全文获取类型
收费全文 | 569篇 |
免费 | 19篇 |
国内免费 | 20篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 12篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 8篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 39篇 |
2005年 | 28篇 |
2004年 | 13篇 |
2003年 | 22篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有608条查询结果,搜索用时 171 毫秒
541.
Herrero EM López-Gonzálvez A Ruiz MA Lucas-García JA Barbas C 《International journal of phytoremediation》2003,5(2):153-167
Brassica napus var. oleifera and Helianthus annus were grown in artificially contaminated soils. Accumulation and translocation of the environmental pollutants zinc, cadmium, lead, and copper, was evaluated in different portions of the plants at two harvesting times. The distribution into the plants of these metal ions, as well as their capacity for contaminant phytoextraction and accumulation was assessed. For this purpose, an analytical method utilizing focused ultrasound employed for extraction and stripping voltammetry for measurement has been optimized and validated for the simultaneous measurement of Zn, Cd, Pb, and Cu in plant extracts. 相似文献
542.
Fambrini M Cionini G Bertini D Michelotti V Conti A Pugliesi C 《Genesis (New York, N.Y. : 2000)》2003,36(1):25-33
The initiation and growth of axillary meristems are fundamental components of plant architecture. Here, we describe the mutant missing flowers (mf) of Helianthus annuus characterized by the lack of axillary shoots. Decapitation experiments and histological analysis indicate that this phenotype is the result of a defect in axillary meristem initiation. In addition to shoot branching, mutation affects floral differentiation. The indeterminate inflorescence of sunflower (capitulum) is formed of a large flat meristem which produces floret primordia in multiple spirals. In wildtype plants a bisecting crease divides each primordium in two distinct bumps that adopt different fate. The peripheral (abaxial) part of the primordium becomes a small leaf-like bract and the adaxial part becomes a flower. In the mf mutant, the formation of flowers at the axil of bracts is precluded. Histological analyses show that in floret primordia of the mutant a clear subdivision in dyads is not established. The primordia progressively bend inside and only large involucral floral bracts are developed. The results suggest that the MISSING FLOWERS gene is essential to provide or perceive an appropriate signal to the initiation of axillary meristems during both vegetative and reproductive phases. 相似文献
543.
The effect of abscisic acid (ABA) treatment on growth pigments and antioxidant defense system were investigated in seedlings of Helianthus annuus (cvs. Nantio F1 and Özdemirbey) subjected to drought and waterlogging stress. In addition, seedlings were sprayed with 10 M ABA three times every other day. Relative growth rate (RGR) was significantly reduced in both genotypes under drought stress, however, this growth inhibition was less in ABA-treated plants. Total chlorophyll content increased by drought stress in both genotypes. Ascorbate was not influenced by drought, while α-tocopherol increased in cv. Nantio F1. Ascorbate and α-tocopherol increased with drought stress in cv. Özdemirbey. ABA treatment decreased ascorbate and β-carotene contents while it increased α-tocopherol and xanthophylls contents under drought stress. The activity of superoxide dismutase (SOD) in both genotypes increased under drought stress-ABA combinations. Catalase (CAT) activity decreased under drought stress and drought-ABA combinations while it increased under waterlogging stress. Glutathione reductase (GR) activity decreased under drought stress but recovered with ABA treatment. The results suggested that ABA treatments have different effects on the components of antioxidant defense system in H. annuus genotypes and ABA may contribute drought-induced oxidative stress tolerance but not effects under waterlogging stress. 相似文献
544.
The contribution of epistasis to 15 morphological traits differentiating two annual sunflowers (Helianthus annuus and H. debilis ssp. cucumerifolius) and to hybrid pollen sterility was estimated in a first generation backcross (BC1) mapping population. Analysis of digenic interactions among quantitative trait loci (QTLs) with significant main effects revealed significant interaction effects for six of the 15 morphological traits and for pollen sterility. Likewise, a genome-wide scan of all possible two-locus combinations detected additional significant interactions for three of the traits with significant epistasis in the original analysis: stem pigmentation, phyllary pubescence, and pollen viability. However, these were the only traits of the 16 examined in which detected interactions explained more than 5% of phenotypic variance. The implications of these findings for adaptive evolution and for the introgression of advantageous morphological QTLs across a natural hybrid zone between these taxa are discussed. 相似文献
545.
