全文获取类型
收费全文 | 18883篇 |
免费 | 1279篇 |
国内免费 | 1779篇 |
专业分类
林业 | 1356篇 |
农学 | 970篇 |
基础科学 | 798篇 |
2078篇 | |
综合类 | 9625篇 |
农作物 | 1449篇 |
水产渔业 | 911篇 |
畜牧兽医 | 2533篇 |
园艺 | 1385篇 |
植物保护 | 836篇 |
出版年
2024年 | 119篇 |
2023年 | 381篇 |
2022年 | 807篇 |
2021年 | 859篇 |
2020年 | 754篇 |
2019年 | 749篇 |
2018年 | 615篇 |
2017年 | 915篇 |
2016年 | 615篇 |
2015年 | 892篇 |
2014年 | 940篇 |
2013年 | 1165篇 |
2012年 | 1664篇 |
2011年 | 1673篇 |
2010年 | 1570篇 |
2009年 | 1338篇 |
2008年 | 1426篇 |
2007年 | 1249篇 |
2006年 | 1081篇 |
2005年 | 884篇 |
2004年 | 495篇 |
2003年 | 358篇 |
2002年 | 337篇 |
2001年 | 314篇 |
2000年 | 280篇 |
1999年 | 127篇 |
1998年 | 34篇 |
1997年 | 43篇 |
1996年 | 24篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 26篇 |
1992年 | 33篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1972年 | 2篇 |
1964年 | 2篇 |
1963年 | 4篇 |
1962年 | 5篇 |
1956年 | 6篇 |
1955年 | 4篇 |
1932年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
161.
162.
In this paper the inevitable trend of constructing open ecosystem in modern settlement environment was discussed through the history of the settlement environment and the characters of modern settlement environment.The ecological crisis,change of the modern life and the citizens' needs and the ecological system character show,that it is important for sustainable development of the settlement environment to construct open ecosystem.The construction of modern habitation and the city room embodies the concept of open ecosystem.Then,in construction and research of modern settlement,the ecological viewpoint and method should be applied. 相似文献
163.
The analysis of vibration response of structure with TMD is carried out under earthquake ,considering the ground-structure interaction. The varying rule of square difference of displacement of structure with the TMD on or off by changing the first inherent frequency is also presented .It has been proved by comparing and analyzing that a TMDstructure with optimum parameters can efficiently reduce the vibration of structure under strong wind and earthquake,when the main frequency of the ground motion is within the range of TMD vibration reducing frequency. 相似文献
164.
The paper analyzes the difference of the pathogenic varieties and the relationship of the variety composition,allording to the historic material to the varieties of the main hybid fece varieties in Southeast Sichuan during 1992 to 1998.It's the first time to advance to use the camparison on rate of pathogenic isolates between norm and refrieving to define the susceptible extent of the varity.It's an scientific base to adjust the structures of the vartieties,to reach the objective of the macroscopic regulating to rice blast. 相似文献
165.
Aiming at knowledge representation problem of expert system for rotary machinery fault diagnosis, semantic net knowledge representation is discussed. Semantic net to represent expert knowledge of rotary machinery fault diagnosis is explored. Its realizing method is afforded in computer language, in addition, demostrating model is also developed in Visual C++. The result shows good validity of the knowledge representation. 相似文献
166.
Vibration & Noise Analysis on Double-ring Gear Reducer 总被引:1,自引:0,他引:1
Double-ring gear reducer with Central inputting shaft is studied. The basic structure of reducer as well as testing equipment, probe spot and testing method of Structure-borne noise and air-borne noise is presented. Based on frequency spectrum of each point, amplitude spectrum of structure-borne noise and testing results of air-borne noise, the authors analyze the vibration characters and latent faults of double-ring gear reducer, coming to the value and the cause of the noise, providing theoretical basis for proper design of the double-ring gear reducer and method of reducing its vibration and noise. 相似文献
167.
The torsion vibration of main transmission system of 1 450 rolling mill is tested:The torsion vibration frequency and amplification coefficient of torque are obtained.Basing on part of the measured date and theoretical analysis,the measure is developed for preventive method;it is of important theoretic sense and high engineering practical value for reducing accident and controlling torsion vibration. 相似文献
168.
169.
170.
从研究全射流喷头水力尺寸与可靠性的关系入手,寻找提高产品可靠性的方法。提出了影响喷头工作稳定可靠性的主要因素为主射流的附壁时间及主射流的附壁力。探讨了接嘴插拔深度及其内孔直径、作用区位差S、盖板出口位差H1和H2、出口间隙C等关键水力尺寸及其相互之间配合对主射流附壁时间及主射流的附壁力的影响,进而得出对喷头可靠性的影响。最后得出要使喷头运转稳定可靠,需对喷头的水力尺寸进行深入的研究,找出水力尺寸间的最佳组合。 相似文献