全文获取类型
收费全文 | 1455篇 |
免费 | 91篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 27篇 |
2020年 | 12篇 |
2019年 | 25篇 |
2018年 | 37篇 |
2017年 | 27篇 |
2016年 | 31篇 |
2015年 | 60篇 |
2014年 | 81篇 |
2013年 | 71篇 |
2012年 | 122篇 |
2011年 | 118篇 |
2010年 | 59篇 |
2009年 | 57篇 |
2008年 | 129篇 |
2007年 | 101篇 |
2006年 | 96篇 |
2005年 | 90篇 |
2004年 | 80篇 |
2003年 | 97篇 |
2002年 | 79篇 |
2001年 | 13篇 |
2000年 | 19篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1546条查询结果,搜索用时 15 毫秒
1.
Summary A cloned gene with an insertion, which was made by introducing cat, was ligated to the cloning site of the phage gt11. P1 phage grown on cells lysogenized with the recombinant phage could transduce the mutant gene into the original site on the Escherichia coli chromosome. 相似文献
2.
Distribution of Glycinebetaine in Old and Young Leaf Blades of Salt-Stressed Barley Plants 总被引:4,自引:0,他引:4
Nakamura Toshihide; Ishitani Manabu; Harinasut Poontariga; Nomura Mika; Takabe Teruhiro; Takabe Tetsuko 《Plant & cell physiology》1996,37(6):873-877
In barley plants exposed to stepwise salt-stress (up to 200mM NaCl), sodium and chloride ions accumulated preferentiallyin old rather than in young leaf blades. Furthermore, the levelof glycinebetaine in young leaf blades was approximately threetimes that in old leaf blades.
3Present address: Department of Biochemistry, Faculty of Science,Kasesart University, Bangkok, 10900 Thailand 相似文献
3.
The catalytic activity of the CD45 membrane-proximal phosphatase domain is required for TCR signaling and regulation. 总被引:10,自引:2,他引:8
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cell surface expression of CD45, a receptor-like protein tyrosine phosphatase (PTPase), is required for T cell antigen receptor (TCR)-mediated signal transduction. Like the majority of transmembrane PTPases, CD45 contains two cytoplasmic phosphatase domains, whose relative in vivo function is not known. Site-directed mutagenesis of the individual catalytic residues of the two CD45 phosphatase domains indicates that the catalytic activity of the membrane-proximal domain is both necessary and sufficient for restoration of TCR signal transduction in a CD45-deficient cell. The putative catalytic activity of the distal phosphatase domain is not required for proximal TCR-mediated signaling events. Moreover, in the context of a chimeric PTPase receptor, the putative catalytic activity of the distal phosphatase domain is not required for ligand-induced negative regulation of PTPase function. We also demonstrate that the phosphorylation of the C-terminal tyrosine of Lck, a site of negative regulation, is reduced only when CD45 mutants with demonstrable in vitro phosphatase activity are introduced into the CD45-deficient cells. These results demonstrate that the phosphatase activity of CD45 is critical for TCR signaling, and for regulating the levels of C-terminal phosphorylated Lck molecules. 相似文献
4.
Yrjö Helariutta Paula Elomaa Mika Kotilainen Pauli Seppänen Teemu H. Teeri 《Plant molecular biology》1993,22(2):183-193
We are approaching corolla differentiation in Compositae by studying the regulation of flavonoid pathway genes during inflorescence development in gerbera. We have cloned a dfr cDNA from a ray floret corolla cDNA library of Gerbera hybrida var. Regina by a PCR technique based on homologies found in genes isolated from other plant species. The functionality of the clone was tested in vivo by complementing the dihydrokaempferol accumulating petunia mutant line RL01. By Southern blot analysis, G. hybrida var. Regina was shown to harbour a small family of dfr genes, one member of which was deduced to be mainly responsible for the DFR activity in corolla. Dfr expression in corolla correlates with the anthocyanin accumulation pattern: it is basipetally induced, epidermally specific and restricted to the ligular part of corolla. By comparing the dfr expression in different floret types during inflorescence development, we could see that dfr expression reflects developmental schemes of the outermost ray and trans florets, contrasted with that of the disc florets. 相似文献
5.
