全文获取类型
收费全文 | 102篇 |
免费 | 5篇 |
国内免费 | 13篇 |
专业分类
120篇 |
出版年
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 4篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 1篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1961年 | 1篇 |
1958年 | 3篇 |
1957年 | 6篇 |
1956年 | 3篇 |
1955年 | 1篇 |
1954年 | 1篇 |
1953年 | 7篇 |
1952年 | 4篇 |
排序方式: 共有120条查询结果,搜索用时 15 毫秒
81.
Different vulnerabilities of Quercus ilex L. to freeze- and summer drought-induced xylem embolism: an ecological interpretation 总被引:8,自引:3,他引:5
Quercus ilex L. growing in the southern Mediterranean Basin region is exposed to xylem embolism induced by both winter freezing and summer drought. The distribution of the species in Sicily could be explained in terms of the different vulnerability to embolism of its xylem conduits. Naturally occurring climatic conditions were simulated by: (1) maintaining plants for 3h at ambient temperatures of 0, -1.5, -2.5, -5.0 and -11°C; and (2) allowing plants to dry out to ratios of their minimum diurnal leaf water potentials (Ψ1) to that at the turgor loss point (Ψtlp) of 0.6, 0.9, 1.05, 1.20 and 1.33. The loss of hydraulic conductivity of one-year-old twigs reached 40% at -1.5°C and at Ψ1/ΨtlP= 1.05. Recovery from these strains was almost complete 24 h after the release of thermal stress or after one irrigation, respectively. More severe stresses reduced recovery consistently. The percentages of xylem conduits embolized following application of the two stresses, were positively related to xylem conduit diameter. The capability of the xylem conduits to recover from stress was positively related to the conduit diameter in plants subjected to summer drought, but not in the plants subjected to winter freezing stress. The ecological significance of the different vulnerabilities to embolism of xylem conduits under naturally occurring climatic conditions is discussed. 相似文献
82.
The possible role in drought resistance played by sclerophyllywas studied in the Mediterranean oaks Quercus ilex, Q. suberand Q. pubescens. Studies were conducted on leaves at 30, 50and 80% of their final surface area, as well as on mature leavesof the current year's growth in June and September and on 1-year-oldleaves. Leaves of different ages of the three species showed quite differentdegrees of sclerophylly (DS). Q. ilex leaves reached the definitiveDS of 1.75 g dm2 during leaf expansion; Q. pubescensleaves hardened at the end of their expansion, with a finalDS of 0.93 g dm2; Q. suber showed the lowest DS of 0.76g dm2. Leaf conductance to water vapour (g1) of 1-year-old leaves ofQ. ilex, measured in the field, showed a duration of the g1peak values about twice that of the other two species. The minimumleaf relative water content (RWC), however, was near the samein the three species, indicating that water loss was recoveredpartly by Q. ilex leaves. This was apparently due to the higherbulk modulus of elasticity ( 相似文献
83.
MATSUMOTO JIRO; LYNCH THOMAS J.; GRABOWSKI SUSAN; RICHARDS CHRISTINA M.; LO SZECHENG L.; CLARK CARL; KERN DALE; TAYLOR JOHN D.; TCHEN T.T.; ISHIKAWA TAKATOSHI; MASAHITO PRINCE; TAKAYAMA SHOZO 《Integrative and comparative biology》1983,23(3):569-580
The objectives of this paper are to describe 1) the developmentof new research systems for biochemical comparison of cellulartraits between normal and tumorous pigment cells of fish origin,2) the similarity and dissimilarity between these two categoriesof pigment cells with regard to growth, differentiation andpigment translocating activities and 3) the potentials of thesetumorous pigment cells to manifest multiple differentiation.The development of research systems has been achieved by theestablishment of 1) methods to obtain homogenous populationsof viable, cultivatable xanthophores (erythrophores) and melanophoresfrom goldfish skins, 2) permanent cell lines from goldfish erythrophoromas(tumors derived from erythrophores) and from Nibe croaker irido-melanophoromas(tumors composed of mixed populations of iridophore- and melanophore-likecells) and 3) procedures to induce differentiation in normaland tumorous stem cells (including the formation of pigmentsand ability to undergo pigment translocation in response tocAMP, to the neurotransmitter epinephrine and to the hormonesACTH and melatonin). Two kinds of tumorous pigment cell linesexamined herein have the ability to form, in addition to variouspigments, structures similar to dermal skeletons and lentoidbodies. These findings strongly suggest the possibility thatthese fish pigment cell tumors are neural crest stem cell tumorsin nature. 相似文献
84.
