全文获取类型
收费全文 | 1007篇 |
免费 | 38篇 |
专业分类
林业 | 224篇 |
农学 | 19篇 |
391篇 | |
综合类 | 79篇 |
农作物 | 33篇 |
水产渔业 | 32篇 |
畜牧兽医 | 233篇 |
园艺 | 7篇 |
植物保护 | 27篇 |
出版年
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 28篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 33篇 |
2012年 | 42篇 |
2011年 | 40篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 44篇 |
2007年 | 59篇 |
2006年 | 54篇 |
2005年 | 41篇 |
2004年 | 31篇 |
2003年 | 39篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1943年 | 6篇 |
1936年 | 6篇 |
1935年 | 8篇 |
1933年 | 11篇 |
1928年 | 11篇 |
1926年 | 13篇 |
1919年 | 10篇 |
1911年 | 8篇 |
1896年 | 6篇 |
1895年 | 6篇 |
排序方式: 共有1045条查询结果,搜索用时 33 毫秒
41.
Karl Gösswald 《Journal of pest science》1943,19(3):30-34
Ohne Zusammenfassung
Mit 10 Abbildungen 相似文献
42.
Salinity is a major constraint to irrigated rice production, particularly in semi-arid and arid climates. Irrigated rice is
a well suited crop to controlling and even decreasing soil salinity, but rice is a salt-susceptible crop and yield losses
due to salinity can be substantial. The objective of this study was to develop a highly predictive screening tool for the
vegetative growth stage of rice to estimate salinity-induced yield losses. Twenty-one rice genotypes were grown over seven
seasons in a field trials in Ndiaye, Senegal, between 1991 and 1995 and were subjected to irrigation with moderately saline
water (3.5 mS cm-1, electrical conductivity) or irrigation with fresh water. Potassium/sodium ratios of the youngest three leaves (K/NaLeaves) were determined by flame photometry at the late vegetative stage. Grain yield was determined at maturity. All cultivars
showed strong log-linear correlations between K/NaLeaves and grain yield, but intercept and slope of those correlations differed between seasons for a given genotype and between
genotypes. The K/NaLeaves under salinity was related to grain yield under salinity relative to freshwater controls. There was a highly significant
correlation (p < 0.001) between K/NaLeaves and salinity-induced grain yield reduction: the most susceptible cultivars had lowest K/NaLeaves and the strongest yield reductions. Although there were major differences in the effects of salinity on crops in both the
hot dry season (HDS) and the wet season, the correlation was equally significant across cropping seasons. The earliest possible
time to establish the relationship between K/NaLeaves under salinity and grain yield reduction due to salinity was investigated in an additional trial in the HDS 1998. About 60
days after sowing, salinity-induced yield loss could be predicted through K/NaLeaves with a high degree of confidence (p < 0.01). A screening system for salinity resistance of rice, particularly in arid and semi-arid climates, is proposed based
on the correlation between K/NaLeaves under salinity and salinity-induced yield losses.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
Ulrich Schuler Petra Erbe Mehdi Zarei Wanida Rangubpit Adichat Surinkum Karl Stahr Ludger Herrmann 《植物养料与土壤学杂志》2011,174(4):536-544
According to the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006), the differentiation of Acrisols and Alisols is based on the cation‐exchange capacity of clay, which cannot be directly determined in the field, but needs expensive and time‐consuming soil‐chemical analyses. This is an unsatisfactory situation for pedologists, who urgently require a rapid field method to distinguish illuviation‐type reference soil groups (Alisols, Acrisols, Luvisols, Lixisols). In this study, we tested the ability of gamma‐ray spectrometry to separate major WRB reference soil groups in the field. The underlying hypothesis is that Alisols and Acrisols are distinguished by their clay mineral composition, which should be reflected by geochemistry and consequently gamma‐ray radiation (i.e., K‐containing illite vs. K‐free kaolinite). Highly significant differences in their gamma‐ray spectrum for K, Th, and U were found for limestone and its soils. Especially the K and Th signatures allowed a clear separation of Acrisols and Alisols. In general, the surface radiation was sufficient to separate these soils. Best results were revealed considering parent rock and the whole soil profile. This means by using a portable radiometer and a pH meter, all illuviation‐type reference soil groups could be distinguished in this case. If applicable at other sites, this approach could enormously reduce expenditures for soil‐chemical analysis needed to assist soil classification. 相似文献
44.
T. Schmitt Druct Yusftattung Schüpler Tabricius und Karl Suebenguth 《Forstwissenschaftliches Centralblatt》1921,43(2):69-79
Ohne Zusammenfassung 相似文献
45.
46.
Human-wildlife conflict in the Kingdom of Bhutan: Patterns of livestock predation by large mammalian carnivores 总被引:1,自引:0,他引:1
We examined predation activity throughout Bhutan by tiger (Panthera tigris), common leopard (Panthera pardus), snow leopard (Uncia uncia) and Himalayan black bear (Ursus thibetanus) on a variety of livestock types using data gathered over the first two years (2003-2005) of a compensation scheme for livestock losses. One thousand three hundred and seventy five kills were documented, with leopards killing significantly more livestock (70% of all kills), than tigers (19%), bears (8%) and snow leopards (2%). About 50% of livestock killing were of cattle, and about 33% were of horses, with tigers, leopards and snow leopards killing a significantly greater proportion of horses than predicted from availability. Examination of cattle kills showed that leopards killed a significantly greater proportion of smaller prey (e.g., calves), whereas tigers killed a significantly greater proportion of larger prey (e.g., bulls). Overall, livestock predation was greatest in summer and autumn which corresponded with a peak in cropping agriculture; livestock are turned out to pasture and forest during the cropping season, and subsequently, are less well guarded than at other times. Across Bhutan, high horse density and low cattle and yak density were associated with high rates of livestock attack, but no relationship was found with forest cover or human population density. Several northern districts were identified as ‘predation hotspots’, where proportions of livestock lost to predation were considerable, and the ratio of reported kills to relative abundance of livestock was high. Implications of our findings for mitigating livestock losses and for conserving large carnivores in Bhutan are discussed. 相似文献
47.
