全文获取类型
收费全文 | 9276篇 |
免费 | 418篇 |
国内免费 | 14篇 |
专业分类
林业 | 588篇 |
农学 | 229篇 |
基础科学 | 84篇 |
1591篇 | |
综合类 | 1610篇 |
农作物 | 365篇 |
水产渔业 | 822篇 |
畜牧兽医 | 3372篇 |
园艺 | 278篇 |
植物保护 | 769篇 |
出版年
2024年 | 19篇 |
2023年 | 59篇 |
2022年 | 90篇 |
2021年 | 155篇 |
2020年 | 211篇 |
2019年 | 208篇 |
2018年 | 206篇 |
2017年 | 218篇 |
2016年 | 210篇 |
2015年 | 185篇 |
2014年 | 254篇 |
2013年 | 449篇 |
2012年 | 542篇 |
2011年 | 708篇 |
2010年 | 368篇 |
2009年 | 353篇 |
2008年 | 636篇 |
2007年 | 623篇 |
2006年 | 592篇 |
2005年 | 574篇 |
2004年 | 608篇 |
2003年 | 571篇 |
2002年 | 504篇 |
2001年 | 98篇 |
2000年 | 90篇 |
1999年 | 93篇 |
1998年 | 81篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 62篇 |
1994年 | 61篇 |
1993年 | 50篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 58篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 40篇 |
1982年 | 26篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 15篇 |
排序方式: 共有9708条查询结果,搜索用时 0 毫秒
111.
112.
ABSTRACT The fungal plant pathogen Microsphaeropsis amaranthi is a candidate bioherbicide for the control of weedy Amaranthus species since it grows and sporulates readily in culture, is a pathogen of a number of important weed species, and is host-restricted to the family Amaranthaceae. This study was designed to determine the optimum and limiting environmental conditions for the efficacy of foliar applications of M. amaranthi for the control of common waterhemp. The greatest disease severity and the greatest plant biomass reductions were found when a prolonged leaf wetness period of >/= 12 h at 18 to 24 degrees C was provided after application. Disease severity and plant biomass reductions were greater when plants were treated at an earlier stage of development. Disease severity and impact were limited when shorter leaf wetness periods were provided, with negligible disease observed on plants provided with =6 h leaf wetness. When common waterhemp seedlings were sprayed in the field weekly through the summer of 2004 with conidial suspensions of M. amaranthi, only 7 of 14 applications resulted in disease and only 3 applications resulted in more than slight disease flecks. Moderate levels of disease were observed when applications had been made on days with moderate temperatures and leaf wetness duration in excess of 12 h following application. We confirm the pathogenicity of M. amaranthi against common waterhemp and demonstrate that the unformulated pathogen can cause disease in the field. Nonetheless, the weather conditions of the Midwestern United States, where common waterhemp control would be desired, are infrequently conducive to infection. The continued candidacy of M. amaranthi as a bioherbicide for the control of common waterhemp in the Midwest-ern United States will require that its efficacy under suboptimal environmental conditions be improved. 相似文献
113.
Shoji Sonoda Xueyan ShiDunlun Song Youjun ZhangJianhong Li Gang WuYong Liu Ming LiPei Liang David WariMasaya Matsumura Chieka MinakuchiToshiharu Tanaka Tadashi MiyataXiwu Gao 《Pesticide biochemistry and physiology》2012,102(2):142-145
In addition to the allele frequencies of the L1014F and T929I mutations which are involved in nerve-insensitive resistance to a pyrethroid, those of the M918I mutation were examined using field strains obtained in China, Thailand, and Japan during 2009-2011. Results show that the resistance allele frequencies at the L1014F site were 89-100%, 97-100% and 65-85%, respectively, for strains in China, Thailand, and Japan. The respective allele frequencies at the T929I site were 86-100%, 70-97% and 58-84% for Chinese, Thai, and Japanese strains. With low frequencies up to 27%, M918I was found in Japan and China, but not in Thailand. The strain homozygous for the M918I and L1014F mutations was established and its resistance level to a pyrethroid was examined. The strain lacks a portion of the sodium channel gene corresponding to the 3′ portion of exon 18a, intron 18, and the 5′ portion of exon 18b. Nevertheless, the strain showed a similar level of resistance to that which was homozygous for the T929I and L1014F mutations. 相似文献
114.
115.
116.
117.
Waseem Akbar Anilkumar Gowda Jeffrey E Ahrens Jason W Stelzer Robert S Brown Scott L Bollman John T Greenplate Jeffrey Gore Angus L Catchot Gus Lorenz Scott D Stewart David L Kerns Jeremy K Greene Michael D Toews David A Herbert Dominic D Reisig Gregory A Sword Peter C Ellsworth Larry D Godfrey Thomas L Clark 《Pest management science》2019,75(3):867-877
118.
