全文获取类型
收费全文 | 7993篇 |
免费 | 414篇 |
国内免费 | 798篇 |
专业分类
林业 | 707篇 |
农学 | 639篇 |
基础科学 | 304篇 |
752篇 | |
综合类 | 3668篇 |
农作物 | 634篇 |
水产渔业 | 328篇 |
畜牧兽医 | 1232篇 |
园艺 | 523篇 |
植物保护 | 418篇 |
出版年
2024年 | 51篇 |
2023年 | 139篇 |
2022年 | 324篇 |
2021年 | 331篇 |
2020年 | 306篇 |
2019年 | 296篇 |
2018年 | 200篇 |
2017年 | 338篇 |
2016年 | 253篇 |
2015年 | 380篇 |
2014年 | 372篇 |
2013年 | 452篇 |
2012年 | 588篇 |
2011年 | 569篇 |
2010年 | 518篇 |
2009年 | 434篇 |
2008年 | 510篇 |
2007年 | 498篇 |
2006年 | 375篇 |
2005年 | 320篇 |
2004年 | 224篇 |
2003年 | 270篇 |
2002年 | 388篇 |
2001年 | 327篇 |
2000年 | 244篇 |
1999年 | 151篇 |
1998年 | 45篇 |
1997年 | 44篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1965年 | 3篇 |
1963年 | 1篇 |
1962年 | 4篇 |
1956年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有9205条查询结果,搜索用时 15 毫秒
181.
道路交通的通达性是城市空间相互作用和经济联系的重要前提。本研究利用ArcGIS的网络分析和空间分析功能在对石羊河流域公路交通网络通达性定量评价的基础上,采用引力、潜力和场强模型对区域内7个县(区)的空间相互作用程度、城市潜力值和城市的辐射场强进行定量测度和比较分析。研究发现,凉州区对区域内城市作用力最强,城市对外相互作用潜力大,辐射带动作用强度高。区域整体上形成了以金川区、凉州区为中心的辐射中心,其对区域内其他县、区的辐射强度随交通距离增加和道路通达性降低而不断减小。 相似文献
182.
Qizhong SUN Fengqin GAO Zhu YU Ya TAO Shufen ZHAO Yimin CAI 《Animal Science Journal》2012,83(4):305-309
Effects of lactic acid bacteria (LAB) inoculants and cellulase additives on fermentation quality and chemical compositions of shrub silages were studied by using a small‐scale fermentation system. Two LAB inoculants of Qingbao (Lactobacillus plantarum, Pediococcus acidilacticii, Lactobacillus casei and Clostridium phage) and Caihe (Lactobacillus plantarum, Lactobacillus brevis and Pediococcus acidilactici) and a commercial cellulase made from Trichoderma reesei were used as additives for intermediate pea‐shrub, rush bushclover, arborescent ceratoides and shrubby silage preparation. The crude protein, neutral detergent fiber and water‐soluble carbohydrate contents of the four shrub materials were 10.1–14.2, 62.6–67.2 and 1.9–3.5% on a dry matter basis, respectively. All shrub silages had pH 3.40–4.43, ammonia‐N 0.1–0.2% g/kg and lactic acid 1.3–2.9% on a fresh matter basis. The silage quality of LAB‐inoculated silages did not have a greater effect than control silages, except shrubby silage preparation. Silages treated with the cellulase, the pH of rush bushclover and shrubby sweetvetch silage were significantly (P < 0.05) lower and the lactic acid content were significantly (P < 0.05) higher than the control silages. The results confirmed that shrub contained a relatively high content of crude protein; its silages can be preserved in good quality, and they are new potential resources for livestock feed. 相似文献
183.
