首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   11304篇
  免费   725篇
  国内免费   882篇
林业   758篇
农学   851篇
基础科学   326篇
  1696篇
综合类   3470篇
农作物   1696篇
水产渔业   284篇
畜牧兽医   2231篇
园艺   1120篇
植物保护   479篇
  2024年   59篇
  2023年   237篇
  2022年   396篇
  2021年   461篇
  2020年   428篇
  2019年   571篇
  2018年   529篇
  2017年   438篇
  2016年   675篇
  2015年   918篇
  2014年   1016篇
  2013年   1013篇
  2012年   992篇
  2011年   708篇
  2010年   570篇
  2009年   573篇
  2008年   467篇
  2007年   496篇
  2006年   561篇
  2005年   426篇
  2004年   215篇
  2003年   156篇
  2002年   129篇
  2001年   111篇
  2000年   139篇
  1999年   71篇
  1998年   82篇
  1997年   43篇
  1996年   44篇
  1995年   74篇
  1994年   41篇
  1993年   34篇
  1992年   26篇
  1991年   22篇
  1990年   31篇
  1989年   20篇
  1988年   15篇
  1987年   13篇
  1986年   7篇
  1985年   27篇
  1984年   17篇
  1983年   9篇
  1982年   6篇
  1981年   18篇
  1980年   11篇
  1979年   4篇
  1978年   3篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
近几年来兴宁市积极推广优质稻的生产,种植面积逐年增加。结合兴宁市优质稻栽培实践,总结了目前的示范推广情况,最后提出了配套的技术要点。  相似文献   
42.
连狮1 号是以连云港地区菜农提供的中狮头自留种为原始种,经4 代自交提纯选育成的大白菜新品种。株型紧凑, 整齐度较好,叶球为长筒翻心形,叶片呈长倒卵形,叶表面具有较深核桃纹并带稀疏茸毛。株高35 cm,外叶数约10 片, 叶球高28~32 cm、横径22~27 cm,单个叶球质量3.5~4.0 kg,每667 m2 叶球产量4 700 kg 左右,净菜率达83%。生育期 为90~95 d(天),田间抗病毒病、霜霉病、根肿病能力优于对照中狮头,适合在江苏、安徽、山东等地及其相近气候条件 地区秋季种植。  相似文献   
43.
The effects of the severity and timing of leaf removal(LR) on the amino acids of Sauvignon Blanc grapes and wines were studied during the 2017 growing season. High-performance liquid chromatography(HPLC) was used to analyze the amino acids profiles of grape berries and wines. The basal leaves were removed at three time points(40, 56 and 72 days after flowering, named LR40, LR56 and LR72, respectively) at two severity levels(one at which the first, third, and fifth basal leaves of each shoot were removed(50% level); and another at which the first six basal leaves were removed(100% level)). The results showed that leaf removal had little impact on total soluble solids(°Brix), titratable acidity, pH or berry weight. The LR72-50% treated grapes had higher berry weight, titratable acidity and °Brix than those of the other treatments. The highest concentrations of total amino acids and of total amino acids except proline were detected in LR72-50% treated grapes(2 952.58 and 2 764.36 mg L~(-1), respectively); the lowest were detected in LR72-100% treated grapes(2 172.82 and 2 038.71 mg L~(-1), respectively). LR72-50% treatment significantly promoted the synthesis of aspartic acid, serine, arginine, alanine, aminobutyric acid and proline at both severity levels for grapes, the concentrations of all of these amino acids were increased relative to the control concentrations. The LR72-50%, LR40-100% and LR72-100% treated wines had higher total amino acids concentrations and higher concentrations of some individual amino acids, such as arginine, alanine and serine, than did the control wines. Of all the amino acids studied, glycine, tyrosine, cysteine, methionine and lysine were not significantly influenced by the timing or severity basal defoliation in grapes and wines. The present study reveals the effects of the timing and severity of leaf removal on the amino acids profiles of grapes and wines.  相似文献   
44.
以陕西榆林山地矮化密植梨枣树为研究对象,分析了不同水肥浓度对涌泉根灌枣树生育期内叶面积指数、果实发育和产量的影响。结果表明,不同水肥处理叶面积指数在枣树果实膨大期达到高峰,且稳定持续至果实成熟期末期,随后叶面积指数开始下降。叶面积指数随着萌芽展叶期灌水量的增加而增加,所有水肥处理下,枣数叶面积指数最大的是高水中肥处理(W1N2);所有处理中,高水、低水处理与低肥相组合,果实体积最大,中灌水处理为不施肥时果实的体积最大。单位枝长的果实数目最高的是中水中肥处理(W2N2),最低的是低水处理(W3),在一定范围内,适当施肥能促进枣果单位枝长的果实数目的增加,但肥液浓度过大,反而会抑制其增加。在一定条件下,所有处理中产量最高的是中水中肥处理(W2N2),产量超过2000kg/亩,最低的是低水高肥处理(W3N1),产量不到1000kg/亩。因此可以选择中水中肥处理(W2N2),能获得最高的产量。  相似文献   
45.
