全文获取类型
收费全文 | 6567篇 |
免费 | 49篇 |
国内免费 | 75篇 |
专业分类
林业 | 273篇 |
农学 | 77篇 |
基础科学 | 32篇 |
710篇 | |
综合类 | 2191篇 |
农作物 | 233篇 |
水产渔业 | 62篇 |
畜牧兽医 | 2831篇 |
园艺 | 86篇 |
植物保护 | 196篇 |
出版年
2014年 | 28篇 |
2012年 | 474篇 |
2011年 | 516篇 |
2010年 | 115篇 |
2009年 | 59篇 |
2008年 | 392篇 |
2007年 | 408篇 |
2006年 | 402篇 |
2005年 | 389篇 |
2004年 | 336篇 |
2003年 | 307篇 |
2002年 | 324篇 |
2001年 | 214篇 |
2000年 | 228篇 |
1999年 | 132篇 |
1997年 | 24篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 41篇 |
1993年 | 63篇 |
1992年 | 48篇 |
1991年 | 49篇 |
1990年 | 67篇 |
1989年 | 60篇 |
1988年 | 112篇 |
1987年 | 105篇 |
1986年 | 61篇 |
1985年 | 82篇 |
1984年 | 99篇 |
1983年 | 95篇 |
1982年 | 69篇 |
1981年 | 44篇 |
1980年 | 41篇 |
1979年 | 36篇 |
1977年 | 20篇 |
1975年 | 24篇 |
1974年 | 38篇 |
1973年 | 41篇 |
1972年 | 43篇 |
1971年 | 23篇 |
1970年 | 29篇 |
1966年 | 22篇 |
1963年 | 48篇 |
1960年 | 28篇 |
1959年 | 25篇 |
1958年 | 28篇 |
1957年 | 31篇 |
1955年 | 25篇 |
1954年 | 20篇 |
1886年 | 25篇 |
排序方式: 共有6691条查询结果,搜索用时 15 毫秒
31.
Constable P Muir W Sisson D 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1999,13(1):5-13
Ventricular relaxation is altered in a number of cardiac disorders affecting domestic animals. Clinical determination of the ventricular relaxation rate can provide useful information regarding disease severity and response to therapy. We believe that the current gold standard for assessing left ventricular relaxation requires measurement of ventricular luminal pressure at end-expiration using a high-fidelity catheter. Ventricular pressure should be digitized at ≥200 Hz for the period of pressure fall between the minimum rate of change of ventricular pressure and 10 mm Hg above left ventricular end-diastolic pressure of the preceding beat. The rate of relaxation then should be determined from the digitized data by Marquardt nonlinear least squares parameter estimation using an exponential decay model with nonzero asymptote. The major disadvantage in using an invasive method for evaluating left ventricular relaxation is that it requires general anesthesia in animals that frequently are categorized as high-risk anesthetic patients. Noninvasive estimates of ventricular relaxation using echocardiographic parameters such as isovolumic relaxation time, peak early filling rate, and time from end-systole to peak filling rate provide a crude and nonspecific assessment of ventricular relaxation that can be obtained from conscious animals. Determinations of these echocardiographic indices are of limited usefulness in assessing changes in ventricular relaxation associated with disease progression or therapeutic intervention, unless concurrent estimates of left atrial pressure, mitral valve characteristics, and left ventricular compliance are available. 相似文献
32.
<正> 接近或高于皮肤温度的气温,常使鸡食欲减退,体重变轻,产蛋量下降,蛋壳薄而脆弱,血钙水平降低,因而被视为“高温”。据文献报道,血液雌二醇一17β对血钙水平有重要影响。那末,高温情况下鸡的血液雌二醇水平怎样?利用外源雌二醇能否缓解高温对鸡的不良影响?过去未见报道。本试验的目的,就是了解鸡在高温环境中对外源雌二醇的反应。 相似文献
33.
<正> 水分经土壤输入草坪草根,由根输入叶,最后由叶输入大气。由此看来,土壤水分状况、植物和大气蒸发需要量是影响草坪覆盖物耗水量的主要因素,某些研究表明,草坪草的耗水量随土壤有效水分的增加而增加(Biran 等1981;Ekern,1966;Mantell,1966;Marsb 等,1980;Torey 等,1969)。喜冷草坪草的耗水量较喜暖草坪草大 相似文献
34.
Thirty-six mice were inoculated intranasally with Bordetella parapertussis organisms (isolated from sheep with chronic non-progressive pneumonia) to study their deposition and clearance in the lower respiratory tract. The deposition of the organism was greater in the trachea than in the lungs. At 48 hours after inoculation, almost 100% of organisms were cleared from the trachea but only 55% of organisms were cleared from the lungs. This result correlates well with the morphological changes seen previously in the pulmonary parenchyma and airways of mice and lambs experimentally infected with this organism. 相似文献
35.
