全文获取类型
收费全文 | 459篇 |
免费 | 21篇 |
国内免费 | 28篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2019年 | 1篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 13篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 6篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 17篇 |
2008年 | 17篇 |
2007年 | 20篇 |
2006年 | 36篇 |
2005年 | 27篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 22篇 |
2001年 | 25篇 |
2000年 | 19篇 |
1999年 | 21篇 |
1998年 | 9篇 |
1997年 | 31篇 |
1996年 | 12篇 |
1995年 | 3篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有508条查询结果,搜索用时 15 毫秒
1.
2.
Fructan biosynthesis in excised leaves of Lolium temulentum L. 总被引:2,自引:2,他引:0
ANDREW J. CAIRNS 《The New phytologist》1989,112(4):465-473
3.
This paper presents information about the release of nitrogen and phosphorus from dying grass roots and the capture of phosphorus by other, living plants. We have paid particular attention to the part played by mycorrhizas in this phosphorus capture, and the possible importance of mycorrhizal links between dying and living roots.WhenLolium perenne plants were grown with ample nutrients and their roots then detached and buried in soil, about half the nitrogen and two-thirds of the phosphorus was lost in three weeks, but only one-fifth of the dry weight. The C:N and C:P ratios suggest that microbial growth in the roots would at first be C-limited but would become N- and P-limited within three weeks.Rapid transfer of32P can occur from dying roots to those of a living plant if the two root systems are intermingled. The amount transferred was substantially increased in two species-combinations that are known to form mycorrhizal links between their root systems. In contrast, in a species-combination where only the living (receiver) plant could become mycorrhizal no significant increase of32P transfer occurred. This evidence, although far from conclusive, suggests that mycorrhizal links between dying and living roots can contribute to nutrient cycling. This research indicates a major difference in nutrient cycling processes between perennial and annual crops. 相似文献
4.
5.
Fructan biosynthesis in excised leaves of Lolium temulentum L. 总被引:10,自引:10,他引:0
6.
The fate of sheep urine-N applied to an upland grass sward at four dates representing widely differing environmental conditions,
was followed in soil (0–20 cm) and in herbage. Urine was poured onto 1-m2 plots to simulate a single urination in August 1984 (warm and dry), May (cool), July and August 1985 (cool and wet) at rates
equivalent to 40–52 g N m−2.
The transformation of urine-N (61–69% urea-N) in soil over a 6–7 week period followed the same general pattern when applied
at different times during the season; rapid hydrolysis of urea, the appearance of large amounts of urine-N as ammonium in
soil extracts, and the appearance of nitrate about 14 days after application. The magnitude of “apparent” nitrification however
differed markedly with environmental conditions, being greatest in May 1985 when a maximum of 76% of the inorganic soil N
was in the form of nitrate. At all other application dates nitrate levels were relatively low. With the August 1984 application
soil inorganic N returned to control levels (given water only) after 31 days but considerable amounts remained in soil for
60–90 days with the other applications.
Weekly cuts to 3-cm indicated that increases in herbage dry matter and N yields in response to urine application were greatest
in absolute terms after the May 1985 application and continued for at least 70 days with all applications. Relative to control
plots the May application resulted in a 3-fold increase in herbage DM compared with corresponding values of 6-, 5-, and 7-fold
increases with the August 1984, July and August 1985 applications. Recovery of urine-N in herbage was poor averaging only
17% of that applied at different dates, while recovery in soil extracts was incomplete. The exact routes of loss (volatilisation,
leaching, denitrification or immobilisation) were not quantified but it is evident that substantial amounts of urine-N can
be lost from the soil-plant system under upland conditions. 相似文献
7.
8.
O. I. Joarder N. H. Joarder P. J. Dale 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,73(2):286-291
Summary Immature gramineous leaves provide a convenient system for comparing the response of cells in culture with their state of differentiation. Callusing frequency is compared with leaf segment position, leaf age and in vivo mitotic activity in Lolium multiflorum. (1) In a succession of one millimeter sections from the immature leaf base, callus was formed from the first and second sections but not the third or subsequent sections. The frequency of those explants callusing decreased with distance from the base of the leaf and with leaf age (or leaf extension growth). (2) In vivo, the proportion of cells in mitosis declined from around 10–14% at the base of young leaves to zero at 5 mm from the base and beyond. Mitotic activity also declined in leaves as they aged, and dividing cells were not observed in leaves 30 days from initiation or older. (3) A high frequency of callus formation was associated with a high mitotic index in the explant. But for corresponding mitotic indices, cells further away from the leaf base were less responsive in culture. (4) It is proposed that cells are becoming differentiated even in highly meristematically active regions of the leaf and concomitantly losing their ability to respond in culture. 相似文献
9.
Erasmus Otabbong 《Plant and Soil》1990,123(1):89-93
The effect of Si(OH)4 on Cr toxicity and elemental concentrations in ryegrass were investigated in a growth chamber using an acid and a neutral
mineral soil. Each soil was treated with 50 mg Cr, as CrO3, kg−1 soil dry weight, singly, or in combination with 25 mg Si as Si(OH)4. Plants growing in unamended soils were used as controls.
Chromium toxicity, expressed as decrease in shoot or root dry weight, was increased by the Si. This increase was accompanied
by a higher Cr uptake particularly on the acid soil. The shoot and root dry weights were significantly correlated (P=1%) with the concentration of Cr, where r=−0.80 and −0.65, respectively. Uptake of Al, Cu, Fe, P and Zn did not show any
consistent relationship to the magnitude of Cr toxicity. 相似文献
10.
Z. Rengel 《Plant and Soil》1990,128(2):185-189
Ammonium acetate and BaCl2-triethanolamine were used to desorb Mg2+ from the root Donnan free space (DFS) of 23-d-old ryegrass (Lolium multiflorum Lam. cvs. Gulf and Wilo). Amounts of desorbed Mg2+ increased with the increase in Mg2+ activity of the nutrient solution. Slightly less Mg2+ was desorbed by Ba2+ than by NH4
+. Previously published data on short-term net Mg2+ uptake by intact 23-d-old ryegrass plants of the two cultivars were linearly related to the amount of exchangeable Mg+ desorbed from the root DFS (r2=0.90 and 0.81 for the desorption by NH4
+ and Ba2+, respectively). A sward of Mg2+ ions attracted to the negative charges of the cell surface is suggested to represent a part of a pool of Mg2+ available for active transport through the plasmalemma. 相似文献