Jennifer D. Watts Mary Farina John S. Kimball Luke D. Schiferl Zhihua Liu Kyle A. Arndt Donatella Zona Ashley Ballantyne Eugénie S. Euskirchen Frans-Jan W. Parmentier Manuel Helbig Oliver Sonnentag Torbern Tagesson Janne Rinne Hiroki Ikawa Masahito Ueyama Hideki Kobayashi Torsten Sachs Daniel F. Nadeau John Kochendorfer Marcin Jackowicz-Korczynski Anna Virkkala Mika Aurela Roisin Commane Brendan Byrne Leah Birch Matthew S. Johnson Nima Madani Brendan Rogers Jinyang Du Arthur Endsley Kathleen Savage Ben Poulter Zhen Zhang Lori M. Bruhwiler Charles E. Miller Scott Goetz Walter C. Oechel 《Global Change Biology》2023,29(7):1870-1889
Arctic-boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic-boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (Reco), net ecosystem CO2 exchange (NEE; Reco − GPP), and terrestrial methane (CH4) emissions for the Arctic-boreal zone using a satellite data-driven process-model for northern ecosystems (TCFM-Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM-Arctic to obtain daily 1-km2 flux estimates and annual carbon budgets for the pan-Arctic-boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO2-C year−1. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH4 emissions from tundra and boreal wetlands (not accounting for aquatic CH4) were estimated at 35 Tg CH4-C year−1. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high-latitude carbon status and also indicates a continued need for integrated site-to-regional assessments to monitor the vulnerability of these ecosystems to climate change. 相似文献
6.
The effects of several experimental parameters on the performance characteristics of a competitive-type immunochromatographic assay of milk progesterone were studied. Increasing the size of the colloidal gold particles used as a label increased both maximal signal obtained and sensitivity of the assay measured as slope of the progesterone standard curve. The concentration of the antibody used to prepare the detection zone was found to be a critical factor, in that low concentrations of antibody resulted in a poor sensitivity. The compatibilities of various buffer systems with the assay were studied. The assay worked well with buffers having a broad pH range of 4·5–8·5. 相似文献
7.
Toshinobu Tokumoto Masakane Yamashita Mika Tokumoto Yoshinao Katsu Ryo Horiguchi Hiroko Kajiura Yoshitaka Nagahama 《The Journal of cell biology》1997,138(6):1313-1322
Immediately before the transition from metaphase to anaphase, the protein kinase activity of maturation or M-phase promoting factor (MPF) is inactivated by a mechanism that involves the degradation of its regulatory subunit, cyclin B. The availability of biologically active goldfish cyclin B produced in Escherichia coli and purified goldfish proteasomes (a nonlysosomal large protease) has allowed the role of proteasomes in the regulation of cyclin degradation to be examined for the first time. The 26S, but not the 20S proteasome, digested recombinant 49-kD cyclin B at lysine 57 (K57), producing a 42-kD truncated form. The 42-kD cyclin was also produced by the digestion of native cyclin B forming a complex with cdc2, a catalytic subunit of MPF, and a fragment transiently appeared during cyclin degradation when eggs were released from metaphase II arrest by egg activation. Mutant cyclin at K57 was resistant to both digestion by the 26S proteasome and degradation at metaphase/anaphase transition in Xenopus egg extracts. The results of this study indicate that the destruction of cyclin B is initiated by the ATP-dependent and ubiquitin-independent proteolytic activity of 26S proteasome through the first cutting in the NH2 terminus of cyclin (at K57 in the case of goldfish cyclin B). We also surmise that this cut allows the cyclin to be ubiquitinated for further destruction by ubiquitin-dependent activity of the 26S proteasome that leads to MPF inactivation. 相似文献
8.
