全文获取类型
收费全文 | 13828篇 |
免费 | 573篇 |
国内免费 | 432篇 |
出版年
2023年 | 106篇 |
2022年 | 167篇 |
2021年 | 167篇 |
2020年 | 195篇 |
2019年 | 299篇 |
2018年 | 320篇 |
2017年 | 220篇 |
2016年 | 263篇 |
2015年 | 314篇 |
2014年 | 678篇 |
2013年 | 1000篇 |
2012年 | 455篇 |
2011年 | 645篇 |
2010年 | 517篇 |
2009年 | 697篇 |
2008年 | 725篇 |
2007年 | 769篇 |
2006年 | 659篇 |
2005年 | 694篇 |
2004年 | 574篇 |
2003年 | 534篇 |
2002年 | 479篇 |
2001年 | 325篇 |
2000年 | 276篇 |
1999年 | 308篇 |
1998年 | 297篇 |
1997年 | 243篇 |
1996年 | 205篇 |
1995年 | 228篇 |
1994年 | 220篇 |
1993年 | 200篇 |
1992年 | 170篇 |
1991年 | 138篇 |
1990年 | 123篇 |
1989年 | 112篇 |
1988年 | 125篇 |
1987年 | 120篇 |
1986年 | 85篇 |
1985年 | 125篇 |
1984年 | 182篇 |
1983年 | 130篇 |
1982年 | 147篇 |
1981年 | 115篇 |
1980年 | 110篇 |
1979年 | 98篇 |
1978年 | 50篇 |
1977年 | 55篇 |
1976年 | 44篇 |
1975年 | 34篇 |
1974年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
11.
Larval hemolymph tyrosinase activity in Drosophila melanogaster was detected with high performance liquid chromatography with electrochemical detection. The enzyme hydroxylated L-tyrosine, and oxidized the diphenol substrates L-dopa and dopamine. In larvae of a selected immune-reactive strain the rates of tyrosine hydroxylation, dopa oxidation, and dopamine oxidation were markedly increased during the early stages of melanotic encapsulation of the eggs of the parasitic wasp Leptopilina boulardi. Tyrosinase activity was not modified in parasitized larvae of a selected susceptible strain of D. melanogaster, in which hosts the parasitoids developed unmolested. During the same period of parasitization, the amount of free tyrosine in immune reactive larvae was approximately three times higher than in susceptible hosts. These data indicate that the tyrosinase system of the immune reactive strain is activated during parasitization, and this results in the synthesis of some precursors which ultimately produce a melanotic and sclerotic capsule around the eggs of the parasite. Based on known genetic information of the enzyme system in Drosophila, it appears that at least two genes may be involved in the activation process, one associated with the proenzyme for monophenol oxidase activity, and the second with the proenzyme for diphenol oxidase activity. 相似文献
12.
Reviewed are works concerning the mechanisms of collagen (type I) fibril packing and the influence of macromolecular structure and physicochemical parameters of the medium on the process. 相似文献
13.
Using benzo(a)pyrene (BaP) as a probe for aryl hydrocarbon hydroxylase (AHH) activity, differences in mixed-function oxidase (MFO) activity were observed using microspectrofluorimetry in single living cells during long term treatment with 3-methylcholanthrene (3-MC) or carbaryl. Although these two compounds differ in chemical structure, similar effects were observed in 3T3 cell populations. The results suggest that the two compounds activate the same enzymatic system and that individual cells of a supposed homogeneous cell population are not equally sensitive to xenobiotics, i.e. subpopulations were observed which have differences in AHH activity. 相似文献
14.
《Cell reports》2020,30(3):630-641.e5
- Download : Download high-res image (118KB)
- Download : Download full-size image
15.
16.
17.
