全文获取类型
收费全文 | 253643篇 |
免费 | 15216篇 |
国内免费 | 1386篇 |
专业分类
林业 | 23660篇 |
农学 | 14310篇 |
基础科学 | 3194篇 |
43487篇 | |
综合类 | 25401篇 |
农作物 | 17314篇 |
水产渔业 | 16556篇 |
畜牧兽医 | 95905篇 |
园艺 | 6541篇 |
植物保护 | 23877篇 |
出版年
2021年 | 2684篇 |
2020年 | 3022篇 |
2019年 | 3808篇 |
2018年 | 4047篇 |
2017年 | 4509篇 |
2016年 | 4862篇 |
2015年 | 4506篇 |
2014年 | 5809篇 |
2013年 | 16435篇 |
2012年 | 6634篇 |
2011年 | 8624篇 |
2010年 | 7662篇 |
2009年 | 8140篇 |
2008年 | 7757篇 |
2007年 | 6822篇 |
2006年 | 7346篇 |
2005年 | 6664篇 |
2004年 | 6331篇 |
2003年 | 6156篇 |
2002年 | 5482篇 |
2001年 | 5795篇 |
2000年 | 5582篇 |
1999年 | 5183篇 |
1998年 | 4122篇 |
1997年 | 4146篇 |
1996年 | 3899篇 |
1995年 | 4406篇 |
1994年 | 3842篇 |
1993年 | 3550篇 |
1992年 | 4176篇 |
1991年 | 4467篇 |
1990年 | 4150篇 |
1989年 | 4062篇 |
1988年 | 3608篇 |
1987年 | 3695篇 |
1986年 | 3610篇 |
1985年 | 3818篇 |
1984年 | 3642篇 |
1983年 | 3408篇 |
1982年 | 2859篇 |
1981年 | 2762篇 |
1980年 | 2752篇 |
1979年 | 3143篇 |
1978年 | 2853篇 |
1977年 | 2607篇 |
1976年 | 2542篇 |
1975年 | 2326篇 |
1974年 | 2562篇 |
1973年 | 2473篇 |
1972年 | 2201篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
G L Carroll D M Boothe S M Hartsfield E A Martinez A C Spann A Hernandez 《Journal of the American Veterinary Medical Association》2001,219(9):1263-1267
OBJECTIVE: To evaluate disposition of butorphanol after i.v. and i.m. administration, effects on physiologic variables, and analgesic efficacy after i.m. administration in llamas. DESIGN: Nonrandomized crossover study. ANIMALS: 6 healthy adult male llamas. PROCEDURE: Butorphanol (0.1 mg/kg [0.045 mg/lb] of body weight) was administered i.m. first and i.v. 1 month later. Blood samples were collected intermittently for 24 hours after administration. Plasma butorphanol versus time curves were subjected to pharmacokinetic analysis. Two months later, butorphanol (0.1 mg/kg) was administered i.m., and physiologic variables and analgesia were assessed. RESULTS: Extrapolated peak plasma concentrations after i.v. and i.m. administration were 94.8 +/- 53.1 and 34.3 +/- 11.6 ng/ml, respectively. Volume of distribution at steady state after i.v. administration was 0.822 +/- 0.329 L/kg per minute and systemic clearance was 0.050 +/- 0.014 L/kg per minute. Slope of the elimination phase was significantly different, and elimination half-life was significantly shorter after i.v. (15.9 +/- 9.1 minutes) versus i.m. (66.8 +/- 13.5 minutes) administration. Bioavailability was 110 +/- 49% after i.m. administration. Heart rate decreased and rectal temperature increased. Somatic analgesia was increased for various periods. Two llamas became transiently sedated, and 2 became transiently excited after butorphanol administration. CONCLUSIONS AND CLINICAL RELEVANCE: Although i.v. administration of butorphanol results in a short half-life that may limit its analgesic usefulness, the elimination half-life of butorphanol administered i.m. is likely to be clinically useful. The relationship among plasma butorphanol concentration, time, and analgesia differed with the somatic analgesia model; clinically useful analgesia may occur at lower plasma concentrations than those reported here. 相似文献
262.
263.
I.-S. Park G. C. Choi D. S. Kim Y. K. Nam 《Journal of the World Aquaculture Society》2002,33(4):494-500
For the evaluation of hormonal control of spermiation in fish, a method to quanify the spermiation response of mature Rhynchocypris oxycephalus (Sauvage and Dabry) to hormonal therapy is described. Spermatocrit was determined after 7 min centrifugation at 18,000 ± g and sperm density was estimated by a standard hemocytomer method. Sperm density can be predicted from spermatocrit since their relationship is linear as described by the regression equation, Y = 3.68X - 27.18 ( R 2 = 0.82, N = 50). where Y is spermatocrit and × is sperm density. Milt production by mature R. oxycephalus was highest at 24 h after injection of 1,000 IU human chorionic gonadotropin (HCG) and 50 μg luteinizing hormone-releasing hormone analogue (LHRHa) per kg body weight. Increased milt production coincided with low spermatocrit and sperm density levels. These results demonstrate that spermiation in mature R. oxycephalus can be reliably evaluated by a spermatocrit method and that HCG and LHRHa are effective in stimulating of spermiation in this species. 相似文献
264.
265.
