全文获取类型
收费全文 | 5451篇 |
免费 | 318篇 |
国内免费 | 858篇 |
专业分类
林业 | 348篇 |
农学 | 410篇 |
基础科学 | 1638篇 |
1741篇 | |
综合类 | 1473篇 |
农作物 | 85篇 |
水产渔业 | 258篇 |
畜牧兽医 | 367篇 |
园艺 | 63篇 |
植物保护 | 244篇 |
出版年
2024年 | 44篇 |
2023年 | 121篇 |
2022年 | 203篇 |
2021年 | 230篇 |
2020年 | 218篇 |
2019年 | 262篇 |
2018年 | 177篇 |
2017年 | 274篇 |
2016年 | 336篇 |
2015年 | 243篇 |
2014年 | 297篇 |
2013年 | 319篇 |
2012年 | 399篇 |
2011年 | 399篇 |
2010年 | 337篇 |
2009年 | 295篇 |
2008年 | 297篇 |
2007年 | 314篇 |
2006年 | 290篇 |
2005年 | 219篇 |
2004年 | 191篇 |
2003年 | 161篇 |
2002年 | 142篇 |
2001年 | 136篇 |
2000年 | 120篇 |
1999年 | 93篇 |
1998年 | 71篇 |
1997年 | 77篇 |
1996年 | 58篇 |
1995年 | 65篇 |
1994年 | 60篇 |
1993年 | 40篇 |
1992年 | 40篇 |
1991年 | 36篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1974年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有6627条查询结果,搜索用时 15 毫秒
41.
Chen HuaZhou Jiaqi 《保鲜与加工》1990,(4):1-6
Based on the maximum flow principle about networks, a network flow approach to reliability evaluation in large scale netwerks ty mixing inereasing flow with decreasing flow is proposed in this paper.This approach gets the initial flow of each branch in a r.etwork associated with a state of the retwork by decreasing flows of some branches correlative to another state of the network.As a result, the number of flow compute required can be reduced enormously.The numerical example shows that the approach is powerful. The comparison of this approach with the minimal cutset one is also given in this paper. 相似文献
42.
The 2D motif method is a surface characterization method promising to separate roughness and waviness from a profile and is adopted by ISO,so is meaningful to extend this method to 3D.Vincent's watershed algorithm is employed for the generation of 3D-motif.A smallest area selecting criteria is proposed for the use of clearing the small motifs which are concerned as noise.As there are no manipulating factors as 2D-method,a multi-scale analysis is employed based on area and depth criteria,the use of depth criteria is to prevent the combination of two adjacent motifs if there is a significant peak on the border of them.Finally the surface of C(100) are analyzed by the presented method,the texture of this surface has been characterized. 相似文献
43.
44.
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
45.
46.
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
47.
48.
49.
Load dynamic matching of supply and demand side based on the utilization of urban sewage heat energy
Flowing dynamic characteristics and its temperature dynamic characteristics of a three-level sewage pipe network in Chongqing were analyzed. A mall's building whole year load was simulated. In the adverse condition of wastewater flow, the market construction peak discharge heat was compared with the sewage heat load, the balance between the most adverse flow and the building demand was found. Explored supply and demand matching method between urban sewage and city building load in flow adverse condition to take full advantage of the urban sewage cold and hot resources. the composite system was adeptcd to make up the most unfavorable flow time of sewage average heat load and the construction load difference; it also puts forward principle of load sharing and control strategy aimed at compound system. 相似文献
50.