全文获取类型
收费全文 | 5557篇 |
免费 | 226篇 |
国内免费 | 14篇 |
专业分类
林业 | 401篇 |
农学 | 233篇 |
基础科学 | 39篇 |
660篇 | |
综合类 | 579篇 |
农作物 | 214篇 |
水产渔业 | 218篇 |
畜牧兽医 | 3032篇 |
园艺 | 45篇 |
植物保护 | 376篇 |
出版年
2019年 | 45篇 |
2018年 | 68篇 |
2017年 | 102篇 |
2016年 | 87篇 |
2015年 | 58篇 |
2014年 | 81篇 |
2013年 | 205篇 |
2012年 | 157篇 |
2011年 | 178篇 |
2010年 | 112篇 |
2009年 | 123篇 |
2008年 | 220篇 |
2007年 | 214篇 |
2006年 | 183篇 |
2005年 | 205篇 |
2004年 | 180篇 |
2003年 | 185篇 |
2002年 | 174篇 |
2001年 | 205篇 |
2000年 | 199篇 |
1999年 | 185篇 |
1998年 | 54篇 |
1997年 | 73篇 |
1996年 | 66篇 |
1995年 | 57篇 |
1994年 | 47篇 |
1993年 | 63篇 |
1992年 | 127篇 |
1991年 | 136篇 |
1990年 | 135篇 |
1989年 | 138篇 |
1988年 | 108篇 |
1987年 | 122篇 |
1986年 | 103篇 |
1985年 | 97篇 |
1984年 | 93篇 |
1983年 | 67篇 |
1982年 | 39篇 |
1979年 | 81篇 |
1978年 | 63篇 |
1977年 | 73篇 |
1976年 | 46篇 |
1975年 | 69篇 |
1974年 | 85篇 |
1973年 | 74篇 |
1972年 | 75篇 |
1971年 | 56篇 |
1970年 | 70篇 |
1969年 | 51篇 |
1968年 | 44篇 |
排序方式: 共有5797条查询结果,搜索用时 0 毫秒
961.
Effects of water exchange protocols on water quality,sedimentation rate and production performance of Penaeus monodon in earthen ponds 下载免费PDF全文
Rajeeb K Mohanty Atmaram Mishra Dileep K Panda Dhiraj U Patil 《Aquaculture Research》2015,46(10):2457-2468
This study was carried out in farmers' fields to quantify the total water and consumptive water use in grow‐out culture of Penaeus monodon under recommended package of practice with two different water management protocols: T1, with no water exchange and T2, with regulated water exchange. Treatment‐wise estimated total water use, was 2.09 and 2.43 ha‐m 122 day?1, while the computed consumptive water use index (m3 kg?1 biomass) was 5.35 and 6.02 in T1 and T2 respectively. Lower rates of water exchange (T2) showed significantly improved (P < 0.05) crop performance in terms of performance index (19.75 ± 0.75), production‐size index (74.1 ± 3.4), survival rate (80.13 ± 1.7%) and productivity (2.44 ± 0.08 t) over the zero water exchange. The shrimp pond water quality suitability index (WQSI) infers that regulated water exchange (T2) improved the overall suitability of water quality for shrimp culture. WQSI up to 90 days of culture ranged between 7.5–9.0 in T2, needs little management while in the last month of rearing, it was good with moderate management requirements. Treatment‐wise sediment load ranged between 50.4–56.3 m3 t?1 shrimp biomass. High intensity of water exchange and low apparent feed conversion ratio influenced in lowering the sedimentation rate. Regulated water exchange protocol (T2) performed well (higher net total water productivity and net consumptive water productivity) against no water exchange (T1). A higher OV:CC ratio (ratio of the output value to the cost of cultivation) indicated that T2 had a distinct edge over the T1 protocol. 相似文献
962.
The present research was undertaken to explor the possibility of arbuscular mycorrhizal(AM) association with Asteraceae plants in the arid lands of Saudi Arabia(Al-Ghat, Buraydah, Thumamah and Huraymila). AM fungal colonization in the roots, spore numbers in the rhizosphere soil, fungal species diversity and correlation between AM properties and soil properties were determined. The highest colonization was in Conyza bonariensis(65%) from Al-Ghat, Anthemis cotula(52%) from Buraydah and C. bonariensis(53%) from Thumamah. The lowest was in Vernonia schimperi(41%) from Al-Ghat, Pulicaria undulata(25%) from Buraydah, Acanthospermum hispidum(34%) from Thumamah, Asteriscus graveolens(22%) and V. schimperi(22%) from Huraymila. Vesicular and arbuscular colonization were also presented in all plant species examined. The number of spores were 112–207 in Al-Ghat, 113–133 in Buraydah, 87–148 in Thumamah and 107–158 in Huraymila. Funneliformis mosseae, Glomus etunicatum, G. fasciculatum and G. aggregatum were identified. Relative frequency of AM fungal species varied widely and was irrespective of location and plant species. Diversity index varied with the rhizosphere soils of different plant species at various locations. Soil properties varied with locations and no distinct correlations were observed among the soil properties, root colonization and the number of spores. The results of the present study specified the association of AM fungi in different plants of Asteraceae and its significance in the ecological functioning of annual plants in the punitive environments of the rangelands in Saudi Arabia. 相似文献
963.
