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61.
Kubi C Billiouw M Van Den Bossche P 《The Onderstepoort journal of veterinary research》2007,74(3):223-229
Trypanosomal infections in female Glossina morsitans morsitans were investigated in an area in the Eastern Province of Zambia between 1992 and 1994. A total of 4416 flies were captured, aged using the ovarian ageing method and screened for trypanosomal infections in both the mouthparts, salivary glands and the midgut. Congolense-type infections were identified in 4.8% of the flies. Vivax-type and immature infections were identified in 1.8% and 6.8% of the flies, respectively. The prevalence of congolense-type, vivax-type and immature infections increased with age. For vivax-type infections the age-prevalence relationship could be described by a model assuming a constant per capita rate of infection. For congolense-type and midgut infections, a polynomial term was added to the model significantly improving the fit. The per capita at which flies become infected was significantly higher for immature compared to mature infections. Observations strongly suggest that tsetse acquire new midgut infections at any age and that maturation of these infections is not limited to those obtained during the first blood meal. 相似文献
62.
Miguel Mellado Lucía M. Treviño María I. Chavez Francisco G. Véliz Ulises Macías-Cruz Leonel Avendaño-Reyes José E. García 《Reproduction in domestic animals》2023,58(1):39-47
The objective of this retrospective study was to assess the effect of receiving a single (n = 50,285) or double (n = 4392) artificial insemination (AI), 12 h apart, within a timed artificial insemination protocol on pregnancy per AI (P/AI) in nulliparous heifers (inseminated with either sex-sorted or conventional semen) and pluriparous Holstein cows in a commercial dairy herd. Also, this study aimed to investigate the relationship between temperature-humidity index (THI) and time of the first AI and fertility. Fertility of cows receiving two AI with normothermia (THI <68) was higher (p < .05) than cows receiving a single AI (42.9% vs. 36.4%). P/AI of cows receiving two AI with severe heat stress (THI >85) was higher (p < .05) than cows receiving a single AI (21.0% vs. 12.6%). Regardless of heat stress conditions, applying the first AI in the morning increased (p < .05) P/AI in cows with double AI than in cows whose first AI occurred in the afternoon (38.4 vs. 33.3%). With moderate heat stress, and sexed-sorted semen, P/AI to timed AI was higher (65.0 vs. 51.9%; p < .05) in heifers receiving double AI than those serviced once. It was concluded that double AI, 12 h apart, enhanced fertility at timed AI than herd mates with a single AI, particularly with heat stress at breeding. 相似文献
63.
W. Wolters Nadi Selim Ghobrial H. M. Van Leeuwen M. G. Bos 《Irrigation and Drainage Systems》1989,3(2):103-123
A study of the water balances of The Fayoum irrigated lands and Lake Qarun was made to investigate the management of the irrigation
system and the efficiency of irrigation water use. The two water balances are strongly interrelated. The drainage flow to
Lake Qarun and the water level of the Lake are in delicate balance. A rise in Lake level causes the inundation of adjacent
land. Management of The Fayoum water balance assumes control over irrigation water flows, but this control has technical and
organizational limitations.
Also discussed is the influence of irrigation practices in The Fayoum on the water balance (e.g., the autumn flushing of fields
and farmers' preference for not irrigating at night in winter).
Notwithstanding a high overall efficiency, irrigation efficiency during the winter is low. The reasons for this are given,
together with the constraints against improving system management.
Improved uniformity of the division and application of irrigation water will enable a better technical control of flows and
will result in better water management in The Fayoum.
Abbreviations: FID — Fayoum Irrigation Department, 1 feddan (fe) — 0.4 ha, 1 mcm — 1 million cubic metres: an average annual flow of 3.17
m3/s gives 100 mcm, m3/fe.year — supplied volume (m3) per surface area (fe) per year: 1000 m3/fe.year equals 240 mm/year, MSL — Mean Sea Level 相似文献
64.
W. G. M. Bastiaanssen T. Van der Wal T. N. M. Visser 《Irrigation and Drainage Systems》1996,10(1):1-23
The success of water management in large irrigation schemes with composites of soil, crop, wetness and micro-meteorological conditions is difficult to quantify. Performance assessment indicators, being among others a function of evaporation, are useful tools to evaluate the actual functioning of an irrigation system. The inevitable spatial variability of evaporation in large irrigation schemes makes its determination with conventional point measurements almost impossible. A new remote sensing evaporation parameterization algorithm has been tested with high resolution Landsat Thematic Mapper data for the Eastern Nile Delta, Egypt. Although the implementation of such an algorithm requires assumptions to be made, the current case study shows that these assumptions do not hamper the estimation of actual and potential evaporation at regional scale. The actual evaporation has been used to express the uniformity of crop water use which is related to the equity of irrigation water distribution. The coefficient of variance in actual evaporation between 53 differenent irrigation districts is 10% on average. The relative evaporation was considered to determine whether the crop was adequately irrigated. The relative evaporation was more than 75% for 48 out of 53 irrigation districts. It is concluded, that improved information on actual crop growth conditions through remote sensing provides an essential insight into the planning of real-time and seasonal irrigation water deliveries. 相似文献
65.
