全文获取类型
收费全文 | 8025篇 |
免费 | 271篇 |
国内免费 | 526篇 |
专业分类
林业 | 713篇 |
农学 | 447篇 |
基础科学 | 679篇 |
1332篇 | |
综合类 | 4842篇 |
农作物 | 140篇 |
水产渔业 | 113篇 |
畜牧兽医 | 321篇 |
园艺 | 99篇 |
植物保护 | 136篇 |
出版年
2024年 | 29篇 |
2023年 | 84篇 |
2022年 | 113篇 |
2021年 | 135篇 |
2020年 | 120篇 |
2019年 | 187篇 |
2018年 | 111篇 |
2017年 | 184篇 |
2016年 | 224篇 |
2015年 | 231篇 |
2014年 | 360篇 |
2013年 | 367篇 |
2012年 | 711篇 |
2011年 | 792篇 |
2010年 | 784篇 |
2009年 | 589篇 |
2008年 | 574篇 |
2007年 | 618篇 |
2006年 | 565篇 |
2005年 | 488篇 |
2004年 | 436篇 |
2003年 | 278篇 |
2002年 | 166篇 |
2001年 | 156篇 |
2000年 | 105篇 |
1999年 | 81篇 |
1998年 | 73篇 |
1997年 | 50篇 |
1996年 | 42篇 |
1995年 | 26篇 |
1994年 | 25篇 |
1993年 | 30篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1963年 | 2篇 |
1962年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有8822条查询结果,搜索用时 15 毫秒
71.
72.
天然花色苷的资源收集及稳定性测定 总被引:2,自引:0,他引:2
通过天然花色苷材料野外采集,共得到50种植物的花色苷样品,采用pH 1.0/pH 4.5溶液吸光值(△OD)差值法,对这些花色苷提取液进行了1年的测定和筛选,筛选出了花色苷颜色稳定性较好的桔梗(Platycodon grandiflorua A.)、蜀葵(Althaea. Rosea L.)、翠雀(Delphinium grandiflorum L.)和日本红菊(Chrysanthemum morifolium Ramat)等4种植物资源。对这4种花色苷进行酸碱性、光照、金属离子、热处理等条件下的稳定性测定,表明在pH4.0以下稳定,高于pH4.0稳定性则明显下降。日光、pH 1.0条件下上述4种花色苷溶液的半衰期分别为339d、255d、226d和234d。钙、镁离子对花色苷的稳定性无影响,铝、铜、锡和铁的存在降低花色苷的稳定性,其中铝影响较小,铜锡影响较大,铁影响最大。在100℃ 20min pH1.0热处理下色素损失率分别为2.7%、29.2%、20.0%和7.1%。桔梗花色苷稳定性明显优于其余3种花色苷。结果表明上述4种花色苷有希望开发成为食品色素添加剂。 相似文献
73.
74.
To construct data warehouse with heterogeneous, self-governing and distributed database system is a challenge. Two problems have to be solved: one is how to collect data from heterogeneous data sources by an effective method, the other is how to clear up and change the format of the data collected from data sources. The opening and the interact-operation property of Web Services is Analyzed. A Data Collection System based on Web Services, which communicates with heterogeneous data sources with SOAP and HTTP, has been designed. A Data Collector is introduced to clear up and to transform data with composition technology. The pivotal XML technology of transforming and loading up the data are discussed. 相似文献
75.
Zeng Fanqi Zhou Ming Wang Yong 《保鲜与加工》1993,(4):150-154
This paper proposes a model framework, which describes the function requirements and the common characterstics of vehicle transport management. With the frame, a computer vehicle transportation managerment information system(QCMIS)is in troduced here and it has already been put into practice. The key technical points is also explained in the paper. 相似文献
76.
Considering information asymmetry between inside and outside of the firms,this paper discusses the financing strategy of M&A,and builds a model.According to the model,we can see that the firm with relatively expected low-productivity will choose equity financing for M&A,and the firm with relatively expected high-productivity will choose debt financing for M&A,and the firm with expected medium-productivity will not choose financing from outside.In the case of undeveloped capital market and financing tools in China,the conclusion of the model has some extent significance for helping firms to choose financing strategy for M&A rationally. 相似文献
77.
Today the information globalization is the trend of society development. The information technology has great influence not only on the mode of life and production, but also on the urban social and economic structure. In order to fit in with the change in this regard, the urban land-use distribution, residential mode, traffic pattern and so on should be changed correspondingly. Therefore, this change will lead to the development and evolution of whole urban spatial structure. In this paper, the development tendency of urban spatial structure in the information age is analyzed and some proposals on city planning and construction are put forward. 相似文献
78.
TAN Wen-an 《保鲜与加工》2004,(12):73-77
By analyzing the process of enterprise information engineering construction and intra relationship among information system requirement, business process modeling, application system constructing and project management, one of 4 meta model composed of requirement engineering, process engineering, application system engineering and support engineering is proposed for enterprise information engineering. The developments and applications of the business processes and its application systems are integrated into the same development space and application space. Basing on this, a prototype system composed of requirement modeling environment, business process modeling environment, application system modeling environment, and support engineering environment has been designed and built, which is used for supporting enterprise information engineering constructing. It is valued for the enterprise information engineering construction in our country. 相似文献
79.
This paper introduces a method of solving the problem of leather cavity measurement in shoe CAD/CAM by industrial CT technology. Concentrating on peculiarity and requirement of leather cavity measurement, this paper presents a X-ray industrial CT system scheme, which not only satisfy the requirement of leather cavity measurement but also can achieve general industrial CT. measurement. The achievement on data collection system and motion control of stepping motor is emphasized. 相似文献
80.
The solution of the office automation system for the universities is given. The detail steps on developing an office automation system through Lotus Notes are described. 相似文献