全文获取类型
收费全文 | 183685篇 |
免费 | 9174篇 |
国内免费 | 61篇 |
专业分类
192920篇 |
出版年
2021年 | 1070篇 |
2020年 | 1001篇 |
2019年 | 992篇 |
2018年 | 3412篇 |
2017年 | 3287篇 |
2016年 | 5662篇 |
2015年 | 9952篇 |
2014年 | 9723篇 |
2013年 | 11152篇 |
2012年 | 12069篇 |
2011年 | 9305篇 |
2010年 | 6537篇 |
2009年 | 5232篇 |
2008年 | 6621篇 |
2007年 | 6527篇 |
2006年 | 6021篇 |
2005年 | 11445篇 |
2004年 | 9873篇 |
2003年 | 7821篇 |
2002年 | 5128篇 |
2001年 | 3225篇 |
2000年 | 2479篇 |
1999年 | 3235篇 |
1998年 | 1076篇 |
1992年 | 3101篇 |
1991年 | 3082篇 |
1990年 | 3039篇 |
1989年 | 2893篇 |
1988年 | 2795篇 |
1987年 | 2523篇 |
1986年 | 2288篇 |
1985年 | 2379篇 |
1984年 | 1741篇 |
1983年 | 1377篇 |
1982年 | 873篇 |
1981年 | 833篇 |
1979年 | 1635篇 |
1978年 | 1199篇 |
1977年 | 996篇 |
1976年 | 1000篇 |
1975年 | 1279篇 |
1974年 | 1426篇 |
1973年 | 1437篇 |
1972年 | 1264篇 |
1971年 | 1255篇 |
1970年 | 1110篇 |
1969年 | 1105篇 |
1968年 | 991篇 |
1967年 | 1018篇 |
1966年 | 808篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
In this paper we quantify and characterize the expression of recombinant beta-lactoglobulin (rBLG) in prokaryote and eukaryote cells. In Escherichia coli we used the pET26 vector, which permits the secretion of rBLG in periplasm. We studied the expression of rBLG in COS-7 cells and in vivo in mouse tibialis muscle. The expression of rBLG was measured by two immunoassays specific, respectively, for BLG in its native and denatured conformation. We observed that rBLG was essentially expressed in a denatured form in E. coli even in the periplasm, whereas rBLG in eukaryote cells was found in its native conformation. 相似文献
25.
A new internal perfusion method has been developed which allows control of the internal solute composition in squid axons. The superiority of this technique compared to the old perfusion methods is shown by the experiments performed which have reproduced, both qualitatively and quantitatively, the Na+ and Ca2+ fluxes observed in intact and dialyzed axons. Compared with the internal dialysis, the perfusion method has the advantage that the permeability barrier give by the porous capillary has been eliminated. This allows the introduction into the axon of solutes with very high molecular weight, at the same time that a fast and reliable internal control can be achieved. 相似文献
26.
S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism. 相似文献
27.
28.
29.
S. Dubrou J. Konjek E. Macheras B. Welté L. Guidicelli E. Chignon M. Joyeux J. L. Gaillard B. Heym T. Tully G. Sapriel 《Applied and environmental microbiology》2013,79(18):5498-5508
Nonpigmented and late-pigmenting rapidly growing mycobacteria (RGM) have been reported to commonly colonize water production and distribution systems. However, there is little information about the nature and distribution of RGM species within the different parts of such complex networks or about their clustering into specific RGM species communities. We conducted a large-scale survey between 2007 and 2009 in the Parisian urban tap water production and distribution system. We analyzed 1,418 water samples from 36 sites, covering all production units, water storage tanks, and distribution units; RGM isolates were identified by using rpoB gene sequencing. We detected 18 RGM species and putative new species, with most isolates being Mycobacterium chelonae and Mycobacterium llatzerense. Using hierarchical clustering and principal-component analysis, we found that RGM were organized into various communities correlating with water origin (groundwater or surface water) and location within the distribution network. Water treatment plants were more specifically associated with species of the Mycobacterium septicum group. On average, M. chelonae dominated network sites fed by surface water, and M. llatzerense dominated those fed by groundwater. Overall, the M. chelonae prevalence index increased along the distribution network and was associated with a correlative decrease in the prevalence index of M. llatzerense, suggesting competitive or niche exclusion between these two dominant species. Our data describe the great diversity and complexity of RGM species living in the interconnected environments that constitute the water production and distribution system of a large city and highlight the prevalence index of the potentially pathogenic species M. chelonae in the distribution network. 相似文献
30.
Spongelike alginate nanoparticles as a new potential system for the delivery of antisense oligonucleotides. 总被引:3,自引:0,他引:3
I Aynié C Vauthier H Chacun E Fattal P Couvreur 《Antisense & nucleic acid drug development》1999,9(3):301-312
The aim of this study was to design a new antisense oligonucleotide (ON) carrier system based on alginate nanoparticles and to investigate its ability to protect ON from degradation in the presence of serum. Pharmacokinetics and tissue distribution of ON-loaded nanoparticles have been determined after intravenous administration. An original and dynamic process for ON loading into polymeric nanoparticles has been applied. It is based on the diffusion of ON or ON/polylysine complex into the nanoparticle or the alginate gel, respectively. Indeed, the single coincubation of ON with nanoparticles led, within a few days, to an extremely efficient association. The diffusion kinetic of ON was shown to be dependent on several parameters, incubation temperature, ON concentration, presence or absence of polylysine, polylysine molecular weight, and nanoparticle preparation procedure. This new alginate-based system was found to be able to protect [33P]-radiolabeled ON from degradation in bovine serum medium and to modify their biodistribution, as an important accumulation of radioactivity was observed in the lungs, in the liver, and in the spleen after intravenous administration into mice. ON may be associated efficiently with calcium alginate in a colloidal state. Such nanosponges are promising carriers for specific delivery of ON to lungs, liver, and spleen. 相似文献