AIM:To investigate the inhibitory effect of thioredoxin 1 (Trx-1) over-expression on oxidative stress injury in 1-methyl-4-phenylpyridinium (MPP+)-induced rat pheochromocytoma PC12 cells by regulating NF-κB signaling pathway.METHODS:The PC12 cells were damaged by treatment with MPP+ at 1, 3 and 5 mmol/L, and the optimal concentration of 3 mmol/L was selected. The cell viability was measured by MTT assay. The oxidative stress indexes lactate dehydrogenase (LDH) activity, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in the cell culture supernatant were detected, and the protein expression of Trx-1 was determined by Western blot. Lentiviral infection with Ad-Trx-1-GFP sequence was used to establish a model of MPP+-treated PC12 cells with Trx-1 over-expression. The effects of Trx-1 over-expression on the cell viability, oxidative stress responses and NF-κB signaling pathway were determined by MTT assay, commercial kits and Western blot. The effects of phorbol 12-myristate 13-acetate (PMA), an activator of NF-κB signaling pathway, on the viability and oxidative stress of PC12 cells were observed. The NF-κB signaling pathway inhibitor pyrrolidine dithiocarbamate (PDTC) was used in MPP+-treated PC12 cells with Trx-1 over-expression, and the cell viability and oxidative stress responses were measured. RESULTS:The viability of PC12 cells, SOD activity in the supernatant and protein expression of Trx-1 were decreased, while LDH activity and MDA content in the supernatant were increased significantly by treatment with MPP+ at 1, 3 and 5 mmol/L. The effect of MPP+ at 3 mmol/L and 5 mmol/L was significantly greater than that at 1 mmol/L (P<0.05), and no significant difference between 3 mmol/L and 5 mmol/L was observed (P>0.05). The inhibitory effect of MPP+ on the viability of PC12 cells, and the oxidative stress injury and activation of NF-κB signaling pathway induced by MPP+ were significantly attenuated by over-expression of Trx-1. The inhibitory effect of MPP+ on the viability of PC12 cells and the oxidative stress injury induced by MPP+ were promoted by the activation of NF-κB signaling pathway, while the protective effects of Trx-1 over-expression on the MPP+-treated PC12 cells were enhanced by the inhibition of NF-κB signaling pathway. CONCLUSION:Over-expression of Trx-1 protects MPP+-treated PC12 cells from oxidative stress injury by regulating NF-κB signaling pathway.  相似文献   
46.
湘紫薯174 是以浙紫薯1 号为母本、浙紫薯3 号为父本杂交选育而成的食用型紫心甘薯新品种,薯块纺锤形,薯皮 紫红色,薯肉紫色,结薯较集中整齐,单株结薯4~5 个,大中薯率82.7% 以上,熟食味好,抗黑斑病,中抗根腐病、茎线 虫病和薯瘟病;每667 m2 鲜薯产量1 913~2 359 kg,薯干产量549~736 kg;花青素含量为714.5 mg · kg-1(FW)。适宜在湖 南、湖北、江西、江苏、浙江等地春夏薯区种植。  相似文献   
47.
通过大田试验研究了400克/升氯氟醚菌唑悬浮剂防治香蕉叶斑病效果及其对香蕉产量的影响。研究结果表明,分别以20毫升、13.3毫升、10毫升400克/升氯氟醚菌唑悬浮剂兑水60公斤分3次喷雾施药,第二次施药后14d后对香蕉叶斑病防治效果在60.43-66.52%,第三次施药后14d后对香蕉叶斑病防治效果在75.72-80.72%,并对香蕉的单株产量有明显增产效果。其中尤以20毫升400克/升氯氟醚菌唑悬浮剂兑水60公斤剂量喷雾处理的效果最好。  相似文献   
48.
LI Xuemei 《干旱区科学》2020,12(3):374-396
Short-term climate reconstruction, i.e., the reproduction of short-term(several decades) historical climatic time series based on the relationship between observed data and available longer-term reference data in a certain area, can extend the length of climatic time series and offset the shortage of observations. This can be used to assess regional climate change over a much longer time scale. Based on monthly grid climate data from a Coupled Model Inter-comparison Project phase 5(CMIP5) dataset for the period of 1850–2000, the Climatic Research Unit(CRU) dataset for the period of 1901–2000 and the observed data from 53 meteorological stations located in the Tianshan Mountains region(TMR) of China during the period of 1961–2011, we calibrated and validated monthly average temperature(MAT) and monthly accumulated precipitation(MAP) in the TMR using the delta, physical scaling(SP) and artificial neural network(ANN) methods. Performance and uncertainty during the calibration(1971–1999) and verification(1961–1970) periods were assessed and compared using traditional performance indices and a revised set pair analysis(RSPA) method. The calibration and verification processes were subjected to various sources of uncertainty due to the influence of different reconstructed variables, different data sources, and/or different methods used. According to traditional performance indices, both the CRU and CMIP5 datasets resulted in satisfactory calibrated and verified MAT time series at 53 meteorological stations and MAP time series at 20 meteorological stations using the delta and SP methods for the period of 1961–1999. However, the results differed from those obtained by the RSPA method. This showed that the CRU dataset produced a low degree of uncertainty(positive connection degree) during the calibration and verification of MAT using the delta and SP methods compared to the CMIP5 dataset. Overall, the calibrated and verified MAP had a high degree of uncertainty(negative connection degree) regardless of the dataset or reconstruction method used. Therefore, the reconstructed time series of MAT for the period of 1850(or 1901)–1960 based on the CRU and CMIP5 datasets using the delta and SP methods could be used for further study. The results of this study will be useful for short-term(several decades) regional climate reconstruction and longer-term(100 a or more) assessments of regional climate change.  相似文献   
49.
襄垣县是山西省有机旱作试点县,根据其自然条件,通过总结该县有机旱作发展现状、制约因素及潜力分析,提出适宜的对策措施,为今后有机旱农业的发展提供一定的参考。  相似文献   
50.
西府海棠锈病是危害西府海棠的最重要病害,造成叶片枯黄、早落,影响次年的开花与结果。本研究,分析了近年来病害严重发生的环境影响因素,并提出防治技术方案。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号