全文获取类型
收费全文 | 119489篇 |
免费 | 6577篇 |
国内免费 | 70篇 |
专业分类
林业 | 5791篇 |
农学 | 4265篇 |
基础科学 | 755篇 |
14859篇 | |
综合类 | 17087篇 |
农作物 | 4379篇 |
水产渔业 | 6263篇 |
畜牧兽医 | 63734篇 |
园艺 | 1544篇 |
植物保护 | 7459篇 |
出版年
2018年 | 1800篇 |
2017年 | 1923篇 |
2016年 | 1848篇 |
2015年 | 1605篇 |
2014年 | 1941篇 |
2013年 | 4560篇 |
2012年 | 3478篇 |
2011年 | 4203篇 |
2010年 | 2841篇 |
2009年 | 2811篇 |
2008年 | 4177篇 |
2007年 | 3998篇 |
2006年 | 3866篇 |
2005年 | 3570篇 |
2004年 | 3523篇 |
2003年 | 3504篇 |
2002年 | 3276篇 |
2001年 | 4248篇 |
2000年 | 4108篇 |
1999年 | 3332篇 |
1998年 | 1453篇 |
1997年 | 1329篇 |
1996年 | 1248篇 |
1995年 | 1378篇 |
1994年 | 1309篇 |
1993年 | 1228篇 |
1992年 | 2564篇 |
1991年 | 2707篇 |
1990年 | 2878篇 |
1989年 | 2639篇 |
1988年 | 2478篇 |
1987年 | 2398篇 |
1986年 | 2369篇 |
1985年 | 2257篇 |
1984年 | 1891篇 |
1983年 | 1652篇 |
1982年 | 1075篇 |
1979年 | 1681篇 |
1978年 | 1317篇 |
1977年 | 1126篇 |
1976年 | 1135篇 |
1975年 | 1159篇 |
1974年 | 1325篇 |
1973年 | 1362篇 |
1972年 | 1363篇 |
1971年 | 1282篇 |
1970年 | 1250篇 |
1969年 | 1210篇 |
1967年 | 1094篇 |
1966年 | 1047篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The uterine and umbilical vessels of 12 pregnant ponies were catheterised to study foetal metabolism. The effects of this procedure on maternal and foetal cardiovascular, respiratory, metabolic and adrenocortical activity were monitored during and after surgery. Premedication with acepromazine-butorphanol-detomidine was followed by induction of anaesthesia with detomidine and ketamine and maintenance, using mechanical ventilation, with halothane in oxygen and nitrous oxide. Mean maternal arterial blood pressure was greater than 70 mmHg during anaesthesia and arterial oxygen tension remained over 100 mmHg. The foetuses were adequately oxygenated but were hypercapnic and lactic acidaemic. Most maternal and foetal blood gases and metabolites had returned to normal by 24 h, although foetal plasma lactate fell more slowly. The maternal adrenocortical discharge was less severe than reported previously and plasma cortisol had fallen to basal levels by 48 h after surgery. Foetal plasma cortisol remained low and did not change during or after surgery. Arterio-venous metabolite and gas tension differences across the uterine and umbilical circulations were slightly greater at operation than in the recovery period, suggesting that uteroplacental perfusion may have been impaired during surgery. Post-operative recovery of the mare and foetus was satisfactory and subsequent problems associated with the foetal catheters were not related to the anaesthesia or surgery. 相似文献
22.
29 samples of commonly used surfaces were tested for their water characteristics (litre weight, water capacity, water binding, water evaporation) and their contribution to airborne fungal spores (dust formation, dust setting). The results are discussed in comparison to the literature with regard to the environment. The results are: 1. Any surface--no matter of what material--eventually causes air pollution with fungal spores and dust. 2. Correct watering prevents air pollution by any surface. 3. Artificial products have no advantage over natural materials in the parameters tested. 4. The question of proper disposal of old surface material has to be clarified before purchase. The results show that a mixture of sand and wood shavings should be recommended as a surface for indoor arenas, especially in regard to environmental protection and proper disposal. 相似文献
23.
24.
D. Bilalis P. Efthimiadis & G. Karagiannis 《Journal of Agronomy and Crop Science》2001,187(2):121-126
The effect of three herbicides, diclofop-methyl (DM), imazamethabenz-methyl (IM) and fenoxaprop-ethyl (FE), was investigated at the recommended rate (×) and double the recommended rate (2×) in a durum wheat crop. FE had the smallest effect on root system characteristics, while IM had the greatest effect. For all herbicides, the double rate treatment gave a greater statistical reduction than the single rate for root system characteristics. FE had the smallest effect on the activity of aerobic microorganisms, while DM gave the greatest reduction, 10 days after application, and all three herbicides reduced earthworm abundance. DM gave the smallest reduction in the number of tillers and in plant height, while the double rate of IM gave the greatest reduction. For all three herbicides, double the recommended rate resulted in a significant reduction in the weight of 1000 seeds, while no statistically significant deviations were noted at the recommended rate. Finally, the use of all three herbicides resulted in significantly lower statistical yields compared to the sample (control plot), although there were no significant statistical differences among them, for either recommended or double recommended rates. 相似文献
25.
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
26.
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
27.
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
28.
The study describes plumage modifications and specific feather malformations, as related to the domestication process of different poultry species. The modifications include naked necks, leg feathering, frizzle feathering, silky feathering, fat quills, and feather abnormalities caused by behavioural hypertrophies. Most of these plumage modifications correspond to the breed standard for exhibition poultry fancy. However, they impair the normal function of these animals. The negative influences comprise disorders in social behaviour, loss of typical plumage functions and disabilities of normal mobility, as well as genetic defects and pathogenic predispositions. 相似文献
29.
Anthony S. Moore BVSc MVSc Gregory K. Ogilvie David M. Vail 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(5):343-344
Twenty-five dogs with malignant lymphoma refractory to chemotherapy were treated with actinomycin D at a median dose of 0.7 mg/m2 (range, 0.5 to 0.9 mg/m2 ) every 3 weeks. The dogs treated had received between 2 and 8 chemotherapeutic agents (median 7), for a median of 266 days before being treated with actinomycin D. For 23 of the 25 dogs, previous chemotherapy included doxorubicin. No dog responded to actinomycin D chemotherapy. 相似文献
30.
N Machida T Nakamura K Kiryu S Haramaki K Too 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(6):1213-1216
A 20-year-old pony mare with persistent ventricular tachycardia (VT) was examined cardiopathologically. At necropsy, the heart was enlarged and rounded with both ventricular dilatation. In a longitudinal section of the ventricular septum, a large grayish white patchy lesion (5 x 25 mm) was detected in the relatively higher portion. Microscopically, the lesion was extensive myocardial fibrosis located in the vicinity of the proximal part of the left bundle branch. Partially the fibrotic lesion was in contact with the branch. Such a lesion might play an important role in creating a suitable background for the development of VT via automaticity or reentry mechanism. 相似文献