全文获取类型
收费全文 | 2078篇 |
免费 | 182篇 |
国内免费 | 420篇 |
专业分类
林业 | 101篇 |
农学 | 746篇 |
基础科学 | 37篇 |
333篇 | |
综合类 | 765篇 |
农作物 | 352篇 |
水产渔业 | 74篇 |
畜牧兽医 | 115篇 |
园艺 | 87篇 |
植物保护 | 70篇 |
出版年
2024年 | 20篇 |
2023年 | 50篇 |
2022年 | 74篇 |
2021年 | 91篇 |
2020年 | 118篇 |
2019年 | 124篇 |
2018年 | 95篇 |
2017年 | 102篇 |
2016年 | 115篇 |
2015年 | 130篇 |
2014年 | 145篇 |
2013年 | 135篇 |
2012年 | 153篇 |
2011年 | 160篇 |
2010年 | 123篇 |
2009年 | 138篇 |
2008年 | 135篇 |
2007年 | 110篇 |
2006年 | 109篇 |
2005年 | 94篇 |
2004年 | 71篇 |
2003年 | 52篇 |
2002年 | 46篇 |
2001年 | 37篇 |
2000年 | 41篇 |
1999年 | 31篇 |
1998年 | 30篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1977年 | 1篇 |
1963年 | 1篇 |
1962年 | 7篇 |
1955年 | 2篇 |
排序方式: 共有2680条查询结果,搜索用时 31 毫秒
11.
AFLP是一种新的分子遗传标记技术,它结合了RFLP和PCR技术的优点,具有RFLP的稳定性和PCR的高效性,被称为“最有威力的分子遗传标记”或“下一代分子标记”。相对于国外而言,我国在这方面的研究还比较少。本文综述了扩增片段长度多态性(AFLP)这种遗传标记的原理、技术特点、技术发展及其在动物遗传多样性、种质鉴定、遗传图谱构建、基因定位和标记辅助育种等研究中的应用。 相似文献
12.
Distribution of alpha‐neoendorphin,ACTH (18–39) and beta‐endorphin (1–27) in the alpaca brainstem
下载免费PDF全文
![点击此处可从《Anatomia, histologia, embryologia》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Manuel L. Sánchez Eliana de Souza Luis A. Aguilar Rafael Coveñas 《Anatomia, histologia, embryologia》2018,47(5):481-492
Using an immunocytochemical technique, we have studied in the alpaca brainstem the distribution of immunoreactive structures containing prodynorphin (alpha‐neoendorphin)‐ and pro‐opiomelanocortin (adrenocorticotrophin hormone (18–39) (ACTH), beta‐endorphin (1–27))‐derived peptides. No peptidergic‐immunoreactive cell body was observed. Immunoreactive fibres were widely distributed, although in most of the brainstem nuclei the density of the peptidergic fibres was low or very low. In general, the distribution of the immunoreactive fibres containing the peptides studied was very similar. A close anatomical relationship occurred among the fibres containing alpha‐neoendorphin, ACTH or beta‐endorphin (1–27), suggesting a functional interaction among the three peptides in many of the brainstem nuclei. The number of fibres belonging to the prodynorphin system was higher than that of the pro‐opiomelanocortin system. A moderate/low density of immunoreactive fibres was observed in 65.11% (for alpha‐neoendorphin (1–27)), 18.18% (for ACTH) and 13.95% (for beta‐endorphin) of the brainstem nuclei/tracts. In the alpaca brainstem, a high density of immunoreactive fibres was not observed. The neuroanatomical distribution of the immunoreactive fibres suggests that the peptides studied are involved in auditory, motor, gastric, feeding, vigilance, stress, respiratory and cardiovascular mechanisms, taste response, sleep‐waking cycle and the control of pain transmission. 相似文献
13.
14.
适度卷曲有利于提高水稻叶片的光合效率,增加植株光合产物的有效积累量。我们利用甲基磺酸乙酯(EMS)处理籼型水稻保持系西农1B,获得一个稳定遗传的水稻半外卷叶突变体。该突变体从十叶期开始各叶片逐渐向外卷曲直至半卷状,并伴随茎秆半矮化和叶片披垂,暂被命名为semi-outcurved leaf 1(sol1)。与野生型(WT)相比,sol1的叶片卷曲指数均达到30%以上(P<0.01);倒一、倒二、倒三、倒四节节间长度和穗长极显著缩短,倒一、倒二、倒三叶的叶夹角显著或极显著增加;有效穗数、千粒重、每穗实粒数、结实率显著或极显著下降,一次枝梗数则增加11.3%(P<0.05)。sol1的蒸腾速率、胞间CO2浓度、气孔导度显著高于野生型。石蜡切片显示,sol1倒一叶的泡状细胞体积变小,数量显著增多,表皮细胞体积略微增大。遗传分析表明,sol1的半外卷叶性状受1对隐性核基因调控,定位于6号染色体标记JY6-3和JY6-10之间165 kb的物理范围内,共含15个注释基因。qRT-PCR结果表明,与泡状细胞相关的内卷基因和外卷叶基因RL14、Roc5、REL1在突变体sol1中呈不同程度的上调,NRL、BRD1、OsHox32、ADL1、LC2则呈不同程度的下调。研究结果为SOL1基因的克隆和功能研究奠定了基础。 相似文献
15.
