全文获取类型
收费全文 | 20253篇 |
免费 | 345篇 |
国内免费 | 251篇 |
专业分类
林业 | 999篇 |
农学 | 409篇 |
基础科学 | 255篇 |
1890篇 | |
综合类 | 7247篇 |
农作物 | 671篇 |
水产渔业 | 358篇 |
畜牧兽医 | 7812篇 |
园艺 | 673篇 |
植物保护 | 535篇 |
出版年
2023年 | 113篇 |
2022年 | 133篇 |
2021年 | 128篇 |
2020年 | 120篇 |
2019年 | 163篇 |
2018年 | 165篇 |
2017年 | 78篇 |
2016年 | 145篇 |
2015年 | 141篇 |
2014年 | 316篇 |
2013年 | 216篇 |
2012年 | 1358篇 |
2011年 | 1560篇 |
2010年 | 506篇 |
2009年 | 396篇 |
2008年 | 1299篇 |
2007年 | 1271篇 |
2006年 | 1273篇 |
2005年 | 1238篇 |
2004年 | 1153篇 |
2003年 | 1065篇 |
2002年 | 1011篇 |
2001年 | 696篇 |
2000年 | 801篇 |
1999年 | 413篇 |
1998年 | 217篇 |
1997年 | 231篇 |
1996年 | 184篇 |
1995年 | 200篇 |
1994年 | 254篇 |
1993年 | 247篇 |
1992年 | 256篇 |
1991年 | 254篇 |
1990年 | 212篇 |
1989年 | 215篇 |
1988年 | 196篇 |
1987年 | 244篇 |
1986年 | 187篇 |
1985年 | 186篇 |
1984年 | 178篇 |
1983年 | 132篇 |
1982年 | 133篇 |
1981年 | 103篇 |
1980年 | 64篇 |
1978年 | 90篇 |
1977年 | 64篇 |
1976年 | 51篇 |
1974年 | 75篇 |
1973年 | 78篇 |
1972年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
在丽水市滩圩经过几年的引种雷竹试验,现已初具规模,生长良好,据此提出今后在滩圩引种发展雷竹的成功经验,应注意做好造林地、造林季节的选择,改良土壤,做好抗旱防涝等措施。 相似文献
902.
Citrus response to salinity: growth and nutrient uptake 总被引:1,自引:0,他引:1
To determine the effects of salinity on relative growth rate (RGR), net assimilation rate on a leaf weight basis (NAR(w)), leaf weight ratio (LWR), and nutrient uptake and utilization of citrus, we grew four citrus rootstocks (sour orange, Cleopatra mandarin, Carrizo citrange and Citrus macrophylla) in nutrient solutions containing 0, 10, 20, 40 or 80 mM NaCl for 20, 40 or 60 days. For each element analyzed, specific absorption rate (SAR) and specific utilization rate on a leaf basis (SUR(L)) were calculated for the period between Days 40 and 60. Relative growth rate decreased with time for all treatments and rootstocks. Salt treatment significantly reduced both RGR and NAR(w), whereas LWR showed no definite trend. In all rootstocks, NAR(w), but not LWR, was significantly correlated with RGR, indicating that NAR(w) was an important factor underlying the salinity-induced differences in RGR among the citrus rootstocks. At Day 60, salinity had a significant effect on leaf concentrations of Cl, Na, K, Ca, Mg, P, Fe, Mn and Zn and on the SAR and SUR(L) of most elements. In general, RGR was correlated with SAR and SUR(L). Therefore, in addition to osmotic effects and the inhibitory effects of high concentrations of Cl(-) and Na(+), an imbalance of essential nutrients may also contribute to the reduction in plant growth under saline conditions. 相似文献
903.
