全文获取类型
收费全文 | 1812篇 |
免费 | 108篇 |
出版年
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 30篇 |
2017年 | 13篇 |
2016年 | 23篇 |
2015年 | 37篇 |
2014年 | 53篇 |
2013年 | 99篇 |
2012年 | 94篇 |
2011年 | 102篇 |
2010年 | 72篇 |
2009年 | 55篇 |
2008年 | 74篇 |
2007年 | 117篇 |
2006年 | 97篇 |
2005年 | 102篇 |
2004年 | 130篇 |
2003年 | 107篇 |
2002年 | 123篇 |
2001年 | 50篇 |
2000年 | 34篇 |
1999年 | 33篇 |
1998年 | 25篇 |
1997年 | 34篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 20篇 |
1993年 | 26篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有1920条查询结果,搜索用时 15 毫秒
81.
Populations often have very complex hierarchical structure. Therefore, it is crucial in genetic monitoring and conservation biology to have a reliable estimate of the pattern of population subdivision. F(ST)'s for pairs of sampled localities or subpopulations are crucial statistics for the exploratory analysis of population structures, such as cluster analysis and multidimensional scaling. However, the estimation of F(ST) is not precise enough to reliably estimate the population structure and the extent of heterogeneity. This article proposes an empirical Bayes procedure to estimate locus-specific pairwise F(ST)'s. The posterior mean of the pairwise F(ST) can be interpreted as a shrinkage estimator, which reduces the variance of conventional estimators largely at the expense of a small bias. The global F(ST) of a population generally varies among loci in the genome. Our maximum-likelihood estimates of global F(ST)'s can be used as sufficient statistics to estimate the distribution of F(ST) in the genome. We demonstrate the efficacy and robustness of our model by simulation and by an analysis of the microsatellite allele frequencies of the Pacific herring. The heterogeneity of the global F(ST) in the genome is discussed on the basis of the estimated distribution of the global F(ST) for the herring and examples of human single nucleotide polymorphisms (SNPs). 相似文献
82.
Takeda N Maemura K Horie S Oishi K Imai Y Harada T Saito T Shiga T Amiya E Manabe I Ishida N Nagai R 《The Journal of biological chemistry》2007,282(45):32561-32567
Cardiovascular diseases are closely related to circadian rhythm, which is under the control of an internal biological clock mechanism. Although a biological clock exists not only in the hypothalamus but also in each peripheral tissue, the biological relevance of the peripheral clock remains to be elucidated. In this study we searched for clock-controlled genes in vascular endothelial cells using microarray technology. The expression of a total of 229 genes was up-regulated by CLOCK/BMAL2. Among the genes that we identified, we examined the thrombomodulin (TM) gene further, because TM is an integral membrane glycoprotein that is expressed primarily in vascular endothelial cells and plays a major role in the regulation of intravascular coagulation. TM mRNA and protein expression showed a clear circadian oscillation in the mouse lung and heart. Reporter analyses, gel shift assays, and chromatin immunoprecipitation analyses using the TM promoter revealed that a heterodimer of CLOCK and BMAL2 binds directly to the E-box of the TM promoter, resulting in TM promoter transactivation. Indeed, the oscillation of TM gene expression was abolished in clock mutant mice, suggesting that TM expression is regulated by the clock gene in vivo. Finally, the phase of circadian oscillation of TM mRNA expression was altered by temporal feeding restriction, suggesting TM gene expression is regulated by the peripheral clock system. In conclusion, these data suggest that the peripheral clock in vascular endothelial cells regulates TM gene expression and that the oscillation of TM expression may contribute to the circadian variation of cardiovascular events. 相似文献
83.
Kijima Yusuke Wantong Wang Igarashi Yoji Yoshitake Kazutoshi Asakawa Shuichi Suzuki Yutaka Watabe Shugo Kinoshita Shigeharu 《Marine biotechnology (New York, N.Y.)》2022,24(5):895-910
Marine Biotechnology - Most mammals, including humans, show obvious aging phenotypes, for example, loss of tissue plasticity and sarcopenia. In this regard, fish can be attractive models to study... 相似文献
84.
