全文获取类型
收费全文 | 97340篇 |
免费 | 5392篇 |
国内免费 | 2955篇 |
专业分类
林业 | 5988篇 |
农学 | 6342篇 |
基础科学 | 2486篇 |
12627篇 | |
综合类 | 19178篇 |
农作物 | 4059篇 |
水产渔业 | 4737篇 |
畜牧兽医 | 42137篇 |
园艺 | 1802篇 |
植物保护 | 6331篇 |
出版年
2022年 | 945篇 |
2021年 | 1460篇 |
2020年 | 1410篇 |
2019年 | 1560篇 |
2018年 | 1798篇 |
2017年 | 2110篇 |
2016年 | 1891篇 |
2015年 | 2071篇 |
2014年 | 2186篇 |
2013年 | 4407篇 |
2012年 | 3614篇 |
2011年 | 4130篇 |
2010年 | 3340篇 |
2009年 | 3098篇 |
2008年 | 3722篇 |
2007年 | 3636篇 |
2006年 | 3498篇 |
2005年 | 3235篇 |
2004年 | 2412篇 |
2003年 | 2429篇 |
2002年 | 2241篇 |
2001年 | 2913篇 |
2000年 | 2959篇 |
1999年 | 2620篇 |
1998年 | 1370篇 |
1997年 | 1243篇 |
1996年 | 1090篇 |
1995年 | 1196篇 |
1994年 | 1158篇 |
1993年 | 1058篇 |
1992年 | 1830篇 |
1991年 | 1948篇 |
1990年 | 1754篇 |
1989年 | 1677篇 |
1988年 | 1567篇 |
1987年 | 1521篇 |
1986年 | 1470篇 |
1985年 | 1394篇 |
1984年 | 1132篇 |
1983年 | 1060篇 |
1979年 | 1026篇 |
1978年 | 787篇 |
1977年 | 760篇 |
1975年 | 781篇 |
1974年 | 938篇 |
1973年 | 902篇 |
1972年 | 860篇 |
1971年 | 788篇 |
1970年 | 825篇 |
1969年 | 795篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A field experiment was conducted with different nitrogen regimes to assess the growth and yield performance of wheat genotypes which differ in nitrate assimilation potential. Genotypic differences in biomass accumulation were observed at different growth stages. The nitrogen treatment had little effect on biomass accumulation at early stages of growth, while at later stages of growth there was enhanced biomass accumulation when N was applied in more than two splits. On an average, genotypes with high nitrate reductase activity (the 'HNR' genotypes) accumulated 14.2 % more biomass than the genotypes with low nitrate reductase activity ('LNR' genotypes) when an extra dose (40 kg N ha−1 ) of nitrogen was given at the time of anthesis. The application of nitrogen in more than two splits increased grain yield of both 'HNR' and 'LNR' genotypes mainly by increasing grain weight per ear. The application of an extra dose of nitrogen (40 kg N ha−1 ) at the time of anthesis increased grain yield of 'HNR' genotypes by 38.5 % as compared to 'LNR' genotypes. 相似文献
32.
Muscle biopsies were taken from the middle gluteal muscle of 28 Standardbred trotters, 3-4 years of age. The 13 horses in Group T were trained consistently from 18 months of age, whereas the 15 horses in Group UT were not exposed to any systematic training before 3 years of age. Group T horses had a lower percentage of Type IIB fibres (31%) than did Group UT horses (39%). Citrate synthase (CS) activity, representing oxidative capacity, was higher in Group T (72 mmol kg-1 min-1) than in Group UT (47 mmol kg-1 min-1). Biopsies were taken from 4 horses in each group when they were foals and then annually until 3-4 years of age. Results from this study indicate that regular training of Standardbreds from 18 months of age resulted in increased CS activity and a decrease in the percentage of Type IIB fibres. This study shows that training, not growth, is the main factor that induces a high oxidative capacity and a high Type IIA/IIB fibre ratio in muscle of Standardbred trotters. 相似文献
33.
