全文获取类型
收费全文 | 71365篇 |
免费 | 4683篇 |
国内免费 | 6323篇 |
专业分类
林业 | 5131篇 |
农学 | 3809篇 |
基础科学 | 3253篇 |
7044篇 | |
综合类 | 35382篇 |
农作物 | 5271篇 |
水产渔业 | 2798篇 |
畜牧兽医 | 11412篇 |
园艺 | 5004篇 |
植物保护 | 3267篇 |
出版年
2024年 | 326篇 |
2023年 | 1415篇 |
2022年 | 3488篇 |
2021年 | 3163篇 |
2020年 | 3050篇 |
2019年 | 2858篇 |
2018年 | 2099篇 |
2017年 | 3590篇 |
2016年 | 2257篇 |
2015年 | 3534篇 |
2014年 | 3638篇 |
2013年 | 4477篇 |
2012年 | 6163篇 |
2011年 | 6367篇 |
2010年 | 5977篇 |
2009年 | 5073篇 |
2008年 | 5172篇 |
2007年 | 4857篇 |
2006年 | 3950篇 |
2005年 | 3125篇 |
2004年 | 1984篇 |
2003年 | 1333篇 |
2002年 | 1408篇 |
2001年 | 1282篇 |
2000年 | 1097篇 |
1999年 | 396篇 |
1998年 | 42篇 |
1997年 | 21篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 2篇 |
1981年 | 8篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1962年 | 12篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 3篇 |
1956年 | 34篇 |
1955年 | 12篇 |
1953年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A new type of inorganic anchoring material is developed as a substitution for anchoring adhesive to overcome some imperfections in the process of planting reinforcing steel bar.The mix proportion of the anchoring material is determined by experiments.The compressive strength,adhesive force to concrete,volume stability and anchoring force with steel bar are studied.The early strength of the anchoring inorganic material is quite high: for 1d up to 38.5MPa and 3d up to 60MPa.It is a good adhesive to concrete and the adhesive strength of 28d is about 2MPa.The anchoring material will have tiny volume expansion with the age,which is beneficial to enhancing the anchoring force.The essential component of the inorganic anchoring material is cement-based material,so some defects of the organic macromolecular material can be avoided,such as poor stability and requirement for vigorous construction conditions.Its characteristics in early strength,adhesive force to concrete and volume expansion can satisfy the requirement of the construction to the planting reinforcing steel bar and the loading force,thus it can be used as a substituting material for anchoring adhesive. 相似文献
992.
993.
With the development of circulating fluidized bed boiler(CFB),the study field of external heat exchanger(EHE) is greater in extent and degree.In order to research the working process of EHE,the model which deals with flow and heat transfer of EHE for 300MW CFB of Dong Fang Boiler Grou PCo.Ltd.is presented.Based on the cell modeling theory,the EHE is divided into several chamber by heating surfaces.The mass and energy conservation equations of each cell have been developed according to some reasonable assumption.The complete mathematical model has been compiled by Fortran and solved by classical Algorithm of Runge-Kutta.The static test and perturbation experiment of simulating model has been performed.The simulation results show that the model has been reached the steady state rapidly,the dynamic responses are reasonable and the modeling presented in the paper is reliable and appropriate. 相似文献
994.
The colored patterns on arbitrary cut plane is an important method in 3D data-field visualization of finite element.By using the technology of the Object-Oriented Programming and the method of scan-line,the colored patterns on arbitrary cut plane are given.The example by the OPENGL of Visual C++ R6 can support the theory satisfactorily. 相似文献
995.
XU Jiang WANG Wei-zhong YANG Xiu-gui WANG Hongl Disaster Control Engineering Under the State Ministry of Education Chongqing University Chongqing Chin 《保鲜与加工》2004,(12):60-62
The deformation characteristics of the fine-sandstone is studied under the loading and unloading conditions at the three different deformation-rates and the two different stress-levels. The experimental results show that there is really the plastic-loop in the deformation curve for the loading deformation curve is different from the unloading deformation curve. But the plastic-loop is nearly unchangeable since the second circulate loading. The residual-deformation is be almost zero since the second circulate loading, and that the slope of the deformation curve increases as the deformation-rate increases, and that the residual-deformation increases as the stress-levels increases. 相似文献
996.
A novel edge detection algorithm is proposed by implementing fuzzy image enhancement at different scales.The implement of this algorithm can reduce the negative influence bring from the non-maximum suppression algorithm which select only one threshold.The success of the approach depends on the selection of a general fuzzy operator(GFO) for the enhancement of contrast of region after smoothing of image at different scales.Consequently,it is more obvious that coarse intensity changes are obtained at a large scale whereas the fine details of intensity changes are obtained at a small scale.A pretty performance is obtained by used this work. 相似文献
997.
998.
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
999.
The structural defects of the heart are often reflected in the sounds that heart produces. Because of the non-stationary of the PCG signal, it is important to maintain its time-frequency character. We discuss the Short-Time Fourier Transform (STFT) method and the wavelet method. Some normal and abnormal heart sounds were analyzed by these methods. We can see the advantage and disadvantage of them obviously from the examples. 相似文献
1000.
With the rapid increase of the Internet user and widely application of Web,the current network technology is facing great challenge. More and more multimedia operations occupy plenty of bandwidth,and result in the network congestion. Therefore,people begin to use QoS to utilize the bandwidth effectively,and ensure the transport of the emergent operation data. The paper introduces the protocols and basic components of QoS,then expatiates the conception and the basic principles of policy control QoS, moreover,emphasizes the structure model of policy control QoS and how it runs. At last,it introduces the transport process of data packets under the control of policies in a policy control QoS system,and how to make the policies in the real world. 相似文献