全文获取类型
收费全文 | 50363篇 |
免费 | 2970篇 |
国内免费 | 1598篇 |
专业分类
林业 | 2849篇 |
农学 | 3043篇 |
基础科学 | 1302篇 |
7209篇 | |
综合类 | 9951篇 |
农作物 | 2333篇 |
水产渔业 | 2326篇 |
畜牧兽医 | 21464篇 |
园艺 | 1019篇 |
植物保护 | 3435篇 |
出版年
2022年 | 701篇 |
2021年 | 902篇 |
2020年 | 944篇 |
2019年 | 977篇 |
2018年 | 1118篇 |
2017年 | 1335篇 |
2016年 | 1188篇 |
2015年 | 1215篇 |
2014年 | 1341篇 |
2013年 | 2628篇 |
2012年 | 2279篇 |
2011年 | 2455篇 |
2010年 | 1956篇 |
2009年 | 1880篇 |
2008年 | 2204篇 |
2007年 | 1987篇 |
2006年 | 1877篇 |
2005年 | 1572篇 |
2004年 | 1312篇 |
2003年 | 1225篇 |
2002年 | 1112篇 |
2001年 | 1456篇 |
2000年 | 1428篇 |
1999年 | 1138篇 |
1998年 | 570篇 |
1997年 | 537篇 |
1996年 | 489篇 |
1995年 | 539篇 |
1994年 | 481篇 |
1993年 | 394篇 |
1992年 | 762篇 |
1991年 | 871篇 |
1990年 | 750篇 |
1989年 | 789篇 |
1988年 | 716篇 |
1987年 | 653篇 |
1986年 | 682篇 |
1985年 | 600篇 |
1984年 | 470篇 |
1983年 | 418篇 |
1979年 | 554篇 |
1978年 | 431篇 |
1976年 | 365篇 |
1975年 | 396篇 |
1974年 | 461篇 |
1973年 | 474篇 |
1972年 | 447篇 |
1970年 | 369篇 |
1969年 | 400篇 |
1967年 | 359篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
In a flock of sheep to which food with excess copper (= Cu) had been fed for some months 39 animals died of chronic copper toxicosis. In 5 sheep of this flock the plasma concentrations of the enzymes glutamate dehydrogenase (GLDH), sorbitol dehydrogenase (SDH), aspartate-amino-transferase (ASAT) and copper were measured several times over a period of 100 days. At day 23, 58 and 97 needle biopsies of the liver were taken. The biopsies were used for histological examination and Cu-analysis. After 100 days the sheep were slaughtered and chronic copper poisoning was diagnosed by raised Cu concentration and typical histological alterations in the liver. The activities of GLDH and SDH in the plasma of the 5 sheep were consistently above normal, ASAT activity and the plasma Cu level were raised only occasionally. The results of Cu determination in biopsy samples were of little predictive value compared with post mortem Cu analysis of the liver. 相似文献
132.
C. R. GREGORY dvm I. M. GOURLEY dvm PhD Diplomateacvs N. J. TAYLOR bs J. M. CULLEN vmd A. EVANS dvm L. J. ISAAC aht L. D. COWGILL dvm 《Veterinary surgery : VS》1986,15(6):441-443
After renal allografting, cyclosporin-A was administered to one partially nonmatched dog that was followed for 79 days. Cyclosporin-A and prednisolone were administered to one nonmatched dog that was followed for 805 days. Side effects encountered with cyclosporin-A included lymphocytic dermatitis, papillomatosis, bacterial and fungal infections, and B lymphocyte hyperplasia. 相似文献
133.
影响老瓜头泌蜜量主导因素的研究 总被引:1,自引:0,他引:1
老瓜头自然分布于沙漠地带。在老瓜头开花期,天气变化无常。我们研究了对老瓜头泌蜜量起关键影响作用的气象因子。根据当地气候的变化规律进行预测预报,指导养蜂者正确选择场地,以夺取老瓜头蜜高产。 相似文献
134.
