全文获取类型
| 收费全文 | 4017篇 |
| 免费 | 1557篇 |
| 国内免费 | 353篇 |
专业分类
| 林业 | 62篇 |
| 农学 | 673篇 |
| 基础科学 | 434篇 |
| 522篇 | |
| 综合类 | 1556篇 |
| 农作物 | 578篇 |
| 水产渔业 | 59篇 |
| 畜牧兽医 | 1592篇 |
| 园艺 | 164篇 |
| 植物保护 | 287篇 |
出版年
| 2025年 | 119篇 |
| 2024年 | 111篇 |
| 2023年 | 139篇 |
| 2022年 | 309篇 |
| 2021年 | 292篇 |
| 2020年 | 241篇 |
| 2019年 | 249篇 |
| 2018年 | 177篇 |
| 2017年 | 184篇 |
| 2016年 | 191篇 |
| 2015年 | 247篇 |
| 2014年 | 294篇 |
| 2013年 | 306篇 |
| 2012年 | 480篇 |
| 2011年 | 473篇 |
| 2010年 | 352篇 |
| 2009年 | 367篇 |
| 2008年 | 203篇 |
| 2007年 | 376篇 |
| 2006年 | 351篇 |
| 2005年 | 133篇 |
| 2004年 | 85篇 |
| 2003年 | 30篇 |
| 2002年 | 30篇 |
| 2001年 | 27篇 |
| 2000年 | 16篇 |
| 1999年 | 25篇 |
| 1998年 | 26篇 |
| 1997年 | 14篇 |
| 1996年 | 18篇 |
| 1995年 | 4篇 |
| 1994年 | 2篇 |
| 1991年 | 3篇 |
| 1989年 | 1篇 |
| 1988年 | 2篇 |
| 1987年 | 15篇 |
| 1986年 | 15篇 |
| 1985年 | 1篇 |
| 1984年 | 1篇 |
| 1982年 | 1篇 |
| 1981年 | 2篇 |
| 1980年 | 1篇 |
| 1978年 | 1篇 |
| 1977年 | 1篇 |
| 1963年 | 3篇 |
| 1962年 | 2篇 |
| 1956年 | 6篇 |
| 1955年 | 1篇 |
排序方式： 共有5927条查询结果，搜索用时 0 毫秒
1.
Xiang ZHANG Qiu-zhi RUI Pan-pan LIANG Chen-hua WEI Guo-qiang DENG Yuan CHEN Yuan CHEN Zhao-di DONG De-hua CHEN 《农业科学学报》2018,17(9):1991-1998
This study was conducted to investigate the effects of alternating high temperature on Cry1Ac protein content on Bt cotton cultivars Sikang 1(SK-1,a conventional cultivar)and Sikang 3(SK-3,a hybrid cultivar).In 2011 and 2012,cotton plants were subjected to high temperature treatments ranging from 32 to 40℃ in climate chambers to investigate the effects of high temperature on boll shell insecticidal protein expression.The experiments showed that significant decline of the boll shell insecticidal protein was detected at temperatures higher than 38℃ after 24 h.Based on the results,the cotton plants were treated with the threshold temperature of 38℃ from 6:00 a.m.to 6:00 p.m.followed by a normal temperature of 27℃ during the remaining night hours(DH/NN)in 2012 and 2013.These treatments were conducted at peak boll growth stage for both cultivars in study periods of 0,4,7,and 10 d.Temperature treatment of 32℃ from 6:00 a.m.to 6:00 p.m.and 27℃ in the remaining hours was set as control.The results showed that,compared with the control,after the DH/NN stress treatment applied for 7 d,the boll shell Cry1Ac protein content level was significantly decreased by 19.1 and 17.5% for SK-1 and by 15.3 and 13.7% for SK-3 in 2012 and 2013,respectively.Further analysis of nitrogen metabolic physiology under DH/NN showed that the soluble protein content and the glutamic pyruvic transaminase(GPT)activities decreased slightly after 4 d,and then decreased sharply after 7 d.The free amino acid content and the protease content increased sharply after 7 d.The changes in SK-1 were greater than those in SK-3.These results suggest that under DH/NN stress,boll shell Cry1Ac protein content decline was delayed.Reduced protein synthesis and increased protein degradation in the boll shell decreased protein content,including Bt protein,which may reduce resistance to the cotton bollworm. 相似文献
2.
