全文获取类型
收费全文 | 9410篇 |
免费 | 587篇 |
国内免费 | 31篇 |
出版年
2023年 | 109篇 |
2022年 | 281篇 |
2021年 | 525篇 |
2020年 | 254篇 |
2019年 | 301篇 |
2018年 | 402篇 |
2017年 | 277篇 |
2016年 | 377篇 |
2015年 | 533篇 |
2014年 | 580篇 |
2013年 | 706篇 |
2012年 | 713篇 |
2011年 | 620篇 |
2010年 | 369篇 |
2009年 | 329篇 |
2008年 | 371篇 |
2007年 | 371篇 |
2006年 | 298篇 |
2005年 | 263篇 |
2004年 | 240篇 |
2003年 | 199篇 |
2002年 | 190篇 |
2001年 | 128篇 |
2000年 | 114篇 |
1999年 | 89篇 |
1998年 | 52篇 |
1997年 | 46篇 |
1996年 | 47篇 |
1995年 | 36篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 70篇 |
1991年 | 78篇 |
1990年 | 75篇 |
1989年 | 66篇 |
1988年 | 70篇 |
1987年 | 54篇 |
1986年 | 43篇 |
1985年 | 58篇 |
1984年 | 51篇 |
1983年 | 45篇 |
1982年 | 31篇 |
1980年 | 34篇 |
1979年 | 40篇 |
1978年 | 45篇 |
1977年 | 33篇 |
1976年 | 35篇 |
1974年 | 43篇 |
1973年 | 27篇 |
1970年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
A quantitative and qualitative survey of the indigenous Endogone population in wheat field soil and vesicular-arbuscular mycorrhiza in wheat roots as influenced by season and by the stage of development of the wheat plant was made. The number of Endogone spores in wheat field soil remained relatively unchanged in winter until January during the period of maximum root growth. The extent of formation of arbuscules was influenced by the stage of development of the wheat plants. 相似文献
192.
193.
Khan NA 《Molecular & general genetics : MGG》1975,136(1):55-61
Temperature-sensitive mutants affecting maltose utilization in the yeast Saccharomyces cerevisiae have been isolated. Two such mutants although failing to ferment maltose at the restrictive temperature, have normal induced level of maltase. The third mutant (UNT-37) not only failed to ferment maltose but has 5-6 fold less induced level of maltase at the restrictive temperature than the parental strain. The genetic control mechanisms of maltase induction and maltose utilization have been discussed. 相似文献
194.
Amol A. Verma Tejasvi Hora Hae Young Jung Michael Fralick Sarah L. Malecki Lauren Lapointe-Shaw Adina Weinerman Terence Tang Janice L. Kwan Jessica J. Liu Shail Rawal Timothy C.Y. Chan Angela M. Cheung Laura C. Rosella Marzyeh Ghassemi Margaret Herridge Muhammad Mamdani Fahad Razak 《CMAJ》2021,193(23):E859
195.
We previously reported the antifungal properties of a monoterpene phenol “Eugenol” against different Candida strains and have observed that the addition of methyl group to eugenol drastically increased its antimicrobial potency. Based on the results and the importance of medicinal synthetic chemistry, we synthesized eugenol-tosylate and its congeners (E1-E6) and tested their antifungal activity against different clinical fluconazole (FLC)- susceptible and FLC- resistant C. albicans isolates alone and in combination with FLC by determining fractional inhibitory concentration indices (FICIs) and isobolograms calculated from microdilution assays. Minimum inhibitory concentration (MIC) results confirmed that all the tested C. albicans strains were variably susceptible to the semi-synthetic derivatives E1-E6, with MIC values ranging from 1–62 μg/ml. The test compounds in combination with FLC exhibited either synergy (36%), additive (41%) or indifferent (23%) interactions, however, no antagonistic interactions were observed. The MICs of FLC decreased 2–9 fold when used in combination with the test compounds. Like their precursor eugenol, all the derivatives showed significant impairment of ergosterol biosynthesis in all C. albicans strains coupled with down regulation of the important ergosterol biosynthesis pathway gene-ERG11. The results were further validated by docking studies, which revealed that the inhibitors snugly fitting the active site of the target enzyme, mimicking fluconazole, may well explain their excellent inhibitory activity. Our results suggest that these compounds have a great potential as antifungals, which can be used as chemosensitizing agents with the known antifungal drugs. 相似文献
196.
Jordan Bai Muhammad Farid Abdul-Rahman Anne Rifkin-Graboi Yap-Seng Chong Kenneth Kwek Seang-Mei Saw Keith M. Godfrey Peter D. Gluckman Marielle V. Fortier Michael J. Meaney Anqi Qiu 《PloS one》2012,7(10)
We studied a sample of 75 Chinese, 73 Malay, and 29 Indian healthy neonates taking part in a cohort study to examine potential differences in neonatal brain morphology and white matter microstructure as a function of ethnicity using both structural T2-weighted magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). We first examined the differences in global size and morphology of the brain among the three groups. We then constructed the T2-weighted MRI and DTI atlases and employed voxel-based analysis to investigate ethnic differences in morphological shape of the brain from the T2-weighted MRI, and white matter microstructure measured by fractional anisotropy derived from DTI. Compared with Malay neonates, the brains of Indian neonates’ tended to be more elongated in anterior and posterior axis relative to the superior-inferior axis of the brain even though the total brain volume was similar among the three groups. Although most anatomical regions of the brain were similar among Chinese, Malay, and Indian neonates, there were anatomical variations in the spinal-cerebellar and cortical-striatal-thalamic neural circuits among the three populations. The population-related brain regions highlighted in our study are key anatomical substrates associated with sensorimotor functions. 相似文献
197.
