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   150737篇
  免费   8567篇
  国内免费   94篇
林业   5412篇
农学   4480篇
基础科学   976篇
  17116篇
综合类   28178篇
农作物   5957篇
水产渔业   7256篇
畜牧兽医   78671篇
园艺   1792篇
植物保护   9560篇
  2018年   1932篇
  2017年   2256篇
  2016年   2057篇
  2015年   1810篇
  2014年   2209篇
  2013年   5645篇
  2012年   4073篇
  2011年   4983篇
  2010年   3174篇
  2009年   3262篇
  2008年   4784篇
  2007年   4562篇
  2006年   4398篇
  2005年   4052篇
  2004年   3900篇
  2003年   3953篇
  2002年   3728篇
  2001年   4830篇
  2000年   4788篇
  1999年   3786篇
  1998年   1560篇
  1997年   1515篇
  1996年   1409篇
  1995年   1724篇
  1994年   1550篇
  1993年   1505篇
  1992年   3229篇
  1991年   3371篇
  1990年   3182篇
  1989年   3279篇
  1988年   2982篇
  1987年   3179篇
  1986年   3244篇
  1985年   3097篇
  1984年   2483篇
  1983年   2187篇
  1982年   1537篇
  1981年   1346篇
  1979年   2197篇
  1978年   1817篇
  1977年   1573篇
  1976年   1491篇
  1975年   1601篇
  1974年   2014篇
  1973年   2073篇
  1972年   1989篇
  1971年   1857篇
  1970年   1779篇
  1969年   1607篇
  1967年   1402篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
When susceptibility to virulent Pasteurella multocida was compared, there was no significant (P greater than 0.05) difference between caponized and uncaponized tom turkeys. Neither was there any significant (P greater than 0.05) difference between the surviving caponized and uncaponized toms in the development of serum anti-P. multocida antibody. However, at 28 weeks of age, the average live body weight of the caponized toms was significantly (P less than 0.05) lower than that of the uncaponized toms. Turkeys were caponized when 9 weeks old, and different groups were exposed to P. multocida when 13, 18, 23, and 28 weeks old.  相似文献   
72.
Eight Friesian cross cows three months pregnant to a single Friesian bull were immunised against East Coast fever by infection with Theileria parva (Muguga) sporozoite stabilate and treatment with pyrrolidino-methyl tetracycline. They were challenged with the homologous stock four times before calving and a fifth time after calving, and resisted all five challenges which killed all of the five groups of five susceptible controls. Calves born to these hyperimmunised dams were fully susceptible on challenge with the same stabilate, as were susceptible cows from the same farm and their calves. In both instances the calves died three to seven days earlier than the cows which were approximately 10 times heavier. These results show that one- to two-month-old taurine calves from artificially immunised dams are not protected from experimental T parva sporozoite challenge and that there is no inherent calfhood resistance to East Coast fever.  相似文献   
73.
Fingerling red tilapia ( Oreochromis mossambicus ± O. niloticus ) were orally administered 17-α-methyltestosterone (MT) under a warmwater (27.0 ± 0.5 C) and coolwater (21.5 ± 0.5 C) thermal regime. In the warmwater experiment, fish received either 0, 1, 5, 10, 30, 60, or 100 mg MT/kg feed for 75 days. In the coolwater experiment, fish received 0, 10, or 60 mg MT/kg feed for 75 days followed by a 34 day withdrawal period. After 75 days, fish receiving 60 mg MT/kg feed (best treatment) in the warmwater and coolwater experiments exhibited significantly higher growth rates than controls by 35.3 and 45.8%, respectively. Likewise, feed conversion among groups receiving 60 mg MT/kg feed in the warmwater and coolwater experiments were significantly better than the controls (1.14 versus 1.30 and 1.44 versus 1.77, respectively). During the withdrawal period, no significant differences in growth rates or feed conversion were observed between the control and treatment groups. MT treatment significantly affected the body composition (whole body and empty carcass) of the red tilapia in both experiments, elevating percent moisture and protein values, but depressing percent fat values. Results demonstrated that incorporation of MT into fingerling diets offers potential for extending the period when tilapias actively feed and grow in temperate climates.  相似文献   
74.