《Agricultural Water Management》2005,71(2):131-143
Soil water and salinity are crucial factors influencing crop production in arid regions. An autumn irrigation system employing the application of a large volume of water (2200–2600 m3 ha−1) is being developed in the Hetao Irrigation District of China, since the 1980s with the goal to reduce salinity levels in the root zone and increase the water availability for the following spring crops. However, the autumn irrigation can cause significant quantities of NO3− to leach from the plant root zone into the groundwater. In this study, we investigated the changes in soil water content, NO3–N and salinity within a 150 cm deep soil profile in four different types of farmlands: spring wheat (FW), maize (FM), spring wheat–maize inter-planting (FW–M) and sunflower (FS). Our results showed that (1) salt losses mainly occurred in the upper 60 cm of the soil and in the upper 40 cm for NO3–N; (2) the highest losses of salt and NO3–N could be observed in FW, whereas the lowest losses were found in FW–M.NO3–N concentration, pH and electrical conductivity (EC) in the groundwater were also monitored before and after the autumn irrigation. We found that the autumn irrigation caused the groundwater concentration of NO3–N to increase from 1.73 to 21.6 mg L−1, thereby, exceeding the standards of the World Health Organization (WHO). Our results suggest that extensive development of inter-planting tillage might be a viable measure to reduce groundwater pollution, and that the application of optimized minimum amounts of water and nitrogen to meet realistic yield goals, as well as the timely application of N fertilizers and the use of slow release fertilizers can be viable measures to minimize nitrate leaching. 相似文献
3.
Fogging with formaldehyde of citrus packinghouses when the fruit are absent is a practice to control conidia of Penicillium digitatum (Pers.) Sacc., the cause of citrus green mold. Replacements for formaldehyde in these facilities are needed because of worker and environmental health issues. To evaluate the effectiveness of candidate sanitizers, craft wood sticks with conidia of P. digitatum were attached throughout commercial citrus ethylene degreening rooms and either water alone or the sanitizers were applied. The rooms were 20 ± 2 °C and humidified to 85–90% relative humidity. Aldehydes, peroxygen compounds, sodium hypochlorite, chlorine dioxide, quaternary ammonium, alcohols, one phenolic compound, and one organic acid were applied with a compressed air assisted atomizer or fan atomizer in a volume of approximately 6 L per 100 m3 of room volume dispensed over a 3 h period. Rates applied were expressed as active ingredient per m3 of room volume. All were compared to formaldehyde applied at 1.98 g m−3 of room volume. After 24 h, the craft wood sticks were retrieved, and germination of the conidia assessed. Five sanitizers reduced germination of conidia by more than 95% and equaled formaldehyde in effectiveness. They were (effective rates): (1) glutaraldehyde (0.1 g m−3); (2) hydrogen peroxide (4.4 g m−3); (3) Citrisol (1.0 g m−3), a proprietary mineral oxychloride oxidizer; (4) acetic acid (5.3 g m−3); and (5) peracetic acid (2.4 g m−3). The toxicity of effective sanitizers was determined by exposure of P. digitatum conidia for 10 min to concentrations of each and the proportion of survivors used to estimate EC50 and EC99 concentrations. The toxicity of the sanitizers in this assay did not predict their effectiveness when applied by fogging, probably because other factors, such as distribution, persistence, droplet size, or vapor pressure also influenced their effectiveness. 相似文献
4.
5.
