全文获取类型
收费全文 | 17756篇 |
免费 | 1123篇 |
国内免费 | 1665篇 |
专业分类
林业 | 1344篇 |
农学 | 1216篇 |
基础科学 | 1061篇 |
1952篇 | |
综合类 | 8273篇 |
农作物 | 1237篇 |
水产渔业 | 715篇 |
畜牧兽医 | 2724篇 |
园艺 | 1197篇 |
植物保护 | 825篇 |
出版年
2024年 | 112篇 |
2023年 | 346篇 |
2022年 | 764篇 |
2021年 | 872篇 |
2020年 | 820篇 |
2019年 | 733篇 |
2018年 | 516篇 |
2017年 | 871篇 |
2016年 | 531篇 |
2015年 | 950篇 |
2014年 | 940篇 |
2013年 | 1050篇 |
2012年 | 1415篇 |
2011年 | 1481篇 |
2010年 | 1426篇 |
2009年 | 1289篇 |
2008年 | 1298篇 |
2007年 | 1158篇 |
2006年 | 1015篇 |
2005年 | 850篇 |
2004年 | 469篇 |
2003年 | 297篇 |
2002年 | 314篇 |
2001年 | 272篇 |
2000年 | 272篇 |
1999年 | 129篇 |
1998年 | 64篇 |
1997年 | 46篇 |
1996年 | 31篇 |
1995年 | 38篇 |
1994年 | 34篇 |
1993年 | 39篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1965年 | 1篇 |
1962年 | 4篇 |
1957年 | 1篇 |
1956年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 306 毫秒
241.
242.
通过一些查新的实例.讨论了在查新实践中如何应用新颖性的判断原则,对查新课题的新颖性进行判断,介绍了农业科技查新中新颖性的判断方法。 相似文献
243.
先进制造技术的发展趋势及其应用 总被引:1,自引:0,他引:1
分析了我国先进制造技术的内涵和特点,阐述了先进机械制造技术的发展趋势及其在我国的应用。 相似文献
244.
果树生产是宁化县农业经济的重要组成部分,是农民增收致富的主要途径。全县果树栽培面积5366hm^2,年产量3.6万t,产值3800万元。其中,梨、桃等落叶果树面积占92.7%,柑橘、杨梅、枇杷等常绿果树面积仅占7.3%。 相似文献
245.
AIM: To investigate the effect of sodium nitrite (SN) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and its underlying mechanism in mice. METHODS: All male Institute of Cancer Research (ICR) mice were randomly divided into five groups: Control group; LPS group; and SN 4.8 nmol/L, SN 48 nmol/L, SN 480 nmol/L (ip) groups. Lung wet weight/dry weight (W/D) ratio and permeability were detected. Neutrophil infiltration in bronchoalveolar lavage fluid (BALF) was measured by cel1 counting and morphological changes in lung tissues were assayed by hematoxylin-eosin staining. The 1evels of interleukin-10 (IL-10) and tumor necrosis factor-α (TNF-α) in lung were detected. Nitric oxide (NO) level and nitric oxide synthase (NOS) activity in lung were measured according to the specification. RESULTS: Compared to lung in LPS-induced ALI mice, at doses of 4.8 nmol/L and 48 nmol/L, not 480 nmol/L, SN markedly decreased the lung W/D ratio, total leukocyte number and neutrophil percentage in the BALF, lung permeability, and TNF-α/IL-10 ratio, in lung. SN at dose of 480 nmol/L markedly increased the lung NO level compared to control group. In addition, SN decreased the total NOS and inducible NOS (iNOS) activities compared to LPS-induced ALI mice. CONCLUSION: These results indicate that the protective effect of SN against LPS-induced ALI in mice is associated with the low dose SN-induced NO, as well as the subsequent decrease in iNOS activity and TNF-α/IL-10 ratio. 相似文献
246.
