全文获取类型
收费全文 | 589篇 |
免费 | 22篇 |
国内免费 | 17篇 |
出版年
2023年 | 7篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 37篇 |
2013年 | 54篇 |
2012年 | 27篇 |
2011年 | 46篇 |
2010年 | 36篇 |
2009年 | 53篇 |
2008年 | 48篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有628条查询结果,搜索用时 140 毫秒
581.
The making of strand-specific M13 probes 总被引:1,自引:0,他引:1
Joachim Messing 《Gene》1982,17(3):271-277
A novel approach has been developed for the preparation of highly radioactive, strand-specific M13 probes. A universal primer, complementary to the region 5' to the multiple cloning sites of M13mp7, was used to initiate the DNA synthesis of the complementary strand of the M13 sequence downstream from the inserted sequence. The synthesis of the (?) strand, which was labeled with a radioactively labeled precursor, did not proceed to completion so that the inserted sequence was kept single-stranded. Thus, a partially double-stranded probe that had the specificity of this inserted sequence was obtained. As an example for the application of single-stranded specific hybridization probes, an M13mp7 subclone of a zein cDNA clone of maize (A30) was labeled and used in a dot hybridization test to select from the hundreds of M13mp7 subclones of the zein genomic clone, 24, the sequences complementary to the probe. The specificity of the probe was confirmed by dideoxy chain terminator sequencing experiments. 相似文献
582.
Pre-anthesis high-temperature acclimation alleviates damage to the flag leaf caused by post-anthesis heat stress in wheat 总被引:5,自引:0,他引:5
The objective of this study was to investigate the effect of pre-anthesis high-temperature acclimation on leaf physiology of winter wheat in response to post-anthesis heat stress. The results showed that both pre- and post-anthesis heat stresses significantly depressed flag leaf photosynthesis and enhanced cell membrane peroxidation, as exemplified by increased O2− production rate and reduction in activities of antioxiditave enzymes. However, under post-anthesis heat stress, plants with pre-anthesis high-temperature acclimation (HH) showed much higher photosynthetic rates than those without pre-anthesis high-temperature acclimation (CH). Leaves of HH plants exhibited a higher Chl a/b ratio and lower chlorophyll/carotenoid ratio and superoxide anion radical release rate compared with those of the CH plants. In addition, antioxidant enzyme activities in HH plants were significantly higher than in CH. Coincidently, expressions of photosythesis-responsive gene encoding Rubisco activase B (RcaB) and antioxidant enzyme-related genes encoding mitochondrial manganese superoxide dismutase (Mn-SOD), chloroplastic Cu/Zn superoxide dismutase (Cu/Zn-SOD), catalase (CAT) and cytosolic glutathione reductase (GR) were all up-regulated under HH, whereas a gene encoding a major chlorophyll a/b-binding protein (Cab) was up-regulated by post-anthesis heat stress at 10 DAA, but was down-regulated at 13 DAA. The changes in the expression levels of the HH plants were more pronounced than those for the CH. Collectively, the results indicated that pre-anthesis high-temperature acclimation could effectively alleviate the photosynthetic and oxidative damage caused by post-anthesis heat stress in wheat flag leaves, which was partially attributable to modifications in the expression of the photosythesis-responsive and antioxidant enzymes-related genes. 相似文献
583.
584.
量子点-人表皮生长因子纳米荧光探针的制备及其对卵巢癌细胞SKOV-3的识别 总被引:1,自引:0,他引:1
在连接试剂1-乙基-3(3-二甲基胺基丙基)碳二亚胺盐酸盐(1-ethyl-3(3-dimethylamino propyl)-carbodiimide,EDC)的作用下,将水相合成的量子点(Quantumdots,QDs)与人表皮生长因子(Epidermal growth factor,EGF)进行了连接,通过毛细管电泳、吸收光谱以及荧光光谱对连接前后的QDs进行了表征,获得的QDs—EGF可识别卵巢癌细胞SKOV-3。 相似文献
585.
