全文获取类型
收费全文 | 2500篇 |
免费 | 170篇 |
国内免费 | 1篇 |
专业分类
林业 | 93篇 |
农学 | 59篇 |
基础科学 | 19篇 |
265篇 | |
综合类 | 467篇 |
农作物 | 127篇 |
水产渔业 | 153篇 |
畜牧兽医 | 1340篇 |
园艺 | 47篇 |
植物保护 | 101篇 |
出版年
2021年 | 31篇 |
2020年 | 24篇 |
2019年 | 44篇 |
2018年 | 34篇 |
2017年 | 37篇 |
2016年 | 46篇 |
2015年 | 42篇 |
2014年 | 36篇 |
2013年 | 151篇 |
2012年 | 80篇 |
2011年 | 123篇 |
2010年 | 65篇 |
2009年 | 53篇 |
2008年 | 96篇 |
2007年 | 85篇 |
2006年 | 86篇 |
2005年 | 73篇 |
2004年 | 79篇 |
2003年 | 67篇 |
2002年 | 78篇 |
2001年 | 64篇 |
2000年 | 67篇 |
1999年 | 37篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 25篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 47篇 |
1991年 | 45篇 |
1990年 | 43篇 |
1989年 | 51篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 43篇 |
1985年 | 32篇 |
1984年 | 35篇 |
1983年 | 36篇 |
1981年 | 25篇 |
1980年 | 32篇 |
1979年 | 35篇 |
1978年 | 32篇 |
1977年 | 21篇 |
1976年 | 27篇 |
1974年 | 30篇 |
1973年 | 34篇 |
1972年 | 31篇 |
1971年 | 21篇 |
1970年 | 21篇 |
1969年 | 27篇 |
排序方式: 共有2671条查询结果,搜索用时 31 毫秒
41.
Katja N. Koeppel Peter Geertsma Brian F. Kuhn Ockert L. van Schalkwyk Peter N. Thompson 《The Onderstepoort journal of veterinary research》2022,89(1)
Rabies is a zoonotic disease that remains endemic in large parts of southern Africa because of its persistence in wildlife and domestic dog vectors. The black-backed jackals (Canis mesomelas) is primarily the wildlife vector responsible for rabies outbreaks in northern parts of South Africa. Two trials were carried out to investigate antibody responses to the oral rabies vaccine Raboral V-RG® in black-backed jackals under captive and free-ranging conditions. In captive jackals 10/12 (83%; 95% confidence interval [CI]: 52% – 98%), seroconverted after single oral vaccination. Nine captive jackals had protective antibody titres (> 0.5 IU/mL) at 4 weeks (median: 2.1 IU/mL; inter quartile range [IQR]: 0.6–5.7) and 10 jackals had at 12 weeks (median: 3.5 IU/mL; IQR: 1.5–8.3) and three maintained antibody titres for up to 48 weeks (median: 3.4 IU/mL; IQR: 2.0–6.3). Four sites were baited with Raboral V-RG® vaccine for wild jackals, using fishmeal polymer and chicken heads. Baits were distributed by hand or from vehicle at three sites in north-eastern South Africa, with an average baiting density of 4.4 baits/km2 and at one site in central South Africa, at 0.12 baits/km2. This resulted in protective antibody titres in 3/11 jackals (27%; 95% Cl: 6–61) trapped between 3 and 12 months after baiting in north-eastern South Africa, compared with 4/7 jackals (57%; 95% Cl: 18–90) trapped after 3–18 months in central South Africa. This study shows the potential utility of oral rabies vaccination for the control of wildlife-associated rabies in north-eastern and central South Africa, but extensive studies with wider distribution of bait are needed to assess its potential impact on rabies control in wild jackals. 相似文献
42.
