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   91096篇
  免费   5761篇
  国内免费   55篇
林业   3939篇
农学   3539篇
基础科学   639篇
  11566篇
综合类   13663篇
农作物   3390篇
水产渔业   5093篇
畜牧兽医   48112篇
园艺   1215篇
植物保护   5756篇
  2020年   776篇
  2019年   975篇
  2018年   1680篇
  2017年   1931篇
  2016年   1737篇
  2015年   1448篇
  2014年   1777篇
  2013年   3820篇
  2012年   3042篇
  2011年   3704篇
  2010年   2400篇
  2009年   2389篇
  2008年   3570篇
  2007年   3304篇
  2006年   3217篇
  2005年   2740篇
  2004年   2631篇
  2003年   2654篇
  2002年   2435篇
  2001年   3418篇
  2000年   3323篇
  1999年   2567篇
  1998年   991篇
  1997年   1054篇
  1996年   893篇
  1995年   1033篇
  1994年   903篇
  1993年   903篇
  1992年   1850篇
  1991年   1927篇
  1990年   1860篇
  1989年   1862篇
  1988年   1612篇
  1987年   1597篇
  1986年   1628篇
  1985年   1528篇
  1984年   1225篇
  1983年   1033篇
  1982年   715篇
  1979年   1061篇
  1978年   819篇
  1975年   816篇
  1974年   898篇
  1973年   864篇
  1972年   807篇
  1971年   796篇
  1970年   800篇
  1969年   780篇
  1968年   709篇
  1967年   734篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
Monepantel (MNP) is a novel anthelmintic compound launched into the veterinary pharmaceutical market. MNP is not licenced for use in dairy animals due to the prolonged elimination of its metabolite monepantel sulphone (MNPSO2) into milk. The goal of this study was to evaluate the presence of potential in vivo drug‐drug interactions affecting the pattern of milk excretion after the coadministration of the anthelmintics MNP and oxfendazole (OFZ) to lactating dairy cows. The concentrations of both parent drugs and their metabolites were measured in plasma and milk samples by HPLC. MNPSO2 was the main metabolite recovered from plasma and milk after oral administration of MNP. A high distribution of MNPSO2 into milk was observed. The milk‐to‐plasma ratio (M/P ratio) for this metabolite was equal to 6.75. Conversely, the M/P ratio of OFZ was 1.26. Plasma concentration profiles of MNP and MNPSO2 were not modified in the presence of OFZ. The pattern of MNPSO2 excretion into milk was also unchanged in animals receiving MNP plus OFZ. The percentage of the total administered dose recovered from milk was 0.09 ± 0.04% (MNP) and 2.79 ± 1.54% (MNPSO2) after the administration of MNP alone and 0.06 ± 0.04% (MNP) and 2.34 ± 1.38% (MNPSO2) after the combined treatment. The presence of MNP did not alter the plasma and milk disposition kinetics of OFZ. The concentrations of the metabolite fenbendazole sulphone tended to be slightly higher in the coadministered group. Although from a pharmacodynamic point of view the coadministration of MNP and OFZ may be a useful tool, the presence of OFZ did not modify the in vivo pharmacokinetic behaviour of MNP and therefore did not result in reduced milk concentrations of MNPSO2.  相似文献   
992.
The pharmacokinetics of cefquinome were studied in healthy and Pasteurella multocida‐infected rabbits after a single intramuscular (IM) injection at 2 mg/kg of its sulfate salt. Twelve female New Zealand white rabbits (2.0–2.5 kg) were used; six of them served as controls, and the other six had been infected with P. multocida; the experiments were conducted 1–2 days after nasal inoculation of P. multocida when rabbits showed the signs of respiratory infection. Plasma concentrations of cefquinome were determined using high‐performance liquid chromatography. The values of elimination half‐life, area under the curve, area under the first moment curve, and mean residence time were significantly lower in infected rabbits (0.48 hr, 4.54 hr*μg/ml, 3.63 hr* hr*μg/ml and 0.8 hr, respectively) than healthy rabbits (0.72 hr, 9.11 hr*μg/ml, 9.85 hr* hr*μg/ml and 1.1 hr, respectively), whereas total body clearance was significantly higher in infected than healthy rabbits. Therefore, P. multocida infection caused significant changes in some of the pharmacokinetic parameters of cefquinome in rabbits. These pharmacokinetic changes may affect dose regimen when used in P. multocida‐infected rabbits.  相似文献   
993.
A transdermal formulation of the nonsteroidal anti‐inflammatory drug, flunixin meglumine, has been approved in the United States and Canada for single‐dose administration. Transdermal flunixin meglumine was administered to 10 adult Holstein cows in their second or third lactation at the label dose of 3.33 mg/kg every 24 hr for three total treatments. Plasma flunixin concentrations were determined using high‐pressure liquid chromatography with mass spectroscopy (HPLC ‐MS ). Pharmacokinetic analysis was completed on each individual animal with noncompartmental methods using computer software. The time to maximum drug concentration (T max) was 2.81 hr, and the maximum drug concentration was 1.08 μg/ml. The mean terminal half‐life (T½) was determined to be 5.20 hr. Clearance per fraction absorbed (Cl/F) was calculated to be 0.294 L/hr kg?1, and volume of distribution of fraction (V z/F ) absorbed was 2.20 L/kg. The mean accumulation factor was 1.10 after three doses. This indicates changes in dosing may not be required when giving multiple doses of flunixin transdermal. Further work is required to investigate the clinical efficacy of transdermal flunixin after multiple daily doses.  相似文献   
994.
