全文获取类型
收费全文 | 12389篇 |
免费 | 704篇 |
国内免费 | 1390篇 |
专业分类
林业 | 1543篇 |
农学 | 1812篇 |
基础科学 | 1034篇 |
1880篇 | |
综合类 | 4124篇 |
农作物 | 908篇 |
水产渔业 | 494篇 |
畜牧兽医 | 1445篇 |
园艺 | 482篇 |
植物保护 | 761篇 |
出版年
2024年 | 28篇 |
2023年 | 128篇 |
2022年 | 381篇 |
2021年 | 482篇 |
2020年 | 416篇 |
2019年 | 430篇 |
2018年 | 316篇 |
2017年 | 481篇 |
2016年 | 449篇 |
2015年 | 519篇 |
2014年 | 541篇 |
2013年 | 631篇 |
2012年 | 744篇 |
2011年 | 806篇 |
2010年 | 798篇 |
2009年 | 790篇 |
2008年 | 740篇 |
2007年 | 699篇 |
2006年 | 692篇 |
2005年 | 562篇 |
2004年 | 313篇 |
2003年 | 282篇 |
2002年 | 322篇 |
2001年 | 325篇 |
2000年 | 256篇 |
1999年 | 315篇 |
1998年 | 305篇 |
1997年 | 234篇 |
1996年 | 198篇 |
1995年 | 215篇 |
1994年 | 187篇 |
1993年 | 200篇 |
1992年 | 144篇 |
1991年 | 133篇 |
1990年 | 100篇 |
1989年 | 105篇 |
1988年 | 79篇 |
1987年 | 50篇 |
1986年 | 23篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1965年 | 3篇 |
1964年 | 3篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
131.
浅析中国种业的基本特征 总被引:1,自引:1,他引:1
本文从我国特殊的国情、特殊的消费群体、特殊的产品、特殊的产业四个方面揭示了中国种业的基本特征. 相似文献
132.
Peng Donglin Dai Zhengyuan Zheng Lianqin 《保鲜与加工》1997,(1):104-108
The characteristics of pretreatment and cyclic control stream are analysed:the form of cyclic embedded hardware circuit,the idea for designing the pretreatment program.The chart model of the system is established preliminarily. 相似文献
133.
ZHOU Zheng 《保鲜与加工》2002,(6):139-142
The processes, microstructures, properties and mechanisms of DIMOX in synthesizing Al/Al 2O 3 by Al-Mg-Si alloy are reviewed and their problems are considered mainly as following:non_homogeneous oxidation growth of Al/Al 2O 3 at the surface of melts and the porosity of Al/Al 2O 3 limites structural application of Al/Al 2O 3 composite. The mechanisms and models of microchannel,magnesium action,silicon action,and induction are outlined. Several problems which need to be noticed are pointed out,which are diffusion and transfer of oxygen in aluminium melts;the role of MgO and MgAl 2O 4 at outer layer;the reaction feature of solid_gas in the oxidation microstructures of Al_Mg_Si alloy;SiO 2 induction mechanism of silicon and its correlation with the mechanism of magnesium action in Al_Mg_Si alloy. 相似文献
134.
The green is as a symbol of no pollution,no public harm and environmental protection. The green automobile is the inevitable results that the automobile technique continuously developes. A new style vehicle--the green automobile is the urgent solicit of environmental protection is developed. The automobile industry can develop continuously. This article mainly discusses the importance of the green auto_mobile's research and development,the development status in quo and prospect of the green auto_mobile technique in the world,and states the relationship between the green automobile technique and environmental protection from green technical system theoretically clarify the study of green automobile,including its design and the system,the manufacture and its technology,the energy,the rebuild engineering and a series of subjects. How to evaluate the cycle and the evaluable mark of the green automobile,the prospect of green automobile are pointed out. 相似文献
135.
136.
During the implementation of Cleanroom Model, there are a lot of particular problems need to be resolved, which make it indispensable to grasp the essence and the principles of CRM. The article is on the essential research work in the design procedure of the Cleanroom technology. Through the analysis, it proposes a general architecture, based on which the entry point of the solving process and the distribution of the reducing procedure are introduced. 相似文献
137.
Zheng Xiaoqing 《保鲜与加工》1995,(4):9-17
In view of the complication of compreliensive evaluation to development projectplanning alternatives,an AHP model for comprehensive evaluation to the alternatives is advanced,the way of determinating the weight of each index affecting the aIternatives' quality is expounded,and the general methods of evaluating the alternatives with the indexes are given. 相似文献
138.
LIN Yuan-hu LI Run-fang SHI Tai-he LIANG Zheng LIN Teng-jiao Goods SWPI ngqing Chin 《保鲜与加工》2004,(8):1-6
It is difficult to calculate the penetration rate (ROP) of percussion drilling. In the early research, the empirical or semiempirical formulae of the ROP are derived from the laboratory or field data collected by the researchers. However, the ROP value of the formulae is not as accurate as that in the field. Benefiting from the dynamic model, the geometric structure model and the theory of the roller cone bit, the mathematical model of the hammer bit, the mathematical model of the true bottom hole and the mathematical model between the tooth and the rock of the hammer bit are established. Hence the ROP of the air percussion drilling can be predicted by simulation. Field tests show the models are reliable and the results are coincident with that in the field. The research can help to redesign the hammer bit and optimize the drilling parameters. 相似文献
139.
A new method is introduced to measure the conductivity of brain. This method uses magnetic excitation to induce eddy currents inside the brain matter and measures the magnetic field caused by the induced eddy current. The theoretical basis of this method is analyzed and the measurement system is introduced. The aufhors do the experiment and draw a conclusion that the method provided is feasible. 相似文献
140.
Microstructures, Reaction Kinetics and Properties of Reaction Between Magnesium and Silica Glass 下载免费PDF全文
In earlier calculation models,the stiffness centers in frame-shear wall structures have been located by the structural torsion stiffness.However,the results are illogical owing to the difference between the distortion character and the shears distribute mechanism of the frames and shear walls.In this paper,a new formula for calculating story stiffness is introduced,which can consider the stiffness of the frames and shear walls at the same time.The structural stiffness centers,the torsion eccentric distances and torsion effect are calculated,and the stiffness of elements is considered also.It is shown that the concept of the presented stiffness model is clear and the results are reasonable,which can be used to calculate the appreciative torsion effect. 相似文献