全文获取类型
收费全文 | 312篇 |
免费 | 18篇 |
国内免费 | 46篇 |
专业分类
林业 | 28篇 |
农学 | 44篇 |
基础科学 | 109篇 |
65篇 | |
综合类 | 99篇 |
农作物 | 1篇 |
水产渔业 | 8篇 |
畜牧兽医 | 12篇 |
园艺 | 4篇 |
植物保护 | 6篇 |
出版年
2024年 | 5篇 |
2023年 | 15篇 |
2022年 | 14篇 |
2021年 | 21篇 |
2020年 | 7篇 |
2019年 | 25篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 20篇 |
2011年 | 17篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
排序方式: 共有376条查询结果,搜索用时 218 毫秒
71.
王喆 《安徽农业大学学报》2008,(6):84-86
窗在《呼啸山庄》成为了整体意象中一个不可或缺的有机组成部分之一,它承载了女作家的丰富情感及人物命运和小说思想主题的众多内容,昭示着心灵的向往与追求,积淀着丰富的文化底蕴,给人以灵魂的净化和哲理的感悟。女作家艾米莉通过这一意象,展现了 19 世纪资本主义现实社会中难以实现的理想与抱负。 相似文献
72.
从资源环境系统的内部结构出发,将资源环境评价体系分为生产系统和环境治理系统,针对该结构建立了扩展强自由处置性下的网络DEA模型——E-NSBM模型,将其与窗口分析法相结合,对2005-2012年中国各省资源环境效率进行了评价。结果表明:我国经济发达地区的生产系统效率普遍较高而环境治理系统效率较低;中、西部地区环境治理系统效率较高,但东部地区环境治理系统效率改进幅度最大;综合效率表现差的省份普遍表现为高的能耗强度、碳排放强度和硫强度。因此,各省应根据各自发展需要来确定资源环境效率的改进途径。 相似文献
73.
The proportion of radiation load through glass windows in building energy analysis is comparatively great;it is regarded as linear relation with temperature in BIN method,which is extremely a rough method.It is not only because the relation between such radiation load and temperature is far from linear relationship,but also there is lack of objective standard for the selection of corresponding representative temperature to the load.To solve this problem,calculating the maximum factor D_(J max) firstly,then get the hourly corresponding relation of load and temperature by multiplying the hourly cool load coefficient.The practical relation of load and temperature could be obtained by counting up the average load to each temperature at each direction;the load calculation method is still simple using a series of statistic data.A comparison has been made between this method and the former one.As it is the real reflection of relation between the temperature and load,the precision of load calculation is enhanced.The process using this method to calculate load for south facing window in Chengdu is given in this paper. 相似文献
74.
Signal detecting is the first task for Burst communication. The paper proposes an improved double sliding window algorithm to detect burst signal based on the feature of preamble sequence. Additionally, theory analysis and computer simulation of the improved algorithm are also made in several typical channels. At last, the algorithm is realized with FPGA, and the result indicates that the improved algorithm can detect burst signal only within the time of 6 symbols, obviously improving the capability of signal detecting algorithm. 相似文献
75.
智能除草机器人在草坪作业时,易受到外界扰动以及系统不确定性的影响,从而导致轨迹跟踪收敛时间长以及跟踪效果差等问题。因此,设计一种面向轨迹跟踪的自适应快速积分终端滑模控制算法。首先,考虑驱动轮动力学特性以及未建模误差、外界干扰、动静摩擦等不确定性因素,建立除草机器人的动力学模型。然后基于所建立的动力学模型,设计自适应快速积分终端滑模控制器。所提出的控制器结合了快速终端滑模、积分滑模和自适应估计技术的优点,能够实现期望的跟踪性能并抑制控制信号抖动。同时,在不需要明确系统不确定性和外界干扰上界的情况下,可以通过所设计自适应估计项进行实时补偿,提高系统的鲁棒性。最后,通过仿真和试验验证了该方法的有效性。试验结果表明,所设计的控制器能够使跟踪误差在有限时间内快速收敛,并且横向误差绝对值不超过0.097 9 m,纵向误差绝对值不超过0.102 6 m,航向角误差绝对值不超过0.057 8 rad,保证除草机器人准确跟踪作业路径,同时具有较强的鲁棒性。 相似文献
76.
Nairoby Pacheco‐Carln Danitzia A. Guerrero‐Tortolero Lucero B. Cervantes‐Montoya Ilie S. Racotta Rafael Campos‐Ramos 《Aquaculture Research》2021,52(1):77-93
Constant and oscillating egg incubation temperatures on embryonic development and early larval morphology were studied in longfin yellowtail (Seriola rivoliana Valenciennes). We investigated the effects of constant temperatures from 16 to 32°C on embryo development and larval morphology at hatch, and whether oscillating temperature during embryogenesis could lead to larval morphological variations. After hatching, larval morphology and development during yolk sac (YS) utilization were examined in larvae at constant temperatures and larvae at 25°C that had oscillating temperature during egg incubation. Hatching rates were > 75%, only decreasing to ~ 50% at 30°C. At constant temperatures, the largest larvae occurred at 22 and 24°C. The oscillating temperature did not affect the timing of embryo development but resulted in larger and smaller larvae with a smaller and bigger YS, respectively, with a similar hatching time. Therefore, a growth response occurred in embryos during a window of development before hatching, depending on the adaptive response to temperature (spawn‐specific). After hatching, most of the YS was absorbed within 24 hr in all treatments, and the growth of the larval head was a priority with an optimal development at 26°C. There was compensatory growth in smaller larvae resulting in similar sizes after YS utilization, but larvae showed variations in body structure that could be important in further aquaculture research. 相似文献
77.
WANG Hai ning 《保鲜与加工》2012,(5):126-131
Taking a coconut shell powder activated carbon (PAC) as the carrier and butyl acetate titanate with ethanol as raw materials, TiO2/AC(activated carbon) photocatalyst was prepared through sol-gel and impregnation method, and batch experiments were carried out to investigate its performances of removing Carbamazepine from artificial water. The results indicate that TiO2/AC has a better removal of carbamazepine than powder TiO2 and PAC. In the same condition, the removal of carbamazepine in TiO2/AC system is 1.7 times than that in TiO2. When the initial concentration of Carbamazepine is 10 mg/L, and the dosage of TiO2/AC is 500 mg/L, in which the load capacity of TiO2 is 11.2%, the removal rate reaches at 91.5% while the PH is 1.0. The reaction of photocatalytic degradation process can be accorded with two-step dynamics kinetics with different concentrations. The constant of secondary reaction is inversely proportional to concentration. Using Langmuir-Hinshelwood (L-H) model, it concludes that the apparent adsorption equilibrium constant Ka is 9.215×10 3 L/mol, and the surface reaction rate constant Kr is 3.678×10 -6 mol/(L·min). Thus, microwave irradiation is the best way for catalyst regeneration. 相似文献
78.
79.
80.