全文获取类型
收费全文 | 575篇 |
免费 | 47篇 |
专业分类
林业 | 46篇 |
农学 | 14篇 |
基础科学 | 7篇 |
75篇 | |
综合类 | 50篇 |
农作物 | 10篇 |
水产渔业 | 10篇 |
畜牧兽医 | 364篇 |
园艺 | 12篇 |
植物保护 | 34篇 |
出版年
2023年 | 5篇 |
2021年 | 13篇 |
2020年 | 23篇 |
2019年 | 18篇 |
2018年 | 11篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 18篇 |
2013年 | 16篇 |
2012年 | 37篇 |
2011年 | 29篇 |
2010年 | 29篇 |
2009年 | 19篇 |
2008年 | 34篇 |
2007年 | 35篇 |
2006年 | 35篇 |
2005年 | 23篇 |
2004年 | 36篇 |
2003年 | 39篇 |
2002年 | 18篇 |
2001年 | 7篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1981年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1960年 | 2篇 |
1957年 | 3篇 |
1948年 | 2篇 |
1940年 | 3篇 |
1939年 | 2篇 |
排序方式: 共有622条查询结果,搜索用时 210 毫秒
31.
A two-year-old female alpaca suddenly became lame on its right hindlimb. Eight days later clinical and radiographic examinations showed that the patella had become temporarily fixed within the supratrochlear notch of the femur. Under general anaesthesia an abrasion trochleoplasty followed by fascial imbrication was carried out. After two weeks in supporting slings, the animal put full weight on the leg, and six months after the surgery it showed no signs of lameness or recurrence of the upward fixation. 相似文献
32.
33.
Steiner WR 《Science (New York, N.Y.)》1929,70(1818):413-416
34.
Sahab Hedjazi Othar Kordsachia Rudolf Patt Ahmad Jahan Latibari Ulrike Tschirner 《Industrial Crops and Products》2009,29(1):27-36
Alkaline sulfite–anthraquinone (AS/AQ) pulping of wheat straw and totally chlorine free (TCF) bleaching of resulting pulps was investigated. Wheat straw was supplied by the Ferdosii University Experimental Station in Northeastern Iran, cleaned and chopped into about 3–5 cm long pieces. In the AS/AQ pulping experiments, the active alkali charge on oven dry wheat straw, heating time to maximum cooking temperature, AQ dose and liquor to straw ratio were kept constant at 16%, 60 min, 0.1% and 4/1, respectively. The alkali ratio, Na2SO3/NaOH, calculated as NaOH, was varied from 20/80 to 80/20. Cooking time at maximum temperature was varied from 30 to 90 min and maximum cooking temperature was adjusted between 152 and 160 °C. Reference soda and soda/AQ pulps were produced.AS/AQ and soda/AQ pulps with kappa numbers below 15 were produced easily. Cooking of corresponding soda pulps under comparable conditions stopped at a kappa number of 25. The characteristics of unbleached AS/AQ, soda/AQ and soda pulps were compared. AS/AQ and soda/AQ pulps had similar tensile strength but tear was in favor to AS/AQ. The latter had much higher yield and brightness.TCF bleaching of AS/AQ pulp was performed in O Q (OP) or O Q (OP) P sequences. Oxygen delignification (O) resulted in a delignification degree of approximately one third. Followed by a chelating treatment (Q) and a subsequent (OP) stage under drastic conditions a brightness of 82.7% ISO was achieved in an O Q (OP) sequence. The sequence O Q (OP) P, with 2% H2O2 in the final P stage, improved brightness from 77.2% ISO after the OP stage to 83.6% ISO. Bleaching led to only small losses in tensile and burst strength but enhanced tear strength. Short beating in a Jokro mill was sufficient to attain good pulp strength. The results of this study indicate that AS/AQ pulping and TCF bleaching is a convincing alternative to produce high-quality pulp from wheat straw for writing and printing paper. 相似文献
35.
Nils-Erik Ahlberg Med Dr Fredrik Hoppe VDM Ulrike Kelter MD† Leif Svensson PHD‡ 《Veterinary radiology & ultrasound》1985,26(2):43-47
The influence of body position on volume and x-ray attenuation of the lungs of three Beagles was investigated with computed tomography. In left and right lateral recumbency, the dependent lung had decreased volume and increased x-ray attenuation compared with ventral recumbency. Volume and x-ray attenuation of the nondependent lung, however, were unchanged. In dorsal recumbency, there was a vertical gradient of x-ray attenuation being increased dorsally and decreased ventrally compared with ventral recumbency where regional differences in x-ray attenuation were not found. Results indicate a risk of overlooking a mass in the dependent pulmonary parenchyma of dogs in lateral and dorsal recumbency. Regional differences in x-ray attenuation of the lungs of dogs can be avoided if the radiographs are obtained with the dog in ventral recumbency. 相似文献
36.
