全文获取类型
收费全文 | 49507篇 |
免费 | 2198篇 |
国内免费 | 5377篇 |
专业分类
林业 | 5995篇 |
农学 | 8115篇 |
基础科学 | 4646篇 |
8310篇 | |
综合类 | 14169篇 |
农作物 | 2518篇 |
水产渔业 | 1842篇 |
畜牧兽医 | 6582篇 |
园艺 | 1551篇 |
植物保护 | 3354篇 |
出版年
2024年 | 142篇 |
2023年 | 481篇 |
2022年 | 1310篇 |
2021年 | 2018篇 |
2020年 | 1772篇 |
2019年 | 1840篇 |
2018年 | 1258篇 |
2017年 | 1704篇 |
2016年 | 1690篇 |
2015年 | 2296篇 |
2014年 | 2101篇 |
2013年 | 2612篇 |
2012年 | 3053篇 |
2011年 | 3335篇 |
2010年 | 3119篇 |
2009年 | 2906篇 |
2008年 | 2692篇 |
2007年 | 2701篇 |
2006年 | 2637篇 |
2005年 | 2615篇 |
2004年 | 1165篇 |
2003年 | 970篇 |
2002年 | 791篇 |
2001年 | 825篇 |
2000年 | 1004篇 |
1999年 | 1339篇 |
1998年 | 1195篇 |
1997年 | 1009篇 |
1996年 | 941篇 |
1995年 | 871篇 |
1994年 | 868篇 |
1993年 | 772篇 |
1992年 | 712篇 |
1991年 | 582篇 |
1990年 | 484篇 |
1989年 | 390篇 |
1988年 | 261篇 |
1987年 | 187篇 |
1986年 | 92篇 |
1985年 | 74篇 |
1984年 | 51篇 |
1983年 | 38篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 25篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1965年 | 9篇 |
1963年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
871.
雏鸭饲粮锰适宜水平的研究 总被引:4,自引:0,他引:4
采用玉米-豆饼型饲粮(含Mn19ppm),对210只1日龄北京雏鸭进行补锰试验,试验分7组,锰添加水平(试剂级MnSO_4·H_2O)按1~7组顺序依次为0,20,45,60,85,110,135ppm,试验期3周,研究雏鸭饲粮锰适宜水平。结果为,饲粮锰水平不影响雏鸭体增重,日采食量和饲料转化率(P>0.05);胫骨锰浓度随饲粮锰水平增加呈线性上升(P<0.01);肝、肾、胰、心组织锰浓度和肝脏含锰的SOD酶活性可与饲粮锰水平拟合为相应的二次曲线模式(P<0.001),上述软组织锰浓度和肝SOD酶活性达到平衡时,所需饲粮锰依次为110.05,100.00,122.91,113.99和116.00ppm。综合试验结果考虑,雏鸭饲粮锰适宜水平为110ppm。 相似文献
872.
农产品是整个食品链条的最上游,有效控制农产品的质量安全,对于保障食用安全、维护社会稳定具有重要意义。目前,社会各界对强化农产品管理力度的呼声越来越大,制定农产品质量安全管理的专门法——《农产品质量安全法》已成众望所归。文章拟从立法的意义和功能角度,对《农产品质量安全法》进行法学理论梳理,期望通过本文的论述,能够进一步澄清《农产品质量安全法》法理思路。 相似文献
873.
以华南某1 500头规模种猪场2009年到2010年1 502窝长白猪分娩信息进行优化、选配减少近交畸形的研究,结果显示血缘选配优化时将近交系数控制在1%比3%效果明显,平均产活仔数从10.39头/窝提高到10.46头/窝(P>0.05),畸形率从10.30%下降到4.79%(P<0.01);对其中402窝出现畸形仔猪... 相似文献
874.
“仙湖3号”鸭属快大、瘦肉型新品种,成活率高,49天龄体重3.0~3.5kg,父母代种鸭具有产蛋率高,受精率高,孵化率高等优点,是“仙湖”鸭课题组培育的一个优良品系。本文简要介绍提高“仙湖3号”种鸭生产性能的技术措施,希望通过改进饲养管理,提高经济效益。 相似文献
875.
