全文获取类型
收费全文 | 2750篇 |
免费 | 169篇 |
国内免费 | 2篇 |
专业分类
2921篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 39篇 |
2021年 | 62篇 |
2020年 | 23篇 |
2019年 | 42篇 |
2018年 | 58篇 |
2017年 | 41篇 |
2016年 | 84篇 |
2015年 | 145篇 |
2014年 | 174篇 |
2013年 | 196篇 |
2012年 | 266篇 |
2011年 | 229篇 |
2010年 | 171篇 |
2009年 | 154篇 |
2008年 | 198篇 |
2007年 | 167篇 |
2006年 | 160篇 |
2005年 | 126篇 |
2004年 | 124篇 |
2003年 | 113篇 |
2002年 | 67篇 |
2001年 | 61篇 |
2000年 | 59篇 |
1999年 | 40篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2921条查询结果,搜索用时 0 毫秒
1.
The foodborne pathogenStaphylococcus aureus is distinguished by its ability to grow within environments of extremely high osmolarity (e.g., foods with low water activity values). In the present study, we examined the accumulation of intracellular organic solutes withinS. aureus strain ATCC 12600 when cells were grown in a complex medium containing high concentrations of NaCl. Consistent with previous reports [Measures JC (1975) Nature 257:398–400; Koujima I, et al. (1978) Appl Environ Microbiol 35:467–470; and Anderson CB, Witter LD (1982) Appl Environ Microbiol 43:1501–1503], intracellular proline was found to accumulate to high concentrations. However, NMR spectroscopy of cell extracts revealed glycine betaine to be the predominant intracellular organic solute accumulated within cells grown at high osmolarity. In additional experiments, we examined the growth rate ofS. aureus in a defined medium of high osmolarity and found it to be stimulated significantly by the presence of either exogenous proline or glycine betaine. Highest growth rates were obtained when the defined medium was supplemented with glycine betaine. 相似文献
2.
S. O. Hwang G. H. Gil Y. J. Cho K. R. Kang J. H. Lee J. C. Bae 《Applied microbiology and biotechnology》1985,22(2):108-113
Summary A process for l-phenylalanine production was studied using a tyrosine auxotrophic regulatory mutant of Escherichia coli, resistant to both -2-thienyl-dl-alanine and p-fluoro-dl-phenylalanine. Fermentations were carried out in a 30-1 fermentor with intermittent feeding of glucose plus phosphate. The mutant accumulated l-phenylalanine in the fermentation broth up to 15 g/l at pH 7.0 and 33°C. Column chromatography on a strong cation exchanger was employed as the most effective step in the purification of l-phenyl-alanine from the broth. This step brought about 4-fold concentration of the product with 96% recovery. 相似文献
3.
Comparison of lodging safety factor of untreated and succinic Acid 2,2-dimethylhydrazide-treated shoots of mulberry tree 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This study examined the lodging resistance of mulberry tree (Morus bombycis Koidz. cv Kenmochi) shoots treated or not treated with succinic acid 2,2-dimethylhydrazide (SADH). The lodging safety factor, an indicator of lodging resistance, was defined as the ratio of critical lodging load to the leaf fresh weight observed, provided that the distribution of the critical lodging load along the stem was similar to that of the leaf fresh weight observed. The critical lodging load was experimentally estimated by loading weights onto the stems. In the untreated trees, the lodging safety factor was maintained at about 3.2. In the SADH-treated trees, the stem elongation was inhibited to about 80% of that in the untreated trees, and the percentage of shoot dry matter partitioned into the leaves was always larger than that of the untreated trees. This dwarfing of the stem caused by SADH increased the critical lodging load supported by the unit stem dry weight, while this large investment of materials in leaves increased the leaf fresh weight supported by the unit stem dry weight. Since the increments canceled each other, the lodging safety factor of the SADH-treated shoots was similar to that of the untreated ones. These results suggest that the shoot formation of the mulberry tree is controlled to maintain the lodging safety factor at a constant level. 相似文献
4.