Steiss J Braund K Wright J Lenz S Hudson J Brawner W Hathcock J Purohit R Bell L Horne R 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1999,13(6):540-548
A condition colloquially referred to as "limber tail" and "cold tail" is familiar to people working with hunting dogs, primarily Pointers and Labrador Retrievers. The typical case consists of an adult dog that suddenly develops a flaccid tail. The tail either hangs down from the tail base or is held out horizontally for several inches from the tail base and then hangs straight down or at some degree below horizontal. Initially, the hair on the dorsal aspect of the proximal tail may be raised and dogs may resent palpation of the area 3-4 inches (8-10 cm) from the tail base. Most dogs recover spontaneously within a few days to weeks. Anecdotal reports suggest that anti-inflammatory drugs administered within 24 hours after onset hasten recovery. Less than one half of affected dogs experience a recurrence. Affected Pointers almost always have a history of prolonged cage transport, a hard workout the previous day, or exposure to cold or wet weather Most owners and trainers familiar with the condition do not seek veterinary assistance. In cases where people are not familiar with this disease, other conditions such as a fracture, spinal cord disease, impacted anal glands, or prostatic disease have been incorrectly diagnosed. We examined 4 affected Pointers and found evidence of coccygeal muscle damage, which included mild elevation of creatine kinase early after onset of clinical signs, needle electromyographic examination showing abnormal spontaneous discharges restricted to the coccygeal muscles several days after onset, and histopathologic evidence of muscle fiber damage. Specific muscle groups, namely the laterally positioned intertransversarius ventralis caudalis muscles, were affected most severely. Abnormal findings on thermography and scintigraphy further supported the diagnosis. 相似文献
36.
With the keeping of cattle in bigger herds problems arise, which require a modified veterinary approach. In stead of and in addition to the treatment of individual animals improvement of hygiene, intensification of prophylaxis, fast recognition (herd diagnostics) and interregional comparability have to be established. Beside the conventional field veterinarian, who is consulted on request primarily for the treatment of single animals, specialists in team practices as an alternative, permanently employed veterinarians or firm contracts with a health service up to integrated herd control are thinkable. The clarification and control of infectious diseases of the respiratory tract in cattle operations require an exact analysis of the environmental conditions and the identification of etiologic agents. Special attention has to be drawn to the evaluation of the barn climate and the respective taking of samples concerning the actual disease situation. 相似文献
37.
Dickinson PJ Keel MK Higgins RJ Koblik PD LeCouteur RA Naydan DK Bollen AW Vernau W 《Veterinary pathology》2000,37(2):160-167
Two oligodendrogliomas in two domestic cats involved mainly the rostral brain stem, midbrain, fourth ventricle, and cerebellum. Both cats were aged neutered males presenting with clinical neurologic deficits suggestive of a brain stem lesion. Magnetic resonance imaging of both tumors demonstrated lesions with a pattern of heterogeneous contrast enhancement and multifocal lesions in one cat. Routine cerebrospinal fluid analysis was normal in one cat and suggestive of an inflammatory disease in the other. Oligodendroglioma cells were seen in cytospin preparations of cerebrospinal fluid from both cats. In each cat, the tumors occurred intraventricularly in the midbrain and fourth ventricle with aggressive intraparenchymal infiltration. There was extensive growth into the basilar subarachnoid space of the midbrain and brain stem in one cat. One tumor was well differentiated, and the other was an anaplastic subtype. Immunostaining for several myelin- and oligodendroglia-specific antigens was negative with formalin-fixed tumors and with unfixed frozen samples from one cat. In both tumors, component cells of the intratumoral vascular proliferations were positive for human von Willebrand factor VIII antigen or smooth muscle actin. Immunocytochemical reactivity for glial fibrillary acidic protein identified both reactive astrocytes and a subpopulation of minigemistocytes in both tumors. Ultrastructurally, the tumor cells were unremarkable except for their prominent desmosomal junctions and paucity of microtubules. 相似文献
38.
Burgess K Moore A Rand W Cotter SM 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2000,14(4):456-462
A review of 60 cases of immune-mediated hemolytic anemia (IMHA) in the dog was performed in order to characterize the disease and to identify potential prognostic indicators. Dogs ranged in age from 1 to 13 years, with a mean age of 6.5 years. The 2 most commonly affected breeds were Cocker Spaniels and Labrador Retrievers. Fifty-two of the 60 dogs tested (87%) were autoagglutination positive and spherocytes were present in 45 (75%). Forty-one (89%) of 46 patients tested positive for the presence of immunoglobulin on the red blood cell surface (Coombs assay). The most common clinical signs at presentation were lethargy, weakness, pale mucous membranes, icterus, hemoglobinuria, and anorexia. PCV less than 25% was present in 59 (98%) dogs. At the time of presentation, 35 dogs (58%) had a nonregenerative anemia, whereas 25 patients (42%) had a regenerative response. Thrombocytopenia was seen in 41 (68%) dogs. Nine of 34 dogs (26%) had a prolonged prothrombin time, 19 of 34 (56%) had a prolonged activated partial thromboplastin clotting time, and 12 of 34 (35%) had abnormal fibrinogen concentrations. All dogs received prednisone at immunosuppressive doses (2.2-4.4 mg/kg PO as a single or divided dose every 24 hours) and cyclophosphamide as primary therapy. Forty-one dogs (63%) received cyclophosphamide at 50 mg/m2 q24h for 4 days, whereas 9 dogs (15%) received an initial high dose (200 mg/m2) followed by 3 days of a lower dose (50 mg/m2 q24h). No statistical difference in survival times was found for either protocol. Thirteen dogs were treated with azathioprine in addition to cyclophosphamide and prednisone. The median survival time of dogs that received all 3 drugs was 370 days as compared to 9 days for those dogs that were treated with cyclophosphamide and prednisone alone. Thirty-one (52%) dogs died from the disease, 13 (22%) dogs were alive, and 15 (25%) dogs were lost to follow-up. The median length of survival for all dogs was 21 days. Eight dogs that were discharged from the hospital suffered a relapse (PCV < 25%). 相似文献
39.