全文获取类型
收费全文 | 51865篇 |
免费 | 4493篇 |
国内免费 | 4808篇 |
专业分类
林业 | 3875篇 |
农学 | 5369篇 |
基础科学 | 3763篇 |
7400篇 | |
综合类 | 20367篇 |
农作物 | 2782篇 |
水产渔业 | 3911篇 |
畜牧兽医 | 8162篇 |
园艺 | 1389篇 |
植物保护 | 4148篇 |
出版年
2024年 | 326篇 |
2023年 | 829篇 |
2022年 | 1519篇 |
2021年 | 1765篇 |
2020年 | 2122篇 |
2019年 | 2839篇 |
2018年 | 2023篇 |
2017年 | 2896篇 |
2016年 | 2968篇 |
2015年 | 2753篇 |
2014年 | 3149篇 |
2013年 | 3483篇 |
2012年 | 4768篇 |
2011年 | 4270篇 |
2010年 | 3452篇 |
2009年 | 2957篇 |
2008年 | 2612篇 |
2007年 | 2797篇 |
2006年 | 2347篇 |
2005年 | 1917篇 |
2004年 | 1466篇 |
2003年 | 1107篇 |
2002年 | 881篇 |
2001年 | 764篇 |
2000年 | 714篇 |
1999年 | 627篇 |
1998年 | 524篇 |
1997年 | 454篇 |
1996年 | 396篇 |
1995年 | 417篇 |
1994年 | 324篇 |
1993年 | 288篇 |
1992年 | 306篇 |
1991年 | 251篇 |
1990年 | 242篇 |
1989年 | 215篇 |
1988年 | 154篇 |
1987年 | 89篇 |
1986年 | 57篇 |
1985年 | 14篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1962年 | 9篇 |
1956年 | 5篇 |
1955年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
There is growing recognition of the link between the non-native pet trade and the introduction and establishment of invasive species due to the release and escape of non-native pets. However, it is unclear whether participants in the pet trade recognize the magnitude of this invasion risk. Successful mitigation of the pet trade invasion risk requires stakeholder support for, and participation in, regulations. We conducted 29 interviews in Florida to investigate key stakeholders’ opinions about the pet trade invasion risk and the effectiveness of potential regulations to mitigate this risk. Respondents framed the effectiveness of regulations in terms of their feasibility. Respondents also identified lack of trust and the existence of an adversarial relationship among stakeholder groups as major barriers to managing the pet trade invasion risk. Compliance with regulations may be improved if policy makers and managers utilize participatory decision-making to engage stakeholders in management of this risk. 相似文献
112.
QU Chun-feng LI Sheng LI Hui DU Feng-jiao LEI Wei WU Zhu-lian LI Xiang-ping SHI De-shun 《中国畜牧兽医》2015,42(7):1621-1629
Cloning buffalo AQP9 gene and analyzing its expression in buffalo tissues.A pair of primers was designed according to the released bovine AQP9 sequences in GenBank,which was used to clone buffalo AQP9 gene.The AQP9 gene was amplified by RT-PCR,whose nucleotide sequence and protein structure were analyzed by bioinformatics methods.The expression of AQP9 in buffalo tissues was assayed by Real-time quantitative PCR.The expression of AQP9 gene in buffalo ovary and testis tissue was detected by immunohistochemical staining method.The results showed that the cloned ORF length of buffalo AQP9 gene was 888 bp,which coded 295 amino acids.The results of multiple sequence comparison showed that the nucleotide sequence of buffalo AQP9 shared 99%,90%,97% and 88% homologeous compared with that of Bos taurus,Sus scrofa,Ovis ariessis and Homo sapiens,respectively,while shared 99%,86%,97%,83% homologeous for amino acids,respectively.Phylogenetic tree analysis indicated that AQP9 gene was highly conservative in the evolutionary process.Real-time quantitative PCR results showed that AQP9 gene expressed in buffalo liver,lung,brain,skin,testis and ovary tissues with different levels,had the most abundant expression in liver,followed by in skin and testis,less observed in lung and ovary.The results of immunohistochemical staining showed that the expression of AQP9 protein varied with the development of buffalo ovarian tissue,and gradually enhanced with follicle development.In testicular tissue,AQP9 protein expressed in spermatocyte and leydig cells of developmental stage testis.These results indicated that we had successfully cloned buffalo AQP9 gene sequences.The expression and its function of AQP9 in buffalo ovaries and testes might play an important role in follicle development and spermatogenesis. 相似文献
113.