M. T. Cheres J. F. Miller J. M. Crane S. J. Knapp 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,100(6):889-894
Heterosis is significant for seed yield and is one of the driving forces behind the hybrid seed industry in cultivated sunflower
(Helianthus annuus L). Heterotic groups in sunflower, if any other than the female and male inbred-line groups exist, have not been well studied
or described. The primary aims of this study were to assess the utility and validity of a series of proposed heterotic groups
and estimate correlations between genetic distance, heterosis, and hybrid performance for seed yield in sunflower. Fortytwo
female by male heterotic group (A × R) and 81 female by female heterotic group (A × B) single-cross hybrids were grown in
Corvallis, Ore., and Casselton, N.D., in 1996 and 1997. Heterosis was significant for seed yield and plant height but not
for seed oil concentration and days to flowering. Genetic distances were significantly correlated with hybrid seed yield when
estimated from AFLP fingerprints (G
D) (r = 0.63 for A × R and 0.79 for A × B hybrids), but not from coancestries (G
C) (r = -0.02 for A × R and 0.54 for A × B hybrids). G
D (R
2 = 0.4) was a poor predictor of hybrid seed yield. The proposed heterotic groups in sunflower seem to have utility, but do
not seem to be as strongly differentiated as those in corn (Zea mays L.). The highest-yielding hybrids were from the BC× RB heterotic pattern; however, several BC× BC hybrids (within-group hybrids) were among the top-yielding hybrids. The outstanding performance of certain BC× BC hybrids casts some doubt on the validity of the BC group. Substantial genetic diversity seems to be present within and between heterotic groups in sunflower.
Received: 1 September 1998 / Accepted: 14 September 1999 相似文献
546.
Mundel C Baltz R Eliasson A Bronner R Grass N Kräuter R Evrard JL Steinmetz A 《Plant molecular biology》2000,42(2):291-302
547.
During sunflower (Helianthus annuus L.) seed formation there was an active period of lipid biosynthesis between 12 and 28 days after flowering (DAF). The maximum
in-vitro acyl-acyl carrier protein (ACP) thioesterase activities (EC 3.1.2.14) were found at 15 DAF, preceding the largest
accumulation of lipid in the seed. Data from the apparent kinetic parameters, V
max and K
m, from seeds of 15 and 30 DAF, showed that changes in acyl-ACP thioesterase activity are not only quantitative, but also qualitative,
since, although the preferred substrate was always oleoyl-ACP, the affinity for palmitoyl-ACP decreased, whereas that for
stearoyl-ACP increased with seed maturation. Bisubstrate assays carried out at 30 DAF seemed to indicate that the total activity
found in mature seeds is due to a single enzyme with 100/75/15 affinity for oleoyl-ACP/stearoyl-ACP/palmitoyl-ACP. In contrast,
at 15 DAF, enzymatic data together with partial sequences from cDNAs indicated the presence of at least two enzymes with different
properties, a FatA-like thioesterase, with a high affinity for oleoyl-ACP, plus a FatB-like enzyme, with preference for long-chain
saturated fatty acids, both being expressed during the active lipid biosynthesis period. Competition assays carried out with
CAS-5, a mutant with a higher content of palmitic acid in the seed oil, indicated that a modified FatA-type thioesterase is
involved in the mutant phenotype.
Received: 17 December 1999 / Accepted: 25 February 2000 相似文献
548.
Flooding of excised roots or roots of intact aeroponically grown sunflower ( Helianthus annuus L. cv. Russian) caused a reduction in the activity of ATPases of microsomal membrane vesicles within 1 day. With increasing flooding of up to 3 days, the enzyme activity in the roots declined. During the same period, enzyme activity gradually increased in the non-flooded aeroponically grown roots. Continuous aeration during flooding either maintained the activity of the enzyme to the level of the controls or enhanced it. The ATPase did not require MgSO4 and had a much higher activity at pH 6.7 than at pH 8.5. The activity of the ATPases was markedly inhibited by sodium orthovanadate. There was 8 to 44% stimulation of the activity of the ATPases due to KCl in the absence as well as presence of MgSO4 . These data indicate that a substantial proportion of the ATPases, and thus the interface vesicles, could be of plasma membrane origin. 相似文献
549.
为探讨菊芋(Helianthus tuberosus)悬浮培养细胞对盐胁迫的生理响应,在0、50、100、150、200 mmol·L-1NaCl处理下测定了细胞的生物量、相对细胞活力、抗氧化酶活性以及过氧化氢、丙二醛、脯氨酸、可溶性糖、可溶性蛋白质的含量,测定了总酚含量并鉴别、定量分析了14种酚类化合物。结果表明:盐胁迫显著减弱了菊芋悬浮细胞的活力,抑制了细胞的增长,200 mmol·L-1NaCl处理下细胞生长基本上停止。盐胁迫诱发了细胞氧化胁迫,丙二醛含量显著增加,抗坏血酸过氧化物酶、过氧化物酶活性以及总酚含量、部分酚类化合物含量均随NaCl浓度升高而增加,酚类物质和抗氧化酶系统共同参与了应对氧化胁迫的抗氧化作用。脯氨酸在菊芋悬浮细胞应对NaCl渗透胁迫的渗透调节作用中扮演了重要的角色,而可溶性糖发挥的作用不大。 相似文献
550.