M. L. Killian S. L. Swenson A. L. Vincent J. G. Landgraf B. Shu S. Lindstrom X. Xu A. Klimov Y. Zhang A. S. Bowman 《Zoonoses and public health》2013,60(3):196-201
Influenza‐like illness was noted in people and pigs in attendance at an Ohio county fair in August 2007. The morbidity rate in swine approached 100% within 1–2 days of initial clinical signs being recognized, and approximately two dozen people developed influenza‐like illness. Triple‐reassortant swine H1N1 influenza viruses were identified in both pigs and people at the fair. The identified viruses (A/Sw/OH/511445/2007, A/Ohio/01/2007, and A/Ohio/02/2007) were similar to H1N1 swine influenza viruses currently found in the U.S. swine population. This case illustrates the possibility of transmission of swine influenza in settings where there is close human/swine interaction. 相似文献
184.
185.
AIM: To down-regulate expression of c-myc through antisense therapy and to investigate its effect on the sensitivity of osteosarcoma MG-63 cells to cisplatin-induced apoptosis. METHODS: The recombinant adenovirus (Ad-Asc-myc) encoding antisense c-myc fragment was constructed and transfected into osteosarcoma MG-63 cells in vitro in order to down-regulate the expression of c-myc, and the change in the sensitivity to cisplatin-induced apoptosis was observed. MTT, Western blot, RT-PCR, flow cytometry (FCM) and electron microscope were used to evaluate tumor cell proliferation in vitro, genes expression related to apoptosis regulation and effects on the sensitivity of osteosarcoma MG-63 cells to cisplatin-induced apoptosis. RESULTS: Ad-Asc-myc down-regulated the expression of c-myc protein after transfected MG-63 cells for 48 h, combined with the treatment of 2.0 mg/L cisplatin for 2 h inhibited tumor cell proliferation in vitro by 38.0%. RT-PCR revealed that Ad-Asc-myc down-regulated the expression of Bcl-2 and up-regulated the expression of Bax. No appreciable change was observed in the expression of E2F-1. FCM showed that Ad-Asc-myc induced apoptosis in intransfected cells, and rendered it more sensitive to cisplatin. CONCLUSION: Antisense c-myc is able per se to induce apoptosis and sensitize osteosarcoma cells to cisplatin-induced apoptosis. 相似文献
186.
187.
AIM: The cancer biology has showed that overexpression of oncogenes is responsible for the progression of human malignancies,antisense technology can block a certain gene expression.Caffeine has enhancement effect on chemotherapy of osteosarcoma cells to cisplatin,we constructed the recombinant adenovirus (Ad-Asc-myc) encoding antisense c-myc fragment and investigated its effect on the in vitro sensitivity of osteosarcoma MG-63 cells to cisplatin.METHODS: The recombinant adenovirus (Ad-Asc-myc) encoding antisense c-myc fragment was constructed by cloning c-myc cDNA of about 750 base pairs in a reverse direction into adenovirus vector.Ad-Asc-myc and caffeine was used respectively or together to co-operate with cisplatin to treat the osteosarcoma MG-63 cells in vitro,and Western blotting,MTT,flow cytometry (FCM),electron microscope were used to evaluate expression of c-Myc protein,tumor cell proliferation in vitro,apoptosis and cell cycle analysis.RESULTS: Ad-Asc-myc was obtained with the titer of 2×1012 pfu/L.Ad-Asc-myc down-regulated the expression of c-Myc protein,Ad-Asc-myc or caffeine enhanced the effects of 2.0,5.0 mg/L cisplatin on MG-63 cells.Moreover,Ad-Asc-myc combined with caffeine significantly enhanced this effects,not only on cisplatin-induced apoptosis,but also on tumor cells proliferation in vitro.The expression of bcl-2 was downregulated,bax were upregulated,while there was no change in the expression of E2F-1.FCM analysis showed that cisplatin treatment induced a block in S phase,and caffeine reversed this block and speeded up the progression of cells out of the S phase.Ad-Asc-myc induced obvious G2/M phase arrest in transfected cells.CONCLUSION: Ad-Asc-myc combined with caffeine may enhance apoptosis-induced and chemotherapy effects of osteosarcoma MG-63 cells to cisplatin. 相似文献
188.
189.
190.