全文获取类型
收费全文 | 101643篇 |
免费 | 5182篇 |
国内免费 | 11079篇 |
专业分类
林业 | 12536篇 |
农学 | 16079篇 |
基础科学 | 9589篇 |
16958篇 | |
综合类 | 30112篇 |
农作物 | 5282篇 |
水产渔业 | 3710篇 |
畜牧兽医 | 13813篇 |
园艺 | 3381篇 |
植物保护 | 6444篇 |
出版年
2024年 | 216篇 |
2023年 | 1024篇 |
2022年 | 2728篇 |
2021年 | 3951篇 |
2020年 | 3694篇 |
2019年 | 3574篇 |
2018年 | 2484篇 |
2017年 | 3568篇 |
2016年 | 3432篇 |
2015年 | 4579篇 |
2014年 | 4374篇 |
2013年 | 5437篇 |
2012年 | 6431篇 |
2011年 | 7051篇 |
2010年 | 6620篇 |
2009年 | 6220篇 |
2008年 | 5871篇 |
2007年 | 5865篇 |
2006年 | 5655篇 |
2005年 | 5037篇 |
2004年 | 2396篇 |
2003年 | 2112篇 |
2002年 | 1635篇 |
2001年 | 1834篇 |
2000年 | 2140篇 |
1999年 | 2560篇 |
1998年 | 2521篇 |
1997年 | 2107篇 |
1996年 | 1914篇 |
1995年 | 1875篇 |
1994年 | 1594篇 |
1993年 | 1500篇 |
1992年 | 1328篇 |
1991年 | 1086篇 |
1990年 | 932篇 |
1989年 | 757篇 |
1988年 | 587篇 |
1987年 | 376篇 |
1986年 | 222篇 |
1985年 | 111篇 |
1984年 | 99篇 |
1983年 | 77篇 |
1982年 | 76篇 |
1981年 | 57篇 |
1980年 | 35篇 |
1979年 | 29篇 |
1978年 | 12篇 |
1965年 | 13篇 |
1964年 | 19篇 |
1963年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
41.
杨军威 《畜牧兽医科学(电子版)》2021,(4):188-189
畜牧养殖业污染问题是畜牧养殖生产过程中的常见问题,对于养殖业也有一定的影响,直接影响畜牧产品质量及动物疫病防治工作。该文针对畜牧养殖业污染现状进行分析研究,阐述畜牧养殖污染问题现状,并综合新疆地区的畜牧养殖业发展状态,提出畜牧养殖污染问题综合治理的有效对策。 相似文献
42.
Wang Zhun Zhang Hengheng Dong Qiang Gui Huiping Wang Xiangru Pang Nianchang Li Yongnian Niu Jing Jin Dingsha Wang Sujie Zhang Xiling Song Meizhen 《棉花学报》2021,32(6):538-551
[Objective] The aim of this study is to evaluate nitrogen efficient cotton germplasms and improve nitrogen use efficiency. [Method] Eighty cotton germplasms were selected and evaluated in the hydroponic experiment under low (0.25 mmol·L-1) and high (5 mmol·L-1) nitrogen concentration. Different traits for screening were identified and nitrogen use efficiency types were classified. Field experiments were also performed for comparison and confirmation of the identified germplasms. [Result] The results showed that there were significant differences in the total plant dry matter, shoot nitrogen accumulation and nitrogen absorption efficiency in cotton germplasms at the two nitrogen levels. Based on coefficient of variation, principal component analysis and correlation, six traits including total plant dry matter, shoot dry matter, root dry matter, total nitrogen accumulation, shoot nitrogen accumulation and nitrogen absorption efficiency were used as screening indicators. According to the Heatmap clustering analysis and the nitrogen efficiency comprehensive index, two germplasms (Lu05R59 and CCRI 69) were identified as low nitrogen tolerant and nitrogen efficient, and two germplasms (Coker 201 and Xinluzhong 30) as low nitrogen sensitive and nitrogen inefficient. The results of field experiment were consistent with the results of the hydroponic culture at the seedling stage. [Conclusion] It was finally determined that Lu05R59 and CCRI 69 were the low nitrogen tolerant and nitrogen efficient germplasms, and Coker 201 and Xinluzhong 30 were low nitrogen sensitive and nitrogen inefficient germplasms. The results of these studies provide the possibility for screening and rapid identification of nitrogen use efficiency in cotton at the seedling stage, and provide the ideal materials and theoretical basis for further study of cotton nitrogen efficient. 相似文献
43.