本实验在国内首次建立了描记奶牛子宫内压的体内微型压力传感器法,为对子宫进行生理、病理及药理学研究提供了一个实用手段。 本实验利用压力传感器法描记了16头母牛产后4小时和24小时的子宫内压并同时测定了血浆17β-雌二醇和孕酮的水平,其中胎衣正常排出7头(NRFM),胎衣不下9头(RFM)。结果如下:产后4小时NRFM和RFM牛子宫活动单位(平均收缩压×10分钟收缩次数)分别为183.19±19.15和37.12±16.79(P<0.01);产后24小时子宫活动单位NRFM牛为32.75±4.5,RFM牛为31.65±6.33(P>0.05),此时静注30单位催产素后子宫活动单位分别增加17.4和5.5倍(P<0.01)。NRFM牛产后4和24小时血浆17β-雌二醇水平为99.96±42.69和27.16±10.92pg/ml,RFM牛为188.06±63.85和106.93±72.28pg/ml(P<0.01);产后4和24小时血浆孕酮水平NRFM牛为2.0802±0.4072和1.9815±0.4312ng/ml,RFM牛分别为1.9635±0.6208和1.8734±0.6017ng/ml(P>0.05)。 相似文献
114.
对41份偃麦草Elytrigia repens种质资源的16个外部性状变异及其分布规律进行研究,并在对16个指标性状进行相关分析及主成分分析的基础上,对34份材料进行聚类分析。结果表明,偃麦草种内形态指标变异较大,变异系数为4.88%~33.30%,其中叶层高度变异系数最大,达33.30%,其次为旗叶长(26.03%),而种子宽度、种子长度、种子厚度、颖长、叶长变异较小,均在10.0%以下;海拔高度与偃麦草生殖枝高呈显著正相关(P0.01),与颖长呈显著负相关(P0.01),而在纬度上的相关性却呈现相反趋势;经度仅与穗下第1节间长呈显著正相关(P0.01);在对外部性状相关分析及主成分分析的基础上,通过聚类分析,在欧氏距离5.0处,34份偃麦草材料可被划分为高大型、偏高大型、特殊型、低矮型4个类型,且特殊型和低矮型均具有开发为草坪草的潜能。 相似文献
115.
基于线性谱聚类的林地图像中枯死树监测 总被引:1,自引:0,他引:1
【目的】将基于线性谱聚类超像素的方法应用在森林病虫害防治领域,可智能监测无人机森林虫害图像中的枯死树,为森林有害生物的监测工作提供技术支撑。【方法】分别以湖北省受松材线虫与辽宁省受红脂大小蠹侵害的松林无人机图像为试验数据,首先使用线性谱聚类超像素分割算法将图像划分为多个超像素;然后基于枯死树木的颜色特征,初步提取可能为枯死树的超像素区域;最后基于枯死树木与其他干扰地物具有不同的纹理特征,计算超像素的区域密度和缝隙量,利用支持向量机对初步提取的超像素进行分类,从而检测出图像中的枯死树。【结果】基于线性谱聚类超像素和支持向量机的枯死树监测方法可有效排除与枯死树木颜色相近的其他干扰地物,较准确地提取出枯死树木。使用该方法与基于植被颜色指数的阈值分割方法、基于简单线性迭代聚类超像素和随机森林的方法,对35幅受灾松林无人机图像进行试验,并选用交并比、虚警率和漏检率3个评价指标对3种方法进行定量对比分析。结果表明,基于线性谱聚类超像素的方法监测出的枯死树区域最精确,其监测结果与人工检测结果的交并比均值大于58%,且虚警率和漏检率均优于另外2种方法。【结论】基于线性谱聚类超像素的枯死树监测方法能实现松林中枯死树的快速、准确检测及定位。 相似文献
116.
