全文获取类型
收费全文 | 1619篇 |
免费 | 100篇 |
国内免费 | 127篇 |
专业分类
林业 | 179篇 |
农学 | 229篇 |
基础科学 | 279篇 |
201篇 | |
综合类 | 780篇 |
农作物 | 8篇 |
水产渔业 | 26篇 |
畜牧兽医 | 109篇 |
园艺 | 2篇 |
植物保护 | 33篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 31篇 |
2021年 | 41篇 |
2020年 | 34篇 |
2019年 | 55篇 |
2018年 | 28篇 |
2017年 | 42篇 |
2016年 | 49篇 |
2015年 | 46篇 |
2014年 | 55篇 |
2013年 | 77篇 |
2012年 | 101篇 |
2011年 | 122篇 |
2010年 | 87篇 |
2009年 | 79篇 |
2008年 | 81篇 |
2007年 | 111篇 |
2006年 | 104篇 |
2005年 | 75篇 |
2004年 | 67篇 |
2003年 | 61篇 |
2002年 | 44篇 |
2001年 | 49篇 |
2000年 | 33篇 |
1999年 | 34篇 |
1998年 | 27篇 |
1997年 | 29篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 30篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 27篇 |
1990年 | 32篇 |
1989年 | 24篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 5篇 |
1985年 | 4篇 |
排序方式: 共有1846条查询结果,搜索用时 15 毫秒
41.
基于AutoCAD2000的二维图形自动编程软件的开发 总被引:2,自引:0,他引:2
介绍了基于AUTOCAD2000、采用Visual LISP作为开发工具的二维图形自动编程系统的开发,并详细介绍了数据结构、实体排序技术及各模块之间数据流的传送.并通过实例讲解了软件的应用。 相似文献
42.
This paper designed and developed a multi-objective programming (MOP) model to illustrate the dynamic relationship among technologies, productive activities, constraints and farmers’ objectives in the peri-urban vegetable production system and use the model as an economic tool in analysing probable consequences of a given action or innovation on the farm. The best compromise solution was generated using four analytical steps, as follows: single-objective optimization (to determine the ideal and anti-ideal values of the objective functions); constrained optimization (to generate the set of Pareto non-dominated solutions); cluster analysis (to trim down efficient set into smaller homogeneous groups); and compromise programming (to determine where the best compromise solution lies). 相似文献
43.
基础变形模量对坝体的安全运行和受力有着十分重要的意义,特别是高拱坝,需要良好的基础变形模量,但是在一定的荷载运行工况下,并不是意味着基础变形模量越高坝体应力、稳定、变形状况就越好。基于上述观点,利用多目标非线性规划方法对锦屏拱坝最优基础变形模量进行了研究,给出了拱坝在最优基础变形模量条件下坝体应力、稳定、变形及基础处理费用等特征值。研究表明:经过基础变形模量的优化,能有效改善坝体应力、位移、稳定等多项指标。 相似文献
44.
The general nonlinear programming with linear constraints was investigated. In the algorithm, the method of contributing set was used. Comparing with the general contributing set method, the descending dimension method was used to solve the sub-problem with equality constraints in iterative procedure and the problem with inequality constraints. The algorithm is effective by the numerical test. Finally, it was proved that the iteration points are descending, when the objective functions are convex. 相似文献
45.
ANSYS has become an effective tool for finite element analysis of masonry structure, but there is few common conclusions for reference. According to the characteristics of ANSYS and the essence of the analysis, some key problems in finite element analysis of masonry structure with ANSYS, such as structural modelling, material constitution, the damage criterion, iterative algorithm, convergence criterion, simulation of prestressing force and so on, are discussed in this paper. Based on the test results of typical masonry structures, the applicability of ANSYS to masonry structural analysis is studied and some suggestions for the application of ANSYS are presented. 相似文献
46.
The paper aims to investigate natural frequency of delaminated advanced grid stiffened composite plates by hump resonance method.The composite laminated plate element and the rib element are adapted to simulate the laminated plate and the ribs.Based on the composite laminated plate and beam element model considering first-order shear effect,a damping model on the basis of Rayleigh damping model in conjunction with Adams' strain energy method(MSE) and a Hertz nonlinear dynamic contact model to avoid the overlap and penetration phenomenon between the upper and lower sub-laminates at the delaminated region.A numerical analysis method of dynamic response for the delaminated composite plates is carried out by precise time-integration method,and then the natural frequencies are achieved when the dynamic deflections reach the hump peak.For the frequency-domain analysis provided in the former research papers,it is a difficult problem to avoid the embedded phenomenon in the mode shapes at the delamination zone,while in the current time-domain analysis,the embedded phenomenon can be successfully overcome by using nonlinear contact model.By vibration excitation test,the specimens were excited by different excited frequency and the amplitude frequency response characteristics obtained are used to extract the frequency.The extracted frequencies of the narrow delaminated composite plates measured,which agrees well with the predicted natural frequencies. 相似文献
47.
48.
49.
50.
CHEN Yao-hui~ 《保鲜与加工》2004,(8):86-91
We prove a Donsker type approximation theorem for the fractional Brownian motion in the case of the Hurst index greater than one half. With this approximation we construct an elementary market model that converges weakly to the fractional analogue of the Black Scholes model. We show that there exist arbitrage opportunities in this model. 相似文献