全文获取类型
收费全文 | 45418篇 |
免费 | 1859篇 |
国内免费 | 4658篇 |
专业分类
林业 | 3799篇 |
农学 | 4881篇 |
基础科学 | 3688篇 |
5865篇 | |
综合类 | 20317篇 |
农作物 | 2680篇 |
水产渔业 | 1770篇 |
畜牧兽医 | 5046篇 |
园艺 | 1409篇 |
植物保护 | 2480篇 |
出版年
2024年 | 352篇 |
2023年 | 838篇 |
2022年 | 1551篇 |
2021年 | 1659篇 |
2020年 | 1682篇 |
2019年 | 1969篇 |
2018年 | 1277篇 |
2017年 | 2077篇 |
2016年 | 2382篇 |
2015年 | 2160篇 |
2014年 | 2616篇 |
2013年 | 2665篇 |
2012年 | 3849篇 |
2011年 | 3717篇 |
2010年 | 2948篇 |
2009年 | 2731篇 |
2008年 | 2391篇 |
2007年 | 2629篇 |
2006年 | 2192篇 |
2005年 | 1704篇 |
2004年 | 1273篇 |
2003年 | 989篇 |
2002年 | 768篇 |
2001年 | 639篇 |
2000年 | 583篇 |
1999年 | 586篇 |
1998年 | 498篇 |
1997年 | 439篇 |
1996年 | 371篇 |
1995年 | 406篇 |
1994年 | 321篇 |
1993年 | 281篇 |
1992年 | 314篇 |
1991年 | 257篇 |
1990年 | 230篇 |
1989年 | 214篇 |
1988年 | 147篇 |
1987年 | 90篇 |
1986年 | 48篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1979年 | 5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
181.
黏虫体内两种微管蛋白基因cDNA序列的克隆与序列分析 总被引:1,自引:0,他引:1
以黏虫4龄幼虫为材料提取总RNA,利用RT-PCR和cDNA末端快速扩增技术(RACE),分别扩增得到该虫的α和β微管蛋白基因的cDNA序列各1条。其中α微管蛋白基因的cDNA序列1 443个碱基,包括一个1 353个碱基的开放阅读框,编码一个含450个氨基酸的蛋白,分子量约为50.0ku。氨基酸的142~148位存在一个微管蛋白标志信号片段GGGTGSG,在氨基酸序列的C-端有一个酪氨酸残基,N-端存在一个对转录后调控非常重要的保守区MRECI序列,以上特点与其他昆虫α微管蛋白氨基酸序列相同。黏虫β微管蛋白基因cDNA序列含1 906个碱基,开放读码框1 344个碱基,编码氨基酸447个,分子量约为50.2ku,等电点4.75。1~4个氨基酸MREI为β微管蛋白转录后调控信号,140~146GGGTGSG位同样存在一个微管蛋白标志信号片段。序列比对表明,克隆的α和β微管蛋白基因与其他昆虫的α和β微管蛋白基因在核苷酸和氨基酸水平上都是高度同源的,黏虫与家蚕(Bombyx mori)α微管蛋白的氨基酸序列同源性达到99.3%,与其他3种夜蛾科昆虫α微管蛋白的氨基酸序列同源性更是达到100%。黏虫与家蚕β微管蛋白的氨基酸序列同源性达到98.7%,与烟草天蛾β微管蛋白的氨基酸序列同源性达到99.6%。两个基因的cDNA序列已经登录GenBank并获得登录号分别为EU100016和EU234504。 相似文献
182.
塔克拉玛干沙漠腹地纵向沙垅表面沙物质粒度特征 总被引:7,自引:1,他引:7
本文对塔克拉玛干沙漠腹地纵向沙垅表面沙粒、丘间地沙粒进行了粒度分析。结果表明,沙垅以极细沙为主,平均粒径3.06Φ,沙粒从沙垅迎风侧到背风侧逐渐变细。沙丘沙比丘间地沙分选好,沙垅背风侧比迎风侧分选好。沙粒属极负偏,偏度-0.22,丘间地沙比沙丘沙更趋向负偏。峰度1.38,属尖峰态。粒径与偏度和峰度成正相关,分选和偏度成良好负相关。沙丘沙以单峰态为主,累积频率曲线为2~3段式,丘间地以双峰态为主,累积频率曲线为3~4段。大尺度地形对沙粒段式没有影响,对各段组分含量相对大小有影响。 相似文献
183.
184.
为明确木瓜秀粉蚧Paracoccus marginatus Williams et Granara de Willink 1922在中国的潜在适生区,基于中国820个气象站点的气象数据和未来气候变化数据,结合木瓜秀粉蚧的生物学特性,利用CLIMEX模型对该虫在中国当前气候以及未来气候条件下的潜在适生区进行预测。结果显示,木瓜秀粉蚧在中国的潜在适生区主要在南方,适生区面积占全国陆地总面积的9.07%。高适生区主要包括海南省、广东省南部、广西壮族自治区南部以及福建省和云南省小部分地区。在未来气候条件下,2050年木瓜秀粉蚧的潜在适生区将进一步扩大,适生区面积所占比例将增加至15.46%,且有向北移动的趋势。表明木瓜秀粉蚧对中国南方地区的农业潜在威胁巨大,建议将该虫增补为检疫对象,并加强检疫监管和种群动态监测。 相似文献
185.
