全文获取类型
收费全文 | 29724篇 |
免费 | 2168篇 |
国内免费 | 1690篇 |
专业分类
33582篇 |
出版年
2024年 | 66篇 |
2023年 | 355篇 |
2022年 | 865篇 |
2021年 | 1454篇 |
2020年 | 975篇 |
2019年 | 1229篇 |
2018年 | 1194篇 |
2017年 | 854篇 |
2016年 | 1247篇 |
2015年 | 1941篇 |
2014年 | 2169篇 |
2013年 | 2324篇 |
2012年 | 2670篇 |
2011年 | 2345篇 |
2010年 | 1493篇 |
2009年 | 1257篇 |
2008年 | 1542篇 |
2007年 | 1354篇 |
2006年 | 1186篇 |
2005年 | 997篇 |
2004年 | 812篇 |
2003年 | 702篇 |
2002年 | 543篇 |
2001年 | 481篇 |
2000年 | 379篇 |
1999年 | 421篇 |
1998年 | 248篇 |
1997年 | 271篇 |
1996年 | 258篇 |
1995年 | 223篇 |
1994年 | 220篇 |
1993年 | 154篇 |
1992年 | 217篇 |
1991年 | 187篇 |
1990年 | 130篇 |
1989年 | 106篇 |
1988年 | 80篇 |
1987年 | 109篇 |
1986年 | 82篇 |
1985年 | 69篇 |
1984年 | 52篇 |
1983年 | 36篇 |
1982年 | 36篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1975年 | 21篇 |
1974年 | 18篇 |
1972年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In this paper, a highly conservedpiggyBac-like sequence, designated as McrPLE was cloned from a lepidopteran insect, Macdunnoughia crassisigna. It is 2 472 bp long in full length with a single open reading frame and encodes a 595 amino acid transposase. It shares identical terminal and sub-terminal repeats with T. ni IFP2 and is flanked by the typical TTAA target-site duplications. Alignment and phylogenetic analysis revealed that McrPLE had greater than 99.5% identity and appeared to be the closest one in phylogeny to IFP2 among the PLEs so far found in various species. Plasmid-based excision and transposition assay proved it was mobile in cell culture. Otherwise, McrPLE element and all other highly conserved IFP2 sequences reported previously were found to share three common nucleotide substitutions. This suggests that the original IFP2 may be a related variant of a predecessor element that became widespread. The existence of nearly identical piggyBac sequence in reproductively isolated species was thought also a strong indication of horizontal transmission, which raises important considerations for the stability and practical use ofpiggyBac transformation vectors. 相似文献
992.
Na Zhang Xing Huang Yaning Bao Bo Wang Hongxia Zeng Weishun Cheng Mi Tang Yuhua Li Jian Ren Yuhong Sun 《Physiology and Molecular Biology of Plants》2017,23(3):619-628
The early auxin responsive SAUR family is an important gene family in auxin signal transduction. We here present the first report of a genome-wide identification of SAUR genes in watermelon genome. We successfully identified 65 ClaSAURs and provide a genomic framework for future study on these genes. Phylogenetic result revealed a Cucurbitaceae-specific SAUR subfamily and contribute to understanding of the evolutionary pattern of SAUR genes in plants. Quantitative RT-PCR analysis demonstrates the existed expression of 11 randomly selected SAUR genes in watermelon tissues. ClaSAUR36 was highly expressed in fruit, for which further study might bring a new prospective for watermelon fruit development. Moreover, correlation analysis revealed the similar expression profiles of SAUR genes between watermelon and Arabidopsis during shoot organogenesis. This work gives us a new support for the conserved auxin machinery in plants. 相似文献
993.
