全文获取类型
收费全文 | 2548篇 |
免费 | 161篇 |
国内免费 | 218篇 |
专业分类
林业 | 219篇 |
农学 | 168篇 |
基础科学 | 99篇 |
219篇 | |
综合类 | 1074篇 |
农作物 | 89篇 |
水产渔业 | 239篇 |
畜牧兽医 | 539篇 |
园艺 | 38篇 |
植物保护 | 243篇 |
出版年
2024年 | 41篇 |
2023年 | 92篇 |
2022年 | 103篇 |
2021年 | 137篇 |
2020年 | 126篇 |
2019年 | 145篇 |
2018年 | 67篇 |
2017年 | 124篇 |
2016年 | 132篇 |
2015年 | 109篇 |
2014年 | 171篇 |
2013年 | 153篇 |
2012年 | 160篇 |
2011年 | 179篇 |
2010年 | 141篇 |
2009年 | 132篇 |
2008年 | 125篇 |
2007年 | 133篇 |
2006年 | 132篇 |
2005年 | 83篇 |
2004年 | 74篇 |
2003年 | 61篇 |
2002年 | 54篇 |
2001年 | 37篇 |
2000年 | 38篇 |
1999年 | 31篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 18篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1986年 | 2篇 |
排序方式: 共有2927条查询结果,搜索用时 15 毫秒
121.
122.
123.
124.
The Quasi static tests of one steel frame and two the composite deep beams infilled steel frames were carried out. The effects of the deep beams on the load capacity, ductility, hysteretic property and energy dissipation of pure steel structure were analyzed. It is found that the hysteresis curve is a straight line with the constant of the stiffness at the beginning and without residual deformation. And the hysteresis curve of specimen was full after yielding, and the skeleton curves had a clear plastic flow phase with triple linear. The lateral drifts of the beam specimens at failure were 1/25 and 1/22. The composite deep beams enhance the initial stiffness, yield load and maximum load bearing capacity of steel frame. Therefore, seismic performance of the composite deep beams is better. 相似文献
125.
试验旨在通过研究地面平养模式下不同饲养密度对蛋鸡行为、外观、血液应激指标及生产性能的影响,筛选保证蛋鸡福利状况及生产性能的最大饲养密度,为我国推广地面平养模式蛋鸡福利养殖奠定理论基础。将780只苏禽绿壳蛋鸡按舍内密度分为四组,其中地面平养分为低密度组(6只/m^2)、中密度组(8只/m^2)、高密度组(10只/m^2),笼养组为对照组,每组3个重复。试验期为18~27周龄,蛋鸡行为学数据均采用视频录像收集,在27周龄末进行翅静脉采血和福利外观评价,统计分析24~27周龄生产性能。结果显示:笼养蛋鸡的产蛋率,攻击、刻板等非福利行为均显著高于平养组(P<0.05),脚垫损伤、羽毛评分、应激激素浓度(CORT、ACTH)显著低于平养组(P<0.05)。地面平养各组间,高密度组蛋鸡料蛋比显著高于低、中密度组(P<0.05);低、中密度组蛋鸡行走和休息时间比例均显著高于高密度组(P<0.05);低密度组蛋鸡啄羽行为显著低于高密度组(P<0.05),但与中密度组差异不显著(P>0.05);低、中密度组蛋鸡脚垫损伤、背羽损伤显著低于高密度组(P<0.05);高密度组蛋鸡血清中CORT和ACTH浓度显著低于低、中密度组(P<0.05)。由此可见,平养蛋鸡比笼养蛋鸡行为表现更积极,羽毛覆盖度更好,但应激水平和足部损伤较高、生产性能较低;在试验场地模式下,推荐8只/m2为最佳饲养密度。 相似文献
126.