1959—1960年作者等在江西、湖南等地区配合大面积防治森林害虫之际,开展了DDT等化学药剂对于不同越冬时期的马尾松毛虫幼虫的毒效试验。据野外观察结果,将马尾松毛虫越冬幼虫划分为5个时期。即越冬前活动期、越冬前期、越冬期、越冬后期、越冬后活动期。试验证明:不同化学药剂对越冬松毛虫幼虫的毒效随着不同时期和温度条件而变化。就一般论:DDT的效果,在比较低温(日均温10—20℃)时特别显著;666及敌百虫的效果,在比较高温时(20℃以上)为显著。其中尤以敌百虫为更甚。DDT对不同时期幼虫的毒效大小为:越冬后期>越冬前期>越冬期>越冬前活动期>越冬后活动期≥夏季(4-5龄)幼虫;其中以越冬后期幼虫抵抗力最弱。从原则上论这是施药的最适宜时期,从25% DDT乳剂4,000倍稀释液在越冬后期(2,3月间)施用,毒效可达92%以上,用6,000倍稀释液亦达82%以上。如用γ6%可湿性666,800倍稀释液在越冬前、后期使用,毒效可达70-80%以上。50%敌百虫乳剂在温度20℃以上时(越冬前、后活动期)毒效显著增高。此时如用5,000-6,000倍稀释液喷洒,毒效可达70-80%左右。由此,作者认为:在长江以北,每年发生2代以下的松毛虫地区,可用DDT和666稀释液在越冬前、后期进行防治。长江以南,每年发生2代以上的马尾松毛虫地区,不但可用DDT、666来防治越冬前、后期幼虫;而且在幼树林地内越冬期的幼虫亦可防治。在上述地区内,敌百虫乳剂仅适于在越冬前、后活动期或夏季幼虫期温度较高时使用。就一般论,在越冬前期施用药剂时,如能选定在寒流侵袭之前喷射,效果更为显著。 相似文献
86.
在离体猫丘脑脑片上观察了乙酰胆碱对外膝体中继神经元膜的低阈值T-型钙电导的影响。电流箝位和电压箝位实验结果都显示:将膜电位箝制到给药前的对照水平,排除了乙酰胆碱的去极化作用后,大多数(82%)外膝外神经元的低阈值钙电导仍然被乙酰胆碱所抑制。说明这种抑制作用独立于乙酰胆碱引起的膜电位变化,而是对低阈值T-型钙通道的直接作用。 相似文献
87.
Ozone induced emissions of biogenic VOC from tobacco: relationships between ozone uptake and emission of LOX products 总被引:5,自引:0,他引:5
JONATHAN BEAUCHAMP ARMIN WISTHALER ARMIN HANSEL EINHARD KLEIST MARCO MIEBACH ÜLO NIINEMETS ULI SCHURR & JÜRGEN WILDT 《Plant, cell & environment》2005,28(10):1334-1343
Volatile organic compound (VOC) emissions from tobacco ( Nicotiana tabacum L. var. Bel W3) plants exposed to ozone (O3 ) were investigated using proton-transfer-reaction mass-spectrometry (PTR-MS) and gas chromatography mass-spectrometry (GC-MS) to find a quantitative reference for plants' responses to O3 stress. O3 exposures to illuminated plants induced post-exposure VOC emission bursts. The lag time for the onset of volatile C6 emissions produced within the octadecanoid pathway was found to be inversely proportional to O3 uptake, or more precisely, to the O3 flux density into the plants. In cases of short O3 pulses of identical duration the total amount of these emitted C6 VOC was related to the O3 flux density into the plants, and not to ozone concentrations or dose–response relationships such as AOT 40 values. Approximately one C6 product was emitted per five O3 molecules taken up by the plant. A threshold flux density of O3 inducing emissions of C6 products was found to be (1.6 ± 0.7) × 10−8 mol m−2 s−1 . 相似文献
88.
