全文获取类型
收费全文 | 16507篇 |
免费 | 1585篇 |
国内免费 | 2436篇 |
专业分类
20528篇 |
出版年
2024年 | 89篇 |
2023年 | 320篇 |
2022年 | 668篇 |
2021年 | 996篇 |
2020年 | 762篇 |
2019年 | 913篇 |
2018年 | 824篇 |
2017年 | 545篇 |
2016年 | 769篇 |
2015年 | 1156篇 |
2014年 | 1401篇 |
2013年 | 1343篇 |
2012年 | 1661篇 |
2011年 | 1440篇 |
2010年 | 954篇 |
2009年 | 873篇 |
2008年 | 989篇 |
2007年 | 805篇 |
2006年 | 710篇 |
2005年 | 609篇 |
2004年 | 546篇 |
2003年 | 463篇 |
2002年 | 365篇 |
2001年 | 205篇 |
2000年 | 188篇 |
1999年 | 148篇 |
1998年 | 105篇 |
1997年 | 104篇 |
1996年 | 86篇 |
1995年 | 97篇 |
1994年 | 65篇 |
1993年 | 48篇 |
1992年 | 61篇 |
1991年 | 39篇 |
1990年 | 40篇 |
1989年 | 28篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1950年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Elymus L. is the largest genus in Triticeae, containing about 150 species with four recognized genome donors (St, H, P, and W).
Traditionally, the genome compound of this genus is identified based on cytological data. Recently, molecular phylogenetic
analysis was used to investigate its genomic combination. Here we describe a restriction fragment length polymorphism (RFLP)
assay based on digesting alcohol dehydrogenase (Adh) amplicons with two restriction enzyme combinations, EcoRI–HindIII and EcoRI–PstI, which easily can be used to distinguish Elymus and its closely related genera genomes. The method includes only four steps: (1) amplifying nuclear Adh genes with universal primers; (2) purifying and cloning PCR products; (3) digesting plasmids with restriction enzymes that
identify a given genome; (4) running the digested products on an agarose gel and identify the sample based on the restriction
profiles. Results showed that: (1) PCR products ranged from 1,200 to 2,000 bp; (2) Adh2 gene was amplified from all the tested genomes; Adh1 gene was amplified from almost all of the tested genomes except the W genome; Adh3 gene was amplified only from the St genome; (3) the EcoRI–HindIII combination was effective to distinguish different Adh gene types (Adh1, Adh2, and Adh3); (4) the Adh2–EcoRI–PstI fragments could be used to distinguish Elymus and its closely related genera genomes. Therefore, This RFLP assay provides an inexpensive and simple means of identifying
Elymus genomes. 相似文献
992.
Sweet flag (Acorus calamus L.) and yellow flag (Iris pseudacorus L.) have been used increasingly in constructed wetlands (CWs) for treatment of eutrophic wastewater. In order to properly match plant species with the type of wastewater being treated, it is important to know the performance of plant species under different NO3−/NH4+ ratios. We investigated dry matter (DW) production and N content of A. calamus and I. pseudacorus under five NO3−/NH4+ ratios (100/0, 75/25, 50/50, 25/75, and 0/100) in a hydroponic system. Results showed that the two species exhibited different preferences for NO3− and NH4+. Total DW, shoot DW, and N content were greater with NO3−/NH4+ ratios of 50/50 and 75/25 than otherwise for A. calamus, but these parameters were only higher under the sole NO3− treatment in I. pseudacorus. We conclude that A. calamus could be best used for treating wastewater in constructed wetlands with NO3−/NH4+ ratios between 50/50 and 75/25, while I. pseudacorus for treating wastewater with NO3− only to achieve the highest biomass production and efficiency in the removal of N. 相似文献
993.
Qing-Song Shao Qiao-Sheng Guo Yan-Ming Deng Hai-Peng Guo 《Biochemical Systematics and Ecology》2010,38(6):1160-1169
The diversity and genetic relationship among 29 populations of Chrysanthemum morifolium, one of Chrysanthemum indicum and one of Chrysanthemum nankingense from China were analyzed using morphological traits and molecular markers. Twenty morphological traits were scored as well as 182 ISSR marker-fragments, as amplified by 22 primers [the percentage of polymorphic bands (PPB): 81.87%], and 243 SRAP marker-fragments as generated by 26 primer pairs (PPB: 75.72%). Mantel’s test indicated significant correlation (r = 0.624) of morphological trait and SRAP. By contrast, the morphological trait showed low correlation with ISSR (r = 0.246). Cluster analysis showed groupings of the accessions according to all four methods correlated well with their geographic region of origin, and most populations from the south of China were classified into one cluster and most populations from the north of China were classified into another cluster. Finally, an appropriate strategy for conserving the C. morifolium germplasm was proposed. 相似文献
994.