Postulation of leaf-rust resistance genes in Czech and Slovak barley cultivars and breeding lines 总被引:3,自引:0,他引:3
Leaf‐rust resistance (Rph) genes in 61 Czech and Slovak barley cultivars and 32 breeding lines from registration trials of the Czech Republic were postulated based on their reaction to 12 isolates of Puccinia hordei with different combinations of virulence genes. Five known Rph genes (Rph2, Rph3, Rph4, Rph7, and Rph12) and one unknown Rph gene were postulated to be present in this germplasm. To corroborate this result, the pedigree of the barley accessions was analysed. Gene Rph2, as well as Rph4, originated from old European cultivars. The donor of Rph3, which has been mainly used by Czech and Slovak breeders, is ‘Ribari’ (‘Baladi 16’). Rph12 originates from barley cultivars developed in the former East Germany. Rph7 in the registered cultivar ‘Heris’ originates from ‘Forrajera’. A combination of two genes was found in 10 cultivars. Nine heterogeneous cultivars were identified; they were composed of one component with an identified Rph gene and a second component without any resistance gene. No gene for leaf rust resistance was found in 17 of the accessions tested. This study demonstrates the utility of using selected pathotypes of P. hordei for postulating Rph genes in barley. 相似文献
117.
118.
黑龙江龙口自然保护区黑熊春季生境选择 总被引:4,自引:0,他引:4
分别于2008年4~5月和2009年4~5月,在龙口自然保护区对黑熊春季生境选择进行了研究,野外工作共设置87个10 m×10 m样方,并调查12个生态因子,其中利用样方41个,对照样方46个。通过Vanderploeg &Scavia选择指数得到,黑熊喜爱选择处于高海拔(〉450 m)、上坡位有石砬子且草本盖度适中(10%~40%)的生境,倾向选择乔木密度高(〉10株/100 m2)、郁闭度大(〉40%)、灌木密度较低(〈10%)、隐蔽级低(〈30%)、倒木密度大(〉1根/100 m2)、陡坡(〉30°)且向阳的针阔混交林。主成分分析与资源选择函数分析共同得到海拔、坡度、坡位、植被类型对黑熊生境选择影响较大,坡向和倒木密度影响较小的结果。综合分析,将Vanderploeg & Scavia选择指数、主成分分析与资源选择函数相结合可以更好地反映黑熊生境选择情况。 相似文献
119.
奶牛乳房炎是奶牛的常见病和多发病之一,给奶牛业带来巨大的经济损失,严重制约着奶牛业的发展。为了进一步了解乳房炎的调控机理,对已发表的5套大肠杆菌感染奶牛乳腺上皮细胞的表达谱芯片数据统一进行预处理,并整合大肠杆菌感染1、6、24 h的基因富集分析,以期得到更可靠的影响奶牛乳房炎的关键基因和通路。结果发现,感染1、6和24 h数据集的分析结果中共同下调通路分别为9、30和17个,分析结果确定了一些奶牛乳房炎相关的通路及基因,为进一步揭示其调控机理提供参考。 相似文献
120.
A. E. Joetzke K. A. Sterenczak N. Eberle S. Wagner J. T. Soller I. Nolte J. Bullerdiek H. Murua Escobar D. Simon 《Veterinary and comparative oncology》2010,8(2):87-95
Overexpression of high mobility group A (HMGA) genes was described as a prognostic marker in different human malignancies, but its role in canine haematopoietic malignancies was unknown so far. The objective of this study was to analyse HMGA1 and HMGA2 gene expression in lymph nodes of canine lymphoma patients. The expression of HMGA1 and HMGA2 was analysed in lymph node samples of 23 dogs with lymphoma and three control dogs using relative quantitative real‐time RT‐PCR. Relative quantity of HMGA1 was significantly higher in dogs with lymphoma compared with reference samples. HMGA2 expression did not differ between lymphoma and control dogs. With the exception of immunophenotype, comparison of disease parameters did not display any differences in HMGA1 and HMGA2 expression. The present findings indicate a role of HMGA genes in canine lymphoma. This study represents the basis for future veterinary and comparative studies dealing with their diagnostic, prognostic and therapeutic values. 相似文献