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991.
Aeschynomene virginica is a rare annual plant found in freshwater tidal wetlands of the eastern United States. We hypothesized that standing vegetation and water inundation were two important environmental factors in its population dynamics. To test these hypotheses, we sowed seeds into plots with undisturbed vegetation or plots with all aboveground vegetation removed in 1998 and 1999. Presence/absence of seedlings was noted and seedling survival to reproduction, final size, and seed set were measured throughout both growing seasons. Seedling establishment from germination to the first true leaf stage increased with decreasing water depth. Vegetation removal plots had greater seedling establishment, higher seedling survival, and higher seed set per plant than non-removal plots. In a greenhouse study designed to test the effects of water level on seed germination and seedling establishment, no seedlings established in submerged soils, and seed germination and seedling establishment were lower in waterlogged soil than in wet soil. Physical stress associated with deeper water likely limits the distribution of A. virginica to higher elevations, where seeds that colonize patches with low vegetative cover are more likely to produce reproductive adults that produce more seeds relative to patches with established vegetation. A. virginica appears to be a fugitive species specializing on open habitat patches in tidal wetlands. This species may be dependent on disturbances for population establishment and maintenance. 相似文献
992.
Ovules and Seeds in Subfamily Phyllanthoideae (Euphorbiaceae): Structure and Systematic Implications
Lingelsheimia ) are distinct from the rest of the subfamily in having a thick inner integument (over six cells thick), an exotegmen composed
of cuboidal cells (type II), and vascular bundles in the outer integument and, as molecular evidence also suggests, should
be transferred to a separate family Putranjivaceae. Hymenocardieae (Didymocistus and Hymenocardia), whose positions have been controversial, are monophyletic in sharing endotestal seeds with a collapsed exotegmen which
is unknown elsewhere in Euphorbiaceae. The genera seem to require separation from the Euphorbiaceae. In addition, a morphological
heterogeneity of the two large genera Cleistanthus and Phyllanthus, as well as of tribe Antidesmeae subtribe Scepinae were also discussed.
Received 20 October 2000/ Accepted in revised form 14 January 2001 相似文献
993.
To determine the breeding system of Lycium cestroides,several treatments were performed: self-, cross-, and geitonogamous pollinations, autonomous self-pollination, and a control
(flowers exposed to natural pollinators). Production and quality of fruits and seeds as well as pollen tube growth were evaluated
for each treatment. Experimental pollinations indicate that L. cestroides is self-incompatible since fruits were obtained only under cross-, and open-pollination treatments. However, in self- and
geitonogamous hand pollinations, as well as in autonomous self-pollination, pollen tubes developed successfully and reached
the ovules. The speed of pollen tube growth did not differ significantly among the different hand-pollinated flowers (cross-,
self-, and geitonogamous). These facts indicate the presence of an ovarian self-incompatibility system. Significant differences
were observed in fruit set, fruit size, and seed number per fruit between cross-pollinated flowers and open pollination (control).
These results could be explained in terms of quantity and quality of pollination in each case.
Received: 2 November 2000 / Revision accepted: 26 January 2001 相似文献
994.
鄂北高贵山种子植物区系研究 总被引:1,自引:0,他引:1
通过对高贵山地区143科504属954种种子植物的统计分析,显示了该植物区系成分的丰富性,南北植物融合性,温带成分的主体性和原始,孑遗植物以及珍稀濒危植物的集中性,说明该植物区系在华东植物区系向华中植物区系过渡中起着重要的作用。 相似文献
995.
The effect of phenols on respiratory enzymes in seed germination 总被引:1,自引:0,他引:1
Low molecular weight phenolic compounds were identified in two soilswith different vegetative cover, Fagus sylvatica, L. andPinus laricio, Poiret, spp. calabrica, and were tested atdifferent concentrations on seed germination of Pinuslaricio, and on respiratory and oxidative pentose phosphate pathwayenzymes involved in the first steps of seed germination. The data obtained showthat there are marked differences in the phenolic acid composition of the twoinvestigated soils. All the phenolic compounds bioassayed inhibited seedgermination and those extracted from Pinus laricio soilwere particularly inhibitory. We also found that the non-germination of seedsisstrongly correlated to the inhibition of the activities of enzymes ofglycolysisand the oxidative pentose phosphate pathway. 相似文献
996.