XIAO Gang ZHANG Zhen-qian LIU Rui-yang YIN Chang-fa WU Xian-meng TAN Tai-long GUAN Chun-yun 《中国农业科学(英文版)》2013,(6):962-970
Based on the sequence of a novel expressed sequence tag (EST), the full-length cDNA of 1 017 nucleotides was cloned from Brassica napus cv. Xiangyou 15 through rapid amplification of cDNA ends (RACE). The gene was designated as Bnhol34 (HQ585980), encoding a protein of 338 amino acids. BLAST analysis showed no high degree of sequence identity to any known gene. The calculated molecular weight of the Bnhol34 protein was 36.23 kDa, and the theoretical isoelectric point was 8.74. The Bnhol34 was also cloned from a high oleic acid mutant 854-1 through homologous cloning. There was no difference between the two Bnhol34 genes. Bnhol34 was localized in a tissue-specific manner in B. napus, and its expression level was about eight-fold greater in Xiangyou 15 seeds than in 854-1. The promoter region sequences of Bnhol34 were then isolated from Xiangyou 15 and 854-1, and a 93-bp deletion was found to occur in the Bnhol34 promoter region of 854-1. Three abscisic acid-responsive cis-elements (ABRE) were identified in the promoter region of Xiangyou 15. Real-time PCR analyses revealed that exogenous abscisic acid increased Bnhol34 expression by about four-fold in Xiangyou 15 seeds, yet did not change Bnhol34 expression in 854-1. It appeared that Bnhol34 might be abscisic acid insensitive in 854-1. 相似文献
247.
248.
China has taken a foreign direct investment‐based approach toward increasing its capital and knowledge base, and developing into an innovative economy. However, little quantitative evidence exists about the factors that drive innovations of foreign‐invested enterprises (FIEs) there. This paper uses survey data from high‐technology firms in Shanghai to discuss factors affecting their innovativeness. It takes the concepts of absorptive capacity, export orientation, and innovation‐related cooperation as a starting point. It highlights how the interplay of strategies and resources affects innovativeness and heterogeneity of FIEs. The most innovative FIEs are endowed with a strong human capital base and R&D activities, which at the same time target export markets and whose cooperative partners involve firms other than their parent company. The results underline the necessity to differentiate between the different types of FIEs when examining their innovativeness. 相似文献
249.
以果蔗(Badila)茎尖脱毒组培苗为材料,利用间歇浸没式生物反应器(Temporary immersion bioreactors TIBs)进行组培快繁的技术体系的研究。结果表明:(1)使用TIBs系统进行甘蔗组织培养一代增殖较传统方法高出10倍以上;(2)TIBs系统以第4代继代材料为宜;(3)接种密度在10~15株/L培养基最有利于甘蔗组培苗的增殖和生长;(4)TIBs系统中6-BA浓度为0.5~1.0mg/L时适合于增殖培养,NAA浓度为4mg/L时有利于根的诱导;(5)浸没间歇频率在1min/3h时增殖和生长表现较为优异,1min/6h时有利于根的诱导和根的生长。 相似文献
250.
In recent years, numerous studies have evaluated the effect of plant function diversity on ecosystem functions such as productivity and soil nutrient status. We performed a redundancy analysis (RDA) to examine the relationship between plant functional diversity, productivity and soil nitrogen in a chronosequence of abandoned fields in sub-alpine meadow in the eastern part of the Tibet Plateau, China. We found that along the secondary succession sequence, legume richness and aboveground biomass significantly increased and both were positively correlated with total species richness (S) and aboveground biomass (T-bio). This pattern suggests that legume richness increases community productivity. In addition, we found that total aboveground biomass, legume and grass richness were positively correlated with soil microbial nitrogen (MBN), the ratio of microbial nitrogen to soil total nitrogen (MBN/TN) and the ratio of soil organic carbon and soil total nitrogen (C/N), whereas they were negatively correlated with soil total nitrogen (TN), organic carbon (Corg), and microbial carbon (MBC). Contrary to our predictions grasses such as Stipa grandis, Scirpus tripueter, Koeleria cristata were more closely associated with MBN, MBN/TN than legumes such as Oxytropis ochrocephala, Thermopsis lanceolate and Astragalus polycladus. The late-successional grass Kobresio humilis had a stronger positive correlation with NH4-N as compared to the legumes and NO3-N was not associated with any legume species. This suggests that the grasses and legumes have a synergetic positive influence on the ecosystem properties, especially nitrogen. Therefore, in this N-limited, plant community diversity of both legumes and grasses has a strong influence on ecosystem changes during succession. 相似文献