全文获取类型
收费全文 | 11707篇 |
免费 | 431篇 |
国内免费 | 1048篇 |
专业分类
林业 | 970篇 |
农学 | 936篇 |
基础科学 | 1458篇 |
1852篇 | |
综合类 | 4345篇 |
农作物 | 917篇 |
水产渔业 | 56篇 |
畜牧兽医 | 814篇 |
园艺 | 1000篇 |
植物保护 | 838篇 |
出版年
2024年 | 32篇 |
2023年 | 146篇 |
2022年 | 274篇 |
2021年 | 361篇 |
2020年 | 332篇 |
2019年 | 455篇 |
2018年 | 271篇 |
2017年 | 273篇 |
2016年 | 315篇 |
2015年 | 425篇 |
2014年 | 680篇 |
2013年 | 752篇 |
2012年 | 1418篇 |
2011年 | 1454篇 |
2010年 | 980篇 |
2009年 | 1087篇 |
2008年 | 469篇 |
2007年 | 1125篇 |
2006年 | 947篇 |
2005年 | 396篇 |
2004年 | 142篇 |
2003年 | 84篇 |
2002年 | 68篇 |
2001年 | 58篇 |
2000年 | 94篇 |
1999年 | 75篇 |
1998年 | 56篇 |
1997年 | 46篇 |
1996年 | 38篇 |
1995年 | 50篇 |
1994年 | 46篇 |
1993年 | 46篇 |
1992年 | 36篇 |
1991年 | 36篇 |
1990年 | 34篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1962年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
91.
为分析抗菌肽粗提物对肉鸡生长性能、粪便微生物菌群结构及经济效益的影响,试验选择体重相近的21日龄白羽肉鸡600只,随机分成4组,每组15个重复,每个重复10只,1组为空白对照组饲喂基础日粮,试验2、3、4组在基础日粮中分别添加1.0%、1.5%、2.0%的抗菌肽粗提物,试验期为21 d。结果表明:(1)试验2、3、4组的平均采食均高于1组(P > 0.05)|试验3、4组的平均日增重较1组比分别提高11.0%、9.4%(P < 0.05),料重比较1组比分别降低18.5%、15.2% (P < 0.05)|(2)试验3、4组粪便中大肠杆菌的含量较1组分别降低14.3%、18.0%(P < 0.05),试验3、4组粪便中乳酸杆菌、双歧杆菌的含量较1组比分别提高4.6%、6.7%、14.5%、12.3%(P < 0.05)|(3)试验3、4组每只肉鸡经济效益较1组比分别提高19.3%、17.7%。综上,1.5%抗菌肽粗提物添加可以提高白羽肉鸡生长性能,改善粪便微生物菌群结构,提高其经济效益。
[关键词] 抗菌肽粗提物|白羽肉鸡|生长性能|粪便微生物菌群结构|经济效益 相似文献
92.
93.
张正友法的摄像机标定试验 总被引:1,自引:0,他引:1
针对机器视觉领域的摄像机标定问题,采用介于自标定与传统标定之间张正友法,对Sunway-130D数字摄像机进行标定。本研究首先阐述张正友法标定原理,即利用针孔模型匹配模板平面与其所成图像中的角点,计算出图像和模板之间的单应性矩阵,利用该单应矩阵线性解出摄像机内部参数,并由单应矩阵求出理想成像模型下的摄像机外部参数。然后考虑非线性畸变因素,求出畸变系数的初始值,最后对所有的标定参数进行迭代修正,通过非线性优化得到所有标定参数的最优解。制作模板并采集模板图像,利用MATLAB提取模板图像角点坐标并进行标定。结果表明:该方法可以有效地对摄像机进行标定;绝大多数偏差在(-1.5,1.5)像素之间,个别偏差超过1.5个像素,达到像素级精度,有较高标定精度。研究结果为进一步研究农业机械机器人奠定基础。 相似文献
94.
为实现低成本检测电力线谐波,开发基于STM32F103RBT6嵌入式微控制器的电力谐波采样设备,使用CS5463电量采集芯片及以Zigbee传输参数的无线电参数检测器,实现0.4 k V农村低压电网的电参数采集检测及电量计量。介绍设备的总体架构、软硬件设计思路以及实现方案。测试结果表明:设备能够在短时间内进行谐波采样和分析,具有稳定性强、可扩展性强、成本低廉等优点。 相似文献
95.
基于机器视觉的蒜头最大横切面直径分级方法 总被引:1,自引:0,他引:1
针对中国蒜头分选率和分选精度较低而影响其商品价值等现状,设计了一套基于机器视觉技术的大蒜蒜头分选系统,以蒜头最大横切面直径作为分级标准,利用VC6.0编程实现上述分级模型的算法。试验选择3 2 0个金乡蒜头样本对其进行测试,该装置对蒜头总体筛选精度达到9 0.9 3 7 5%。试验结果表明:利用机器视觉技术可以对大蒜蒜头进行分级。 相似文献
96.
