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   1188篇
  免费   64篇
  国内免费   38篇
  2023年   8篇
  2022年   17篇
  2021年   14篇
  2020年   21篇
  2019年   13篇
  2018年   21篇
  2017年   22篇
  2016年   27篇
  2015年   21篇
  2014年   25篇
  2013年   81篇
  2012年   25篇
  2011年   30篇
  2010年   25篇
  2009年   35篇
  2008年   35篇
  2007年   46篇
  2006年   52篇
  2005年   36篇
  2004年   33篇
  2003年   35篇
  2002年   50篇
  2001年   33篇
  2000年   36篇
  1999年   62篇
  1998年   71篇
  1997年   62篇
  1996年   38篇
  1995年   30篇
  1994年   35篇
  1993年   27篇
  1992年   33篇
  1991年   32篇
  1990年   25篇
  1989年   17篇
  1988年   21篇
  1987年   13篇
  1986年   10篇
  1985年   10篇
  1984年   19篇
  1983年   10篇
  1982年   8篇
  1981年   8篇
  1980年   6篇
  1979年   3篇
  1978年   4篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1973年   1篇
排序方式: 共有1290条查询结果,搜索用时 343 毫秒
71.
松鼠几项生态生理指标季节变化的比较   总被引:6,自引:0,他引:6  
李俊生  马建章  宋延龄  曾治高 《生态学报》2002,22(11):1995-2000
研究了分布于我国大、小兴安岭林区松鼠体重、身体热值、脂肪含量、灰分含量以及水分含量的季节变化。松鼠体重存在明显的季节性变化和性别差异 ,春季 ,雄性松鼠体重明显小于雌性个体 ,而其它季节 ,雄性大于雌性。冬季体重最低(3 3 1 .9~ 3 45 .1 g) ,秋季体重最高 (3 78.1~ 3 89.9g) ,体重降低了 9.41 %~ 1 4.0 7%。大、小兴安岭松鼠身体热值、脂肪含量和水分含量季节变动范围为 6.2 71~ 8.60 9k J/g和 6.891~ 8.41 3 k J/g,8.81 %~ 2 1 .3 7%和 9.47%~ 2 2 .0 1 % ,67.1 2 %~73 .3 8%和 66.3 5 %~ 71 .73 % ;灰分含量不存在季节差异 ,大、小兴安岭年平均值分别为 1 2 .0 4%± 1 .1 7%和 1 1 .2 7%±2 .0 7%。环境温度、食物资源和繁殖状况是影响东北松鼠体重和身体组成季节性差异的主要因素  相似文献   
72.
The effects of salinity on the morphogenesis of various organs of kidney bean (Phaseolus vulgaris L.) and eggplant (Solanum melongena L.) plants grown in nosterile culture and of explants from these organs grown in vitro were studied. Salt stress was produced by adding NaCl (0.5 and 1.0%) to water or the Murashige and Skoog nutrient medium. Salt stress suppressed rhizogenesis, particularly profoundly in the salt-sensitive beans. Callus cultures obtained from different organs differed in their salt tolerance, which was evaluated from the callus growth. Under salinity conditions, homologous structures of the two crops differed markedly in survival and regeneration. Different organs and corresponding explants of one and the same plant differed in the threshold sensitivity to salinity, which indicates the organ-specificity of salt resistance.  相似文献   
73.
利用RAPD标记鉴定甜菜无融合生殖的同一性   总被引:2,自引:2,他引:0  
目的:对具有无融合生殖特性的带有白花甜菜染色体的栽培甜菜单体附加系M14三代材料进行同一性鉴定。方法:通过RAPD随机扩增技术对M14三代材料的基因组DNA的扩增多态性进行分析。结果表明,M141998年、1999年、2000年三代材料的RAPD位点高度一致,遗传相似度S=1,遗传距离D=0,从而表明M14三代个体完全一样。结论:初步确定M14材料无融合生殖基因在其后代中是稳定传递的。  相似文献   
74.
Using enzymic digestion with pectinase, controlled Smith degradation and NMR-spectroscopy, some structural features of the hairy region of pectic polysaccharide termed silenan SV from the aerial part of campion Silene vulgaris (Moench) Garke (Oberna behen (L.) Ikonn) were elucidated.

Silenan was subjected to enzymic digestion with pectinase to furnish the polysaccharide fraction (SVP). The contained residues of -galacturonic acid (43%), arabinose, galactose and rhamnose as main constituents. The backbone of the hairy region of silenan was found to consist of -1,4-galactopyranosyl uronic acid and 2-O-glycosylated rhamnopyranose residues. The side chains contained linear regions of residues of -1,5-linked arabinofuranose and β-1,3-, β-1,4-linked galactopyranose. Silenan SV and its fragment SVP were subjected to Smith degradation to give fractions SVS and SVPS. These contain the residues of terminal and 2-substituted -arabinofuranose as well as residues of terminal, 3-, and 2,3-substituted β-galactopyranose. In addition, NMR-spectral data confirmed that the residues of -rhamnopyranose 2-O-glycosylated with the residues of -1,4-galactopyranosyl uronic acid of the backbone occurred in the core of SVPS and, therefore, in the backbone of silenan SV.

