全文获取类型
收费全文 | 24972篇 |
免费 | 1308篇 |
国内免费 | 10篇 |
专业分类
林业 | 877篇 |
农学 | 755篇 |
基础科学 | 154篇 |
3617篇 | |
综合类 | 3534篇 |
农作物 | 911篇 |
水产渔业 | 1343篇 |
畜牧兽医 | 13261篇 |
园艺 | 271篇 |
植物保护 | 1567篇 |
出版年
2019年 | 251篇 |
2018年 | 417篇 |
2017年 | 509篇 |
2016年 | 473篇 |
2015年 | 338篇 |
2014年 | 459篇 |
2013年 | 993篇 |
2012年 | 795篇 |
2011年 | 954篇 |
2010年 | 687篇 |
2009年 | 669篇 |
2008年 | 971篇 |
2007年 | 917篇 |
2006年 | 809篇 |
2005年 | 738篇 |
2004年 | 646篇 |
2003年 | 707篇 |
2002年 | 606篇 |
2001年 | 804篇 |
2000年 | 801篇 |
1999年 | 633篇 |
1998年 | 275篇 |
1997年 | 282篇 |
1995年 | 262篇 |
1994年 | 230篇 |
1993年 | 236篇 |
1992年 | 427篇 |
1991年 | 519篇 |
1990年 | 435篇 |
1989年 | 411篇 |
1988年 | 403篇 |
1987年 | 409篇 |
1986年 | 364篇 |
1985年 | 393篇 |
1984年 | 342篇 |
1983年 | 290篇 |
1982年 | 246篇 |
1979年 | 387篇 |
1978年 | 294篇 |
1977年 | 295篇 |
1976年 | 299篇 |
1975年 | 318篇 |
1974年 | 332篇 |
1973年 | 303篇 |
1972年 | 291篇 |
1971年 | 245篇 |
1969年 | 289篇 |
1968年 | 269篇 |
1967年 | 327篇 |
1966年 | 304篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
PRELIMINARY STUDIES ON THE TRANSLOCATION OF 14 C-LABELLED HERBICIDES IN BRACKEN (PTERIDIUM AQUILINUM)
G. I. McINTYRE 《Weed Research》1962,2(1):51-59
Summary. The translocation of 14 C-labelled herbieides in field bracken has been sludied in some preliminary experiments by means of autoradiography. A detailed account is given of the methods employed. It is shown that when 2,4-D is applied to fronds at different stages of development movement of the tracer into the rhizome is considerably greater from parts of the frond which are still immature. Trasnslocation within the frond is predominantly basipetal at all stages of development; within the rhizome the direction of movement appears to be determined primarily by the nature of the vascular connections with the treated pinna.
In a comparison between the translocation of 2,4-D, 4-CPA and dalapon no difference was apparent after 24 hours, but when the treatment period was extended to 96 hours there was evidence that 4-CPA bad been translocated in a considerably greater amount than either of the other two herbicides.
Rechrches iréliminaires sur la migration des herbieides marqués am14 C dans la fougrère algle (Pteridium aquilinum) 相似文献
In a comparison between the translocation of 2,4-D, 4-CPA and dalapon no difference was apparent after 24 hours, but when the treatment period was extended to 96 hours there was evidence that 4-CPA bad been translocated in a considerably greater amount than either of the other two herbicides.
Rechrches iréliminaires sur la migration des herbieides marqués am
135.
G. I. McINTYRK 《Weed Research》1962,2(3):165-176
Summary. Previous findings suggested that the translocation in Agropyron repens of 2,2-dichloropropionic acid (dalapon) may be considerably affected by the transpiration rate. This relationship has been studied further in the present investigation using 14 C-labelled material and autoradiography.
It was found that when dalapon was applied to the leaves and the treated plants were placed in darkness a reduction in the transpiration rate of ca. 90% was associated with a marked increase in the amount of dalapon translocation into the roots and tillers. The evidence provided by the autoradiographs was confirmed by a quantitative assay of the14 C present in the roots. It was also found, however, that translocation was not appreciably affected either by a 50% reduction in the light intensity or when the transpiration rate was reduced by placing the plaints under conditions of high humidity in the light or by the application of white petroleum jelly to the leaves. An alternative hypothesis, namely that the effect of darkness on the movement of the herbicide might be due to changes induced in the normal pattern of assimilate translocation was also investigated but was not supported by the results obtained. Further experimentss, in which various parts of the treated shoot were placed in the dark, suggested that the effect of darkness on the translocation of dalapon is exerted primarily on the treated leaf itself.
Etudes sur to migration dans Agropyron repens de l'acide 2,2-dichloropropionique marqué avec14 C 相似文献
It was found that when dalapon was applied to the leaves and the treated plants were placed in darkness a reduction in the transpiration rate of ca. 90% was associated with a marked increase in the amount of dalapon translocation into the roots and tillers. The evidence provided by the autoradiographs was confirmed by a quantitative assay of the
Etudes sur to migration dans Agropyron repens de l'acide 2,2-dichloropropionique marqué avec
136.
I M Skurikhin 《Journal of the Association of Official Analytical Chemists》1989,72(2):294-297
To evaluate the suitability of the analytical methods used in determining food safety, a new metrological characteristic "MQS" is suggested. MQS is defined as the absolute minimum quantity in micrograms of a substance that can be determined in a test solution (solubilized test portion). MQS accounts for 2 factors: (a) the necessity for a reliable determination of ML (maximum permitted level, i.e., regulatory tolerance), and (b) the optimum quantity of test portion of a food product to be analyzed, and thus assists in evaluating the suitability of a method to assure food safety. The MQS of 8 toxic elements in any food are As, 3; Cd, 0.5; Cu, 20; Fe, 50; Hg, 0.2; Pb, 4; Sn, 200; Zn, 100 micrograms. To characterize the applicability of any given method, the specific minimum limit of determination, MQSM, must be established for each method. The method in question may be used to control food safety only if MQSM is less than MQS. MQSM values are given for the common polarographic and colorimetric methods for determining these elements. 相似文献
137.
138.
139.
1. The effect of early exposure of heavy breed (HB) chicks to an anti‐oestrogen (tamoxifen—TAM) on later adiposity was studied.
2. TAM administration at the embryonic stage, but not at the day of hatching, reduced adiposity in females but not in males, at 8 to 9 weeks of age. This reduction in adiposity in females minimised or even alleviated the excess of fat in females compared to males. 相似文献
140.