites of the mutations in these var2 alleles were determined. We isolated eight point mutations. Five alleles resulted in an amino acid substitution. Three of the five amino acid substitutions occurred in Walker A and B motifs of the ATP-binding site, and one occurred in the central pore motif. These mutations were considered to profoundly suppress the ATPase and protease activities. In contrast, one mutation was found in a region that contained no obvious signature motifs, but a neighboring sequence, Gly–Ala–Asp, was highly conserved among the members of the AAA protein family. Site-directed mutagenesis of the corresponding residue in E. coli FtsH indeed showed that this residue is necessary for proper ATP hydrolysis and proteolysis. Based on these results, we propose that the conserved Gly–Ala–Asp motif plays an important role in FtsH activity. Thus, characterization of the var2 alleles could help to identify the physiologically important domain of FtsH. 相似文献
993.
Carbonic Anhydrase Activities in Pea Thylakoids 总被引:2,自引:1,他引:1
Moskvin OV Shutova TV Khristin MS Ignatova LK Villarejo A Samuelsson G Klimov VV Ivanov BN 《Photosynthesis research》2004,79(1):93-100
Pea thylakoids with high carbonic anhydrase (CA) activity (average rates of 5000 µmol H+ (mg Chl)–1 h–1 at pH 7.0) were prepared. Western blot analysis using antibodies raised against the soluble stromal -CA from spinach clearly showed that this activity is not a result of contamination of the thylakoids with the stromal CA but is derived from a thylakoid membrane-associated CA. Increase of the CA activity after partial membrane disintegration by detergent treatment, freezing or sonication implies the location of the CA in the thylakoid interior. Salt treatment of thylakoids demonstrated that while one part of the initial enzyme activity is easily soluble, the rest of it appears to be tightly associated with the membrane. CA activity being measured as HCO3
– dehydration (dehydrase activity) in Photosystem II particles (BBY) was variable and usually low. The highest and most reproducible activities (approximately 2000 µmol H+ (mg Chl)–1 h–1) were observed in the presence of detergents (Triton X-100 or n-octyl--D-glucopyranoside) in low concentrations. The dehydrase CA activity of BBY particles was more sensitive to the lipophilic CA inhibitor, ethoxyzolamide, than to the hydrophilic CA inhibitor, acetazolamide. CA activity was detected in PS II core complexes with average rate of 13,000 µmol H+ (mg Chl)–1 h–1 which was comparable to CA activity in BBY particles normalized on a PS II reaction center basis.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
994.
The effects of 24-epibrassinolide (24-epiBL) on seedling growth, antioxidative system, lipid peroxidation, proline and soluble
protein content were investigated in seedlings of the salt-sensitive rice cultivar IR-28. Seedling growth of rice plants was
improved by 24-epiBL treatment under salt stress conditions. When seedlings treated with 24-epiBL were subjected to 120 mM
NaCl stress, the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6) and glutathione reductase (EC 1.6.4.2)
did not show significant difference, whereas the activity of ascorbate peroxidase (EC 1.11.1.11) significantly increased.
Increased activity of peroxidase (EC 1.11.1.7) under NaCl stress showed remarkable decrease in the 24-epiBL+NaCl-applied group.
Lipid peroxidation level significantly increased under salt stress but decreased with 24-epiBL application revealing that
less oxidative damage occurred in this group (24-epiBL+NaCl). In addition, increased proline content in the NaCl-applied group
was decreased by 24-epiBL application in the 24-epiBL+NaCl-applied group. Soluble protein content was increased by 24-epiBL
application even under NaCl stress, being also higher than control conditions (no 24-epiBL or NaCl treatment). 24-epiBL treatment
considerably alleviated oxidative damage that occurred under NaCl-stressed conditions and improved seedling growth in part
under salt stress in sensitive IR-28 seedlings. 相似文献
995.
Cytochromes b561 (cyts b561) constitute a family of eukaryotic membrane proteins, catalysing ascorbate (Asc)-mediated trans-membrane electron transport, and hence likely involved in Asc regeneration. A class of proteins (DoH-CB) has been identified in plants and animals, containing the cyt b561 electron-transport domain (CB), combined with the catecholamine-binding regulatory domain of dopamine-beta-hydroxylase (DoH). A mammalian DoH-CB protein was previously reported to function as a cell-derived growth factor receptor (SDR2). We have performed an in silico analysis on DoH-CB proteins from Arabidopsis thaliana and demonstrate that structural features of both CB and DoH domains are well conserved. The combination of both domains may have evolved from a functional interaction between a cyt b561 and a DoH-containing protein, illustrating the so-called "Rosetta Stone" evolutionary principle, and this hypothesis is supported by sequence comparisons. DoH-CB proteins form a newly identified group of proteins, likely to play a key role in catecholamine action in plants. It is suggested that these proteins may function as trans-membrane electron shuttles, possibly regulated by catecholamines. The role and action of catecholamines in plants is poorly documented, but it is clear that they are involved in many aspects of growth and development. Whether the DoH-CB proteins functionally interact with Asc, as is the case for cyts b561, remains to be determined. 相似文献
996.
