全文获取类型
收费全文 | 673篇 |
免费 | 81篇 |
出版年
2021年 | 7篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 17篇 |
2013年 | 27篇 |
2012年 | 31篇 |
2011年 | 32篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 26篇 |
2007年 | 28篇 |
2006年 | 24篇 |
2005年 | 31篇 |
2004年 | 25篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 20篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 14篇 |
1972年 | 5篇 |
1971年 | 9篇 |
1969年 | 5篇 |
1968年 | 6篇 |
1967年 | 6篇 |
1966年 | 6篇 |
排序方式: 共有754条查询结果,搜索用时 15 毫秒
1.
In continuously stirred tank reactor experiments, with manure as substrate at thermophilic temperatures, the use of volatile fatty acids (VFA) as process indicators was investigated. Changes in VFA level were shown to be a good parameter for indicating process instability. The VFA were evaluated according to their relative changes caused by changes in hydraulic loading, organic loading or temperature. Butyrate and isobutyrate together were found to be particularly good indicators. Butyrate and isobutyrate concentrations increased significantly 1 or 2 days after the imposed perturbation, which makes these acids suitable for process monitoring and important for process control of the anaerobic biological system. In addition it was shown in a batch experiment that VFA at concentrations up to 50 mM did not reduce the overall methane production rate. This showed that VFA accumulation in anaerobic reactors was the result of process imbalance, not the cause of inhibition, thus justifying the use of VFA as process indicators. 相似文献
2.
Thymus cells from guinea pigs were separated according to buoyant density by centrifugation with PVP-coated colloidal silica particles (Percoll). By creating an S-shaped density gradient, two populations (referred to as peak-I and peak-II cells) were obtained which differed in size as well as ability to spontaneous proliferation in vitro. Peak I contained low density cells of large size and was highly enriched with DNA-synthesizing cells. These continued to proliferate in culture for at least 30 h as demonstrated by mitotic studies in the intervals 0-10 and 20-30 h. In order to grow in vitro, however, the cycling cells of peak I depended on the medium (RPMI 1640) being supplemented with L-alanine. The high density cells of peak II constituted 70% of the thymocytes and had a small and uniform volume. This population was depleted of proliferating cells. The simple and rapid separation of these two major populations is considered a useful first step for the further characterization of thymocyte subpopulations. We suggest that peak I primarily includes proliferating precursor cells from the cortex as well as mature, immunocompetent cells. Peak II consists largely of small cortical cells. 相似文献
3.
In this article we discuss the moral and legal aspects of causing the death of a terminal patient in the hope of extending their life in the future. We call this theoretical procedure cryothanasia. We argue that administering cryothanasia is ethically different from administering euthanasia. Consequently, objections to euthanasia should not apply to cryothanasia, and cryothanasia could also be considered a legal option where euthanasia is illegal. 相似文献
4.
Complex ganglioside expression and tetanus toxin binding by PC12 pheochromocytoma cells 总被引:7,自引:0,他引:7
K M Walton K Sandberg T B Rogers R L Schnaar 《The Journal of biological chemistry》1988,263(4):2055-2063
Ganglioside expression and tetanus toxin binding were studied in the rat pheochromocytoma cell line PC12. Seven ganglioside species were readily detected in extracts of PC12 cells; two were identified as tri- and tetrasialogangliosides, which are common brain constituents but unusual components of neuronal cell lines. Carbohydrate composition, acid and enzyme hydrolyses, and mass spectral analysis revealed that the major species is GT 1b, a predominant mammalian brain ganglioside previously reported to support high affinity tetanus toxin binding (Rogers, T. B., and Snyder, S. H. (1981) J. Biol. Chem. 256, 2402-2407). Direct binding of 125I-tetanus toxin to PC12 gangliosides on TLC plates revealed selective binding to the tri- and tetrasialogangliosides. Radioiodinated toxin also bound with high affinity to intact PC12 cells or their isolated membranes. The binding affinity (Kd = 1.25 nM), density of receptors (Bmax = 238 pmol/mg of membrane protein), and dependence on pH, ionic strength, and temperature were similar to those previously reported for toxin binding to rat brain synaptic membranes. Differentiation of PC12 cells caused an increase in expression of the tri- and tetrasialogangliosides and a closely matched increase in tetanus toxin binding to cell membranes. These data provide evidence that complex gangliosides may act as tetanus toxin receptors, and demonstrate the utility of the PC12 cell line for studies of tetanus toxicity and complex ganglioside expression. 相似文献
5.
