全文获取类型
收费全文 | 823篇 |
免费 | 64篇 |
专业分类
林业 | 28篇 |
农学 | 14篇 |
基础科学 | 2篇 |
88篇 | |
综合类 | 94篇 |
农作物 | 28篇 |
水产渔业 | 32篇 |
畜牧兽医 | 546篇 |
园艺 | 31篇 |
植物保护 | 24篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 28篇 |
2019年 | 43篇 |
2018年 | 27篇 |
2017年 | 32篇 |
2016年 | 29篇 |
2015年 | 21篇 |
2014年 | 32篇 |
2013年 | 37篇 |
2012年 | 68篇 |
2011年 | 77篇 |
2010年 | 42篇 |
2009年 | 25篇 |
2008年 | 67篇 |
2007年 | 54篇 |
2006年 | 46篇 |
2005年 | 30篇 |
2004年 | 43篇 |
2003年 | 39篇 |
2002年 | 39篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1974年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有887条查询结果,搜索用时 15 毫秒
821.
Amy J. Alwood DVM Benjamin M. Brainard VMD Elizabeth LaFond DVM DACVS Kenneth J. Drobatz DVM MCSE DACVECC DACVIM Lesley G. King MVB DACVECC DACVIM 《Journal of Veterinary Emergency and Critical Care》2006,16(3):176-183
Objective: To determine the frequency of postoperative pulmonary complications (PPCs) in dogs following laparotomy, characterize the nature of PPCs, and identify disease‐related risk factors for PPCs in dogs. Design: Retrospective clinical study. Setting: University‐affiliated small animal teaching hospital. Animals: One hundred and sixty‐two dogs without preoperative pulmonary pathology that underwent laparotomy surgery. Interventions: None. Measurements and main results: Cases were evaluated for factors including patient signalment, preexisting disease, primary and ancillary surgical procedure(s), development of postoperative pulmonary disease, characteristics of perioperative hospitalization and therapy, and survival. Twenty‐two percent of dogs in the study developed PPCs. PPCs included respiratory arrest (n=4), acute respiratory distress syndrome (ARDS) (n=3), pneumonia (n=8), hypoventilation (n=13), and transient hypoxemia (n=8). Dogs that developed PPCs had a significantly longer duration of oxygen therapy, longer duration of stay in intensive care unit (ICU), and decreased survival. Dogs with perioperative vomiting or regurgitation were more likely to develop PPCs. Animals that underwent exploratory laparotomy for biliary or septic peritonitis were also more likely to develop PPCs. Conclusions: PPCs occur in dogs following laparotomy and contribute significantly to the morbidity and mortality of these surgical patients. In this patient population, animals with vomiting, regurgitation, or peritonitis may be at a higher risk of developing PPCs. Animals with the identified risk factors should be monitored carefully postoperatively for development of pulmonary complications. 相似文献
822.
The mucosal margin of the urethra is best assessed by positive contrast urethrography, but ultrasonography offers complementary information such as urethral wall thickness and size of medial iliac lymph nodes. Ultrasonography of the urethra is quick, noninvasive and does not require sedation or general anesthesia. In patients with complete urethral obstruction, ultrasonography may be the only way to image the urethra. Twelve dogs which were presented to Tufts University School of Veterinary Medicine with clinical signs referable to the urinary bladder, urethra or vagina were examined ultrasonographically. Seven were neutered females and five were neutered males. Each dog had a hyperechoic, nonshadowing line at the epithelial surface of the proximal urethra. In the seven female patients and one of the males, the urethral wall was also thick and hypoechoic to surrounding tissue. In the other males, the urethral epithelial changes were at the level of the prostate, and the limits of the urethra were not visible. In six dogs, the urethral change was the only abnormality seen, while in six, bladder wall, bladder luminal and/or prostatic parenchymal changes were also detected. Three patients had hydronephrosis, and one had enlarged medial iliac lyumph nodes. Biopsies were obtained via suction with urinary catheterization (n = 6), exploratory celiotomy (n = 3), urethroscopy (n = 2), or at post-mortem (n = 1). A histopathologic diagnosis of urethral transitional cell carcinoma was obtained in ten dogs. The ultrasonographic appearance was not pathognomonic for transitional cell carcinoma, as one dog with transitional cell dysplasia and one dog with severe ulcerative and necrosupperative cystitis and urethral stricture had similar findings. 相似文献
823.
