全文获取类型
收费全文 | 27216篇 |
免费 | 1297篇 |
国内免费 | 2881篇 |
专业分类
林业 | 2347篇 |
农学 | 3552篇 |
基础科学 | 1418篇 |
4124篇 | |
综合类 | 10944篇 |
农作物 | 1673篇 |
水产渔业 | 1833篇 |
畜牧兽医 | 2458篇 |
园艺 | 1151篇 |
植物保护 | 1894篇 |
出版年
2024年 | 189篇 |
2023年 | 526篇 |
2022年 | 817篇 |
2021年 | 951篇 |
2020年 | 1028篇 |
2019年 | 1205篇 |
2018年 | 842篇 |
2017年 | 1338篇 |
2016年 | 1599篇 |
2015年 | 1291篇 |
2014年 | 1549篇 |
2013年 | 1747篇 |
2012年 | 2152篇 |
2011年 | 2199篇 |
2010年 | 1675篇 |
2009年 | 1661篇 |
2008年 | 1425篇 |
2007年 | 1486篇 |
2006年 | 1108篇 |
2005年 | 1003篇 |
2004年 | 742篇 |
2003年 | 603篇 |
2002年 | 547篇 |
2001年 | 451篇 |
2000年 | 447篇 |
1999年 | 356篇 |
1998年 | 317篇 |
1997年 | 316篇 |
1996年 | 266篇 |
1995年 | 239篇 |
1994年 | 214篇 |
1993年 | 209篇 |
1992年 | 166篇 |
1991年 | 166篇 |
1990年 | 149篇 |
1989年 | 112篇 |
1988年 | 66篇 |
1987年 | 70篇 |
1986年 | 27篇 |
1985年 | 34篇 |
1984年 | 28篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
采用外包角钢加固的钢筋混凝土柱,其加固效果和安全性与诸多因素,如加固设计、加固施工工艺、加固端锚固构造、加固角钢的增钢率与增箍率、原柱所处的应力状态、使用过程中的维护管理等有关。对外包钢加固钢筋混凝土柱过程中影响其加固效果和安全性的诸多因素的安全性防范措施进行了初步的分析研究和探讨。 相似文献
122.
123.
三棱栎种子特性与其致濒关系初步分析 总被引:3,自引:0,他引:3
三棱栎是云南特有种,国家二级保护植物,主要分布在澜沧、沧源、孟连、西盟、勐腊等县.研究表明,其萌发温度在20~35℃范围内,萌发率在5.3%~9.1%之间.4个不同分布地和8种温度条件下萌发率差异不显著.本文认为三棱栎濒危的主要原因是:(1)三棱栎果实结实率低;(2)果实的特殊形状,不利于传播;(3)幼苗缺乏竞争力.针对三棱栎的濒危现状和原因,提出了三棱栎的一些保护措施. 相似文献
124.
125.
XIANG Li-jun WANG Bo-chu DUAN Chuan-ren LIU Liu WANG Qing-hongnistry of Education College of Bioengineering Chongqing University Chongqing Chin 《保鲜与加工》2004,(10):71-74
The paper researches on the degradation of LAS (Linear Alkyl benzene Sulphonate) by combining AS1.860 immobilized with low intensity ultrasonic irradiation. The paper also discusses the influence of pH, rotary velocity, LAS concentration and the condition of low intensity ultrasonic irradiation on the degradation of LAS, the degradation rate of LAS is the main index of our experiment, the results of orthogonal test shows that low ultrasonic irradiation can increase the metabolizing of microorganism cells and facilitate the biodegradation of immobilized cells to LAS, here we research the degradation condition of 50mg/L LAS simulation wastewater with low ultrasonic irradiation, and the results show that the influence is obvious, the optimization degradation rate is about 83%, nine point five percent higher than that of the immobilized cells without ultrasonic irradiation. 相似文献
126.
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
127.
According to the new requirement of sustainable development in the new stage, this paper puts forward the definition of the safeguarding capacity of regional sustainable development and uses some statistical methods of frequency statistics and principal component analysis to construct the index system of safeguarding capacity. Then it takes the data of the Three Gorges reservoir area for example to make empirical analysis, and provides efficient measurement tools to further measure the regional sustainability together with its safeguarding capacity, and therefore helps the government and the relevant organizations to establish more scientific policies of sustainable development. 相似文献
128.
Using gained experimental data to develop the models of stable flow stresses at high temperature plastic deformation by statistical methods for alloy materials, precision of the models is poor and at the same time the processes of modeling are complicated with great workload. On the basis of the data obtained on Gleeble-1500 Thermal Simulator,the predicting models for the relation between stable flow stress during high temperature plastic deformation and deformation strain, strain rate and temperature for 1420 Al-Li alloy have been developed with BP Artificial Neural Network method. The results show that the model on basis of BPNN is practical and it reflects the real feature of the deforming process. It states that the difference between the real value and the output of the model is in order of 5 percent. 相似文献
129.
For raveling out the main shortage of tendering which is the reasonable sector is unreasonable of making the bid evaluation uncertain. In order to eliminate subjective factor, this paper quantificationally analyses the price in bidding and establishes the sector selecting bid model based on the sector estimate idea, which tries to provide a new method and academic basic for determining the reasonable sector. Finally, the article gives an example to prove that the model is feasible and effective and it tries to ensure the bidding assessment public, equitable and just. 相似文献
130.
Wu Chenbo Liang Xiaoping 《保鲜与加工》1997,(2):117-122
The flowfield and temperature field are numerically Simulated by the mathematical model of the fluid flow and heat transfer in circular combustion chamber widened suddenly. The distributions and influence factors of the flow field and temperature field are studied in it. The results have the guiding significance for the design of combustion chamber. The mathematical models can serve as the quantitative analysis methods for design. 相似文献