全文获取类型
收费全文 | 5586篇 |
免费 | 342篇 |
国内免费 | 1328篇 |
专业分类
林业 | 411篇 |
农学 | 637篇 |
基础科学 | 1394篇 |
1439篇 | |
综合类 | 2541篇 |
农作物 | 121篇 |
水产渔业 | 135篇 |
畜牧兽医 | 345篇 |
园艺 | 97篇 |
植物保护 | 136篇 |
出版年
2024年 | 39篇 |
2023年 | 167篇 |
2022年 | 273篇 |
2021年 | 295篇 |
2020年 | 296篇 |
2019年 | 367篇 |
2018年 | 227篇 |
2017年 | 363篇 |
2016年 | 487篇 |
2015年 | 378篇 |
2014年 | 432篇 |
2013年 | 404篇 |
2012年 | 589篇 |
2011年 | 508篇 |
2010年 | 356篇 |
2009年 | 314篇 |
2008年 | 224篇 |
2007年 | 280篇 |
2006年 | 239篇 |
2005年 | 163篇 |
2004年 | 144篇 |
2003年 | 118篇 |
2002年 | 62篇 |
2001年 | 61篇 |
2000年 | 55篇 |
1999年 | 37篇 |
1998年 | 50篇 |
1997年 | 47篇 |
1996年 | 49篇 |
1995年 | 47篇 |
1994年 | 26篇 |
1993年 | 34篇 |
1992年 | 26篇 |
1991年 | 30篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有7256条查询结果,搜索用时 15 毫秒
71.
72.
This paper investigates the coordinated operation of the progress planning with the resource planning when carrying out engineering projects and puts forward a method of "RSM" under the resource limit conditions. Then, the "RSM" was improved to avoid complicated calculation. This method not only reduces the calculating work by hand but saves computer's memory as well, making the time-resource optimization work more quick and convenient. 相似文献
73.
Liu Mingyu 《保鲜与加工》1997,(3):26-31
Through the analysis in this paper,the optimum relation of the discharging current peak interval t m ,the discharging loop equivalent inductance L and equivalent resistance R is obtained.This paper analyze the original discharging loop equivalent inductance L ,which provides an effective method for adjustment and selection of inductance L to realize the optimization energy saving design of the welding machine. 相似文献
74.
75.
Zeag Yongning Tong Fu 《保鲜与加工》1989,(2):43-49
An optimization approach for multi-relational joins based on
the matching concept in graph theory is introduced. The basic idea lies in constructing a join graph from an expression of N-relation query, and seeking for a maximun matching with minimun total weight. The algorithm for bipartition(X, Y) is proposed in this paper. 相似文献
76.
Based on the analysis and study on some existed models for two-dimensional Guillotine Cutting-Stock problem, it is pointed out that some kinds of the models may miss some good cutting patterns,and some may result in inadequate solutions because of only considering the patterns with the smallest waste. A kind of revised two-dimensional cutting-stock models are developed,which transform the two-dimensional problem into the one-dimensional one using the dimension-decreasing heuristic method and whose initial patterns are considered comprehensively. In this kind of models, not only the least waste,but also the other constraints,such as the demands and the relative area of the order plates are considered. 相似文献
77.
A structural optimization algorithm is performed for single-layer Kiewit reticulated dome by means of ANASYS. In the process of optimum design, the overall weight is taken as objective function; the stress constraints and stability constraints etc are considered. Meanwhile, the geometrical non-linearity is taken into account. Then the overall stability analysis for the optimized single-layer reticulated dome is operated. The results show that the optimization design is reliable. 相似文献
78.
The multicarrier-code division multiple access (MC-CDMA),which is the combination of direct sequence CDMA (DS-CDMA) and orthogonal frequency division multiplexing (OFDM) techniques, offers various advantages over single-carrier CDMA system. Some of the advantages are that MC-CDMA systems possess can remove the intersymbol interference (ISI) and enhance narrow-band interference suppression capabilities. So the MC-CDMA technique becomes a focus in the field of mobile communication. The authors introduce the typical MC-CDMA system model, discuss the decision statisticalvariable in Rayleigh fading channel included the CW interference, and give the expressions of probability of error in uplink. An approach is proposed with Modified Equal Gain Combining (MEGC) to decrease the effect of CW interference. Theoretical analysis and numerical results show that the anti-CW interference performance of MC-CDMA system can be improved used the MEGC approach. 相似文献
79.
The Lexicographic method has subjective and empirical character,so a weighting coefficient is introduced by considering the importance and proportion of each individual object,the preferable result of every individual object can be confirmed by comparing the degree of similarity between the perfect one and the ecumenic one and the Fuzzy optimization will be perfect.The effectiveness of these methods is illustrated by a fuzzy optimal design of the three-bar truss. 相似文献
80.
In the past, the criterion for calibration has almost invariably been the stellar oriented ballistic camera,the method is a point to point comparison on the identical coordinate system. Deficiencies is follows: The request of weather is severe(cloudless night); The period is often long; the measure equipment of high precision can't be calibrated. While EMBET methods is used in calibration, it does not need criterion and it demands only that the measure elements is larger than 3,and the trajectory and many system errors of the measure elements can be simultaneously calculated with the measure data sequences. The error models of related equipments' measure elements and the EMBET of typical equipment group are given. The EMBET method is successfully used in Accuracy-analysis of Satellite Launch. 相似文献