Soil physical conditions in a New York orchard after eight years under different groundcover management systems 总被引:3,自引:0,他引:3
An experiment was conducted near Ithaca, New York, to compare orchard soil and groundcover management systems (GMSs) in a silty clay loam soil (mixed, mesic, Glosaquic Hapludalf). Three replications of four GMS treatments were randomly assigned to 12 plots and maintained since 1992 in 2 m-wide strips within tree rows: (1) Sod: Red fescue (Festuca rubra) turfgrass mowed biweekly; (2) Post-HBS: Post-emergence applications of glyphosate herbicide in May and July annually; (3) Pre-HBS: Pre-emergence applications of paraquat, diuron and norflurazon herbicides each May; and (4) Mulch: A 15-cm depth layer of shredded hardwood bark mulch, renewed triennially. After eight years of continuous treatments, we compared soil physical conditions and hydraulic properties in these GMSs. Bulk density was lower and soil porosity greater under Mulch than other GMSs. Infiltration was more rapid under Mulch than other GMSs, and under Post-HBS than Sod. Saturated hydraulic conductivity ranged from 6 × 10–4 m.s–1under Sod to 12 × 10–4 m.s–1 under Mulch plots, and was equivalent in Sod and Pre-HBS, lower in Sod than Post-HBS or Mulch treatments, higher in Post-HBS than Pre-HBS, and higher in Mulch than all other GMSs. Volumetric soil water content at field capacity ranged from 0.47 under Mulch to 0.40 under Sod, and was not significantly different among GMSs between 0.99 and 39.22 kPa of pressure. GMS treatments and related management practices at this orchard had substantially different long-term effects on soil physical conditions. Compaction and reduced infiltration in Sod compared with other GMSs were attributed to tractor wheel traffic during mowing. Mulch treatments improved soil conditions relative to other GMSs. Greater infiltration rates and hydraulic conductivity under Post-HBS compared with Pre-HBS suggest relative advantages of post-emergence herbicides. 相似文献
997.
1992-1995年对四个不同类型苹果园进行了系统调查,结果表明引入夏至草、泥胡菜等有益杂草并与树行间种植的紫花苜蓿搭配的生草园,捕食性天敌发生量大,种群稳定,发生高峰期较免耕园、清耕园提前7d左右;害虫发生量低,种群数量变化平稳,无突增现象,生草园在未施用任何杀虫、杀螨剂的情况下,树冠上蚜虫、叶螨和潜叶蛾的平均虫口密度均低于免耕园、清耕稀植园和密植园。生草园寄生性天敌的数量亦明显增加,金纹细蛾的寄生率高达62.7%,分别是免耕园、清耕稀植和密植园的1.34倍、16.9倍和17.9倍。果园植被多样化可使地面植被上的天敌数量逐年成倍提高,生草第3年捕食性天敌的数量是生草当年的12.5倍,树冠上天敌量亦明显增加,益害比大大提高,生草第2年树冠上最大蝽螨比为1∶14.4,与原先油菜与紫花苜蓿搭配生草5年的效果相近。除当年生草果园(1992年)早期施用1次杀螨剂—螨克外,1993、1994年均未施用任何杀虫、杀螨剂,通过天敌的自然控制作用,有效地控制果树害螨、蚜虫和金纹细蛾等次生性害虫的为害。 相似文献
998.
999.
苦丁茶良种采穗圃营建技术 总被引:3,自引:2,他引:1
将苦丁茶优良单株的无性系后代应用于栽培,根据“适地适树”原则选择采穗圃圃地,并对部分环境因子加以改良,利用修剪、施肥等综合技术措施,对采穗圃进行抚育管理。采穗圃建立2年后,植株高达952cm、基径24cm、冠幅1079cm×1172cm、分枝61条,表现出了较快的生长速度和较强的适应性 相似文献
1000.
热分析是在程序控制温度下自动连续跟踪物质的物理性质与温度关系的一类技术。尤其是差热分析和热重法与其他手段联合,可用于化合物稳定性、分解机理和相转变等方面的研究。由于种子是一个复杂化合物的有机体,我们期望发现各不同种子化合物之间在成份上和组成方式上的共性和差异性,从热化学的角度对木本植物进行热化学分类。我们选用针叶类两个科(松科、杉木科)的种子进行了DTA、TG、550℃裂解气相色谱分析;300℃逸出成份分析,发现松科种子DTA图上在240±5℃有一个共同的吸热峰,而杉木则出现在320±5℃。TG曲线同科的不同种之间非常相似,逸出成份分析和裂解气相色谱分析同科的不同种之间也具共同特征,且又显示出一定的差异性。这种分类方法是可靠的,且可为树木(或植物)分类学提供更有价值的信息。 相似文献