全文获取类型
收费全文 | 17419篇 |
免费 | 116篇 |
专业分类
林业 | 3814篇 |
农学 | 1348篇 |
基础科学 | 141篇 |
3039篇 | |
综合类 | 727篇 |
农作物 | 2158篇 |
水产渔业 | 1891篇 |
畜牧兽医 | 1263篇 |
园艺 | 1158篇 |
植物保护 | 1996篇 |
出版年
2023年 | 10篇 |
2022年 | 15篇 |
2021年 | 32篇 |
2020年 | 27篇 |
2019年 | 36篇 |
2018年 | 2794篇 |
2017年 | 2755篇 |
2016年 | 1279篇 |
2015年 | 118篇 |
2014年 | 95篇 |
2013年 | 126篇 |
2012年 | 871篇 |
2011年 | 2192篇 |
2010年 | 2149篇 |
2009年 | 1296篇 |
2008年 | 1335篇 |
2007年 | 1602篇 |
2006年 | 54篇 |
2005年 | 110篇 |
2004年 | 116篇 |
2003年 | 165篇 |
2002年 | 70篇 |
2001年 | 16篇 |
2000年 | 50篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 17篇 |
1987年 | 6篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1968年 | 10篇 |
1967年 | 5篇 |
1966年 | 5篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
A modern computer-based simulation tool (WaterMan) in the form of a game for on-farm water management was developed for application in training events for farmers, students, and irrigators. The WaterMan game utilizes an interactive framework, thereby allowing the user to develop scenarios and test alternatives in a convenient, risk-free environment. It includes a comprehensive soil water and salt balance calculation algorithm. It also employs heuristic capabilities for modeling all of the important aspects of on-farm water management, and to provide quantitative performance evaluations and practical water management advice to the trainees. Random events (both favorable and unfavorable) and different strategic decisions are included in the game for more realism and to provide an appropriate level of challenge according to player performance. Thus, the ability to anticipate the player skill level, and to reply with random events appropriate to the anticipated level, is provided by the heuristic capabilities used in the software. These heuristic features were developed based on a combination of two artificial intelligence approaches: (1) a pattern recognition approach and (2) reinforcement learning based on a Markov decision processes approach, specifically the Q-learning method. These two approaches were combined in a new way to account for the difference in the effect of actions taken by the player and action taken by the system in the game world. The reward function for the Q-learning method was modified to reflect the suggested classification of the WaterMan game as what is referred to as a partially competitive and partially cooperative game. 相似文献
72.
Dothistroma needle blight (DNB) is a serious needle disease of conifers that primarily affects pine species (Pinus spp.). Dothistroma septosporum is one of the DNB pathogens that has a diverse range of host species excluding Pinus armandii. In 15 inoculated P. armandii seedlings, D. septosporum acervuli were observed in 43 infected needles of ten seedlings with a mean disease severity of 1.11% at 25 weeks after inoculations, demonstrating the potential of D. septosporum to cause symptoms on the needles of P. armandii via artificial inoculation. The disease severity of P. armandii was similar to the positive control, Pinus nigra (median 0.75 for P. armandii to 0.70 for P. nigra), thus, P. armandii acts under artificial conditions as a susceptible host species. 相似文献
73.
74.
75.
Purpose
Carbon nanomaterials (CNMs) have attracted a great deal of research interest for their potential environmental applications because of their unique properties. Adsorption of organic chemicals on CNMs was reported to be important in controlling their environmental risks. However, the kinetics of the adsorption is hardly investigated in literature. The objective of this work was, therefore, to quantitatively describe the sorption kinetics of 17 α-ethinyl estradiol (EE2) and bisphenol A (BPA) on CNMs as compared to activated carbon (AC). 相似文献76.
Ruijuan Li Jinfeng Zhao Chuanfan Sun Wenjing Lu Chengjin Guo Kai Xiao 《Frontiers of Agriculture in China》2010,4(2):195-209
As a kind of enzyme widely existing in eukaryotic species, especially in grains and oil seeds, phytases play an important
role in the degradation of some phosphates containing organic molecules. So far, phytases derived from various species have
been successfully used as animal feed additives. It has also been experimentally verified that phytases have a potential use
in generating crop germplasm with high phosphorus use efficiency, based on their biochemical role in releasing Pi from the
phytate and its derivatives. In this paper, the biochemical properties, molecular characterizations, functions and the potential
application perspective of phytases are reviewed and commented on, aiming at the further exploration of the biochemical and
molecular characterizations, and promotion of the application of phytases, a kind of important enzyme possessing potential
use in animal feeding and creation of high P use crop cultivars, in the future. 相似文献
77.
78.
Xing-Pu Li Su-Que Lan Ye-Lun Zhang Yu-Ping Liu 《Genetic Resources and Crop Evolution》2010,57(7):1007-1012
Pericarp color in wheat is an important trait related to nutrients and health benefits. Identification of molecular markers
closely linked to the grain color genes will help utilize pericarp trait in wheat breeding. Genetic studies involving F1, F2, and F3 populations from the cross Jizi 439 (purple grain)/Gao8901 (white grain) showed that the purple grain color was controlled
by two genes. By using the bulked segregant analysis (BSA) approach, two DNA pools were established from the dark purple-grain
and white-grain plants respectively. Among the 230 pairs of microsatellite primers used in this study, two markers showed
polymorphism in DNA pools, parents, F1 and F2 populations. Linkage analysis indicated that the two markers Xgwm47 and Xgwm155 were linked with two purple pigment genes. One of the purple pigment genes is located on chromosome 2AS and is 34.7cM away
from the marker Xgwm47, whereas another gene is mapped on 3AL with 14.7cM away from marker Xgwm155. 相似文献
79.
80.