全文获取类型
收费全文 | 48169篇 |
免费 | 2532篇 |
国内免费 | 4856篇 |
专业分类
林业 | 5607篇 |
农学 | 6353篇 |
基础科学 | 3319篇 |
7883篇 | |
综合类 | 15563篇 |
农作物 | 3068篇 |
水产渔业 | 2021篇 |
畜牧兽医 | 6848篇 |
园艺 | 1835篇 |
植物保护 | 3060篇 |
出版年
2024年 | 194篇 |
2023年 | 688篇 |
2022年 | 1498篇 |
2021年 | 1991篇 |
2020年 | 1871篇 |
2019年 | 1936篇 |
2018年 | 1300篇 |
2017年 | 1820篇 |
2016年 | 1626篇 |
2015年 | 2046篇 |
2014年 | 2120篇 |
2013年 | 2608篇 |
2012年 | 3112篇 |
2011年 | 3261篇 |
2010年 | 3138篇 |
2009年 | 2932篇 |
2008年 | 2695篇 |
2007年 | 2699篇 |
2006年 | 2478篇 |
2005年 | 2139篇 |
2004年 | 1143篇 |
2003年 | 1028篇 |
2002年 | 1119篇 |
2001年 | 1086篇 |
2000年 | 1063篇 |
1999年 | 1153篇 |
1998年 | 972篇 |
1997年 | 872篇 |
1996年 | 722篇 |
1995年 | 696篇 |
1994年 | 626篇 |
1993年 | 569篇 |
1992年 | 488篇 |
1991年 | 454篇 |
1990年 | 329篇 |
1989年 | 290篇 |
1988年 | 248篇 |
1987年 | 151篇 |
1986年 | 76篇 |
1985年 | 42篇 |
1984年 | 51篇 |
1983年 | 35篇 |
1982年 | 31篇 |
1981年 | 32篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1974年 | 10篇 |
1965年 | 6篇 |
1964年 | 8篇 |
1956年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
高校不仅担负教书育人的根本任务,其作为重要的社会力量,也承担着定点扶贫的责任与使命.高校在定点扶贫过程中,可以充分发挥科技、人才以及智力等独特优势.经过多年的不断探索,已有许多高校探索出定点扶贫的经典模式.基于西北农林科技大学"三团一队"定点扶贫模式在帮扶合阳县所取得的成效以及"三团一队"保障机制不健全、扶贫工作主要发力点不突出、多主体共同参与程度不够以及社会力量吸引不足的困境,探索优化路径,以此来完善"三团一队"定点扶贫模式. 相似文献
2.
3.
对某饲料厂不同阶段猪用4种颗粒饲料的物理性能包括直径、长度、硬度、容重、含粉率和耐久性指数(Pellet Durability Index, PDI)等进行测定,对结果进行归类总结并采用统计学的方法参照有关标准进行分析。结果表明,4种颗粒饲料直径在2.87~3.94 mm之间,母猪料直径最大,小猪料最小,两两之间差异显著(P<0.05),而且随着猪只年龄的增加,颗粒饲料的直径呈递增趋势。颗粒长度在8.62~11.94 mm之间,以大猪料最长,小猪料最短,长径比偏高。颗粒硬度在3.86~6.47 kg之间,以大猪料最大,小猪料最小,中小猪料显著低于大猪料和母猪料(P<0.05),只有小猪料符合有关要求。颗粒容重在576.7~614.6 g/L之间,母猪料最大,小猪料最小,两两之间差异显著(P<0.05),与直径呈相同的增减趋势。含粉率以小猪料最大,且只有小猪料与大猪料之间差异显著(P<0.05)。颗粒PDI以大猪料最大,小猪料最小,各阶段猪料的含粉率和PDI均符合有关要求。建议饲料厂家注重颗粒饲料物理性能指标的控制,调整饲料配方和工艺参数,不断改进颗粒饲料的质量。 相似文献
4.
为分析全省平均以及各气候带光能、热量、水分资源的时空变化特征,使用云南115站及6个气候带代表站1961—2018年的气候要素计算各地农业气候资源统计量。结果表明,光能资源变化以减少趋势为主,出现显著突变,各气候带太阳辐射变化可能会引起云南太阳辐射高低值中心发生变化,2009年以来辐射明显增加可能会导致太阳辐射出现新的变化趋势和突变点;热量资源一致显著增加,喜凉及喜温作物的活动积温、积温持续时间及无霜期长度均显著增加,并且呈现初日提前、终日推后的趋势,对作物生长有利;水分资源总体呈现减少趋势,尤其21世纪以来下降趋势明显,亚热带地区暖干化现象突出,干旱风险等级较高。 相似文献
5.
Antimicrobial peptides are a class of proteins with antibacterial functions. In this study, the anti-lipopolysaccharide factor isoform 3 gene (ALFPm3), encoding an antimicrobial peptide from Penaeus monodon with a super activity was expressed in Chlamydomonas reinhardtii, which would develop a microalga strain that can be used for the antimicrobial peptide production. To construct the expression cluster, namely pH2A-Pm3, the codon optimized ALFPm3 gene was fused with the ble reporter by 2A peptide and inserted into pH124 vector. The glass-bead method was performed to transform pH2A-Pm3 into C. reinhardtii CC-849. In addition to 8 μg/mL zeocin resistance selection, the C. reinhardtii transformants were further confirmed by genomic PCR and RT-PCR. Western blot analysis showed that the C. reinhardtii-derived ALFPm3 (cALFPm3) was successfully expressed in C. reinhardtii transformants and accounted for 0.35% of the total soluble protein (TSP). Furthermore, the results of antibacterial assay revealed that the cALFPm3 could significantly inhibit the growth of a variety of bacteria, including both Gram-negative bacteria and Gram-positive bacteria at a concentration of 0.77 μM. Especially, the inhibition could last longer than 24 h, which performed better than ampicillin. Hence, this study successfully developed a transgenic C. reinhardtii strain, which can produce the active ALFPm3 driven from P. monodon, providing a potential strategy to use C. reinhardtii as the cell factory to produce antimicrobial peptides. 相似文献
6.
