全文获取类型
收费全文 | 34603篇 |
免费 | 1904篇 |
国内免费 | 3498篇 |
专业分类
林业 | 3978篇 |
农学 | 4418篇 |
基础科学 | 2465篇 |
5349篇 | |
综合类 | 11250篇 |
农作物 | 2263篇 |
水产渔业 | 1458篇 |
畜牧兽医 | 5205篇 |
园艺 | 1383篇 |
植物保护 | 2236篇 |
出版年
2024年 | 108篇 |
2023年 | 397篇 |
2022年 | 944篇 |
2021年 | 1293篇 |
2020年 | 1234篇 |
2019年 | 1166篇 |
2018年 | 852篇 |
2017年 | 1243篇 |
2016年 | 1163篇 |
2015年 | 1562篇 |
2014年 | 1535篇 |
2013年 | 1812篇 |
2012年 | 2308篇 |
2011年 | 2502篇 |
2010年 | 2268篇 |
2009年 | 2158篇 |
2008年 | 2118篇 |
2007年 | 2070篇 |
2006年 | 1890篇 |
2005年 | 1645篇 |
2004年 | 832篇 |
2003年 | 716篇 |
2002年 | 641篇 |
2001年 | 622篇 |
2000年 | 728篇 |
1999年 | 832篇 |
1998年 | 679篇 |
1997年 | 638篇 |
1996年 | 574篇 |
1995年 | 566篇 |
1994年 | 505篇 |
1993年 | 445篇 |
1992年 | 369篇 |
1991年 | 325篇 |
1990年 | 282篇 |
1989年 | 249篇 |
1988年 | 226篇 |
1987年 | 132篇 |
1986年 | 83篇 |
1985年 | 48篇 |
1984年 | 51篇 |
1983年 | 39篇 |
1982年 | 39篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 17篇 |
1974年 | 7篇 |
1965年 | 9篇 |
1964年 | 10篇 |
1956年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
11.
Pengfang Zhu Zhendong Tian Zhichao Pan Xin Feng 《The Journal of Horticultural Science and Biotechnology》2018,93(5):466-473
Anthocyanins are responsible for the colour of many fruits, vegetables, flowers, and coloured-leaved trees. Ornamental kale (Brassica oleracea L. var. acephala DC) is widely cultivated for its colourful inner leaves. To investigate the relationship between the degree of colouration and anthocyanin distribution, content, and composition in ornamental kale, the authors studied the pigment characteristics of five cultivars with different coloured leaves (white, pink, red, purple, and purple-black). Microscopy observation, spectrophotometer, and high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis of fresh inner leaves revealed that pink, red, and purple colourations were associated with high levels of anthocyanin, while purple-black was the result of the combination of anthocyanins and chlorophyll. In the coloured cultivars, anthocyanins were abundant mainly in the first and second cell layers below the epidermis in both the hypocotyls and inner leaves. No anthocyanin was found in the white-leaved phenotype cultivar. Anthocyanin content increased as leaf colour deepened from pink, red, to purple cultivars, which had little chlorophyll and carotenoid. The authors identified eight anthocyanins in the four coloured cultivars, including one non-acylated, four monoacylated, and three diacylated cyanidin glycosides. Cyanidin-3-(sinapoyl)(feruloyl)-diglucoside-5-glucoside was the most abundant anthocyanin in the four coloured cultivars followed by cyanidin-3-(sinapoyl)-diglucoside-5-glucoside. The analysis of anthocyanin accumulation characterisation provides important information on evaluating colouration patterns in coloured plants, and will be helpful for breeding desired leaf colours in ornamental kale. 相似文献
12.
13.
通过目测进行分类的方式很难准确界定矾根品种叶色。为建立一套更为科学的基于叶色表型的矾根品种分类体系,笔者利用色差仪对72个矾根品种共计432个样品的叶色进行测定,对获得的L、a、b 3个色度值进行聚类分析,将72个矾根品种分为褐色系、深绿色系、黄色系、灰绿色系、浅绿色系5类色系。对矾根品种各色系的L、a、b值进行相关性分析,发现叶片正面的L值与a值、a值与b值呈负相关,L值与b值呈正相关,但相关性不明显;叶片背面的L值与a值、a值与b值呈负相关,L值与b值呈显著正相关。从多重比较的结果中可以看出,矾根品种各色系之间的L、a、b色度值差异显著,尤其是各色系间叶正面的颜色差异较大,在矾根品种选育工作中,叶片正面的颜色将作为主要参考。 相似文献
14.
