全文获取类型
收费全文 | 19053篇 |
免费 | 2681篇 |
国内免费 | 1462篇 |
出版年
2023年 | 285篇 |
2022年 | 349篇 |
2021年 | 663篇 |
2020年 | 637篇 |
2019年 | 810篇 |
2018年 | 775篇 |
2017年 | 618篇 |
2016年 | 810篇 |
2015年 | 1198篇 |
2014年 | 1382篇 |
2013年 | 1526篇 |
2012年 | 1784篇 |
2011年 | 1665篇 |
2010年 | 1075篇 |
2009年 | 962篇 |
2008年 | 1132篇 |
2007年 | 994篇 |
2006年 | 934篇 |
2005年 | 777篇 |
2004年 | 704篇 |
2003年 | 572篇 |
2002年 | 500篇 |
2001年 | 346篇 |
2000年 | 308篇 |
1999年 | 275篇 |
1998年 | 164篇 |
1997年 | 135篇 |
1996年 | 109篇 |
1995年 | 89篇 |
1994年 | 103篇 |
1993年 | 79篇 |
1992年 | 138篇 |
1991年 | 127篇 |
1990年 | 118篇 |
1989年 | 104篇 |
1988年 | 88篇 |
1987年 | 83篇 |
1986年 | 80篇 |
1985年 | 85篇 |
1984年 | 64篇 |
1983年 | 53篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1979年 | 50篇 |
1978年 | 40篇 |
1977年 | 37篇 |
1976年 | 41篇 |
1975年 | 35篇 |
1974年 | 34篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
1.
2.
Xiaojing Dang Thu Giang Tran Thi Guanshan Dong Hui Wang Wisdom Mawuli Edzesi Delin Hong 《Planta》2014,239(6):1309-1319
Key message
Twenty-seven QTLs were identified for rice seed vigor, in which 16 were novel QTLs. Fifteen elite parental combinations were designed for improving seed vigor in rice.Abstract
Seed vigor is closely related to direct seeding in rice (Oryza sativa L.). Previous quantitative trait locus (QTL) studies for seed vigor were mainly derived from bi-parental segregating populations and no report from natural populations. In this study, association mapping for seed vigor was performed on a selected sample of 540 rice cultivars (419 from China and 121 from Vietnam). Population structure was estimated on the basis of 262 simple sequence repeat (SSR) markers. Seed vigor was evaluated by root length (RL), shoot length (SL) and shoot dry weight in 2011 and 2012. Abundant phenotypic and genetic diversities were found in the studied population. The population was divided into seven subpopulations, and the levels of linkage disequilibrium (LD) ranged from 10 to 80 cM. We identified 27 marker–trait associations involving 18 SSR markers for three traits. According to phenotypic effects for alleles of the detected QTLs, elite alleles were mined. These elite alleles could be used to design parental combinations and the expected results would be obtained by pyramiding or substituting the elite alleles per QTL (apart from possible epistatic effects). Our results demonstrate that association mapping can complement and enhance previous QTL information for marker-assisted selection and breeding by design. 相似文献3.
孢粉学是解决植物分类中疑难类群物种微形态分化的重要方法,随着分子系统学的发展,结合这两门学科的优势可以更加有效地解决疑难类群的分类学问题。鳞盖蕨属(Microlepia)是一个分类困难的疑难类群,采用孢粉学与分子系统学一一对应的方法,以及居群取样方式,选取280份样本,联合4个叶绿体片段(rbcL、trnL-F、psbA-trnH和rps4),采用最大似然法和贝叶斯法构建该属的系统发生关系,在此基础上对凭证标本中100份材料的孢子进行观察和分析。综合分子系统学和孢粉学的研究结果,得出结论:(1)在形态学研究中广泛被接受的15个物种得到了单系支持,并厘清了分类困难的复合群;(2)发现边缘鳞盖蕨(M. marginata)可能存在隐性种;(3)建议恢复过去归并处理为异名的瑶山鳞盖蕨(M. yaoshanica)、罗浮鳞盖蕨(M. lofoushanensis)、四川鳞盖蕨(M. szechuanica)以及滇西鳞盖蕨(M. subspeluncae);(4)提出鳞盖蕨属可能存在杂交现象;(5)提出鳞盖蕨属完整的属下分类建议。 相似文献
4.
5.
植物对UV-B辐射增强应答的分子机制及信号级联研究进展 总被引:1,自引:0,他引:1
地表的UV-B辐射量伴随着大气平流层臭氧层的变薄而不断增强,给地球生态系统带来严重影响.UV-B主要通过抑制植物光合作用、伤害生物膜及DNA等生物大分子来影响其生长发育,最终导致生物量及产量降低,甚至致死.植物在进化过程中形成了自我防护及防御机制,如DNA损伤的自我修复,活性氧自由基的酶促及非酶促清除机制,以及紫外吸收物质的诱导合成等;同时,在植物中也有许多物质及不同途径来感受和应答UV-B胁迫.本文从UV-B辐射增强对植物造成损伤的主要途径、植物对UV-B辐射增强的应答机制及信号级联过程等方面的研究进展进行综述. 相似文献
6.