S. Hosseini F. Heyman U. Olsson A. Broberg D. Funck Jensen M. Karlsson 《Plant pathology》2014,63(3):708-714
Phytophthora niederhauserii, P. pisi, P. sojae and P. vignae are closely related species that are pathogenic to various legume plants. While P. sojae and P. vignae are reported to specifically infect soybean and cowpea, respectively, P. pisi is reported to attack pea and faba bean. Phytophthora niederhauserii is considered to have a broad host range. Zoospores of some Phytophthora species are chemotactically attracted to the isoflavones that are secreted by their host plants. The focus of the current study was to determine the chemotaxic behaviour of zoospores from closely related legume‐root infecting Phytophthora species and to investigate the correlation, if any, to host preference as determined by greenhouse pathogenicity tests. The results showed that P. sojae and P. vignae were attracted to the non‐soybean isoflavone prunetin as well as to the soybean isoflavones genistein and daidzein, which is in contrast with their host specificity on soybean and cowpea, respectively. On the other hand, P. pisi and P. niederhauserii were only attracted to prunetin, previously reported to be produced by pea, but not to the isoflavones associated with the non‐host soybean. The lack of responsiveness to genistein and daidzein in P. pisi may represent a recent adaptation to the host specialization towards pea. However, the affinity of P. niederhauserii to prunetin shows that this trait can also be present in taxa not specifically associated with legume hosts. 相似文献
964.
U. Carlsson-Granér B. E. Giles P. H. Thrall 《European journal of plant pathology / European Foundation for Plant Pathology》2014,138(3):499-511
We use data from species of the anther-smut fungi and the host plants Lychnis alpina and Silene dioica to show that spatial structuring at different scales can influence patterns of disease and host resistance. Patterns of disease and host resistance were surveyed in an archipelago subject to land-uplift where populations of S. dioica constitute an age-structured metapopulation, and in three contrasting areas within the mainland range of L. alpina, where population distributions range from continuous, through patchy but spatially connected to highly isolated demes. In S. dioica, disease levels depend on the age, size and density of local patches and populations. Disease is most predictably found in larger dense host patches and populations of intermediate age, and more frequently goes extinct in small old populations. The rate of local disease spread is affected by the level of host resistance; S. dioica populations showing an increase in disease over time are more susceptible than populations where the disease has remained at low levels. Among-population variation in resistance is driven by founding events and populations remain differentiated due to limited gene flow between islands. As observed in the L. alpina system, when populations are more connected, a greater fraction of populations have disease present. Results from a simulation model argue that, while increased dispersal in connected systems can increase disease spread, it may also favour selection of host resistance which ultimately reduces disease levels within populations. This could explain the observed lower disease prevalence in L. alpina in regions where populations are more continuous. 相似文献
965.
Coastal areas in the southeastern USA are prone to hurricanes and strong storms that may cause salt-water influx to freshwater aquatic sediments. These changes in environmental conditions may impact sediment processes including nitrogen (N) cycling. The relative abilities of sediment microbial communities from two freshwater golf course retention ponds that drain into the adjacent wetlands, and two proximal saline wetland ponds, to remove nitrate (NO3−) were compared to assess whether low concentrations of sulfide changed N-transformation processes. Microcosms were incubated with NO3-N (300 μg g dw−1) alone, and with NO3-N and sulfide (H2S) (100 and 200 μg g dw−1). Nitrous oxide (N2O), nitrite (NO2−), NO3−, ammonium (NH4+), SO42− and acid volatile sulfides were analyzed over time. The acetylene block technique was used to measure denitrification in sediment microcosms with no added H2S. Denitrification was measured without acetylene (C2H2) addition in microcosms with added H2S. With no added H2S, denitrification was greater in the freshwater retention ponds than in the wetland ponds. Although low H2S concentrations generally increased NO3-N removal rates at all sites, lag periods were increased and denitrification was inhibited by low sulfide in the freshwater sediments, as evidenced by the greater concentrations of N2O that accumulated compared to those in the wetland sediments. In addition to the inability of the freshwater sediments to convert N2O to N2 in the absence of C2H2, anomalously high transient NO2-N concentrations accumulated in the retention pond samples. NH4-N formation generally decreased due to H2S addition at the freshwater sites; NH4-N formation increased initially at the wetland sites, but was greater when no H2S was added. Storm events that allow influx of SO42−-containing seawater into freshwater systems may change the dominant N species produced from nitrate reduction. Even low concentrations of sulfide produced incomplete denitrification and decreased formation of NH4+ in these coastal freshwater sediments. 相似文献
966.