Asymmetric warming and frequent temperature extremes are the consequences of climate change that are affecting crop growth and productivity over the globe while heat stress at early filling stage is of serious concern for the early-season rice in double cropping rice system of South China. In present study we assessed different short-term water management strategies to cope with the high temperature at early filling stage in rice. Water was applied as flood irrigation at two various depths i.e., 4–5 cm (I1) and 5–10 cm (I2) during 9:00–18:00 and then drained off at 18:00 as well as applied over-head during different time spans i.e., over-head sprinkle irrigation during 11:00–12:00, 13:00–14:00 and 14:00–15:00 at 60–80% relative humidity (RH) at early filling stage and regarded as S1, S2 and S3, respectively. A control was maintained with the maintenance of 1 cm water layer as normal farmer practice of this region. A fragrant rice cultivar, ‘Yuxiangyouzhan’ in early March (regarded as early season rice) in both 2014–15 and the effectiveness of different water management strategies were measured by estimating physio-biochemical responses, photosynthesis, yield and quality of rice exposed to high temperature stress at early filling stage. Our results showed that water treatments lowered lipid peroxidation (in terms of reduced malondialdehyde (MDA) contents) whilst proline and protein contents were affected differently. The water treatments also regulated the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), nevertheless, improved plant photosynthesis and gas exchange, rice yield and quality attributes considerably by lowering severity of canopy temperatures than control (CK). On average, both flood and sprinkler water application were proved effective against high temperature stress, nonetheless, flood irrigated treatments were remained more effective than sprinkler which provided 26.58 and 43.63% higher grain yields in 2014–15, respectively than CK. On average, 5.58 and 11.92% higher grain yields were recorded in flood irrigation than sprinkler irrigation whereas among individual water application treatments, I1 was noted as the most effective regarding grain yield of rice (26.76 and 49.35% higher yield than CK) in both years which suggests that maintenance of 4–5 cm water layer might be helpful for the rice to withstand against high temperature stress at post heading and/or early filling stage in early-season rice production in South China. 相似文献
6.
Echinochloa colona (L.) Link. is one of the most problematic weeds across the world. It is an annual C4 summer grass, native to tropical and subtropical Asia, emerged as a serious and persistent threat in 35 cropping systems in more than 60 countries. E. colona is reported as an important associated weed species in transplanted and direct-seeded rice. Diverse ecotypes, high seed production, short seed dormancy, rapid growth, competitive potential, allelopathic interaction, and resistance against several herbicides makes it a more adaptable and persistent challenge in various agro-ecosystems. Development of resistance to recommended or higher doses of numerous herbicides, including ametryn, atrazine, bispyribac-sodium, clefoxidym, cyhalofop-butyl, fenoxaprop-p-ethyl, glyphosate, metribuzin, propanil, and triazine, is a serious concern for the farming and scientific community. Crop infestation with resistant E. colona biotypes may ultimately increase the weed control cost. Unfortunately, investigations on seed dormancy release, genetic diversity, allelopathic interference, and competitive ability of this weed are inadequate in accomplishing its appropriate control in different environments. Therefore, a comprehensive review is presented here to gather the existing information, to pin point key findings, and to highlight the research gaps in the biology, interference, and management of E. colona. Different management options have been discussed in relation with eco-biology of this noxious weed. The potential research endeavours have also been highlighted in order to provide an insight of its existing scenario and to facilitate the future management strategies. 相似文献
7.
