首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   720篇
  免费   31篇
林业   71篇
农学   72篇
基础科学   1篇
  124篇
综合类   44篇
农作物   38篇
水产渔业   53篇
畜牧兽医   282篇
园艺   10篇
植物保护   56篇
  2022年   4篇
  2021年   18篇
  2020年   10篇
  2019年   14篇
  2018年   16篇
  2017年   19篇
  2016年   19篇
  2015年   25篇
  2014年   22篇
  2013年   62篇
  2012年   49篇
  2011年   44篇
  2010年   23篇
  2009年   16篇
  2008年   34篇
  2007年   44篇
  2006年   37篇
  2005年   47篇
  2004年   37篇
  2003年   34篇
  2002年   26篇
  2001年   25篇
  2000年   22篇
  1999年   14篇
  1998年   7篇
  1997年   2篇
  1995年   7篇
  1994年   4篇
  1993年   2篇
  1992年   5篇
  1991年   4篇
  1990年   8篇
  1989年   6篇
  1988年   4篇
  1987年   6篇
  1985年   4篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1979年   6篇
  1978年   3篇
  1977年   2篇
  1976年   1篇
  1975年   3篇
  1974年   1篇
  1972年   2篇
  1967年   1篇
  1956年   1篇
  1952年   2篇
排序方式: 共有751条查询结果,搜索用时 171 毫秒
141.
Resistance to soybean mosaic virus (SMV) is imperative for soybean (Glycine max (L.) Merr.) production in the Tohoku region. Molecular markers for SMV resistance were previously reported for U.S. SMV strains, but they cannot be applied because of the differences in strain classification between Japan and the U.S. A U.S. variety ‘Harosoy’ has been used mainly as a donor of resistance to SMV strains C and D in a Japanese breeding program, resulting in resistant varieties such as ‘Fukuibuki.’ Because ‘Harosoy’ harbors the Rsv3 gene conferring resistance to the virulent SMV strain groups, G5 through G7, it appears that the Rsv3 gene confers resistance to strains C and D. In this study, we introduced resistance to the two strains from ‘Fukuibuki’ into a leading variety ‘Ohsuzu’ by recurrent backcrossing with marker-assisted selection. All lines selected with markers near Rsv3 showed resistance to the strains, suggesting that the Rsv3 locus is responsible for the resistance. Three years of trials showed that one of the breeding lines, ‘Tohoku 169,’ was equivalent to ‘Ohsuzu’ with respect to agricultural characteristics such as seed size, maturity date, and seed yield, except for the SMV resistance.  相似文献   
142.
Histiocytic sarcoma (HS) is a rare neoplasm of macrophages or dendritic cells with a poor prognosis in dogs. As the apoptosis inhibitor of macrophage (AIM) is characteristically expressed in canine macrophages, we hypothesised that AIM is involved in the development or progression of HS in dogs. In this study, AIM expression in the tumour region and serum AIM levels in dogs with HS was assessed. Additionally, the effects of AIM overexpression on HS cell viability were investigated using a HS cell line that was selected from five validated HS cell lines. Immunohistochemistry showed that AIM expression was observed in the cytoplasm of the HS cells. CD36, a candidate AIM receptor, was also observed on the cell membrane of HS cells. When the serum AIM level was detected in 36 dogs with HS and 10 healthy dogs via western blot analysis, the AIM levels in the HS dogs were significantly higher than those in the controls. AIM mRNA expression in the 5 HS cell lines varied but was higher than that in the other tumour-derived lines. Among the five HS cell lines, DH82 originally had lower AIM and the highest CD36 expression. When AIM was overexpressed in DH82, therein cell growth speed and invasion, apoptosis inhibition and phagocytic activity were strongly upregulated. These data suggest that elevated intra-tumour expression of AIM could induce the progression of HS cells in dogs. Moreover, elevated serum AIM levels in dogs with HS could serve as a biomarker of HS.  相似文献   
143.
Microsatellite loci were developed for Gynochthodes boninensis, an endemic climbing plant in the Bonin Islands. Using a Roche 454 GS Junior next-generation sequencer, 158 microsatellite loci were designed. Of the 48 microsatellite loci tested, 37 were successfully amplified and 25 were polymorphic in two populations of G. boninensis. For the 25 polymorphic loci, the mean expected heterozygosities per locus were 0.303 in the Chichijima Island population and 0.310 in the Hahajima Island population, respectively. There was no evidence of linkage disequilibrium in either population, but one locus showed significant deviation from Hardy–Weinberg equilibrium in one population. The microsatellite loci developed in this study will be useful for future studies of population genetics of G. boninensis. In particular, because this species is androdioecious (males and hermaphrodites coexist), characterizing the species gene flow is crucial to understanding the evolution and maintenance of this rare sexual system.  相似文献   
144.