20 water-soluble antigen have been identified with the help of rabbit antisera to extracts of the early gastrula ectoderm and neural plate in Rana temporaria. All of them were also found in the early blastula embryos and unfertilized eggs. The identified antigens are characterized by a definite embryospecificity. As the development proceeds, the concentration of these antigens in the embryonic tissues decreases until the complete disappearance of corresponding immunoelectrophoretic reactions. By this characteristic all antigens under study are subdivided into four groups: I--five antigens identified at the early developmental stages only (until hatching, stage 29); II--nine antigens present up to stages 33--35; III--three antigens followed up to stages 39--40 (well formed tadpole); IV--three antigens were found at all developmental stages under study up to stages 45--47. 11 out of 20 identified antigens have antigenic similarity with the proteins of blood serum of adult amphibians. Besides, the early gastrula ectoderm contains antigens similar with those of the brain of adult amphibians. 相似文献
9.
Malene Nygaard Alexander Kopatz James M. D. Speed Michael D. Martin Tommy Prest Oddmund Kleven Mika Bendiksby 《Ecology and evolution》2022,12(8)
The species we have studied the spatiotemporal genetic change in the northern dragonhead, a plant species that has experienced a drastic population decline and habitat loss in Europe. We have added a temporal perspective to the monitoring of northern dragonhead in Norway by genotyping herbarium specimens up to 200 years old. We have also assessed whether northern dragonhead has achieved its potential distribution in Norway. To obtain the genotype data from 130 herbarium specimens collected from 1820 to 2008, mainly from Norway (83) but also beyond (47), we applied a microfluidic array consisting of 96 SNP markers. To assess temporal genetic change, we compared our new genotype data with existing data from modern samples. We used sample metadata and observational records to model the species'' environmental niche and potential distribution in Norway. Our results show that the SNP array successfully genotyped all included herbarium specimens. Hence, with the appropriate design procedures, the SNP array technology appears highly promising for genotyping old herbarium specimens. The captured genetic diversity correlates negatively with distance from Norway. The historical‐modern comparisons reveal similar genetic structure and diversity across space and limited genetic change through time in Norway, providing no signs of any regional bottleneck (i.e., spatiotemporal stasis). The regional areas in Norway have remained genetically divergent, however, both from each other and more so from populations outside of Norway, rendering continued protection of the species in Norway relevant. The ENM results suggest that northern dragonhead has not fully achieved its potential distribution in Norway and corroborate that the species is anchored in warmer and drier habitats. 相似文献
10.
Mahabub Alam Hiroki Shima Yoshitaka Matsuo Nguyen Chi Long Mitsuyo Matsumoto Yusho Ishii Nichika Sato Takato Sugiyama Risa Nobuta Satoshi Hashimoto Liang Liu Mika K. Kaneko Yukinari Kato Toshifumi Inada Kazuhiko Igarashi 《The Journal of biological chemistry》2022,298(7)
Methionine adenosyltransferase (MAT) catalyzes the synthesis of S-adenosylmethionine (SAM). As the sole methyl-donor for methylation of DNA, RNA, and proteins, SAM levels affect gene expression by changing methylation patterns. Expression of MAT2A, the catalytic subunit of isozyme MAT2, is positively correlated with proliferation of cancer cells; however, how MAT2A promotes cell proliferation is largely unknown. Given that the protein synthesis is induced in proliferating cells and that RNA and protein components of translation machinery are methylated, we tested here whether MAT2 and SAM are coupled with protein synthesis. By measuring ongoing protein translation via puromycin labeling, we revealed that MAT2A depletion or chemical inhibition reduced protein synthesis in HeLa and Hepa1 cells. Furthermore, overexpression of MAT2A enhanced protein synthesis, indicating that SAM is limiting under normal culture conditions. In addition, MAT2 inhibition did not accompany reduction in mechanistic target of rapamycin complex 1 activity but nevertheless reduced polysome formation. Polysome-bound RNA sequencing revealed that MAT2 inhibition decreased translation efficiency of some fraction of mRNAs. MAT2A was also found to interact with the proteins involved in rRNA processing and ribosome biogenesis; depletion or inhibition of MAT2 reduced 18S rRNA processing. Finally, quantitative mass spectrometry revealed that some translation factors were dynamically methylated in response to the activity of MAT2A. These observations suggest that cells possess an mTOR-independent regulatory mechanism that tunes translation in response to the levels of SAM. Such a system may acclimate cells for survival when SAM synthesis is reduced, whereas it may support proliferation when SAM is sufficient. 相似文献