首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   718篇
  免费   52篇
  770篇
  2023年   3篇
  2022年   14篇
  2021年   20篇
  2020年   9篇
  2019年   12篇
  2018年   20篇
  2017年   23篇
  2016年   15篇
  2015年   37篇
  2014年   34篇
  2013年   54篇
  2012年   54篇
  2011年   46篇
  2010年   27篇
  2009年   23篇
  2008年   29篇
  2007年   37篇
  2006年   28篇
  2005年   30篇
  2004年   31篇
  2003年   23篇
  2002年   14篇
  2001年   20篇
  2000年   19篇
  1999年   15篇
  1998年   9篇
  1996年   6篇
  1993年   3篇
  1992年   10篇
  1991年   8篇
  1990年   8篇
  1989年   9篇
  1988年   5篇
  1987年   3篇
  1986年   7篇
  1985年   6篇
  1984年   4篇
  1983年   5篇
  1982年   6篇
  1981年   3篇
  1980年   5篇
  1979年   2篇
  1978年   5篇
  1976年   2篇
  1975年   3篇
  1974年   6篇
  1972年   2篇
  1971年   3篇
  1969年   2篇
  1963年   2篇
排序方式: 共有770条查询结果,搜索用时 0 毫秒
721.
722.
723.
Spices such as coriander, cumin, turmeric, chilli collected from a local market were found to be highly contaminated with bacteria and fungi. A dose of 10 kGy was required to reduce the total bacterial count below detectable levels, while a dose of only 5 kGy was required to eliminate the fungal contamination. Coliforms were totally eliminated at a radiation dose of 5 kGy. During a 6 months storage of irradiated and unirradiated spices, the irradiated spices were found to retain good microbiological quality.  相似文献   
724.
725.
The “extended” type of short chain dehydrogenases/reductases (SDR), share a remarkable similarity in their tertiary structures inspite of being highly divergent in their functions and sequences. We have carried out principal component analysis (PCA) on structurally equivalent residue positions of 10 SDR families using information theoretic measures like Jensen–Shannon divergence and average shannon entropy as variables. The results classify residue positions in the SDR fold into six groups, one of which is characterized by low Shannon entropies but high Jensen–Shannon divergence against the reference family SDR1E, suggesting that these positions are responsible for the specific functional identities of individual SDR families, distinguishing them from the reference family SDR1E. Site directed mutagenesis of three residues from this group in the enzyme UDP‐Galactose 4‐epimerase belonging to SDR1E shows that the mutants promote the formation of NADH containing abortive complexes. Finally, molecular dynamics simulations have been used to suggest a mechanism by which the mutants interfere with the re‐oxidation of NADH leading to the formation of abortive complexes. Proteins 2014; 82:2842–2856. © 2014 Wiley Periodicals, Inc.  相似文献   
726.
The aim of this study was to identify genetic variants associated with rheumatoid arthritis (RA) risk in black South Africans. Black South African RA patients (n = 263) were compared with healthy controls (n = 374). Genotyping was performed using the Immunochip, and four-digit high-resolution human leukocyte antigen (HLA) typing was performed by DNA sequencing of exon 2. Standard quality control measures were implemented on the data. The strongest associations were in the intergenic region between the HLA-DRB1 and HLA-DQA1 loci. After conditioning on HLA-DRB1 alleles, the effect in the rest of the extended major histocompatibility (MHC) diminished. Non-HLA single nucleotide polymorphisms (SNPs) in the intergenic regions LOC389203|RBPJ, LOC100131131|IL1R1, KIAA1919|REV3L, LOC643749|TRAF3IP2, and SNPs in the intron and untranslated regions (UTR) of IRF1 and the intronic region of ICOS and KIAA1542 showed association with RA (p < 5 × 10−5). Of the SNPs previously associated with RA in Caucasians, one SNP, rs874040, locating to the intergenic region LOC389203|RBPJ was replicated in this study. None of the variants in the PTPN22 gene was significantly associated. The seropositive subgroups showed similar results to the overall cohort. The effects observed across the HLA region are most likely due to HLA-DRB1, and secondary effects in the extended MHC cannot be detected. Seven non-HLA loci are associated with RA in black South Africans. Similar to Caucasians, the intergenic region between LOC38920 and RBPJ is associated with RA in this population. The strong association of the R620W variant of the PTPN22 gene with RA in Caucasians was not replicated since this variant was monomorphic in our study, but other SNP variants of the PTPN22 gene were also not associated with RA in black South Africans, suggesting that this locus does not play a major role in RA in this population.  相似文献   
727.
In both types of crosses (3n C.G.×4n D 154 and 4n D 154×3n C.G.) pods were found to set. In the first case pods shed within 4 days. In the second case pods were found to persist till maturity. Only a few uppermost ovules were found to be fertilized. Pollen tubes were seen to reach the ovules within 24 hours. In 4n D 154×3n C.G. fusion of sperm with the egg was not noted to be complete till 3 days but the secondary nucleus is fertilized by other sperm. In 3n C.G.×D 154 fusion of sperm with egg or with polars was not complete within 3 days. Signs of degeneration of ovules were noted on the 5th day in both cases.  相似文献   
728.
A status survey of Asian Elephants Elephas maximus was conducted in the 9 north-eastern states of India. The habitat is contiguous with that in Bhutan, Myanmar and Bangladesh. Although the estimated population of 11 000 elephants is higher than in other regions of the Indian Sub-continent, it is fragmented and a number of small inviable isolated populations have formed. About 35% of the population is partly protected, but protection is inadequate. More areas and migration routes need to be protected. Man–elephant conflict is serious in many areas. A comprehensive Action Plan with a more pragmatic protected-area network has been proposed.  相似文献   
729.
Surface plasmon polariton (SPP) excitation of the coupled light at small contact area of chromium pillars as the interface of metastructured gold funnel layer and silica medium can be enhanced locally in the gold meta-funnel-structured filter. In the present investigation, the filter is comprised of three layers, namely gold meta-funnels, nano-sized chromium pillars, and silica as the substrate. The incoming infrared (IR) waves, coupled with the excited plasmons at the first and second layers, form an excitation, known as deformed plasmon polariton. Asymmetric distribution of localized SPPs takes place owing to the inherent converging plasmonic feature of the gold funnel structure. The formation of reflection peaks with different magnitudes at different incidence angles of the polarized wave in the spectral characteristics makes the structure prominent for filtering the IR waves. Moreover, the gold meta-funnel-structured filter possesses the additional feature of distinguishing the type of polarized incidence wave. It was found that the transmission remains maximum corresponding to the normal incidence of the TE-polarized waves, whereas the TM-polarized waves over the same wavelength range are almost blocked for any value of incidence angle. The existence of transmission peaks corresponding to the TE waves demonstrates another application of this device as metastructured polarizer filter.  相似文献   
730.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号