全文获取类型
收费全文 | 991篇 |
免费 | 78篇 |
国内免费 | 91篇 |
专业分类
林业 | 52篇 |
农学 | 89篇 |
基础科学 | 39篇 |
72篇 | |
综合类 | 477篇 |
农作物 | 33篇 |
水产渔业 | 220篇 |
畜牧兽医 | 111篇 |
园艺 | 26篇 |
植物保护 | 41篇 |
出版年
2024年 | 6篇 |
2023年 | 15篇 |
2022年 | 31篇 |
2021年 | 35篇 |
2020年 | 43篇 |
2019年 | 32篇 |
2018年 | 32篇 |
2017年 | 27篇 |
2016年 | 66篇 |
2015年 | 42篇 |
2014年 | 76篇 |
2013年 | 63篇 |
2012年 | 100篇 |
2011年 | 89篇 |
2010年 | 78篇 |
2009年 | 61篇 |
2008年 | 44篇 |
2007年 | 42篇 |
2006年 | 47篇 |
2005年 | 34篇 |
2004年 | 26篇 |
2003年 | 22篇 |
2002年 | 21篇 |
2001年 | 18篇 |
2000年 | 20篇 |
1999年 | 20篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有1160条查询结果,搜索用时 15 毫秒
71.
人类认识事物运动并对其运动施控的过程有三次“质”的飞跃阶段。理,工科本科教育基本定位于人类认识的第三次“质”的飞跃阶段,而经济管理类本科教育则横跨人类认识的全过程,即定位于第一,二,三次“质”的飞跃阶段,因而其教育教学的特性与理,工科不同,更注重应付不确定性因素与风险因素以及由此导致的知识综合性,交叉性,初中性与多变性,这些特性决定了经济管理类本科教育理论课教学的多元化特色,笔称之为“二元三法”体系,即针对经济管理类本科教育五类理论课程的划分或设置以及不同课程特性的差异,对不同程程可分别或复合式采取传统讲授,专题讲座和案例分析三种方法。 相似文献
72.
我校非测绘专业测量学课程教学改革 总被引:1,自引:0,他引:1
对我校测量学教学改革进行研究与探讨,指出非测绘专业测量学教学中存在的问题,并有针对性地提出了测量学教学改革的对策。 相似文献
73.
针对职业教育理论与实践脱离的问题,以环境监测与治理技术专业为例,围绕该专业面向的职业岗位的要求,在职业岗位分析的基础上,构建出由"职业基础课程+职业岗位课程+职业拓展课程"组成的课程体系,突出了职业岗位要求在课程框架中的主线地位。 相似文献
74.
Summary The inheritance of resistance to coffee berry disease (CBD) has been studied by applying a preselection test to F2 progenies of a half diallel cross between 11 coffee varieties with different degrees of resistance and to sets of parental, F1, F2, B11 and B12 generations of crosses between resistant and susceptible varieties. True resistance to CBD appears to be controlled by major genes on three different loci. The highly resistant variety Rume Sudan carries the dominant R- and the recessive K-genes. The non-allelic interaction between these two genes is of a duplicate nature. The R-locus has multiple alleles with R
1R1alleles present in Rume Sudan and the somewhat less effective R
2R2alleles in a variety like Pretoria, which also has the K-gene. The moderately resistant variety K7 carries only the recessive K-gene. The arabica-like variety Hibrido de Timor (a natural interspecific arabica x robusta hybrid) carries one gene for CBD resistance on the T-locus with intermediate gene action. It probably inherited this gene from its robusta parent. There is circumstantial evidence that the resistance to CBD is of a stable nature, but it is advisable to accumulate in one genotype as many resistance genes as possible by combining in the breeding programme the resistance of Rume Sudan with that of Hibrido de Timor. 相似文献
75.
