全文获取类型
收费全文 | 13886篇 |
免费 | 668篇 |
国内免费 | 1595篇 |
专业分类
林业 | 1577篇 |
农学 | 2375篇 |
基础科学 | 1177篇 |
2203篇 | |
综合类 | 4121篇 |
农作物 | 866篇 |
水产渔业 | 462篇 |
畜牧兽医 | 1952篇 |
园艺 | 486篇 |
植物保护 | 930篇 |
出版年
2024年 | 35篇 |
2023年 | 134篇 |
2022年 | 366篇 |
2021年 | 512篇 |
2020年 | 515篇 |
2019年 | 480篇 |
2018年 | 357篇 |
2017年 | 469篇 |
2016年 | 500篇 |
2015年 | 632篇 |
2014年 | 583篇 |
2013年 | 704篇 |
2012年 | 828篇 |
2011年 | 898篇 |
2010年 | 840篇 |
2009年 | 777篇 |
2008年 | 731篇 |
2007年 | 800篇 |
2006年 | 723篇 |
2005年 | 700篇 |
2004年 | 340篇 |
2003年 | 416篇 |
2002年 | 483篇 |
2001年 | 462篇 |
2000年 | 379篇 |
1999年 | 413篇 |
1998年 | 313篇 |
1997年 | 273篇 |
1996年 | 215篇 |
1995年 | 213篇 |
1994年 | 213篇 |
1993年 | 175篇 |
1992年 | 167篇 |
1991年 | 115篇 |
1990年 | 95篇 |
1989年 | 106篇 |
1988年 | 79篇 |
1987年 | 39篇 |
1986年 | 19篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
当年常温育苗的稚贝生长期主要在8~11月,12月~翌年2月为越冬期。采用 W—a·L~b 这一幂函数描述稚贝壳长与体重的相关关系(W 代表体重、L 代表壳长)。风浪小、饵料丰富的内湾及虾池是稚贝适宜的中间育成水域。早育苗、早出库增加稚贝有效生长时间是获得大规格种苗的关键。稚贝壳长达5.0~6.0mm 时应及时分苗,调整网目及密度,保持网袋流水畅通。沙蚕、海星、蟹类是稚贝的敌害,夏季高温容易造成1龄贝大量死亡。 相似文献
992.
994.
当前我国科研人员窘迫的收入情况与日益增加的中央财政科研投入形成鲜明的反差。国务院颁发的《关于改进加强中央财政科研项目和资金管理的若干意见》,对这种科研分配的不合理现状进行了针对性改进。该文结合当前项目的申请、执行、预算、绩效等争议热点,对该《意见》对科研管理工作的实质性指导意义进行了简要阐述。 相似文献
995.
以山东省小型渔船为研究对象,用回归分析方法,求出了小型渔船主要参数间关系,并给出了船长、船宽、吃水、船型系数,设计纵倾的估算公式和取值范围。 相似文献
996.
针对近海渔业资源大幅衰退、生物生存环境日益恶化、生态容量下降呈荒漠化的现状,以中国海洋渔业经济保持可持续发展为目的,提出研究和投放高效耐久型人工鱼礁建设海洋牧场的必要和可行性,旨在恢复和平衡海洋生态食物链系统,改善局部的鱼类生存环境,充分利用海域有限空间,高效地保护生态资源。研究重点为降低人工鱼礁使用成本,可提高投资所能获得长期的经济收益。,对比了国内外同类研究进展和实施现代人工鱼礁这类渔业工程的现状。高效耐久型人工鱼礁对调整和优化海洋产业结构、带动促进海洋渔业和相关产业经济的增长发展均具有重大的战略意义和深远的历史意义。 相似文献
997.
Hong-tao Chang Xiu-yuan He Yu-Feng Liu Lu Chen Quan-hai Guo Qiu-ying Yu Jun Zhao Xin-wei Wang Xia Yang Chuan-qing Wang 《Journal of veterinary science (Suw?n-si, Korea)》2014,15(3):399-407
A recombinant replication-defective adenovirus expressing the major epitopes of porcine circovirus-2 (PCV-2) capsid protein (rAd/Cap/518) was previously constructed and shown to induce mucosal immunity in mice following intranasal delivery. In the present study, immune responses induced by intranasal immunization with a combination of rAd/Cap/518 and cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODN) were evaluated in mice. The levels of PCV-2-specific IgG in serum and IgA in saliva, lung, and intestinal fluids were significantly higher in the group immunized with rAd/Cap/518 and CpG ODN than animals immunized with rAd/Cap/518 alone. The frequencies of IL-2-secreting CD4+ T cells and IFN-γ-producing CD8+ T cells were significantly higher in the combined immunization group than mice immunized with rAd/Cap/518 alone. The frequencies of CD3+, CD3+CD4+CD8-, and CD3+CD4-CD8+ T cells in the combined immunization group were similar to that treated with CpG ODN alone, but significantly higher than mice that did not receive CpG ODN. PCV-2 load after challenge in the combined immunization group was significantly lower than that in the phosphate-buffered saline placebo group and approximately 7-fold lower in the group treated with CpG ODN alone. These results indicate that rAd/Cap/518 combined with CpG ODN can enhance systemic and local mucosal immunity in mice, and represent a promising synergetic mucosal vaccine against PCV-2. 相似文献
998.
