全文获取类型
收费全文 | 12093篇 |
免费 | 599篇 |
国内免费 | 1211篇 |
专业分类
林业 | 803篇 |
农学 | 970篇 |
基础科学 | 1975篇 |
2508篇 | |
综合类 | 5040篇 |
农作物 | 592篇 |
水产渔业 | 214篇 |
畜牧兽医 | 641篇 |
园艺 | 292篇 |
植物保护 | 868篇 |
出版年
2024年 | 51篇 |
2023年 | 236篇 |
2022年 | 404篇 |
2021年 | 394篇 |
2020年 | 422篇 |
2019年 | 477篇 |
2018年 | 326篇 |
2017年 | 497篇 |
2016年 | 662篇 |
2015年 | 537篇 |
2014年 | 658篇 |
2013年 | 759篇 |
2012年 | 1003篇 |
2011年 | 904篇 |
2010年 | 711篇 |
2009年 | 766篇 |
2008年 | 615篇 |
2007年 | 810篇 |
2006年 | 624篇 |
2005年 | 522篇 |
2004年 | 390篇 |
2003年 | 364篇 |
2002年 | 237篇 |
2001年 | 221篇 |
2000年 | 188篇 |
1999年 | 150篇 |
1998年 | 155篇 |
1997年 | 114篇 |
1996年 | 97篇 |
1995年 | 124篇 |
1994年 | 90篇 |
1993年 | 84篇 |
1992年 | 78篇 |
1991年 | 56篇 |
1990年 | 53篇 |
1989年 | 35篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
141.
Mathematical model of power frequency electric field is established based on Charge Simulation Method(CSM) to analyze power frequency electric field caused by EHV lines with overhead ground wires and its effect, which are entering the megalopolis. Calculative method on the electric field under the transmission lines is analyzed and validated. According to the criterion of environmental evaluation, the distributing characteristic of electric field is summarized, in case of various arrangement manners of lines. At last, some advice and methods of eliminating electric field under the transmission lines entering the megalopolis is proposed with regard to protecting environment. 相似文献
142.
143.
Yun Zhengqing Tan Bangding 《保鲜与加工》1993,(5):79-84
Based on [l].this paper presents a new spline-BEM for calculating 3-D electrostatic fields,in which bi-cubic B-splines are used as basis functions. The corner problem in BEM and the extreme conditions for splines are circumvented. The numerical results presented show that the global approximation .convergence and stability of the method are satisfactory. 相似文献
144.
Feng Hailiang Wu Junliang 《保鲜与加工》1997,(6):108-113
Some conceptions of stable quaternion matrices and some judging criteria are given.The Robrach theorem,Taussky theorem,Ostrowski Schneider theorem and Gerschgorin theorem are generalized to quaternion field.The conclusion about two quaternion matrices,i.e.,inferior positive matrices are unstable,interior negative matrices are stable and some other results are pointed out. 相似文献
145.
146.
LIU Qing-song~ 《保鲜与加工》2004,(4):15-19
The mechanism of television interference is discussed from High voltage transmission line. Then the computational model is established, and scattering fields are calculated with the finite-difference time-domain(FDTD) method, and the results are visualized. The scattering effects of High voltage transmission lines on horizontal polarization waves (corresponding to TM mode) are greater than on vertical polarization waves (corresponding to TE mode). 相似文献
147.
148.
149.
An experimental study on consolidation and drainage of two gravels with different grading was carried out using high - pressure large - scale tri - axial testing facility. A concept of equivalent surrounding pressure is introduced. An analysis was carried out on the effect and mechanism of reinforcement, experimental surrounding pressure and soil properties. Results show that the reinforcement can improve the strength and failure strain of the material and delay the failure of the soil. The effect of reinforcement of soil - gravel depends on the surrounding pressure and weathering of the gravel. 相似文献
150.
A nonlinear finite element analysis of 4 RC deep flexural simply supported beams with the program VT2 is presented. Crack development and failure modes , longitudinal reinforcement strain distributions and load -deflection curves were compared as a result in order to evaluate the validity of the disturbed stress field model to analyse such deep simply supported beam. 相似文献