The bacterial flagellar motor is one of the most complex and sophisticated nanomachineries in nature. A duty ratio D is a fraction of time that the stator and the rotor interact and is a fundamental property to characterize the motor but remains to be determined. It is known that the stator units of the motor bind to and dissociate from the motor dynamically to control the motor torque depending on the load on the motor. At low load, at which the kinetics such as proton translocation speed limits the rotation rate, the dependency of the rotation rate on the number of stator units N implies D: the dependency becomes larger for smaller D. Contradicting observations supporting both the small and large D have been reported. A dilemma is that it is difficult to explore a broad range of N at low load because the stator units easily dissociate, and N is limited to one or two at vanishing load. Here, we develop an electrorotation method to dynamically control the load on the flagellar motor of Salmonella with a calibrated magnitude of the torque. By instantly reducing the load for keeping N high, we observed that the speed at low load depends on N, implying a small duty ratio. We recovered the torque-speed curves of individual motors and evaluated the duty ratio to be 0.14 ± 0.04 from the correlation between the torque at high load and the rotation rate at low load. 相似文献
85.
Shogo Tamura Masato Mukaide Yumi Katsuragi Wataru Fujii Koya Odaira Nobuaki Suzuki Nagaharu Tsukiji Shuichi Okamoto Atsuo Suzuki Takeshi Kanematsu Akira Katsumi Akira Takagi Katsuhide Ikeda Jun Ueyama Masaaki Hirayama Katsue Suzuki-Inoue Tadashi Matsushita Tetsuhito Kojima Fumihiko Hayakawa 《The Journal of biological chemistry》2022,298(5)
Bone marrow development and endochondral bone formation occur simultaneously. During endochondral ossification, periosteal vasculatures and stromal progenitors invade the primary avascular cartilaginous anlage, which induces primitive marrow development. We previously determined that bone marrow podoplanin (PDPN)-expressing stromal cells exist in the perivascular microenvironment and promote megakaryopoiesis and erythropoiesis. In this study, we aimed to examine the involvement of PDPN-expressing stromal cells in postnatal bone marrow generation. Using histological analysis, we observed that periosteum-derived PDPN-expressing stromal cells infiltrated the cartilaginous anlage of the postnatal epiphysis and populated on the primitive vasculature of secondary ossification center. Furthermore, immunophenotyping and cellular characteristic analyses indicated that the PDPN-expressing stromal cells constituted a subpopulation of the skeletal stem cell lineage. In vitro xenovascular model cocultured with human umbilical vein endothelial cells and PDPN-expressing skeletal stem cell progenies showed that PDPN-expressing stromal cells maintained vascular integrity via the release of angiogenic factors and vascular basement membrane-related extracellular matrices. We show that in this process, Notch signal activation committed the PDPN-expressing stromal cells into a dominant state with basement membrane-related extracellular matrices, especially type IV collagens. Our findings suggest that the PDPN-expressing stromal cells regulate the integrity of the primitive vasculatures in the epiphyseal nascent marrow. To the best of our knowledge, this is the first study to comprehensively examine how PDPN-expressing stromal cells contribute to marrow development and homeostasis. 相似文献
86.
Apoptotic cells of an epithelial cell line, AsPC-1, release monocyte chemotactic S19 ribosomal protein dimer 总被引:8,自引:0,他引:8
Nishimura T Horino K Nishiura H Shibuya Y Hiraoka T Tanase S Yamamoto T 《Journal of biochemistry》2001,129(3):445-454
A pancreatic carcinoma cell line, AsPC-1, underwent apoptosis in vitro when heat-treated for 60 min at 43 degrees C. Apoptotic AsPC-1 cells liberated a monocyte chemotactic factor into the culture supernatant 24 to 30 h after the heat-treatment. This factor was immunologically identified as the cross-linked homodimer of S19 ribosomal protein (RP S19), since the majority of the chemotactic activity was absorbed by both anti--RP S19 rabbit antibodies and an anti--isopeptide bond monoclonal antibody immobilized on agarose beads. Intracellular transglutaminase activity increased during the apoptotic process, reaching the peak strength between 18 and 24 h after the heat-treatment. A recombinant RP S19 acquired the monocyte chemotactic capacity when incubated with the apoptotic cell extract obtained at the 18th hour. The chemotactic activity acquirement as well as the transglutaminase activity were blocked by treatment of the extract with anti--type II transglutaminase rabbit antibodies. When the recombinant RP S19 was treated with an authentic type II transglutaminase, the dimerization of RP S19 concomitant with the generation of the monocyte chemotactic activity was observed. Peptide-map analyses involving amino acid sequencing demonstrated that the inter-molecular isopeptide bond was heterogeneous: Gln12 or Gln137 and Lys29 or Lys122 were cross-linked. Site-directed mutagenic analysis indicated that the cross-linking of Gln137, but not other residues such as Gln12, Lys29, and Lys122, was essential for expression of the chemotactic activity. 相似文献
87.