Taichiro Ishige Hiromi Hara Takashi Hirano Hideyuki Mannen Tomohiro Kono Kei Hanzawa 《Animal Science Journal》2016,87(3):311-320
In this study, we identified a cluster of 14 avian β‐defensins (AvBD; approximately 66 kbp) in the Japanese quail, Coturnix japonica. Except for AvBD12 (CjAvBD12) and ‐13, the CjAvBDs coding sequences exhibited greater than 78.0% similarity to the respective orthologous chicken AvBD genes (GgAvBD). The putative amino acid sequence encoded by each CjAvBD contained six cysteine residues and the GXC (X1‐2) motif considered essential for the β‐defensin family. Each CjAvBDs also formed a sub‐group with the respective orthologous genes of various bird species in a phylogenetic tree analysis. Synteny between the CjAvBD cluster and GgAvBD cluster was confirmed. The CjAvBD cluster was mapped on the long‐arm end of chromosome 3 by linkage analysis based on single nucleotide polymorphisms (SNPs) of CjAvBD1 and CjAvBD12 (approximately 46kbp), as well as GgAvBD cluster. We also confirmed that CjAvBD1, ‐4, ‐5, ‐9, and ‐10 are transcribed in 20 tissues, including immune and digestive tissues. However, our experimental data indicated that the CjAvBD cluster lacks the AvBD3 and ‐7 loci, whereas the CjAvBD101α, ‐101β, and ‐101θ loci arose from gene duplication of the AvBD6 orthologous locus in the CjAvBD cluster after differentiation between Coturnix ‐ Gallus. 相似文献
186.
土地资源利用现状的区域差异及可持续利用研究——以南京市为例 总被引:2,自引:0,他引:2
在科学确定大城市市域土地资源利用现状区域差异指标评价体系的基础上,通过动态聚类方法,以乡(镇)为单位,对南京市郊区和郊县的土地利用现状进行分区,并分析了不同土地利用现状区土地利用特征,提出了不同区域土地资源可持续利用的政策取向 相似文献
187.
J.C. Goud A.J. Termorshuizen 《European journal of plant pathology / European Foundation for Plant Pathology》2002,108(8):771-782
Two experiments were performed in two consecutive years to test whether isolates of different vegetative compatibility groups (VCGs) differ in their ability to cause disease in woody ornamentals, to study the host specificity of the isolates and to get an insight into disease development in woody hosts. A range of woody ornamental plant species, including Acer campestre, Acer platanoides, Acer pseudoplatanus, Catalpa bignonioides, Cotinus coggygria, Robinia pseudoacacia, Rosa canina, Syringa vulgaris and Tilia cordata, were root-dip inoculated with six isolates of Verticillium dahliae, belonging to the two VCGs that occur in the Netherlands (VCG NL-1 and VCG NL-2). Isolates belonging to each VCG caused severe symptoms of verticillium wilt in most plant species tested. Disease progress differed between plant species, but was generally the same for the two VCGs. No overall differences in virulence were observed between the two VCGs for external wilt symptoms, number of dead plants, or shoot length. No significant VCG × plant species interactions were present for these characteristics. However, isolates of VCG NL-1 caused more vascular discolouration than did isolates of VCG NL-2. Isolates within VCGs often differed considerably in their virulence to certain hosts, as shown by highly significant isolate × plant species interactions. Isolates were more virulent on their original host. These findings imply that VCG identification does not contribute to disease prediction for a range of woody hosts. 相似文献
188.
Toshihiro NADE Jun-ichi SABURI Tsuyosi ABE Tetsuo NAKAGAWA Toshiaki OKUMURA Satsuki MISUMI Kunihiko SAITO Tadashi KAWAMURA Kazuhisa FUJITA 《Animal Science Journal》2007,78(6):567-574
The carcass composition of crossbred Japanese Black × Limousin F2 cattle was examined in order to find an accurate carcass composition equation. The test animals included 17 steers and 17 heifers. The 28 image measurements from the area encircling the vertical line to the thoracic vertebra and the line from the thoracic vertebra between the sixth and seventh rib‐bones were measured by computer image analysis. The relationships between the 29 parameters that added the carcass left side weight of the animal and the carcass composition were suggested. The carcass composition included muscle weight, muscle ratio, fat weight and fat ratio. The carcass composition from steers was estimated by an equation composed of these three or four parameters (R2 = 90.80%, 79.30%, 90.75% and 73.70%, respectively). The selected parameters were measured without cutting the thoracic vertebra. The carcass composition from heifers was estimated by an equation composed of two to four parameters (R2 = 96.15%, 90.98%, 93.60% and 88.22%, respectively). The parameters for the estimation of the muscle and fat weight, and muscle and fat ratio are very similar. Furthermore, the equations using the parameters could estimate the carcass composition from the Japanese Black × Limousin cattle resource population. 相似文献
189.
190.