《Peptides》2016
Metformin, α-glucosidase inhibitors (α-GIs), and dipeptidyl peptidase 4 inhibitors (DPP-4Is) reduce hyperglycemia without excessive insulin secretion, and enhance postprandial plasma concentration of glucagon-like peptide-1 (GLP-1) in type-2 diabetes mellitus (T2DM) patients. We assessed add-on therapeutic effects of DPP-4I anagliptin in Japanese T2DM patients treated with metformin, an α-GI miglitol, or both drugs on postprandial responses of GLP-1 and glucose-dependent insulinotropic polypeptide (GIP), and on plasma concentration of the appetite-suppressing hormone leptin. Forty-two Japanese T2DM patients with inadequately controlled disease (HbA1c: 6.5%–8.0%) treated with metformin (n = 14), miglitol (n = 14) or a combination of the two drugs (n = 14) received additional treatment with anagliptin (100 mg, p.o., b.i.d.) for 52 weeks. We assessed glycemic control, postprandial responses of GLP-1 and glucose-dependent insulinotropic polypeptide (GIP), and on plasma concentration of leptin in those patients. Add-on therapy with anagliptin for 52 weeks improved glycemic control and increased the area under the curve of biologically active GLP-1 concentration without altering obesity indicators. Total GIP concentration at 52 weeks was reduced by add-on therapy in groups treated with miglitol compared with those treated with metformin. Add-on therapy reduced leptin concentrations. Add-on therapy with anagliptin in Japanese T2DM patients treated with metformin and miglitol for 52 weeks improved glycemic control and enhanced postprandial concentrations of active GLP-1/total GIP, and reduce the leptin concentration. 相似文献
18.
Peter J. Meloncelli 《Carbohydrate research》2010,345(16):2305-2322
The ABO histo-blood group system is one of the most clinically important antigen families. As part of our overall goal to prepare the entire set of the A, B and H type I-VI antigens for a range of biochemical investigations, we report herein the synthesis of the type I and II antigens with a 7-octen-1-yl aglycone. This linker was chosen to facilitate not only the future conjugation of the antigens to a protein or solid support but also the synthesis of the H type I and II octyl glycosides for enzyme kinetic studies. 相似文献
19.
《Peptides》2016
The TcTLE peptide (TLEEFSAKL) is a CD8+ T cell HLA-A*0201-restricted epitope derived from the Trypanosoma cruzi KMP-11 protein that is efficiently processed, presented and recognized by CD8+ T cells from chagasic patients. Since the immunogenic properties of wild-type epitopes may be enhanced by suitable substitutions in secondary anchor residues, we have studied the effect of introducing specific mutations at position 3, 6 and 7 of the TcTLE peptide. Mutations (E3L, S6V and A7F) were chosen on the basis of in silico predictions and in vitro assays were performed to determine the TcTLE-modified peptide binding capacity to the HLA-A*0201 molecule. In addition, the functional activity of peptide-specific CD8+ T cells in HLA-A2+ chagasic patients was also interrogated. In contrast to bioinformatics predictions, the TcTLE-modified peptide was found to have lower binding affinity and stability than the original peptide. Nevertheless, CD8+ T cells from chronic chagasic patients recognized the TcTLE-modified peptide producing TNF-α and INF-γ and expressing CD107a/b, though in less extension than the response triggered by the original peptide. Overall, although the amino acids at positions 3, 6 and 7 of TcTLE are critical for the peptide affinity, they have a limited effect on the immunogenic properties of the TcTLE epitope. 相似文献
20.
The role of the polypeptide matrix in electron transfer processes in proteins has been studied in two distinct systems: first
in a protein where the induced ET is artificial, and second as part of the catalytic cycle of an enzyme. Azurins are structurally
well-characterized blue single-copper proteins consisting of a rigid β-sheet polypeptide matrix. We have determined rate constants
and activation parameters for intramolecular long-range electron transfer between the disulfide radical anions (generated
by pulse radiolysis) and the copper(II) centre as a function of driving force and nature of the intervening medium in a large
number of wild-type and single-site-mutated proteins. In ascorbate oxidase, for which the three-dimensional structure is equally
well characterized, the internal ET from the type-I Cu(I) to the trinuclear Cu(II) centre has been studied. We find that the
results correlate well with distance through well-defined pathways using a through-bond electron tunnelling mechanism.
Received: 2 January 1997 / Accepted: 6 February 1997 相似文献