全文获取类型
收费全文 | 295262篇 |
免费 | 16324篇 |
国内免费 | 724篇 |
专业分类
林业 | 24058篇 |
农学 | 14170篇 |
基础科学 | 3036篇 |
44506篇 | |
综合类 | 40405篇 |
农作物 | 17409篇 |
水产渔业 | 17292篇 |
畜牧兽医 | 120471篇 |
园艺 | 6426篇 |
植物保护 | 24537篇 |
出版年
2019年 | 3719篇 |
2018年 | 4040篇 |
2017年 | 4466篇 |
2016年 | 4843篇 |
2015年 | 4403篇 |
2014年 | 5743篇 |
2013年 | 16370篇 |
2012年 | 6904篇 |
2011年 | 8962篇 |
2010年 | 7575篇 |
2009年 | 8053篇 |
2008年 | 8331篇 |
2007年 | 7396篇 |
2006年 | 8017篇 |
2005年 | 7252篇 |
2004年 | 7164篇 |
2003年 | 6898篇 |
2002年 | 6296篇 |
2001年 | 7115篇 |
2000年 | 6855篇 |
1999年 | 6102篇 |
1998年 | 4247篇 |
1997年 | 4316篇 |
1996年 | 4055篇 |
1995年 | 4725篇 |
1994年 | 4183篇 |
1993年 | 3859篇 |
1992年 | 5343篇 |
1991年 | 5645篇 |
1990年 | 5393篇 |
1989年 | 5379篇 |
1988年 | 4845篇 |
1987年 | 4962篇 |
1986年 | 4985篇 |
1985年 | 5169篇 |
1984年 | 4548篇 |
1983年 | 4291篇 |
1982年 | 3331篇 |
1981年 | 3209篇 |
1980年 | 3122篇 |
1979年 | 4097篇 |
1978年 | 3561篇 |
1977年 | 3147篇 |
1976年 | 3030篇 |
1975年 | 2998篇 |
1974年 | 3481篇 |
1973年 | 3469篇 |
1972年 | 3335篇 |
1971年 | 3252篇 |
1970年 | 3132篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
Sodium selenite was mixed in a commercial pig food so as to increase the original selenium content (0.126 ppm) by 1.2 ppm. The supplemented food was given to 7 pigs during 78 days. A control group of as many pigs was given the non-supplemented commercial food. The pigs were killed, starting 4 hours after the last selenium-supplemented food had been given and then with intervals during the next 14 days. Small but significant increases of tissue selenium were noticed in liver and striated muscle as compared with the control animals. The kidneys showed no increase. 相似文献
984.
Uptake of I131-labelled triiodothyronine by erythrocytes (EU test) as a test of thyroid function has been studied in cattle. The normal EU value for 141 Swedish Red-and-white cows was 6.99 ± 0.95 (range 4.45–10.23) at an incubation time of one hour. Statistically significantly higher values were obtained for newly-calved cows. The EU values for calves are significantly higher but by 12 to 18 months of age decline to the same level as for older cows.The principle of the test is described and the results obtained compared with those for human beings. The EU test is suitable for screening thyroid function for large groups of animals and for studying associations between thyroid activity and different production qualities. 相似文献
985.
J. L. HAMMERTON 《Weed Research》1965,5(1):13-26
Summary. Seeds of Polygonam persiaria were collected from seven localities during 1962. In 1963 plants of these seven populations were grown in the field and sampled at regular intervals over the period 21st June to 13th August. At all samplings there were differences between populations in total dry weight, in leaf area index and in total nitrogen content, and populations also differed in the date of flowering. The populations also differed significantly in relative growth rate, leaf area ratio, net assimilation rate and relative nitrogen absorption rate. The variations in net assimilation rate did not appear to be closely associated with variations in leaf area index. Certain growth attributes were correlated with the latitude of origin, and it is tentatively suggested that the populations may represent genetically distinct latitudinal ecotypes.
Études sur des espèces de mauvaises herbes du genre Polygonum L. 相似文献
Études sur des espèces de mauvaises herbes du genre Polygonum L. 相似文献
986.
987.
Codex alimentarius approach to pesticide residue standards 总被引:1,自引:0,他引:1
R B Maybury 《Journal of the Association of Official Analytical Chemists》1989,72(3):538-541
To protect consumers' health, most countries have maximum legal limits for pesticide residues in foods. Trade difficulties can arise when limits differ between countries. The Codex Alimentarius Commission was established in 1962 to implement the Joint FAO/WHO Food Standards Programme, the purpose of which is to protect consumer health and ensure fair practices in international food trade. The Codex Committee on Pesticide Residues (CCPR), an intergovernmental body which advises the Commission on matters related to pesticide residues, is responsible for establishing maximum residue limits (MRLs) for pesticides in foods and feeds that move in international trade. Codex MRLs are based on residue data obtained mainly from supervised trials that reflect approved pesticide use in accordance with "good agricultural practice." MRLs must be toxicologically acceptable in terms of estimated pesticide intake by consumers. CCPR Working Groups examine problems related to establishing and implementing MRLs, including sampling and methods of analysis. Despite time and effort expended, acceptance and application of Codex MRLs face many problems in international trade. 相似文献
988.
Maximum forest productivity will only be realized through intensified management of mineral nutrition. This review examines selected individual tree and stand nutrition models. Nutrient supply is defined by mass flow and diffusion processes in a forest environment. Additionally, structures of biomass accumulation models are considered as well as nutritional limitations on assimilation functions and carbon allocation patterns. 相似文献
989.
The radii of radiation-induced color halos(RICHs) surrounding radioactive mineral inclusions in mica generally correspond closely to the calculated range of common uranogenic and thorogenic alpha particles in mica. Many exceptions are known, however, and these variants have led investigators to some rather exotic interpretations. Three RICHs found in quartz are identified as aluminum hole-trapping centers. Whereas the inner radii of these RICHs closely match the predicted range of the most energetic common alphas(39 micrometers), the color centers observed extend to 100 micrometers. Migration of valence-band holes down a radiation-induced charge potential might account for enigmatic RICHs. Such RICHs provide natural experiments in ultraslow charge diffusion. 相似文献
990.