全文获取类型
收费全文 | 35750篇 |
免费 | 1505篇 |
国内免费 | 16篇 |
专业分类
林业 | 1542篇 |
农学 | 1096篇 |
基础科学 | 224篇 |
5861篇 | |
综合类 | 4661篇 |
农作物 | 1410篇 |
水产渔业 | 1506篇 |
畜牧兽医 | 18283篇 |
园艺 | 495篇 |
植物保护 | 2193篇 |
出版年
2021年 | 315篇 |
2020年 | 373篇 |
2019年 | 465篇 |
2018年 | 698篇 |
2017年 | 785篇 |
2016年 | 690篇 |
2015年 | 454篇 |
2014年 | 696篇 |
2013年 | 1920篇 |
2012年 | 1165篇 |
2011年 | 1490篇 |
2010年 | 1050篇 |
2009年 | 961篇 |
2008年 | 1412篇 |
2007年 | 1383篇 |
2006年 | 1233篇 |
2005年 | 1059篇 |
2004年 | 1028篇 |
2003年 | 939篇 |
2002年 | 886篇 |
2001年 | 820篇 |
2000年 | 811篇 |
1999年 | 628篇 |
1998年 | 309篇 |
1997年 | 275篇 |
1995年 | 313篇 |
1992年 | 434篇 |
1991年 | 451篇 |
1990年 | 470篇 |
1989年 | 479篇 |
1988年 | 381篇 |
1987年 | 379篇 |
1986年 | 403篇 |
1985年 | 375篇 |
1984年 | 353篇 |
1983年 | 337篇 |
1979年 | 494篇 |
1978年 | 346篇 |
1977年 | 387篇 |
1976年 | 479篇 |
1975年 | 494篇 |
1974年 | 538篇 |
1973年 | 496篇 |
1972年 | 452篇 |
1971年 | 360篇 |
1970年 | 381篇 |
1969年 | 438篇 |
1968年 | 451篇 |
1967年 | 454篇 |
1966年 | 447篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Assessing the potential impacts of alternative landscape designs on amphibian population dynamics 总被引:2,自引:1,他引:2
An individual-based, spatially explicit population model was used to predict the consequences of future land-use alternatives for populations of four amphibian species in two central Iowa (midwest USA) agricultural watersheds. The model included both breeding and upland habitat and incorporated effects of climatic variation and demographic stochasticity. Data requirements of the model include life history characteristics, dispersal behavior, habitat affinities, as well as land use and landcover in geographic information systems databases. Future scenarios were ranked according to change in breeder abundance, saturation, and distribution, compared to baseline conditions. Sensitivity of simulation results to changes in model parameters was also examined. Simulated results suggest that while all four species modeled are likely to persist under present and future scenario conditions, two may be more at risk from future landscape change. Although the study species are all widespread generalists regarded as having a low conservation priority, they depend on wetlands and ponds, increasingly endangered habitats in agricultural landscapes. Broader conservation strategies in the region would ensure that these currently common organisms do not become the endangered species of the future.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
102.
We describe the classification of landscapes characterised bymineral soil using a model that calculates soil moisture availability on amonthly basis. Scotland is used as a case study area. The model uses potentialsoil moisture deficit, estimated using broad scale (40 × 40 km)climate patterns, in conjunction with meteorological station measurements toobtain finer scale values of climatic soil moisture deficit. Point estimates ofsoil available water are obtained for soil characteristics using appropriatepedotransfer functions, and geostatistical techniques are used to upscale theresults and interpolate to a 1-km grid. Known heterogeneityin soil physical characteristics is used to provide local corrections to thepotential soil moisture deficit, estimated using the climatic variables above.Temporal profiles of monthly water content are modelled for each1-km location and classified into six classes usingunsupervised cluster analysis. The spatial distribution of these classesreflects regional variations in the availability of moisture and energy, onwhich finer-grained topographic patterns are superimposed. In the case study,the broad scale spatial heterogeneity of heathlands and grasslands on mineralsoils in Scotland is shown to be strongly related to the soil moistureclassification. The results can be used in studies investigating the patternsofdistribution of communities at the landscape and regional scale.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
103.
