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   120945篇
  免费   2661篇
  国内免费   2677篇
  2024年   27篇
  2023年   352篇
  2022年   737篇
  2021年   1502篇
  2020年   963篇
  2019年   1184篇
  2018年   12802篇
  2017年   11337篇
  2016年   8539篇
  2015年   2382篇
  2014年   2381篇
  2013年   2618篇
  2012年   6897篇
  2011年   15028篇
  2010年   13303篇
  2009年   9436篇
  2008年   11148篇
  2007年   12559篇
  2006年   1483篇
  2005年   1513篇
  2004年   1823篇
  2003年   1706篇
  2002年   1416篇
  2001年   822篇
  2000年   626篇
  1999年   490篇
  1998年   290篇
  1997年   292篇
  1996年   261篇
  1995年   228篇
  1994年   247篇
  1993年   179篇
  1992年   202篇
  1991年   177篇
  1990年   131篇
  1989年   121篇
  1988年   122篇
  1987年   80篇
  1986年   61篇
  1985年   52篇
  1984年   47篇
  1983年   42篇
  1982年   19篇
  1980年   12篇
  1972年   248篇
  1971年   279篇
  1965年   14篇
  1962年   24篇
  1944年   12篇
  1940年   10篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Owing to the exceptional intracellular distribution and the heterogeneous expression pattern during transformation and metastasis in various tumors, the EF-hand calcium-binding protein S100A2 attracts increasing attention. Unlike the majority of S100 proteins, S100A2 expression is downregulated in many cancers and the loss in nuclear expression has been associated with poor prognosis. On the other hand, S100A2 is upregulated in some cancers. This mini review highlights the general characteristics of S100A2 and discusses recent findings on its putative functional implication as a suppressor or promoter in cancerogenesis.  相似文献   
122.
A TaqMan quantitative real-time polymerase chain reaction (qPCR) assay was developed for the detection and enumeration of three Pseudomonas species belonging to the mendocina sublineage (P. oleovorans, P. pseudoalcaligenes, and P. oleovorans subsp. lubricantis) found in contaminated metalworking fluids (MWFs). These microbes are the primary colonizers and serve as indicator organisms of biodegradation of used MWFs. Molecular techniques such as qPCR are preferred for the detection of these microbes since they grow poorly on typical growth media such as R2A agar and Pseudomonas isolation agar (PIA). Traditional culturing techniques not only underestimate the actual distribution of these bacteria but are also time-consuming. The primer–probe pair developed from gyrase B (gyrB) sequences of the targeted bacteria was highly sensitive and specific for the three species. qPCR was performed with both whole cell and genomic DNA to confirm the specificity and sensitivity of the assay. The sensitivity of the assay was 101 colony forming units (CFU)/ml for whole cell and 13.7 fg with genomic DNA. The primer–probe pair was successful in determining concentrations from used MWF samples, indicating levels between 2.9 × 103 and 3.9 × 106 CFU/ml. In contrast, the total count of Pseudomonas sp. recovered on PIA was in the range of <1.0 × 101 to 1.4 × 105 CFU/ml for the same samples. Based on these results from the qPCR assay, the designed TaqMan primer–probe pair can be efficiently used for rapid (within 2 h) determination of the distribution of these species of Pseudomonas in contaminated MWFs.  相似文献   
123.
124.
125.
Complex ecological pressures affect the social dynamics of many primate species, but it is unclear how they affect primate speciation. Molecular tools are often used to answer questions about the evolutionary histories and social systems of primates. Mitochondrial DNA (mtDNA), in particular, is frequently used to answer many of these questions, but because it is passed from mothers to offspring it reveals only the histories of females. In many species, including chimpanzees, females generally disperse from their natal groups while males are philopatric, and thus differences in dispersal patterns likely leave different signatures in the genome. We previously analyzed samples from 187 unrelated male and female chimpanzees in Nigeria and Cameroon using 21 autosomal microsatellites and mtDNA sequences. Here, we examine the contributions of males and females in shaping the genetic history of these chimpanzees by genotyping a subset of 56 males at 12 Y-chromosome microsatellites. We found that Y-chromosome population structure differed from the results of analysis of mtDNA haplotypes. The results also revealed that males in rainforest habitats (Guinean and Congolian rainforests) are more closely related to one another than those inhabiting the savanna-woodland mosaic ecotone in central Cameroon. In contrast, the pattern of female relatedness did not differ across habitats. We hypothesize that these differences in population structure and patterns of relatedness among males in different habitat types may be due to differences in the community dynamics of chimpanzees in the ecotone vs. rainforests, and that these factors contribute to making Cameroon an engine of diversification for chimpanzees. Broadly, these results demonstrate the importance of habitat variation in shaping social systems, population genetics, and primate speciation.  相似文献   
126.
