全文获取类型
收费全文 | 168529篇 |
免费 | 9256篇 |
国内免费 | 100篇 |
专业分类
林业 | 7571篇 |
农学 | 5588篇 |
基础科学 | 1000篇 |
21142篇 | |
综合类 | 26787篇 |
农作物 | 6370篇 |
水产渔业 | 8447篇 |
畜牧兽医 | 87904篇 |
园艺 | 2159篇 |
植物保护 | 10917篇 |
出版年
2019年 | 1653篇 |
2018年 | 2580篇 |
2017年 | 2867篇 |
2016年 | 2647篇 |
2015年 | 2325篇 |
2014年 | 2854篇 |
2013年 | 6775篇 |
2012年 | 5120篇 |
2011年 | 6035篇 |
2010年 | 4087篇 |
2009年 | 4177篇 |
2008年 | 6035篇 |
2007年 | 5828篇 |
2006年 | 5514篇 |
2005年 | 5088篇 |
2004年 | 4868篇 |
2003年 | 4905篇 |
2002年 | 4544篇 |
2001年 | 5615篇 |
2000年 | 5434篇 |
1999年 | 4395篇 |
1998年 | 1748篇 |
1997年 | 1744篇 |
1996年 | 1627篇 |
1995年 | 1928篇 |
1994年 | 1636篇 |
1993年 | 1670篇 |
1992年 | 3337篇 |
1991年 | 3452篇 |
1990年 | 3430篇 |
1989年 | 3487篇 |
1988年 | 3156篇 |
1987年 | 3176篇 |
1986年 | 3145篇 |
1985年 | 2982篇 |
1984年 | 2447篇 |
1983年 | 2177篇 |
1982年 | 1478篇 |
1979年 | 2107篇 |
1978年 | 1692篇 |
1977年 | 1489篇 |
1976年 | 1450篇 |
1975年 | 1524篇 |
1974年 | 1880篇 |
1973年 | 1887篇 |
1972年 | 1880篇 |
1971年 | 1701篇 |
1970年 | 1712篇 |
1969年 | 1604篇 |
1967年 | 1402篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
982.
Antibodies to Coxiella burnetii have been found in the Danish dairy cattle population with high levels of herd and within herd seroprevalences. However, the prevalence of antibodies to C. burnetii in Danish beef cattle remains unknown. The objectives of this study were to (1) estimate the prevalence and (2) identify risk factors associated with C. burnetii seropositivity in Danish beef and dairy cattle based on sampling at slaughter. 相似文献
983.
Ultrastructure of the tubular glands in the isthmus region of the oviduct in laying and natural moulting commercial egg‐type chickens 下载免费PDF全文
Mary‐Cathrine Nyasha Madekurozwa Mike M. Mpango 《Anatomia, histologia, embryologia》2018,47(5):493-497
The study investigated the ultrastructural characteristics of tubular gland and duct cells, as well as luminal gland cells in the isthmus region of the oviduct of laying and natural moulting hens. Tubular glands in laying birds were composed of type 1 and 2 cells. Based on the preponderance of each cell type, in relation to the location of a developing egg in the oviduct of the domestic fowl, these gland cells may represent different functional states of the same cell. The findings of the study on natural moulting birds suggest that autophagy is a process confined to the early stages of degeneration, while necrosis occurs in the terminal stages. 相似文献
984.
985.
Lack of effect of recombinant bovine interferon alpha I1 in the treatment of experimentally-induced bovine warts. 下载免费PDF全文
Fifteen four-month old calves were inoculated, on five scarified sites on each side of the neck, with a suspension of ground wart tissue from a steer naturally infected with bovine papilloma virus 1. Warts started to appear about one month postinfection and were measurable in ten calves two months postinfection, when the trial started. After stratification on the size of the warts, all fifteen calves were allocated randomly to one of the following treatment groups: twice weekly intramuscular injections of 5 mg recombinant bovine interferon alpha I1 (rBoIFN alpha I1), weekly injection of 5 mg of rBoIFN alpha I1 or placebo, for three weeks. The biggest wart on each calf at the beginning of the trial was measured and photographs of all warts were taken weekly for five weeks. An analysis of covariance on the log of the volumes of warts during the five weeks of the trial showed a significant difference between groups (p = 0.026). Warts in treated groups tended to grow faster than in the placebo group. 相似文献
986.