The sensitivity of stem diameter variations (SDV) measured with linear variable transducer (LVDT) sensors as indicators of plant water status in tomato was evaluated. Two tomato crops were grown sequentially in a sandy loam soil in an unheated plastic greenhouse. These were an autumn–winter tomato crop (autumn crop) and a spring–summer tomato crop (spring crop). One drying cycle of 61 days was imposed to the autumn crop in winter at 92 days after transplanting (DAT). Two drying cycles, each of 29 days, were applied to the spring crop, to young (58 DAT) and mature plants (121 DAT). For each drying cycle, four replicate plots did not receive irrigation, and four were well watered. During each drying cycle, LVDT sensors continuously measured SDV, and daily measurements were made of leaf (Ψ
leaf) and stem water potential (Ψ
stem). SDV data was interpreted using the SDV-derived indices, maximum daily shrinkage (MDS) and stem growth rate (SGR). The response of SDV-derived indices to water deficit differed with (1) climatic conditions during stress imposition and (2) crop age. In the winter drying cycle of the autumn crop, the responses of the SDV-derived indices to soil drying were relatively small and slower than Ψ
leaf and Ψ
stem. Under warmer conditions, the SDV-derived indices were much more responsive to soil drying. In rapidly growing young plants, where SDV was characterized by high SGR and small MDS, SGR was the most sensitive SDV-derived index. In more mature plants with little stem growth, MDS was the most sensitive SDV-derived index. In mature plants grown in warm to hot conditions, MDS (1) responded at a similar time or earlier than Ψ
leaf and Ψ
stem and (2) had larger “signal” values (ratio of values from unwatered to control plants) than Ψ
leaf and Ψ
stem. However, there was appreciably more “noise” (coefficient of variation, CV) associated with the SDV-derived indices, giving lower “sensitivity” values, determined from “signal” to “noise” ratios, than for Ψ
leaf and Ψ
stem. Regression analysis between MDS of well-watered plants and climatic variables gave best results for a linear relationship between MDS and daily maximum vapor pressure deficit. There were strong linear relationships between MDS and Ψ
leaf for each drying cycle. The slopes of these relationships differed with crop age indicating that there was no constant relationship between MDS and Ψ
leaf for a whole season. Overall these results demonstrated that MDS and SGR can be sensitive indicators of the water status of tomato crops under conditions of moderate to high evaporative demand. However, the variability associated with the SDV-derived indices and the changing MDS–Ψ
leaf relationship with crop age represent major issues regarding the development of irrigation scheduling protocols for tomato. 相似文献
43.
P. James K. Tzoulas M.D. Adams A. Barber J. Box J. Breuste T. Elmqvist M. Frith C. Gordon K.L. Greening J. Handley S. Haworth A.E. Kazmierczak M. Johnston K. Korpela M. Moretti J. Niemelä S. Pauleit M.H. Roe J.P. Sadler C. Ward Thompson 《Urban Forestry & Urban Greening》2009,8(2):65-75
In recent years social, economic and environmental considerations have led to a reevaluation of the factors that contribute to sustainable urban environments. Increasingly, urban green space is seen as an integral part of cities providing a range of services to both the people and the wildlife living in urban areas. With this recognition and resulting from the simultaneous provision of different services, there is a real need to identify a research framework in which to develop multidisciplinary and interdisciplinary research on urban green space. In order to address these needs, an iterative process based on the delphi technique was developed, which comprised email-mediated discussions and a two-day symposium involving experts from various disciplines. The two outputs of this iterative process were (i) an integrated framework for multidisciplinary and interdisciplinary research and (ii) a catalogue of key research questions in urban green space research. The integrated framework presented here includes relevant research areas (i.e. ecosystem services, drivers of change, pressures on urban green space, human processes and goals of provision of urban green space) and emergent research themes in urban green space studies (i.e. physicality, experience, valuation, management and governance). Collectively these two outputs have the potential to establish an international research agenda for urban green space, which can contribute to the better understanding of people's relationship with cities. 相似文献
44.
N. J. Grünwald G. A. Forbes W. Perez-Barrera J. E. Stewart V. J. Fieland M. M. Larsen 《Plant pathology》2019,68(3):557-565
An unknown Phytophthora species was discovered in the central Peruvian Andes on blighted foliage of the native South American plant species Urera lacineata. Urera is a genus of native flowering shrubs in the nettle family Urticaceae. This new taxon Phytophthora urerae sp. nov. is herewith formally described based on extensive morphological analysis, phylogenetic analysis of nuclear and mitochondrial loci, and AFLP analysis. Phytophthora urerae sp. nov. is a close relative of the Irish famine pathogen, Phytophthora infestans, and only the third clade 1c taxon described from South America to date. In contrast to the clade 1c taxon Phytophthora andina, first described in South America as a hybrid, P. urerae does not appear to be a hybrid based on cloning and sequencing nuclear loci. Findings of new species in South America may provide novel insights into the origin and evolutionary history of clade 1c Phytophthora species. 相似文献
45.
Waseem Akbar Anilkumar Gowda Jeffrey E Ahrens Jason W Stelzer Robert S Brown Scott L Bollman John T Greenplate Jeffrey Gore Angus L Catchot Gus Lorenz Scott D Stewart David L Kerns Jeremy K Greene Michael D Toews David A Herbert Dominic D Reisig Gregory A Sword Peter C Ellsworth Larry D Godfrey Thomas L Clark 《Pest management science》2019,75(3):867-877
46.
