首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   17756篇
  免费   1123篇
  国内免费   1665篇
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
  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.
以竹笋为原料,研究一种新型绿色产品糖醋麻竹笋的加工工艺。采用正交试验辅以感官评分确定影响产品质量的关键工艺脱涩、保脆和最佳配方。研究结果表明,最佳脱涩工艺为0.1%柠檬酸处理10 min;最佳保脆工艺为0.2%CaCl2溶液浸泡30 min;糖醋麻竹笋的最佳配方为酸用量35%,蒜用量5%,盐用量3%,糖用量22%。采用此工艺条件,可得到笋肉黄白、汤汁澄清、酸甜可口、蒜香宜人并具有麻竹笋天然味道的糖醋麻竹笋产品,食用方便,市场前景广阔。  相似文献   
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.
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.
人参果PVM病毒的克隆与鉴定   总被引:1,自引:1,他引:0  
通过对武威市凉州区人参果感病植株所表现出来的花叶、皱缩、植株矮小等症状观察,初步判断可能感染了马铃薯M病毒(PVM)。结合分子生物学手段,提取感病人参果叶片总RNA,采用RT-PCR方法扩增到一段长300 bp的基因序列,连接至PMD19-T载体并测序。测序结果同GeneBank中PVM CP基因序列[GI:361071296]同源性达到了98.97%,说明成功克隆到了PVM基因片段, 即供试人参果确实感染了PVM病毒。  相似文献   
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号