全文获取类型
收费全文 | 312009篇 |
免费 | 17003篇 |
国内免费 | 691篇 |
专业分类
林业 | 24480篇 |
农学 | 14194篇 |
基础科学 | 2992篇 |
46291篇 | |
综合类 | 40722篇 |
农作物 | 17461篇 |
水产渔业 | 18064篇 |
畜牧兽医 | 133147篇 |
园艺 | 6536篇 |
植物保护 | 25816篇 |
出版年
2019年 | 3727篇 |
2018年 | 4326篇 |
2017年 | 4684篇 |
2016年 | 5027篇 |
2015年 | 4481篇 |
2014年 | 5855篇 |
2013年 | 16571篇 |
2012年 | 7786篇 |
2011年 | 10073篇 |
2010年 | 7933篇 |
2009年 | 8337篇 |
2008年 | 9355篇 |
2007年 | 8520篇 |
2006年 | 9055篇 |
2005年 | 8235篇 |
2004年 | 8078篇 |
2003年 | 7839篇 |
2002年 | 7237篇 |
2001年 | 8265篇 |
2000年 | 7822篇 |
1999年 | 6982篇 |
1998年 | 4386篇 |
1997年 | 4421篇 |
1996年 | 4158篇 |
1995年 | 4799篇 |
1994年 | 4241篇 |
1993年 | 3948篇 |
1992年 | 5746篇 |
1991年 | 6078篇 |
1990年 | 5812篇 |
1989年 | 5748篇 |
1988年 | 5302篇 |
1987年 | 5306篇 |
1986年 | 5361篇 |
1985年 | 5487篇 |
1984年 | 4895篇 |
1983年 | 4484篇 |
1982年 | 3482篇 |
1981年 | 3312篇 |
1980年 | 3280篇 |
1979年 | 4367篇 |
1978年 | 3773篇 |
1977年 | 3401篇 |
1976年 | 3122篇 |
1975年 | 3074篇 |
1974年 | 3688篇 |
1973年 | 3646篇 |
1972年 | 3372篇 |
1971年 | 3223篇 |
1970年 | 3136篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils. 相似文献
52.
A. Younger 《Soil Use and Management》1989,5(4):150-154
Abstract. Comparisons of crop production on recently reinstated soil in Northumberland have shown that the reduced yield potential of such soil may not be inevitable. Storage of soil in bunds did not greatly reduce subsequent crop yields, but failure to drain the land did. Provided an effective drainage scheme was installed, arable and grass crops could be grown successfully, responding very well to additions of nitrogen fertilizer and other normal good husbandry practices. To date it seems that neither deep cultivation nor the use of grass leys were as effective in the restoration process as had been expected. 相似文献
53.
L. AUDIGÉ 《Australian veterinary journal》1992,69(11):268-271
Blood samples were collected from 91 rusa deer (Cervus timorensis russa), immediately after being shot. Serum mean biochemical values from shot deer are presented for blood urea nitrogen, creatinine, creatine kinase, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, total protein, albumin, calcium, and phosphorus. Mean total protein and albumin increased with age. There was an age-associated increase of gamma globulins. Mean creatine kinase activity and creatinine, albumin and phosphorus concentrations were higher in stags than in hinds. Pregnant hinds had lower mean creatine kinase activity and phosphorus and higher mean alanine aminotransferase and total protein than non-pregnant hinds. Mean calcium concentration increased when deer were agitated before bleeding. 相似文献
54.
Three in vitro assays to detect benzimidazole resistance, namely, the egg-hatch assay, tubulin-binding assay, and a larval-development assay, were evaluated by estimating the level of benzimidazole resistance in three field isolates of Haemonchus contortus compared with a susceptible reference strain. Comparisons were also made with estimates of benzimidazole resistance of the three field strains obtained from an in vivo controlled anthelmintic efficacy test. All three in vitro tests showed similar, consistent results which also suggested greater sensitivity than the in vivo assay. These results indicate that selection of an in vitro technique to determine benzimidazole resistance should therefore be based on considerations other than precision, such as technical expertise, availability of equipment, cost and speed in which diagnosis is required. 相似文献
55.
Little is known about the effect of fertilization on the N uptake of sunflowers. A 42 factorial trial with 0, 60, 120 and 180 kg N ha−1 and 0, 15, 30 and 45 kg P ha−1 was conducted over three years. The N content and concentration of leaves, stems and capitula were determined at three growth stages. High N levels increased the N content and concentration of all plant parts at all growth stages sharply. High P levels increased the N content of all plant components through better growth. P has an inconsistent effect on N concentration but tended to decrease it. After flowering the crop assimilated 20 to 25 % of the total N. This implies that N applied can still be applied and utilized by the crop at a late stage. This should be substantiated by further research. 相似文献
56.