《Field Crops Research》2006,98(1):12-19
It is reported that stimulating effect of elevated atmospheric [CO2] on photosynthesis of rice (Oryza sativa L.) is likely to be reduced during the plant growth period. However, there is little information on seasonal changes in dry matter (DM) production and distribution of rice under elevated atmospheric [CO2]. A free-air CO2 enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003, using Wuxiangging 14, a japonica cultivar. The rice was grown at ambient or elevated (ca. 200 μmol mol−1 above ambient) [CO2] and supplied with 25 g N m2, which is the normal N application rate for local farmers. DM accumulation of rice in FACE plots was significantly increased by 40, 30, 22, 26 and 16% on average at tillering, panicle initiation (PI), heading, mid-ripening and grain maturity, respectively. Rice DM production under FACE was significantly enhanced by 41, 27, 15 and 38% on average during the growth periods from transplanting to tillering (Period 1), tillering to PI (Period 2), PI to heading (Period 3) and heading to mid-ripening (Period 4), respectively, but significantly decreased by 25% in the period from mid-ripening to grain maturity (Period 5). In general, seasonal changes in crop response to FACE in both green leaf area index (GLAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production. Under FACE the leaves decreased significantly in proportion to the total above-ground DM over the season, the stems showed an opposite trend, while the spikes depended on crop development stage: showing no change at heading, significant increase (+4%) at mid-ripening and significant decrease (−3%) at grain maturity. Grain yield was stimulated by an average of 13% by FACE, due to increased total DM production rather than any changes in partitioning to the grain. We conclude that the gradual acclimation of rice growth to elevated [CO2] do not occur inevitably, and it could also be altered by environmental conditions (e.g., cultivation technique). 相似文献
8.
《Journal of Cereal Science》2010,51(3):370-375
In rice grains, high amylose content (AC) is correlated with poor grain quality, particularly in indica hybrid rice. To obtain indica hybrid rice with improved cooking and eating qualities, we introduced the antisense Waxy (Wx) gene into 2 elite parental lines of indica hybrid rice by using co-transformation methods. Subsequently, we selected several elite homozygous transgenic lines that did not contain the selectable marker. The expression of the endogenous Wx gene of the selected transgenic lines was significantly downregulated, resulting in low AC in the mature seeds; moreover, the AC in some lines reduced to the level observed in glutinous rice. With the decrease in AC, the gel consistency of the transgenic rice became softer, and the gelatinization temperature tended to be higher than those of the wild types, especially in the case of the Longtefu-derived transformants. We also analyzed the pasting properties of the selected transgenic low-AC lines, and we noted an improvement in the pasting properties of the transgenic rice lines. The results from a field trial indicated that the grain weights of the transgenic lines with lower AC exhibit remarkable reduction compared with those of the wild types. 相似文献
9.
【目的】得到含刚性沉水植物明渠的水流结构。【方法】采用粒子图像测速仪(PIV),用有机玻璃棒模拟刚性植物,在不同来水流量、植物密度条件下对明渠水流结构进行了试验研究。【结果】无植物时平均流速沿垂向呈对数分布规律,有植物时则呈现明显的分区分布特性。无植物时紊动强度值沿垂向变化不大,有植物时在植物顶端位置处紊动最剧烈。流量或植物密度越大,植物顶端位置的流速梯度就越大,植物层上方的流速最大值也越大。植物密度越大,植物顶端位置的紊动强度越大,植物密度对水流紊动强度由最大值减小到最小值的区域影响很大。【结论】刚性沉水植物的存在会改变水流结构,增强紊动掺混,增强流体质点交换和能量传递,且上述影响会随着流量或植物密度的增大而增强。 相似文献
10.
以父母代肉种鸡为材料,以血浆极低密度脂蛋白（very low density lipoprotein,VLDL）质量浓度为选择指标建立肉鸡高脂系和低脂系,个体测定一世代高、低脂系母鸡产蛋性能、种蛋受精率、孵化率、二世代6周龄体质量,观察血浆VLDL质量浓度选择效应。结果显示,一世代低脂系比高脂系早开产6．7d,低脂系40周龄和54周龄产蛋量显著高于高脂系零世代,一世代低脂系种蛋受精率、受精蛋孵化率、入孵蛋孵化率均优于高脂系;二世代高、低脂系6周龄体质量差异不显著。结果表明,对血浆VLDL质量浓度的低向选择使种鸡产蛋性能、种蛋受精率、孵化率产生了有益的间接反应,但对早期体质量没有影响。 相似文献