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   3834篇
  免费   421篇
  国内免费   609篇
  2024年   35篇
  2023年   95篇
  2022年   203篇
  2021年   284篇
  2020年   209篇
  2019年   222篇
  2018年   242篇
  2017年   153篇
  2016年   184篇
  2015年   283篇
  2014年   367篇
  2013年   338篇
  2012年   387篇
  2011年   340篇
  2010年   232篇
  2009年   210篇
  2008年   216篇
  2007年   174篇
  2006年   150篇
  2005年   104篇
  2004年   88篇
  2003年   96篇
  2002年   61篇
  2001年   13篇
  2000年   12篇
  1999年   24篇
  1998年   14篇
  1997年   17篇
  1996年   16篇
  1995年   10篇
  1994年   12篇
  1993年   9篇
  1992年   13篇
  1991年   7篇
  1990年   11篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1982年   6篇
  1981年   2篇
  1980年   3篇
  1972年   2篇
  1970年   3篇
  1967年   1篇
排序方式: 共有4864条查询结果,搜索用时 264 毫秒
131.
We conducted a preliminary study to examine whether Chinese readers’ spontaneous word segmentation processing is consistent with the national standard rules of word segmentation based on the Contemporary Chinese language word segmentation specification for information processing (CCLWSSIP). Participants were asked to segment Chinese sentences into individual words according to their prior knowledge of words. The results showed that Chinese readers did not follow the segmentation rules of the CCLWSSIP, and their word segmentation processing was influenced by the syntactic categories of consecutive words. In many cases, the participants did not consider the auxiliary words, adverbs, adjectives, nouns, verbs, numerals and quantifiers as single word units. Generally, Chinese readers tended to combine function words with content words to form single word units, indicating they were inclined to chunk single words into large information units during word segmentation. Additionally, the “overextension of monosyllable words” hypothesis was tested and it might need to be corrected to some degree, implying that word length have an implicit influence on Chinese readers’ segmentation processing. Implications of these results for models of word recognition and eye movement control are discussed.  相似文献   
132.
133.
As shown by the recent crisis, tax evasion poses a significant problem for countries such as Greece, Spain and Italy. While these societies certainly possess weaker fiscal institutions as compared to other EU members, might broader cultural differences between northern and southern Europe also help to explain citizens’ (un)willingness to pay their taxes? To address this question, we conduct laboratory experiments in the UK and Italy, two countries which straddle this North-South divide. Our design allows us to examine citizens’ willingness to contribute to public goods via taxes while holding institutions constant. We report a surprising result: when faced with identical tax institutions, redistribution rules and audit probabilities, Italian participants are significantly more likely to comply than Britons. Overall, our findings cast doubt upon “culturalist” arguments that would attribute cross-country differences in tax compliance to the lack of morality amongst southern European taxpayers.  相似文献   
134.
Compelling evidences have suggested that high mobility group box-1 (HMGB1) gene plays a crucial role in cancer development and progression. This study aimed to evaluate the effects of single nucleotide polymorphisms (SNPs) in HMGB1 gene on the survival of gastric cancer (GC) patients. Three tag SNPs from HMGB1 gene were selected and genotyped using Sequenom iPEX genotyping system in a cohort of 1030 GC patients (704 in training set, 326 in validation set). Multivariate Cox proportional hazard model and Kaplan-Meier Curve were used for prognosis analysis. AG/AA genotypes of SNP rs1045411 in HMGB1 gene were significantly associated with better overall survival (OS) in a set of 704 GC patients when compared with GG genotypes (HR = 0.77, 95% CI: 0.60–0.97, P = 0.032). This prognostic effect was verified in an independent validation set and pooled analysis (HR = 0.80, 95% CI: 0.62–0.99, P = 0.046; HR = 0.78, 95% CI: 0.55–0.98, P = 0.043, respectively). In stratified analysis, the protective effect of rs1045411 AG/AA genotypes was more prominent in patients with adverse strata, compared with patients with favorable strata. Furthermore, strong joint predictive effects on OS of GC patients were noted between rs1045411 genotypes and Lauren classification, differentiation, stage or adjuvant chemotherapy. Additionally, functional assay indicated a significant effect of rs1045411 on HMGB1 expression. Our results suggest that rs1045411 in HMGB1 is significantly associated with clinical outcomes of Chinese GC patients after surgery, especially in those with aggressive status, which warrants further validation in other ethnic populations.  相似文献   
135.
S-acylation is one of a group of lipid modifications that occurs on eukaryotic proteins, mediated by DHHC-CRD-containing proteins, which plays an important role in regulating the membrane association, trafficking and function of target proteins. Although genome-wide identification of PAT family has been carried out in yeast, mice, humans and Arabidopsis, little is known about apple PAT genes. In this study, a total of 33 putative apple PAT proteins, containing DHHC-CRD by domain analysis, have been identified, and were classified into three groups according to the phylogenetic analysis of PAT proteins in apple and Arabidopsis. More complex TMDs in the most MdPATs revealed the PM location of the gene family. Gene structure, gene chromosomal location and paralogs analysis of MdPAT genes within the apple genome demonstrated that tandem and segmental duplications, as well as whole genome duplications, have likely contributed to the expansion and evolution of the PAT gene family in apple. According to the microarray and expressed sequence tag (ESTs) analysis, the different expression patterns indicate that they may play different roles during fruit development and rootstock-scion interactions process. Moreover, PATs were performed expression profile analyses in different tissues, indicating that the PATs are involved in various aspects of physiological and developmental processes of apple. To our knowledge, this is the first report of a genome-wide analysis of the apple PAT gene family, and this genomic analysis of apple DHHC-CRD PAT genes provides the first step towards a functional study of this gene family in apple.  相似文献   
136.