198.
Ajay Kumar Tiwari Kavita Kumari Neeraj Nath Tiwari Pradeep Kumar Akil Ahmad Khan 《Archives Of Phytopathology And Plant Protection》2013,46(17-20):931-935
During the survey of two successive years 2012–2013, in nearby places of Gorakhpur districts, Uttar Pradesh, India, Arundo donax plants were found to be exhibiting witches’ broom, excessive branching accompanied with little leaf symptoms with considerable disease incidence. Nested PCR carried out with universal primers pair R16F2n/R16R2 employing the PCR (P1/P7) product as a template DNA (1:20) resulted in expected size positive amplification ~1.2 kb in all symptom-bearing plants suggested the association of phytoplasma with witches’ broom disease of Narkat plants. BLASTn analysis of the 16S rRNA gene sequence showed the highest (99%) sequence identity with Candidatus phytoplasma asteris (16SrI group). In phylogenetic analysis, the sequence data showed close relationships with the members of 16SrI phytoplasma and clustered within a single clade of 16SrI group and closed to B subgroup representatives. This is a first report of 16Sr I-B group phytoplasma associated with witches’ broom accompanied with little leaf disease of Narkat in India. 相似文献
199.
Xiangjun Kong Aziz Khan Zhiling Li Jingyi You Fazal Munsif Haodong Kang Ruiyang Zhou 《Saudi Journal of Biological Sciences》2020,27(12):3691-3699
Chalcone synthase (CHS) is a key enzyme and producing flavonoid derivatives as well play a vital roles in sustaining plant growth and development. However, the systematic and comprehensive analysis of CHS genes in island cotton (G. barbadense) has not been reported yet especially response to cytoplasmic male sterility (CMS). To fill this knowledge gap, a genome-wide investigation of CHS genes were studied in island cotton. A total of 20 GbCHS genes were identified and grouped into five GbCHSs. The gene structure analysis revealed that most of GbCHS genes consisted of two exons and one intron, and 20 motifs were identified. Twenty five pairs duplicated events (12 GbCHS genes) were identified including 23 segmental duplication pairs and two tandem duplication events, representing that GbCHS gene family amplification mainly owned to segmental duplication events and evolving slowly. Gene expression analysis exhibited that the GbCHS family genes presented a diversity expression patterns in various organs of cotton. Coupled with functional predictions and gene expression, the abnormal expression of GbCHS06, 10, 16 and 19 might be associated with pollen abortion of CMS line in island cotton. Conclusively, GbCHS genes exhibited diversity and conservation in many aspects, which will help to better understand functional studies and a reference for CHS research in island cotton and other plants. 相似文献
200.
Sedigheh Zakeri Ahmad Raeisi Mandana Afsharpad Qutbuddin Kakar Faezeh Ghasemi Hoda Atta Ghasem Zamani Muhammad Suleiman Memon Masoud Salehi Navid Dinparast Djadid 《Parasitology international》2010,59(1):15-21
In this study, the diversity of Plasmodium vivax populations circulating in Pakistan and Iran has been investigated by using circumsporozoite protein (csp) and merozoite surface proteins 1 and 3α (msp-1 and msp-3α) genes as genetic markers. Infected P. vivax blood samples were collected from Pakistan (n = 187) and Iran (n = 150) during April to October 2008, and were analyzed using nested-PCR/RFLP and sequencing methods. Genotyping pvmsp-1 (variable block 5) revealed the presence of type 1, type 2 and recombinant type 3 allelic variants, with type 1 predominant, in both study areas. The sequence analysis of 33 P. vivax isolates from Pakistan and 30 from Iran identified 16 distinct alleles each, with one allele (R-8) from Iran which was not reported previously. Genotyping pvcsp gene also showed that VK210 type is predominant in both countries. Moreover, based on the size of amplified fragment of pvmsp-3α, three major types: type A (1800 bp), type B (1500 bp) and type C (1200 bp), were distinguished among the examined isolates that type A was predominant among Pakistani (72.7%) and Iranian (77.3%) parasites. PCR/RFLP products of pvmsp-3α with HhaI and AluI have detected 40 and 39 distinct variants among Pakistani and Iranian examined isolates, respectively. Based on these three studied genes, the rate of combined multiple genotypes were 30% and 24.6% for Pakistani and Iranian P. vivax isolates, respectively. These results indicate an extensive diversity in the P. vivax populations in both studies. 相似文献