104.
105.
Prof. Dr. Peter Lüdders 《Erwerbs-Obstbau》2004,46(4-5):117-122
The carambola (Averrhoa carambola L., family Oxalidaceae) is believed to have originated in Sri Lanka and the Moluccas but it has been cultivated in southeast Asia and Malaysia for many centuries. The evergreen tree is slow-growing, has a rounded crown and reaches 6 to 9 m in height. The 5- to 6-angled fruits (6 to 15 cm long and up to 9 cm wide) have thin, waxy, orange-yellow skin and juicy, yellow flesh. The fruit has a more or less pronounced oxalic acid odor and the flavor ranges from very sour to middle sweetish. The carambola is a tropical and subtropical tree, it can tolerate freezing temperature (?2°C) for short periods and sustain little damage. Trees can be propagated by seed, grafting, budding, and air layering. Tissue culture propagation has met only limited success. Plant spacing varies with growing region and cultural practices. Tree training is practiced intensively in different countries. Harvest timing and postharvest handling are critical to successful marketing of fresh fruit. Carambola is a nonclimateric fruit. Growers carefully harvest fruit by hand at color break — light green fruit with yellow color. The storage conditions should be 5 to 10°C and 85 to 95% relative humidity. Most carambola fruit is eaten fresh, used in salads, desserts, and cooked as star-shaped slices; fruit can also be dried, canned and frozen. The leaves have been eaten as a substitute for sorrel. Commercial production occurs in Taiwan, Malaysia, southern China, the Philippines, Australia, USA (Florida, Hawaii), Brazil, Suriname and Guyana. Production and consumption appears on the rise throughout the world and will most likely increase as selection and breeding for superior tasting cultivars with improved handling characteristics and storage conditions are found. 相似文献
106.
S.G. Nykamp DVM P.V. Scrivani DVM A.P. Pease DVM MS 《Veterinary radiology & ultrasound》2004,45(1):23-28
Computed tomography-dacryocystography (CT-DCG) was used to evaluate the nasolacrimal system in four patients (three dogs and one horse) that were admitted for evaluation of chronic epiphora, facial swelling, or facial trauma. The four patients are reviewed and the technique for performing CT-DCG is described. Additionally, the indications for this procedure are discussed. CT-DCG is advantageous because cross-sectional imaging provides superior resolution of the nasolacrimal apparatus and the relatively long, small-diameter, bony nasolacrimal canal in most veterinary patients. 相似文献
107.
The purpose of this retrospective study was to evaluate six cases of equine sarcoidosis for initial presenting symptoms, response to therapy and actual outcome. Dermatologists and dermatopathologists from Europe, the United States, Australia and Canada were contacted to obtain these six cases, as this is a rare disease. Signalment, clinical signs, histological findings, clinical management and outcome were determined via a questionnaire and compared to former reports. There was no age or breed predilection, and four of six horses were geldings. Age of onset ranged from 3 months to 17 years. Onset of the disease was insidious or rapid. Interestingly, in five of six cases, scaling began on the trunk (girth and shoulder). Scaling, crusting and alopecia were seen in all six horses. In one horse, clinical signs of systemic disease were reported and included intermittent fever, prescapular lymphadenopathy, depression, poor body condition and nasal discharge. Treatment included phenylbutazone, deworming agents, antibiotics, short‐term low‐dose corticosteroids, and 1–1.5 mg/kg of prednisolone. One horse showed a partial response to trimethoprim and sulfonamide, and five of six went into clinical remission with corticosteroid treatment. Five of six horses were still alive 1 year after diagnosis; one horse was diagnosed <12 months ago. Two horses are in complete remission 4 and 8 years after diagnosis. In both horses, clinical signs recurred after cessation of therapy and went into remission again with reintroduction of treatment. Both of these horses have been in remission for several years without therapy. Funding: Self‐funded. 相似文献
108.
109.
110.
Comparison of diagnostic accuracy of laparoscopic 3 mm and 5 mm cup biopsies to wedge biopsies of canine livers 下载免费PDF全文