全文获取类型
收费全文 | 44249篇 |
免费 | 2389篇 |
国内免费 | 4308篇 |
专业分类
林业 | 4106篇 |
农学 | 4895篇 |
基础科学 | 3312篇 |
5844篇 | |
综合类 | 17249篇 |
农作物 | 2871篇 |
水产渔业 | 1951篇 |
畜牧兽医 | 6102篇 |
园艺 | 2057篇 |
植物保护 | 2559篇 |
出版年
2024年 | 232篇 |
2023年 | 626篇 |
2022年 | 1539篇 |
2021年 | 1842篇 |
2020年 | 1707篇 |
2019年 | 1689篇 |
2018年 | 1165篇 |
2017年 | 1963篇 |
2016年 | 1528篇 |
2015年 | 2228篇 |
2014年 | 2221篇 |
2013年 | 2579篇 |
2012年 | 3456篇 |
2011年 | 3820篇 |
2010年 | 3442篇 |
2009年 | 3046篇 |
2008年 | 2948篇 |
2007年 | 2689篇 |
2006年 | 2161篇 |
2005年 | 1742篇 |
2004年 | 983篇 |
2003年 | 855篇 |
2002年 | 976篇 |
2001年 | 927篇 |
2000年 | 820篇 |
1999年 | 667篇 |
1998年 | 495篇 |
1997年 | 407篇 |
1996年 | 326篇 |
1995年 | 299篇 |
1994年 | 294篇 |
1993年 | 251篇 |
1992年 | 208篇 |
1991年 | 189篇 |
1990年 | 177篇 |
1989年 | 151篇 |
1988年 | 83篇 |
1987年 | 58篇 |
1986年 | 37篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1964年 | 5篇 |
1963年 | 4篇 |
1962年 | 5篇 |
1956年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
981.
汽车悬架阻尼匹配研究及减振器设计 总被引:3,自引:0,他引:3
为了使车辆满足平顺性要求,对车辆悬架系统阻尼匹配进行了研究,建立了最佳阻尼比设计方法及减振器速度特性分段线性数学模型.以此模型为基础,建立了减振器阎系参数设计数学模型,并对阀系参数进行优化设计.对设计减振器进行了特性试验和整车振动试验,并与原车裁减振器性能进行了对比.结果表明,车辆悬架系统阻尼匹配合理,减振器阀系参数设计方法正确,设计参数值准确、可靠. 相似文献
982.
中小功率内燃机空气滤清器的应用现状 总被引:1,自引:0,他引:1
综述了与空气滤清器研究有关的文献,主要包括空气滤清器的原理,研究现状及发展趋势,并在此基础上提出未来一些课题的可能研究方向. 相似文献
983.
984.
985.
986.
987.
AIM: To study the influence of basic fibroblast growth factor(bFGF) on treating ed palatal perforation in rats. METHODS: bFGF was given to the early palatal perforation in rat. The granulation tissues in perforations were grossly and pathologically obserVed. RESULTS: The the of wound healing was significantly in- crease in the bFGF group (P<0.01 ). bFGF could obviously promote the proliferation of the granulation tissues and fibroblasts. The number of AgNORs granules in fibrablasts were 3.73 ±0.52 in the buy group and 2.11 ±0.31 in control group (P < 0.05). CONCLUSION: bFGF could promote the growth of granulation tissues and had a strong promotion on the wound healing in palatal perforation. It was helpful in repairing palatal perforation. 相似文献
988.
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
989.
QIAN Wei LOU Guo-qiang ZHOU Zhuo-lin WANG Jia LIU Xiu-jie HAO Mao-lin WANG Wan-tie 《园艺学报》2000,36(11):2056-2061
AIM To investigate the role of curcumin (CUR) in lung ischemia/reperfusion (I/R) injury (LIRI) and its relationship with autophagy. METHODS 40 SD rats were randomly divided into sham operation (sham) group, I/R group, solvent (DMSO) group, CUR group and CUR+rapamycin (CUR-Rap) group. The rats were intraperitoneally injected with normal saline, DMSO, CUR or CUR+Rap before operation. After the rat LIRI model was established, the lung tissues were taken to measure W/D, TLW, IAR, and the contents of SOD and MDA were also measured to indicate the oxidative stress level. Light and electron microscopes were used to observed the morphology and ultrastrucure of lung tissues. The expression levels of autophagy-related proteins were determined by Western blot to evaluate autophagy levels. RESULTS Compared with sham group, wet weight/dry weight (W/D), total lung water (TLW), injured alveoli rate(IAR) and malondialdehyde (MDA) content in all other groups were increased, superoxide dismutase (SOD) activity was decreased, the levels of autophagy were increased (P <0.05), and lung tissue injury and cell ultrastructural damage were aggravated in CUR group. Compared with DMSO group, W/D, TLW and IAR and MDA content were decreased, SOD activity was decreased, autophagy levels were also decreased (P <0.05), and lung tissue and cell ultrastructural damage were attenuated. Compared with CUR group, W/D, TLW, IAR and MDA content were increased, SOD activity declined, the autophagy levels were increased (P <0.05), and damage of lung tissues and cells were more serious in CUR-Rap group. CONCLUSION Curcumin attenuates the lung I/R injury in rats, and its mechanism may be related to the reduction of oxidative stress and the inhibition of autophagy. 相似文献
990.