首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   11996篇
  免费   791篇
  国内免费   972篇
林业   1065篇
农学   690篇
基础科学   486篇
  1124篇
综合类   6180篇
农作物   870篇
水产渔业   388篇
畜牧兽医   1597篇
园艺   891篇
植物保护   468篇
  2024年   67篇
  2023年   213篇
  2022年   572篇
  2021年   512篇
  2020年   485篇
  2019年   528篇
  2018年   326篇
  2017年   582篇
  2016年   348篇
  2015年   584篇
  2014年   671篇
  2013年   693篇
  2012年   1104篇
  2011年   1078篇
  2010年   996篇
  2009年   875篇
  2008年   883篇
  2007年   841篇
  2006年   669篇
  2005年   523篇
  2004年   360篇
  2003年   194篇
  2002年   202篇
  2001年   182篇
  2000年   154篇
  1999年   52篇
  1998年   6篇
  1997年   4篇
  1996年   4篇
  1995年   6篇
  1994年   3篇
  1993年   2篇
  1992年   10篇
  1991年   2篇
  1990年   2篇
  1988年   4篇
  1987年   5篇
  1986年   3篇
  1985年   1篇
  1981年   4篇
  1971年   1篇
  1970年   1篇
  1965年   1篇
  1962年   2篇
  1957年   1篇
  1956年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
This article presents an implement of component using COM technology for collecting environmental monitoring data in environment monitoring system. The component makes the separation of data collection and data analysis available.Simultaneously by using the interface of connectable object in COM,itmakes the cooperation of the environment monitoring software with other parts of fault management software available,and also the seamless connection.It improves the system's performance by adding extensibility and potential cooperatibility.  相似文献   
104.
In order to improve waveform performance of light HVDC system, a lot of switches which operate in high frequency are used, which causes large switching losses and results high cost. A new Buck type voltage source converter(BVSC) is proposed. The new BVSC comprises a dual-buck converter and a three-phase inverter operating in grid frequency. Only two high frequency switches are used, which results good output waveform performance. In order to reduce the high frequency switching losses, a novel improved double-frequency Buck type voltage source converter(DBVSC) is also proposed. An additional dual-Buck converter is added to the BVSC, the added dual-Buck converter deals with the fundamental power that operates in low frequency, and BVSC only deals with harmonic power that operates in high frequency. The output waveform is enhanced and the switching losses are reduced in DBVSC, and the power rating is also increased. The DBVSC is very suitable for large power rating application. The one cycle control theory is adopted to control the proposed DBVSC with analog circuit, which is very simple. The proposed DBVSC and control method are verified by simulation.  相似文献   
105.
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   
106.
Dong village is very valuable for research work because of its special regional and national character and rich cultural implication. In this paper, some information about the location, form and features of Dong village is given. Then, the relationship between the culture and the settlement is analyzed, which provides a clue for understanding Dong village and will be beneficial to creating modern human settlements.  相似文献   
107.
The wavelet transform is a new subject developed quickly in the past ten years. Compared with the Fourier transform, the wavelet transform is a part of time-frequency transform. The most important character is that it can be used to transform a signal into basic units at different scales and location, each unit represents a component of original signal difference from others. The wavelet transform has been proven to be a powerful and efficient tool for processing signal due to this character. This paper introduces the de-noising principles of the wavelet transform. It is proved to be an effective method by the simulating analysis.  相似文献   
108.
Pearlitic steel is composed of numerous pearlitic colonies with randomly distributed orientations,and each colony is composed of many alternatively arranged parallel lamellas of ferrite and cementite.The pearlitic steel with fine interlamellar spacing possesses excellent mechanical properties,such as high strength,good resistance against wear,and high fatigue life,etc. Based on the inconsistency of the deformation between the two phases,a strain_equivalent and non_local constitutive model is proposed. Using this model,the effect of the interlamellar spacing of peailitic steel,a fundamental parmeter of the microstructure of pearlitic material, on its macroscopic mechanical behavior can be described without changing the local material parameters for each phase of the material.The asymmetrical cyclic plasticity of both the hot_rolled and the off_line full_length quenched pearlitic steel PD3 is analyzed.The comparison between the computational and the experimental results shows satisfactory agreement.  相似文献   
109.
Image compression is very important in picture archiving and communication system(PACS). The author studied the statistical distribution of image wavelet subimage coefficients and concluded that the distribution of wavelet subimage coefficients is similar to that of Laplasian distribution. On the other hand, in image reconstruction, the coefficient with different amplitude owns different weight, and different accuracy can be applied to different coefficients according to their different weight. Then, the author has designed a image quantization encoding scheme for PACS. In this scheme, they selected the sample-standard-deviation of coefficients in every subimage as the quantization threshold, and accurately encoded those coefficients with higher weight. Also, this algorithm utilized the visual character of human. The test has proved that the main advantages of this method are the simplicity in computing and predictable encoded coefficients, and a high compression efficiency can obtain too.  相似文献   
110.
Intelligent recognition system of gun code is designed , which achieves online recognition of gun code. We applied video camera to get image, and some special technique in this deformed character recognition. As well, we applied dynamic template matching to get a better result.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号