Capnographic documentation of nasoesophageal and nasogastric feeding tube placement in dogs 总被引:1,自引:0,他引:1
Paula A. Johnson DVM F. A. Mann DVM MS DACVS DACVECC John Dodam DVM MS PhD DACVA Keith Branson DVM MS DACVA Colette Wagner-Mann DVM PhD Mark A. Brady DVM Elizabeth Dunphy DVM 《Journal of Veterinary Emergency and Critical Care》2002,12(4):227-233
Objective: To evaluate the ability of capnography to document proper placement of nasoesophageal (NE) and nasogastric (NG) feeding tubes. This study was conducted in 3 phases. Phase I of this study was designed in order to test the efficacy of capnography to distinguish placement of a feeding tube in the alimentary tract versus the respiratory tract. Phase II was designed in order to document that carbon dioxide (CO2) could be measured through a polyvinyl chloride (PVC) feeding tube. Phase III was performed in order to evaluate the technique of continuous monitoring during insertion of the feeding tube into the esophagus and stomach as would be performed during a clinical‐tube placement. Design: Prospective study. Setting: Research laboratory. Animals: 24 adult dogs. Interventions: In Phase I, sedated dogs were instrumented with an intratracheal catheter and an 8 French feeding tube placed nasally into the distal esophagus and later advanced into the stomach. In Phase II, dogs were anesthetized and an 8 French feeding tube was placed down the endotracheal tube, then into the esophagus and later advanced into the stomach. In Phase III, sedated dogs were instrumented with an 8 French feeding tube inserted intranasally and then advanced to the level of the nasopharynx, distal esophagus and, lastly, the stomach. Fluoroscopy was used in order to determine location of the feeding tube. Measurements and main results: Phase I measurements included respiratory rate and CO2 from the trachea, esophagus, and stomach and pH of gastric fluid sample. Phase II measurements included respiratory rate and CO2 from the endotracheal tube, feeding tube in the endotracheal tube, feeding tube in the distal esophagus, and feeding tube in the stomach. Phase III data collection included respiratory rate and CO2 as the tube was passed through the nasal cavity, nasopharynx, esophagus and stomach. Phase I fluid samples were collected from 5 of the 9 dogs and had pH values from 1.68 to 4.20. In both phases, values for the respiratory rate and CO2 from the esophagus and stomach were 0 ± 0, significantly lower (P < 0.001) than the values from the trachea. In Phase II, there was no significant difference between the respiratory rates (P = 0.886) and CO2 (P = 0.705) readings obtained from the endotracheal tube compared to readings from the feeding tube in the endotracheal tube. In Phase III, there was a significant difference (P < 0.001) between the respiratory rates and CO2 readings obtained from the nasal cavity and the nasopharynx when compared to those readings obtained from the esophagus and stomach. Measurement of CO2 and respiratory rate resulted in a reading of 0 every time the feeding tube was in the esophagus or stomach. Conclusions: Capnography may be used in order to detect airway placement of NE and NG tubes. 相似文献
266.
Zhu
Jinzhao Wu Bin Bi Huaxing Zhou Changqing College of Soil Water Conservation Beijing
Forestry UniversityBeijing P.R.China 《中国林学(英文版)》1994,(2)
TheApplicationofGIsinSmallWatershedClassificationinLoessPlateauZhuJinzhao,WuBin,BiHuaxing,ZhouChangqingCollegeofSoilandWaterC... 相似文献
267.
Karen E. Bateman DVM MSc Pamela A. Catton Paul W. Pennock Stephen A. Kruth 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(4):267-272
Eighteen dogs with malignant melanoma of the oral cavity were treated with high-dose per fraction (0–7–21) radiation therapy. Eight hundred cGy was administered on days 0, 7, and 21 for a total dose of 2,400 cGy in 3 weeks. Of 17 dogs evaluated, 9 (53%) had a complete remission and 5 (30%) achieved a partial remission with an overall response rate of 83%. Local failure occurred in 2 of the 9 dogs where a complete response was initially observed. One dog died of intercurrent disease, and one died of metastatic disease without evidence of local recurrence. Five dogs are alive and free of disease 9 to nineteen months from the initiation of therapy. The 0–7–21 protocol was well-tolerated, and acute radiation reactions were low-grade and limited to the skin. The results of this study demonstrate that oral melanomas in dogs are responsive to radiation. 0–7–21 radiation therapy offers a viable alternative to radical excision, especially when tumor volume or location would require cosmetically or functionally debilitating surgery. 相似文献
268.
本文应用酶免疫试验(ELISA)、反向间接血凝试验(RIHA)和中和试验(NT)三种方法对6份疑似HBV感染的待测血清进行测定,借此探讨ELISA检测中出现假阴性现象,认为假阴性是由检测前滞现象引起。 相似文献
269.
270.
A field study utilizing 145 mares of various age and breeding status was conducted to determine reproductive performance under native range conditions with only limited supplemental feeding. All mares had an average initial body condition score of 4.5 and a final score of 5.1 by the time breeding was completed and mares returned to pasture. Average foaling rate was 80%, and mares that had not conceived during the previous breeding season had a foaling rate of 94%, which was higher (P<.05) than 74% for lactating mares. Mares 16 years and older had a significantly lower foaling rate (P<.05) than younger mares. Old mares that were lactating at time of breeding had only a 37% foaling rate, which was less (P<.05) than for young lactating mares. The 94 mares bred by natural cover or artificial insemination that actually foaled required 1.43 cycles per conception. Lactating mares in the oldest age group required more cycles per conception (P<.05) than open mares, and these older, lactating mares also required more cycles per conception than younger mares with foals at side. Those mares diagnosed as pregnant or open at 45 days post breeding had a pregnancy rate of 97%. Average pregnancy loss for all mares was 7.7%. These data indicate that lactating mares in moderate body condition tended to skip a breeding season and that a body condition score of 5 was only marginally acceptable, especially in the case of lactating mares. Authors' address: Equine Science Program, Department of Animal Science, Texas Agricultural Extension Service, Texas A&M University, College Station, TX 77843. Technical Article Number 30023, Texas Agr. Exp. Sta. 相似文献