全文获取类型
收费全文 | 18918篇 |
免费 | 1053篇 |
国内免费 | 975篇 |
出版年
2023年 | 245篇 |
2022年 | 388篇 |
2021年 | 507篇 |
2020年 | 504篇 |
2019年 | 735篇 |
2018年 | 650篇 |
2017年 | 409篇 |
2016年 | 427篇 |
2015年 | 571篇 |
2014年 | 1090篇 |
2013年 | 1364篇 |
2012年 | 824篇 |
2011年 | 1164篇 |
2010年 | 835篇 |
2009年 | 851篇 |
2008年 | 938篇 |
2007年 | 938篇 |
2006年 | 831篇 |
2005年 | 790篇 |
2004年 | 739篇 |
2003年 | 659篇 |
2002年 | 562篇 |
2001年 | 380篇 |
2000年 | 371篇 |
1999年 | 340篇 |
1998年 | 312篇 |
1997年 | 259篇 |
1996年 | 280篇 |
1995年 | 252篇 |
1994年 | 288篇 |
1993年 | 222篇 |
1992年 | 226篇 |
1991年 | 209篇 |
1990年 | 139篇 |
1989年 | 141篇 |
1988年 | 119篇 |
1987年 | 110篇 |
1986年 | 100篇 |
1985年 | 165篇 |
1984年 | 155篇 |
1983年 | 93篇 |
1982年 | 127篇 |
1981年 | 127篇 |
1980年 | 109篇 |
1979年 | 88篇 |
1978年 | 76篇 |
1977年 | 54篇 |
1976年 | 60篇 |
1975年 | 31篇 |
1974年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The inhibition of hepatic glycogen-associated protein phosphatase-1 (PP1-G(L)) by glycogen phosphorylase a prevents the dephosphorylation and activation of glycogen synthase, suppressing glycogen synthesis when glycogenolysis is activated. Here, we show that a peptide ((280)LGPYY(284)) comprising the last five amino acids of G(L) retains high-affinity interaction with phosphorylase a and that the two tyrosines play crucial roles. Tyr284 deletion abolishes binding of phosphorylase a to G(L) and replacement by phenylalanine is insufficient to restore high-affinity binding. We show that a phosphorylase inhibitor blocks the interaction of phosphorylase a with the G(L) C-terminus, suggesting that the latter interaction could be targeted to develop an anti-diabetic drug. 相似文献
992.
993.
Lytic transglycosylases cleave the beta-(1-->4)-glycosidic bond in the bacterial cell wall heteropolymer peptidoglycan between the N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) residues with the concomitant formation of a 1,6-anhydromuramoyl residue. Based on sequence alignments, Ser216 in Pseudomonas aeruginosa membrane-bound lytic transglycosylase B (MltB) was targeted for replacement with alanine to delineate its role in the enzyme's mechanism of action. The specific activity of the Ser216-->Ala MltB derivative was less than 12% of that for the wild-type enzyme, while its substrate binding affinity remained virtually unaltered. These data are in agreement with a role of Ser216 in orienting the N-acetyl group on MurNAc at the -1 subsite of MltB for its participation in a substrate-assisted mechanism of action. 相似文献
994.
Effect of exogenous H(2)O(2) and catalase was tested in liquid cultures of the deoxynivalenol and 15-acetyldeoxynivalenol-producing fungus Fusarium graminearum. Accordingly to previous results, H(2)O(2) supplementation of the culture medium leads to increased toxin production. This study indicates that this event seems to be linked to a general up regulation of genes involved in the deoxynivalenol and 15-acetyldeoxynivalenol biosynthesis pathway, commonly named Tri genes. In catalase-treated cultures, toxin accumulation is reduced, and Tri genes expression is significantly down regulated. Furthermore, kinetics of expression of several Tri genes is proposed in relation to toxin accumulation. Biological meanings of these findings are discussed. 相似文献
995.
996.
Anemia is a symptom in patients with Pearson syndrome caused by the accumulation of mutated mitochondrial DNA (mtDNA). Such mutated mtDNAs have been detected in patients with anemia. This suggested that respiration defects due to mutated mtDNA are responsible for the anemia. However, there has been no convincing experimental evidence to confirm the pathophysiological relation between respiration defects in hematopoietic cells and expression of anemia. We address this issue by transplanting bone marrow cells carrying pathogenic mtDNA with a large-scale deletion (ΔmtDNA) into normal mice. The bone marrow-transplanted mice carried high proportion of ΔmtDNA only in hematopoietic cells, and resultant the mice suffered from macrocytic anemia. They show abnormalities of erythroid differentiation and weak erythropoietic response to a stressful condition. These observations suggest that hematopoietic cell-specific respiration defects caused by mtDNAs with pathogenic mutations are responsible for anemia by inducing abnormalities in erythropoiesis. 相似文献
997.
The inhibitory effects of hypertonic conditions on immune responses have been described in clinical studies; however, the molecular mechanism underlying this phenomenon has yet to be defined. Here we investigate osmotic stress-mediated modification of the NF-kappaB pathway, a central signaling pathway in inflammation. We unexpectedly found that osmotic stress could activate IkappaBalpha kinase but did not activate NF-kappaB. Osmotic stress-induced phosphorylated IkappaBalpha was not ubiquitinated, and osmotic stress inhibited interleukin 1-induced ubiquitination of IkappaBalpha and ultimately blocked expression of cytokine/chemokines. Thus, blockage of IkappaBalpha ubiquitination is likely to be a major mechanism for inhibition of inflammation by hypertonic conditions. 相似文献
998.
999.
W. BOOTH S. M. BOGDANOWICZ P. A. PROD
HL R. G. HARRISON C. SCHAL E. L. VARGO 《Molecular ecology resources》2007,7(4):648-650
Primer sequences and initial characterization are presented for 10 microsatellite loci isolated from the German cockroach, Blattella germanica. In a sample of 30 individuals from a single population sample, all loci were polymorphic with two to 12 alleles segregating per locus and levels of observed heterozygosity ranging from 0.27 to 0.92. One locus showed a deficit of heterozygotes. Experimental conditions are described for polymerase chain reaction multiplexing, which enables the genotyping of eight loci in three electrophoretic runs consisting of one set of three and two sets of two markers. Seven primer sets cross‐amplify in the related Blattella asahinai. 相似文献
1000.
Wang Juan Ni Hong Chen Li Chen Chengbin Song Wenqin 《Frontiers of Biology in China》2007,2(3):272-275
Cancer-related genes harbored in the loss regions containing a high frequency of hepatocellular carcinoma (HCC) were selected.
Related information was gathered and the coding single nucleotide polymorphism (cSNP) sequences were obtained from the single
nucleotide polymorphism (SNP) database. The appropriate primers and oligonucleotide probes were then designed in accordance
with the SNP sites, and subsequently, the gene chips for detecting SNPs were constructed. Genomic DNA was extracted from blood
samples of healthy controls and from patients with HBV infection. The sequences, including the SNPs, were amplified via polymerase
chain reaction (PCR) and labeled using digoxigenin deoxyuridine tri-phosphate (Dig-dUTP). The labeled products were then hybridized
with the SNP chips. Results confirmed that the differences in allele frequencies of three SNPs EGFL3 (rs947345), Caspase9
(rs2308950), and E2F2 (rs3218171) were distinct between HBV-infected patients and controls, suggesting that these SNPs ocuring
in high frequency in HBV-infected individuals may be associated with susceptibility to HCC.
Translated from Acta Scientiarum Naturalium Universitatis Nankaiensis, 2006, 39(3): 1–5 [译自: 南开大学学报(自然科学版)] 相似文献