高岭石-甲醇夹层复合体的合成及其特性 总被引:1,自引:0,他引:1
以水合联胺,10 mol尿素水溶液及甲醇先后与高岭石反应,合成了晶面间距为1.0 nm的高岭石甲醇夹层复合物。复合物不太稳定,在常温下 (约放置72 h) 或1050C加热下 (2 min)晶面间距收缩为0.85 nm。于2000C加热时,晶面间距进一步收缩为0.79 nm。0.79 nm复合物在3000C条件下长时间加热也未再发生变化。由层间膨胀值的大小及甲醇分子的最小厚度推测,0.85 nm及0.79 nm夹层复合体中甲醇分子明显地嵌入了高岭石的结构内部。其甲基可能嵌入了硅氧四面体的六角环空洞中,而羟基嵌入了铝氧八面体内。IR图谱表明0.79 nm复合物中甲醇分子与高岭石的相互作用较之0.85 nm复合物更强。 相似文献
127.
Hou Xueyan Dong Weipin 《保鲜与加工》1991,(3)
A two-story and two-space structure model (1/4 scale) is tested under low-cyclic loading for studying the antiseismic behavior of the brick building with frame on the ground floor. This paper presents mainly the development and pattern of cracks, failure mechanism,hysteresis behavior, strength and stiffness, ductility and energy dissipation. The calculated results by elastic finite elemet method are also compared with the results of test. 相似文献
128.
Bai Shaoliang Zhu Xijun 《保鲜与加工》1990,(1)
In this pager, four full-scale corner joint assemblies of reinforced concrete frame beam and column with different detail structure are tested under low cycle loading, The process of damage development and the characteristics of break of the assemblies in the course of alternately increasing positive and negative bending deformation are learned Strength, stiffness and ductility of assemblies and the various regulations of energy consumption are also studied. Compared with these properties, the anti-seismic behavior is tentatively commented. Besides, the test results of the strain distribution of beam and column longitudinal bars and stress state of joint stirrups are analyzed. 相似文献
129.
以在陕西省杨凌区所采集的黄土样品为研究对象,对不同初始含水率的原状黄土进行了剪切蠕变试验,获取了蠕变曲线和蠕变特征参数,并研究了含水率、剪应力水平对蠕变特性的影响.结果表明,当含水率一定时,剪应力水平对黄土的蠕变特性有较大的影响,表现为剪应力愈大,黄土的蠕变应变愈大;当剪应力水平一定时,含水率对黄土蠕变特性影响明显,表现为含水率愈大,蠕变应变愈大.根据蠕变曲线特征,建立了原状黄土的蠕变本构模型,通过试验数据拟合得到本构模型中的参数.经验证,该模型能较好地模拟杨凌地区原状黄土的蠕变特性. 相似文献
130.
Meiotic behavior of passion fruit somatic hybrids, Passiflora edulis f. flavicarpa Degener + P. amethystina Mikan 总被引:1,自引:0,他引:1
Somatic hybrids (SH) obtained by protoplast fusion were investigated for meiotic behavior in order to determine their possible
use in breeding programs. Flower buds from four genotypes of SH between P. edulis f. flavicarpa (E) and the wild species P.
amethystina (Am) denoted SH (E + Am) # 12, # 13, # 28 and # 35 were collected and the microsporocytes analysed. Meiotic phases
showed the presence of abnormalities such as univalents, bivalents and quadrivalents, laggard chromosomes and anaphase bridges.
At least 14 bivalents were observed in most of the cells of the hybrid plants. The percentage of cells with quadrivalents
ranged from 73.3 in (E + Am) # 13 to 93.3 in (E + Am) # 28 and # 35. Analysis of pollen viability (V) indicated V = 88.23%
for # 12, V = 83.86% for # 13, V = 84.20% for # 28, and V = 72.90% for # 35, and fruit development was observed. The high
pollen viability, together with the multivalent pairing observed in the four somatic hybrids indicates that these materials
can be used for the genetic improvement of yellow passion fruits aiming at introgressions of genes for resistance to diseases
and pests.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献