全文获取类型
收费全文 | 828篇 |
免费 | 8篇 |
国内免费 | 342篇 |
专业分类
林业 | 1篇 |
农学 | 240篇 |
基础科学 | 217篇 |
7篇 | |
综合类 | 587篇 |
农作物 | 8篇 |
水产渔业 | 1篇 |
畜牧兽医 | 54篇 |
植物保护 | 63篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 64篇 |
2015年 | 101篇 |
2014年 | 229篇 |
2013年 | 171篇 |
2012年 | 96篇 |
2011年 | 60篇 |
2010年 | 109篇 |
2009年 | 147篇 |
2008年 | 137篇 |
2007年 | 5篇 |
2006年 | 1篇 |
2003年 | 1篇 |
2002年 | 2篇 |
1996年 | 3篇 |
排序方式: 共有1178条查询结果,搜索用时 15 毫秒
141.
通过利用关节镜技术对26例足球运动员半月板的损伤临床研究显示,26例患者术前Lysholm评分60~74分,平均为67.23±7.24分;术后82~97 分,平均为89.18 ±7.76分。术后Lysholm 评分提高明显,有统计学意义。治愈后的半月板均无并发症、旧伤复发或再次进行手术的病例。所以,针对足球运动员膝关节运动特点,利用关节镜技术诊断其半月板损伤的部位并采用合理的手术方案能有效纠正半月板周围生物力学平衡,恢复膝关节稳定性,防止其进一步退变。 相似文献
142.
143.
Based on the stochastic medium theory, influence on the surrounding rock and soil by tunnel excavation was studied. formula for predicting movement and deformation of rock and soil mass caused by tunnelling were deduced. And especially for the tunnel with circular arch section, half analytic solution for this problem was put forward. Furthermore, a program was developed to compute the movement and deformation of the rock and soil mass resulted from excavation. The deformation failure criterion of stochastic medium for estimating the surroundings safety was provided and was applied in an engineering example, which proved that the results of the research were reasonable and significant for the tunnel safety construction. 相似文献
144.
Microstructure and macro performance of Ultra Low Ion Permeability Cementitious Materials (ULIPCM) were investigated by Micro hardness, MIP and SEM EDXA. It was shown that the compressive strength of ULIPCM was more than 80 MPa, flexural strength was more than 11.0 MPa, and elastic modulus was in the range of 38.0 to 42.0 GPa at the age of 28 days; chloride diffusion coefficient was lower than 0.8×10-13m2·s-1, conductive charge for 6 hours was lower than 300 coulombs; sulfate attack resistance was good; shrinkage at the age of 28 days was lower than 400×10-6. Compared with ordinary concrete with which thickness of interfacial transition zone is 60 to 100 μm, the thickness of interfacial transition zone of ULIPCM was lower than 30 μm. Penetration paths of corrosive medium were effectively interrupted in ULIPCM. And pore structure parameters, such as porosity and the most probable pore radius of ULIPCM, were also obviously optimized in ULIPCM. Besides, few CH crystals were in the ULIPCM aggregate and the interfacial transition zone of ULIPCM. And the orientation of CH crystals was poor. 相似文献
145.
146.
We design a third Hilbert fractal antenna for partial discharge (PD) monitoring in gas insulated substations (GIS) based on fractal principles, and analyze the Hilbert antenna impedance characteristics using an equivalent inductance method of parallel transmission lines. The PD experiment of metal protrusion defect is conducted employing fractal and microstrip antennae. The test results show that the characteristic of the Hilbert fractal antenna has good performance and can detect the PD signal for online monitoring in GIS. A portable online monitoring and locating system for GIS is established using the Hilbert fractal antenna and LabVIEW. The locating accuracy of the PD source in the laboratory meets the requirements of the PD site location. 相似文献
147.
Based on an analysis of the characteristics of reactive power supplies and reactive loads, this paper presents a method for forming a lossless reactive network using an equivalent technique of modeling the branch admittance as a reactive power supply and the branch power loss as a virtual load. A downstream distribution matrix for a power system is constructed based on its reactive lossless network, and the analytical model and its algorithm for tracing reactive power flow (TRPF) is proposed. A method dealing with the abnormal downstream distribution matrix of active power flow also is discussed. The main advantage of the proposed method is that the matrix theory is used to analyze the TRPF model directly and no assumption on the flow distribution is needed. Case studies of the IEEE14 Bus and IEEE30 Bus systems demonstrate the accuracy and the validity of the proposed method. 相似文献
148.
Through technological research of foundation treatments in the collapsible loess areas, we recommend a method of treating foundations in collapsible loess with quicklime piles. We set forth the basic principle of this expansive method. When a very thick foundation in collapsible loess is treated, the computational formula for the volume of expanding material in a quicklime pile is deduced based on cavity expansion theory. This theory is applied to engineering practice. Physical and mechanical properties of the compacted soil are tested. The result shows that the collapsibility of a foundation in loess has been eliminated, its physico mechanical indexes have been improved, and the soil compressibility and the modulus of compressibility also increase remarkably, demonstrating the correctness of the computation theory. The feasibility of the expansive method for very thick collapsible loess areas is further established. 相似文献
149.
To create a model for recycling technology, a waste FR 4 printed circuit board (PCB) recycling process employing supercritical fluid CO2 (SCF CO2) is studied using central composite design. The influence of temperature and treatment time on the PCB delamination ratio, latitudinal tensile strength of glass fiber sheets, and their synthesized effect are analyzed. The optimal temperature and treatment time for FR 4 PCB recycling with SCF CO2 are found by building a quadratic polynomial equation model of output parameters in recycling technology. The accuracy of the derived optimal temperature and treatment time is validated by a series of experiments. 相似文献
150.
A good method for creating a surface borehole for withdrawing coal strata methane is to build before excavation and use during the whole process. But the excavation greatly affects the overlying rock strata, and when the excavation face passes through the 相似文献