全文获取类型
收费全文 | 56066篇 |
免费 | 3268篇 |
国内免费 | 5081篇 |
专业分类
林业 | 5135篇 |
农学 | 4374篇 |
基础科学 | 3018篇 |
5901篇 | |
综合类 | 24493篇 |
农作物 | 3661篇 |
水产渔业 | 2671篇 |
畜牧兽医 | 8722篇 |
园艺 | 3904篇 |
植物保护 | 2536篇 |
出版年
2024年 | 317篇 |
2023年 | 912篇 |
2022年 | 2225篇 |
2021年 | 2453篇 |
2020年 | 2293篇 |
2019年 | 2316篇 |
2018年 | 1635篇 |
2017年 | 2465篇 |
2016年 | 1833篇 |
2015年 | 2750篇 |
2014年 | 2839篇 |
2013年 | 3458篇 |
2012年 | 4711篇 |
2011年 | 4756篇 |
2010年 | 4569篇 |
2009年 | 4185篇 |
2008年 | 3888篇 |
2007年 | 3578篇 |
2006年 | 3061篇 |
2005年 | 2326篇 |
2004年 | 1400篇 |
2003年 | 1061篇 |
2002年 | 1126篇 |
2001年 | 975篇 |
2000年 | 897篇 |
1999年 | 571篇 |
1998年 | 296篇 |
1997年 | 263篇 |
1996年 | 209篇 |
1995年 | 181篇 |
1994年 | 158篇 |
1993年 | 147篇 |
1992年 | 122篇 |
1991年 | 117篇 |
1990年 | 66篇 |
1989年 | 63篇 |
1988年 | 52篇 |
1987年 | 34篇 |
1986年 | 22篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1965年 | 2篇 |
1963年 | 1篇 |
1962年 | 13篇 |
1959年 | 1篇 |
1956年 | 21篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
AIM: To observe effects of homocysteine and antagonized effects of taurine on electronic leakage and free radical production in myocardial mitochondria. METHODS: Myocardial mitochondria of rat heart was isolated, and was broken by supersonic wave to prepare submitochondria. Recombinant of succinic acid cytochrome c reductase was prepared with mitochondria of porcine heart. They were co-incubated with homocysteine and/or taurine with various concentration. The H2O2 and O2- were determined by chemiluminescence methods. The taurine transporter of heart mitochondria and its propert, and effects of homocysteine on its function were studied with glass filter. RESULTS: Homocysteine stimulated oxygen free radical production in heart mitochondria, submitochondria, and succinic acid cytochrome c in a concentration-dependent manner. Although taurine itself did not affect oxygen free radical production, taurine did inhibit oxygen free radical production in mitochondria, submitochondria and succinic acid cytochrome c in a concentration-dependent manner. Taurine transporters of Na+-dependent were existed in mitochondria membrane. Homocysteine inhibited taurine transtport in mitochondria in a concentration-dependent manner. CONCLUSIONS: Taurine inhibited electronic leakage and oxygen free radical production induced by homocysteine in electron transport chain. There were taurine transporters in mitochondria membrane, and transport functions of taurine transporter were inhibited by homocysteine. 相似文献
172.
AIM: To investigate the role of adrenomedullin (AM) in diabetic nephropathy. METHODS: We observed the changes in the expression and secretion of AM, TGF-β1 in the cultured human mesangial cells under high glucose condition and the contents of the laminin and type IV collagen in the supernatants. The effect of intervention with AM was also observed. RESULTS: High glucose condition resulted in increase in the expression and secretion of AM、 TGF-β1、 laminin and type IV collagen. AM reversed the influence of high glucose on the cultured human mesangial cells. CONCLUSION: These results showed that high glucose condition is one of stimulating factors of AM and the renal protective action of AM may be associated with suppression of TGF-β1 and reducing excessive accumulat ion of laminin and type IV collagen. 相似文献
173.
