全文获取类型
收费全文 | 5400篇 |
免费 | 281篇 |
国内免费 | 445篇 |
专业分类
林业 | 210篇 |
农学 | 650篇 |
基础科学 | 12篇 |
332篇 | |
综合类 | 2233篇 |
农作物 | 359篇 |
水产渔业 | 537篇 |
畜牧兽医 | 1191篇 |
园艺 | 294篇 |
植物保护 | 308篇 |
出版年
2024年 | 16篇 |
2023年 | 44篇 |
2022年 | 84篇 |
2021年 | 120篇 |
2020年 | 111篇 |
2019年 | 127篇 |
2018年 | 98篇 |
2017年 | 155篇 |
2016年 | 202篇 |
2015年 | 149篇 |
2014年 | 229篇 |
2013年 | 246篇 |
2012年 | 326篇 |
2011年 | 416篇 |
2010年 | 372篇 |
2009年 | 388篇 |
2008年 | 397篇 |
2007年 | 406篇 |
2006年 | 364篇 |
2005年 | 283篇 |
2004年 | 258篇 |
2003年 | 227篇 |
2002年 | 176篇 |
2001年 | 159篇 |
2000年 | 151篇 |
1999年 | 118篇 |
1998年 | 86篇 |
1997年 | 79篇 |
1996年 | 57篇 |
1995年 | 72篇 |
1994年 | 55篇 |
1993年 | 27篇 |
1992年 | 43篇 |
1991年 | 35篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1962年 | 1篇 |
1956年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有6126条查询结果,搜索用时 62 毫秒
71.
True-to-type clonal fidelity is one of the most important pre-requisites in micropropagation of crop species. Genetic fidelity of in vitro raised 45 plants of gerbera (Gerbera jamesonii Bolus) derived from three different explants, viz., capitulum, leaf and shoot tips, was assessed by 32 ISSR markers, for their genetic stability. Out of 32 ISSR markers, 15 markers produced clear, distinct and scorable bands with an average of 5.47 bands per marker. The markers designed from AG motif amplified more number of bands. The markers anchored at 3′ ends produced high number of consistent bands than unanchored markers. Fifteen ISSR markers generated a total of 3773 bands, out of which 3770 were monomorphic among all the clones. The Jaccard's similarity coefficient revealed that out of 45 clones derived from different explants, 44 were grouped into a single large cluster alongwith the mother plant with a similarity coefficient value of 1.00, whereas one clone (C38) remained ungrouped. The clones derived from capitulum and shoot tip explants did not show any genetic variation, whereas, one of the leaf-derived clones exhibited some degree of variation. 相似文献
72.
73.
流式细胞术在水生生物DNA含量和倍性分析中的应用 总被引:3,自引:0,他引:3
利用流式细胞仪对鲤鱼、银鲫、黄颡、牙鲆等淡水和海水鱼类进行了DNA含量测定或倍性分析。通过几百个样品的测定和分析,认为流式细胞仪在DNA相对含量测定和倍性分析上结果比较稳定一致,可以用于大量样品的测定分析。同时对待测样品的保存、处理及上样量等进行了一系列比较研究,找出最好的保存方法、最简便的样品处理方法和最少的上样量。流式细胞仪在水生生物的遗传育种、种群分化等方面有很重要的应用价值。 相似文献
74.
75.
Abstract: Heterosigma akashiwo virus (HaV) is a large icosahedral virus (∼0.2 μm) harboring a double-stranded DNA (dsDNA) genome (∼294 kbp). The virus is the only member of the genus Raphidovirus in the family Phycodnaviridae. Since its first discovery, a number of ecologic, physiologic and genetic studies about HaV have been conducted; especially, the relationship between H. akashiwo and HaV in nature was studied and viral infection is now regarded as a significant factor influencing the dynamics and termination of H. akashiwo blooms. HaV infection has considerable impacts on H. akashiwo populations in both aspects of fluctuation in biomass (quantity) and changes in clonal composition (quality). Partial sequencing of the HaV genome revealed that a number of genes showed considerable similarity to those of other protist-infecting viruses; still, the phylogenetic position of HaV suggested a number of enigmas in host–virus coevolution. Here are summarized the ecology, physiology and genetics of HaV especially from the viewpoint of the host–virus relationship. 相似文献
76.
This study was performed to obtain information on the occurrence of multiple paternities in three species of viviparous Japanese
surfperch using allelic markers of microsatellite DNA loci. Direct evidence for multiple fertilizations was established by
reconstructing paternal genotypes from the progeny of gravid females. Multiple paternities were ascertained in five of 10
broods of Ditrema temmincki and in three of nine broods of Neoditrema ransonneti, but not in Ditrema viride. The number of patrilines detected in the progeny of D. temmincki and N. ransonneti females were two or three, respectively, as determined by the GERUD v2.0 algorithm for reconstructing parental genotypes
from half-sib progeny arrays. 相似文献
77.
78.
AIM and METHODS: The ratio of mitochondrial DNA (mtDNA) deletion was measured to find the relationship between mtDNA deletion and aged learning and memory deficit. The aged rats were divided into two groups, aged learning and memory deficit group and aged learning and memory normal group. The ratio of mtDNA deletion was measured by dilution polymerase chain reaction. RESULTS: There are deleted mtDNA (about 4834 bp) in the cerebral cortex, hippocampus and cerebellum of both young and aged rats. The ratios of deleted mtDNA were similar in the cerebral cortex,hippocampus and cerebellum of young rats (about 0.00018%). The ratio mtDNA of aged learning and memory normal rats had increased by five-fold in the cerebral cortex and hippocampus, or one-fold in the cerebellum over young rats. The ratio of aged learning and memory dificit rats had increased by one-fold in the cerebral cortex or 0.8-fold in the hippocampus or two-fold in the cerebellum over aged learning and memory normal rats.CONCLUSIONS: There was really the increase of mtDNA in aging rat brain. And this increase was double in amount in aged learning and memory deficit rats compared to the normal learning and memory aged rats. It is suggested that the mtDNA deletions in the brain regions associated with learning and memory may be contributed to the cellular and molecular mechanism of learning and memory deicit with aged rats. 相似文献
79.
80.
AIM To investigate the activation of related repair pathways after bupivacaine-induced neuronal DNA damage by cDNA gene screening. METHODS The bupivacaine-induced SH-SY5Y neuronal damage and DNA damage model was established. The technique of cDNA microplate array was used to screen the 21 important regulatory factors in the DNA damage repair pathway. Post-analysis of these differentially expressed repair genes for the repair pathway enrichment and distribution was performed. The data were analyzed by GraphPad Prism 6 statistical software to compare differences between groups. RESULTS The viability of SH-SY5Y cells treated with bupivacaine at different concentrations (detected by CCK-8 assay) showed that the IC50 value of bupivacaine was 1.5 mmol/L. The comet assay related index (the comet tail) was increased (P <0.05), the phosphorylation level of γH2AX protein was increased (P <0.05), indicating that DNA damage in the SH-SY5Y cells was significantly aggravated after bupivacaine treatment. The results of cDNA microplate assay showed that compared withcontrol group, the differentially expressed genes after bupivacaine treatment were DNA-PKcs , PTEN , NTH1 , RAD9 , CSB , GADD45 , XPD, XPC-HR23B and P53 . The analysis showed that these repair genes were mainly concentrated in the following 3 repair mechanisms: base excision repair, nucleotide excision repair, and non-homologous reconstitution. CONCLUSION The repair genes differentially expressed after neuronal DNA damage caused by local anesthetics are mainly concentrated in the pathways of non-homologous end-joining, base excision repair and nucleotide excision repair. 相似文献