全文获取类型
收费全文 | 200370篇 |
免费 | 13080篇 |
国内免费 | 640篇 |
专业分类
林业 | 22583篇 |
农学 | 13768篇 |
基础科学 | 2918篇 |
39318篇 | |
综合类 | 9441篇 |
农作物 | 16893篇 |
水产渔业 | 15336篇 |
畜牧兽医 | 65587篇 |
园艺 | 6124篇 |
植物保护 | 22122篇 |
出版年
2021年 | 2375篇 |
2020年 | 2771篇 |
2019年 | 3568篇 |
2018年 | 3556篇 |
2017年 | 3904篇 |
2016年 | 4490篇 |
2015年 | 4117篇 |
2014年 | 5468篇 |
2013年 | 15991篇 |
2012年 | 4615篇 |
2011年 | 6119篇 |
2010年 | 6622篇 |
2009年 | 7344篇 |
2008年 | 5635篇 |
2007年 | 4568篇 |
2006年 | 5482篇 |
2005年 | 4707篇 |
2004年 | 4620篇 |
2003年 | 4400篇 |
2002年 | 3783篇 |
2001年 | 3847篇 |
2000年 | 3520篇 |
1999年 | 3762篇 |
1998年 | 3913篇 |
1997年 | 3981篇 |
1996年 | 3728篇 |
1995年 | 4249篇 |
1994年 | 3629篇 |
1993年 | 3327篇 |
1992年 | 3033篇 |
1991年 | 3163篇 |
1990年 | 2850篇 |
1989年 | 2820篇 |
1988年 | 2443篇 |
1987年 | 2500篇 |
1986年 | 2368篇 |
1985年 | 2806篇 |
1984年 | 2811篇 |
1983年 | 2747篇 |
1982年 | 2474篇 |
1981年 | 2444篇 |
1980年 | 2446篇 |
1979年 | 2347篇 |
1978年 | 2253篇 |
1977年 | 2169篇 |
1976年 | 2014篇 |
1975年 | 1756篇 |
1974年 | 1755篇 |
1973年 | 1694篇 |
1971年 | 1436篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
G. B. J. Chapola 《Wood Science and Technology》1989,23(2):131-138
Summary The aim of this study was to investigate the influence of temperature, alkali and cement set on the visco-elastic properties of chip mattresses made in cement and calcium hydroxide, respectively. Two temperatures were used, room temperature and 78°C, believed to represent the limits of the range of temperatures experienced industrially in the manufacture of cement composites. Calcium hydroxide and cement were used to find the effect of alkali and the effect of cement set. The temperature affected the visco-elastic properties by increasing the unrecovered strain, and alkali also increased the unrecoverable strain. The effect of heat and alkali increased when the two were used in combination. In cement chip composites, the effect of cement set was the most dominant that the effect of heat and alkali could not be observed.I am indebted to Dr. A. J. Bolton of the University College of North Wales, Bangor, for his assistance. This study was carried out at this university as an Honours Project 相似文献
232.
233.
M. A. Gomez J. A. Navarro S. Gomez P. Camara J. C. Gomez A. Bernabé 《Anatomia, histologia, embryologia》1989,18(4):305-315
The structure and ultrastructure of the adenohypophyseal pars distalis in kids of the Murciano-granadiana breed (18 males and 12 females), aged 2-3 months and with an average carcass weight of 8 kg has been studied. Techniques of staining (Tetrachrome Herlant's, and Cleveland-Wolfe) and histochemistry (PAS, PAS-OG and BA-PAS-OG) contrasted with immunolabelling (PAP) have been used. In addition an ultrastructural study has been made and nucleus and cytoplasm, secretory granules, mitochondria and lysosomes have been measured with a semiautomatic image analyzer (IBAS-1). TSH cells are found in sagittal section in the anterior area and in an antero-caudodorsal band, and transversally in the ventral and medial region; they are 6% and their average size is 14.15 microns. Ultrastructurally they are a single cellular type with spherical granules whose size is 195 nm in males and 149 in females; these granules are characterized by a clear halo and a variable electronic density. The rough endoplasmic reticulum is found as slightly enlarged vesicles with a homogeneous and moderately electro-dense content or in concentric stratifications. 相似文献
234.