Mertz Christoffer Krarup Sara Jensen Cecilie D. Lindholm Sandy E. H. Kjær Christina Pinborg Lars H. Bak Lasse K. 《Neurochemical research》2020,45(6):1247-1255
Neurochemical Research - Epilepsy is one of the most common chronic neurological conditions. Today, close to 30 different medications to prevent epileptic seizures are in use; yet, far from all... 相似文献
6.
The numbers of macrophages in peritoneal guinea pig hepatomas were significantly (P < 0.005) elevated by the intraperitoneal injection of a covalent conjugate of the chemotactic peptide, formylmethionylleucylphenylalanine (fMLP), and IgG reactive with surface antigens on the hepatoma cells. These conjugates, which were previously shown to be chemotactic for guinea pig peritoneal exudate macrophages in vitro, increased the numbers of macrophages in the tumors approximately twofold when injected either in a single dose or in five doses. Although five injections of unconjugated fMLP were nearly as effective as the IgG-fMLP conjugates, free fMLP did not enhance the numbers of macrophages in tumors when injected as a single dose. Unconjugated IgG had no effect. The mean tumor weights were decreased in those groups of guinea pigs which received IgG-fMLP but statistical significance was not achieved due to tumor weight variability in all groups. 相似文献
7.
8.
Kristin B. Andersson Alexandra V. Finsen Cecilie Sjland Lisbeth H. Winer Ivar Sjaastad Annlaug
degaard William E. Louch Yibin Wang Ju Chen Kenneth R. Chien Ole M. Sejersted Geir Christensen 《Cell calcium》2009,46(3):219-225
Sarco(endo)plasmic reticulum calcium ATPases (SERCA) are cellular pumps that transport Ca2+ into the sarcoplasmic reticulum (SR). Serca2 is the most widely expressed gene family member. The very early embryonic lethality of Serca2null mouse embryos has precluded further evaluation of loss of Serca2 function in the context of organ physiology. We have generated mice carrying a conditional Serca2flox allele which allows disruption of the Serca2 gene in an organ-specific and/or inducible manner. The model was tested by mating Serca2flox mice with MLC-2vwt/Cre mice and with αMHC-Cre transgenic mice. In heterozygous Serca2wt/floxMLC-2vwt/Cre mice, the expression of SERCA2a and SERCA2b proteins were reduced in the heart and slow skeletal muscle, in accordance with the expression pattern of the MLC-2v gene. In Serca2flox/flox Tg(αMHC-Cre) embryos with early homozygous cardiac Serca2 disruption, normal embryonic development and yolk sac circulation was maintained up to at least embryonic stage E10.5. The Serca2flox mouse is the first murine conditional gene disruption model for the SERCA family of Ca2+ ATPases, and should be a powerful tool for investigating specific physiological roles of SERCA2 function in a range of tissues and organs in vivo both in adult and embryonic stages. 相似文献
9.
10.
The precision and accuracy of two versions of the 2-methylindolo-α-pyrone (2-MIP) assay and of a high performance liquid chromatography (HPLC) technique was assessed when applied to analysis of indole-3-acetic acid (IAA) in pine ( Pinus sylvestris ) tissue. In one version of the 2-MIP assay total fluorescence at wavelengths > 450 nm was recorded, whereas in the other version fluorescence spectra were recorded and analyzed. Such analysis revealed the occurrence in some samples of fluorescent contaminants that impaired both precision and accuracy. The precision and accuracy of the 2-MIP assay could be improved by additional sample purification, and the over-all accuracy of the assay was finally verified, at a high level of sample purity, by successive approximation. The precision of the assay was then 14%. Successive approximation also verified that the HPLC technique was accurate at a less advanced stage of sample purity than the 2-MIP assay, and had a precision of 14%. 相似文献