全文获取类型
收费全文 | 72214篇 |
免费 | 4090篇 |
国内免费 | 6583篇 |
专业分类
林业 | 5143篇 |
农学 | 3835篇 |
基础科学 | 3263篇 |
7092篇 | |
综合类 | 35496篇 |
农作物 | 5226篇 |
水产渔业 | 2912篇 |
畜牧兽医 | 11447篇 |
园艺 | 5161篇 |
植物保护 | 3312篇 |
出版年
2024年 | 618篇 |
2023年 | 1522篇 |
2022年 | 3557篇 |
2021年 | 3227篇 |
2020年 | 3147篇 |
2019年 | 3194篇 |
2018年 | 2152篇 |
2017年 | 3594篇 |
2016年 | 2321篇 |
2015年 | 3555篇 |
2014年 | 3666篇 |
2013年 | 4468篇 |
2012年 | 6151篇 |
2011年 | 6356篇 |
2010年 | 5964篇 |
2009年 | 5054篇 |
2008年 | 5168篇 |
2007年 | 4854篇 |
2006年 | 3933篇 |
2005年 | 3111篇 |
2004年 | 1957篇 |
2003年 | 1251篇 |
2002年 | 1235篇 |
2001年 | 1159篇 |
2000年 | 1022篇 |
1999年 | 376篇 |
1998年 | 39篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 2篇 |
1981年 | 7篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1962年 | 12篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 3篇 |
1956年 | 34篇 |
1955年 | 12篇 |
1953年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
The processing characteristics of the front bumper bracket are analyzed,and a reasonable process scheme is worked out.The three-dimensional sheet metal forming analysis software PAM-STAMP are adopted to simulate the bracket's drawing process.Then the surface of die is proved fine through analyzing the FLD diagrams and the forming results.An economical and optimized die structure is decided,and a complete set of dies of the bracket is designed.The spacing block is added in the sizing mold,which control the size precision of end products and assembling columns actively,and finally the certified products.The material utility and the labor productivity are raised,the production cost is saved,and the mold design quality and the efficiency are improved effectively. 相似文献
892.
A method of measuring eyeglass lens power is proposed. A position detector and 3 beams of ray are used to measure the prismatic, spherical and astigmatic powers. Based on the method, an automatic focimeter with simple structure can be developed. The measure errors of prismatic and spherical powers are analyzed, from which it is concluded that the precision of the position detector is the key to the method. 相似文献
893.
Based on the research on the solidifiation of twin-roll casting strip,the analytical model and emulational model of nucleation,the growth of dendrity tip and colunar dendrity transformation to equiaxis dendrity (CET)of twin-roll casting strip solidification are established by means of the principle of metal solidification and modern computer emulational technology.The foundation for the emulational simulation of twin-roll casting strip solidification structure is laid. 相似文献
894.
Control Strategy and Simulation Study on NiMH Battery Quick Charging for Regenerative Braking of HEV
Based on the result of NiMH battery performance experiments, changing trend of maximal temperature and difference in temperature of HEV NiMH battery in different SOC and different charging current is analyzed. Considering the working situation of HEV NiMH battery and the theory of battery quick charging, a control strategy for NiMH battery quick charging is described which adapts to HEV regenerative braking system based on Mascc law. By Modeling and simulating the process of NiMH battery quick charging with this strategy, constant voltage charge method and constant current charge method, validates this control strategy. 相似文献
895.
896.
The study in molecular morphology is given with a highresolution Atomic Force Microscope AFM.IPC-208B.By taking TiN thim film prepared by magnerton sputtering method and polymide(PI) fibre for examples,the preferenthal growing plme of TiN thin film,the atomic arranges of TiN thin film on the preferential growing plme and the surficial micro-structure can be ascertained form the three-dimensional images obtamed by AFM.IPC-208B.These experiments not only identify small structures of the materials,but also affirm that AFM.IPC-208B holds the precision of atomic level and potential application in micro-structure field,at the same time it establishs the groundwork for the application in micro-process kingdom. 相似文献
897.
EEG spot-recording for clinical patients in the bed is always advocated due to easing patients and making them comfortable. But EEG signals recorded in the ward exposed to various noisesand interference is less effective in the EEG analysis. Atemporal-spatial filter is designed for noise removing of clinical EEG signals, the first filtering is temporal filtering using band-pass filter, and the second filtering is spatial filtering with ICA-based spatial filter. Experimental results indicate that various noises and interferences, such as power interference, blinking, eyes movements, muscle moments, ECG artifacts, etc., are removed effectively, individually or simultaneously. 相似文献
898.
汽车是人机协同控制的复杂系统,基于NI PXIe8108实时控制器、PXI7842R数据采集卡、模拟驾驶输入设备及相关软硬件搭建了驾驶模拟仿真系统;用LabVIEW编程语言建立了车辆动力学模型;用虚拟引擎Unity3D软件开发了视景系统;并通过数据库技术使仿真过程与视景系统相结合,实现仿真过程与三维动画实时视景系统的数据交互。结果表明:通过人在环路模拟驾驶仿真实验,使仿真过程中引入了驾驶模拟操纵,实现了人在环路的人机交互式仿真,得到汽车相关性能仿真结果,为驾驶过程中人和汽车协同控制仿真和极端工况下的仿真,提供了一种安全、可靠的人车协同控制仿真环境。 相似文献
899.
The important character of non-magnetic high manganese ZG25 Mn18Cr4 alloy is rapid work-hardening under external stress. With X-ray diffraction and TEM analysis, it is proved that the microstructures of both undeformed and deformed matrixes are austenite and carbide with some striation structure in the matrixes, the amount of stripes in the deformed matrix is obviously more than that in the undeformed matrix. Electronic diffraction analysis confirmed that the stripes in coarse austenite grains are high density lamination fault sheets. A great deal of lamination fault sheets produced by plastic deformation divides up austenite matrix, shortens the free distance of dislocation movement and results in the rapid work-hardening of ZG25Mn18Cr4 alloy. 相似文献
900.