The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd2+ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360 nm and a broad emission spectra between 450 and 650 nm when excited at 370 nm, both characteristic of CdS QDs. Average sizes of 6 and 10 nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H2S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5–5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms. 相似文献
586.
Thomas P. Brennan Pendar Ardalan Han‐Bo‐Ram Lee Jonathan R. Bakke I‐Kang Ding Michael D. McGehee Stacey F. Bent 《Liver Transplantation》2011,1(6):1169-1175
Functioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO2, we are able to grow QDs of adjustable size which act as sensitizers for solid‐state QD‐sensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1‐10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2',7,7'‐tetrakis‐(N,N‐di‐p methoxyphenylamine) 9,9'‐spirobifluorene (spiro‐OMeTAD) as the solid‐state hole conductor. The ALD approach described here can be applied to fabrication of quantum‐confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition. 相似文献
587.
Aynaz Mazandarani Dr. Ali Taravati Dr. Javad Mohammadnejad Dr. Fatemeh Yazdian 《化学与生物多样性》2023,20(9):e202300659
Breast cancer is a malignancy that affects mostly females and is among the most lethal types of cancer. The ligand-functionalized nanoparticles used in the nano-drug delivery system offer enormous potential for cancer treatments. This work devised a promising approach to increase drug loading efficacy and produce sustained release of 5-fluorouracil (5-FU) and Ganoderic acid (GA) as model drugs for breast cancer. Chitosan, aptamer, and carbon quantum dot (CS/Apt/COQ) hydrogels were initially synthesized as a pH-sensitive and biocompatible delivery system. Then, CS/Apt/COQ NPs loaded with 5-FU-GA were made using the W/O/W emulsification method. FT-IR, XRD, DLS, zeta potentiometer, and SEM were used to analyze NP's chemical structure, particle size, and shape. Cell viability was measured using MTT assays in vitro using the MCF-7 cell lines. Real-time PCR measured cell apoptotic gene expression. XRD and FT-IR investigations validated nanocarrier production and revealed their crystalline structure and molecular interactions. DLS showed that nanocarriers include NPs with an average size of 250.6 nm and PDI of 0.057. SEM showed their spherical form, and zeta potential studies showed an average surface charge of +37.8 mV. pH 5.4 had a highly effective and prolonged drug release profile, releasing virtually all 5-FU and GA in 48 h. Entrapment efficiency percentages for 5-FU and GA were 84.7±5.2 and 80.2 %±2.3, respectively. The 5-FU-GA-CS-CQD-Apt group induced the highest cell death, with just 57.9 % of the MCF-7 cells surviving following treatment. 5-FU and GA in CS-CQD-Apt enhanced apoptotic induction by flow cytometry. 5-FU-GA-CS-CQD-Apt also elevated Caspase 9 and downregulated Bcl2. Accordingly, the produced NPs may serve as pH-sensitive nano vehicles for the controlled release of 5-FU and GA in treating breast cancer. 相似文献
588.
589.
Recent progress in computational modeling of the catalytic activation of cobalt–carbon bond cleavage shows that quantum chemical calculations could be an important part of coenzyme B12 research. Particular emphasis has been placed on density functional theory, which is now emerging as a powerful tool to elucidate the electronic structure and spectroscopic properties of the active sites of metalloenzymes. 相似文献
590.
A simple kinetic model for the reductive pentose phosphate cycle is suggested and analyzed. The changes in ATP/NADPH ratio caused by light wavelength alterations have been shown to result in the specific redistribution of metabolites in the cycle. The redistribution permits an explanation of the kinetic patterns of the enhancement effect and chromatic transients of photosynthesis. The spectra of relative ATP concentration have been calculated using enhancement values for green plants and cyanobacteria. Relative changes in quantum yield of photosynthesis were also calculated using data from spectra of relative ATP concentration changes. It is shown that changes in the quantum yield of photosynthesis may be fully explained by means of the spectral dependence of the relative ATP concentration in chloroplasts. It is concluded that the enhancement effect, chromatic transients and the ‘red drop’ of photosynthetic efficiency are not to be considered as exhaustive arguments for the Z-scheme of photosynthesis, although they do not contradict it. 相似文献