The impact of increasing farm size and mechanization on rural income and rice production in Zhejiang province,China 总被引:1,自引:0,他引:1
M. Marrit Van den Berg Huib Hengsdijk Joost Wolf Martin K. Van Ittersum Wang Guanghuo Reimund P. Roetter 《Agricultural Systems》2007
Economic growth in China’s agricultural sector lags behind growth in industry and services, creating an ever widening rural–urban income gap. Development of the non-agricultural sectors offers new opportunities for farmers in China’s more advanced provinces such as Zhejiang. Increased income in the urban sector creates markets for new products, and migrating farmers rent their land to those staying. Until now, the prevailing rice-based systems have been managed mainly using manual labour and animal traction, but the larger farms resulting from migration may facilitate, or even require mechanization. In this study, we use a simulation model of the farm household to analyse the effects of increasing farm size and the transition from rice to vegetable production, while also studying the effects of mechanization. 相似文献
66.
P. J. T. Van Bakel 《Irrigation and Drainage Systems》1988,2(2):125-137
The use of drainage systems for supplementary irrigation is widespread in The Netherlands. One of the operating policies is to raise the surface water level during the growing season in order to reduce drainage (water conservation) or to create subsurface irrigation. This type of operation is based on practical experience, which can be far from optimal.To obtain better founded operational water management rules a total soil water/surface water model was built. In a case study the effects of using the drainage system in a dual-purpose manner on the arable crop production were simulated with the model. Also, the operational rules for managing this type of dual-purpose drainage systems were derived.The average annual simulated increase in crop transpiration due to water conservation and water supply for subsurface irrigation are 6.0 and 5.4 mm.y–1, respectively. This is equivalent with 520 × 103 and 460 × 103 Dfl.y–1 for the pilot region (2 Dfl 1 US $). The corresponding investments and operational costs are 600 × 103 Dfl and 9 × 103 Dfl.y–1 for water conservation and 3200 × 103 Dfl and 128 × 103 Dfl.y–1 for subsurface irrigation. Hence, water conservation is economically very profitable, whereas subsurface irrigation is less attractive.Comparing the management according to the model with current practice in a water-board during 1983 and 1986 learned that benefits can increase with some 50 and 500 Dfl per ha per year, respectively. 相似文献
67.
Water balance estimates of evaporation from ponded rice fields in a semi-arid region 总被引:1,自引:0,他引:1
Evaporation from ponded rice grown on fine-textured soils was calculated using a simple water balance equation, and compared with pan evaporation measured at a regional meteorological station. Crop/pan (Er/Ep) evaporation ratios showed seasonal trends, with values generally exceeding unity during the mid- to late-season ponding period. Mid-summer ratios of Er/Ep for two experimental fields were not significantly different from those reported in a previous study using a different experimental technique, but were higher on a third. On the average, evaporation over the whole ponding period equalled that from a Class A pan. The assumption that the infiltration or seepage term of the water balance may be neglected for fine-textured soils would seriously overestimate Er on one of the three experimental sites. 相似文献
68.
过去人们常认为,由于刚出壳雏鸡的免疫系统尚未发育成熟,同时肠道内缺乏有益的微生物,因而处于高度的敏感期,此时接种沙门氏菌苗产生的保护作用很有限。然而,最新的研究表明,在这些敏感期接种疫苗,可诱发产生保护作用。 相似文献
69.
70.
Van Ngoc Tuong Hoang 《Communications in Soil Science and Plant Analysis》2018,49(7):848-861
This study aims to determine the effects of compost additions and high temperature on N2O and CO2 emissions from a Vietnamese agricultural soil. Soil samples amended with two compost types (commercial compost, SH and chicken compost, CC) at three rates of 1%, 2% and 4% w/w were aerobically incubated at 25°C, 30°C and 35°C for 28 days in the laboratory. N2O and CO2 emissions were determined on days 1, 3, 5, 7, 14, 21 and 28. Our results showed that N2O and CO2 emissions were significantly affected by temperature, compost additions, and their interactions. Greater N2O and CO2 emissions were seen in CC treatments than SH treatments. Higher application rates of CC led to greater N2O and CO2 emissions. In SH treatments, higher temperature lowered N2O emissions but did not affect CO2 emissions. N2O and CO2 emissions were enhanced with CC addition while they showed different responses to increasing temperature. 相似文献