Madagascar ranks as one of the world’s top extinction hotspots because of its high endemism and high rate of habitat degradation. Global climate phenomena such as El Niño Southern Oscillations may have confounding impacts on the island’s threatened biota but these effects are less well known. We performed a demographic study of Propithecus edwardsi, a lemur inhabiting the eastern rainforest of Madagascar, to evaluate the impact of deforestation, hunting, and El Niño on its population and to re-evaluate present endangerment categorization under the IUCN. Over 18 years of demographic data, including survival and fecundity rates were used to parameterize a stochastic population model structured with three stage classes (yearlings, juveniles, and adults). Results demonstrate that hunting and deforestation are the most significant threats to the population. Analysis of several plausible scenarios and combinations of threat revealed that a 50% population decline within three generations was very likely, supporting current IUCN classification. However, the analysis also suggested that changing global cycles may pose further threat. The average fecundity of lemurs was over 65% lower during El Niño years. While not as severe as deforestation or hunting, if El Niño events remain at the current high frequency there may be negative consequences for the population. We suggest that it is most critical for this species continued survival to create more protected areas, not only to thwart hunting and deforestation, but also to give this endangered lemur a better chance to recover from and adapt to altered climate cycles in the future. 相似文献
824.
Moskun AC Jailaubekov AE Bradforth SE Tao G Stratt RM 《Science (New York, N.Y.)》2006,311(5769):1907-1911
Highly energized molecules normally are rapidly equilibrated by a solvent; this finding is central to the conventional (linear-response) view of how chemical reactions occur in solution. However, when a reaction initiated by 33-femtosecond deep ultraviolet laser pulses is used to eject highly rotationally excited diatomic molecules into alcohols and water, rotational coherence persists for many rotational periods despite the solvent. Molecular dynamics simulations trace this slow development of molecular-scale friction to a clearly identifiable molecular event: an abrupt liquid-structure change triggered by the rapid rotation. This example shows that molecular relaxation can sometimes switch from linear to nonlinear response. 相似文献
825.
CO/FT regulatory module controls timing of flowering and seasonal growth cessation in trees 总被引:5,自引:0,他引:5
Böhlenius H Huang T Charbonnel-Campaa L Brunner AM Jansson S Strauss SH Nilsson O 《Science (New York, N.Y.)》2006,312(5776):1040-1043
Forest trees display a perennial growth behavior characterized by a multiple-year delay in flowering and, in temperate regions, an annual cycling between growth and dormancy. We show here that the CO/FT regulatory module, which controls flowering time in response to variations in daylength in annual plants, controls flowering in aspen trees. Unexpectedly, however, it also controls the short-day-induced growth cessation and bud set occurring in the fall. This regulatory mechanism can explain the ecogenetic variation in a highly adaptive trait: the critical daylength for growth cessation displayed by aspen trees sampled across a latitudinal gradient spanning northern Europe. 相似文献
826.
Canine conjunctival tumors of vascular endothelial origin are common, although under-reported. The purpose of this study was to evaluate the epidemiology of and potential risk factors for these tumors. This study evaluated 108 cases (70 hemangiomas, 38 hemangiosarcomas) from 8300 canine submissions between 1989 and 2004. Signalment, location, pigmentation, size, duration, diagnosis, margins, ancillary therapy, and geographic location were recorded. Follow-up information was available for 49 cases. Each case was matched with two unaffected controls and compared using logistic regression analysis. Average age upon presentation was 8.6 years; there was no sex predilection. Risk of conjunctival tumors was statistically different among breed groups (P = 0.0010), demonstrating a propensity to occur in groups likely to have increased outdoor activity. Primary involvement occurred within nonpigmented epithelium along the leading edge of the nictitating membrane (41/108) and temporal bulbar conjunctiva (33/108). The etiology remains unknown; however, the strong site predilection, involvement of nonpigmented epithelium, and development within specific breed classes strongly suggest ultraviolet (UV) light as a significant risk factor. In a full-logistic model including breed, gender, age, and UV exposure, UV was not a statistically significant variable (P = 0.1215). In a reduced-model including UV only, significance was approached (P = 0.0696) and posthoc contrast demonstrated a significant linear trend with increasing UV exposure (P = 0.0147). In separate analysis of risks associated with hemangiosarcoma, compared with hemangioma, breed was not significant while increasing UV exposure was significant (P = 0.0381). Early surgical therapy is recommended and may be curative; however, recurrence is possible and more likely with hemangiosarcomas (11/20). 相似文献
827.