Describing the growth and molt of modern domestic turkey (Meleagris gallopavo) primary wing feathers
Emily M Leishman Nienke van Staaveren Don R McIntyre Jeff Mohr Benjamin J Wood Christine F Baes Alexandra Harlander-Matauschek 《Journal of animal science》2020,98(12)
The use of feathers as noninvasive physiological measurements of biomarkers in poultry research is expanding. Feather molting patterns and growth rates, however, are not well described in domestic poultry. These parameters could influence the measurement of these biomarkers. Therefore, the objective of this study was to describe the juvenile primary feather molting patterns and feather growth rates for domestic turkeys. The 10 primary wing feathers of 48 female turkeys were measured weekly from week 1 (0 d of age) to week 20. Feathers were manually measured, and the presence or absence of each primary feather was recorded weekly. Generalized linear mixed models were used to investigate if feather growth differed between the primary feathers. The molting of the juvenile primary feathers followed a typical descending pattern starting with P1 (5 wk of age), while P9 and P10 had not molted by the end of the study (20 wk of age). The average feather growth rate was 2.4 cm/wk, although there was a significant difference between the 10 primary feathers (P < 0.0001, 2.1 to 2.8 cm/wk). Over time, feather growth followed a pattern where the growth rate reaches a peak and then declines until the feather is molted. The results of this study provide a critical update of patterns of molting and feather growth in primary wing feathers of modern turkeys. This can have implications for the interpretation of physiological biomarkers, such as the longitudinal deposition of corticosterone, in the feathers of domestic turkeys. 相似文献
987.
Effects of the dietary protein to energy ratio on growth,feed utilization and body composition in Macrobrachium nipponense 下载免费PDF全文
N.‐N. Zhang Q.‐Q. Ma W.‐J. Fan Q. Xing Y.‐L. Zhao L.‐Q. Chen J.‐Y. Ye M.‐L. Zhang Z.‐Y. Du 《Aquaculture Nutrition》2017,23(2):313-321
Oriental river prawn (Macrobrachium nipponense) has been widely cultured in Asian countries. However, its nutritional studies are very limited. In the present 8‐week study, we investigated the effects of dietary protein to energy ratio (P/E ratio) on the growth, feed utilization and body composition in juvenile M. nipponense (initial weight 0.302 ±0.03 g). Two‐factor experiment was designed and nine semi‐purified diets were formulated to contain three lipid levels (20, 80 and 140 g kg?1) and three protein levels (330, 380 and 430 g kg?1), producing P/E ratios from 16.5 to 23.4 mg KJ?1 protein. The results indicated that the growth, survival rate and protein efficiency were dose dependently improved by the increased dietary lipid, but not dietary protein content. Increased dietary lipid content and/or protein content increased lipid accumulation in whole body, hepatopancreas and muscle, but did not change the feed intake and hepatopancreas weight. In conclusion, our present study indicated that M. nipponense is a species with relatively high‐energy requirement. It could utilize dietary lipid content up to 140 g kg?1, while the dietary protein with more than 330 g kg?1 would not promote growth and protein efficiency. Taken together, 330 g kg?1 dietary protein and 140 g kg?1 dietary lipid level with P/E ratio 16.49 could be optimum for M. nipponense. 相似文献
988.
Steed PM Tansey MG Zalevsky J Zhukovsky EA Desjarlais JR Szymkowski DE Abbott C Carmichael D Chan C Cherry L Cheung P Chirino AJ Chung HH Doberstein SK Eivazi A Filikov AV Gao SX Hubert RS Hwang M Hyun L Kashi S Kim A Kim E Kung J Martinez SP Muchhal US Nguyen DH O'Brien C O'Keefe D Singer K Vafa O Vielmetter J Yoder SC Dahiyat BI 《Science (New York, N.Y.)》2003,301(5641):1895-1898
Tumor necrosis factor (TNF) is a key regulator of inflammatory responses and has been implicated in many pathological conditions. We used structure-based design to engineer variant TNF proteins that rapidly form heterotrimers with native TNF to give complexes that neither bind to nor stimulate signaling through TNF receptors. Thus, TNF is inactivated by sequestration. Dominant-negative TNFs represent a possible approach to anti-inflammatory biotherapeutics, and experiments in animal models show that the strategy can attenuate TNF-mediated pathology. Similar rational design could be used to engineer inhibitors of additional TNF superfamily cytokines as well as other multimeric ligands. 相似文献
989.
Swingle CF 《Science (New York, N.Y.)》1925,62(1615):544-545
990.