全文获取类型
收费全文 | 4386篇 |
免费 | 282篇 |
国内免费 | 353篇 |
专业分类
林业 | 228篇 |
农学 | 384篇 |
基础科学 | 113篇 |
894篇 | |
综合类 | 1916篇 |
农作物 | 246篇 |
水产渔业 | 451篇 |
畜牧兽医 | 407篇 |
园艺 | 209篇 |
植物保护 | 173篇 |
出版年
2024年 | 26篇 |
2023年 | 65篇 |
2022年 | 117篇 |
2021年 | 140篇 |
2020年 | 160篇 |
2019年 | 186篇 |
2018年 | 125篇 |
2017年 | 198篇 |
2016年 | 226篇 |
2015年 | 181篇 |
2014年 | 200篇 |
2013年 | 250篇 |
2012年 | 311篇 |
2011年 | 278篇 |
2010年 | 298篇 |
2009年 | 301篇 |
2008年 | 211篇 |
2007年 | 233篇 |
2006年 | 214篇 |
2005年 | 166篇 |
2004年 | 157篇 |
2003年 | 124篇 |
2002年 | 124篇 |
2001年 | 118篇 |
2000年 | 93篇 |
1999年 | 80篇 |
1998年 | 49篇 |
1997年 | 65篇 |
1996年 | 49篇 |
1995年 | 43篇 |
1994年 | 57篇 |
1993年 | 37篇 |
1992年 | 36篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有5021条查询结果,搜索用时 15 毫秒
1.
在查清天津市园林主要花灌木刺吸口器害虫桃粉蚜、绣线菊蚜、棉蚜和山楂红蜘蛛发生消长规律的基础上 ,确定了防治适期和结合点 ,筛选出 10 %吡虫啉、绿灵、蚧螨灵、 1. 8%齐螨素和花保5种低、无毒药剂 ,防效均达到 90 %以上。查出天敌 13种 ,并对优势种作了取食量调查 相似文献
2.
3.
4.
5.
6.
Field experiments were conducted to characterize the demography of Abutilon theophrasti and Setaria faberi in a conventionally managed 2‐year (maize/soya bean) rotation, and in 3‐year (maize/soya bean/triticale + red clover) and 4‐year (maize/soya bean/triticale + lucerne/lucerne) rotations managed with 72% and 79% lower herbicide inputs respectively. Rates of weed seedling recruitment, seedling survival and adult plant fecundity were determined for populations in each phase of each rotation and used to calculate annual rates of weed population change, Δ. In both years of the study, Δ for A. theophrasti populations declined or remained stable in all three rotation systems. Despite greater rates of seedling survival and fecundity in maize and soya bean in the 3‐ and 4‐year rotations, increases in Δ for A. theophrasti populations were prevented in these systems because of low fecundity in triticale and low seedling survival and fecundity in lucerne. For Setaria faberi populations, Δ remained stable in the 2‐year rotation, increased in the 3‐year rotation in both years, and increased in the 4‐year rotation in 1 year. The results of this study indicate that when herbicide use is reduced, rotations that include triticale and lucerne can facilitate the suppression of A. theophrasti. Rotations that include lucerne can contribute to restraining S. faberi population growth, given adequate levels of seedling mortality in this crop. 相似文献
7.
华山松,赤松次生韧皮部的解剖学观察 总被引:1,自引:0,他引:1
贺晓 《内蒙古林学院学报》1995,(3):28-33
华山松,赤松次生韧皮部轴向系统由筛胞、韧皮部薄壁细胞及径向片组成,径向系统为射线。径向片和射线中具有蛋白细胞,其特点是细胞核大,细胞质浓,与筛胞之间以单侧筛域相联系。在无功能韧皮部,筛胞和蛋白细胞死亡,被挤毁,射线细胞分裂扩张,并积累后含物。 相似文献
8.
特种稻黑米品种的糙米果皮中,含有大量的稀有天然黑(紫)色素。本文研究了这种色素的提取与分离方法、化学结构及其稳定性,并对其药理作用和应用前景作了简要分析。 相似文献
9.
Pot experiments were conducted to evaluate the level of imazamox tolerance in five red rice ( Oryza sativa L.) and four barnyardgrass (three Echinochloa crus-galli (L.) Beauv. and one Echinochloa oryzoides (Ard.) Fritch) morphologically distinct biotypes collected from rice fields in northern Greece. The susceptibility of barnyardgrass biotypes to propanil was also studied. Red rice biotypes were not controlled by imazamox applied at 40 g ha−1 . In contrast, 80 g imazamox ha−1 provided 56–84% red rice control (averaged across shoot number and fresh weight reduction). Not all barnyardgrass biotypes were susceptible to imazamox applied postemergence. However, propanil applied at 2.6 kg ha −1 controlled the E. crus-galli biotypes well, but propanil applied at rates of 2.6 and 5.2 kg ha −1 was not effective in reducing the shoot number and fresh weight of the E. oryzoides biotype. Propanil applied at 10.4 kg ha −1 reduced the shoot number and fresh weight of this biotype by 78 and 85%, respectively. In most cases, a linear equation ( y = % of control, x = g ha−1 ) provided the best fit for regressions between red rice or barnyardgrass shoot number or fresh weight and imazamox rates. The results of this study suggest that postemergence application of imazamox is not effective against all red rice and barnyardgrass biotypes found in the rice fields of Greece and that significant variability regarding herbicide efficacy among biotypes might exist. 相似文献
10.
A Lillehaug B Bergsj? J Schau T Bruheim T Vik?ren K Handeland 《Acta veterinaria Scandinavica》2005,46(1):23-32
Faecal samples were collected, as part of the National Health Surveillance Program for Cervids (HOP) in Norway, from wild red deer, roe deer, moose and reindeer during ordinary hunting seasons from 2001 to 2003. Samples from a total of 618 animals were examined for verocytotoxic E. coli (VTEC); 611 animals for Salmonella and 324 animals for Campylobacter. A total of 50 samples were cultivated from each cervid species in order to isolate the indicator bacterial species E. coli and Enterococcus faecalis/E. faecium for antibiotic resistance pattern studies. Salmonella and the potentially human pathogenic verocytotoxic E. coli were not isolated, while Campylobacter jejuni jejuni was found in one roe deer sample only. Antibiotic resistance was found in 13 (7.3%) of the 179 E. coli isolates tested, eight of these being resistant against one type of antibiotic only. The proportion of resistant E. coli isolates was higher in wild reindeer (24%) than in the other cervids (2.2%). E. faecalis or E. faecium were isolated from 19 of the samples, none of these being reindeer. All the strains isolated were resistant against one (84%) or more (16%) antibiotics. A total of 14 E. faecalis-strains were resistant to virginiamycin only. The results indicate that the cervid species studied do not constitute an important infectious reservoir for either the human pathogens or the antibiotic resistant microorganisms included in the study. 相似文献