Ethan Deyle Amy M Schueller Hao Ye Gerald M Pao George Sugihara 《Fish and Fisheries》2018,19(5):769-781
Gulf (Brevoortia patronus, Clupeidae) and Atlantic menhaden (Brevoortia tyrannus, Clupeidae) support large fisheries that have shown substantial variability over several decades, in part, due to dependence on annual recruitment. Nevertheless, traditional stock–recruitment relationships lack predictive power for these stocks. Current management of Atlantic menhaden explicitly treats recruitment as a random process. However, traditional methods for understanding recruitment variability carry the very specific hypothesis that the effect of adult biomass on subsequent recruitment occurs independently of other ecosystem factors such as food availability and predation. Here, we evaluate the predictability of menhaden recruitment using a model‐free approach that is not restricted by these strong assumptions. We find that menhaden recruitment is predictable, but only when allowing for interdependence of stock with other ecological factors. Moreover, while the analysis confirms the presence of environmental effects, the environment alone does not readily account for the complexity of menhaden recruitment dynamics. The findings set the stage for revisiting recruitment prediction in management and serve as an instructive example in the ongoing debate about how to best treat and understand recruitment variability across species and fisheries. 相似文献
828.
Jennifer Porter David Conner Jane Kolodinsky Amy Trubek 《Agriculture and Human Values》2017,34(4):921-932
The Real Food Challenge is a national student movement in the United States (U.S.) that aims to shift $1 billion—roughly 20%—of college and university food budgets across the country towards local, ecologically sound, fair, and humane food sources—what they call “real” food—by 2020. The University of Vermont (UVM) was the fifth university in the U.S. to sign the Real Food Campus Commitment, pledging to shift at least 20% of its own food budget towards “real” food by 2020. In order to examine student preference for “real” food on the UVM campus, we analyzed a survey of 904 undergraduate students that used contingent valuation to evaluate students’ willingness-to-pay (WTP) for the “real” attribute. We found that a majority of students are willing to pay a positive premium for “real” food. Furthermore, we found that student characteristics and attitudes significantly influence WTP. Specifically, gender, residency, college, and attitudes about price and origin of food are significant predictors of WTP. 相似文献
829.
IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING FEATURES OF A MULTIFOCAL OLIGODENDROGLIOMA IN THE SPINAL CORD AND BRAIN OF A DOG
下载免费PDF全文
![点击此处可从《Veterinary radiology & ultrasound》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Amy E. Schkeeper Rachel Moon Stephanie Shrader Jey W. Koehler Daniel Linden Amanda R. Taylor 《Veterinary radiology & ultrasound》2017,58(5):E49-E54
An 8‐year‐old neutered male Toy Poodle was presented with chronic, progressive tetraparesis, and possible seizures. Magnetic resonance images demonstrated an extensive, T1 and T2 hyperintense contrast enhancing mass in the cervical spinal cord. Three nodules were present on the surface of the thalamus, with enhancement most evident on delayed images. A diagnosis of high‐grade oligodendroglioma was confirmed with postmortem histopathology and immunohistochemical labeling. Oligodendroglioma should be considered as a differential for T1 hyperintense intraaxial or intramedullary lesions with contrast enhancement. If enhancement is not visualized on postcontrast images, delayed images may be beneficial. 相似文献
830.
IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING FINDINGS IN A CAT WITH SYSTEMIC REACTIVE ANGIOENDOTHELIOMATOSIS
下载免费PDF全文
![点击此处可从《Veterinary radiology & ultrasound》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A 10‐year‐old, castrated male domestic short‐haired cat was presented with an acute history of seizures, lethargy, anorexia, vomiting, and dyspnea. Magnetic resonance imaging of the brain showed multifocal areas of gray matter T2‐weighted hyperintensity. The lesions did not enhance with intravenous contrast. The cat was diagnosed at necropsy with feline systemic reactive angioendotheliomatosis, a rare vascular proliferative disorder for which a treatment has not yet been identified. This report is the first to describe associated magnetic resonance imaging changes for this disease. 相似文献