Utilizing a DUALEM‐421 and inversion modelling to map baseline soil salinity along toposequences in the Hunter Valley Wine district
下载免费PDF全文
![点击此处可从《Soil Use and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In the oldest commercial wine district of Australia, the Hunter Valley, there is the threat of soil salinization because marine sediments underlie the area. To understand the risk requires information about the spatial distribution of soil properties. Electromagnetic (EM) induction instruments have been used to identify and map the spatial variation of average soil salinity to a certain depth. However, soils vary with depth dependent on soil forming factors. We collected data from a single‐frequency and multiple‐coil DUALEM‐421 along a toposequence. We inverted this data using EM4Soil software and evaluated the resultant 2‐dimensional model of true electrical conductivity (σ – mS/m) with depth against electrical conductivity of saturated soil pastes (ECp – dS/m). Using a fitted linear regression (LR) model calibration approach and by varying the forward model (cumulative function‐CF and full solution‐FS), inversion algorithm (S1 and S2), damping factor (λ) and number of arrays, we determined a suitable electromagnetic conductivity image (EMCI), which was optimal (R2 = 0.82) when using the full solution, S2, λ = 3.6 and all six coil arrays. We conducted an uncertainty analysis of the LR model used to estimate the electrical conductivity of the saturated soil‐paste extract (ECe – dS/m). Our interpretation based on estimates of ECe suggests the approach can identify differences in salinity, how these vary with parent material and how topography influences salt distribution. The results provide information leading to insights into how soil forming factors and agricultural practices influence salinity down a toposequence and how this can guide soil management practices. 相似文献
7.
Shi-Zhi Wang Guang-Xin E Yan Zeng Yan-Guo Han Yong-Fu Huang Ri-Su Na 《Reproduction in domestic animals》2021,56(6):936-941
The aim of this study was to analyse the association between single-nucleotide polymorphisms within INHA and ACVR2B and litter size in Dazu black goats. In total, twenty-two SNPs were genotyped in 190 individuals by SNaPshot and resequencing. The results showed that three SNPs (SNP_1, SNP_12 and SNP_13 in this study) were detected to have significant additive genetic effect on the recorded goat litter size (p < .05). The SNP_1 (NC_030809.1), a non-synonymous substitution of G for T at chr2-g. 28314990 in the exon 2 of INHA gene (NM_001285606.1), resulted in homozygote 2 (HOM2) contributed 0.25 and heterozygote (HET) contributed 0.12 larger litter than homozygote 1 (HOM1). Meanwhile, SNP_12 (Chr22-g. 11721225 A > T) and SNP_13 (Chr22-g. 11721227 A > C) (NC_030829.1) simultaneously mutated at the first and third position of a triplet AAA (lysine, K) in the exon 4 of ACVR2B gene (XM_018066623.1) had estimated genetic effects of HOM1 (0.00) and HOM2 (0.03) larger than HET (−0.12). In conclusion, one SNPs (chr2-g. 28314990 T > G) within the exon 2 of INHA and two SNPs (Chr22-g. 11721225 A > T and Chr22-g. 11721227 A > C) i n the exon 4 of ACVR2B gene were highly recommended as candidate markers of litter size in Dazu black goats. A large-scale association study to assess the impact of these variants on litter size is still necessary. 相似文献
8.
Ting Shi Yan-Yan Yu Jia-Jia Dai Yi-Ting Zhang Wen-Peng Hu Li Zheng Da-Yong Shi 《Marine drugs》2021,19(3)
The species Pseudogymnoascus is known as a psychrophilic pathogenic fungus with a ubiquitous distribution in Antarctica. Meanwhile, the study of its secondary metabolites is infrequent. Systematic research of the metabolites of the fungus Pseudogymnoascus sp. HSX2#-11, guided by the method of molecular networking, led to the isolation of one novel polyketide, pseudophenone A (1), along with six known analogs (2–7). The structure of the new compound was elucidated by extensive spectroscopic investigation and single-crystal X-ray diffraction. Pseudophenone A (1) is a dimer of diphenyl ketone and diphenyl ether, and there is only one analog of 1 to the best of our knowledge. Compounds 1 and 2 exhibited antibacterial activities against a panel of strains. This is the first time to use molecular networking to study the metabolic profiles of Antarctica fungi. 相似文献
9.
在渔业方面,贯彻落实“一带一路”倡议,实施渔业“走出去,引进来”战略,促进我国水产养殖业和周边国家地区的交流合作,共同推动区域传统渔业向现代渔业转型升级,是现代渔业发展的必然方向。泰国作为“一带一路”之东盟国家,从泰国的渔业资源现状、渔业产业发展、渔业现阶段存在的优势和不足以及中泰渔业协作发展探索等多个方面进行阐述,通过研究泰国渔业现状及探索中泰渔业协作发展之路,提出技术支撑、资源引进、取长补短、共同进步等相对应的策略与建议,为中国-东盟国家在基于“一带一路”倡议的渔业层面战略发展提供样本。 相似文献
10.