全文获取类型
收费全文 | 238648篇 |
免费 | 14882篇 |
国内免费 | 646篇 |
专业分类
林业 | 23603篇 |
农学 | 13954篇 |
基础科学 | 2940篇 |
42073篇 | |
综合类 | 19676篇 |
农作物 | 16851篇 |
水产渔业 | 16455篇 |
畜牧兽医 | 88656篇 |
园艺 | 6328篇 |
植物保护 | 23640篇 |
出版年
2021年 | 2452篇 |
2020年 | 2846篇 |
2019年 | 3630篇 |
2018年 | 3980篇 |
2017年 | 4280篇 |
2016年 | 4775篇 |
2015年 | 4308篇 |
2014年 | 5692篇 |
2013年 | 16376篇 |
2012年 | 5957篇 |
2011年 | 7772篇 |
2010年 | 7205篇 |
2009年 | 7820篇 |
2008年 | 7090篇 |
2007年 | 6121篇 |
2006年 | 6845篇 |
2005年 | 6002篇 |
2004年 | 5894篇 |
2003年 | 5746篇 |
2002年 | 5048篇 |
2001年 | 5383篇 |
2000年 | 5035篇 |
1999年 | 4874篇 |
1998年 | 4084篇 |
1997年 | 4149篇 |
1996年 | 3895篇 |
1995年 | 4471篇 |
1994年 | 3837篇 |
1993年 | 3485篇 |
1992年 | 3909篇 |
1991年 | 4153篇 |
1990年 | 3747篇 |
1989年 | 3771篇 |
1988年 | 3344篇 |
1987年 | 3352篇 |
1986年 | 3300篇 |
1985年 | 3677篇 |
1984年 | 3451篇 |
1983年 | 3299篇 |
1982年 | 2761篇 |
1981年 | 2690篇 |
1980年 | 2697篇 |
1979年 | 2980篇 |
1978年 | 2707篇 |
1977年 | 2567篇 |
1976年 | 2417篇 |
1975年 | 2214篇 |
1974年 | 2357篇 |
1973年 | 2275篇 |
1972年 | 2002篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
Clark RG Henderson HV Hoggard GK Ellison RS Young BJ 《New Zealand veterinary journal》1987,35(8):126-133
Blood samples from 433 periparturient recumbent cows submitted by veterinary practitioners to Ruakura Animal Health Laboratory during 1983 and 1984 were analysed and results related to whether cows recovered, died or were euthanased. Generally cows were sampled only once and the time varied from 15 minutes to 20 days after becoming recumbent. During 1983 serum calcium, magnesium, phosphorus, creatine phosphokinase (CK), aspartate amino transferase (AST), glutamate dehydrogenase (GDH), gamma glutamyl transferase (GGT) were analysed. In 1984 serum urea, creatinine, fibrinogen and haematological examination (haemoglobin, haematocrit, total and differential white cell counts) were added to the panel. Overall 39% of cows recovered, 30% died and 32% were destroyed. Precalving cows had 111% more deaths and 7% less survivors than postcalving recumbent cows (P<0.1). There was little difference (3%) in euthanasia prevalence. Tests that were most useful in predicting a lack of recovery were serum urea and muscle enzymes. Using these tests and duration of recumbency when sampled a model was produced to predict the probability of recovery from 254 cases. 相似文献
992.
McKenna PB 《New Zealand veterinary journal》1987,35(6):94-97
A new approach to the interpretation of faecal egg counts using a simple "formula", is described. It is suggested that adoption of this procedure may enable the likely level and frequency distribution of strongyle worm burdens (Nematodirus excluded) in young sheep flocks to be estimated. The potential relevance of this information to the diagnosis of gastrointestinal parasitism is discussed. 相似文献
993.
Gossett KA Root CR Cleghorn B Church GE Turk JR Turk MA 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1987,16(4):97-101
Hookworm infected dogs had higher blood basophil counts than hookworm negative dogs. Dogs with occult heartworm infection (i.e., without microfilaremia) had higher blood neutrophil counts than heartworm negative dogs. The percentage of eosinophils in peripheral lymph nodes was higher in heartworm infected, microfilaremic dogs than in both occult infected dogs and heartworm negative dogs. Heartworm or intestinal parasitic infection had no other significant effects on hematologic parameters or peripheral lymph node cytology. 相似文献
994.
