全文获取类型
收费全文 | 4944篇 |
免费 | 192篇 |
国内免费 | 3篇 |
专业分类
林业 | 247篇 |
农学 | 203篇 |
基础科学 | 36篇 |
787篇 | |
综合类 | 1271篇 |
农作物 | 233篇 |
水产渔业 | 315篇 |
畜牧兽医 | 1539篇 |
园艺 | 110篇 |
植物保护 | 398篇 |
出版年
2023年 | 22篇 |
2022年 | 26篇 |
2021年 | 64篇 |
2020年 | 74篇 |
2019年 | 94篇 |
2018年 | 92篇 |
2017年 | 84篇 |
2016年 | 93篇 |
2015年 | 68篇 |
2014年 | 89篇 |
2013年 | 186篇 |
2012年 | 263篇 |
2011年 | 349篇 |
2010年 | 191篇 |
2009年 | 151篇 |
2008年 | 336篇 |
2007年 | 340篇 |
2006年 | 383篇 |
2005年 | 330篇 |
2004年 | 333篇 |
2003年 | 309篇 |
2002年 | 302篇 |
2001年 | 60篇 |
2000年 | 35篇 |
1999年 | 49篇 |
1998年 | 51篇 |
1997年 | 30篇 |
1996年 | 36篇 |
1995年 | 36篇 |
1994年 | 30篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 37篇 |
1988年 | 27篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 27篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 23篇 |
1979年 | 15篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1975年 | 16篇 |
1974年 | 24篇 |
排序方式: 共有5139条查询结果,搜索用时 0 毫秒
951.
N. Richard Knowles W. M. Iritani L. D. Weller 《American Journal of Potato Research》1985,62(6):289-300
Plant growth from Russet Burbank seed-tubers of different ages was compared as affected by source of meristematic tissue (apical or basal) and NAA treatment. In controlled environment studies, single-eye seedcores from 17-mo-old seed-tubers produced twice as many shoots compared to those from 5-and 29-mo-old seed-tubers. Seed-tuber age and shoot dry weight/core were inversely related. Dry weight/shoot decreased as age increased to 17 mo and then remained unchanged from 17 to 29 mo. Apical meristems lost growth potential faster than basal meristems as age advanced. Meristem physiological age apparently depends on relative position of the buds as well as on the chronological age of the seed-tuber. NAA (10–40 mg/l) decreased the number of shoots/core, had no effect on shoot dry weight/core but increased the dry weight/shoot when applied to seedcores from 20-mo-old seed-tubers. On seedcores from 8-mo-old seed-tubers. NAA decreased the shoot dry weight (g/core, g/shoot). In field studies, NAA (100 mg/l) increased the total tuber yield of plants grown from seedpieces cut from 8-and 20-mo-old seed-tubers. These increases were manifested in age-specific effects on tuber grade. The effects of seedtuber age on plant growth and tuber yield were partially overcome by seedpiece treatment with NAA. 相似文献
952.
The pharmacological variety of conotoxins, diverse peptides found in the venoms of marine cone snails, is well recognized. Venoms from each of the estimated 500 species of cone snails contain 50 to 200 distinct biologically active peptides. Most conotoxins characterized to date target receptors and ion channels of excitable tissues, such as ligand-gated nicotinic acetylcholine, N-methyl-D-aspartate, and type 3 serotonin receptors, as well as voltage-gated calcium, sodium, and potassium channels, and G-protein-coupled receptors including α-adrenergic, neurotensin, and vasopressin receptors, and the norepinephrine transporter. Several conotoxins have shown promise in preclinical models of pain, convulsive disorders, stroke, neuromuscular block, and cardioprotection. The pharmacological selectivity of the conotoxins, coupled with the safety and efficacy demonstrated in preclinical models, has led to their investigation as human therapeutic agents. In the following review, we will survey the pharmacology and therapeutic rationale of those conotoxins with potential clinical application, and discuss the unique challenges that each will face in the course of their transition from venom component to human therapeutic. 相似文献
953.
Dale R. Mutch Donald Penner Frank Roggenbuck Richard W. Chase 《American Journal of Potato Research》1984,61(9):577-586
Chemical vine desiccation is an important management practice for late season potatoes (Solanum tuberosum L.) in Michigan. A number of desiccants are registered; however, most Michigan growers apply dinoseb (2-sec- butyl-4,6-dinitrophenol). Greenhouse experiments were initiated to evaluate the potential of ammonium salts and ethephon (2-chloroethyl)phosphonic acid) to increase the efficacy of the chemical harvest aids dinoseb and endothall (7-oxabicyclo[2,2,1]heptane-2,3-dicarboxylic acid) on potato vines. Temperature and potato vine position were evaluated to determine their influence on vine desiccation. All treatments with endothall applied at 0.6 kg/ha resulted in unsatisfactory potato vine desiccation. Ethephon and ammonium sulfate increased efficacy of dinoseb. High temperature both before and after treatment contributed to greater dinoseb efficacy. The horizontal placing of potato vines resulted in the desired desiccation rating of 9.0 or greater using the combination of dinoseb at 2.8 kg/ha, plus ammonium sulfate at 9 kg/ha plus 2.4 L/ha X-77 surfactant.3 相似文献
954.
Four potato varieties were subjected to water stress under controlled conditions. Leaf relative water content, leaf diffusive resistance, and photosynthesis were measured on stressed and unstressed plants during a stress period and during the recovery period following stress relief. Subsequent to the stress, plants were grown to maturity with optimal water supply. Mature plants were harvested and tuber yield and haulm production measured. Stressed plants of all varieties exhibited an increase in leaf diffusive resistance and a decrease in relative water content, transpiration, and photosynthesis as soil moisture decreased. Significant varietal differences in leaf diffusive resistance of stressed plants are apparent and offer promise for development of a screening technique for varietal sensitivity to drought based on stomatal response to water deficits. 相似文献
955.
Summary Trials were carried out in 1984, 1985 and 1986, on a sandy loam soil with an average content of 133 mg/l available potassium
in which the effect of source (KCl, K2SO4) and rate (0, 300, 600, 900 kg K2O/ha) of potassium fertilizer on yield, tuber size, dry matter, reducing sugar, fry test colour and finish fried quality was
examined for two cultivars (Pentland Dell, Maris Piper).
The results indicate a strong influence of cultivar on all measured characters, the rate of potassium fertilizer also gave
significant changes in quality and yield and there were significant year effects. The effect of source of potassium was not
significant. 相似文献
956.
957.
Richard N. Arteca B. W. Poovaiah L. K. Hiller 《American Journal of Potato Research》1980,57(6):241-247
Electron microprobe and neutron activation analysis were used to evaluate the distribution of elements within potato tubers having the physiological disorder hollow heart. Both methods of analysis correlated well for all elements tested. In hollow heart tubers, there were significantly higher Ca++ levels in the stem end than in the bud end; however, a Ca++ gradient in the control was not evident. The stem to bud end ratios for Ca++ were highest in the hollow heart tubers. A Cl? gradient from stem to bud end was obvious in both the hollow heart and control tubers. In the control tubers, K+ was highest in the bud end and lowest in the stem end. There was no K+ gradient in hollow heart tubers, but in the area adjacent to the hollow it was higher than at both ends. 相似文献
958.
959.
960.