全文获取类型
收费全文 | 2849篇 |
免费 | 238篇 |
国内免费 | 139篇 |
专业分类
林业 | 249篇 |
农学 | 84篇 |
基础科学 | 31篇 |
60篇 | |
综合类 | 1339篇 |
农作物 | 45篇 |
水产渔业 | 91篇 |
畜牧兽医 | 1258篇 |
园艺 | 46篇 |
植物保护 | 23篇 |
出版年
2024年 | 23篇 |
2023年 | 79篇 |
2022年 | 97篇 |
2021年 | 104篇 |
2020年 | 108篇 |
2019年 | 136篇 |
2018年 | 63篇 |
2017年 | 126篇 |
2016年 | 144篇 |
2015年 | 107篇 |
2014年 | 177篇 |
2013年 | 147篇 |
2012年 | 280篇 |
2011年 | 264篇 |
2010年 | 201篇 |
2009年 | 210篇 |
2008年 | 157篇 |
2007年 | 150篇 |
2006年 | 140篇 |
2005年 | 121篇 |
2004年 | 87篇 |
2003年 | 65篇 |
2002年 | 53篇 |
2001年 | 34篇 |
2000年 | 33篇 |
1999年 | 24篇 |
1998年 | 20篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 16篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有3226条查询结果,搜索用时 562 毫秒
991.
992.
993.
Diagnostic ultrasound, a non-invasive mode for imaging soft tissues, requires for its use an understanding of sound and sound-tissue interaction physics. Ultrasound frequencies from 1.0 to 10.0 MHz are created by electrical stimulation of piezoelectric crystals. These crystals are housed within transducers, which, when applied to the body surface with a coupling agent will produce sound waves, referred to as the sound beam, which are propagated through the soft tissues of the body. When the sound beam encounters tissue interfaces of differing acoustic impedance, a portion of the sound beam is reflected back to the transducer which also acts as a receiver. Echoes returning from soft tissue acoustic interfaces are converted to electrical impulses and displayed on an oscilloscope screen as a cross section of the tissue. Lower frequency sound beams penetrate further into soft tissue, but have poorer resolving capabilities, than higher frequency sound beams. A, B, and M-modes are the three basic forms of ultrasound used in soft tissue imaging. A-mode ultrasonic imaging is a one-dimensional display of echo amplitudes versus distance. B-mode ultrasonic imaging produces an accurate two-dimensional cross sectional image of soft tissues. M-mode ultrasonic imaging is an adaptation of B-mode to evaluate moving structures of the heart. Fluid-filled cystic structures have characteristic clear (anechoic) central areas with acoustic enhancement of the back wall of the cyst and deeper structures. Solid masses have echoes in their central portion with resultant poor accentuation of deeper structures. Application of ultrasound to animals requires hair removal since trapped air is a barrier to transmission of the sound beam. Gas-filled bowel and bone are effective barriers to ultrasonic imaging because of their large acoustic impedance differences compared to soft tissues. The position of the focal point of a focused transducer relative to tissue interfaces is important to accurately depict tissue character. For example, the focal point of the transducer should be superficial to the back wall when scanning cystic structures. When solid lesions, such as liver metastases, are scanned a focal point that lies deep to the lesion should be selected in order to accentuate sound beam attenuation. Time-gain compensation (TGC) settings are important to produce a balanced scan with equal echo production within like tissues throughout the depth of ultrasound tissue penetration. Initial TGC settings can be made from knowledge of the focal point of the particular transducer, but may have to be adjusted during scanning to produce a balanced image. Ultrasound is an attractive imaging modality in animals since it is noninvasive and presents no known hazard to the operator or patient. 相似文献
994.
12味中药及其复方对大肠杆菌的体外抑菌试验 总被引:4,自引:0,他引:4
采用体外抑菌试验方法,观察十二味中药及几个复方对大肠杆菌K88和溶血性大肠杆菌的体外抑菌试验。试验结果:12味中药中,有9味中药(冰片、狼毒、白砒、斑蝥、重楼、红芽大戟、白花蛇舌草、黄连、三棵针)均对大肠杆菌K88有抑制作用,其中11味中药(冰片、狼毒、紫贝天葵、白砒、斑蝥、重楼、樟脑、红芽大戟、白花蛇舌草、黄连、三棵针)均对溶血性大肠杆菌有抑制作用。组成的1~7个复方,均对大肠杆菌K88和溶血性大肠杆菌有抑制作用。复方5与恩诺沙星(1‰)时大肠杆菌K88的抑菌作用比较,前者优于后者,其差异显著(P<0.05);复方5与恩诺沙星(1‰)对溶血性大肠杆菌的抑菌作用比较,前者优于后者,其差异极显著(P<0.01),黄连与恩诺沙星相配有协同作用。 相似文献
995.
