全文获取类型
收费全文 | 3317篇 |
免费 | 196篇 |
国内免费 | 423篇 |
专业分类
林业 | 402篇 |
农学 | 357篇 |
基础科学 | 147篇 |
373篇 | |
综合类 | 1490篇 |
农作物 | 216篇 |
水产渔业 | 232篇 |
畜牧兽医 | 262篇 |
园艺 | 269篇 |
植物保护 | 188篇 |
出版年
2024年 | 26篇 |
2023年 | 87篇 |
2022年 | 127篇 |
2021年 | 146篇 |
2020年 | 143篇 |
2019年 | 174篇 |
2018年 | 110篇 |
2017年 | 148篇 |
2016年 | 197篇 |
2015年 | 160篇 |
2014年 | 184篇 |
2013年 | 242篇 |
2012年 | 256篇 |
2011年 | 253篇 |
2010年 | 194篇 |
2009年 | 179篇 |
2008年 | 173篇 |
2007年 | 175篇 |
2006年 | 130篇 |
2005年 | 117篇 |
2004年 | 89篇 |
2003年 | 88篇 |
2002年 | 78篇 |
2001年 | 64篇 |
2000年 | 71篇 |
1999年 | 38篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 30篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 29篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有3936条查询结果,搜索用时 15 毫秒
1.
Time course of grain filling pattern in two rice (Oryza sativa L.) cultivars, grown under normal and low light intensities, was studied. The number of spikelets, partially filled grains and high density grains were monitored at a 5 day interval during grain filling period from uniform panicles tagged at anthesis. The low light tolerant cultivar Swarnaprabha had more high density grains and less partially filled grains throughout the grain filling period and at harvest compared to cultivar Ratna under both normal and low light intensities. Further, the opening of spikelets in two flushes in Swarnaprabha seemed to result in a more efficient resource allocation and hence better yield as compared to Ratna, in which the opening of spikelets was in a single flush on day 10. 相似文献
2.
3.
Influence of death struggle on the structural changes in chub mackerel muscle during chilled storage
Masashi Ando Masao Joka Satoshi Mochizuki Koh-Ichi Satoh Yasuyuki Tsukamasa Yasuo Makinodan 《Fisheries Science》2001,67(4):744-751
ABSTRACT: Chub mackerel (34–35 cm, approximately 500 g), which were caught by fishing with a rod and line at the Bungo Channel, Oita prefecture, were rested overnight in a fish preserve and either killed by decapitation (control group) or allowed to struggle in air for 30 min (struggled group). Muscle samples were excised every 4 h, and measurements on breaking strength and histological observations were done for both groups. The breaking strength of muscle in the control group was significantly higher than that in the struggled group, whereby a decrease in breaking strength was delayed for 12 h compared to the struggled group. Light microscopy showed space extension among muscle cells in association with a decrease in breaking strength. Especially in the struggled group, the extended area was larger and the difference in area was significant at the time when breaking strength showed a significant difference. Using electron microscopy, the extended area showed cut and/or disappeared collagen fibrils. From these results, it was demonstrated that struggling to death promoted the degradation of collagen fibrils and the weakening of connective tissue and, resultantly, led to the faster softening of muscle of chub mackerel. 相似文献
4.
Kamonpan Awaiwanont Wisnu Gunarso Munefumi Sameshima Seiichi Hayashi Gunzo Kawamura 《Fisheries Science》2001,67(5):804-810
ABSTRACT: Morphology of the photoreceptor cells and tapetum of the Japanese anchovy Engraulis japonicus was studied by histologically and by chemical analysis. The Japanese anchovy has a duplex retina. The cones form parallel rows consisting of alternately placed long cones and bifid cones. Both types of cones are intimately associated and form triple units that are regularly spaced along the row of cones. The rods are grouped and stacked. This fish has a retinal tapetum lucidum composed of guanine and hypoxanthine. Three structures of the tapetum lucidum were recognized: platelet, diamond and rod types. Photomechanical changes include movements of the photoreceptor cells and the retinal tapetum. The retina of the Japanese anchovy is thought to be highly sensitive and well adapted to a dim light environment. 相似文献
5.