Sunho Lee Changhoon Kim Jihyae Ann Shivaji A. Thorat Eunhye Kim Jongmi Park Sun Choi Peter M. Blumberg Robert Frank-Foltyn Gregor Bahrenberg Hannelore Stockhausen Thomas Christoph Jeewoo Lee 《Bioorganic & medicinal chemistry letters》2017,27(18):4383-4388
A series of 1-substituted 3-(t-butyl/trifluoromethyl)pyrazole C-region analogues of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamides were investigated for hTRPV1 antagonism. The structure activity relationship indicated that the 3-chlorophenyl group at the 1-position of pyrazole was the optimized hydrophobic group for antagonistic potency and the activity was stereospecific to the S-configuration, providing exceptionally potent antagonists 13S and 16S with Ki(CAP) = 0.1 nM. Particularly significant, 13S exhibited antagonism selective for capsaicin and NADA and not for low pH or elevated temperature. Both compounds also proved to be very potent antagonists for rTRPV1, blocking in vivo the hypothermic action of capsaicin, consistent with their in vitro mechanism. The docking study of compounds 13S and 16S in our hTRPV1 homology model indicated that the binding modes differed somewhat, with that of 13S more closely resembling that of GRT12360. 相似文献
994.
4个Y-STR基因座银染复合扩增 总被引:8,自引:2,他引:8
建立一个复合扩增体系,同时扩增DYS391、GATA-A4、GATA-A10和GATA-H4 4个Y染色体特异性的STR基因座,并用聚丙烯酰胺凝胶电泳和银染显色技术进行基因分型。采用该复合扩增系统调查广东汉族311名无关男性个体的单倍型频率,这4个基因座分别检出5、7、6和5个等位基因,其基因多样性分别为0.4623、0.6972、0.7173、0.6015。共检出98种单倍型,单倍型基因多样性为0.9755。该复合扩增体系在建立Y染色体STR数据库,研究群体遗传和进行法医学鉴定有重要意义。
Abstract:A multiplex PCR system has been developed to amplify 4 Y-chromosome specific short tandem repeats(STR),DYS391,GATA-A4,GATA-A10 and GATA-H4,simultaneously.PCR products were separated by polyacrylamide gels electrophoresis followed by silver stain.When 311 unrelated males from the Han population in Guangdong were detected by the multiplex system,DYS391,GATA-A4,GATA-A10 and GATA-H4 showed 5,7,6 and 5 alleles respectively.Total 98 haplotypes could be identified.Gene diversity value for the 4 STR was 0.4623,0.6972,0.7173 and 0.6015 respectively.The gene diversity value for the haplotypes of the 4 Y-STR reached 0.9755.The four Y-STR multiplex system will be very powerful for establishing Y-STR database,exploring human origin,paternity testing and personal identification. 相似文献
995.
Cholesterol represents one of the key constituents of small, dynamic, sterol- and sphingolipid-enriched domains on the plasma
membrane. It has been reported that many viruses depend on plasma membrane cholesterol for efficient infection. In this study,
the role of the plasma membrane cholesterol in porcine reproductive and respiratory syndrome virus (PRRSV) infection of MARC-145
cells was investigated. Pretreatment of MARC-145 cells with methyl-β-cyclodextrin (MβCD), a drug used to deplete cholesterol
from cellular membrane, significantly reduced PRRSV infection in a dose-dependent manner. This inhibition was partially reversed
by supplementing exogenous cholesterol following MβCD treatment, suggesting that the inhibition of PRRSV infection was specifically
mediated by removal of cellular cholesterol. Further detailed studies showed that depletion of cellular membrane cholesterol
significantly inhibited virus entry, especially virus attachment and release. These results indicate that the presence of
cholesterol in the cellular membrane is a key component of PRRSV infection. 相似文献
996.
997.
A M Sun G M Healy I Vacek H G Macmorine 《Biochemical and biophysical research communications》1977,79(1):185-189
Monolayer cultures have been derived from bovine embryonic pancreatic cells grown in medium CMRL-1969 supplemented with foetal calf serum. The isolate has been subcultivated up to 10 population doublings. Insulin secretion from the cells into the culture medium declined with increasing passages. Of several insulin secretagogues, glucagon was found to be effective in potentiating insulin release from the cultivated cells into the medium. Insulin secretion rose to approximately 600 μU/culture/day in the presence of glucagon as compared to an average of 10 μU/culture/day in the control. This may be the first demonstration of a beta cell line developed from bovine embryonic pancreas. 相似文献
998.