Shinano T  Osaki M  Kato M 《Tree physiology》2001,21(9):617-624
Twenty-four temperate tree species were classified into three groups based on cluster analysis of relative growth rate, nitrogen concentration, nitrogen-production efficiency, nitrogen-distribution ratio and nitrogen-use efficiency as follows: Group I (Asteridae and Rosidae), Group II (Dilleniidae and Hamamelidae) and Group III (Coniferopsidae). Relative growth rate (RGR) was high in Group II, moderate in Group I and low in Group III. The regression coefficient for the relationship between RGR and leaf nitrogen concentration was higher in Group II than in Group I, and no relationship was observed in Group III. Parameter analysis of RGR indicated that RGR per unit leaf nitrogen was important for all three groups, but that the allocation of nitrogen to leaves was particularly important in Groups I and II. The ratio of dark respiratory rate (R) to net photosynthetic rate (A) was higher in Group I than in Group II. Neither A nor R was measured in the Group III species. A linear relationship was observed between leaf nitrogen concentration and A in Group II, but this relationship was not evident in Group I.  相似文献   
145.
1H-Nuclear magnetic resonance (NMR) microscopy was used to study freezing behavior in wintering leaf buds of Momi fir (Abies firma Sieb. et Zucc.) and Japanese red pine (Pinus densiflora Sieb. et Zucc.). The images acquired predominantly reflected the density of mobile (i.e., non-ice) protons mainly from unfrozen water. By comparing images taken at various subfreezing temperatures, we determined which tissues produced the high and low temperature exotherms detected by differential thermal analyses. Typical extra-organ freezing was successfully imaged in leaf buds of A. firma. The bud scales readily froze at -7 degrees C, but shoot primordia remained supercooled to -14 degrees C in December buds and to -21 degrees C in March buds. The size of supercooled shoot primordia was reduced with decreasing temperature, indicating a gradual decrease in water content of the shoot primordia. In contrast, the signal from shoot primordia of P. densiflora disappeared between -7 and -14 degrees C, corresponding to the high temperature exotherm at -8 degrees C, indicating extracellular freezing of the shoot primordia. The xylem and bark tissues readily froze at -7 degrees C in A. firma and between -7 and -14 degrees C in P. densiflora. We conclude that NMR microscopy can noninvasively provide more spatially specific information about freezing behavior in leaf buds than traditional methods such as differential thermal analysis. In particular, it allows the organized and harmonized freezing behaviors in complex organs to be visualized directly thereby revealing the diversity of mechanisms involved in freezing behaviors.  相似文献   
146.
An understanding of spatial variations in gas exchange parameters in relation to the light environment is crucial for modeling canopy photosynthesis. We measured vertical, horizontal and azimuthal (north and south) variations in photosynthetic capacity (i.e., the maximum rate of carboxylation: Vcmax), nitrogen content (N), leaf mass per area (LMA) and chlorophyll content (Chl) in relation to relative photosynthetic photon flux (rPPF) within a Fagus crenata Blume crown. The horizontal gradient of rPPF was similar in magnitude to the vertical gradient of rPPF from the upper to the lower crown. The rPPF in the north quadrant of the crown was slightly lower than in the south quadrant. Nitrogen content per area (Narea), LMA and Vcmax were strictly proportional to rPPF, irrespective of the vertical direction, horizontal direction and crown azimuth, whereas nitrogen content per dry mass, Chl per area and photosynthetic capacity per dry mass (Vm) were fairly constant. Statistical analyses separating vertical trends from horizontal and azimuthal trends indicated that, although horizontal and vertical light acclimation of leaf properties were similar, there were two significant azimuthal variations: (1) Vcmax was lower in north-facing leaves than in south-facing leaves for a given Narea, indicating low photosynthetic nitrogen-use efficiency (PNUE) of north-facing leaves; and (2) Vcmax was lower in north-facing leaves than in south-facing leaves for a given LMA, indicating low Vm of the north-facing leaves. With respect to the low PNUE of the north-facing leaves, there were no significant azimuthal variations in leaf CO2 conductance from the stomata to the carboxylation site. Biochemical analysis indicated that azimuthal variations in nitrogen allocation to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and in nitrogen allocation between carboxylation (Rubisco and other Calvin cycle enzymes) and light harvesting machinery (Chl pigment-protein complexes) were not the main contributor to the difference in PNUE between north- and south-facing leaves. Lower specific activity of Rubisco may be responsible for the low PNUE of the north-facing leaves. Anatomical analysis indicated that not only high leaf density, which is compatible with a greater fraction of non-photosynthetic tissue, but also thick photosynthetic tissue contributed to the low Vm in the north-facing leaves. These azimuthal variations may need to be considered when modeling canopy photosynthesis based on the Narea-Vcmax or LMA-Vcmax relationship.  相似文献   
147.