通过对白屈菜低温应答过程的转录组分析发现膜脂不饱和化相关基因的表达在一定过程中发生变化,脂肪酸去饱和酶基因FAD2在随温度的变化趋势为正"V"型,且表达量变化显著。利用NCBI等在线软件对序列进行相关生物学信息分析,并对白屈菜FAD家族成员FAD2基因的完整开放阅读框(ORF)进行克隆,并命名为CmFAD2。选用克隆载体pMD-19-T,转化大肠杆菌DH5α,测序验证序列正确性及完整性。将目的基因与植物表达载体pRI-201-AN连接构建重组DNA pRI-201-AN-Cm FAD2,电击法转化农杆菌LBA4404,利用菌液PCR法验证成功。该基因可作为药用植物抗寒品种创制的候选基因。 相似文献
15.
The M43 domain-containing metalloprotease RcMEP1 in Rhizoctonia cerealis is a pathogenicity factor during the fungus infection to wheat 下载免费PDF全文
Wheat(Triticum aestivum L.) is an important staple crop for global human. The necrotrophic fungus Rhizoctonia cerealis is the causal pathogen of sharp eyespot, a devastating disease of wheat. Herein, we identified RcMEP1, a zinc metalloproteaseencoding gene from R. cerealis genomic sequences, and characterized its pathogenesis function. RcMEP1 expressed at markedly-high levels during R. cerealis infection process to wheat. The predicted protein RcMEP1 comprises of 287 amino acid residues and contains a signal peptide and a M43 metalloprotease domain harboring the active site motif(HEVGHWLGLYH). The assays of Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana leaves indicated that RcMEP1 is an apoplastic elicitor of cell death, and that the predicted signal peptide functions and is required for secretion and cell death-induction. The purified RcMEP1 protein and its M43 domain peptide were individually able to induce plant cell death and H2 O2 accumulation, and to inhibit expression of host chitinases when infiltrated into wheat and N. benthamiana leaves, while the M43 domain-deleting peptide and negative control lacked the capacity. Moreover, compared with the control pretreatment, the purified RcMEP1 protein or its M43-domain peptide resulted in enhanced pathogenesis in the inoculated wheat, whereas the M43 domain-deleting peptide failed. These results suggest that RcMEP1 acted as an important pathogenicity factor during R. cerealis infection to wheat and that its signal peptide and M43 domain are required for the secretion and pathogenesis of RcMEP1. This study provides insights into pathogenesis role of M43 domain-containing metalloproteases during R. cerealis infection to wheat. 相似文献
16.
Effect of dietary calcium or phosphorus deficiency on bone development and related calcium or phosphorus metabolic utilization parameters of broilers from 22 to 42 days of age 下载免费PDF全文
YANG Yun-feng XING Guan-zhong LI su-fen SHAO Yu-xin ZHANG Li-yang LU Lin LUO Xu-gang LIAO Xiu-dong 《农业科学学报》2020,19(11):2775-2783
This experiment was conducted to investigate the effect of dietary calcium (Ca) or phosphorus (P) deficiency on bone development and related Ca or P metabolic utilization parameters of broilers from 22 to 42 days of age based on our previous study, which indicated that dietary Ca or P deficiency impaired the bone development by regulating related Ca or P metabolic utilization parameters of broilers from 1 to 21 days of age. A total of 504 one-day-old Arbor Acres male broilers were randomly assigned to 1 of 4 treatments with 7 replicates in a completely randomized design, and fed the normal control and Ca- or P-deficient diets from 1 to 21 days of age. At 22 days of age, the broilers were further fed the normal control diet (0.90% Ca+0.35% non-phytate P (NPP)), the P-deficient diet (0.90% Ca+0.18% NPP), the Ca-deficient diet (0.30% Ca+0.35% NPP) or the Ca and P-deficient diet (0.30% Ca+0.18% NPP), respectively. The results showed that dietary Ca or P deficiency decreased (P<0.05) tibia bone mineral density (BMD), bone breaking strength (BBS), ash content, tibia ash Ca content and serum P content on days 28 and 42, but increased (P<0.05) tibia alkaline phosphatase (ALP) activity of broilers on day 42 compared with the control group. Furthermore, the broilers fed the P-deficient diet had the lowest (P<0.05) tibia BMD, BBS, ash content, serum P content and the highest (P<0.05) serum Ca content on day 28 compared with those fed the Ca-deficient or Ca and P-deficient diets. The results from the present study indicated that the bone development and related Ca or P metabolic utilization parameters of broilers were the most sensitive to dietary P deficiency, followed by dietary Ca deficiency or Ca and P-deficiency; dietary Ca or P deficiency impaired the bone development possibly by regulating serum Ca and P contents as well as tibia Ca content and ALP activity of broilers from 22 to 42 days of age. 相似文献
17.
