全文获取类型
收费全文 | 39487篇 |
免费 | 1976篇 |
国内免费 | 4549篇 |
专业分类
林业 | 2775篇 |
农学 | 4514篇 |
基础科学 | 599篇 |
4678篇 | |
综合类 | 18154篇 |
农作物 | 2984篇 |
水产渔业 | 2720篇 |
畜牧兽医 | 5149篇 |
园艺 | 1635篇 |
植物保护 | 2804篇 |
出版年
2024年 | 92篇 |
2023年 | 434篇 |
2022年 | 857篇 |
2021年 | 1074篇 |
2020年 | 1147篇 |
2019年 | 1352篇 |
2018年 | 979篇 |
2017年 | 1617篇 |
2016年 | 2038篇 |
2015年 | 1789篇 |
2014年 | 1377篇 |
2013年 | 2062篇 |
2012年 | 3027篇 |
2011年 | 2948篇 |
2010年 | 2351篇 |
2009年 | 2162篇 |
2008年 | 2443篇 |
2007年 | 2925篇 |
2006年 | 2643篇 |
2005年 | 2009篇 |
2004年 | 1664篇 |
2003年 | 1154篇 |
2002年 | 935篇 |
2001年 | 852篇 |
2000年 | 793篇 |
1999年 | 658篇 |
1998年 | 532篇 |
1997年 | 500篇 |
1996年 | 466篇 |
1995年 | 474篇 |
1994年 | 389篇 |
1993年 | 420篇 |
1992年 | 383篇 |
1991年 | 342篇 |
1990年 | 311篇 |
1989年 | 221篇 |
1988年 | 176篇 |
1987年 | 116篇 |
1986年 | 116篇 |
1985年 | 51篇 |
1984年 | 28篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1963年 | 6篇 |
1962年 | 6篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Jie Liu Rumi Fujita Michiko Sato Kuniyoshi Shimizu Fumiko Konishi Kiyoshi Noda Shoichiro Kumamoto Chie Ueda Hisatoshi Tajiri Shuhei Kaneko Yoshitaro Suimi Ryuichiro Kondo 《Journal of Wood Science》2005,51(2):189-192
The inhibitory effects of 102 methanol extracts of 40 mycelia, 9 culture fluids, and 53 fruiting bodies of 40 strains of Ganoderma lucidum on 5-reductase were investigated. The methanol extract of the fruiting body of each strain was found to show the strongest 5-reductase inhibitory activity among the extracts tested. 相似文献
992.
993.
994.
主要综述了季铵盐类化合物(QAC)在用作木材防腐剂时的耐腐性、抗流失性及其与木材的结合机理等方面的研究概况,分析了实验室耐腐性和野外实验耐腐性结果不一致的原因。此外也介绍了对季铵盐进行改性处理方面的一些研究进展。 相似文献
995.
Mathieu Fortin Gaétan Daigle Chhun-Huor Ung Jean Bégin Louis Archambault 《European Journal of Forest Research》2007,126(4):573-585
This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity
in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance
structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level
approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum
likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized
residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover,
compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more
accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure
may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth
modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates
are valid when the number of observations is large. 相似文献
996.
Cao Jin-zhen Yu Li-li You Xiao-di Kamdem D. Pascal 《中国林学(英文版)》2007,9(4):239-245
In order to clarify the interaction between copper and wood substances in wood treated with copper containing water-borne wood preservatives, the dielectric constant ε′ and dielectric loss factor ε″ of untreated wood and wood treated with four concentration levels of copper-ethanolamine (Cu-EA) solutions were determined within a temperature range from –100 to 40°C and a frequency range from 100 to 1 MHz. Three dielectric relaxation processes were observed in the ε″ spectrum; among them R-I is based on the reorientation of methylol groups in the amorphous region of wood cell walls and R-II is related to wood extractives. R-III appeared in Cu-EA treated wood, and its magnitude decreases with the concentration of Cu-EA solutions used in this experiment. This relaxation process was considered to be based on the reorientation of copper-ethanolamine-wood complexes in wood cell walls. At low copper retention, the hydrogen in the complex can form hydrogen bonding with adjacent hydroxyl groups, which results in a strong bonding state between copper and wood; at high copper retention, the numerous copper-ethanolamine complexes not only hinder them from forming hydrogen bonding with adjacent wood molecules due to steric hindrance, but also weaken the interaction between wood molecules themselves, which corresponds to reducing ε″ values of both R-I and R-III processes. The results explain the fact of in-creasing copper leaching in wood treated with high concentration copper-based water-borne preservatives. 相似文献
997.
在气候干燥、寒冷的西北地区 ,引进具有耐干旱、贫瘠 ,抗寒冷 ,抗盐碱等多种优良特性的常绿或准常绿饲料灌木四翅滨藜 ,经过 2a生长全过程的栽培试验 ,观测结果表明 :在不同土壤类型下 ,新梢生长量、扦插育苗的成活率、保存率都表现出差异性。但移栽苗的成活率、保存率差异不大 ,表现出较强的适应性。而在中、强盐碱性土壤、(粗 )砂土中仍能正常生长 ,但新梢生长量低 ,分枝减少 相似文献
998.
999.
1000.