B H Janke 《Journal of the American Veterinary Medical Association》1989,195(8):1114-1115
A toxic dose of selenium administered by IM injection to a 3-year-old Chihuahua resulted in pulmonary edema and death. The compound had been dispensed to the owner inadvertently in combination with a vitamin E preparation. Vitamin and mineral products often are considered safe for use in megadoses by the uninformed public. The potential danger of selenium overdosage should not be underestimated. 相似文献
34.
Ovine-derived fibroblasts were used to validate an insulin-like growth factor I (IGF-I) membrane-receptor binding assay system. Competitive binding using fibroblasts revealed that half-maximal inhibition of 125I-IGF-I binding by IGF-I was 2.3 nM. SDS-polyacrylamide gel electrophoresis analysis of specific protein-associated 125I-IGF-I was consistent with the migration of 125I-IGF-I-labeled Type I IGF receptor alpha-subunits at Mr 133,000 daltons. Further, the efficiency of two cell solubilization methods was examined and time-dependent binding equilibrium was determined for the membrane assay system. Satellite cell-derived myotubes were subsequently isolated from primary satellite cell cultures established from the semimembranosus muscles of high and low efficiency-of-gain (EOG) Targhee rams, and IGF-I receptor dynamics were measured. A membrane competitive binding study revealed that half-maximal inhibition of 125I-IGF-I binding was achieved by 1-ng IGF-I for low, and 10-ng IGF-I for high, EOG myotube membrane preparations. Kd values were similar between the high EOG (4.78 nM) and low EOG (2.95 nM) groups; however, receptor concentrations (Bmax) appeared to differ between groups. High EOG membrane receptor Bmax was 3.88 pmole/micrograms protein (19.87 pmole/micrograms DNA), whereas low EOG membrane receptor Bmax was 1.22 pmole/micrograms protein (9.28 pmole/micrograms DNA). These preliminary findings support the hypothesis that genetic selection for EOG results in altered satellite cell responsiveness to IGF-I. 相似文献
35.
36.
S Katsuda H Hosomi M Shiomi Y Watanabe 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(4):669-673
Effects of atherosclerosis on the mean value and daily variation of arterial pressure were studied in 12 Watanabe-heritable hyperlipidemic (WHHL) rabbits aged 12 to 35 months and 25 normal Japanese white rabbits aged 6 to 30 months. A pressure catheter was inserted through the left subclavian artery under pentobarbital anesthesia. A few days after the catheterization, the mean arterial pressure (MAP) of the rabbits, which were active and in a good state of appetite, was recorded by an analogue-to-digital converter every second for about 6 hrs and stored in a computer. The mean (M) and standard deviation (SD) in the WHHL rabbit, calculated from each successive MAP record, ranged widely from 85.8 to 131.4 mmHg and 5.6 to 12.6 mmHg, respectively. There was no significant correlation between M and SD in the WHHL rabbit. M and variance (V) of MAP in the WHHL rabbit were significantly higher than those in the normal rabbit. M did not show any significant change with increasing ages, whereas SD increased significantly with aging in the WHHL rabbit. Concentrations of serum total cholesterol and triglyceride in the WHHL rabbit were 475 and 328 mg/dl, which were about nine and seven times as high as those in the normal rabbit, respectively. Macroscopic and histopathological examinations of the aorta revealed development and spread of sclerotic lesions with aging in the WHHL rabbit. We can conclude that development of atherosclerosis with aging in the WHHL rabbit causes malfunction of the baroreceptors, which contributes to hypertension and lability of arterial pressure. 相似文献
37.
J Jieyuan P B Spradbrow 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1992,39(5):388-390
Chickens were given various fowlpox vaccines on food pellets--a commercial vaccine (strain M), and the same strain after a single passage on chorio-allantoic membrane or in chicken embryo fibroblasts. All three oral vaccines induced antibodies at levels similar to those induced by commercial strain M administered to the wingweb. The oral vaccine derived from chorio-allantoic membrane gave protection similar to that obtained with vaccine administered by the wingweb, but this required a thousandfold more virus. 相似文献
38.
39.
40.