Zhiqi Zhang Gang Shu Xiaotong Zhu Junming Guo Han Cai Songbo Wang Lina Wang Ping Gao Qianyun Xi Yongliang Zhang Li Yuan Qingyan Jiang 《畜牧与生物技术杂志(英文版)》2014,(4):406-413
Background:Fatty acid(FA) composition is the most important parameter affecting the flavor and nutritional value of the meat.The final and the only committed step in the biosynthesis of triglycerides is catalyzed by diacylglycerol acyltransferase 2(DGAT2).The role of DGAT2 in lipid accumulation has been demonstrated in adipocytes,However,little is known about the effect of DGAT2 on the FA composition of these cells.Methods:To investigate the role of DGAT2 in regulating lipid accumulation,FA composition and the expression of adipogenic genes,we cloned the open reading frame of the porcine DGAT2 gene and established 3T3-L1 cells that overexpressed DGAT2.Cells were then cultured in differentiation medium(DM) without FA,with a mixture of FAs(FA-DM),or containing a ~(13)C stable isotope-labeled FA mixture(IFA-DM).The FA composition of adipocytes was analyzed by gas chromatography-mass spectrometry and gas chromatography-isotope ratio mass spectrometry.Quantitative PCR and western blotting were employed to detect expression of adipogenic genes in 3T3-L1 adipocytes cultured with FA-DM for 12 d.Results:The triacylglyceride(TAG) content was significantly higher in 3T3-L1 adipocytes overexpressing DGAT2 than in control cells.When cultured in DM or FA-DM for 12 d,cells overexpressing DGAT2 showed a higher proportion of unsaturated FAs(C16:1 and C18:1).However,when cells overexpressing DGAT2 were cultured with FA-DM for30 min,the FA composition was almost identical to that of controls.Further,the proportion of stable isotope-labeled FAs were similar in 3T3-L1 adipocytes overexpressing DGAT2 and control cells cultured in IFA-DM for 12 d.These results collectively indicate that the higher proportion of mono-unsaturated FAs,C16:1 and C18:1,may originate from de novo FA synthesis but not from the uptake of specific FAs from the medium.This hypothesis is further supported by evidence that both mRNA and protein expression of genes involved in FA synthesis(ACACA,FASN,SCD1,and A-FABP? 相似文献
999.
Background
Highly automated cage-rearing systems are becoming increasingly popular in China. However, a high stocking density can cause oxidative stress and decrease broiler performance. The tryptophan (TRP) derivative 5-hydroxytryptophan (5-HT) has been shown to preserve membrane fluidity in birds suffering from oxidative stress. Therefore, this experiment was conducted to determine the effects of dietary TRP supplementation on performance, breast meat quality and oxidative stress in broilers reared in cages with a high or low stocking density.Methods
Female Arbor Acres broilers (25-d-old, n = 144) were randomly allocated to 1 of 4 treatments. The birds were fed a diet based on corn, soybean meal, cottonseed meal and corn gluten meal containing either 0.18 or 0.27% TRP and were housed with stocking densities of 11 or 15.4 birds/m2 in a 2 × 2 factorial experiment. Broiler performance was evaluated from d 25 to 42. Eight birds from each treatment were slaughtered on d 42 and plasma and breast muscle samples were collected to measure biochemical indices.Results
A higher stocking density tended to be associated with reduced weight gain (P < 0.10), and significantly increased plasma glutamic-pyruvic transaminase (GPT) activity (P < 0.001). Increased dietary TRP significantly reduced the activities of lactic dehydrogenase and GPT while increasing total cholesterol in the plasma (P < 0.01), reducing drip loss of breast muscle (P < 0.10) and improving feed efficiency (P < 0.10).Conclusions
An increase in dietary TRP, 1.5-fold higher than the standard supplementation level, can alleviate oxidative stress as well as improve welfare and feed efficiency in broilers reared in cages with a high stocking density. 相似文献1000.
Bing Guo Kritaya Kongsuwan Paul L Greenwood Guanghong Zhou Wangang Zhang Brian P Dalrymple 《畜牧与生物技术杂志(英文版)》2014,5(1):35