全文获取类型
收费全文 | 1705篇 |
免费 | 57篇 |
国内免费 | 53篇 |
专业分类
林业 | 55篇 |
农学 | 51篇 |
基础科学 | 39篇 |
347篇 | |
综合类 | 681篇 |
农作物 | 24篇 |
水产渔业 | 61篇 |
畜牧兽医 | 457篇 |
园艺 | 79篇 |
植物保护 | 21篇 |
出版年
2024年 | 11篇 |
2023年 | 30篇 |
2022年 | 44篇 |
2021年 | 45篇 |
2020年 | 42篇 |
2019年 | 48篇 |
2018年 | 35篇 |
2017年 | 48篇 |
2016年 | 45篇 |
2015年 | 58篇 |
2014年 | 82篇 |
2013年 | 58篇 |
2012年 | 90篇 |
2011年 | 105篇 |
2010年 | 89篇 |
2009年 | 77篇 |
2008年 | 79篇 |
2007年 | 93篇 |
2006年 | 84篇 |
2005年 | 63篇 |
2004年 | 55篇 |
2003年 | 55篇 |
2002年 | 48篇 |
2001年 | 47篇 |
2000年 | 42篇 |
1999年 | 32篇 |
1998年 | 29篇 |
1997年 | 30篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 38篇 |
1993年 | 41篇 |
1992年 | 23篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 17篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1982年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1815条查询结果,搜索用时 31 毫秒
31.
本文用ICPS-1000Ⅱ型等离子光谱仪,分别测定了苋菜、油菜、芹菜中的钾、钠、钙、镁、磷、铜、铁、锌、锰、锶十种元素的含量,标准曲线浓度与强度的相关系数(r=0.999)。在几种蔬菜中苋菜铁的含量高,苋菜5个品种中棠东红最高,而且锌、铜、钙、镁等也比较高。测定的7种油菜中,徐州苔菜锌铜比、锰铜比及锌铜锰总量高于其它品种。 相似文献
32.
33.
实验室的比较研究表明:熔样温度以600℃较为理想,有省电、省时和测定值稳定可靠的优点,对镍坩埚的剥蚀作用也较弱。 相似文献
34.
35.
The characteristics of the reflectance spectra of clay minerals and their influences on the reflectance spectra of soils are dealt with in the paper.The results showed that dominant clay minerals in soils could be distinguished in light of the spectral -form parameters of the reflectance spectra of soils,thus making it possible to develop a quick method to determine clay minerals by means of reflectance spectra of soils in the lab.and providing a theoretic basis for remote sensing of clay minerals in soils with a high resolution imaging spectrometer. 相似文献
36.
37.
38.
以水稻为主的种植系统对土壤有机质状况的影响 总被引:1,自引:1,他引:1
XIAO Yong-Lan ZHANG Yang-Zhu HU Rui-Zhi HUANG Yun-Xiang ZHOU Qing YUAN Zheng-Ping YANG Dong-Ping SHU Li 《土壤圈》1997,7(4):349-354
A long-term simulation experiment was carried out to study the effect of rice-based cropping system, green manure and ground-water level on soil organic matter. Soil organic matter content increased when upland soil was puddled and cropped under submerged conditions. Among all treatments, soil organic matter contents in the treatments of rice-rice-flooded fallow in winter (WF) were the highest, those in the treatments of rice-rice-astragalus (WG) came the second, and those in the treatments of rice-rice-rape (WR) were the lowest. At the same rate of green manure application, the degrees of organo-mineral complexing in soils of treatments WG and WR were higher than those of treatment WF. After 9-year rice cultivation, the state of combination of humus in heavy fraction varied with treatments. The relative content of loosely bonded humus decreased in the order of WR > WG > WF, and it correlated significantly with Se availability. 相似文献
39.
氮肥施用对冬小麦籽粒产量和氮素表观损失的影响 总被引:16,自引:0,他引:16
Excessive nitrogen (N) fertilizer application to winter wheat is a common problem on the North China Plain. To determine the optimum fertilizer N rate for winter wheat production while minimizing N losses, field experiments were conducted for two growing seasons at eight sites, in Huimin County, Shandong Province, from 2001 to 2003. The optimum N rate for maximum grain yield was inversely related to the initial soil mineral N content (Nmin) in the top 90 cm of the soil profile before sowing. There was no yield response to the applied N at the three sites with high initial soil mineral N levels (average 212 kg N ha^-1). The average optimum N rate was 96 kg N ha^-1 for the five sites with low initial soil Nmin (average 155 kg N ha^-1) before sowing. Residual nitrate N in the top 90 cm of the soil profile after harvest increased with increasing fertilizer N application rate. The apparent N losses during the wheat-growing season also increased with increasing N application rate. The average apparent N losses with the optimum N rates were less than 15 kg N ha^-1, whereas the farmers' conventional N application rate resulted in losses of more than 100 kg N ha^-1. Therefore, optimizing N use for winter wheat considerably reduced N losses to the environment without compromising crop yields. 相似文献
40.
以X射线衍射分析,研究了长江上游山地土壤的粘土矿物组成。根据土壤粘土矿物组成分类,划分了粘土矿物地带,采用土壤结构恢复试验,比较了不同粘土矿物组成土壤的结构形成特征。 相似文献