l-proline (Pro) is a precursor of ornithine, which is converted into polyamines via ornithine decarboxylase (ODC). Polyamines plays a key role in the proliferation of intestinal epithelial cells. The study investigated the effect of Pro on polyamine metabolism and cell proliferation on porcine enterocytes in vivo and in vitro. Twenty-four Huanjiang mini-pigs were randomly assigned into 1 of 3 groups and fed a basal diet that contained 0.77% alanine (Ala, iso-nitrogenous control), 1% Pro or 1% Pro + 0.0167% α-difluoromethylornithine (DFMO) from d 15 to 70 of gestation. The fetal body weight and number of fetuses per litter were determined, and the small and large intestines were obtained on d 70 ± 1.78 of gestation. The in vitro study was performed in intestinal porcine epithelial (IPEC-J2) cells cultured in Dulbecco''s modified Eagle medium-high glucose (DMEM-H) containing 0 μmol/L Pro, 400 μmol/L Pro, or 400 μmol/L Pro + 10 mmol/L DFMO for 4 d. The results showed that maternal dietary supplementation with 1% Pro increased fetal weight; the protein and DNA concentrations of the fetal small intestine; and mRNA levels for potassium voltage-gated channel, shaker-related subfamily, member 1 (Kv1.1) in the fetal small and large intestines (P < 0.05). Supplementing Pro to either gilts or IPEC-J2 cells increased ODC protein abundances and polyamine concentrations in the fetal intestines and IPEC-J2 cells (P < 0.05). In comparison with the Pro group, the combined administration of Pro and DFMO reduced the expression of ODC protein and spermine concentration in the fetal intestine, as well as the concentrations of putrescine, spermidine and spermine in IPEC-J2 cells (P < 0.05). Meanwhile, the percentage of cells in the S-phase and the mRNA levels of proto-oncogenes c-fos and c-myc were increased in response to Pro supplementation, whereas depletion of cellular polyamines with DFMO increased tumor protein p53 (p53) mRNA levels (P < 0.05). Taken together, dietary supplementation with Pro improved fetal pig growth and intestinal epithelial cell proliferation via enhancing polyamine synthesis. 相似文献
44.
45.
46.
The prognosis of liver cancer was inferior among tumors. New medicine treatments are urgently needed. In this study, a novel exopolysaccharide EPS364 was purified from Vibrio alginolyticus 364, which was isolated from a deep-sea cold seep of the South China Sea. Further research showed that EPS364 consisted of mannose, glucosamine, gluconic acid, galactosamine and arabinose with a molar ratio of 5:9:3.4:0.5:0.8. The relative molecular weight of EPS364 was 14.8 kDa. Our results further revealed that EPS364 was a β-linked and phosphorylated polysaccharide. Notably, EPS364 exhibited a significant antitumor activity, with inducing apoptosis, dissipation of the mitochondrial membrane potential (MMP) and generation of reactive oxygen species (ROS) in Huh7.5 liver cancer cells. Proteomic and quantitative real-time PCR analyses indicated that EPS364 inhibited cancer cell growth and adhesion via targeting the FGF19-FGFR4 signaling pathway. These findings suggest that EPS364 is a promising antitumor agent for pharmacotherapy. 相似文献
47.
48.
49.
50.