89.
L O Sillerud C H Han M W Bitensky A A Francendese 《The Journal of biological chemistry》1986,261(10):4380-4388
Carbon-13 nuclear magnetic resonance (NMR) methods have been applied to a study of the structure and metabolism of the triacylglycerols from rat epididymal fat pad adipocytes. Complete NMR signal assignments are provided for adipocytes, the extracted triacylglycerols, and methyl esters of the derived fatty acids. 13C NMR yielded rapid, nondestructive, quantitative analysis of the amounts of unsaturation of the fatty acyl chains; in cells from rats given ad libitum access to a standard laboratory diet the predominant fatty acids were found to be palmitate (29.9%), oleate (27.9%), and linoleate (34.1%). These results agreed with gas chromatographic separation of the derived methyl esters of the extracted lipids. Lipid dynamics were examined in situ and showed a substantial restriction of motion of glyceride-glycerol as compared with free glycerol; the nuclear magnetic spin-lattice relaxation times for free glycerol of 2.52 +/- 0.12 (C1,3) and 4.37 +/- 0.21 (C2) s decreased to 0.15 +/- 0.009 and 0.21 +/- 0.013 s, respectively, upon esterification. Segmental motion of the chains, monitored by relaxation time measurements, increased progressively from the alpha-carbon (nT1 = 0.70 s) to the methyl ends of the chains (nT1 = 9.63). The incorporation of C-13-labeled substrates ([1-13C]glucose and [3-13C]lactate) into the glycerol moiety of triacylglycerols was monitored in real time, in the presence of insulin. Lactate (10 mM) inhibited the incorporation of glucose (5.5 mM) into glyceride-glycerol. Lipolysis at the natural abundance level of 13C was measured in the presence of 10 microM isoproterenol. Simultaneous lipogenesis and lipolysis were found to occur in situ and were measured with the aid of [1-13C]glucose and isoproterenol; the labeling pattern of medium glycerol versus extracted triacylglycerols was significantly different from that found using natural abundance glucose. Our results indicate that 13C NMR is a useful new method for the real-time monitoring of lipid structure and metabolism in vivo. 相似文献
90.
GLENN YANNIC LOÏC PELLISSIER SYLVAIN DUBEY RODRIGO VEGA PATRICK BASSET STEFANO MAZZOTTI ELENA PECCHIOLI CRISTIANO VERNESI HEIDI C. HAUFFE JEREMY B. SEARLE JACQUES HAUSSER 《Biological journal of the Linnean Society. Linnean Society of London》2012,105(4):864-880
The aim of the present study was to investigate the genetic structure of the Valais shrew (Sorex antinorii) by a combined phylogeographical and landscape genetic approach, and thereby to infer the locations of glacial refugia and establish the influence of geographical barriers. We sequenced part of the mitochondrial cytochrome b (cyt b) gene of 179 individuals of S. antinorii sampled across the entire species' range. Six specimens attributed to S. arunchi were included in the analysis. The phylogeographical pattern was assessed by Bayesian molecular phylogenetic reconstruction, population genetic analyses, and a species distribution modelling (SDM)‐based hindcasting approach. We also used landscape genetics (including isolation‐by‐resistance) to infer the determinants of current intra‐specific genetic structure. The phylogeographical analysis revealed shallow divergence among haplotypes and no clear substructure within S. antinorii. The starlike structure of the median‐joining network is consistent with population expansion from a single refugium, probably located in the Apennines. Long branches observed on the same network also suggest that another refugium may have existed in the north‐eastern part of Italy. This result is consistent with SDM, which also suggests several habitable areas for S. antinorii in the Italian peninsula during the LGM. Therefore S. antinorii appears to have occupied disconnected glacial refugia in the Italian peninsula, supporting previous data for other species showing multiple refugia within southern refugial areas. By coupling genetic analyses and SDM, we were able to infer how past climatic suitability contributed to genetic divergence of populations. The genetic differentiation shown in the present study does not support the specific status of S. arunchi. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 864–880. 相似文献