Intramammary infusion of an Enterococcus faecium SF68 preparation promoted the involution of drying off Holstein cows partly related to neutrophil‐associated matrix metalloproteinase 9 下载免费PDF全文
Attapol Tiantong Hsing‐Yi Peng Shuen‐Ei Chen Piya Piamya Wen‐Bor Liu Ming‐Tsao Chen Chi Yu Hajime Nagahata Chai‐Ju Chang 《Animal Science Journal》2015,86(1):111-119
A problem for dairy cows following milk stasis is to cope with a high risk of intramammary infection and there is a need to initiate an extensive renewal of secretory modules in mammary glands so that milk production in next lactation may be optimized. We recently reported that ultrasonicated Enterococcus faecium SF68 (SF68) is compatible with cow mammary glands and an enhancer of innate immunity during the immediate post‐milk stasis period. The current study further examines the concomitant effect of ultrasonicated SF68 on mammary tissue remodeling. Four Holstein cows each received intramammary infusions of regular antibiotic dry‐cow formula (positive control) and two different doses of SF68 in different quarters. Analyses of individual quarter secretion samples showed faster neutrophil infiltration, earlier modifications in protein composition, including caseins and lactoferrins, as well as more prompt elevation of the specific unit of 92‐kDa matrix metalloproteinase 9 (MMP9) in SF68‐infused quarters compared to the positive controls. Intramammary infusion of ultrasonicated SF68 seems able to accelerate the regression of mammary synthetic capacity and potentiate the breakdown of glandular extracellular matrix, indicating a more efficient mammary gland involution. Correlation analyses imply that the ability of ultrasonicated SF68 to induce faster neutrophil chemotaxis and the associated MMP9 release is partly responsible. 相似文献
876.
877.
Luying Sun Fengbin Song Shengqun Liu Qingjun Cao Fulai Liu 《Archives of Agronomy and Soil Science》2013,59(14):1932-1943
ABSTRACTSustainable agricultural management practices have attracted increasing attention due to their significant roles in benefiting the functions and sustainability of agro-ecosystems. An integrated agricultural practice (IP) in a maize cropping system was developed by changing row spacing, adopting no-tillage and residue return in the Northeast China. A 12-year field study was carried out to evaluate the effect of IP and conventional practice (CP) on soil physical properties, microbial biomass and enzyme activity during the cropping season. The results showed that soil organic matter under IP was increased by 17.4, 9.88 and 6.69% in June, August and October, respectively, than CP. IP enhanced microbial biomass C (by 31.7, 25.1 and 30.4% in June, August and October) and activities of invertase, urease and phosphatase (by 27.2–38.0, 78.9–182 and 9.8–29.0%) compared to CP, possibly attributing to an increase in the soil microbial community. Furthermore, the soil pH, water content, nitrogen and phosphorus contents, microbial biomass and some specific enzyme activities varied with sampling time. It is concluded that IP improved soil quality and health by increasing organic matter content and microbial biomass and activity in maize field in Northeast China, suggesting that IP is a feasible management technology for sustainable agriculture. 相似文献
878.
Arginine (ARG) exerts many beneficial effects on animal body and enhanced angiogenesis, lactogenesis, which finally leads to the improvement in nitrogen (N) metabolism, reproduction, lactation, immunity and growth. Unfortunately, unprotected ARG will be degraded in the rumen and its price is high, thus feeding rumen-protected ARG seems to be uneconomical. Alternatively, N-carbamoyl glutamate (NCG) is structural analogue of N-acetyl glutamate, cofactor of cabamoyl phosphate synthetasel, is lower in rumen degradation compared to ARG. Additionally, rumen epithelial and duodenal cells have potentially utilized the NCG for ureagenesis. Supplementation of NCG to high yielding dairy cows increased plasma concentration of ARG and nitric oxide, decreased the plasma ammonia N and improved lactation performance and N utilization. Supplementation of NCG enhanced pregnancy rates in rats, improved litter size and fetal survival rate, thereby improved the reproductive performance of sows. Oral NCG supplementation increases plasma ARG and somatotropin levels, and increased growth rate and muscle protein synthesis in nursing piglets. The NCG is potential a relatively cheaper source of feed additive to offer vital compensation over oral administration of ARG, resulting in improved ruminant animal health and production. In this article, we reviewed the mechanism of AfiG biosynthesis by NCG and their significance in growth, reproduction, milk production and N utilization in ruminant animals. 相似文献
879.
880.
显微注射Ca^2+激活小鼠M Ⅱ期卵母细胞 总被引:2,自引:0,他引:2
胞质内显微注入Ca^2+可以激活小鼠M Ⅱ期卵母细胞,且随着卵龄的增加,激活率明显升高。卵龄小于16h(hCG注射后)注射Ca^2+引起的激活率很低,卵龄超过18h,激活率达到50%以上。卵龄小于16h的卵母细胞,卵内注入超纯水未能激活卵母细胞,而在18 ̄19h卵龄组,注射水的对照组激活率为35%,但显著或极显著地低于注射Ca^2+的试验组。激活前注射EDTA卵母细胞的激活率约为30%,激活后注射 相似文献