全文获取类型
收费全文 | 1765篇 |
免费 | 76篇 |
专业分类
林业 | 59篇 |
农学 | 34篇 |
基础科学 | 25篇 |
253篇 | |
综合类 | 440篇 |
农作物 | 82篇 |
水产渔业 | 58篇 |
畜牧兽医 | 740篇 |
园艺 | 43篇 |
植物保护 | 107篇 |
出版年
2021年 | 9篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 37篇 |
2016年 | 42篇 |
2015年 | 29篇 |
2014年 | 31篇 |
2013年 | 63篇 |
2012年 | 91篇 |
2011年 | 114篇 |
2010年 | 46篇 |
2009年 | 38篇 |
2008年 | 105篇 |
2007年 | 101篇 |
2006年 | 135篇 |
2005年 | 118篇 |
2004年 | 107篇 |
2003年 | 121篇 |
2002年 | 105篇 |
2001年 | 25篇 |
2000年 | 24篇 |
1999年 | 27篇 |
1998年 | 10篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 19篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1975年 | 13篇 |
1974年 | 20篇 |
1973年 | 14篇 |
1972年 | 22篇 |
1970年 | 6篇 |
1969年 | 10篇 |
1965年 | 8篇 |
排序方式: 共有1841条查询结果,搜索用时 31 毫秒
41.
Grossinger Robin M. Striplen Charles J. Askevold Ruth A. Brewster Elise Beller Erin E. 《Landscape Ecology》2007,22(1):103-120
Historical records provide information to land managers and landscape ecologists attempting to understand current trajectories in altered landscapes. In this study, we synthesized a heterogeneous array of historical sources to reconstruct historical land cover in California’s Santa Clara Valley (a.k.a. “Silicon Valley”). To increase and assess accuracy, we used the triangulation of overlapping, independent data sources and the application of certainty level standards. The region has been subject to extensive urbanization, so we also evaluated the applicability of historical landscape reconstructions to the altered landscape. We found evidence for five major land cover types prior to significant Euro–American modification. Valley freshwater marsh, wet meadow, alkali meadow, willow grove, and valley oak savanna have all experienced extreme decline (85–100%) since Euro–American settlement. However, comparison of historical land cover patterns to contemporary land use suggested several new strategies for environmental recovery, despite the limitations of surrounding urbanization. We also observed a temporal shift in riparian habitat along the mainstem of Coyote Creek, from a relatively open mixture of riparian scrub, sycamore woodland, and unvegetated gravel bars to dense riparian forest, likely resulting from stream flow regulation. By identifying former land cover patterns we provide a basis for evaluating local landscape change and setting restoration targets, including the identification of residual features and under-recognized land cover types. These findings suggest that reliable historical landscape reconstructions can be developed in the absence of standardized historical data sources and can be of value even in highly modified regions. 相似文献
42.
43.
Phase II Clinical Trial of Carboplatin in Canine Transitional Cell Carcinoma of the Urinary Bladder 总被引:4,自引:3,他引:1
Ruthanne Chun Deborah W. Knapp William R. Widmer Dennis B. DelNicola Nita W. Glickman Thomas Kuczek Amalia Degortari Connie M. Han 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1997,11(5):279-283
Fourteen dogs with histologically-confirmed transitional cell carcinoma (TCC) of the urinary bladder were treated with 300 mg/m2 carboplatin every 3 weeks. Response to therapy was assessed with abdominal radiography, double contrast cystography, urinary bladder ultrasonography and thoracic radiography before therapy and at 6–week intervals during therapy. Dogs were monitored for hematologic toxicity with a CBC and platelet count performed immediately before and 10 to 14 days after carboplatin treatment. Tumor responses included progressive disease in 11 dogs and stable disease in 1 dog. Two dogs were euthanized due to carboplatin toxicity before assessment of tumor response. Toxicity included thrombocytopenia with or without neutropenia in 7 dogs and gastrointestinal toxicity in 6 dogs. Carboplatin therapy was not beneficial in the treatment of TCC in the 14 dogs in this study. 相似文献
44.