徐海祥 《湖南农业大学学报(自然科学版)》1993,20(2)
In this paper, the author proved the partial regularity of the generalized solutions of the super critical growth elliptic system. Furthermore, the everywhere regularity of generalized solutions of three special systems are obtained. 相似文献
6.
7.
为探究淡干海参泡发工艺,以烟台淡干海参为原料,通过正交试验得到最优工艺条件为:121 ℃、0.12 MPa高温高压处理20 min,全程使用蒸馏水,泡发温度4 ℃,泡发时间48 h,采用该工艺泡发的海参质量和长度分别为泡发前干海参的14.5倍和2.7倍,复水比为9.2,其硬度、弹性、适口性、持水力及营养价值均高于市面上常压煮制常温泡发的海参。该研究结果为科学、方便地食用和推广淡干海参提供了理论依据。 相似文献
8.
以3个不同低温弱光耐性甜椒(Capsicum annuum L.)材料为试材,研究其在不同低温弱光下幼苗生长形态与生理指标的变化差异及其成株期产量水平的差异状况。结果表明:昼夜温度15℃/5℃、光照强度4 000 lx、光照8 h、处理时间15 d是筛选甜椒耐低温弱光材料的适宜选择压力,开展度变化量是最佳的形态鉴定指标,茎粗、株高的变化量可作形态鉴定的参考指标。在此条件下,开展度以及茎粗、株高变化量的大小与材料的低温弱光耐受性的表现相一致。耐低温弱光材料茎的增粗与株的增高明显、叶片萎垂现象轻微,生长受到的抑制程度较轻,且与不耐低温弱光材料在开展度变化指标上的差异显著,易于正确地鉴定出低温弱光耐性材料。 相似文献
9.
小麦植株感染条锈病后叶片花青素含量会发生明显变化。为了在地块尺度上利用冬小麦花青素值实现条锈病害的直观、快速监测,通过监测叶片花青素含量评估小麦条锈病严重程度,2021年获取感染条锈病的小麦田块的无人机RGB影像和采集地面病害区域的花青素含量数据,利用影像提取采样点感兴趣区的光谱特征参数和基于灰度共生矩阵的纹理特征参数,采用连续投影算法(SPA)结合相关性分析优选特征参数,分别采用单一光谱特征参数和组合参数,结合主成分回归(PCR)、拉索回归(LR)、随机森林回归(RFR)、梯度提升回归(GBR)和误差反向传播神经网络(BPNN)等方法构建了小麦花青素含量估算模型,并利用最优模型反演了田块的花青素含量。结果表明,图像光谱特征结合纹理特征后,花青素估算模型的R2增大,RMSE减小,模型精度显著提升。基于组合特征参数构建的随机森林模型精度最高,验证集R2、RMSE和MAE分别为0.801、0.026、0.021。该模型具有良好的花青素含量估算能力,得到的花青素值分布图与条锈病的空间分布具有一致性,能够定量化、可视化地反映病害严重程度。 相似文献
10.
嫩绿粘虫板对水稻稻飞虱成虫诱集监测效果 总被引:1,自引:0,他引:1
本文采用嫩绿粘虫板和灯光诱集2种方法对水稻稻飞虱成虫进行同地对比诱集监测。结果表明, 嫩绿粘虫板对3种飞虱总体、白背飞虱和褐飞虱诱集量与测报灯之间无显著差异, 其诱虫趋势与测报灯诱虫趋势基本同步或趋于一致。嫩绿粘虫板对水稻生长前中期白背飞虱迁入峰的监测优于测报灯, 表现为迁入高峰期诱虫量多和峰形明显。嫩绿粘虫板对灰飞虱诱虫量与测报灯诱虫量有明显差异, 诱虫峰次少于测报灯, 监测效果次于测报灯。气象因子、非靶标昆虫等对嫩绿粘虫板诱测无不利影响。运用嫩绿粘虫板可在非灯诱区监测点监测迁飞性白背飞虱。 相似文献