A structured model of dual-limitation kinetics 总被引:2,自引:0,他引:2
A structured model of substrate-utilization kinetics that encompasses dual-limitation conditions, caused by simultaneously low concentrations of the electron donor and the electron acceptor, is developed by incorporating the internal cofactor responses into the kinetic variables. The structured model is based on an assumption that the maximum specific electron-donor-oxidation rate (q(md)) is not a constant, but is linearly controlled by the intracellular chemical potentials, log(NAD/NADH) and log(ATP/ADP . P(i)). Determination of the kinetic parameters for the dual-limitation model, using experimental data from the companion article, verifies that q(md) varies and demonstrates that the NAD/NADH ratio affects q(md) in a positive direction; thus, an increase of the ratio increases the rate of electron-donor utilization. Because the internal NAD/NADH ratio rises with an increase in S(ar) the specific electron-donor-utilization rate is accelerated by high S(a). Since the ratio also increases as the specific electron-donor-utilization rate falls, the specific rate is intrinsically accelerated by the cofactor response when it becomes low due to a depletion of electron donor. Because the cofactor responses upon changes of the external substrate concentrations are systematic, the dual-limitation model can be expressed as a function of only external concentrations of electron donor and electron acceptor, which results in a multiplicative (double-Monod) form. Thus, dual limitation by both substrates reduces the overall reaction rate below the rate expected from single limitation by only one, the most severely limiting, substrate. (c) 1996 John Wiley & Sons, Inc. 相似文献
5.
Homologous recombination of monkey alpha-satellite repeats in an in vitro simian virus 40 replication system: possible association of recombination with DNA replication. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
To study homologous recombination between repeated sequences in an in vitro simian virus 40 (SV40) replication system, we constructed a series of substrate DNAs that contain two identical fragments of monkey alpha-satellite repeats. Together with the SV40-pBR322 composite vector encoding Apr and Kmr, the DNAs also contain the Escherichia coli galactokinase gene (galK) positioned between two alpha-satellite fragments. The alpha-satellite sequence used consists of multiple units of tandem 172-bp sequences which differ by microheterogeneity. The substrate DNAs were incubated in an in vitro SV40 DNA replication system and used to transform the E. coli galK strain DH10B after digestion with DpnI. The number of E. coli galK Apr Kmr colonies which contain recombinant DNAs were determined, and their structures were analyzed. Products of equal and unequal crossovers between identical 172-bp sequences and between similar but not identical (homeologous) 172-bp sequences, respectively, were detected, although those of the equal crossover were predominant among all of the galK mutant recombinants. Similar products were also observed in the in vivo experiments with COS1 cells. The in vitro experiments showed that these recombinations were dependent on the presence of both the SV40 origin of DNA replication and SV40 large T antigen. Most of the recombinant DNAs were generated from newly synthesized DpnI-resistant DNAs. These results suggest that the homologous recombination observed in this SV40 system is associated with DNA replication and is suppressed by mismatches in heteroduplexes formed between similar but not identical sequences. 相似文献
6.
7.
8.
Immunocytochemical localization of casein kinase II during interphase and mitosis 总被引:15,自引:1,他引:14
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have developed specific antibodies to synthetic peptide antigens that react with the individual subunits of casein kinase II (CKII). Using these antibodies, we studied the localization of CKII in asynchronous HeLa cells by immunofluorescence and immunoelectron microscopy. Further studies were done on HeLa cells arrested at the G1/S transition by hydroxyurea treatment. Our results indicate that the CKII alpha and beta subunits are localized in the cytoplasm during interphase and are distributed throughout the cell during mitosis. Further electron microscopic investigation revealed that CKII alpha subunit is associated with spindle fibers during metaphase and anaphase. In contrast, the CKII alpha' subunit is localized in the nucleus during G1 and in the cytoplasm during S. Taken together, our results suggest that CKII may play significant roles in cell division control by shifting its localization between the cytoplasm and nucleus. 相似文献
9.
10.
Genetic and biochemical approaches have contributed to an explosion of literature on cell-cycle control. Regulation of the cell-cycle is controlled by a series of kinases and phosphatases. Key control points are during the G(1)-S and G(2)-M transitions. During both transitions, cyclins interact with a specific kinase to allow a cell to pass through that phase. The meiotic maturation of oocytes, fertilization and embryo development are all events influenced by cell-cycle regulation. Understanding cell-cycle control should provide new ways for gamete and embryo biologists to approach culture and development problems. 相似文献