48.
OBJECTIVE: To determine if screw loosening in triple pelvic osteotomies (TPO) is minimized when screws cranial to the ilial osteotomy had maximal sacral purchase. STUDY DESIGN: Prospective study. ANIMALS: Forty-six dogs with decreased acetabular coverage of the femoral head and minimal degenerative joint changes. METHODS: TPOs were performed where screws cranial to the ilial osteotomy were inserted to maximally engage sacral bone. Data collected were: use of ilial and ischial cerclage wire, screw length, ventrodorsal radiographic sacral width (most caudal aspect), pelvic canal diameter, and sacral penetration of the 3 cranial screws. On all subsequent radiographs, changes in screw position, pelvic canal diameter, and sacral purchase were noted. RESULTS: For 69 TPOs, 414 screws were used. Mean radiographic cranial screw length was 34.54 mm. Combined sacral depth of all 3 screws was 93.3% of sacral width. All osteotomies healed uneventfully. Twenty-four screws (6%) loosened with 12 being in the most cranial positions. Use of ischial or ilial cerclage wires did not statistically influence screw loosening. Pelvic diameter decreased by a mean of 7.79% from postoperative radiographs to the last radiographic recheck. CONCLUSIONS: By sufficiently engaging the sacrum with screws cranial to the ilial osteotomy, implant failures can be avoided and screw loosening minimized when a 6-hole TPO plate is used. CLINICAL RELEVANCE: To minimize screw-loosening in TPO, screws inserted cranial to the ilial osteotomy should be inserted to maximum sacral depth without penetrating the vertebral canal. 相似文献
49.
Pietro Perrino G. Battista Polignano Karl Hammer Christian O. Lehmann 《Genetic Resources and Crop Evolution》1984,32(4):197-206
Summary The mission was carried out within the Mediterranean Programme of the IBPGR in April/May 1983 with participants from the Socialist People's Libyan Arab Jamahiriya (Agricultural Research Centre, Tarabulus), the Istituto del Germoplasma, Bari, and the Zentralinstitut für Genetik und Kulturpflanzenforschung, Gatersleben. In Tripolitania, the Fezzan- and Ghadmis-areas 316 samples, mostly cereals and vegetables, have been collected. In Tripolitania and the Ghadmis-area the land-races have been nearly completely replaced by new varieties. In the Fezzan genetic erosion is in progress. There, several cereal- and vegetable-land-races could still be collected. The land-races may be useful for breeding programmes.
Bericht über eine Reise in die Sozialistische Libysche Arabische Volksjamahiriya 1983 zur Sammlung autochthoner Sippen von Kulturpflanzen
Zusammenfassung Die Reise erfolgte im Rahmen des Mediterranean Programme des IBPGR im April/Mai 1983 mit Teilnehmern aus der Sozialistischen Libyschen Arabischen Volksjamahiriya (Agricultural Research Centre, Tarbulus), des Istituto del Germoplasma, Bari, und des Zentralinstituts für Genetik und Kulturpflanzenforschung, Gatersleben. In Tripolitanien, dem Fezzan und dem Gebiet von Ghadmis wurden 316 Proben, meist von Getrieden und Gemüsen, gesammelt. In Tripolitanien und dem Gebiet von Ghadmis sind die Landsorten fast vollständig von neueren Sorten verdrängt worden. Im Fezzan schreitet die Generosion fort. Hier konnten noch zahlreiche Getreide- und Gemüselandsorten gesammelt werden. Die Landsorten können für Züchtungsprogramme nützlich sein.
1983 .
— 1983 . ( .-. ), . , 316 , . . , . .相似文献
50.
Christian Gosch Richard Alexander Gottsberger Karl Stich Thilo Christopher Fischer 《European journal of plant pathology / European Foundation for Plant Pathology》2012,134(4):835-845
Fire blight caused by the gram-negative bacterium Erwinia amylovora is a major disease of pome fruit like apple (Malus domestica) or pear (Pyrus communis). Detection of the pathogen is hampered by low titres usually being present during initial flower infection and the brief time frame for analysis to decide upon subsequent countermeasures. Here we describe a loop-mediated isothermal amplification of DNA (LAMP) assay for genomic DNA of Erwinia amylovora, which relies on a highly specific primer design that excludes amplification from typical DNA sources of the orchard biological system and from sample handling. The assay enables the fast detection of down to approximately 20?cfu of pure Erwinia amylovora or 100?fg genomic DNA (corresponding to approximately 25 E. amyolovora equivalents) per reaction within 45?min. Fast and reliable detection of E. amylovora in orchard samples by naked eye is achieved through a visual colour change indication with hydroxynaphthol blue. The assay avoids use of complex technical devices and is thus suitable for field testing. 相似文献