Costimulatory molecule-targeted antibody therapy of a spontaneous autoimmune disease 总被引:19,自引:0,他引:19
Humans and mice deficient in Fas, a tumor necrosis factor (TNF)-receptor family member, cannot induce apoptosis of autoreactive cells, and consequently develop progressive lymphoproliferative disorders and lupus-like autoimmune diseases. Previous studies have shown that short-term administrations of agonistic monoclonal antibodies against CD137, another TNF-receptor family member, activate T cells and induce rejection of allografts and established tumors. Here we report that treatment with an agonistic monoclonal antibody to CD137 (2A) blocks lymphadenopathy and spontaneous autoimmune diseases in Fas-deficient MRL/lpr mice, ultimately leading to their prolonged survival. Notably, 2A treatment rapidly augments IFN-gamma production, and induces the depletion of autoreactive B cells and abnormal double-negative T cells, possibly by increasing their apoptosis through Fas- and TNF receptor-independent mechanisms. This study demonstrates that agonistic monoclonal antibodies specific for costimulatory molecules can be used as novel therapeutic agents to delete autoreactive lymphocytes and block autoimmune disease progression. 相似文献
999.
Yan H Sun X Sun S Wang S Zhang J Wang R An P Yang F Kang W 《International journal of biological macromolecules》2011,48(5):720-725
HPLC analysis proved that Coptis chinensis glycan contained Ara, Man, and Gal. The monosaccharide constituents of Phellodendron amurense glycan were determined by HPLC analysis. HPLC analysis proved that P. amurense glycan contained Ara, Xyl, Glu, and Gal. FT-IR spectrum of C. chinensis glycan and P. amurense glycan showed the characteristic absorption peaks of carbohydrate polymers. Exposure of the human skin to ultraviolet radiation (UVR) leads to depletion of cutaneous antioxidants, regulation of gene expression and ultimately to the development of skin diseases. In the present study, free radical scavenging activity of C. chinensis and P. amurense glycan were evaluated. The photoprotective effect of C. chinensis and P. amurense glycan against UV-induced oxidative damage was also investigated in skin. At the concentration range employed, the two glycans showed strong free radical scavenging activity. Ultraviolet radiation reduced skin antioxidant enzyme and immunity activities in animals. Administration of C. chinensis and P. amurense glycans dose-dependently significantly increased skin antioxidant enzyme and immunity activities in animals. In conclusion, C. chinensis and P. amurense glycans present photoprotective properties, which can be attributed to molecules, such as flavonoids and carotenoids, which act as UV-absorbing molecules and as antioxidants, as well as stimulate immunity activities in animals. 相似文献
1000.
The most economically important group of species in the genus Amaranthus is the A. hybridus species complex, including three cultivated grain amaranths, A. cruentus, A. caudatus, and A. hypochondriacus, and their putative wild progenitors, A. hybridus, A. quitensis, and A. powellii. Taxonomic confusion exists among these closely related taxa. Internal transcribed spacer (ITS) of nuclear ribosomal DNA, amplified fragment length polymorphism (AFLP), and double-primer fluorescent intersimple sequence repeat (ISSR) were employed to reexamine the taxonomic status and phylogenetic relationships of grain amaranths and their wild relatives. Low ITS divergence in these taxa resulted in poorly resolved phylogeny. However, extensive polymorphisms exist at AFLP and ISSR loci both within and among species. In phylogenetic trees based on either AFLP or ISSR or the combined data sets, nearly all intraspecific accessions can be placed in their corresponding species clades, indicating that these taxa are well-separated species. The AFLP trees share many features in common with the ISSR trees, both showing a close relationship between A. caudatus and A. quitensis, placing A. hybridus in the same clade as all grain amaranths, and indicating that A. powellii is the most divergent taxon in the A. hybridus species complex. This study has demonstrated that both AFLP and double-primer fluorescent ISSR have a great potential for generating a large number of informative characters for phylogenetic analysis of closely related species, especially when ITS diversity is insufficient. 相似文献