In a growth chamber experiment, 70-day-old seedlings of 10 conifer species were inoculated with Colletotrichum gloeosporioides conidia to determine the host range of the fungus. Based on the percentage of seedlings affected and the disease severity on individual seedlings, the order of most to least susceptibility was: western hemlock (WH), mountain hemlock, western larch, Sitka spruce, Engelmann spruce, Douglas-fir (coastal form, then interior form), white spruce and ponderosa pine; lodgepole pine and western red cedar remained unaffected. Inoculation of WH needles showed that within 24 h C. gloeosporioides conidia germinate and appressoria (penetration structures) form. A growth chamber study demonstrated that the pathogen can infect WH at needle wetness periods as short as 15 min; number of needles affected was higher at 0.5 h, but did not increase further even when wetness was extended up to 8 h. The results are discussed in relation to blight management of greenhouse-grown conifer seedlings.Portion of a Bachelor of Science (Honors) thesis, Department of Biology, University of Victoria, Victoria, British Columbia. 相似文献
45.
Stephen J. Adolphson Michael L. Dunn Sarah Nielsen‐Barrows Dennis L. Eggett Frost M. Steele 《Cereal Chemistry》2016,93(5):508-512
Many Mexican women are deficient in folic acid. Fortification of the corn tortilla could be an effective way to help increase the folic acid levels among the Mexican population. Previous studies have shown significant folic acid losses in the masa dough as it is held before baking. This loss in folic acid could be owing to utilization by lactic acid bacteria naturally present in the masa. The objective of this study was to determine the effect of bacteria native to corn masa on the folic acid content in masa. Bacteria in dough samples from six mills in Guadalajara, Mexico, were isolated and identified. Bacterial isolates were inoculated into sterile fortified corn masa flour, which was converted to masa and held at 56°C for 0, 3, and 6 h, replicating the conditions of freshly milled masa as held before baking. All samples, including the control, showed losses of folic acid between 66 and 79% w/w in the first 3 h of incubation. Because folic acid degradation in the sterile control sample was not different than the inoculated sample results, the decline in folic acid was not owing to bacteria (mainly Streptococcus spp.) present in the masa flour but appeared to be a chemical degradation related to time and temperature. 相似文献
46.
Paige E. Axelrood Melody Neumann David Trotter Reed Radley Gwen Shrimpton John Dennis 《New Forests》1995,9(1):35-51
Twelve Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlots from coastal British Columbia were assayed for seedborne Fusarium. All of the seedlots were contaminated with Fusarium. Percent of nonstratified seeds from individual seedlots harboring Fusarium ranged from 0.3% to 95.4%. Sixty-seven percent of the seedlots had Fusarium on less than 2% of the seeds. Post-stratification seedborne Fusarium levels were significantly less for running water imbibition compared to standing water imbibition. However, seedling growth at a container nursery was not consistently different for stratified seed imbibed initially in standing or running water. Fusarium disease symptoms were not observed in the nursery environment. The species of Fusarium isolated from seed were F. acuminatum, F. avenaceum, F. lateritium, F. moniliforme, F. oxysporum, F. poae and F. sambucinum. Twelve Fusarium isolates, comprising six species, were assessed for pathogenicity. Disease symptoms were observed after four weeks incubation and Fusarium isolates ranged in virulence from low to high. Fusarium oxysporum isolates were the most pathogenic. 相似文献
47.
A VALENTINE‐SHAPED CARDIAC SILHOUETTE IN FELINE THORACIC RADIOGRAPHS IS PRIMARILY DUE TO LEFT ATRIAL ENLARGEMENT 下载免费PDF全文
Trisha J. Oura Aisha N. Young Bruce W. Keene Ian D. Robertson Dennis E. Jennings Donald E. Thrall 《Veterinary radiology & ultrasound》2015,56(3):245-250
Conflicting information has been published regarding the cause of a valentine‐shaped cardiac silhouette in dorsoventral or ventrodorsal thoracic radiographs in cats. The purpose of this retrospective, cross‐sectional study was to test the hypothesis that the valentine shape is primarily due to left atrial enlargement. Images for cats with a radiographic valentine‐shaped cardiac silhouette and full echocardiography examination were retrieved and independently reviewed. A subjective scoring system was used to record severity of radiographic valentine shape. Subjective radiographic evidence of left atrial enlargement in a radiographic lateral projection and a final diagnosis based on medical records were also recorded. A total of 81 cats met inclusion criteria. There was a strong positive correlation (P < 0.001) between echocardiographic left atrial size and severity of radiographic valentine shape. There was no effect of echocardiographic right atrial size on the severity of valentine shape, except when concurrent with severe left atrial enlargement. In this situation, right atrial enlargement increased the likelihood of observing a severe valentine shape. There was no effect of right atrial enlargement on the shape of the cardiac silhouette when left atrial enlargement was absent or only mild to moderate. There was no correlation between the category of final diagnosis of cardiac disease and the severity of valentine shape. Findings from this study supported the hypothesis that a valentine‐shaped cardiac silhouette in radiographs is due primarily to left atrial enlargement in cats, with right atrial enlargement only impacting the shape if concurrent with severe left atrial enlargement. 相似文献
48.