N. A. Khan 《Journal of Agronomy and Crop Science》1996,176(5):331-334
In a field trial conducted during 1992–93 and 1993–94, the effect of basal (B) nitrogen (N) (45 and 60 kg N ha−1 ) and foliar application (F) of water (W) or 10 kg N ha−1 and 400 or 600 ppm ethrel (E) (2-Chloro ethyl phosphonic acid) at 70 days after sowing was studied on leaf area index and dry mass at 90 days and pod number per plant, seeds per pod, 1000 seed weight, seed yield, oil content and oil vield at harvest of mustard ( Brassica juncea L. Czern & Coss.) cv. T-59. Recommended basal (B) application of 90 kg N ha (BN90 ) was used as control. On the basis of 2 year data it was found that basal application of 60 kg N and foliar spray of 10 kg N ha −1 and 600 ppm ethrel gave higher values for growth and yield characteristics and enhanced seed yield and oil yield by 12.5 and 14.8%, respectively over control BN90. 相似文献
135.
Selectivity of Amblygaster sirm by gill nets of seven mesh sizes ranging from 2.3 to 3.8 cm stretched mesh was studied for a period of 12 months in the coastal waters off Negombo on the west coast of Sri Lanka. The size range of fish caught was 9.0–22.0 cm. Selection by mesh sizes smaller than 3.0 cm was towards the lower end of the selection curve.
Estimated values for selection factors ranged from 5.11 to 6.03 and those for optimum selection lengths varied from 12.9 to 19.7 cm. The highest selection factor was observed for 2.9 cm mesh, probably due to wedging of larger individuals in this mesh. 相似文献
136.
Field experiments were conducted at Tamil Nadu Rice Research Institute, Aduthurai, India, during the wet seasons of 1992 and 1993 to study the effect of full and partial substitution of fertiliser N with green manure N (Sesbania rostrata) on nitrogen uptake, yield attributes and yield of rice. The experiment consisted of eight treatments with two levels of N (100 and 200 kg ha−1 ) and three sources of N application viz., fertilizer, integrated (1:1 fertilizer and green manure N) and green manure N compared to the recommended practice (150 kg fertilizer plus 6.25 t ha−1 (72 kg N) green manure) and a no N control. Nitrogen application markedly increased the N uptake. Combined use of the two N sources at 200 and 222 kg N ha−1 and of single fertilizer N at 200 kg N ha−1 recorded the maximum N uptake, increased the yield attributes such as number of panicles per unit area, weight per panicle, number of total and filled grains per panicle and test weight. At 200 kg N ha−1 full substitution of N by green manure reduced the grain yield but only partial substitution of N by green manure resulted in almost similar yield as single fertilizer N. Thus 200 kg N ha−1 applied in equal proportions of fertilizer and green manure N can be recommended for medium duration rice cultivars. 相似文献
137.
In vitro viability of cryopreserved equine embryos following different freezing protocols.
下载免费PDF全文
![点击此处可从《Canadian journal of veterinary research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P Poitras P Guay D Vaillancourt N Zidane M Bigras-Poulin 《Canadian journal of veterinary research》1994,58(4):235-241
The main objective of this study was to evaluate two freezing protocols and the effect of agar embedding on survival of day 6.5 equine embryos. A total of 133 embryos were used, in one group (n = 51), embryos were first embedded in agar before the freezing protocol was started. A freezing protocol to -30 degrees C or -33 degrees C was used before plunging embryos into liquid nitrogen (LN2). The embryos were thawed in water at 37 degrees C, evaluated and placed in culture. After 24 h culture, the embryos were evaluated for their morphology and development. No differences were observed between embryos plunged at -30 degrees or at -33 degrees C in LN2. The analysis of the morphology and development after thawing showed that the diameter and developmental stage at freezing correlated with embryo survival. Morula and early blastocyst stages of development were associated with better quality after freezing and thawing and had a better potential to survive after in vitro culture (p < 0.05) compared to more advanced stages. The agar failed to protect embryos from zona pellucida damage, but a tendency to prevent rupture was observed in larger embedded embryos. 相似文献
138.
139.
140.
糖类寄生螨快速分离检验方法 总被引:1,自引:0,他引:1
本文对糖类寄生螨的快速分离检验方法进行了改进。将糖类溶解后,经过500目/英寸标准检验筛进行过筛分离。此方法对各种可溶性糖类中的寄生螨类能取得100%的快速分离检验结果。 相似文献