全文获取类型
收费全文 | 17862篇 |
免费 | 1209篇 |
国内免费 | 1760篇 |
专业分类
林业 | 1242篇 |
农学 | 968篇 |
基础科学 | 804篇 |
1755篇 | |
综合类 | 8697篇 |
农作物 | 1315篇 |
水产渔业 | 939篇 |
畜牧兽医 | 2912篇 |
园艺 | 1416篇 |
植物保护 | 783篇 |
出版年
2024年 | 98篇 |
2023年 | 396篇 |
2022年 | 902篇 |
2021年 | 876篇 |
2020年 | 815篇 |
2019年 | 695篇 |
2018年 | 559篇 |
2017年 | 896篇 |
2016年 | 597篇 |
2015年 | 979篇 |
2014年 | 995篇 |
2013年 | 1144篇 |
2012年 | 1550篇 |
2011年 | 1666篇 |
2010年 | 1568篇 |
2009年 | 1272篇 |
2008年 | 1317篇 |
2007年 | 1173篇 |
2006年 | 924篇 |
2005年 | 664篇 |
2004年 | 465篇 |
2003年 | 246篇 |
2002年 | 311篇 |
2001年 | 284篇 |
2000年 | 263篇 |
1999年 | 91篇 |
1998年 | 12篇 |
1997年 | 18篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1981年 | 1篇 |
1966年 | 1篇 |
1962年 | 2篇 |
1956年 | 8篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
151.
AIM:To study the role of ghrelin in cell protection by up-regulating heat shock protein 70 (HSP70) and inhibiting apoptosis induced by oxidative stress through extracellular regulated protein kinases 1/2 (ERK1/2) signaling pathway in the PC12 cells. METHODS:Sodium nitoprusside (SNP) was used to induce oxidative stress injury in the PC12 cells. The cultured PC12 cells were divided into SNP-injured group (incubated with SNP at 0.5 mmol/L for 6, 12, 18 and 24 h), ghrelin pretreatment group (ghrelin at 100 nmol/L was given 30 min before adding SNP); HSP70 inhibitor group (quercetin at 10 μmol/L was added 60 min before ghrelin treatment), ERK inhibitor group (ERK 1/2 inhibitor PD98059 was added 60 min before ghrelin treatment) and control group (added same amount of culture medium only). The apoptotic rate was detected by flow cytometry. The protein expression was determined by Western blot and immunocytochemistry. RESULTS:Compared with control group, the apoptotic rate of PC12 cells in SNP-injured group was significantly increased (P<0.05). Compared with SNP-injured group, ghrelin (100 nmol/L) pretreatment significantly inhibited SNP-induced apoptosis of PC12 cells (P<0.05), and significantly up-regulated the protein expression of HSP70 (P<0.05). Time-effect analysis showed that ghrelin had the most significant effect at 18 h after SNP injury. Quercetin, an inhibitor of HSP 70, significantly reduced the anti-apoptotic effect of ghrelin (P<0.05). Ghrelin pretreatment promoted the phosphorylation of ERK1/2. ERK1/2 inhibitor PD98059 significantly inhibited the effects of ghrelin on up-regulation of HSP70 expression (P<0.05). CONCLUSION:Ghrelin upregulates the expression of HSP70 and inhibits the apoptosis in the PC12 cells induced by oxidative stress by promoting the phosphorylation of ERK1/2. 相似文献
153.
目的观察5年生人工种植人参超微粉对自发性高血压大鼠(SHR)的降压作用,并初步探讨其作用机制。方法将50只SHR随机分为对照组、阳性药卡托普利组及人参超微粉0.5、1.0、2.0 g/kg组,每组10只。采用尾动脉测压法测量SHR给药前及给药后30、60、90天的动脉血压,测定超声心动图及血清血管紧张素Ⅱ(Ang Ⅱ)、内皮素(ET)、去甲肾上腺素(NE)、一氧化氮(NO)、白介素-6(IL-6)、肿瘤坏死因子-α(TNF-α)、丙二醛(MDA)及超氧化物歧化酶(SOD)等指标,初步探讨其降压机制。结果人参超微粉0.5、1.0 g/kg于给药30、60、90天均可使SHR的平均动脉压明显降低(P0.05或P0.01),使Ang Ⅱ、ET、NE、MDA及TNF-α含量明显降低,SOD活性明显增加(P0.05或P0.01),对超声心动图、血清NO及IL-6含量无明显影响(P0.05)。结论人参超微粉长期服用可产生降压作用,其机制可能与抑制交感神经与肾素-血管紧张素系统,改善内皮功能紊乱以及抗自由基氧化损伤等作用有关。 相似文献
154.
155.
LI Yan-jun SONG Shao-rui GUO Ya-fen LAN Gan-qiu CHEN Bao-jian YAN Xue-yu WU Yan-jun JIANG Qin-yang 《中国畜牧兽医》2015,42(7):1770-1776
The atherosclerosis (AS) model was prepared in Guangxi Bama mini-pig,and the atherosclerosis index (AI) was preliminarily identified in occurrence of AS to provide the basis for the preparation of related models.20 Guangxi Bama mini-pigs were randomly divided into control group and experimental group which were fed with high fat and cholesterol diet to prepare the AS model.Blood biochemical indexes were detected in the process of model preparation and the correlation between AI and the results of vascular slices was analyzed to initially draw up AI of AS.The results of vascular slices showed that the incidence rates of AS of Guangxi Bama mini-pigs in experimental group and control group were 20% and 0,respectively.The association analysis between the results of vascular slices and AI in the pathogenic Guangxi Bama mini-pigs preliminarily suggested that AI was above 3.8 and lasted for more than 3 months during the attack. 相似文献
156.
157.
农业产业和经济发展速度的加快及科学技术水平的提高,使机械设计和制造技术在农业产业中大规模的推广应用。马铃薯作为农业产业重要的组成部分,通过提高其种植技术和水平可以间接地发展其种植潜力。该文在马铃薯种植期间以微型原种播种机为例,通过对原种种植农艺的分析,对关键部件的设计方案展开研究。 相似文献
158.
159.
In order to investigate the genetic diversity and the origin of evolutionary relationship of Zhongdian yak,we analyzed the complete sequence of 15 individuals Cytb gene,its sequence polymorphism was analyzed,and the phylogenetic tree was constructed.The results showed that the length of the nucleotide sequence were 1 140 bp,with nucleotide frequencies of 26.3%,31.8%,13.1% and 28.8% for T,A,G and C,respectively.Three haplotypes were identified of 15 individuals,with 3 polymorphic sites,including two conversions,one transversion,haplotype diversity was 0.2571 and nucleotide diversity was 0.00035.Phylogenetic analysis suggested that Zhongdian yak and Bos mutusc clustered firstly,then gathered with Bison bison,which indicated that there were high genetic similarity and closer genetic relationship,genetic similarity with other cattle genus was relatively low.Combining with the proof of molecular biology and paleontology,the result supported the point that Bos grunniens and Bos mutus were classified as an alone genus in Bovinae. 相似文献
160.