全文获取类型
收费全文 | 27047篇 |
免费 | 1117篇 |
国内免费 | 3104篇 |
专业分类
林业 | 1440篇 |
农学 | 2572篇 |
基础科学 | 886篇 |
3718篇 | |
综合类 | 10908篇 |
农作物 | 1789篇 |
水产渔业 | 1199篇 |
畜牧兽医 | 5539篇 |
园艺 | 1923篇 |
植物保护 | 1294篇 |
出版年
2024年 | 122篇 |
2023年 | 385篇 |
2022年 | 745篇 |
2021年 | 940篇 |
2020年 | 929篇 |
2019年 | 1191篇 |
2018年 | 870篇 |
2017年 | 1176篇 |
2016年 | 1455篇 |
2015年 | 1260篇 |
2014年 | 1384篇 |
2013年 | 1588篇 |
2012年 | 1904篇 |
2011年 | 1975篇 |
2010年 | 1729篇 |
2009年 | 1741篇 |
2008年 | 1509篇 |
2007年 | 1594篇 |
2006年 | 1352篇 |
2005年 | 980篇 |
2004年 | 782篇 |
2003年 | 632篇 |
2002年 | 510篇 |
2001年 | 430篇 |
2000年 | 415篇 |
1999年 | 391篇 |
1998年 | 275篇 |
1997年 | 366篇 |
1996年 | 347篇 |
1995年 | 303篇 |
1994年 | 292篇 |
1993年 | 297篇 |
1992年 | 336篇 |
1991年 | 332篇 |
1990年 | 281篇 |
1989年 | 134篇 |
1988年 | 87篇 |
1987年 | 53篇 |
1986年 | 40篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1962年 | 6篇 |
1956年 | 14篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
D. Bilalis P. Efthimiadis & G. Karagiannis 《Journal of Agronomy and Crop Science》2001,187(2):121-126
The effect of three herbicides, diclofop-methyl (DM), imazamethabenz-methyl (IM) and fenoxaprop-ethyl (FE), was investigated at the recommended rate (×) and double the recommended rate (2×) in a durum wheat crop. FE had the smallest effect on root system characteristics, while IM had the greatest effect. For all herbicides, the double rate treatment gave a greater statistical reduction than the single rate for root system characteristics. FE had the smallest effect on the activity of aerobic microorganisms, while DM gave the greatest reduction, 10 days after application, and all three herbicides reduced earthworm abundance. DM gave the smallest reduction in the number of tillers and in plant height, while the double rate of IM gave the greatest reduction. For all three herbicides, double the recommended rate resulted in a significant reduction in the weight of 1000 seeds, while no statistically significant deviations were noted at the recommended rate. Finally, the use of all three herbicides resulted in significantly lower statistical yields compared to the sample (control plot), although there were no significant statistical differences among them, for either recommended or double recommended rates. 相似文献
3.
4.
5.
J. Müller 《Journal of Agronomy and Crop Science》1993,171(4):217-235
Dry Matter Production, CO2 Exchange, Carbohydrate and Nitrogen Content of Winter Wheat at Elevated CO2 Concentration and Drought Stress
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO2 concentration and changing climatic conditions on agricultural ecosystems. In this context, detailed knowledge is required about the possible effects on crop growth and physiological processes. To this aim, the influence of an elevated CO2 concentration and of drought stress on dry matter production, CO2 exchange, and on carbohydrate and nitrogen content was studied in two winter wheat varieties from shooting to milk ripeness. Elevated CO2 concentration leads to a compensation of drought stress and at optimal water supply to an increase of vegetative dry matter and of yield to the fourfold value. This effects were caused by enhanced growth of secondary tillers which were reduced in plants cultivated at atmospheric CO2 concentration. Analogous effects in the development of ear organs were influenced additionally by competitive interactions between the developing organs. The content and the mass of ethanol soluble carbohydrates in leaves and stems were increased after the CO2 treatment and exhausted more completely during the grain filling period after drought stress. Plants cultivated from shooting to milk ripeness at elevated CO2 concentration showed a reduced response of net photosynthesis rate to increasing CO2 concentration by comparison with untreated plants. The rate of dark respiration was increased in this plants. 相似文献
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO
6.
为改善中锰白口铸铁的韧性以扩大其应用范围,本文探讨了C, Si, Mn等合金元素、变质处理和热处理工艺对中Mn白口铸铁组织和性能的影响. 相似文献
7.
在椭圆型偏微分方程数值解法中,经常遇到M-阵与Stielt-jes-阵,本文进一步拓广M-阵的概念,并研究它们的性质及其在线性方程组迭代解法中的作用。 相似文献
8.
9.
以苯—乙醇为夹带剂,研究超临界CO2流体不同处理压力、温度、时间对福建产杉木、马尾松、檫木木材渗透性的影响。结果表明,在35 MPa内,处理压力的增大有利于3种木材渗透性的提高;杉木在处理温度为40℃时,渗透性的变化率达到最大,为493%,马尾松和檫木在处理温度为45℃时,渗透性的变化率达到最大,分别为479%和349%;较佳的处理时间为30 min。 相似文献
10.
本文介绍一种新研制出的挖掘机特性测试仪。仪器应用微机技术、自动采集挖掘机特性的电压和电流数据、可在通用示波器上显示或X—y记录仪绘出挖掘机特性曲线。输入标准特性参数后,自动计算并打印出丰满系数,电流和电压测试数据。采样速度为2160点/秒,精度为±1%,量程满足目前使用的4~23m~3电铲.仪器工作可靠,操作维护方便,为挖掘机的调试提供了一个先进的工具。 相似文献