Derek Herbert Kevin A. Walker Lindsey J. Price David J. Cole Kenneth E. Pallett Stuart M. Ridley John L. Harwood 《Pest management science》1997,50(1):67-71
Acetyl-CoA carboxylase catalyses the first committed step in fatty acid (and acyl lipid) formation. The enzyme has been shown to exert a high degree of flux control for lipid biosynthesis in leaves and, therefore, it is not surprising that chemicals which can inhibit it effectively are successful herbicides. These chemicals belong mainly to the cyclohexanedione and aryloxyphenoxypropionate classes and are graminicides. The reason for the selectivity of these herbicides towards grasses lies in the nature of the target site, acetyl-CoA carboxylase. Recent advances in our knowledge of acetyl-CoA carboxylases from sensitive and resistant plants has revealed some important facts. Dicotyledons, which are resistant, have a multi-enzyme complex type of carboxylase in their chloroplasts while grasses have a multifunctional protein. Both divisions of plants have two isoforms of the enzyme, the second being in the cytosol. Detailed study of multifunctional forms of acetyl-CoA carboxylases, which have different sensitivities to herbicides, suggests that herbicide resistance is correlated with cooperativity of herbicide binding to the native dimeric form of the carboxylase. © 1997 SCI. 相似文献
119.
The effects of adjuvants on the performance of a dispersible concentrate formulation (DCI) of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine (I) were investigated. The method involved assessment, under glasshouse conditions, of the therapeutic (curative) control of infections of powdery mildew (Erysiphe graminis DC f.sp. hordei Marchal) on barley (Hordeum vulgare, L.) eight to nine days after spray application to plants that had been inoculated one day prior to spraying. The results from the first trial showed that marked improvements (∽five-fold) in the performance of DCI could be obtained by the spray tank addition of some types of surfactant adjuvants and a series of further trials investigating a wide range of adjuvants was conducted. Nonylphenol, alkylamine and alcohol ethoxylates varying in mean ethylene oxide content between 5 and 20 moles were highly effective. There were indications that optimum performance enhancements were obtained with these surfactants containing between 5 and 10 moles ethylene oxide. Lower enhancements, sometimes only marginal, were obtained from trisiloxane, phosphate ester, propylene oxide, alkylamine-propylene oxide and castor oil ethoxylates and also alkyl polyglucoside biosurfactants. Negligible adjuvant enhancements were observed with emulsifiable paraffinic/naphthenic and rape seed oils, though slightly better enhancements were seen with an emulsifiable transmethylated rape seed oil and, interestingly, larger enhancements with an emulsifiable lipophilic alcohol. A final trial identified the alcohol ethoxylate, ‘Dobanol’ 91-6, as the most effective adjuvant and that its optimum application rate under glasshouse conditions was 250 g ha-1. This information will be used to guide the design of field trials. © 1997 SCI 相似文献
120.
David J Schuster Rajinder S Mann Marco Toapanta Roberto Cordero Sandra Thompson Sabrina Cyman Aaron Shurtleff Roy F Morris II 《Pest management science》2010,66(2):186-195
BACKGROUND: Biotype B of the sweetpotato whitefly, Bemisia tabaci (Genn.), is a worldwide pest that has developed resistance to many insecticides, including the neonicotinoid class. Florida field populations were monitored for susceptibility to the neonicotinoids imidacloprid and thiamethoxam using a cut leaf petiole bioassay method. RESULTS: Average RR50 values for imidacloprid increased from 3.7 in 2000 to 12.0 in 2003; decreased to 5.0 and 2.5 in 2004 and 2005, respectively; and then increased to 26.3 and 23.9 in 2006 and 2007, respectively. Populations with RR50 values of about 50 to 60 during generation one reverted to RR50 values of ?4 in six generations, when reared without further exposure to imidacloprid. Average RR50 values for thiamethoxam increased from 2.0 in 2003 to 24.7 in 2006 and decreased to 10.4 in 2007. Populations with RR50 values of about 22, 32 and 53 during generation one declined to 8, 5 and 6, respectively, after being reared for five generations without exposure to thiamethoxam. The correlation coefficient from the 26 populations that were bioassayed both with imidacloprid and thiamethoxam showed a significant positive correlation (R2 = 0.58) between these populations. CONCLUSION: The high level of RR50 values to imidacloprid and thiamethoxam suggest an unstable decline in the susceptibility of B. tabaci to imidacloprid and thiamethoxam, with possible cross‐resistance or predisposition for dual resistance selection. Copyright © 2009 Society of Chemical Industry 相似文献