全文获取类型
收费全文 | 12702篇 |
免费 | 309篇 |
国内免费 | 631篇 |
专业分类
林业 | 1332篇 |
农学 | 1173篇 |
基础科学 | 517篇 |
1854篇 | |
综合类 | 1767篇 |
农作物 | 769篇 |
水产渔业 | 654篇 |
畜牧兽医 | 4348篇 |
园艺 | 389篇 |
植物保护 | 839篇 |
出版年
2023年 | 88篇 |
2022年 | 155篇 |
2021年 | 236篇 |
2020年 | 203篇 |
2019年 | 220篇 |
2018年 | 246篇 |
2017年 | 390篇 |
2016年 | 390篇 |
2015年 | 494篇 |
2014年 | 437篇 |
2013年 | 459篇 |
2012年 | 740篇 |
2011年 | 663篇 |
2010年 | 431篇 |
2009年 | 351篇 |
2008年 | 406篇 |
2007年 | 313篇 |
2006年 | 351篇 |
2005年 | 1036篇 |
2004年 | 793篇 |
2003年 | 541篇 |
2002年 | 179篇 |
2001年 | 215篇 |
2000年 | 143篇 |
1999年 | 283篇 |
1998年 | 121篇 |
1997年 | 105篇 |
1996年 | 84篇 |
1992年 | 172篇 |
1991年 | 197篇 |
1990年 | 198篇 |
1989年 | 175篇 |
1988年 | 199篇 |
1987年 | 137篇 |
1986年 | 157篇 |
1985年 | 124篇 |
1984年 | 103篇 |
1979年 | 134篇 |
1978年 | 96篇 |
1977年 | 91篇 |
1975年 | 138篇 |
1974年 | 129篇 |
1973年 | 117篇 |
1972年 | 141篇 |
1971年 | 118篇 |
1970年 | 94篇 |
1969年 | 102篇 |
1968年 | 114篇 |
1967年 | 126篇 |
1966年 | 102篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
W L?scher 《DTW. Deutsche tier?rztliche Wochenschrift》1992,99(2):51-54
The article considers the attractions and dangers of homeopathic therapy from the view of a pharmacologist. Homeopathic drugs may exert pharmacodynamic (but also toxic) effects at low dilutions (D0-D6), but there is no scientific proof for specific effects of higher dilutions except for substances with a high toxic potential. Most homeopathic drugs have no reasonable basis for clinical use but, in case of toxic compounds, especially those with carcinogenic or allergic potential, homeopathy may bear risks for the animal and, because of residues in food animals, also for humans. Thus, homeopathic treatment should not be used when effective conventional treatments are available, and the use of homeopathic drugs with toxic potential should be avoided. 相似文献
12.
双孢蘑菇覆土层有益微生物消长规律 总被引:1,自引:0,他引:1
将土样制备成稀释液,采用平板涂布培养法,分析双孢蘑菇覆土期、充分发菌期,原基形成期、采收前和采收后2d5个时期土样中几种有益微生物和消长规律。结果表明,原基表成前和采收后,采白色和采收后2d5下时期土样中几种有益微生物的消化规律。结果表明,原其开前和采收后,采白色孢杆菌(Bacillus)、固氮苗(Azotobacter)和假单胞杆菌(Pseudomonas)数量增加;链霉菌(Streptomyces)数量增减比较平缓,而土灰色芽孢杆菌的数量一直呈下降趋势。 相似文献
13.
14.
15.
16.
E C?té 《Veterinary Clinics of North America: Small Animal Practice》2001,31(6):1129-45, v
Severe heart disease may cause hypotension and hypoperfusion, and ultimately circulation may cease altogether. These two clinical syndromes are cardiogenic shock and cardiac arrest, respectively. This review summarizes the causes and clinical features of each, and describes the treatment options available to clinicians managing patients in cardiogenic shock. 相似文献
17.