B‐cell maturation antigen (BCMA) is expressed on normal and malignant plasma cells and represents a potential target for therapeutic intervention. In this study, we characterized the mechanism underlying the protein kinase B (Akt) and c‐Jun N‐terminal kinase (JNK) pathways and BCMA interactions in regulating multiple myeloma (MM) cell survival. It was found that the expression levels of B cell‐activating factor (BAFF) and BCMA were increased in MM cells as compared with those in normal controls. The proliferation of U266 cells was induced by recombinant human BAFF (rhBAFF) and could also be decreased by BCMA siRNA. The expression of Bcl‐2 protein was up‐regulated, and Bax protein was down‐regulated after rhBAFF treatment, which could be reversed by BCMA siRNA. Similarly, the protein p‐JNK and p‐Akt were activated by rhBAFF and could be changed by BCMA siRNA. In addition, the BCMA mRNA and protein expression levels were decreased after treatment with Akt and JNK pathway inhibitors. These results suggest that Akt and JNK pathways are involved in the regulation of BCMA. A novel BAFF/BCMA signalling pathway in MM may be a new therapeutic target for MM. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
127.
Systems biology is an approach to explain the behaviour of a system in relation to its individual components. Synthetic biology uses key hierarchical and modular concepts of systems biology to engineer novel biological systems. In my opinion the next step in biology is to use molecule-to-phenotype data using these approaches and integrate them in the form a periodic table. A periodic table in biology would provide chassis to classify, systematize and compare diversity of component properties vis-a-vis system behaviour. Using periodic table it could be possible to compute higher-level interactions from component properties. This paper examines the concept of building a bio-periodic table using protein fold as the fundamental unit.  相似文献   
128.
Ferruh Aşçi 《Biologia》2009,64(6):1146-1149
In this study, the structural characteristics, unique features, various organ measurements of males and females of the water mite Atractides (Atractides) turcicus sp. n. from Turkey are described. In addition, the study compares their characteristics with related species.  相似文献   
129.
Connective tissue growth factor (CTGF/CCN2) is overexpressed in diabetes. Diabetic rats possess myocardial and cardiomyocyte hypertrophy. In a recent report, Wang and colleagues (Am J Physiol Cell Physiol. 2009 Jul 22. [Epub ahead of print]) show that CCN2 directly mediates cardiomyocyte hypertrophy as well as that induced by high glucose and fatty acid. CCN2 acted via the TrkA receptor. These data are the subject of this commentary, and emphasize that CCN2 may be an excellent target for therapy in diabetes.  相似文献   
130.
PacBio RS II is the first commercialized third-generation DNA sequencer able to sequence a single molecule DNA in real-time without amplification. PacBio RS II’s sequencing technology is novel and unique, enabling the direct observation of DNA synthesis by DNA polymerase. PacBio RS II confers four major advantages compared to other sequencing technologies: long read lengths, high consensus accuracy, a low degree of bias, and simultaneous capability of epigenetic characterization. These advantages surmount the obstacle of sequencing genomic regions such as high/low G+C, tandem repeat, and interspersed repeat regions. Moreover, PacBio RS II is ideal for whole genome sequencing, targeted sequencing, complex population analysis, RNA sequencing, and epigenetics characterization. With PacBio RS II, we have sequenced and analyzed the genomes of many species, from viruses to humans. Herein, we summarize and review some of our key genome sequencing projects, including full-length viral sequencing, complete bacterial genome and almost-complete plant genome assemblies, and long amplicon sequencing of a disease-associated gene region. We believe that PacBio RS II is not only an effective tool for use in the basic biological sciences but also in the medical/clinical setting.  相似文献   
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