Ground spiders on a cultivated field near Groβenzersdorf (Lower Austria) in the winter months 322 adult spiders caught with pitfall traps on a field near Groβenzersdorf in the period 3. X 1973–5. III 1974 showed: Erigonidae, Linyphiidae,Pachygnatha (Tetragnathinadae) are dominating. 19 spp. have been recognized, most of them being already known as eurochronous or diplochronous respectively. The whole spider fauna resembles very mmuch the situation found in mid-Germany (Leipzig) byGeiler (1963). 相似文献
37.
38.
Spatial structure of wood composites in relation to processing and performance characteristics 总被引:1,自引:0,他引:1
Summary A rationale is presented for developing a mathematical model which describes a randomly packed, short-fibre-type wood composite. The model will utilize probability theory to insure random packing both in terms of flake position and orientation. Knowledge about the spatial relationship between wood elements will be used, in future, to predict a number of physical parameters associated with the composite structure. This will be accomplished by first developing a single-layer-flake model and subsequently proceeding to a multi-layer mat structure.Financial support for this work from NSERC/Canada through a strategic research grant is gratefully acknowledged 相似文献
39.
An immersion technique for studying wood wettability 总被引:1,自引:1,他引:1
Summary The wetting properties of wood were studied by a modification of the Wilhelmy technique. This method involved continuously monitoring the force exerted on a wood specimen as it was immersed at a controlled rate into a liquid. Wettability was expressed in terms of the area under the force-immersion curve and was referred to in this study as wettability index. The applicability of the technique was demonstrated for padauk and white spruce wood specimens heated for various time periods. The wettability of these woods in both distilled water and sodium hydroxide solutions decreased with increasing heating time. Sodium hydroxide solution yielded higher wettability index values, indicating that it was a better wetting agent than distilled water. The pH of the sodium hydroxide solution had a strong influence on magnitude of the wettability index. The possibility of using the technique for examining wood surface inactivation in relation to bonding with different adhesives is discussed.The authors gratefully acknowledge the assistance of Dr. W. G. Warren and his staff for the statistical analyses and curve fitting. Dr. Casilla also expresses his gratitude to the National Research Council of Canada and to the Canadian Forestry Service, Department of the Environment, for a postdoctoral fellowship 相似文献
40.
Hans Steiner 《Journal of pest science》1968,41(9):129-131
Zusammenfassung Nach einer neueren Definition der integrierten Sch?dlingsbek?mpfung werden die Voraussetzungen genannt, die zur praktischen
Anwendung dieses Verfahrens notwendig sind. Die Feststellung und Benützung wirtschaftlicher Schadensschwellen ist dabei besonders
wichtig. Ferner wird auf die Bedeutung der richtigen Wahl chemischer Pflanzenschutzmittel hingewiesen, solange selektive Pr?parate
noch nicht entwickelt und biologische Bek?mpfungsverfahren noch nicht praxisreif sind. Nicht eine pl?tzliche Umstellung von
der konventionellen zur integrierten Sch?dlingsbek?mpfung ist erstrebenswert, sondern ein schrittweises Vorgehen, das den
jeweiligen M?glichkeiten angepa?t werden mu?. Damit k?nnen auch jetzt schon beachtliche Erfolge erzielt werden.
Summary A new definition of the integrated control concept is given and the perequisites for practical application are mentioned. Knowledge and use of economic injury levels is of vital importance in this respect. Furthermore, the importance of the choice of pesticides to be used is stressed, as selective materials are not available yet, and purely biological control can not yet be applied in practice. A change from the conventional chemical pest control system into an integrated pest control system has to be realized step by step according to increasing knowledge and experience. With this integrated control system remarkable results have been obtained.
Résumé Après avoir établi une définition de la lutte integrée, l'auteur indique les conditions à remplir pour l'application pratique de cette méthode. La détermination et l'emploi de seuils de tolérance économiques est particulièrement important. En outre l'importance du choix judicieux des produits antiparasitaires chimiques est soulignée, compte tenu du fait des produits sélectifs ne sont pas encore développés et des procédés de lutte biologique pas encore m?rs pour la pratique. Un changement rapide de la lutte conventionelle à la lutte integrée n'est pas désirable, mais plut?t une évolution progressive qui soit adapté au fur et à mesure aux possibilités du moment. Ainsi, des succés considérables peuvent déjà être obtenus à brève échéance.相似文献