This paper presents the findings of an exploratory study on ethnoveterinary medicines used for backyard pigs and backyard chickens in Trinidad and Tobago. Research data was collected from 1995 to September 2000. Six plants are used for backyard pigs. Crushed leaves of immortelle (Erythrina pallida, E. micropteryx) are used to remove dead piglets from the uterus. Leaf decoctions of bois canôt (Cecropia peltata) and bamboo (Bambusa vulgaris) are used for labour pains or leaves are fed as a postpartum cleanser. Boiled green papaya fruit (Carica papaya) is fed to pigs to induce milk let-down. The leaves and flowers of male papaya plants (Carica papaya) are fed to de-worm pigs. Sour orange juice (Citrus aurantium) is given to pigs to produce lean meat, and coffee grounds are used for scours. Eyebright and plantain leaves (Plantago major) are used for eye injuries of backyard chickens. Worm grass (Chenopodium ambrosioides) and cotton bush (Gossypium species) are used as anthelmintics. Aloe gel (Aloe vera) is used for internal injuries and the yellow sap from the cut Aloe vera leaf or the juice of Citrus limonia is used to purge the birds. A literature review revealed few toxicity concerns and the potential usefulness of the plants. 相似文献
996.
Marcellin-Little DJ Levine D Canapp SO 《Clinical Techniques in Small Animal Practice》2007,22(4):171-182
The shoulder joint is the most mobile of all main limb joints. While its primary motion is in a sagittal plane, the shoulder has a significant amount of abduction and adduction, and internal and external rotation. Its stability is ensured by the joint capsule, by its specialized bands (medial and lateral glenohumeral ligaments), and by large tendons located inside (eg, tendon of origin of the biceps brachii muscle) or immediately outside the joint (eg, supraspinatus, infraspinatus, teres minor, and subscapularis). Sprains or strains of all supporting structures of the canine shoulder have now been reported and the shoulder pathology resembles the pathology of the human shoulder that includes strains and tears of the rotator cuff muscles, adhesive capsulitis, and calcific tendonitis. 相似文献
997.
Riviere JE 《Veterinary journal (London, England : 1997)》2007,174(3):462-471
The purpose of this article is to make an educated guess as to what veterinary pharmacology will look like in two decades. By examining the past, it is evident that change is incremental unless a transforming discovery occurs. In the last few decades, such events have dramatically changed medicine and pharmacology, however they have not percolated through the system to the effect that novel drugs have replaced our traditional armamentarium. The effect of six transforming technologies (continued advances in computer technology, microfluidics, nanotechnology, high-throughput screening, control and targeted drug delivery, pharmacogenomics) on veterinary therapeutics is examined. These should lead toward more efficacious and safer drugs across most therapeutic classes due to both increases in our knowledge base as well as more efficient drug development. Shorter term improvements in drug delivery should be seen. Although this growth in technology would portend major advances over the next few decades, economic and regulatory constraints must still be overcome for these new drugs or therapeutic approaches to become common practice. 相似文献
998.
999.
应用超高效液相色谱-串联质谱技术,建立了3种中兽药制剂中非法添加阿莫西林和氨苄西林的检测方法。样品经50%乙腈水溶液提取、稀释后进行分析。实验采用0.2%甲酸乙腈溶液与0.2%甲酸水溶液作为流动相进行梯度洗脱,经Atlantis T3柱(2.1 mm×150 mm,5μm)分离,通过多反应监测模式进行测定。结果表明,阿莫西林和氨苄西林在1~50 ng/m L的范围内线性关系良好,最低检测限分别为0.5 mg/g和0.2 mg/g。阿莫西林回收率在83.4%~95.8%之间,RSD为2.0%~4.6%;氨苄西林回收率在85.1%~97.2%,RSD为1.7%~4.0%。本方法准确、可靠,可用于中兽药制剂中非法添加阿莫西林和氨苄西林的检测。 相似文献
1000.
应用超高效液相色谱-串联质谱技术,建立了兽用中药制剂穿心莲注射液和鱼腥草注射液中非法添加庆大霉素的检测方法。样品经水溶解后,稀释。采用20mmol/L HFBA乙腈与20mmol/L HFBA水溶液作为流动相进行梯度洗脱,经ACQUITY HSS PFP色谱柱分离,通过多反应监测模式进行测定。庆大霉素在0.04~2 μg/mL的范围内线性关系良好,相关系数0.9994。平均回收率为98.2%~100.3%,相对标准偏差均小于2.4%。检测限为0.2%,定量限为0.4%,该法准确、简单、快速。 相似文献