群体成员大小差异对不同生境鲤科鱼类集群行为的影响 总被引:1,自引:0,他引:1
为研究群体成员大小差异对不同喜好生境鱼类集群行为特征的影响, 实验分别以鳊(Parabramis pekinensis)和中华倒刺鲃(Spinibarbus sinensis)幼鱼为实验对象, 比较分析4尾等大小(E)和不等大小(2大2小, NE)实验鱼群体的自发游泳速度、空间分布以及对恐吓刺激反应等集群行为参数的差异。结果显示: (1)和鳊相比, 中华倒刺鲃有更高的自发游泳速度、速度同步性和排列方向的极性, 但二者对恐吓刺激的反应率及反应的协调一致性相似; (2)当群体成员大小出现差异时, 两种鱼群体排列方向的极性不受影响, 且大小个体成员间的速度及其同步性均没有差异, 但整体的速度同步性与等大小群体相比有所下降; (3)个体间距离数据显示, 个体大小差异不会影响两种鱼群体的凝聚力; (4)群体成员在两种鱼群中偏好位置不同, 当群体成员大小不同时, 大个体成员更偏好占据领头鱼位置; (5)群体成员大小的差异导致两种鱼对刺激的反应率下降。研究表明: 中华倒刺鲃具有更高的活跃性、更好的群体运动的协调性, 可能与其流水生境相关; 当群体成员大小出现差异时, 成员不分大小在整体上协调运动的速度和方向, 并保持群体有较高的凝聚力, 但两种鱼类自发游泳速度调整策略截然不同(鳊大小个体速度妥协趋同, 而中华倒刺鲃低速个体速度提高); 群体成员大小差异导致鱼群对恐吓刺激的反应率有所下降, 可能原因包括体形差异导致的社会因素造成敏锐性下降、信息交流效率受阻和(或)集群收益代价出现分化影响一致决策的形成等。 相似文献
7.
Zinc‐Air Batteries: Atomic Modulation of FeCo–Nitrogen–Carbon Bifunctional Oxygen Electrodes for Rechargeable and Flexible All‐Solid‐State Zinc–Air Battery (Adv. Energy Mater. 13/2017) 下载免费PDF全文
8.
9.
Yuejing Zhang Hui Liu Xinhui Zhang Shurui Wang Chongxi Liu Chao Yu Xiangjing Wang Wensheng Xiang 《Antonie van Leeuwenhoek》2014,106(2):219-225
A novel actinomycete, designated strain NEAU-zh8T, was isolated from a root of Viola philippica Car collected in China and characterized using a polyphasic approach. 16S rRNA gene sequence similarity studies showed that strain NEAU-zh8T belongs to the genus Micromonospora, being most closely related to Micromonospora chokoriensis 2-9(6)T (99.9 %), Micromonospora saelicesensis Lupac 09T (99.3 %) and Micromonospora lupini Lupac 14NT (99.0 %). gyrB gene analysis also indicated that strain NEAU-zh8T should be assigned to the genus Micromonospora. The cell-wall peptidoglycan consisted of meso-diaminopimelic acid and glycine. The major menaquinones were MK-10(H4), MK-10(H2) and MK-10(H6). The phospholipid profile contained diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. The major fatty acids were iso-C15:0, C16:0 and C17:0 10-methyl. A combination of DNA–DNA hybridization results and some physiological and biochemical properties indicated that strain NEAU-zh8T could be readily distinguished from the closest phylogenetic relatives. Therefore, it is proposed that strain NEAU-zh8T represents a novel Micromonospora species, for which the name Micromonospora violae sp. nov. is proposed. The type strain is NEAU-zh8T (=CGMCC 4.7102T=DSM 45888T). 相似文献
10.
Zhihuan Chen Pengyan Liu Yanhua Liu Hui Tang Yunping Chen Liping Zhang 《Antonie van Leeuwenhoek》2014,106(6):1127-1137
Triacylglycerols (TAGs), synthesized in the microsomal membranes of eukaryotes, serve as a primary storage form of carbon and energy in microorganisms. For this reason, TAGs produced by organisms have great potential to become biofuels and facilitate researchers to look for alternative renewable sources of energy. The present study describes the identification and functional characterization of a type-2 diacylglycerol acyltransferase from Rhodosporidium diobovatum, designated as RdDGAT, which catalyzed the final step of TAG synthesis. A full-length cDNA clone for RdDGAT was obtained, and its biological activity was proven by being expressed in a Saccharomyces cerevisiae quadruple mutant that was defective in TAG synthesis. Enzymatic assays were performed and finally the existence of TAGs in the transformed Saccharomyces cerevisiae quadruple mutant was determined using the method of thin-layer chromatography. Substrate preference experiments revealed that RdDGAT preferred unsaturated fatty acids over saturated ones. Through further analysis, we assume that the evolution and expression characteristics of the RdDGAT gene perhaps is the result of adaption to its oligotrophic and cold living environment. 相似文献