SAR,EC与水温对辽西褐土入渗速率的影响研究 总被引:1,自引:0,他引:1
土壤入渗速率是影响灌溉水产流、侵蚀的重要因素之一。为了研究不同水温、不同SAR/EC下辽西褐土入渗速率,进行了室内变水头渗透试验。结果表明:SAR,EC一定时,渗透系数随着灌溉水水温的升高而增大,水温从15℃升至35℃,土壤渗透系数增大了1.3倍;随着灌溉水SAR增加、EC降低,土壤渗透系数会下降,水温35℃情况下SAR从0.7(mmol/L)0.5增大至12.0(mmol/L)0.5,EC从2.0dS/m减小至0.5dS/m时,土壤渗透系数由0.000 698cm/s减小至0.000 338cm/s,渗透系数下降了51.6%。相关分析表明水温、SAR/EC对渗透系数的影响显著,回归分析分别建立了沟灌土壤渗透系数与水温、SAR/EC二次函数数学模型,相关性极好。 相似文献
97.
GAO Feng HE Jian-bin ZHANG Yi LONG Miao LI Lin LI Yan-peng HAN Yang WANG Xue JIANG Li-ying YANG Shu-hua 《中国畜牧兽医》2016,43(2):471-476
The study was aimed to explore the protective effect of sulforaphane (SFN) on the reproductive function of male mice with cadmium poisoning.40 healthy clean grade male Kunming mice were randomly divided into four groups:control group (H2O),cadmium chloride group (2.3 mg/kg CdCl2),sulforaphane group (10 mg/kg SFN),sulforaphane + cadmium chloride group (10 mg/kg SFN+2.3 mg/kg CdCl2),and continuous administration for 10 d,all mice were executed by dislocated cervical vertebra at 2 d after the last administration,and then the pathologic changes of testicular tissues,organ coefficient of testicle and epididymis,sperm quality and concentration of testosterone were tested.Additionally,the contents of GSH and MDA,and the activities of T-SOD in testis were also detected at the same time. Compared with the control group,pathology damages were observed in cadmium chloride group,organ coefficient of testis and epididymis,sperm quality and levels of testosterone extremely significantly decreased (P<0.01),the activities of T-SOD and GSH content were extremely significantly decreased (P<0.01),and the concentration of MDA was extremely significantly enhanced (P<0.01).Compared with the control group,the activity of T-SOD and concentration of GSH in sulforaphane group were significantly increased (P<0.05),and the concentration of MDA was not significant different between the control group and sulforaphane group (P>0.05).While compared with the cadmium chloride group,the sperm motility rate and sperm total count in sulforaphane and cadmium chloride group were extremely significantly increased (P<0.01),the organ coefficient of testicle and epididymis was increased significantly (P<0.05),the concentration of GSH and activity of T-SOD in testicular tissue were extremely significantly increased (P<0.01),and the concentration of MDA was extremely significantly decreased (P<0.01).The results indicated that sulforaphane had the protection effect on reproduction function of male mice with cadmium poisoning. 相似文献
98.
YAO Wei YU Xue-wu CAO Dong ZHAO Xiao-tong GU Gui-bo CHEN Yao ZHANG Lei LIU Yao-chuan FENG Jun-ke 《中国畜牧兽医》2016,43(11):3080-3084
In order to understand the main bacterial pathogen species causing dairy cow mastitis in Liaoning, as well as the characteristics of drug sensitivity of the pathogenic E.coli,the milk samples from 75 dairy cows with clinical manifestations for mastitis in certain large-scale dairy farm in Liaoning were collected.The bacteria in milk were cultured and isolated with biochemical methods and in vitro drug sensitivity tests were processed with the isolated E.coli strains.The results showed that the main bacterial pathogen for dairy cow mastitis were E.coli(separation rate 58.7%),S.aureus(64.0%)and S.agalactiae(54.7%),and multiple infection including double and triple infection were identified.The drug sensitivity tests on the isolated E.coli indicated that the E.coli isolates were highly resistant to sulfonamides(resistance rate>85%)and chloramphenicol(resistance rate>30%),and they were relatively low resistant to ampicillin(9.5%),ciprofloxacin(9.5%),ceftiofur(7.1%)and ofloxacin(4.8%).The results was able to provide reliable theoretical basis for prevention and control of dairy cow mastitis in Liaoning area. 相似文献
99.
Xiao-ying He Li-bing Ma Xiao-ning He Wan-tong Si Yue-Mao Zheng 《Journal of veterinary science (Suw?n-si, Korea)》2016,17(2):145-152
Previous studies have established a bovine mammary gland epithelia cells in vitro model by the adenovirus-mediated telomerase (hTERT-bMGEs). The present study was conducted to confirm whether hTERT-bMGEs were effective target cells to improve the efficiency of transgenic expression and somatic cell nuclear transfer (SCNT). To accomplish this, a mammary-specific vector encoding human lysozyme and green fluorescent protein was used to verify the transgenic efficiency of hTERT-bMGEs, and untreated bovine mammary gland epithelial cells (bMGEs) were used as a control group. The results showed that the hTERT-bMGEs group had much higher transgenic efficiency and protein expression than the bMGEs group. Furthermore, the nontransgenic and transgenic hTERT-bMGEs were used as donor cells to evaluate the efficiency of SCNT. There were no significant differences in rates of cleavage or blastocysts or hatched blastocysts of cloned embryos from nontransgenic hTERT-bMGEs at passage 18 and 28 groups (82.8% vs. 81.9%, 28.6% vs. 24.8%, 58.6% vs. 55.3%, respectively) and the transgenic group (80.8%, 26.5% and 53.4%); however, they were significantly higher than the bMGEs group (71.2%, 12.8% and 14.8%), (p < 0.05). We confirmed that hTERT-bMGEs could serve as effective target cells for improving development of somatic cell cloned cattle embryos. 相似文献
100.