M.L. Castor BS R.E. Wooley DVM PhD E.B. Shotts PhD J. Brown DVM PhD J.B. Payeur DVM PhD 《Journal of Equine Veterinary Science》1989,9(5)
During an outbreak of equine salmonellosis in a veterinary teaching hospital 20 Salmonella isolates were cultured from sick horses (13 isolates) or from the hospital environment (7 isolates). Three serotypes were isolated from the environment including: S. give, S. newportand S. agona. The serotypes isolated from horses included: S. give, S. newport and S. anatum. Examination of antibiotic profiles, presence of plasmids, production of bacteriocins and hemagglutination of erythrocytes implied a common origin for the equine and environmental isolates. 相似文献
235.
236.
对新疆地区啤酒花上的土耳其斯坦叶螨 Tetranychus turkestani Ugarov et Nik-lski 的生物学、发生特点及防治对策进行了初步探讨。该螨寄丰广,为害啤酒花叶片和球果。在啤酒花的毛蕊期和球果生长期有2个发生高峰。本文以啤酒花越冬期,营养生长期、生殖生长期害螨和天敌发生特点,提出了不同的防治方法和技术关键。 相似文献
237.
Edwin H. Robinson JamesA. Steeby J. Robert Brent 《Journal of the World Aquaculture Society》1989,20(4):256-260
Two 7 day feeding trials were conducted with channel catfish swim-up fry to evaluate growth, feed conversion ratio, and body composition of fish fed one of the following feeds: salmon starter, catfish starter, or trout starter. Fish fed the salmon or trout starter feeds gained 50–75% more weight, converted feed more efficiently, and had higher body fat stores than fish fed the catfish starter feed. This may be related to the higher protein and energy content of these two feeds. It may be advantageous to feed salmonid starter feeds to hatchery reared catfish fry; however, it is not known whether or not the improved performance observed in the hatchery continues once the fish are stocked into nursery and grow out ponds. 相似文献
238.
R. A. S. White 《The Journal of small animal practice》1989,30(10):543-549
Sixty-two dogs with laryngeal paralysis were presented over a three year period. Presenting clinical signs included inspiratory stridor (100 per cent), exercise intolerance or syncopal episodes (81 per cent), loss or alteration in phonation (48 per cent) and coughing or gagging when eating (29 per cent). Causes of the paralysis were determined as traumatic (two dogs), neoplastic (two dogs), iatrogenic (two dogs), congenital (one dog) and idiopathic (55 dogs). Unilateral arytenoid lateralisation was performed in all dogs. The perioperative complication rate was approximately 10 per cent, while the success rate as judged by owners one year postoperatively was greater than 90 per cent. The technique avoided many of the recorded complications of intralaryngeal surgery. Operative times were short and the requirement for postoperative monitoring was minimal. Increasing familiarity with the technique favourably influenced the incidence of complications and the success rate. 相似文献
239.
J. C. Scott-Moncrieff G. S. Elliott A. Radoveky W. E. Blevins 《The Journal of small animal practice》1989,30(12):696-699
A 14-year-old domestic shorthaired cat was presented because of swelling of the digits and lameness. A solitary lung mass was observed on thoracic radiographs. Clinical and pathological evaluation confirmed a primary pulmonary squamous cell carcinoma metastatic to a single digit on each foot. Other metastatic lesions were present in the left popliteal lymph node and in the left iliac vein. 相似文献
240.
Summary Crystallization experiments starting from highly concentrated solutions of cellulose in trifluoroacetic acid (TFA) resulted
in white crystalline particles with diameters of as much as 0.5 mm. The plate-like particles consist of lamellae arranged
perpendicular to the surface. The lamellae are grown from thin scale-like platelets showing clear diffraction reflexes and
an internal parallel structure. Parallel structures were also detected in partially hydrolyzed cellulose. It is concluded
that cellulose chains of low DP tend to rearrange themselves by a side by side accumulation of extended molecules. 相似文献