全文获取类型
收费全文 | 4804篇 |
免费 | 246篇 |
国内免费 | 633篇 |
专业分类
林业 | 447篇 |
农学 | 399篇 |
基础科学 | 1297篇 |
805篇 | |
综合类 | 1567篇 |
农作物 | 106篇 |
水产渔业 | 142篇 |
畜牧兽医 | 701篇 |
园艺 | 71篇 |
植物保护 | 148篇 |
出版年
2024年 | 31篇 |
2023年 | 77篇 |
2022年 | 155篇 |
2021年 | 178篇 |
2020年 | 203篇 |
2019年 | 233篇 |
2018年 | 173篇 |
2017年 | 226篇 |
2016年 | 259篇 |
2015年 | 231篇 |
2014年 | 279篇 |
2013年 | 349篇 |
2012年 | 355篇 |
2011年 | 383篇 |
2010年 | 301篇 |
2009年 | 260篇 |
2008年 | 279篇 |
2007年 | 282篇 |
2006年 | 246篇 |
2005年 | 200篇 |
2004年 | 139篇 |
2003年 | 135篇 |
2002年 | 108篇 |
2001年 | 79篇 |
2000年 | 59篇 |
1999年 | 63篇 |
1998年 | 55篇 |
1997年 | 70篇 |
1996年 | 44篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 33篇 |
1992年 | 24篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有5683条查询结果,搜索用时 187 毫秒
51.
You lihua Wu Huibi Sun Renbo Wang Daivu 《保鲜与加工》1992,(4):48-53
The basic equations of wall plates of MAN' S dry gas holders are derived in this paper. According to the law of cylindrical bending given by the finite element results .we derive some approximate formula calculating the deflection and stresses of the wall plates from the basic equations. Compared with the known approximate calculating method.the method car. obviously increase the percision. 相似文献
52.
According to existent problems on design and application of the cylindrical cam mechanism with the slide roller-follower, the one correct concept about profile design and pressure angle is presented. Based on this concept, the theoretical profile,practical profile,meshing surface equations and pressure angle formula of the cam mechanism are built up by using opp.rotation analysis and offset surface principle. This method is very simple and clear, and avoids the abstract analysing process in meshing principle. The mathematic models built by this paper can be used to design,manufacture and check this type of cam mechanism correctly, and also create conditions to make deeply meshing property analysis of this mechanism. 相似文献
53.
54.
An experimental study on consolidation and drainage of two gravels with different grading was carried out using high - pressure large - scale tri - axial testing facility. A concept of equivalent surrounding pressure is introduced. An analysis was carried out on the effect and mechanism of reinforcement, experimental surrounding pressure and soil properties. Results show that the reinforcement can improve the strength and failure strain of the material and delay the failure of the soil. The effect of reinforcement of soil - gravel depends on the surrounding pressure and weathering of the gravel. 相似文献
55.
The dead-time inserted into the switching signals of inverters case the dead-time effect of output voltage distortion. The influence of dead-time on output voltage in inverters is analyzed in detail, Then, a new switching strategy, which can provide excellent inverter output voltage distortion correction, is proposed. At last, the experiment results of inverter are presented to demonstrate the practicability and validity of the control strategy. 相似文献
56.
Dynamic mathematical model, which is based on the character of the 200 MW tubine lbricating oil system, is established by means of modularization. On the basis of dynamic mathematical models, simulation model of the startu Pprocess of hign pressure startu Poil pum Pis created with the Visual Fortran language. The validity of this model has been verified by the simulation experiments and analysis. The simulation helps to forecast the dynamic characteristic to high pressure startu Poil pum Pand have some directive significance to design method of lubricating oil system. 相似文献
57.
58.
59.
60.