MICHAEL M. PAVLETIC DVM DiplomateACVs MARILYN KOSTOLICH DVM PHILIP KOBLIK DVM PhD STEVE ENGLER VMD 《Veterinary surgery : VS》1987,16(4):283-293
Latissimus dorsi and cutaneous trunci myocutaneous flaps of equal dimension and location were randomly elevated on opposite sides of the thorax in 10 dogs (group 1) and resutured to their respective bed. The procedure was repeated in four additional dogs (group 2); however, the short perforating branches of the thoracodorsal artery and vein were divided at the base of each cutaneous trunci myocutaneous flap, whereas the cutaneous pedicle and underlying cutaneous trunci muscle were divided in the latissimus dorsi myocutaneous flaps to determine subsequent skin survivability and the major source of circulation of each myocutaneous flap. There was little difference in the percentage of skin survival between the latissimus dorsi and cutaneous trunci myocutaneous flaps in group 1 dogs. Circulation to the "skin island" of group 2 latissimus dorsi myocutaneous flaps originated from intramuscular anastomotic connections between the major branch of the thoracodorsal artery entering the latissimus dorsi muscle and the proximal lateral intercostal arteries perforating the muscle. Ligation of the short perforating branches of the thoracodorsal artery resulted in partial skin necrosis in all group 2 cutaneous trunci myocutaneous flaps. Results from this study indicate that it is unnecessary to elevate the latissimus dorsi muscle for major skin flap elevation and survival. The thicker latissimus dorsi myocutaneous flap is more difficult to develop surgically and appears to have no clinical major advantage over the more mobile cutaneous trunci myocutaneous flap or the adjacent thoracodorsal axial pattern flap for closure of large skin defects within the radius of flap rotation. 相似文献
995.
J. E. M. Scheerboom P. W. M. Van Adrichem M. A. M. Taverne 《Veterinary research communications》1987,11(3):253-269
With electromyography and strain gauges the uterine motility of the sow during the oestrous cycle and early pregnancy was studied. Special attention was paid to characterization of myometrial activity at the time of intrauterine migration of blastocysts.From recordings of 4 animals (3 became pregnant) 3 types of electrical spiking activity (each could be correlated with an elevation of the strain gauge tension) were discerned. Two of them appeared regularly and were suitable for analysis: High Voltage Slow Acticity (with relative high amplitude and low frequency of spikes) and Low Voltage Fast Activity (with relative low aplitude and high frequency of spikes).The sexual status markedly influenced myometrial activity: during prooestrus and oestrus only one type of electrical activity was present whereas the myoelectrical complex (an episode of this activity and the subsequent interval of inactivity) was shorter than 10 min. During dioestrus the myoelectrical complex was longer than 10 min and High Voltage Slow Activity (solely on the cervix and bifurcation) and Low Voltage Fast Activity occurred simultaneously in episodes which mainly appeared to originate on the bifurcation.The characteristics of uterine activity during pregnancy were similar to those of a cyclic sow until day 12. It was only on day 12 that gestation appeared from an increased frequency of myoelectrical complexes.It is concluded that Low Voltage Fast Activity as it was found on the uterine horn at days 8–9 might be involved in the process of intra-uterine migration of blastocysts. In cyclic and in pregnant animals the patterns of Low Voltage Fast Activity were similar. Therefore, the occurrence of Low Voltage Fast Activity is independent of the actual presence of blastocysts. It seems to be exhibited in dependence on the ovarian hormones. 相似文献
996.
997.
B. Ann Becker 《Veterinary research communications》1987,11(5):443-456
Stress, stressors and the stress response are terms which represent concepts rather than oeing precisely definable. No single theory of stress has been universally accepted. Selye's General Adaptation Syndrome of stress remains the primary theory for the basis of stress research in food-producing animals; however, other concepts and theories have been developed. This paper reviews current theories and suggests that the complexity of research on stress in food-producing animals can be attributed to the lack of concrete theories and concepts regarding identifiable stressors, the endocrine responses stimulated by potential stressors and the complex and integrated biological changes in the neuro-endocrine system resulting from exposure to hypothesized stressors. 相似文献
998.
Fatty acid profiles and sensory and carcass traits of tissues from steers and swine fed an elevated monounsaturated fat diet 总被引:4,自引:0,他引:4
L C St John C R Young D A Knabe L D Thompson G T Schelling S M Grundy S B Smith 《Journal of animal science》1987,64(5):1441-1447
Twelve Angus X Hereford steers were assigned to either a control high-energy diet or a test diet consisting of 20% rapeseed at the expense of 20% corn. Twelve pigs were allotted to a control diet and two test diets containing either 10 or 20% canola oil (CO). Both CO and oil in the rapeseed contained 60 to 64% oleic acid. Cattle fed rapeseed exhibited little effect from the diet due to apparent indigestibility of the rapeseed. Total saturated fatty acids decreased from 40% in adipose tissue of the control pigs to 15% in the 20% CO-fed pigs. The ratio of monounsaturated to saturated fatty acids (M/S) increased from 1.19 in adipose tissue from control pigs to 3.63 with the addition of 20% CO to the diet. In muscle, the M/S ratio increased from 1.21 in control pigs to 2.46 in the 20% CO treatment group. The percentage of the saturated fatty acids in muscle decreased from 42% in the control to 23% in the 20% CO treatment. Significant increases in "oiliness" and decreases in fat firmness were observed when increasing levels of canola oil were fed. Sensory traits, cooking loss and shear-force values of pork chops were similar among treatment groups. In conclusion, monounsaturated fatty acid content can be elevated substantially in pork without adversely influencing the quality of the meat, thus producing a product perceived to be more healthful by the consumer. 相似文献
999.
1000.