全文获取类型
收费全文 | 3557篇 |
免费 | 174篇 |
国内免费 | 3篇 |
专业分类
林业 | 235篇 |
农学 | 94篇 |
基础科学 | 27篇 |
631篇 | |
综合类 | 585篇 |
农作物 | 111篇 |
水产渔业 | 323篇 |
畜牧兽医 | 1439篇 |
园艺 | 101篇 |
植物保护 | 188篇 |
出版年
2023年 | 17篇 |
2022年 | 20篇 |
2021年 | 67篇 |
2020年 | 72篇 |
2019年 | 90篇 |
2018年 | 86篇 |
2017年 | 100篇 |
2016年 | 83篇 |
2015年 | 61篇 |
2014年 | 90篇 |
2013年 | 144篇 |
2012年 | 217篇 |
2011年 | 279篇 |
2010年 | 161篇 |
2009年 | 142篇 |
2008年 | 271篇 |
2007年 | 270篇 |
2006年 | 256篇 |
2005年 | 258篇 |
2004年 | 237篇 |
2003年 | 209篇 |
2002年 | 194篇 |
2001年 | 25篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 28篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 25篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1973年 | 5篇 |
1971年 | 2篇 |
1948年 | 4篇 |
1938年 | 2篇 |
1904年 | 2篇 |
排序方式: 共有3734条查询结果,搜索用时 31 毫秒
81.
Mark Sklansky Gregg Levine Dielle Havlis Nicole West Michael Renner Curtis Rimmerman Rae Stone 《Journal of zoo and wildlife medicine》2006,37(4):454-463
Safe and effective echocardiography would represent a valuable tool for marine mammal veterinarians and physiologists evaluating the dolphin heart. Unfortunately, conventional ultrasound technology (transthoracic echocardiography) has been limited by logistic, anatomic, and behavioral challenges. Five mature male Atlantic bottlenose dolphins (Tursiops truncatus) were trained for echocardiographic imaging (four for both transthoracic and transesophageal imaging, and one for only transthoracic imaging). It was noted that transesophageal image quality transiently improved when the dolphins spontaneously exhaled. Subsequently, dolphins were conditioned to hold their breath following forced exhalation, and imaging proceeded during such behavioral breath holds. Over 25 transthoracic and 100 transesophageal echocardiographic studies were performed, including both two-dimensional imaging and color flow mapping. Transthoracic imaging yielded poor-quality images of only small portions of the heart. In contrast, transesophageal imaging, which improved dramatically with behavioral breath holding following exhalation, yielded consistently high-quality images of the entire heart (mitral, tricuspid, aortic, and pulmonary valves, atrial and ventricular septa, left and right atria, left and right ventricles, and ascending aorta and main pulmonary artery). Color flow mapping demonstrated mild tricuspid regurgitation in all dolphins, and mild aortic regurgitation in one dolphin found to have a pedunculated mass arising from the sinutubular junction just above the aortic valve. There were no complications in nonsedated dolphins. The heart of the bottlenose dolphin can be safely, effectively, and reproducibly evaluated with the use of transesophageal echocardiography in conjunction with behavioral breath holding following forced exhalation. This approach, and the normative echocardiographic data generated from this work, lays the foundation for future echocardiographic studies of cetaceans. 相似文献
82.