88.
Incubation of rat thymocytes with the inhibitors of protein phosphatase such as calyculin A and okadaic acid resulted in an increase in DNA fragmentation. These effects were dependent on the concentration of the inhibitors and the incubation time. Analyses of the fragmented DNA revealed the production of approximately 50 kbp of DNA and a 180 bp DNA ladder. In addition, a laser scanning-microscopic analysis showed that these compounds caused nuclear condensation. Thus, these results demonstrated that protein phosphatase inhibitors induced thymocyte apoptosis. The inhibitors of protein phosphatase increased the phosphorylation of proteins of approximately 15 kDa. The phosphorylation of proteins preceded the DNA fragmentation induced by these inhibitors. Judging from acetic acid-urea-Triton X-100 gel electrophoresis, the phosphorylated proteins were histone H1 and H2A/H3. Therefore, these results suggest that phosphorylation of histones triggers the DNA fragmentation of thymocytes undergoing apoptosis. 相似文献
89.
Amino acid similarity often needs to be considered in DNA sequence comparison to elucidate gene functions. We propose a Smith-Waterman-like algorithm which considers amino acid similarity and insertions/deletions in sequences at the DNA level and at the protein level in a hybrid manner. The algorithm is applied to cDNA sequences of Oryza sativa and those of Arabidopsis thaliana. The results are compared with the results of application of NCBI's tblastx program (which compares the sequences in the BLAST manner after translation). It is shown that the present algorithm is very helpful in discovering nucleotide insertions/deletions originating from experimental errors as well as amino acid insertions/deletions due to evolutionary reasons. 相似文献
90.
Synthesis and physical and physiological properties of 4'-thioRNA: application to post-modification of RNA aptamer toward NF-kappaB
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report herein full details of the preparation of 4′-thiouridine, -cytidine, -adenosine and -guanosine phosphoramidites based on our synthetic protocol via the Pummerer reaction. Fully modified 4′-thioRNAs containing four kinds of 4′-thioribonucleoside units were prepared according to the standard RNA synthesis. The Tm values and thermodynamic parameters of a series of duplexes were determined by UV melting and differential scanning calorimetry (DSC) measurements. The resulting overall order of thermal stabilities for the duplexes was 4′-thioRNA:4′-thioRNA >> 4′-thioRNA:RNA > RNA:RNA > RNA:DNA > 4′-thioRNA:DNA. In addition, it was shown that the dominant factor in the stability of the duplexes consisting of 4′-thioRNA was enthalpic in character. The CD spectra of not only 4′-thioRNA:RNA and 4′-thioRNA:4′-thioRNA but also 4′-thioRNA:DNA were all similar to those of duplexes in the A-conformation. The stability of 4′-thioRNA in human serum was 600 times greater than that of natural RNA. Neither the RNA:RNA nor the 4′-thioRNA:4′-thioRNA duplexes were digested under the same conditions. The first example of a post-modification of an RNA aptamer by 4′-thioribonucleoside units was demonstrated. Full modification of the aptamer thioRNA3 resulted in complete loss of binding activity. In contrast, modifications at positions other than the binding site were tolerated without loss of binding activity. The post-modified RNA aptamer thioRNA5 was thermally stabilized and resistant toward nuclease digestion. The results presented in this paper will, it is hoped, contribute to the development of 4′-thioRNA as a new generation of artificial RNA. 相似文献