J. Kocielniak 《Journal of Agronomy and Crop Science》1993,171(2):73-81
Night chilling (5 °C) subsequently lowered photosynthetic intensity in the leaves of maize seedlings at 20 °C through an increase in leaf diffusive resistance brought on by lower tissue water content in morning hours. A more significant increase in leaf diffusion resistance was observed when soil temperature was lowered than in the case of lower air temperature.
The unfavorable effect of soil and air cooling temperature on photosynthesis was limited by air saturated with water vapour. However, as a result of lowering the night temperature from 5 °C to 1 °C, the efficiency of the protective influence of higher atmospheric humidity was decreased. This demonstrates that the participation of factors unrelated to plant water status in inhibiting photosynthesis increases with lower night temperatures.
An additional reason for inhibited photosynthesis following cool nights was a decrease in chlorophyll accumulation, below 50 μg per 1 cm2 of leaf area. 相似文献
The unfavorable effect of soil and air cooling temperature on photosynthesis was limited by air saturated with water vapour. However, as a result of lowering the night temperature from 5 °C to 1 °C, the efficiency of the protective influence of higher atmospheric humidity was decreased. This demonstrates that the participation of factors unrelated to plant water status in inhibiting photosynthesis increases with lower night temperatures.
An additional reason for inhibited photosynthesis following cool nights was a decrease in chlorophyll accumulation, below 50 μg per 1 cm
57.
In a companion paper we derived the correct analysis for gerechte designs with uncorrected errors. Here we show that this correct analysis cannot be justified by the usual randomization argument. However, when the regions are rectangular there is a randomization procedure which validates an analysis with three separate error terms. We also outline other developments in design and analysis that may be more satisfactory. 相似文献
58.
P.A. Burrough 《Soil Use and Management》1989,5(1):3-8
Abstract. Good land management needs information about land resources and the processes taking place in the landscape. In practical land evaluation this information is often expressed in terms of land qualities. The original survey data are stored in geographical information systems where they can be used to estimate the values of appropriate land qualities. Land qualities are complex attributes of land used in planning that may be derived from the original attributes through empirical threshold or regression models, or from process-based deterministic or stochastic simulation models. In order to improve estimates of the distribution of land qualities in space and time, and hence to improve planning decisions, the models require data with a much better spatial resolution than is usually available. The problems and dangers associated with the ad hoc linkage of simulation models and GIS are discussed. Particular attention needs to be paid to the problems of error propagation and costs and benefits when using models. 相似文献
59.
A survey on coccidial infections in goats from central Spain was carried out. Fifty-five goat farms from 28 localities belonging to the three bioclimatic subregions of the area were visited. Individual samples (702) were obtained from the rectum of 130 young (under 1 year of age) and adult (572 over 1 year of age) goats. Coproscopical analyses showed a 100% prevalence and a moderate average intensity (7606.48 +/- 17918.78 Eimeria oocysts per gram of faeces), although wide variations were seen among herds and among individuals within each goat flock. Statistical analysis showed a strong age-related reduction in oocysts output in goats up to 4 years of age. The intensity of coccidial infections (young and adult goats, herds) was independent of the prevailing bioclimatic conditions. Heavier infections in young goats were found in bigger herds, whereas adult goats from these same big flocks (over 300 animals) showed the lowest oocyst output. Under our conditions, neither the female restocking rate nor the age structure seemed to play a significant role in the intensity of the Eimeria infections. 相似文献
60.
Plasma triglyceride concentration during intravenous infusions of propofol and Intralipid in sheep 总被引:1,自引:0,他引:1
B. M. Q. Weaver D. Raptopoulos † G. E. Staddon W. W. Mapleson‡ 《Veterinary anaesthesia and analgesia》1996,23(1):15-19
Plasma triglyceride concentrations were measured in sheep given Intralipid or propofol, which is carried in a vehicle very similar to 10% Intralipid. A bolus dose was administered followed immediately by an infusion of the same agent for 2 h. In the animals that received propofol, the measured concentration increased by a mean amount of 3.39 mmol/l when the infusion rate was l ml/min (Group Pl) and by 7.13 mmol/l when it was 2 ml/min (Group P2). When 10% Intralipid was administered and infused at 1 ml/min (Group I10), the measured concentration increased only by 0.95 mmol/l. One hour after stopping the infusion, the excess of measured concentration over baseline had decreased in the Pl and I 10 groups to 0.52 and 0.13, respectively, of the corresponding maximum excess. The method adopted for measuring plasma triglycerides is widely used in hospitals; however, an incidental observation revealed that it is inappropriate in the presence of injections of propofol or Intralipid. Despite this, evidence and argument are presented to support the conclusion that, with propofol, plasma triglyceride concentrations increased more rapidly during the infusions and returned to baseline more slowly than with a corresponding amount of Intralipid. 相似文献