Small Shorea stenoptera Burck. (Dipterocarpaceae) trees of reproductive age growing in an arboretum in west Java were studied to determine the pattern of vegetative shoot development, the time and method of floral initiation and the effect of paclobutrazol on floral enhancement. Vegetative buds were enclosed by two stipules between which was a leaf primordium, a small axillary vegetative bud and another pair of stipules. This sequence was reiterated five to seven times before the vegetative apex was visible. At the time of floral initiation, axillary buds developed into floral spikes and compound inflorescences formed at the end of drooping branches. A compound inflorescence might bear many floral spikes and each floral spike bore many flowers. The compound inflorescence was a modification of the reiterative developmental pattern observed in vegetative shoots. The time of floral initiation began in late June or early July and continued until about November. Floral enhancement using paclobutrazol as a soil drench was attempted in mid-July, but this was later found to be after the onset of floral initiation, and the treatment failed to enhance flowering; however, it appeared to enhance the rate of floral and fruit development. The similarity in vegetative bud development among dipterocarp genera suggests that the time of floral initiation may be easily determined in many species based on simple dissection techniques. 相似文献
904.
We studied assimilation, stomatal conductance and growth of Mangifera indica L. saplings during long-term exposure to a CO(2)-enriched atmosphere in the seasonally wet-dry tropics of northern Australia. Grafted saplings of M. indica were planted in the ground in four air-conditioned, sunlit, plastic-covered chambers and exposed to CO(2) at the ambient or an elevated (700 micro mol mol(-1)) concentration for 28 months. Light-saturating assimilation (A(max)), stomatal conductance (g(s)), apparent quantum yield (phi), biomass and leaf area were measured periodically. After 28 months, the CO(2) treatments were changed in all four chambers from ambient to the elevated concentration or vice versa, and A(max) and g(s) were remeasured during a two-week exposure to the new regime. Throughout the 28-month period of exposure, A(max) and apparent quantum yield of leaves in the elevated CO(2) treatment were enhanced, whereas stomatal conductance and stomatal density of leaves were reduced. The relative impacts of atmospheric CO(2) enrichment on assimilation and stomatal conductance were significantly larger in the dry season than in the wet season. Total tree biomass was substantially increased in response to atmospheric CO(2) enrichment throughout the experimental period, but total canopy area did not differ between CO(2) treatments at either the first or the last harvest. During the two-week period following the change in CO(2) concentration, A(max) of plants grown in ambient air but measured in CO(2)-enriched air was significantly larger than that of trees grown and measured in CO(2)-enriched air. There was no difference in A(max) between trees grown and measured in ambient air compared to trees grown in CO(2)-enriched air but measured in ambient air. No evidence of down-regulation of assimilation in response to atmospheric CO(2) enrichment was observed when rates of assimilation were compared at a common intercellular CO(2) concentration. Reduced stomatal conductance in response to atmospheric CO(2) enrichment was attributed to a decline in both stomatal aperture and stomatal density. 相似文献
905.
木麻黄苗期生长特性和生物产量的研究 总被引:1,自引:0,他引:1
通过木麻黄实生苗年生长节律的研究,划分了苗木的生长时期,确定了影响苗木高、径生长的主导因子。同时探讨了木麻黄1年生苗的生物产量积累和分配特点,查明了密度对苗木生物产量的影响,提出了木麻黄适宜的育苗密度和苗木生物量估测模型。 相似文献
906.
山核桃刻蚜的形态特征,发生规律和防治方法 总被引:1,自引:0,他引:1
山核桃刻蚜的形态特征、发生规律和防治方法胡一民,叶安定,胡华英(安徽省林科所,合肥,230031)(安徽省歙县林业局)山核桃是良好的木本食用油料时,也是近年来深受人们欢迎的芳香干果,安徽省的宁国、歉县、绩溪及浙江临安、昌化、淳安等大量种植。然而,最近... 相似文献
907.
908.
909.
910.
巨尾桉去皮主干含水率分布规律的探讨 总被引:1,自引:0,他引:1
通过对巨尾桉去皮主干含水率的测定和分析表明:其含水率的分布是随着树干上的位置升高而呈直线上升,树干3H/10处的含水率最具代表性,1.3m与H/2处的含水率的均值可为树干含水率平均值 相似文献