Cecilia Rohdin Douglas Gilliam Caroline A. O’Leary Dennis P. O’Brien Joan R. Coates Gary S. Johnson Karin Hultin J?derlund 《Acta veterinaria Scandinavica》2015,57(1)
Background
Hereditary ataxias with similar phenotypes were reported in the Smooth-Haired Fox Terrier, the Jack Russell Terrier and the Parson Russell Terrier. However, segregation analyses showed differing inheritance modes in these breeds. Recently, molecular genetic studies on the Russell group of terriers found independent mutations in KCNJ10 and CAPN1, each associated with a specific clinical subtype of inherited ataxia. The aim of this study was to clarify whether or not Smooth-Haired Fox Terriers with hereditary ataxia and dogs of other related breeds harbor either of the same mutations. A sub goal was to update the results of KCNJ10 genotyping in Russell group terriers.Findings
Three Smooth-Haired Fox Terriers with hereditary ataxia and two Toy Fox Terriers with a similar phenotype were all homozygous for the KCNJ10 mutation. The same mutation was also found in a heterozygous state in clinically unaffected Tenterfield Terriers (n = 5) and, in agreement with previous studies, in Jack Russell Terriers, Parson Russell Terriers, and Russell Terriers.Conclusions
A KCNJ10 mutation, previously associated with an autosomal recessive spinocerebellar ataxia in Jack Russell Terriers, Parson Russell Terriers, and Russell Terriers segregates in at least three more breeds descended from British hunting terriers. Ataxic members of two of these breeds, the Smooth-Haired Fox Terrier and the Toy Fox Terrier, were homozygous for the mutation, strengthening the likelihood that this genetic defect is indeed the causative mutation for the disease known as “hereditary ataxia” in Fox Terriers and “spinocerebellar ataxia with myokymia, seizures or both” in the Russell group of terriers. 相似文献49.
50.
Csizmadi I Kahle L Ullman R Dawe U Zimmerman TP Friedenreich CM Bryant H Subar AF 《Public health nutrition》2007,10(1):88-96
BACKGROUND AND OBJECTIVE: Despite assumed similarities in Canadian and US dietary habits, some differences in food availability and nutrient fortification exist. Food-frequency questionnaires designed for the USA may therefore not provide the most accurate estimates of dietary intake in Canadian populations. Hence, we undertook to evaluate and modify the National Cancer Institute's Diet History Questionnaire (DHQ) and nutrient database. METHODS: Of the foods queried on the DHQ, those most likely to differ in nutrient composition were identified. Where possible these foods were matched to comparable foods in the Canadian Nutrient File. Nutrient values were examined and modified to reflect the Canadian content of minerals (calcium, iron, zinc) and vitamins (A, C, D, thiamin, riboflavin, niacin, B6, folate and B12). DHQs completed by 13 181 Alberta Cohort Study participants aged 35-69 years were analysed to estimate nutrient intakes using the original US and modified versions of the DHQ databases. Misclassification of intake for meeting the Dietary Reference Intake (DRI) was determined following analysis with the US nutrient database. RESULTS: Twenty-five per cent of 2411 foods deemed most likely to differ in nutrient profile were subsequently modified for folate, 11% for vitamin D, 10% for calcium and riboflavin, and between 7 and 10% for the remaining nutrients of interest. Misclassification with respect to meeting the DRI varied but was highest for folate (7%) and vitamin A (7%) among men, and for vitamin D (7%) among women over 50 years of age. CONCLUSIOn: Errors in nutrient intake estimates owing to differences in food fortification between the USA and Canada can be reduced in Canadian populations by using nutrient databases that reflect Canadian fortification practices. 相似文献