This fMRI study aimed to identify the neural mechanisms underlying the recognition of Chinese multi-character words by partialling out the confounding effect of reaction time (RT). For this purpose, a special type of nonword—transposable nonword—was created by reversing the character orders of real words. These nonwords were included in a lexical decision task along with regular (non-transposable) nonwords and real words. Through conjunction analysis on the contrasts of transposable nonwords versus regular nonwords and words versus regular nonwords, the confounding effect of RT was eliminated, and the regions involved in word recognition were reliably identified. The word-frequency effect was also examined in emerged regions to further assess their functional roles in word processing. Results showed significant conjunctional effect and positive word-frequency effect in the bilateral inferior parietal lobules and posterior cingulate cortex, whereas only conjunctional effect was found in the anterior cingulate cortex. The roles of these brain regions in recognition of Chinese multi-character words were discussed.  相似文献   
137.
姜南  刘卫  李岩  解志红 《微生物学报》2016,56(8):1256-1265
[Objective] Azorhizobium caulinodans ORS571 can fix nitrogen not only as a free-living organism and an associative-symbiotic bacterium by colonizing the root surface of non-leguminous plants, but also as a symbiotic bacterium by interacting with leguminous plant Sesbania rostrata.Due to its ability to grow and fix nitrogen under three conditions, A.caulinodans uses sophisticated chemotaxis signal transduction systems to transform environmental cues into corresponding behavioral responses.Chemotaxis appears crucial for the growth of A.caulinodansin complicated environment and the construction of associative relationship with the plant.However, little is known about the chemotactic pathway of A.caulinodans.Thus, our study aimed to compare the chemotaxis-like genes of A.caulinodans with those of well-studied species.[Methods] NCBI protein BLAST was used for searching sequence similarity with default parameter values against the genomes of A.caulinodans.HMMER3, based on Pfam database, was used for comparative analyses of methyl-accepting chemotaxis protein (MCP).[Results] There was a major chemotaxis cluster in A.caulinodans and the CheR methylated MCPs independently of pentapeptide motif.There were 43 MCP homologs containing diverse signal-sensing architectures in A.caulinodans.In addition,cytoplasmic domains of these MCPs were all composed of 38 heptad repeats.[Conclusion] Despite the extremely high homology presented between the chemotactic system of A.caulinodans and those of well-studied species, A.caulinodans shows its own unique characteristics.The classification of these chemotactic pathways by comparative genomics enables us to better understand how A.caulinodansresponds to changes in environment via exquisite signal transductions in chemotaxis system.  相似文献   
138.
In this article, we discuss the polymerase chain reaction (PCR)–hybridization assay that we developed for high-throughput simultaneous detection and differentiation of Ureaplasma urealyticum and Ureaplasma parvum using one set of primers and two specific DNA probes based on urease gene nucleotide sequence differences. First, U. urealyticum and U. parvum DNA samples were specifically amplified using one set of biotin-labeled primers. Furthermore, amine-modified DNA probes, which can specifically react with U. urealyticum or U. parvum DNA, were covalently immobilized to a DNA–BIND plate surface. The plate was then incubated with the PCR products to facilitate sequence-specific DNA binding. Horseradish peroxidase–streptavidin conjugation and a colorimetric assay were used. Based on the results, the PCR–hybridization assay we developed can specifically differentiate U. urealyticum and U. parvum with high sensitivity (95%) compared with cultivation (72.5%). Hence, this study demonstrates a new method for high-throughput simultaneous differentiation and detection of U. urealyticum and U. parvum with high sensitivity. Based on these observations, the PCR–hybridization assay developed in this study is ideal for detecting and discriminating U. urealyticum and U. parvum in clinical applications.  相似文献   
139.
A wide range of microorganisms found in the rhizhosphere are able to regulate plant growth and development, but little is known about the mechanism by which epiphytic microbes inhibit plant growth. Here, an epiphytic bacteria Stenotrophomonas maltophilia, named as LZMBW216, were isolated and identified from the potato (Solanum tuberosum L. cv. Da Xi Yang) leaf surface. They could decrease primary root elongation and lateral root numbers in Arabidopsis seedlings. The inhibitory effects of LZMBW216 on plant growth were not due to a reduced indole-3-acetic acid (IAA) content, as exogenously applied IAA did not recover the inhibition. Furthermore, LZMBW216 did not affect the expression of DR5::GUS and CycB1;1::GUS. However, we found that LZMBW216 exhibited little effect on the primary root elongation in the pin2 mutant and on the lateral root numbers in the aux1-7 mutant. Moreover, LZMBW216 decreased expressions of AUX1 and PIN2 proteins. Together, these results suggest that root system architecture alterations caused by LZMBW216 may involve polar auxin transport.  相似文献   
140.
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