Olga E. Scholten Ritsert C. Jansen L. C. Paul Keizer Theo S. M. De Bock Wouter Lange 《Euphytica》1996,91(3):331-339
Summary Inheritance of resistance to beet necrotic yellow vein virus (BNYVV) was studied in segregating F2 and backcross families obtained from crosses between resistant plants of the sugar beet selection Holly-1-4 or the wild beet accession Beta vulgaris subsp. maritima WB42 and susceptible parents. Greenhouse tests were carried out, in which seedlings were grown in a mixture of sand and infested soil. Virus concentrations of BNYVV in the rootlets were estimated by ELISA. To discriminate resistant and susceptible plants, mixtures of normal distributions were fitted to log10 virus concentrations, estimated for segregating F1, F2 and BC populations of both accessions. The hypothesis that Holly-1-4 contained one single dominant major gene was accepted. For WB42, results fitted with the hypotheses that resistance was based on either one (or more) dominant major gene(s) showing distorted segregation, or two complementary dominant genes, which are both required for resistance. Resistance from WB42 appeared to be more effective against BNYVV than resistance from Holly-1-4.This research was carried out as part of a PhD study at the Graduate School Experimental Plant Sciences (EPS), Department of Virology, Wageningen, The Netherlands 相似文献
76.
The F2 progenies of crosses between several cowpea (V. unguiculata) lines were investigated for variation of eye pattern and seed coat colour. It was found that three (W, H, O) and five (R, P, B, M, N) major genes control eye pattern and seed coat colour, respectively. The recessive gene (GO) for restricted eye pattern enables the underlying basic white or cream seed coat colour to be observed. A similar effect is obtained with the recessive gene (rr) for colour expression. The expression of mottling (V), possibly a seed coat pattern, may for be observed when it is combined with the genes for certain eye patterns. The significance of these findings in breeding for consumer preference for specific seed coat colour is discussed. 相似文献
77.
Summary Six partially resistant spring barley cultivars were exposed to four barley leaf rust (Puccinia hordei) races in the field and in the greenhouse. The 24 cultivar-race combinations were tested in field plots of 1.5×1.5 m2 in two replications over two years. To reduce the interplot exchange of urediospores each plot was surrounded by winter rye.The level of barley leaf rust varied among cultivars, races and years. In both years the variance for cultivar-race interactions was highly significant and originating largely from the cultivar-race combinations Berac-22. Armelle-22, Armelle-A and Tyra-A. The Berac-22 interaction was towards higher, the other three interactions towards a lower level of barley leaf rust. The reduced rust levels of these three combinations were not due to interactions between the partial resistance of these cultivars and the aggressiveness of the races but to major genes for hypersensitivity not effective to the races 1-2-1 and F, common in Western Europe, but effective against the rare races 22 and A. This was revealed in the greenhouse experiments where all combinations had a susceptible infection type except Armelle-22, Armelle-A and Tyra-A, which showed low infection types in both the seedling and adult plant stages. The urediosori present in the field plots of these three combinations apparently arose from spores derived from other plots; this interplot interchange suggesting partial resistance.The interaction of Berac with race 22 truly was a small race-specific effect within the polygenic, partial resistance of barley to barley leaf rust like the one reported before between Julia and race 18. 相似文献
78.
G. Wricke 《Plant Breeding》2002,121(1):26-28
Previously, kernel weight in rye was considered mostly as a quantitatively inherited trait. F1 plants from parents showing a great difference in kernel weight were selfed and the segregating F2 population was analysed with molecular markers. Two simple sequence repeats markers, one on chromosome 5 and the other on chromosome 7, were found which allowed the genetic analysis of two major genes acting in a complementary way. The analysis of major genes is an advantage in breeding for this important economic trait. In addition it can provide more insight into the genetic structure of this character. This is, in turn, also a prerequisite for future investigations of this trait at the molecular level. 相似文献
79.
Summary S1 to S5 inbred lines, derived from a maize population bred for its overall resistance to three tropical viruses, were screened for resistance to maize streak virus (MSV) by artificial plant infection using viruliferous leafhoppers. Symptoms were rated and intra-line frequency distributions studied for all pedigree inbred lines. Mortality due to MSV was very low among these inbreds. Symptoms appeared later, developed slower and were less severe than in the susceptible control hybrid. Results of a study of 500 S1 and 93 S2 lines suggested that resistance is under genetic control via a system involving loci with major genes (with dominance for resistance) controlling high to complete resistance, associated with a genetic system involving loci with minor genes controlling partial resistance. Lines expressing complete resistance to MSV were developed from 5 cycles of inbreeding and selection. The relevance of such complete and partial resistance is discussed.Abbreviations MRPS
Mean Rating for Plants exhibiting Symptoms 相似文献
80.