AIM: To examine the effects of inhibition of Kupffer cell and splenectomy on intestinal endotoxemia and hepatic injury. METHODS: The hepatic injury model was established by treatment with thioacetamide (TAA). At the same time, inhibition of Kupffer cells by intravenous GdCl3 and splenectomy were performed. Serum alanine aminotransferase (ALT), TNF-α, endotoxin content and phagocytic index were observed. RESULTS: In the TAA+GdCl3 group, and TAA+splenectomy group, the endotoxin content was significently higher than that in normal and TAA group (P<0.05). The plasma TNF-α, ALT and total bilirubin were significantly lower than those in TAA group (P<0.05). CONCLUSION: Inhibition of Kupffer cells and splenectomy increase plasma endotoxin level, but decreases the plasma TNF-α levels and alleviates the hepatic injury induced by TAA. 相似文献
174.
通过 PCR技术 ,以马立克氏病病毒 (MDV) RB1B株基因组 DNA为模板 ,扩增了包括 pp38基因及其启动子 -增强子和终止子在内的 2 2 0 0 bp的核酸片段。将该片段用 Sac 和 Sph 酶定向克隆到 p U C18质粒中 ,构建成重组质粒 ;将重组质粒转染鸡胚成纤维细胞 (CEF) ,用小鼠抗大肠杆菌表达的 pp38血清作间接免疫荧光试验 ,验证 pp38基因的表达。结果 ,在转染的细胞浆中看到了绿色的荧光 ,证实了该启动子的单向启动活性 相似文献
175.
176.
猫细小病毒NS部分基因的克隆及序列分析 总被引:1,自引:0,他引:1
将疫苗用猫细小病毒(FPV)株提取基因组DNA,针对NS特定片段设计引物,利用PCR扩增出了部分基因并将该基因克隆到pMD18-T Vector中测序.结果表明,该基因长613bp,编码204个氨基酸.分离株基因与犬的细小病毒(CPV)、貂的细小病毒(MEV)毒株核苷酸同源性均为99%.氨基酸同源性达到97%、98%以上,与犬、貂的肠炎病毒有密切的亲缘关系. 相似文献
177.
马立克氏病病毒pp38基因启动子和增强子的克隆和序列分析 总被引:4,自引:0,他引:4
参考GeneBank发表的马立克氏病病毒(MDV)国际标准强毒株GA的基因序列,设计合成一对引物,分别以RBIB,814,GD2(广东分离株),J-1-E(北京分离株),Md11,Md5,CV1988等不同毒株的MDV基因组DNA为模板,通过PCR扩增,获得了预期大小的PCR产物。该产物经pGEM-T-easy克隆后测序,将所得序列进行比较分析。结果发现:不同毒株间pp38基因的启动子和增强子序列间有缺失突变,序列的同源性大于95.9%,其中大多数的突变发生在MDV复制的原点附近。 相似文献
178.
179.
Acetylcholinesterase (AChE) was purified by affinity chromatography from two populations of the oriental migratory locust, Locusta migratoria manilensis (Meyen), collected from Huanghua and Pingshan Counties, Hebei Province of China. The purification factors and yields were 1661-fold and 19.3%, respectively, for the Huanghua population, and 3897-fold and 39.6% for the Pingshan population. Both the purification factor and yield were significantly lower in the Huanghua population than in the Pingshan population. AChE activity was almost completely inhibited by 10−6 M eserine and BW284C51, but ?5.8% of AChE activity was inhibited by ethopropazine at the same concentration, suggesting that purified AChE from either population was a typical insect AChE. However, AChE purified from the Huanghua population was 62-, 2.0-, and 1.6-fold less sensitive to inhibition by the three organophosphate compounds, chlorpyrifos oxon, demeton-S-methyl, and paraoxon, respectively, than that from the Pingshan population. Significantly lower purification factor and low yield associated with reduced sensitivity of AChE to inhibition by the organophosphates indicated that AChE purified from the Huanghua population was biochemically and pharmacologically different from that of the Pingshan population. Reduced sensitivity of AChE appeared to contribute to organophosphate resistance in the locust from Huanghua County, where insecticides have commonly been used to manage outbreaks of the locust. 相似文献
180.