全文获取类型
收费全文 | 99583篇 |
免费 | 5194篇 |
国内免费 | 770篇 |
专业分类
林业 | 6775篇 |
农学 | 3791篇 |
基础科学 | 805篇 |
12824篇 | |
综合类 | 17133篇 |
农作物 | 5149篇 |
水产渔业 | 5701篇 |
畜牧兽医 | 44333篇 |
园艺 | 2148篇 |
植物保护 | 6888篇 |
出版年
2021年 | 810篇 |
2020年 | 878篇 |
2019年 | 1074篇 |
2018年 | 4007篇 |
2017年 | 4192篇 |
2016年 | 2589篇 |
2015年 | 1453篇 |
2014年 | 1617篇 |
2013年 | 3060篇 |
2012年 | 3784篇 |
2011年 | 5611篇 |
2010年 | 4336篇 |
2009年 | 3395篇 |
2008年 | 4418篇 |
2007年 | 4537篇 |
2006年 | 2764篇 |
2005年 | 2740篇 |
2004年 | 2450篇 |
2003年 | 2552篇 |
2002年 | 2325篇 |
2001年 | 2521篇 |
2000年 | 2588篇 |
1999年 | 1963篇 |
1998年 | 798篇 |
1997年 | 710篇 |
1995年 | 744篇 |
1993年 | 679篇 |
1992年 | 1543篇 |
1991年 | 1725篇 |
1990年 | 1653篇 |
1989年 | 1605篇 |
1988年 | 1491篇 |
1987年 | 1538篇 |
1986年 | 1591篇 |
1985年 | 1409篇 |
1984年 | 1196篇 |
1983年 | 1024篇 |
1982年 | 687篇 |
1979年 | 1063篇 |
1978年 | 833篇 |
1977年 | 687篇 |
1976年 | 714篇 |
1975年 | 754篇 |
1974年 | 1009篇 |
1973年 | 995篇 |
1972年 | 956篇 |
1971年 | 888篇 |
1970年 | 859篇 |
1969年 | 807篇 |
1967年 | 703篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Blood pressure response to phenylephrine infusion in halothane-anesthetized dogs given acetylpromazine maleate 总被引:2,自引:0,他引:2
J W Ludders J A Reitan R Martucci D L Fung E P Steffey 《American journal of veterinary research》1983,44(6):996-999
To quantitate acetylpromazine-induced alpha-adrenergic receptor blockade, phenylephrine was infused into dogs. The amount of phenylephrine necessary to increase the mean arterial blood pressure (MAP) 50% above base line, with or without the prior administration of acetylpromazine, served to quantify the degree of acetylpromazine-induced alpha-adrenergic receptor blockade. Seven dogs were anesthetized with thiopental, maintained on halothane in oxygen, and mechanically ventilated. All infusions were made through a catheter in the cephalic vein. Continuous recordings were made of MAP and a lead II ECG. After induction of anesthesia, instrumentation, and stabilization of heart rate, MAP, and ventilation, 6 group I dogs were infused with phenylephrine until a 50% increase in MAP was recorded (phenylephrine control). On subsequent research days, each dog was anesthetized, instrumented as described, and given (IV) 1 of 3 dosages of acetylpromazine in the following order--0.05, 0.125, and 0.25 mg/kg. The dose of phenylephrine necessary to increase MAP 50% in the presence of acetylpromazine was recorded. Five group II dogs were studied as in group I, but each dog was given (IM) atropine (0.04 mg/kg) before anesthetization. Two dosages of acetylpromazine were studied in the following order--0.05 and 0.25 mg/kg. Group I dogs, when compared with their phenylephrine controls, were given significantly more phenylephrine to raise MAP 50% at each dose of acetylpromazine studied. The same trend was observed in group II dogs, but at smaller doses of phenylephrine, probably as a result of the positive chronotropic effect of atropine on the heart. 相似文献
993.