995.
Changgui Li Ming Shao Xiaoyu Cui Yingli Song Juan Li Liyong Yuan Hanhua Fang Zhenglun Liang Terry D. Cyr Fengxiang Li Xuguang Li Junzhi Wang 《Biologicals》2010,38(2):284-289
The single radial immunodiffusion (SRID) method currently used to determine the hemagglutinin (HA) content of the inactivated influenza vaccines depends on the availability of reference HA antigen and corresponding anti-serum, updated and provided annually by World Health Organization (WHO) collaborative centers. Particularly early in a pandemic outbreak, reference reagents could be the bottleneck in vaccine development and release. Therefore, other reliable tests capable of quantifying HA content could substantially shorten the time needed for vaccine formulation. Here electrophoretic separation of deglycosylated samples in conjunction with densitometry was used to quantify HA contents of H1N1 vaccine at multiple manufacturing sites. We found the overall consistency between the alternative method and traditional SRID was 88–122% in seven lots of vaccine bulks from four subtypes (types) of influenza vaccine, confirming its suitability to quantify HA content. Moreover, we used the alternative method to prepare a national HA antigen reference in China for quality control of 2009 pandemic influenza A (H1N1) vaccines prior to the arrival of the WHO SRID reference standards, subsequently confirming good agreement between both methods. The alternative method for vaccine quantification enabled the Chinese health authority to approve H1N1 vaccine 1 month earlier than otherwise possible. 相似文献
996.
997.
This work will characterize risk acceptance in China, based on the psychometric paradigm, and explore the determining factors that influence the risk acceptable level to the Chinese public. For this purpose, a survey was conducted including 12 hazards, 10 risk attributes (including risk acceptance), and demographic variables. First, the research attempted to explore Nanjing citizens’ average risk acceptable level for 12 hazards in China. Second, intercorrelation analysis and factor analysis of nine risk attributes were performed to obtain the suitable risk perception factors as independent variables. Three risk perception models of acceptance were constructed, which were named “Environmental risk model,” “Daily risk model,” and “Technical risk model,” that explained 59.0–69.6% of variance separately. In general, the variables of Knowledge, Benefit, and Trust were found to be significant in all models, implying that these variables are the main determining factors. However, in the environmental risk model, the variable of effect was also significant, which means the determining factors would change for different types of hazards. These results could help the Chinese government to improve the communication of risks with the public and make effective mitigation policies to improve people's rational judgment on the acceptability of risks. 相似文献
998.
999.
Tian L Ji BZ Liu SW He CL Jin F Gao J Stanley D Li S 《Archives of insect biochemistry and physiology》2010,75(4):275-286
We report on juvenile hormone (JH) biosynthesis from long‐chain intermediates by specific reproductive tissues and the corpora allata (CA) prepared from adult longhorned beetles, Apriona germari. The testes, male accessory glands (MAGs), ovaries, and CA contained the long‐chain intermediates in the JH biosynthetic pathway, farnesoic acid (FA), methyl farnesoate (MF), and JH III. The testes and ovaries, but not CA, produced radioactive JH III after the addition of 3H‐methionine and, separately, unlabeled methionine, to the incubation medium. We inferred that endogenous FA is methylated to MF in the testes and ovaries. Addition of farnesol led to increased amounts of FA in the testes, MAGs, ovaries, and CA, indicating oxidation of farnesol to FA. Addition of FA to incubation medium yielded increased JH III, again indicating methylation of FA to MF in the testes, MAGs, ovaries, but not CA. Addition of MF to incubation medium also led to JH III, from which we inferred the epoxidation of MF to JH III. JH biosynthesis from farnesol in the testes, MAGs, and ovaries of A. germari proceeds via oxidation to FA, methylation to MF, and epoxidation to JH III. This is a well‐known pathway to JH III, described here for the first time in reproductive tissues of longhorned beetles. © 2010 Wiley Periodicals, Inc. 相似文献
1000.
Using nicking DNA endonuclease (NiDE), we developed a novel technique to clone DNA fragments into plasmids. We created a NiDE cassette consisting of two inverted NiDE substrate sites sandwiching an asymmetric four-base sequence, and NiDE cleavage resulted in 14-base single-stranded termini at both ends of the vector and insert. This method can therefore be used as a ligation-independent cloning strategy to generate recombinant constructs rapidly. In addition, we designed and constructed a simple and specific vector from an Escherichia coli plasmid back-bone to complement this cloning method. By cloning cDNAs into this modified vector, we confirmed the predicted feasibility and applicability of this cloning method. 相似文献