Tuberculosis in wild seals and characterisation of the seal bacillus   总被引:3,自引:0,他引:3  
SUMMARY Tuberculosis was diagnosed in 3 otariid seals found dead on beaches at 3 locations on the south coast of Western Australian between May 1990 and March 1991. This confirms that tuberculosis is present in the 2 native seals (Neophoca cinerea and Arctocephalus forsteri) in Western Australian waters. Mycobacterium sp isolated from the lungs of 2 of the seals were studied to determine the similarity of the strains to each other, to the strains isolated during 1986 from Australian sea lions and New Zealand fur seals kept in captivity at a marine park near Perth, Western Australia, and to a strain isolated in 1988 from a seal trainer who worked with the infected captive seals for 3 years. After restriction endonuclease analysis (REA) with the endonucleases Bst Ell, Bcl I and Pvu II, one of the wild seal strains appeared to have identical DNA fragment patterns to the strains from the captive seals and the seal trainer. The other wild seal isolate had identical REA profiles using Bst EII and Bcl I, but a minor difference was detected using Pvu II. Differences in these isolates were more clearly seen in restriction fragment length polymorphisms after hybridisation with two DNA probes. The secretory protein MPB70, present in M bovis, was not detected in wild seal isolates using sodium dodecyl sulphate polyacrylamide gel electrophoresis and Western blotting techniques. Analysis of protein and DNA fragment profiles indicated that seal tuberculosis isolates form a unique cluster within the M tuberculosis complex.  相似文献   
75.
The effect of salinity on seed germination, plant yield parameters, and plant Na, Cl and K concentrations of chickpea and lentil varieties was studied. Results showed that in both crops percentage emergence was significantly reduced by increasing NaCl levels (0–8dSm?1). From the plant growth studies it was found that differences existed among chickpea and lentil varieties in their response to NaCl application. In chickpea, the variety Mariye showed the comparatively lowest germination percentage and the lowest seedling shoot dry weight in response to salinity and was also among the two varieties which had the lowest relative plant height, shoot and root dry weight and grain yield at maturity. Similarly, variety DZ-10-16-2, which was the second best in germination percentage and the highest in terms of seedling shoot dry weight, also had the highest relative plant height, shoot and root dry weights, and grain yield at maturity. In lentil, however, such relationships were less pronounced. Chloride concentration (mg g?1) in the plant parts at salt levels other than the control was about 2–5 times that of Na. K concentration in the plants was significantly reduced by increasing NaCl levels. Chickpea was generally more sensitive to NaCl salinity than lentil. While no seeds were produced at salinity levels beyond 2dSm?1 in chickpea (no seeds were produced at this salt level in the most sensitive variety, Mariye), most lentil varieties could produce some seeds up to the highest level of NaCl application. Overall, varieties R-186 (lentil) and Mariye (chickpea) were the most sensitive of all varieties. On the other hand, lentil variety NEL-2704 and chickpea variety DZ-10-16-2 gave comparatively higher mean relative shoot and root dry weights, and grain yield, thus showing some degree of superiority over the others. The observed variations among the varieties may be useful indications for screening varieties of both crops for salt tolerance.  相似文献   
76.
77.
Digital diseases are commonly seen in cattle. Cattle affected by digital disorders do not always respond to conservative therapy and require surgery. Surgical procedures for the common digital disorders are described, with emphasis on the different approaches to the distal interphalangeal joint.  相似文献   
78.
Summary The potential for increased productivity of N'Dama cattle in response to small supplementary inputs of proteinaceous by-products has been shown to be substantial under village husbandry conditions in The Gambia. Young N'Dama bulls were used to compare sesame cake with cottonseed as sources of supplementary protein during the wet and early dry seasons of 1987. They were fed 0, 40, 80 or 160 g crude protein/day in these forms for four months. Supplementation significantly increased growth rate from 169 g/d in controls to means of 272 and 271 g/d for those given sesame cake and cottonseed respectively; there were no significant differences among the supplemented groups. During the four months of the dry season immediately after supplementation ceased all previously supplemented groups grew significantly more rapidly than the controls (at leastP<0·05), indicating a substantial carry over effect of the supplements. Over this period the mean gain of the groups previously given sesame cake exceeded that of those that had received cottonseed (217 cf. 158 g/d;P<0·01). The economic benefits of these responses were substantial.
Comparacion de torta de sesamo y de semilla de algodon como fuente suplementaria de proteina para terneros destetos N'Dama en Gambia
Resumen Se ha demonstrado el potencial para incrementar la productividad del ganado N'Dama, como resquesta a peque?as cantidades de insumos suplementarios de proteína, bajo condiciones de villorrio en Gambia. Se utilizaron terneros destetos N'Dama par comparar la torta de sésamo y de semilla de algodón como fuente de proteína suplementaria durate la estaicón lluviosa y principio de la seca del a?o 1987. Se les dió a los animales 0, 40, 80 o 160 g de proteína cruda/día en éstas formas durante cuatro meses. La suplementación incrementó significativamente la tasa de crecimiento, de 169 g/día en controles a 272 y 271 g/día en aquellos que recibieron torta de sésamo y de algodón respectivamente; no hubo diferenca estadística entre los grupos suplementados. Durate los cuatro meses de la estación seca inmediatamente después de que la suplementación fue suspendida, todos los grupos que habían sido suplementados crecieron sgnificativamente más rápido que los controls (P<0·05), indicando un efecto compensatorio en los suplementados. Durante ese período la media de crecimento de los grupos que recibieron torta de sésamo excedió a aquella de los que habían recibido torta de algodón (217 cf. 158 g/d;P<0·01). Los beneficios económicos de estos resultados fueron substanciales.