L.H. Wang X.H. Gu M.Y. Hua S.L. Mao Z.H. Zhang D.L. Peng X.F. Yun B.X. Zhang 《Scientia Horticulturae》2009
The root-knot nematodes (Meloidogyne spp.) are important nematode pests and cause serious diseases in pepper in the world. No molecular markers linked to the nematodes resistance N gene have been reported. In this paper, ‘Carolina Wonder’ (Capsicum annuum L.), a sweet pepper line resistant to root-knot nematode with N gene, ‘20080-5-29’ (C. annuum L.), an inbred line susceptible to root-knot nematode with good horticultural characteristics, and their F2 progeny with 320 individuals were used as materials. Evaluation of resistance and susceptibility of parental lines, F1 and F2 progeny inoculated with root-knot nematodes (Meloidogyne incognita) were carried out. ‘Bulked segregant analysis’ method was used to search for polymorphic markers from 512 pairs of AFLP primers. Based on the assessment of resistance and susceptibility and polymorphism of the AFLP marker in F2 population, the genetic linkage distance between the AFLP marker and the N gene was estimated. One AFLP marker E39/M41-339 was obtained and transferred to a SCAR marker amplifying a 315 bp DNA fragment linked to the N resistant allele and a 331 bp fragment linked to the N+ susceptible allele. The distance between the molecular marker and the nematodes resistance N gene is 6.3 cM. This research delivered a valuable tool for the marker assisted selection of nematodes resistance in pepper. 相似文献
994.
Thomas B. Moorman Jennifer K. Cowan Ellen L. Arthur Joel R. Coats 《Biology and Fertility of Soils》2001,33(6):541-545
Pesticide contamination of soil and groundwater at agricultural chemical distribution sites is a widespread problem in the USA. Alternatives to land-farming or solid waste disposal include biostimulation and phytoremediation. This research investigated the ability of compost, corn stalks, corn fermentation byproduct, peat, manure, and sawdust at rates of 0.5% and 5% (w/w) to stimulate biodegradation of atrazine [6-chloro-N-ethyl-N'-(1-methyethyl)-1,3,5-triazine-2,4-diamine], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] added as a mixture to soil. Initial concentrations were 175ᆾ mg atrazine kg-1 soil, 182ᆭ mg metolachlor kg-1 soil, and 165ᆫ mg trifluralin kg-1 soil. After amendment addition, 30% of the atrazine, 33% of the metolachlor, and 44% of the trifluralin was degraded over 245 days, which included 63 days' aging prior to amendment additions. Atrazine degradation was enhanced by 0.5% manure, 5% peat, and 5% cornstalk amendments compared to nonamended soils. Metolachlor degradation was enhanced by all amendments at the 5% level, except for compost and peat. Amendments had no effect on trifluralin degradation. The 5% addition of compost, manure, and cornstalks resulted in significant increases in bacterial populations and dehydrogenase activity. A second experiment compared the persistence of atrazine, metolachlor, and trifluralin applied in a mixture to their persistence in soil individually. A combined average of 123 mg atrazine kg-1 remained in soil treated with the three-herbicide mixture compared to 31 mg atrazine kg-1 remaining in soil treated with atrazine only. Atrazine mineralization and atrazine-degrading microorganisms were suppressed by high concentrations of metolachlor, but not by trifluralin. 相似文献
995.
C. Ekstrand C. Ingvast‐Larsson L. Olsén M. Hedeland U. Bondesson J. Gabrielsson 《Journal of veterinary pharmacology and therapeutics》2016,39(3):255-263
The cortisol response to glucocorticoid intervention has, in spite of several studies in horses, not been fully characterized with regard to the determinants of onset, intensity and duration of response. Therefore, dexamethasone and cortisol response data were collected in a study applying a constant rate infusion regimen of dexamethasone (0.17, 1.7 and 17 μg/kg) to six Standardbreds. Plasma was analysed for dexamethasone and cortisol concentrations using UHPLC‐MS/MS. Dexamethasone displayed linear kinetics within the concentration range studied. A turnover model of oscillatory behaviour accurately mimicked cortisol data. The mean baseline concentration range was 34–57 μg/L, the fractional turnover rate 0.47–1.5 1/h, the amplitude parameter 6.8–24 μg/L, the maximum inhibitory capacity 0.77–0.97, the drug potency 6–65 ng/L and the sigmoidicity factor 0.7–30. This analysis provided a better understanding of the time course of the cortisol response in horses. This includes baseline variability within and between horses and determinants of the equilibrium concentration–response relationship. The analysis also challenged a protocol for a dexamethasone suppression test design and indicated future improvement to increase the predictability of the test. 相似文献
996.