D. J. A. Brown G. D. Howells T. R. K. Da ziel B. R. Stewart 《Water, air, and soil pollution》1988,41(1-4):25-41
A research watershed liming project is being carried out at Loch Fleet in the Galloway District of southwest Scotland. This acid loch originally supported a brown trout fishery, but the number of fish caught by anglers declined during the 1950's and the fishery eventually disappeared about 20 yr ago. After 2 yr of pretreatment data collection, the first set of land time applications took place in the spring of 1986, and the resulting surface water chemical changes are very encouraging. Increases in pH and Ca concentration and decreases in A1 (especially the toxic labile monomeric fraction) concentrations have been observed in the streams and waters draining the treated subcatchments in the loch itself and in the loch outlet. Also, the normal trend for pH and Ca concentration to fall during periods of high flow in the main feeder stream has been reversed. In the spring of 1987, the loch was restocked with brown trout. Initial indications are that there has been very good survival of these fish, and that they managed to spawn during the 1987/88 winter. The chemical and biological changes brought about by the land treatments are described in detail. 相似文献
47.
The values of length of synodic month, obtained from tidally controlled periodical growth patterns in mollusks and stromatolites for several geologic periods, indicate that the deceleration rate of the earth's rotation has not been constant. Two breaks in slope, in the Pennsylvanian and Cretaceous, may be related to changes in distribution of continents, oceans, and adjacent shallow seas. 相似文献
48.
Olivier M Aggarwal A Allen J Almendras AA Bajorek ES Beasley EM Brady SD Bushard JM Bustos VI Chu A Chung TR De Witte A Denys ME Dominguez R Fang NY Foster BD Freudenberg RW Hadley D Hamilton LR Jeffrey TJ Kelly L Lazzeroni L Levy MR Lewis SC Liu X Lopez FJ Louie B Marquis JP Martinez RA Matsuura MK Misherghi NS Norton JA Olshen A Perkins SM Perou AJ Piercy C Piercy M Qin F Reif T Sheppard K Shokoohi V Smick GA Sun WL Stewart EA Fernando J Tejeda Tran NM Trejo T Vo NT Yan SC Zierten DL Zhao S 《Science (New York, N.Y.)》2001,291(5507):1298-1302
We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases. 相似文献
49.
Twelve long-term ovariectomized (OVX) pony mares were used to determine the effects of dexamethasone (DEX) or progesterone (PR) on concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after administration of gonadotropin releasing hormone (GnRH). All mares were subsequently administered dihydrotestosterone (DHT) to determine if DEX or PR treatment altered the FSH or LH response to this androgen. Daily blood sampling was started on day 1. After a pretreatment injection of GnRH on day 5, four mares were administered DEX at 125 micrograms/kg of body weight (BW), four mares were administered PR at 500 micrograms/kg of BW and four mares were administered vehicle. Injections were given subcutaneously in vegetable shortening daily through day 14. After a second injection of GnRH on day 15, all mares were administered DHT in shortening at 150 micrograms/kg of BW. Injections of DHT were given daily through day 24. A final injection of GnRH was given on day 25. Treatment of mares with DEX 1) reduced (P less than .01) daily LH secretion and briefly increased (P less than .05) daily FSH secretion and 2) increased (P less than .01) the FSH response to exogenous GnRH. Treatment of mares with PR had no effect on daily LH secretion but increased (P less than .05) daily FSH secretion and increased (P less than .01) the FSH response to exogenous GnRH.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
50.
T K Herath H W Ferguson K D Thompson A Adams R H Richards 《Journal of fish diseases》2012,35(11):799-808
Studies on the ultrastructural morphogenesis of viruses give an insight into how the host cell mechanisms are utilized for new virion synthesis. A time course examining salmonid alphavirus 1 (SAV 1) assembly was performed by culturing the virus on Chinook salmon embryo cells (CHSE‐214). Different stages of viral replication were observed under electron microscopy. Virus‐like particles were observed inside membrane‐bound vesicles as early as 1 h following contact of the virus with the cells. Membrane‐dependent replication complexes were observed in the cytoplasm of the cells, with spherules found at the periphery of late endosome‐like vacuoles. The use of intracellular membranes for RNA replication is similar to other positive‐sense single‐stranded RNA (+ssRNA) viruses. The number of Golgi apparatus and associated vacuoles characterized by ‘fuzzy’‐coated membranes was greater in virus‐infected cells. The mature enveloped virions started to bud out from the cells at approximately 24 h post‐infection. These observations suggest that the pathway used by SAV 1 for the generation of new virus particles in vitro is comparable to viral replication observed with mammalian alphaviruses but with some interesting differences. 相似文献