Comparaison entre le tourteau de sesame et la graine de coton comme sources complementaires de proteines pour les taurillons N'Dama sevres en Gambie
Résumé Le potentiel de réponse à de petites quantités supplémentaires de sous-produits proteiniques pour accroitre la productivité de bétail N'Dama, s'est révélé manifeste, dans les conditions d'élevage villageois en Gambie. De jeunes taureaux N'Dama ont été utilisés pour comparer le tourteau de sésame et la graine de coton en tant que source de complémentation protéinique pendant la saison sèche et le début de la saison humide au cours de l'année 1987. Ils ont re?u respectivement 0, 40, 80 ou 160 g de proteines brutes par jour sus ces deux formes pendat quatre mois. Cette supplémentation a accru de fa?on significative le taux de croissance, de 169 g/jour pour les témoins jusqu'à des moyennes de 272 et 271g/jour respectivement pour ceux qui ont re?u du tourteau de sésame et de la graine de coton. Quant aux groupes complémentés, il n'ont révélé aucune différence significative. Pendat les quatre mois de la saison sèche et immédiatement après l'arrêt de la supplémentation, tous les lots ayant fait précédemment l'objet d'une distribution complémentaire ont eu une croissance significativement plus rapide que les animaux témoins, du moins pourP<0,05, ce qui indique un effet important de report des suppléments. Durant cette période, le gain moyen des lots qui ont re?u le tourteau de sésame a dépassé celui des lots auxquels on a donné de la graine de coton, soit 217 g/jour contre 158 g/jour pourP<0,01. Les profits économiques de ces réponses ont été appréciables.
  相似文献   
79.
The cervical patency of six domestic female cats was monitored under sedation by infusion of contrast medium (Omnipaque) into the cranial vagina during early oestrus, mid‐oestrus, late oestrus and interoestrus or a radiopharmaceutical (99mTc‐HSA) during mid‐ and interoestrus in a non‐ovulatory oestrous cycle. The transport of the contrast medium or the radiopharmaceutical through the cervix and within the uterine horns was observed under fluoroscopy and with the aid of scintigraphy. In three of the queens, transcervical transport of contrast medium was demonstrated in all stages of oestrus, in one queen during mid‐oestrus, late oestrus and 1 day after oestrus, and in two queens only during late oestrus. The relations between the cervical patency to the contrast medium and the oestrous behaviour, cornification of the vaginal cells and the serum oestradiol‐17β concentration were evaluated, and a relationship was found between the cervical patency and the degree of vaginal cornification. Transcervical transport of the radiopharmaceutical was observed in three queens during mid‐oestrus. When the cervix was open, hysterography under a fluoroscope and hysteroscintigraphy were performed. The fluoroscopic and scintigraphic recordings revealed the patterns of the uterine contractions during oestrus in both ascending and descending directions, and the movement of the uterine contents back and forth between the uterine horns. The hysterograms were classified according to the shape of the uterine horns and the appearance of the endometrial lining. Spiral‐shaped uterine horns with a smooth inner contour were observed in two queens, and a corkscrew appearance with irregular filling defects in the uterine lumen was shown in two queens that had developed subclinical cystic endometrial hyperplasia. These findings demonstrated that fluids or particles deposited in the cranial vagina of the cat can be transported into the uterus during some stages of the oestrous cycle. The fluoroscopic and scintigraphic techniques developed in this study may be further modified to permit more detailed studies of uterine contractile patterns and sperm transport in the feline female reproductive tract. Hysterography proved useful to diagnose uterine disease. The information on cervical patency is of value also for the development of techniques for artificial insemination in this species, and should be studied also in the ovulatory cycle.  相似文献   
80.
An eight-year-old neutered female Persian cat with a four-year history of relapsing skin disease, characterised by ulcerated nodules with a yellow granular discharge, was examined. A diagnosis of granulomatous dermatitis and panniculitis (pseudomycetoma) caused by Microsporum canis was made on the basis of history, clinical signs, histopathological examination of skin biopsy specimens and culture of macerated tissue. Because previous therapy, comprising repeated surgical excision and the administration of griseofulvin and itraconazole, had not been successful, terbinafine was administered for an eight-month period. However, lesions progressed despite this treatment and the cat was euthanased.  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