16.
Previous studies showed that the yellow seed color gene of a yellow mustard was located on the A09 chromosome. In this study, the sequences of the molecular markers linked to the yellow seed color gene were analyzed, the gene was primarily mapped to an interval of 23.304 to 29.402M. Twenty genes and eight markers’ sequences in this region were selected to design the IP and SCAR primers. These primers were used to screen a BC8S1 population consisting of 1256 individuals. As a result, five IP and five SCAR markers were successfully developed. IP4 and Y1 were located on either side of the yellow seed color gene at a distance of 0.1 and 0.3 cM, respectively. IP1, IP2 and IP3 derived from Bra036827, Bra036828, Bra036829 separately, co-segregated with the target gene. BLAST analysis indicated that the sequences of newly developed markers showed good collinearity with those of the A09 chromosome, and that the target gene might exist between 27.079 and 27.616M. In light of annotations of the genes in this region, only Bra036828 is associated with flavonoid biosynthesis. This gene has high similarity with the TRANSPARENT TESTA6 gene, Bra036828 was hence identified as being the gene possibly responsible for yellow seed color, in our research. 相似文献
17.
Enhancing pedotransfer functions with environmental data for estimating bulk density and effective cation exchange capacity in a data‐sparse situation
下载免费PDF全文
![点击此处可从《Soil Use and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S. I. C. Akpa S. U. Ugbaje T. F. A. Bishop I. O. A. Odeh 《Soil Use and Management》2016,32(4):644-658
Soil bulk density (BD) and effective cation exchange capacity (ECEC) are among the most important soil properties required for crop growth and environmental management. This study aimed to explore the combination of soil and environmental data in developing pedotransfer functions (PTFs) for BD and ECEC. Multiple linear regression (MLR) and random forest model (RFM) were employed in developing PTFs using three different data sets: soil data (PTF‐1), environmental data (PTF‐2) and the combination of soil and environmental data (PTF‐3). In developing the PTFs, three depth increments were also considered: all depth, topsoil (<0.40 m) and subsoil (>0.40 m). Results showed that PTF‐3 (R2; 0.29–0.69) outperformed both PTF‐1 (R2; 0.11–0.18) and PTF‐2 (R2; 0.22–0.59) in BD estimation. However, for ECEC estimation, PTF‐3 (R2; 0.61–0.86) performed comparably as PTF‐1 (R2; 0.58–0.76) with both PTFs out‐performing PTF‐2 (R2; 0.30–0.71). Also, grouping of data into different soil depth increments improves the estimation of BD with PTFs (especially PTF‐2 and PTF‐3) performing better at subsoils than topsoils. Generally, the most important predictors of BD are sand, silt, elevation, rainfall, temperature for estimation at topsoil while EVI, elevation, temperature and clay are the most important BD predictors in the subsoil. Also, clay, sand, pH, rainfall and SOC are the most important predictors of ECEC in the topsoil while pH, sand, clay, temperature and rainfall are the most important predictors of ECEC in the subsoil. Findings are important for overcoming the challenges of building national soil databases for large‐scale modelling in most data‐sparse countries, especially in the sub‐Saharan Africa (SSA). 相似文献
18.
19.
Lihua Ning Guizhen Kan Wenkai Du Shiwei Guo Qing Wang Guozheng Zhang Hao Cheng Deyue Yu 《Breeding Science》2016,66(2):191-203
Tolerance to low-phosphorus soil is a desirable trait in soybean cultivars. Previous quantitative trait locus (QTL) studies for phosphorus-deficiency tolerance were mainly derived from bi-parental segregating populations and few reports from natural population. The objective of this study was to detect QTLs that regulate phosphorus-deficiency tolerance in soybean using association mapping approach. Phosphorus-deficiency tolerance was evaluated according to five traits (plant shoot height, shoot dry weight, phosphorus concentration, phosphorus acquisition efficiency and use efficiency) comprising a conditional phenotype at the seedling stage. Association mapping of the conditional phenotype detected 19 SNPs including 13 SNPs that were significantly associated with the five traits across two years. A novel cluster of SNPs, including three SNPs that consistently showed significant effects over two years, that associated with more than one trait was detected on chromosome 3. All favorable alleles, which were determined based on the mean of conditional phenotypic values of each trait over the two years, could be pyramided into one cultivar through parental cross combination. The best three cross combinations were predicted with the aim of simultaneously improving phosphorus acquisition efficiency and use efficiency. These results will provide a thorough understanding of the genetic basis of phosphorus deficiency tolerance in soybean. 相似文献
20.