Single and multiple dose pharmacokinetics (PK) of mirtazapine transdermal ointment applied to the inner ear pinna of cats were assessed. Study 1 was a randomized, cross‐over single dose study (n = 8). Cats were treated once with 0.5 mg/kg of mirtazapine transdermal ointment applied topically to the inner ear pinna (treatment) or administered orally (control) and then crossed over after washout. Plasma was collected predose and at specified intervals over 96 hr following dosing. Study 2 was a multiple dose study (n = 8). Cats were treated daily for 14 days with 0.5 mg/kg of mirtazapine transdermal ointment applied topically to the inner pinna. Plasma was collected on Day 13 predose and at specified intervals over 96 hr following the final dose. In Study 1, single transdermal administration of mirtazapine resulted in mean Tmax = 15.9 hr, Cmax = 21.5 ng/mL, AUC0‐24 = 100 ng*hr/mL, AUC0‐∞ = 260 ng*hr/mL and calculated half‐life = 26.8 hr. Single oral administration of mirtazapine resulted in mean Tmax = 1.1 hr, Cmax = 83.1 ng/mL, AUC0‐24 = 377 ng*hr/mL, AUC0‐∞ = 434 ng*hr/mL and calculated half‐life = 10.1 hr. Mean relative bioavailability (F) of transdermal to oral dosing was 64.9%. In Study 2, daily application of mirtazapine for 14 days resulted in mean Tmax = 2.1 hr, Cmax = 39.6 ng/mL, AUC0‐24 = 400 ng*hr/mL, AUC0‐∞ = 647 ng*hr/mL and calculated half‐life = 20.7 hr. Single and repeat topical doses of a novel mirtazapine transdermal ointment achieve measurable plasma concentrations in cats.  相似文献   
995.
Mastitis is a common economically relevant problem in dairy farming. As the major entry for pathogens is the papillary duct, one of the first defence mechanisms is the teat sphincter. This sphincter shows a rhythmic contractility of yet unknown origin. Searching for possible modulatory pacemaker cells, teat sphincters of eight cows were stained immunohistochemically with antibodies against CD117 and vimentin and evaluated microscopically for the presence of telocytes. CD117‐ and vimentin‐positive telocytes with telopodes were found in close contact with smooth muscle cells. Our findings present a first evidence of telocytes in the teat of bovines.  相似文献   
996.
The hindlimb of the grasscutter (Thryonomys swinderianus, Temminck‐1827) was studied using 12 adult (≥6 months) rats of either sex with the mean weights of 1.42 ± 0.20 kg and 0.82 ± 0.13 kg for buck (n = 6) and doe (n = 6), respectively (p < .05). Characteristics of the bones were studied by gross observation after their preparation. Measurements of different segments of the hindlimb were also taken, giving a total average length of 31.80 cm. Correlation coefficients between length of bone and weight of rats were positive (p < .05) in bucks for all bone segments, except the pes (p > .05), whereas those in does were all non‐significant (p > .05), with significant sexual dimorphism in the relationships. The average total number of bones in the hindlimb was 92, with no apparent sexual dimorphism. The bones of the hindlimb revealed important differences and similarities in morphology with those of other rodents. The Os coxae presented a relatively large obturator foramen, formed by the ramus of the ischium and shaft of the pubis. The femur had a body and two extremities with a prominent head, well‐defined neck and trochanter. The fibula, a slender bone with triangular‐shaped proximal extremity, ran down the length of tibia with proximal attachment (via cartilage) and distal fusion, leaving an extensive interosseus space. The pes revealed eight tarsals and four metatarsals; each of the metatarsals showed three phalanges.  相似文献   
997.
The objective of the study was to categorize objectively nine breeds of healthy dogs according to pelvic limb standing posture. A total of 135 dogs from different breeds were used and the standing angles of the hip, stifle, and tarsal joints, together with the percentages of the greater trochanter, patella and tuber calcanei heights, with respect to crista iliaca height, were used as discriminant variables for the categorization of pelvic limb posture. All included breeds were allocated to three groups of the standing pelvic limb posture. The best discriminant variables between the three groups were the percentage of patellar height, and the standing angles of the stifle and tarsal joints. German shepherds, Anatolian shepherds, golden retrievers, Rottweilers, Belgian Malinois and Dobermann pinschers were well separated between 89% and 100% success rate for the categorization. The minimal success rate was determined in Berner sennenhunds as the ratio of 75%. It was also determined that Dobermann pinschers had the straightest pelvic limbs, while German shepherds had the most angulated pelvic limbs. Further studies are required to document the impact of postural differences in active and passive structure diseases of the locomotor system of the pelvic limb among dog breeds.  相似文献   
998.
999.
1000.
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