全文获取类型
收费全文 | 801篇 |
免费 | 22篇 |
国内免费 | 72篇 |
专业分类
林业 | 55篇 |
农学 | 38篇 |
基础科学 | 360篇 |
79篇 | |
综合类 | 210篇 |
农作物 | 6篇 |
水产渔业 | 7篇 |
畜牧兽医 | 129篇 |
园艺 | 3篇 |
植物保护 | 8篇 |
出版年
2024年 | 6篇 |
2023年 | 9篇 |
2022年 | 35篇 |
2021年 | 36篇 |
2020年 | 36篇 |
2019年 | 47篇 |
2018年 | 25篇 |
2017年 | 32篇 |
2016年 | 40篇 |
2015年 | 25篇 |
2014年 | 54篇 |
2013年 | 40篇 |
2012年 | 49篇 |
2011年 | 35篇 |
2010年 | 35篇 |
2009年 | 42篇 |
2008年 | 46篇 |
2007年 | 48篇 |
2006年 | 42篇 |
2005年 | 36篇 |
2004年 | 24篇 |
2003年 | 23篇 |
2002年 | 18篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有895条查询结果,搜索用时 15 毫秒
81.
82.
SISUNA-140全道路车加装灭火装置的研制 总被引:5,自引:2,他引:3
通过对我国引进的SISUNA 140全道路车进行技术改造,使之更加适合我国东北林区森林消防的需要.整套灭火装置由水箱、管路系统、水泵几大部分组成,在不破坏原车结构、不改变原车行驶性能的前提下,加装灭火装置,可组成一台森林消防车;卸下灭火装置,又可恢复原车的功能.灭火装置结构合理,装拆方便快捷,灭火效率高,具有推广应用价值. 相似文献
83.
Weijun Fu Zhuojing Fu Hubert Tunney Chaosheng Zhang 《Archives of Agronomy and Soil Science》2013,59(10):1459-1466
Field-scale variation of soil phosphorus (P) information is very important for P fertilizer application and its soil sampling design in grassland. A total of 108 soil samples were collected from a long-term (41 years) grazed grassland P experiment field at Teagasc, Johnstown Castle, Wexford, Ireland, in March 2009. There were six P treatments (P0-0, P0-30, P15-15, P15-5, P30-30, and P30-0) since 1968, with changes since 1999. Each treatment had 6 replicate plots (a total of 36 plots, 3 soil samples per plot). The samples were analyzed for available (Morgan’s) P, potassium (K), magnesium (Mg), lime requirement (LR), and pH. The highest mean available P concentration was found in the P30-30 (30 kg P ha?1 pre- and post-1998) plots, and the lowest mean available P concentration was found in the P0-0 (no P fertilizer since 1968) plots. Significant differences of mean P, Mg, LR, and pH values in different treatments were observed. There was a positive proportional effect for both the 36 plots and the 6 treatments for the P data: the local standard deviation increased with the increase of local mean. The proportional effect should be considered in order to optimize sampling design. Fewer samples can reflect soil P status in fields with low soil P levels, while more attention should be paid to the fields with high P levels in order to reduce environmental consequences of uniform applications. 相似文献
84.
85.
An original variable valve timing mechanism with two-mode intake timing was developed according to the structural characteristics of small medium displacement motorcycle engine. Based on cycle simulation, the effects of the VVT mechanism structural parameters, control parameters and operational parameters on the engine performance were analyzed by embedding the VVT mechanism operational mode and control strategies in the engine cycle simulation. Optimum design for the late intake valve closing, the valve lift, as well as the switching speed of the VVT system was carried out. It has been proved that power and torque of the JH125 motorcycle engine can be effectively improved by loading the new type VVT system. 相似文献
86.
高速电磁阀电磁力全工况关键参数相关性分析 总被引:1,自引:3,他引:1
为揭示各参数对高速电磁阀电磁力影响机理及交互作用规律,更有效地进行高速电磁阀参数设计及匹配,首先建立了高速电磁阀有限元数值仿真模型,并通过试验进行了验证。然后结合试验设计与相关性分析思想,基于中心复合试验设计构造了相关性分析的样本点,并利用有限元数值仿真模型得出全工况平面内其响应值,进而获得了相关系数,揭示了全工况平面内电磁阀关键参数本身形成的6个一次因素及其交互作用形成的21个二次因素与电磁力的相关性变化规律。通过相关性分析得出对高速电磁阀电磁力影响显著的一次因素为线圈匝数和衔铁厚度;而二次因素对高速电磁阀电磁力的影响随各工况点的变化复杂,最后研究了线圈匝数与衔铁厚度、衔铁厚度与阻尼孔位置、阻尼孔位置与半径三组显著因素的交互作用原理,为高速电磁阀设计及其电磁力预测提供了理论指导。 相似文献
87.
This paper uses the training of OC-SVM to analyze the mechanism of the Quantum-behaved particle swarm and develops a method of training OC-SVM based on the directional- QDPSO .The new position of the directional particle is calculated based on the current global best point(gBest), which identified the optimized direction conforms to Zoutendijk fastest decline method principle.In the initialization, the position of one particle is initialized according to SMO, which makes its position nearer to the global optimum solution. The boundary points of subjected plane are concerned as the initialized position of other particles, so as to make the searching area wider.The experiment result shows that the convergence and the generalization of D-QDPSO is good, the misrecognition of D-QDPSO is 0.12% lower than that of SMO, and the operating speed is 2 times faster than that of LPSO. 相似文献
88.
Based on the dependency of the PDTDFB coefficients across the interscale and interdirection and the statistical properties of HMT for the correlation properties, a new HMT in PDTDFB domain was put forward. Compared with the other typical denoising methods, the experimental results demonstrate that the proposed method shows better performance in image denoising, especially in edge maintenance. 相似文献
89.
与液上喷射泡沫灭火系统的相比,液下喷射泡沫灭火系统具有安全可靠,灭火速度快,省投资等优点,但却存在单阀易渗漏问题。针对这一问题,提出了通过在单向阀和控制阀之间增设爆破片,或在灭火系统泡沫喷口处设置泡沫带以及改善单向阀密封性能等解决办法。 相似文献
90.