全文获取类型
收费全文 | 173369篇 |
免费 | 9408篇 |
国内免费 | 843篇 |
专业分类
林业 | 7243篇 |
农学 | 5183篇 |
基础科学 | 1250篇 |
19621篇 | |
综合类 | 35925篇 |
农作物 | 6442篇 |
水产渔业 | 7644篇 |
畜牧兽医 | 87806篇 |
园艺 | 2232篇 |
植物保护 | 10274篇 |
出版年
2019年 | 1570篇 |
2018年 | 2307篇 |
2017年 | 2546篇 |
2016年 | 2312篇 |
2015年 | 2159篇 |
2014年 | 2443篇 |
2013年 | 6264篇 |
2012年 | 4802篇 |
2011年 | 5789篇 |
2010年 | 3850篇 |
2009年 | 3699篇 |
2008年 | 5373篇 |
2007年 | 5255篇 |
2006年 | 4928篇 |
2005年 | 4635篇 |
2004年 | 4276篇 |
2003年 | 4478篇 |
2002年 | 4243篇 |
2001年 | 4708篇 |
2000年 | 4720篇 |
1999年 | 3813篇 |
1998年 | 1642篇 |
1995年 | 1684篇 |
1994年 | 1555篇 |
1992年 | 3272篇 |
1991年 | 3632篇 |
1990年 | 3562篇 |
1989年 | 3559篇 |
1988年 | 3372篇 |
1987年 | 3326篇 |
1986年 | 3424篇 |
1985年 | 3275篇 |
1984年 | 2745篇 |
1983年 | 2426篇 |
1982年 | 1688篇 |
1981年 | 1576篇 |
1979年 | 2564篇 |
1978年 | 2111篇 |
1977年 | 1882篇 |
1976年 | 1850篇 |
1975年 | 2005篇 |
1974年 | 2535篇 |
1973年 | 2460篇 |
1972年 | 2463篇 |
1971年 | 2282篇 |
1970年 | 2262篇 |
1969年 | 2061篇 |
1968年 | 1727篇 |
1967年 | 1898篇 |
1966年 | 1626篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Michael B. New 《Aquaculture (Amsterdam, Netherlands)》1980,21(2):101-128
This paper contains a bibliography of papers published on dietary and nutritional work with shrimps and prawns. In addition, selected papers on related topics, such as the nutrition of other crustacea, the natural food of shrimps and prawns, and physiology, are included. The bibliography is intended to be an aid to existing workers in the field of shrimp and prawn nutrition, to be a launch pad for scientists entering this field for the first time, and to assist those wishing to review specific aspects of this subject. 相似文献
192.
193.
B.J. Macauley 《Soil biology & biochemistry》1979,11(2):175-179
Fungal succession on untreated and fungicide- and insecticide-treated leaves of Eucalyptus pauciflora was compared. Natural succession on untreated leaves fits the general scheme for succession on deciduous tree leaves. Initial colonizers are species of Coelomycetes and Moniliales. When the numbers of Coelomycetes decrease in the late stages of decomposition, the frequency of Penicillium species and species of Zygomycetes increases. The succession is affected only marginally by DDT and dieldrin treatment while benomyl severely restricts the occurrence of most fungal species. The effect of benomyl persists even after exposure for 48 weeks in the field. 相似文献
194.
195.
A proton magnetic resonance spectroscopic method for determining disulfiram in the bulk drug product and in the formulated material was collaboratively studied. The method depends on the use of chloroform-d as a solvent and hexamethylcyclotrisiloxane as the internal standard. No interference from tablet excipients was observed. The method is rapid and specific. Eighteen laboratories analyzed duplicate samples of a bulk drug product, a 250 mg tablet composite, and a 500 mg tablet composite. The average per cent results and standard deviations were 99.7 +/- 1.4, 100.9 +/- 2.0, and 99.9 +/- 2.2, respectively. 相似文献
196.
Little information exists concerning the effects of long-term fungicide programs on the qualitative and quantitative characteristics of fusaria in turfgrasses and in turfgrass soils. These effects were studied on Poa pratensis L, turfgrasses at three locations, using 14 fungicides, one nematicide, and five mixed fungicide programs. Some fungicides increased the numbers of fusaria in soil and thatch, some had no effect, and others greatly reduced the numbers. Changes in Fusarium species' compositions occurred independently from the changes in propagule numbers. The proportion of Fusarium-colonized turfgrass crowns was generally higher in fungicide-treated than in nontreated turfgrasses. 相似文献
197.
E J de Vries J Zeeman R J Esser B Borsje F J Mulder 《Journal of the Association of Official Analytical Chemists》1979,62(6):1285-1291
Vitamin D is determined in preparations containing other fat-soluble vitamins by high performance liquid chromatography (HPLC). The unsaponifiable residue is extracted and separated from interferences by reverse phase chromatography; the fraction corresponding to vitamin D3 is collected and quantitated using normal phase chromatography (amylalcohol-n-hexane as mobile phase) by measuring the vitamin D3 and pre-vitamin D3 peaks at 254 nm. Previtamin D3 content is calculated as vitamin D3 with a conversion factor (determined on the equipment used). Application of the method to vitamin AD3 mixtures in oils gives 98-102% recovery. The reproducibility, using an external standard, is 2-3%, calculated as the coefficient of variation; with an internal standard, the coefficient of variation is 1-1.5%. The method measures potential vitamin D3 content in preparations containing greater than or equal to 200 IU/g in the presence of all known vitamin D3 isomers, vitamin A, and vitamin E. 相似文献
198.
199.
Storage losses in moist hay treated with propionic acid were compared with those occurring in untreated moist hay in two experiments and with field-cured hay in three experiments. Dry matter losses in treated hays ranged from 41 to 8.6% and from 1.7 to 12.6% in untreated hays. Digestible organic matter losses in both treated and untreated hays were generally greater than dry matter losses. Only in one experiment did propionic acid application significantly reduce nutrient losses in moist hays. Nutrient losses, and water-soluble carbohydrate losses in particular, were shown to be correlated with maximum and cumulative bale temperatures during storage in two of the experiments. The rise in hale temperatures during storage was reduced in all three experiments, to a greater or lesser extent, by application of the additive. Loss of propionic acid from the hay during and after application was very large. In the three experiments 86.2, 85.3 and 85.6% of the acid applied was lost by the end of the storage period. Acid distribution studies indicated that variation in acid concentration within bales was as great as between bales. It was concluded that more research is needed into applicator design and position on the baler and into alternative application methods if the benefits of propionic acid as a moist hay preservative are to be fully exploited. 相似文献
200.