Maruyama-Nakashita A Nakamura Y Yamaya T Takahashi H 《The Plant journal : for cell and molecular biology》2004,38(5):779-789
Cytokinin is an adenine derivative plant hormone that generally regulates plant cell division and differentiation in conjunction with auxin. We report that a major cue for the negative regulation of sulfur acquisition is executed by cytokinin response 1 (CRE1)/wooden leg (WOL)/Arabidopsis histidine kinase 4 (AHK4) cytokinin receptor in Arabidopsis root. We constructed a green fluorescent protein (GFP) reporter system that generally displays the expression of the high-affinity sulfate transporter SULTR1;2 in Arabidopsis roots. GFP under the control of SULTR1;2 promoter showed typical sulfur responses that correlate with the changes in SULTR1;2 mRNA levels; accumulation of GFP was induced by sulfur limitation (-S), but was repressed in the presence of reduced sulfur compounds. Among the plant hormones tested, cytokinin significantly downregulated the expression of SULTR1;2. SULTR1;1 conducting sulfate uptake in sultr1;2 mutant was similarly downregulated by cytokinin. Downregulation of SULTR1;1 and SULTR1;2 by cytokinin correlated with the decrease in sulfate uptake activities in roots. The effect of cytokinin on sulfate uptake was moderated in the cre1-1 mutant, providing genetic evidence for involvement of CRE1/WOL/AHK4 in the negative regulation of high-affinity sulfate transporters. These data demonstrated the physiological importance of the cytokinin-dependent regulatory pathway in acquisition of sulfate in roots. Our results suggested that two different modes of regulation, represented as the -S induction and the cytokinin-dependent repression of sulfate transporters, independently control the uptake of sulfate in Arabidopsis roots. 相似文献
997.
998.
Nodzon LA Xu WH Wang Y Pi LY Chakrabarty PK Song WY 《The Plant journal : for cell and molecular biology》2004,40(6):996-1006
Ubiquitin-mediated protein modification plays a key role in many cellular signal transduction pathways. The Arabidopsis gene XBAT32 encodes a protein containing an ankyrin repeat domain at the N-terminal half and a RING finger motif. The XBAT32 protein is capable of ubiquitinating itself. Mutation in XBAT32 causes a number of phenotypes including severe defects in lateral root production and in the expression of the cell division marker CYCB1;1::GUS . The XBAT32 gene is expressed abundantly in the vascular system of the primary root, but not in newly formed lateral root primordia. Treatment with auxin increases the expression of XBAT32 in the primary root and partially rescues the lateral root defect in xbat32 - 1 mutant plants. Thus, XBAT32 is a novel ubiquitin ligase required for lateral root initiation. 相似文献
999.
Sun-A?Kim Seong-Ki?Kim Peter?B.?Kaufman June?Seung?LeeEmail author Soo?Chul?ChangEmail author 《Journal of Plant Biology》2004,47(4):307-313
We investigated chilling-induced changes in ethylene levels in Arabidopsis to find plants with distinct patterns of ethylene
production in the cold-related biosynthetic pathway. The sensitive mutants identified here includedchs1-2,chs4-2, andchs6-2. Among these, plants of thechs4-2 mutant produced more ethylene than did the wild type after both were transferred from 4°C or 10°C to 22°C. This mutant also
showed less freezing tolerance and more electrolyte leakage than the wild-type plants. Our results suggest a relationship
between ethylene biosynthesis and chilling sensitivity in the mutant To determine which of the enzymes involved in ethylene
biosynthesis were induced by chilling, we tested the activities of ACC synthase and ACC oxidase in both mutant and wild-type
plants, and found greater activity by ACC synthase as well as a higher ACC content in the mutants after all the plants were
transferred from 10°C to 22°C. However, ACC oxidase activity did not differ between mutant and wild-type plants in response
to chilling treatment Therefore, we conclude thatchs4-2 mutants produce more ethylene than do other mutants or the wild type during their recovery from chilling conditions. Furthermore,
we believe that ACC synthase is the key enzyme involved in this response. 相似文献
1000.