Cardiopulmonary and sedative effects of intravenous or epidural methadone in conscious dogs 下载免费PDF全文
B. H. B. Vieira L. T. Nishimura L. L. Carvalho A. Auckburally E. Mattos‐Junior 《Journal of veterinary pharmacology and therapeutics》2017,40(6):e65-e68
Cardiopulmonary and sedative effects of intravenous or epidural methadone were compared. Six beagles were randomly assigned to group MIV (methadone 0.5 mg/kg IV + NaCl 0.9% epidurally) or MEP (methadone 0.5 mg/kg epidurally + NaCl 0.9% IV). Cardiopulmonary, blood gas and sedation were assessed at time (T) 0, 15, 30, 60, 120, 240 and 480 min after drug administration. Compared to T0, heart rate decreased at T15–T120 in MIV (p < .001) and T15–T240 in MEP (p < .05); mean arterial pressure was reduced at T15–T60 in MEP (p < .01); respiratory rate was higher at T15 and T30 in both groups (p < .05); pH was lower at T15–T120 in MIV (p < .01) and T15, T30 and T120 in MEP (p < .05); PaCO2 was higher at T15–T60 in MIV (p < .01) and T15, T30 and T120 in MEP (p < .01); sedation scores were higher at T15 and T30 in MIV and T15–T60 in MEP (p < .05). At T120 and T240, sedation score was higher in group MEP compared with group MIV (p < .01) In conclusion, cardiopulmonary and sedative effects of identical methadone doses are similar when administered IV or epidurally to conscious healthy dogs. 相似文献
997.
P W Nel R A Schultz P Jordaan L A Anderson T S Kellerman C Reid 《The Onderstepoort journal of veterinary research》1987,54(4):641-644
Urginea physodes (Jacq.) Bak., a species closely related to or possibly synonymous with U. pusilla, is described and its distribution given. Four bufadienolides were isolated from U. physodes and the approximated LD50 and cumulative effect of some of them determined in guinea pigs. The most toxic one proved to be mildly cumulative. Typical signs of acute cardiac glycoside poisoning, involving the locomotory, gastro-intestinal, respiratory and cardiac system, were seen in the field cases and/or were experimentally induced by the plant. Similar signs could also be induced by injecting the isolated bufadienolide, physodine A, to a sheep. 相似文献
998.
Field trials were conducted in a plastic house artificially infested with an avirulent population of Meloidogyne javanica to determine the durability of the resistance mediated by the Mi gene in tomato rootstocks after repeated cultivation for three consecutive years. Treatments included an experimental rootstock cv. PG76 ( Solanum lycopersicum × Solanum sp.), a commercial rootstock cv. Brigeor ( S. lycopersicum × S. habrochaites ), a resistant tomato cv. Monika ( S. lycopersicum ), and a susceptible cv. Durinta ( S. lycopersicum ). Based on the reproduction index (RI: number of eggs per g root on the resistant cultivar divided by number of eggs per g root on the susceptible cultivar × 100), rootstock cv. PG76 responded as highly resistant (RI = 7%) after the first cropping cycle (3·4 nematode generations), showed intermediated resistance (RI = 33%) after the second cropping cycle (3·3 generations), and was fully susceptible (RI = 94%) after the third cycle (3·3 generations). In contrast, rootstock cv. Brigeor and resistant cv. Monika retained intermediate resistance levels (RI = 41 and 25%, respectively) after the third cropping cycle. Virulent nematode populations were rapidly selected from an avirulent one after repeated cultivation of resistant tomatoes under field conditions. Bioassays conducted under controlled conditions confirmed that selection for virulence occurred more rapidly in plots with cv. PG76 followed by Brigeor and Monika. The nematode population in the field not exposed to Mi resistance remained avirulent to Mi genotypes. The genetic background of the resistant rootstocks and the frequency of cropping were critical factors for the appearance of virulent nematode populations. Irrespective of nematode infection, all resistant tomatoes yielded more than the susceptible cultivar. 相似文献
999.
Huber L. Sanktjohanser A. Bresinsky H. Zöttl Kreutzer A. Bernhart und R. Kennel 《Forstwissenschaftliches Centralblatt》1966,85(1-2):61-64
Ohne Zusammenfassung 相似文献
1000.