全文获取类型
收费全文 | 1049篇 |
免费 | 42篇 |
国内免费 | 1篇 |
专业分类
林业 | 124篇 |
农学 | 24篇 |
基础科学 | 5篇 |
187篇 | |
综合类 | 128篇 |
农作物 | 42篇 |
水产渔业 | 50篇 |
畜牧兽医 | 469篇 |
园艺 | 11篇 |
植物保护 | 52篇 |
出版年
2021年 | 14篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 18篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 42篇 |
2012年 | 34篇 |
2011年 | 33篇 |
2010年 | 30篇 |
2009年 | 28篇 |
2008年 | 45篇 |
2007年 | 38篇 |
2006年 | 34篇 |
2005年 | 33篇 |
2004年 | 39篇 |
2003年 | 38篇 |
2002年 | 17篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 25篇 |
1998年 | 16篇 |
1994年 | 11篇 |
1992年 | 19篇 |
1991年 | 30篇 |
1990年 | 15篇 |
1989年 | 29篇 |
1988年 | 9篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1982年 | 9篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 16篇 |
1973年 | 11篇 |
1972年 | 14篇 |
1970年 | 20篇 |
1969年 | 11篇 |
1968年 | 14篇 |
1967年 | 21篇 |
1966年 | 9篇 |
1936年 | 7篇 |
排序方式: 共有1092条查询结果,搜索用时 875 毫秒
61.
The prediction of grain and stover quality parameters in maize {Zea mays L.) by near infra-red reflectance spectroscopy (NIRS) was studied. A total of 110 grain and 135 stover samples originating from different genotypes and environments were assayed. Calibration equations for content of crude protein (CP), crude fat (CF), starch (ST), and water soluble carbohydrates (WSC) in grain were obtained by multiple linear regression of known manual values on NIRS data from the odd numbered samples. Calibrations for CP, acid detergent fibre (ADF), in vitro digestible organic matter according to the Tilley & Terry (IVDOM-T & T) and the gas production (IVDOM-Gp) method, respectively, and metabolizable energy (ME) in stover were developed analogously. Equations were validated with the evennumbered .samples and for ME additionally with the 1584 stover samples from an experiment with 66 F1 hybrids tested in six environments. The coefficients of multiple determination (R2) of the prediction equations ranged from 0.80 for IVDOM-Gp and ME in stover to 0.94 for CP in grain. Standard errors of calibration (SEC) and prediction (SEP) were in most cases not higher than commonly reported for conventional manual assays. With regard to the correct ranking of hybrids, prediction equations for ME applied well to stover samples from other environments with one exception. We concluded that NIRS can evaluate the quality traits investigated to a similar degree to that of conventional methods of analysis. Since NIRS is simple and safe to operate and allows rapid screening of several quality traits simultaneously, it should be particularly attractive for breeding purposes. 相似文献
62.
Detlef Deumlich Roger Funk Monika Frielinghaus Walter‐Alexander Schmidt Olaf Nitzsche 《植物养料与土壤学杂志》2006,169(3):370-381
Present research in Germany on water, wind, and tillage erosion is examined. Existing soil‐protection strategies, laws, and guidelines are outlined. These are the result of extensive scientific investigations and the adoption of existing international knowledge. The most common methodologies currently used in Germany are reviewed. They allow an estimation of the water‐ and wind‐erosion risks as well as methods for their reduction. The results enable an aim‐orientated, site‐specific, risk‐adequate approach to implementing control measures in an easily understood framework. The most important remaining research problems are explained. 相似文献
63.
Schmidt FH 《Science (New York, N.Y.)》1978,199(4335):1286-1290
64.
65.
Sanloup C Schmidt BC Chamorro Perez EM Jambon A Gregoryanz E Mezouar M 《Science (New York, N.Y.)》2005,310(5751):1174-1177
The reactivity of xenon with terrestrial oxides was investigated by in situ synchrotron x-ray diffraction. At high temperature (T > 500 kelvin), some silicon was reduced, and the pressure stability of quartz was expanded, attesting to the substitution of some xenon for silicon. When the quartz was quenched, xenon diffused out and only a few weight percent remained trapped in samples. These results show that xenon can be covalently bonded to oxygen in quartz in the lower continental crust, providing an answer to the missing xenon problem; synthesis paths of rare gas compounds are also opened. 相似文献
66.
67.
An instrument providing a new, rapid, and accurate method of determining the number and critical radii of condensation nuclei with radii under 200 angstroms is described. Based on the principle of the cloud chamber, the instrument measures transient changes in the attenuation and scattering of a monochromatic light beam by the growing fog droplets. From data obtained the absolute number concentration and radii of condensation nuclei can be calculated. Preliminary studies of aerosol formation in beta-irradiated mixtures of air and sulfur dioxide showed that carbon monoxide and methane inhibit the formation of nuclei; relative rate constants can be deduced. Some applications of this instrument for environmental and basic research are pointed out. 相似文献
68.
Burgmann R Schmidt D Nadeau RM d'Alessio M Fielding E Manaker D McEvilly TV Murray MH 《Science (New York, N.Y.)》2000,289(5482):1178-1182
The Hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace. Dislocation models of the surface deformation adjacent to the Hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at approximately 7 millimeters per year to the bottom of the seismogenic zone along a approximately 20-kilometer-long northern fault segment. Microearthquakes with the same waveform repeatedly occur at 4- to 10-kilometer depths and indicate deep creep at 5 to 7 millimeters per year. The difference between current creep rates and the long-term slip rate of approximately 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern Hayward fault adjacent to the locked 1868 earthquake rupture, which broke the southern 40 to 50 kilometers of the fault. The potential for a major independent earthquake of the northern Hayward fault might be less than previously thought. 相似文献
69.
本文介绍了国产喷雾器喷头的几个主要性能参数与国外著名喷头公司产品的对比结果、并提出了改进我国喷头产品的若干建议。如:1.影响侧向进液式喷头喷量变异的因素。2.缝隙式扇雾喷头药液沉积横向分布中的牛角、对喷杆式喷雾器药液沉积分布均匀性有着极坏的影响。 相似文献
70.