We investigated an effect of the estimation length of the time-series data on the parameter estimates of geometric Brownian motion for log prices. This is to examine how much the estimates vary depending upon the estimation length of the data for the simulation purpose of stochastic modeling. Using the monthly time-series data for akamatsu, sugi, and hinoki from January 1975 to December 2000, our analysis shows that the longer the estimation length, the more stable the estimated value of the drift coefficient and the volatility coefficient of geometric Brownian motion become, implying less variability in the estimates needed for the simulation analysis. On the other hand, the shorter estimation length would tend to reflect such a sudden change in the data as the oil shock or the short-term decreasing or increasing tendency, which results in the large degree of variability in parameter estimates. This stems from the fact that the long estimation length regards a short-term price changes as an intrinsic part of price volatility. These results imply that when conducting a scenario analysis under stochastic environments, for the shorter estimation length, the wider range of parameter settings should be incorporated into the analysis.  相似文献   
148.
The factors involved in the successful escape of overwintered larvae of Epinotia granitalis from host oleoresin in the phloem of Cryptomeria japonica were studied. The mortality, period, and body weight of E. granitalis overwintered larvae while feeding on the phloem of C. japonica were compared with the same parameters for Semanotus japonicus larvae. The seasonal fluctuation in the ability of C. japonica to form traumatic resin canals in the phloem was also assessed. The oleoresin mortality of E. granitalis was low compared with that of S. japonicus. Although both species started feeding on approximately the same date in spring, the feeding period of E. granitalis was only about 24 days, showing that E. granitalis faced the danger of host oleoresin for a shorter period than S. japonicus. The larval weight of E. granitalis was consistently greater than that of S. japonicus through the phloem-feeding period of E. granitalis, and the growth rate was also higher in E. granitalis, suggesting that E. granitalis had a better ability to avoid host oleoresin. These results demonstrated that not only the feeding habits, that is, the tendency of a single larva to feed at several sites, but also the shorter feeding period and larger body size were probably the important factors facilitating escape of E. granitalis from host oleoresin mortality. Furthermore, the ability of C. japonica to form traumatic resin canals increased after the starting date of larval feeding in spring. Because E. granitalis finished feeding before the culmination of the ability of C. japonica to form traumatic resin canals, it was likely that the shorter feeding period was the most important factor in enabling E. granitalis to escape from mortality by host oleoresin.  相似文献   
149.
A technique for screening immune-enhancing polysaccharides in food using the phagocytotic activity of 1,25-dihydroxyvitamin D3 (VD3)-differentiated HL60 cells is presented. HL60 cells, a human acute promyelocytic cell line, can differentiate along the monocytic lineage following exposure to VD3 or phorbol-12-myristate-13-acetate (PMA). For differentiated cells along the monocytic pathway, HL60 cells were maintained in RPMI 1640 medium supplemented with 10% FBS and 120 nM VD3 for more than 1 week. VD3-differentiated HL60 cells were seeded into 48-well plates, YG-labeled microspheres and polysaccharides were added and mixed using a plate shaker at 1100 rpm for 30 s, and then the mixture was incubated overnight at 37 degrees C in 5% CO2. The cells were fixed with 2% formaldehyde and resuspended in phosphate-buffered saline. The rate of phagocytosis was measured with a flow cytometer. VD3-differentiated cells but not non- and PMA-differentiated cells resulted in an elevation of phagocytic activity by various immune-enhancing polysaccharides in foods.  相似文献   
150.
The incidence of primary and secondary glaucoma in dogs was investigated. A total of 1244 dogs received ophthalmologic examinations, including tonometry and gonioscopy. Goniophotographs were taken using a goniolens to evaluate the iridocorneal angle (ICA) as well as pectinate ligament (PL). The anterior width of the ciliary cleft and the total distance from the origin of the PL to the anterior corneal surface were measured from the goniophotographs. Glaucoma was diagnosed based on the cupping of the optic nerve head, clinical signs, ocular changes, and high IOP, and it was synchronized with gonioscopic grades to differentiate between primary and secondary glaucoma. We investigated 1244 dogs of 29 breeds, including the mixed breed; among these, glaucoma was diagnosed in 127 dogs (162 eyes). Of 162 eyes, primary glaucoma was diagnosed in 129 eyes and secondary glaucoma in 33 eyes. Shiba Inu dogs (42 dogs, 33%) showed the highest incidence of glaucoma, followed by Shih-Tzu (21 dogs, 16.5%). Furthermore, all the glaucomatous Shiba Inu dogs had primary glaucoma with abnormal ICA grades and dysplastic PLs. The findings of our study reveal that the Shiba Inu breed in Japan may have a hereditary predisposition to glaucoma.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号