全文获取类型
收费全文 | 240篇 |
免费 | 10篇 |
专业分类
林业 | 77篇 |
农学 | 9篇 |
38篇 | |
综合类 | 29篇 |
农作物 | 5篇 |
水产渔业 | 5篇 |
畜牧兽医 | 73篇 |
园艺 | 4篇 |
植物保护 | 10篇 |
出版年
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1992年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1967年 | 5篇 |
1966年 | 3篇 |
1962年 | 2篇 |
1961年 | 6篇 |
1960年 | 2篇 |
1958年 | 2篇 |
1948年 | 2篇 |
1933年 | 2篇 |
1930年 | 2篇 |
1896年 | 2篇 |
排序方式: 共有250条查询结果,搜索用时 93 毫秒
241.
242.
243.
In contrast to carbon, silicon does not readily form double bonds, and compounds containing silicon-silicon double bonds can usually be stabilized only by protection with bulky substituents. We have isolated a silicon analog of spiropentadiene 1, a carbon double-ring compound that has not been isolated to date. In the crystal structure of tetrakis[tri(t-butyldimethylsilyl)silyl]spiropentasiladiene 2, a substantial deviation from the perpendicular arrangement of the two rings is observed, and the silicon-silicon double bonds are shown to be distorted. Spectroscopic data indicate pronounced interaction between two remote silicon-silicon double bonds in the molecule. Silicon-silicon bonds may be more accessible to synthesis than previously assumed. 相似文献
244.
245.
Jahn Davik 《Euphytica》1993,74(1-2):129-132
Summary An experiment comparing double row plants with four row plots where only the centre two rows were harvested (guarded double row plots) were laid out in two subsequent years. Fresh weight yields, dry matter yields, bulb dry matter content, refractometer index and harvest index were recorded and analyzed statistically. The cultivar x plot type interactions were in none of the cases significant. The increase in error variances when comparing double row plots with guarded double row plots was significant only for harvest index in the first year.Taking into account the low selection intensity when small plots are used, i.e. in early stages of plant breeding programmes, we conclude from these experiments that guarded plots are not necessary when breeding swedes under our growing conditions. 相似文献
246.
Rebecca N. Brown Alfredo Bolanos-Herrera James R. Myers Molly Miller Jahn 《Euphytica》2003,129(3):253-258
Cucurbita moschata cv. Nigerian Local has been used as a source of resistance to Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV), Papaya ringspot virus W (PRSV-W) and Cucumber mosaic virus (CMV) in breeding both Cucurbita moschata and Cucurbita pepo. We used the F1, F2 and BC1 generations derived from the cross C.-moschata cv. Waltham Butternut × Nigerian Local to study the inheritance of resistance to each of the viruses. We confirmed monogenic
dominant resistance to ZYMV previously attributed to Zym, and we report monogenic dominant resistance to WMV and CMV which we propose to designate
Wmv and Cmv, respectively. A single recessive gene, which we propose to designate prv, controls resistance to PRSV. DNA samples were extracted from a Waltham Butternut BC1 F1 population screened with ZYMV and analyzed using randomly amplified polymorphic DNA markers. No RAPD markers linked to ZYMV
resistance were found.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
247.
Murthy VR Evensen NM Jahn BM Coscio MR Dragon JC Pepin RO 《Science (New York, N.Y.)》1972,175(4020):419-421
The lunar mare basalt 15555 from the edge of Hadley Rille has been dated at 3.3x10(9) years by both rubidium-strontium and potassium-argon techniques. Age and trace element abundances closely resemble those of the Apollo 12 mare basalts. Data from lunar basalts obtained thus far indicate that they cannot be derived by simple fractionation from a homogeneous source. 相似文献
248.
249.
Lene?K.?ChristensenEmail author Shrinivasa?K.?Upadhyaya Bernie?Jahn David?C.?Slaughter Eunice?Tan David?Hills 《Precision Agriculture》2005,6(6):539-550
A necessary pre-requisite for variable rate application of plant nutrients to manage inputs in a site-specific manner is a
technique to detect nutrient stresses in plants in real-time. Spectral reflectance of plant canopy may provide a non-destructive
and rapid technique to detect nutrient and water stress in plants. In this study, we investigated the effect of water on nutrient
stress discrimination (nitrogen, N; phosphorus, P; and potassium, K) based on the visible and near infrared reflectance of
maize leaves grown under controlled greenhouse conditions. The analysis of the spectral data indicated that it was challenging
to detect the nutrient deficiencies if the plant water status was unknown. However, if a priori knowledge of water stress
existed, such as a well-watered situation, the ability to discriminate nutrient stress improved significantly. The analysis
of whole plant behaviour (i.e., mean reflectance data from all leaves within a plant) versus leaves located at a specific
location within a plant indicated that knowledge of spatial location of leaves within a plant helped to identify N and P stress
and NPK as a multi-stress condition more clearly. 相似文献
250.
C. R. Brown T. S. Kim Z. Ganga K. Haynes D. De Jong M. Jahn I. Paran W. De Jong 《American Journal of Potato Research》2006,83(5):365-372
High carotenoid potato may have particular value for human health due to the antioxidant properties and the therapeutic value for eye health in patients at risk for macular degeneration. Carotenoid concentrations were determined among the progeny of a cross between two high carotenoid lines derived from diploidPapa Amarilla germplasm from South America. The total carotenoid content ranged from 82 to 2686 µg / 100 g fresh weight (FW). The higher values greatly exceeded the mid-parent value of the cross. An index for yellow tuber flesh color was determined for a subset of the progeny. A cleaved amplified polymorphic sequence (CAPS) assay was developed to distinguish the alleles of beta-carotene hydroxylase (bch) in the two high-carotenoid parents. Abch allele (denoted B) common to the high carotenoid parents co-segregated with yellow flesh in the progeny of a white-flesh x yellow-flesh cross, makingbch an excellent candidate for the classicalY locus, required for yellow tuber flesh. The same allele was also present in all other yellow-fleshed potato clones tested. Genotype atbch explained a portion of the variation of total carotenoid (R2=0.42). Clones homozygous for the B allele (BB) contained, on average, slightly more carotenoid than heterozygous Bb clones, which in turn had much more carotenoid than homozygous bb clones, suggesting a partially dominant gene model. Similarly, bb flesh was significantly less yellow than Bb and BB, the latter two being quite close. Total carotenoid varied considerably between progeny in the Bb and BB genotype categories, suggesting that variation at one or more additional loci have a significant effect on total carotenoid levels. Since the total carotenoid levels in manyPapa Amarilla cultivars and progeny are much higher than those in white- and yellow-fleshed tetraploid cultivars, it may be possible to breed for high carotenoid values in tetraploid germplasm by introducing one or more genes derived fromPapa Amarilla germplasm. 相似文献