全文获取类型
收费全文 | 4697篇 |
免费 | 407篇 |
国内免费 | 7篇 |
专业分类
5111篇 |
出版年
2023年 | 35篇 |
2022年 | 82篇 |
2021年 | 127篇 |
2020年 | 84篇 |
2019年 | 109篇 |
2018年 | 103篇 |
2017年 | 95篇 |
2016年 | 134篇 |
2015年 | 212篇 |
2014年 | 229篇 |
2013年 | 289篇 |
2012年 | 354篇 |
2011年 | 349篇 |
2010年 | 209篇 |
2009年 | 175篇 |
2008年 | 257篇 |
2007年 | 223篇 |
2006年 | 206篇 |
2005年 | 204篇 |
2004年 | 161篇 |
2003年 | 149篇 |
2002年 | 131篇 |
2001年 | 59篇 |
2000年 | 47篇 |
1999年 | 66篇 |
1998年 | 45篇 |
1997年 | 30篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 39篇 |
1992年 | 24篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 25篇 |
1988年 | 28篇 |
1987年 | 31篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 41篇 |
1983年 | 30篇 |
1982年 | 38篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 33篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1974年 | 21篇 |
1973年 | 18篇 |
1972年 | 20篇 |
排序方式: 共有5111条查询结果,搜索用时 15 毫秒
1.
Background
Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation. 相似文献2.
3.
Reconstitution of RecBC DNase activity from purified Escherichia coli RecB and RecC proteins 总被引:8,自引:0,他引:8
I D Hickson C N Robson K E Atkinson L Hutton P T Emmerson 《The Journal of biological chemistry》1985,260(2):1224-1229
The Escherichia coli RecB protein, normally synthesized in low amounts, has been amplified by linkage of the recB gene to the phage lambda leftward promoter in an expression plasmid. From strains harboring this plasmid, RecB protein has been purified to homogeneity by a simple procedure which includes affinity chromatography on a column of RecC protein bound to agarose. The purified RecB protein has DNA-dependent ATPase activity but no exonuclease activity. RecC protein alone has neither ATPase nor exonuclease activity. However, when combined together, the RecB and RecC proteins show the ATP-dependent double-stranded exonuclease properties characteristic of the RecBC DNase. 相似文献
4.
5.
Fusarium graminearum A 3/5 possesses a high affinity system (Km = 32 +/- 8 microM; mean +/- SE) for uptake of choline, which was shown to be energy-dependent and constitutive. The maximum rate of choline uptake by this system was repressed by ammonia and glucose, showing a three-fold increase in maximum activity after nitrogen (2 h) or carbon (4 h) starvation. The system was highly specific for choline with only dimethylethanolamine (Ki = 198 +/- 29 microM), betaine aldehyde (Ki = 95 +/- 14 microM) and chlorocholine (Ki = 352 +/- 40 microM) acting as competitive inhibitors. Hemicholinium-3 acted as a mixed (non-competitive) inhibitor (KIES = 1.9 +/- 0.6 microM; KIE = 3.6 +/- 1.9 microM). 相似文献
6.
7.
8.
9.
Chiara Pavanello Alice Ossoli Arianna Strazzella Patrizia Risè Fabrizio Veglia Marie Lhomme Paolo Parini Laura Calabresi 《Journal of lipid research》2022,63(7):100232
Mutations in the LCAT gene cause familial LCAT deficiency (Online Mendelian Inheritance in Man ID: #245900), a very rare metabolic disorder. LCAT is the only enzyme able to esterify cholesterol in plasma, whereas sterol O-acyltransferases 1 and 2 are the enzymes esterifying cellular cholesterol in cells. Despite the complete lack of LCAT activity, patients with familial LCAT deficiency exhibit circulating cholesteryl esters (CEs) in apoB-containing lipoproteins. To analyze the origin of these CEs, we investigated 24 carriers of LCAT deficiency in this observational study. We found that CE plasma levels were significantly reduced and highly variable among carriers of two mutant LCAT alleles (22.5 [4.0–37.8] mg/dl) and slightly reduced in heterozygotes (218 [153–234] mg/dl). FA distribution in CE (CEFA) was evaluated in whole plasma and VLDL in a subgroup of the enrolled subjects. We found enrichment of C16:0, C18:0, and C18:1 species and a depletion in C18:2 and C20:4 species in the plasma of carriers of two mutant LCAT alleles. No changes were observed in heterozygotes. Furthermore, plasma triglyceride-FA distribution was remarkably similar between carriers of LCAT deficiency and controls. CEFA distribution in VLDL essentially recapitulated that of plasma, being mainly enriched in C16:0 and C18:1, while depleted in C18:2 and C20:4. Finally, after fat loading, chylomicrons of carriers of two mutant LCAT alleles showed CEs containing mainly saturated FAs. This study of CEFA composition in a large cohort of carriers of LCAT deficiency shows that in the absence of LCAT-derived CEs, CEs present in apoB-containing lipoproteins are derived from hepatic and intestinal sterol O-acyltransferase 2. 相似文献
10.
During lung development, Fibroblast growth factor 10 (Fgf10), which is expressed in the distal mesenchyme and regulated by Wnt signaling, acts on the distal epithelial progenitors to maintain them and prevent them from differentiating into proximal (airway) epithelial cells. Fgf10-expressing cells in the distal mesenchyme are progenitors for parabronchial smooth muscle cells (PSMCs). After naphthalene, ozone or bleomycin-induced airway epithelial injury, surviving epithelial cells secrete Wnt7b which then activates the PSMC niche to induce Fgf10 expression. This Fgf10 secreted by the niche then acts on a subset of Clara stem cells to break quiescence, induce proliferation and initiate epithelial repair. Here we show that conditional deletion of the Wnt target gene c-Myc from the lung mesenchyme during development does not affect proper epithelial or mesenchymal differentiation. However, in the adult lung we show that after naphthalene-mediated airway epithelial injury c-Myc is important for the activation of the PSMC niche and as such induces proliferation and Fgf10 expression in PSMCs. Our data indicate that conditional deletion of c-Myc from PSMCs inhibits airway epithelial repair, whereas c-Myc ablation from Clara cells has no effect on airway epithelial regeneration. These findings may have important implications for understanding the misregulation of lung repair in asthma and COPD. 相似文献