全文获取类型
收费全文 | 24915篇 |
免费 | 4408篇 |
国内免费 | 2066篇 |
专业分类
林业 | 2072篇 |
农学 | 2828篇 |
基础科学 | 1528篇 |
4022篇 | |
综合类 | 6442篇 |
农作物 | 1135篇 |
水产渔业 | 3225篇 |
畜牧兽医 | 6633篇 |
园艺 | 1020篇 |
植物保护 | 2484篇 |
出版年
2024年 | 93篇 |
2023年 | 302篇 |
2022年 | 727篇 |
2021年 | 1021篇 |
2020年 | 1256篇 |
2019年 | 1787篇 |
2018年 | 1376篇 |
2017年 | 1727篇 |
2016年 | 1598篇 |
2015年 | 1678篇 |
2014年 | 1758篇 |
2013年 | 2051篇 |
2012年 | 1784篇 |
2011年 | 1823篇 |
2010年 | 1896篇 |
2009年 | 1339篇 |
2008年 | 1288篇 |
2007年 | 1057篇 |
2006年 | 962篇 |
2005年 | 841篇 |
2004年 | 477篇 |
2003年 | 437篇 |
2002年 | 481篇 |
2001年 | 416篇 |
2000年 | 475篇 |
1999年 | 371篇 |
1998年 | 303篇 |
1997年 | 299篇 |
1996年 | 258篇 |
1995年 | 230篇 |
1994年 | 245篇 |
1993年 | 190篇 |
1992年 | 177篇 |
1991年 | 139篇 |
1990年 | 146篇 |
1989年 | 99篇 |
1988年 | 68篇 |
1987年 | 43篇 |
1986年 | 30篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1965年 | 4篇 |
1963年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
盐池半荒漠风沙区土地沙漠化发生发展规律的研究 总被引:1,自引:0,他引:1
本文耐盐池半荒漠风沙区土地沙漠化发生发展规律进行了探讨,主要分析了在土地沙漠化的过程中土壤和植被的变化过程及其成因。 相似文献
92.
93.
94.
95.
96.
97.
七种与小麦近缘的野生植物对禾谷缢管蚜抗性的生化机制 总被引:2,自引:0,他引:2
研究了7种与小麦近缘的多年生野生植物长穗偃麦草Elytrigia elongata、费尔干偃麦草E. ferganensis、垂穗披碱草Elymus nutans、华山新麦草Psathyrostachys huanshanica、竖立鹅观草Roegneria japonensis、鹅观草R. kamoji和R. tsukushiensis对禾谷缢管蚜Rhopalosiphum padi抗性的生化机制.禾谷缢管蚜内禀自然增长率(rm)与叶片游离脯氨酸和蛋氨酸含量呈极显著和显著正相关,其逐步回归方程为:rm=-0.0198 0.1930X脯氨酸** 0.3350X蛋氨酸* ;总酚含量与禾谷缢管蚜内禀自然增长率无显著相关关系;丁布含量与内禀自然增长率呈极显著的负相关(r=-0.941**,p<0.01).低含量的游离脯氨酸﹑蛋氨酸及高含量的丁布是小麦近缘多年生野生物种抗蚜的重要生化因子. 相似文献
98.
AIM: To explore interaction and biological behaviour changes of two kinds of cells-blastocysts and hepatocarcinoma cells in the same microenvironment. METHODS:The models of mouse blastocysts co-cultured with human hepatocarcinoma cell lines were established, then biological behaviours and mutual effects of the two kinds of cells in co-culture system were observed. RESULTS: Compared with control group, hepatocarcinoma cells with differently invasive and metastatic potential significantly enhanced the rates of blastocyst hatchment , attachment and outgrowth(P<0.05). There was no significant difference in those among hepatocarcinoma cells co-cultured groups (P>0.05). The blastocyst hatched and attached to hepatocarcinoma cells with differently invasive and metastatic potential. Then, differential trophoblasts invaded hepatocarcinoma cells. The clear-cut interfaces were gradually formed between both sides. Hepatocarcinoma cells on interface showed changes of growth direction and cell shapes and did not invade blastocysts. CONCLUSIONS: Hepatocarcinoma cells promoted blastocyst development. Blastocysts implanted and invaded hepatocarcinoma cells with differently invasive and metastatic potential in vitro, which indicate that blastocyst implantation in vitro does not relate with the kinds and differential level of interactional cells and the low selectivity maybe relate with high adaptability of early life. 相似文献
99.
AIM: To investigate the role of nitric oxide synthase (NOS), soluble guanylyl cyclase (sGC) and protein kinase C (PKC) signaling in tumor necrosis factor-α (TNF-α)-induced cardioprotection against hypoxia/reoxygenation (H/R) injury. METHODS: Neonatal rat ventricular myocytes were pretreated with TNF-α or sodium nitroprusside (SNP) or L-arginine (L-Arg), respectively, for 12 h and then subjected to continuous hypoxia for 12 h, followed by reoxygenation for 6 h. The manganese superoxide dismutase (Mn-SOD) activity of the cells was measured after H/R. Myocyte injury was determined by the release of lactic dehydrogenase (LDH). RESULTS: TNF-α (105 U/L) significantly increased the Mn-SOD activity and decreased release of LDH from ventricular myocytes. The cardioprotection against H/R injury was induced by the pretreatment with SNP (5 μmol/L) or L-Arg (5 mmol/L), which was blocked by ODQ (10 μmol/L), the specific sGC inhibitor, and Chel (5 μmol/L), the specific PKC inhibitor. Pretreatment with L-NAME (100 μmol/L), ODQ, Chel, antoxidant 2-MPG (400 μmol/L) or tyrosine kinase inhibitor genistein (50 μmol/L) attenuated the increased Mn-SOD activity and reduced LDH level induced by TNF-α. CONCLUSION: The results suggest that NO may play a role in TNF-α-induced cardioprotection, which is mediated by sGC and PKC. 相似文献
100.