On the basis of data obtained, the hairy regions of silenan were suggested to contain mainly the linear chains of β-1,3-, β-1,4-galactopyranan and -1,5-arabinofuranan. The chains of -1,5-linked arabinofuranose, β-1,3- and β-1,4-linked galactopyranose were shown to be involved in the side chains of the hairy region having branching points at 2,3-substituted β-galactopyranose residues.  相似文献   

75.
While studying the behavior of profilin from Phaseolus vulgaris seeds under native conditions, a high molecular weight species suggesting a complex of profilin and associated proteins was observed by Western immunoblotting. This putative complex was also observed when enzyme-linked secondary antibodies alone were used, and this apparently resulted from antibody association, through its glycosyl moieties, with the endogenous carbohydrate-binding activity from the seed extracts. This endogenous activity corresponded to that of purified phytohemagglutinin (PHA). In addition, the P. vulgaris lectin activity was very stable and was observed when the extracts were pretreated with varying concentrations of sodium dodecyl sulfate, Triton X-100, urea and β-mercaptoethanol, or when membrane blots were boiled in water before incubation with antibody. The activity was abolished only if the membrane was boiled in 1% sodium dodecyl sulfate. This finding could also be useful to implement assays for carbohydrate-binding activity from cell or tissue extracts using different visualizable reagents bearing particular glycosyl moieties.  相似文献   
76.
Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO2, due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host–pathogen trophic relationships.  相似文献   
77.
Hymenopterans are an important model for studying the evolution of cooperation in animal societies. Here, we characterize 19 microsatellite loci, isolated from the common wasp Vespula vulgaris, that can be used to study genetic variation in three genera (seven species) within the Vespidae. The number of alleles in V. vulgaris was moderate, varying from 2 to 14, with expected heterozygosity ranging between 0.04 and 0.93. Eleven loci amplified DNA in V. austriaca and Dolichovespula sylvestris, nine in V. germanica, eight in Vespa crabro and V. rufa, seven in D. media and only five loci could be used for D. norwegica.  相似文献   
78.
Sea beets grown from seeds collected in 1989 and 2009 along the coasts of France and adjacent regions were compared for flowering date under controlled conditions. Seeds from both collection years were sown simultaneously and cultivated under the same glasshouse conditions. Date of flowering onset and year of first flowering were recorded. There was an overall northward shift in flowering time of about 0.35° latitude (i.e. 39 km) over the 20‐year period. The southern portion of the latitudinal gradient – that is, from 44.7°N to 47.28°N – flowered significantly later by a mean of 1.78 days, equivalent to a 43.2‐km northward shift of phenotypes. In the northern latitudes between 48.6°N and 52°N, flowering date was significantly earlier by a mean of 4.04 days, corresponding to a mean northward shift of 104.9 km, and this shift was apparently due to a diminished requirement of exposure to cold temperatures (i.e. vernalization), for which we found direct and indirect evidence. As all plants were grown from seed under identical conditions, we conclude that genetic changes occurred in the sensitivity to environmental cues that mediate the onset of flowering in both the northern and the southern latitudes of the gradient. Microevolution and gene flow may have contributed to this change. There was no significant change in the frequency of plants that flowered without vernalization. The lack of vernalization requirement may be associated with environmental instability rather than with climate conditions.  相似文献   
79.
微藻是可广泛用于健康食品及水产养殖的饵料,同时,微藻细胞内积累的油脂可作为可再生生物燃料,因此微藻的生长和代谢受到广泛关注。温度和pH对微藻的生物量积累有很大影响,考察不同温度和pH条件下微藻细胞的生长有助于寻找最佳的条件进行微藻的培养。自絮凝小球藻JSC-7(Chlorella vulgaris JSC-7)可实现自沉降采收,有利于降低微藻生产成本,优化其生长条件对更好地利用该微藻具有重要意义。考察了温度(22∽40℃)及pH(6.0∽10.0)对其细胞生长、叶绿素含量和油脂产量的影响。在所选取的温度及pH范围内,JSC-7细胞均可生长,显示该藻种可以适应广泛的温度和pH条件。适合细胞生长的温度依次为31℃〉28℃〉35℃〉25℃,pH依次为7.0〉8.0〉6.0。pH 8.0时生物量和油脂的积累量最多,说明该藻株在弱碱条件下更适合生长和产油。当温度为31℃、pH为7.0时,可获得最高的生长量(OD690=0.941)、叶绿素含量(19 mg/L)及油脂产量(39.07%/克干重)。  相似文献   
80.
目的:观察中药面膜联合红蓝光治疗仪治疗寻常痤疮临床疗效及安全性。方法:66例寻常痤疮患者按就诊先后顺序随机分为3组:对照组、面膜组、联合组,治疗4周后进行疗效评估,治疗结束后4周随访复发情况。结果:联合组及面膜组疗效高于对照组(P〈0.05)。结论:中药面膜联合红蓝光治疗仪治疗寻常痤疮疗效好,不良反应少,优于单用疗法,痤疮后期维持治疗同样值得重视。  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