全文获取类型
收费全文 | 21164篇 |
免费 | 1243篇 |
国内免费 | 2331篇 |
专业分类
林业 | 2193篇 |
农学 | 2644篇 |
基础科学 | 1915篇 |
3469篇 | |
综合类 | 7317篇 |
农作物 | 1265篇 |
水产渔业 | 857篇 |
畜牧兽医 | 3045篇 |
园艺 | 755篇 |
植物保护 | 1278篇 |
出版年
2024年 | 102篇 |
2023年 | 315篇 |
2022年 | 718篇 |
2021年 | 931篇 |
2020年 | 849篇 |
2019年 | 839篇 |
2018年 | 522篇 |
2017年 | 910篇 |
2016年 | 682篇 |
2015年 | 1072篇 |
2014年 | 999篇 |
2013年 | 1179篇 |
2012年 | 1460篇 |
2011年 | 1519篇 |
2010年 | 1444篇 |
2009年 | 1383篇 |
2008年 | 1269篇 |
2007年 | 1303篇 |
2006年 | 1218篇 |
2005年 | 1083篇 |
2004年 | 547篇 |
2003年 | 389篇 |
2002年 | 367篇 |
2001年 | 350篇 |
2000年 | 387篇 |
1999年 | 445篇 |
1998年 | 345篇 |
1997年 | 313篇 |
1996年 | 259篇 |
1995年 | 287篇 |
1994年 | 206篇 |
1993年 | 236篇 |
1992年 | 192篇 |
1991年 | 149篇 |
1990年 | 134篇 |
1989年 | 92篇 |
1988年 | 73篇 |
1987年 | 60篇 |
1986年 | 37篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1973年 | 2篇 |
1964年 | 2篇 |
1963年 | 3篇 |
1935年 | 1篇 |
1934年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
101.
In order to study and evaluate the feeding environment of the beef cattle farms in Xinjiang, the contents of heavy mentals in the soil from 8 beef cattle farms in Xinjiang Aksu, Yili and Tacheng regions were tested according to the Field of Livestock and Poultry Environment Quality Standard (NY/T 388—1999).The atomic absorption spectroscopic method was used to determine the contents of As, Hg, Pb, Cd, and Cr.The mean contents of As, Hg, Pb, Cd, and Cr in 8 beef cattle farms soil were 0.389, 0.568, 22.708, 0.573 and 149.449 mg/kg, respectively, and they were all below the upper limit of NY/T 388—1999.The comprehensive heavy metal pollution index of 8 beef cattle farms were 0.577 to 0.994, and the index were 0.7 to 1 of two observation points in Yili and one observation point in Tacheng.The soil environment quality of these 3 farms were at the level of slight cleaning.The comprehensive heavy metal pollution index of other five observation points were ≤0.7, the soil environment was in a clean level.The soil environment of beef cattle farms in these three regions conformed to the standards of livestock for environment quality and safe products. 相似文献
102.
103.
Xiao-Peng Lu Yong-Zhong Liu Gao-Feng Zhou Qing-Jiang Wei Hong-Ju Hu Shu-Ang Peng 《Scientia Horticulturae》2011
‘Yandangxueli’ is a pear cultivar with predominant citric acid in the ripe fruit, different from most of pear cultivars such as ‘Gengtouqing’ in which malic acid is the predominant acid type. It was found that ‘Yandangxueli’ accumulated citric acid for three times against that in ‘Gengtouqing’ at fruit ripening stage. To investigate the mechanism of citric acid accumulation in ‘Yandangxueli’, organic acids content, gene expression and enzyme activity were studied in both cultivars. Five genes, Pp:mtCs, Pp:cyAco, Pp:cyIdh, Pp:mtMdh and Pp:cyMe which encoded citric synthase (CS), cytosolic aconitase (cyACO), NADP-dependent isocitrate dehydrogenase (NADP-IDH), NAD-dependent malate dehydrogenase (NAD-MDH) and NADP-dependent malic enzyme (NADP-ME) respectively, were identified from pear fruit. Their expression profiles and the corresponding enzyme activities were determined throughout fruit development in both cultivars. Results from these enzymes indicated that there were no strict relationship between gene expression, enzyme activity and citric acid accumulation. Expression analysis for two Py:vVAtp genes encoding vacuolar H+-ATPase A subunit and one Py:vVpp gene encoding Vacuolar H+-pyrophosphatase showed that they were all with up-regulated expression at the later development stage of ‘Yandangxueli’ but with down-regulated expression in ‘Gengtouqing’. Therefore, it is concluded that the different ability in citric acid transportation and storage might be involved in the high citric acid content in ‘Yandangxueli’. 相似文献
104.
贵州息烽天台山黄心夜合种群结构和动态研究初报 总被引:1,自引:0,他引:1
在以黄心夜合(Michelia martinii)为优势种群的森林群落内设置1200 m2样地,用相邻格子法进行每木调查获取野外资料.通过对种群大小级(立木级)数量特征和分布格局分析,探讨了黄心夜合种群结构和不同发育阶段种群格局动态.结果表明,黄心夜合种群结构呈不完整的金字塔型,中小径级种群缺失较多,但有一定数量的幼苗幼树(Ⅰ级和Ⅱ级),仍属于稳定型种群或进入成熟型阶段.种群不同发育阶段分布格局由集群分布向随机分布转变,集群强度由强变弱,种群密度由大变小,群落仍处于相对稳定阶段. 相似文献
105.
106.
Dvl1及其结构缺失突变体ΔDIX(dsh and axin)和ΔDEP(dsh,Egl-10 and pleckstrin)腺病毒载体的构建并验证其在MSCs(mesenchymal stem cells)中的表达情况。将目的基因定向克隆至pAdTrack-CMV穿梭载体上,并经PmeⅠ线性化后在BJ5183细菌中与pAdEasy-1骨架质粒同源重组,获得重组腺病毒载体,在QBI-293A细胞中包装及扩增,实时荧光定量PCR和Western bolt验证Dvl1在MSCs中的表达情况。经PCR、PacⅠ单酶切鉴定及测序分析,成功构建Ad-Dvl1、Ad-ΔDIX和Ad-ΔDEP腺病毒载体,目的基因序列与GenBank报道一致,并选出150 MOI为最适感染MSCs的感染复数,成功构建了Ad-Dvl1、Ad-ΔDIX和Ad-ΔDEP腺病毒载体,并获得高滴度的病毒子,qPCR和Western blot证实Dvl1在MSCs中高表达并增加了β-catenin在细胞中的累积,为进一步研究Dvl1在MSCs迁移过程的作用奠定了基础。 相似文献
107.
108.
109.