K. U. Sorenmo V. M. Kristiansen M. A. Cofone F. S. Shofer A.‐M. Breen M. Langeland C. M. Mongil A. M. Grondahl J. Teige M. H. Goldschmidt 《Veterinary and comparative oncology》2009,7(3):162-172
This study describes the clinical and histopathological findings in dogs with mammary gland tumours, and compares the histopathological and clinical evidence consistent with progression from benign to malignant to human breast cancer epidemiology. Clinical and histopathological data on 90 female dogs with 236 tumours was included. Dogs with malignant tumours were significantly older than dogs with benign tumours (9.5 versus 8.5 years), P = 0.009. Malignant tumours were significantly larger than benign tumours (4.7 versus 2.1 cm), P = 0.0002. Sixty‐six percent had more than one tumour, and evidence of histological progression was noted with increasing tumour size. Dogs with malignant tumours were significantly more likely to develop new primary tumours than dogs with benign tumours, P = 0.015. These findings suggest that canine mammary tumours progress from benign to malignant; malignant tumours may be the end stage of a histological continuum with clinical and histopathological similarities to human breast carcinogenesis. 相似文献
967.
968.
Gabrielle R. Carter J. Catherine Scott-Moncrieff Andrew U. Luescher George Moore 《Journal of Veterinary Behavior: Clinical Applications and Research》2009,4(6):230-236
The aim of this case controlled study was to determine whether dogs with behavioral problems have evidence of abnormal thyroid function on routine screening tests for hypothyroidism. The hypothesis of the study was that thyroid function, as assessed by serum total thyroxine (TT4) and serum thyroid stimulating hormone (thyrotropin) (TSH) concentrations, is normal in most dogs with behavioral problems. Concentrations of TT4 and TSH in 39 dogs with behavior problems presenting to a veterinary behavior referral clinic (abnormal behavior group), were compared with TT4 and TSH concentrations in 39 healthy control dogs without behavior problems presenting to 5 community veterinary practices (control group). Dogs in the control group were matched for age and breed with the abnormal behavior group. Dogs with behavioral problems had higher TT4 concentrations than dogs without behavioral problems (t-test: t = 2.77, N = 39, P = 0.009), however none of the TT4 values were outside the reference range. There was no significant difference in TSH concentration between the 2 groups. Two dogs with behavior problems and 1 dog without behavior problems had results suggestive of hypothyroidism. All other dogs were considered to be euthyroid. There was no evidence to support a diagnosis of hypothyroidism in the majority of dogs with behavior problems in this study. The higher concentration of TT4 in dogs with behavior problems suggests, however, that alteration in thyroid hormone production or metabolism may occur in some dogs with behavior problems. Further studies that include additional indicators of thyroid status such as serum total triiodothyronine, serum, free thyroxine, and anti-thyroid antibody concentrations are necessary to further evaluate the significance of this finding. 相似文献
969.
970.
Pfukenyi DM Pawandiwa D Makaya PV Ushewokunze-Obatolu U 《Tropical animal health and production》2009,41(4):565-572
To assess the epidemiological features of wildlife rabies in Zimbabwe, a retrospective study covering a period of 12 years
(1992–2003) was conducted using rabies records of the Central Veterinary Laboratories (CVL), Department of Veterinary Technical
Services at Harare. Records of monthly and annual wildlife rabies were perused with regard to total samples submitted to the
CVL and corresponding positive cases. Positive cases were analyzed in relation to the animal species involved, seasonal trends,
and land-use categories. A total of 2107 samples were submitted and 1 540 (73.1%) were positive. Jackals (Canis mesomelas and C. adustus), with a peak occurrence of rabies between January and March were the major maintenance host, representing approximately
91% of the total rabies cases confirmed. The Canidae family recorded the highest number of cases followed by the Viverridae,
Mustelidae, Felidae, Herpestidae and Hyaenidae families in that order. During the present study rabies cases were confirmed
in 7 additional wild animals. The majority of the positive cases (83.7%) were recorded in commercial farming areas in the
northeast parts of the country. 相似文献