A Rae Gandolf Mark G Papich Amy B Bringardner Mark W Atkinson 《Journal of zoo and wildlife medicine》2006,37(2):145-150
This study describes the pharmacokinetics of enrofloxacin following oral and i.v. administration to goral (Nemorrhaedus goral arnouxianus). The objective of this study was to expand upon current antimicrobial treatment options available for use in goral by measuring plasma concentrations and examining the pharmacokinetics of enrofloxacin in these animals. Two single-dose treatments of enrofloxacin were administered to four goral in a crossover design. Single-dose treatments consisted of administration of injectable enrofloxacin i.v. (5 mg/kg) and enrofloxacin tablets (136 mg chewable tablets) dissolved in a grain slurry and administered p.o. (10 mg/kg). Plasma levels of enrofloxacin and its metabolite ciprofloxacin were measured with the use of high-performance liquid chromatography with UV detection. Plasma volume of distribution for i.v. enrofloxacin was 2.15 - 1.01 L/kg, with a mean elimination half-life of 13.3 hr and total body clearance of 0.19+/-0.14 L/kg/hr. The maximum plasma concentration measured for oral enrofloxacin was 2.77 microg/ml, with a mean half-life of 5.2 hr and systemic availability of 14.6%. The area under the plasma concentration over time curve (AUC) for oral enrofloxacin was 21.06 microg/hr/ml. The area under the plasma concentration over time curve generated for oral enrofloxacin in goral yields an area under the plasma concentration over time curve to minimum inhibitory concentration ratio > 100 for many gram-positive and gram-negative bacterial pathogens common to small ruminants. Based on these results, oral enrofloxacin may be considered for further study as a treatment option for susceptible infections in goral. 相似文献
83.
Christine V Fiorello Mark W Cunningham Shauna L Cantwell Julie K Levy Erin M Neer Kenneth Conley Paul M Rist 《Journal of zoo and wildlife medicine》2007,38(2):317-322
A free-ranging, adult male Florida panther (Puma concolor coryi) was immobilized and evaluated for hematuria following routine capture. Prior to anesthetic recovery, the panther was fitted with a telemetry collar. After an initially quiet recovery, the panther began thrashing in the transport cage, and was again immobilized. Pink foam was evident from the nostrils, and crackles were ausculted over the chest, indicating pulmonary edema. Postobstructive pulmonary edema was diagnosed based on history, clinical signs, radiographic evaluation, and blood gas analysis. The animal was treated intensively for several hours with diuretics, oxygen, and manual ventilation. The panther responded rapidly to therapy and was released back into the wild 48 hr after presentation. Postobstructive pulmonary edema, also called negative-pressure pulmonary edema, may be underrecognized in veterinary medicine. In this case, the telemetry collar, in conjunction with anesthetic recovery in a small transport crate, may have contributed to tracheal obstruction. Wildlife veterinarians and biologists should be aware of the risk of airway obstruction when placing tracking collars, and animals should be continuously monitored during anesthetic recovery to ensure the presence of a patent airway. 相似文献
84.
85.
A juvenile cheetah (Acinonyx jubatus) died with rapidly progressive pyrexia, tachypnea, abdominal effusion, and hepatomegaly. Postmortem examination revealed lesions consistent with acute disseminated infection with Toxoplasma gondii. The presence of this organism was confirmed in multiple organs by immunohistochemistry and polymerase chain reaction. To the best of our knowledge, we propose this to be the first reported case of primary acute disseminated toxoplasmosis in a cheetah. 相似文献
86.
Otmar Spring Mark Bachofer Marco Thines Alexandra Riethmüller Markus Göker Franz Oberwinkler 《European journal of plant pathology / European Foundation for Plant Pathology》2006,114(3):309-315
Sequence parts of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA were analysed to screen for the intraspecific
variability of a non-coding genomic region in 15 Plasmopara halstedii populations of different pathotype and geographic origin. Samples revealed uniformity in a ca. 790 Bp fragment comprising
of the ITS-1, 5.8S and front parts of the ITS-2. In contrast, clear differences were found in a ca. 810 Bp fragment of the
ITS-2 thus allowing differentiation between populations of pathotype 100, 310 and 330 and a group of populations representing
pathotypes 700, 701, 703, 710 and 730. Samples of pathotypes 700 to730 originated from Slovakia, France, and Germany, but
were uniform in both ITS sequence parts, thus indicating very recent origin of these highly aggressive physiological races.
The potential use of ITS sequences for pathotype differentiation and phylogenetic studies in P. halstedii is discussed. 相似文献
87.