The objective of the current study was to evaluate the effect of unrepresentative sampling of digesta particulate matter entering the omasal canal on the accuracy of fiber flow measurements. The experimental design comprised one period, one diet, and three cows as experimental units. Within each cow, the physical and chemical composition of digesta particulate matter was assessed at seven sites within the digestive tract. Three Finnish Ayshire dairy cows, equipped with ruminal and simple-T duodenal cannulas, in extended lactation were offered grass silage twice daily on an ad libitum basis. Digesta samples were collected from the rumen (dorsal and ventral sac), reticulum, omasal canal, omasum, duodenum, and rectum to determine particle size distribution in digesta, chemical composition of various particle size fractions, and distribution of two flow markers (Cr-labeled straw and indigestible NDF [INDF]) among particle size fractions. Digesta samples were wet-sieved using sieves of 2.50, 1.25, 0.630, 0.315, 0.160, and 0.080 mm. Particulate matter was analyzed for OM, NDF, and Cr concentrations, and INDF concentration was determined based on 12-d ruminal incubation. The particle size of digesta entering the omasal canal was larger compared with the omasum or the duodenum, suggesting that omasal canal samples were not representative of particle size distribution truly escaping the rumen. The concentration of potentially digestible NDF (PDNDF) decreased with decreasing particle size. The PDNDF concentration of particulate matter retained on all sieves was greatest in the rumen and gradually decreased along the digestive tract. From the reticulorumen to the omasum, the decrease was associated with decreased particle size, reflecting selective passage of particulate matter. In contrast, from the omasum to the duodenum and rectum, the PDNDF concentration decreased within each particle size fraction without effect on particle size, indicating a nonselective passage of particulate matter between these sites. Variation between particle size fractions was slightly greater for Cr concentration than for INDF concentration, indicating that unrepresentative sampling of particulate matter had a greater effect on Cr concentration compared with that of INDF. Owing to unrepresentative sampling, NDF entering the omasal canal was overestimated by 5% using INDF and underestimated by 7% using Cr as a particle phase marker. Of total NDF digestibility, proportionally 0.90, 0.07, and 0.03 occurred in the reticulorumen, omasum, and intestines, respectively. The current results indicate that, despite unrepresentative sampling of digesta particulate matter entering the omasal canal, the errors in determined NDF flow were small. The omasum may have a greater role in postruminal NDF digestion than the intestines. 相似文献
18.
We compared the results of the ACTH stimulation tests with measurements of alkaline phosphatase and serum cholesterol during Lysodren therapy in 23 dogs with pituitary-dependent hyperadrenocorticism. The ACTH stimulation test proved to be a very sensitive parameter, by which the extent of Lysodren under- or overdosage could be reliably estimated. On the other hand, regulation of the individual Lysodren requirement was not possible by measuring AP and serum cholesterol only. However, it is highly probable that those two parameters can be used to evaluate the general state of metabolism, and they appear to be of prognostic value when greatly elevated. 相似文献
19.
两种一年生植物在替代试验中的相互竞争关系 总被引:18,自引:4,他引:14
(1)用替代试验研究了燕麦(Aneva sativa)和箭舌豌豆(Vicia sativa)在混播中的竞争相互作用。为了攻混播比例对两种植物在混播条件下的行为影响,田间试验设为5个混播总密度和5种混播比例,共了5次。(2)方差分析表明,相对总生物量(RYT)和竞争平衡指数(CBI)对总密度,混播比例和生长时间的反应敏感。总密度对RYT和CBI的影响高度显著,在大多数情况下,混播比例对RYT和CBI的影响不显著。(3)本文研究的结果表明,持续时间对RYT和CBI很强的影响,在第1次测定时,RYT值接近1而BI值接近0,这一事实表明,种间无竞争或互惠作用。而在生长旺盛期,种间竞争较为剧烈。(4)本研究结果表明,箭舌豌豆的生长严惩受到燕麦的抑制作用,这说明箭舌豌豆在与燕麦混播时表现为竞争上的弱者。 相似文献
20.
The technique of cystocentesis in dogs and cats was studied. The indications and contraindications of this method are discussed, using illustrations. 相似文献