浙江省耕地多功能价值时空变化与权衡-协同关系 总被引:19,自引:14,他引:5
耕地多功能价值的时空演变与权衡-协同关系测度对于深化耕地可持续利用和管理具有重要意义。该研究以经济快速发展地区浙江省为例,采用价值量化方法对2000、2010和2015年浙江省耕地多功能进行价值评估并分析其时空变化特征。运用Spearman秩相关系数法、双变量空间自相关模型以及可拓展随机性环境影响评估(StochasticImpactsby Regression on Population,Affluence and Technology,STIRPAT)模型探究耕地多功能之间的权衡-协同关系及影响因素。结果表明:1)2000—2015年浙江省耕地多功能总价值下降,地均耕地多功能价值呈现先下降后上升的趋势。其中气体调节、水源涵养和社会保障功能价值下降明显,食物生产和美学景观功能价值增加;耕地多功能总价值在空间上呈现北高南低的分布格局,2000—2015年大部分县市耕地多功能总价值均有不同程度的下降,西南山地丘陵区耕地多功能总价值有所提升。2)浙江省耕地多功能之间主要表现为协同关系,各项功能之间的协同-权衡关系存在空间异质性;2000—2015年,浙江省耕地多功能协同关系总体减弱,在空间上主要表现为高值协同区减少。3)城镇居民可支配收入和地均农业机械总动力对耕地多功能总价值有负面影响,农村居民可支配收入增加有助于耕地多功能总价值的提升。该研究成果可为科学划定耕地利用与保护区,促进耕地多功能的协同利用和提升耕地资源价值提供科学依据。 相似文献
18.
[目的]由于软枣猕猴桃在初代培养中外植体诱导率极低且快繁效果差,因此进行其组织培养技术体系的研究,以期解决其人工种植的难题.[方法]本研究以软枣猕猴桃展叶为外植体,通过采用不同消毒试剂及消毒处理时间,筛选出最佳的灭菌程序;将不同培养基与不同浓度的KT、2,4-D组合,筛选出最佳的初代培养基配方.[结果]选用展叶为外植体,75%CH3CH2OH处理30 s后以10%NaClO处理20 min,0.1%HgCl2处理15 min后无菌水冲洗3~4次,接至pH=5.8的MS+1 mg·L-1 KT+0.5 mg·L-12,4-D+3%白糖+0.55%琼脂培养基上,置于光照2500 lx、8 h·d-1,26℃下培养8 d后有少部分愈伤组织出现,60 d后平均单芽愈伤组织达0.8 g以上,平均单个愈伤组织长度0.7~1.4 cm,属中块愈伤组织.[结论]以本实验得出的愈伤组织培养方法进行培养,可有效提高诱导率,达到快繁的目的. 相似文献
19.
Xiaomei Guo Lifen Ji Longfei Zhu Liling Song Shinan Liu Qiaolu Zang 《The Journal of Horticultural Science and Biotechnology》2018,93(2):142-149
It was reported that the activity of NiR (nitrite reductase) enzyme encoded by the NiR gene was correlated with the regeneration ability in rice. To testify the function of NiR gene in bamboo, seven bamboo species whose calli had different differentiation rate were chosen to analyse their NiR enzyme activity. The results showed that bamboo NiR enzymatic activity had a certain correlation with the regeneration capacity. A NiR gene named DhNiR from Dendrocalamus hamiltonii with high regeneration capacity was cloned. Sequence analysis revealed that the ORF of DhNiR was 1779bp encoding 592 amino acids. Overexpression of DhNiR in rice reduced the time of shoot differentiation and increased the transformation rate, suggesting that DhNiR might play an important role in the regeneration ability of bamboo, and can be applied in regeneration and gene transformation of bamboo and other plant species. 相似文献
20.