Anne E. Desjardins Mark Busman Michael Muhitch Robert H. Proctor 《Physiological and Molecular Plant Pathology》2007,70(4-6):149-160
Zea mays often is colonized with the fungus Gibberella moniliformis, which produces fumonisin toxins. The role of fumonisins in seedling colonization and blight was studied using complementary genetic analyses of host and pathogen. Only one of two fumonisin B1 (FB1)-insensitive maize backcross lines was more resistant than the FB1-sensitive parent to seedling blight, indicating that the increase in FB1-insensitivity was not associated with an increase in resistance. FB1-producing and nonproducing isogenic fungal strains did not differ in ability to cause seedling blight, but the FB1-producing strain was more effective in systemic colonization of seedlings in reciprocal strain challenge tests. Together, these and previous results indicate that the role of fumonisins depends on complex environmental and genetic contexts in this host–pathogen interaction. 相似文献
88.
Philipp B. Gannibal Sonja S. Klemsdal Mark M. Levitin 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(2):175-182
Alternaria tenuissima is a common pathogen on a number of plants described in several geographic regions of the world. Genetic variation within
and between Russian Far East, North West and Caucasus populations of A. tenuissima from wheat was examined. In addition, genetic differences between isolates from various hosts were estimated. In total, 101
isolates of A. tenuissima were studied using amplified fragment length polymorphism (AFLP) with four primer combinations. Wright’s fixation index (F
st), gene flow (N
m) and gene diversity (H
s) were calculated. AFLP banding patterns indicated significant genetic distance and at the same time a low level of gene flow
between the Far East and the two other groups of isolates originating from the European part of country. The degree of similarity
between the North West and Caucasus populations was very high, as was the migration rate. Isolates analysed by UPGMA-based
cluster analysis were grouped according to location of origin but irrespective of plant host. Based on the F
st value, the group of isolates originating from wheat and barley were not found to differ significantly from each other. 相似文献
89.
Lia W. Liefting Anna C. Padovan Karen S. Gibb Ross E. Beever Mark T. Andersen Richard D. Newcomb David L. Beck Richard L.S. Forster 《European journal of plant pathology / European Foundation for Plant Pathology》1998,104(6):619-623
Sequence comparisons and phylogenetic analysis of the 16S rRNA genes and the 16S/23S spacer regions of the phytoplasmas associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases revealed minimal nucleotide differences between them resulting in the formation of a monophyletic group. Therefore, along with Australian grapevine yellows, the phytoplasmas associated with Phormium yellow leaf and papaya dieback should also be considered as Candidatus Phytoplasma australiense. 相似文献
90.
- 1. Three classes of habitat used by groups of fish species classified as conservation and management priorities were developed for the Gerua River (also known as the Girwa River, Karnali River) in the Ganges river basin. This river is large (mean annual discharge ca 1500 m3 s?1, up to 900 m wide), surrounded by protected lands of India and Nepal, and upstream of major diversions and river alterations.
- 2. Fish and habitat sampling was conducted at 45 sites from 2000 to 2003. Data were analysed for 2172 fish of 14 species. Species and life stages found occupying a statistically distinct subset of the river habitats were grouped to identify classes of river habitat for conservation.
- 3. Most species and life‐stage groups specialized on specific habitat conditions revealed by multivariate analyses of variance and a principal component analysis. The most numerous and diverse group (six species, 15 life stages) was associated with deep depositional habitats with sandy substrate. Two species covering three life stages were primarily oriented to erosional habitat marked by fast current velocity with pebble and cobble substrate. A third group of three species of adults and juveniles were intermediate in habitat use.
- 4. River conservation for fish faunas should maintain both erosional and depositional channel habitats with depths, substrates, and current velocity inclusive of the ranges reported. The erosional and depositional nature of the key habitats requires that rivers be maintained with flows capable of channel‐forming functions.