全文获取类型
收费全文 | 149篇 |
免费 | 6篇 |
国内免费 | 8篇 |
专业分类
163篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 12篇 |
2013年 | 7篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 12篇 |
2008年 | 16篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有163条查询结果,搜索用时 0 毫秒
1.
Levels of the cyclic nucleotides, cAMP and cGMP, were determined in four species of pennate diatoms; changes in their levels and ratios were monitored in silicon-starved and light-dark synchronized cultures of Cylindrotheca fusiformis. Content of both cAMP and cGMP changed during the cell cycles: when silicate was added to starved cultures, cAMP, cGMP and DNA levels rose rapidly; cAMP and cGMP declined before DNA synthesis was complete and continued to fall during the events leading to cell separation. In unstarved synchronies, net synthesis of DNA continued until cell separation; 1 h before cell separation cAMP levels fell while those of cGMP rose. The results support the proposal that cAMP and cGMP may play a part in the process of cell division in the diatom, possibly involving silicon. 相似文献
2.
Jacek Najda Jan Gmiński Marian Dróżdż Franciszek Zych 《Biological trace element research》1993,37(2-3):101-106
The influence of silicon-treatment on the levels of TSH and thyroid hormones was studied in rats. Concentrations of thyrotropin (TSH), triiodothyronine (T3), and thyroxine (T4) were estimated in sera of rats receiving per os a soluble silicon compound—sodium metasilicate nonahydrate (Na2SiO3·9H2O), dissolved in the animals' drinking water. An increase in the TSH level in the tested group was observed, without statistically significant differences in T3 and T4 concentrations between the two groups of animals. The results provide evidence for the influence of silicon on the endocrine balance. They could also prove that this chemical element is capable of modifying the rate of some hormones' synthesis. 相似文献
3.
Summary Provision of silicon (0, 0.048, 0.096, 0.24, 0.48, and 0.96 g/1) in the form of silicic acid (H4SiO4) to nodulated cowpea plants(Vignia unguiculata [L.] Walp.) grown in liquid culture resulted in considerable changes in the internal organization of nodule structure. Compared
to the control plants which received no added silicate, bacteroid numbers increased significantly (P ≤ 0.05) at silicate concentrations
of both 0.096 and 0.48 g/1. The number of symbiosomes also increased by 3.2-fold at the silicate concentration of 0.96 g/1
compared to the control. In contrast, the size of bacteroids and symbiosomes decreased significantly (P ≤ 0.05) inside nodules
of silicate-treated plants. The peribacteroid space was also decreased considerably (P ≤ 0.05) with the application of 0.096
and 0.96 g of silicate per liter to plants. However, the size of intercellular spaces adjacent to infected and uninfected
interstitial cells within the nodule medulla increased significantly (P ≤ 0.05) at 0.096 g of silicate per liter followed
by a sharply marked (P ≤ 0.05) decrease with each subsequent increase in silicate application. The result was a large decrease
(P≤0.05) in the area of bacteria-infected tissue occupied by intercellular space at the highest silicate concentration, which
was caused by a significant (P ≤ 0.05) increase in cell wall thickness. Our findings show that the positive effects of silicon
on N2 fixation might actually be due to an increased number of bacteroids and symbiosomes. 相似文献
4.
The potential of solar cells have not been fully tapped due to the lack of energy conversion efficiency. There are three important mechanisms in producing high efficiency cells to harvest solar energy; reduction of light reflectance, enhancement of light trapping in the cell and increment of light absorption. The current work represent studies conducted in surface modification of single-crystalline silicon solar cells using wet chemical etching techniques. Two etching types are applied; alkaline etching (KOH:IPA:DI) and acidic etching (HF:HNO3:DI). The alkaline solution resulted in anisotropic profile that leads to the formation of inverted pyramids. While acidic solution formed circular craters along the front surface of silicon wafer. This surface modification will leads to the reduction of light reflectance via texturizing the surface and thereby increases the short circuit current and conversion rate of the solar cells. 相似文献
5.
Rita Mukhopadhyay Hiranmoy BhattacharjeeBarry P. Rosen 《Biochimica et Biophysica Acta (BBA)/General Subjects》2014
Background
Aquaporins (AQPs), members of a superfamily of transmembrane channel proteins, are ubiquitous in all domains of life. They fall into a number of branches that can be functionally categorized into two major sub-groups: i) orthodox aquaporins, which are water-specific channels, and ii) aquaglyceroporins, which allow the transport of water, non-polar solutes, such as urea or glycerol, the reactive oxygen species hydrogen peroxide, and gases such as ammonia, carbon dioxide and nitric oxide and, as described in this review, metalloids.Scope of review
This review summarizes the key findings that AQP channels conduct bidirectional movement of metalloids into and out of cells.Major conclusions
As(OH)3 and Sb(OH)3 behave as inorganic molecular mimics of glycerol, a property that allows their passage through AQP channels. Plant AQPs also allow the passage of boron and silicon as their hydroxyacids, boric acid (B(OH)3) and orthosilicic acid (Si(OH)4), respectively. Genetic analysis suggests that germanic acid (GeO2) is also a substrate. While As(III), Sb(III) and Ge(IV) are toxic metalloids, borate (B(III)) and silicate (Si(IV)) are essential elements in higher plants.General significance
The uptake of environmental metalloids by aquaporins provides an understanding of (i) how toxic elements such as arsenic enter the food chain; (ii) the delivery of arsenic and antimony containing drugs in the treatment of certain forms of leukemia and chemotherapy of diseases caused by pathogenic protozoa; and (iii) the possibility that food plants such as rice could be made safer by genetically modifying them to exclude arsenic while still accumulating boron and silicon. This article is part of a Special Issue entitled Aquaporins. 相似文献6.
《Bioorganic & medicinal chemistry》2014,22(7):2244-2252
Steroid sulfatase (STS) is a potential target for treatment of postmenopausal hormone-dependent breast cancer. Several steroidal STS inhibitors have been reported, but steroidal compounds are difficult to optimize and may interact with other targets. On the other hand, we have shown that diphenylmethane (DPM) derivatives act as estrogen receptor (ER) agonists and antagonists. Here, we aimed to design and synthesize non-steroidal DPM-type STS inhibitors that would also serve as pro-estrogen antagonists, releasing a metabolite with ERα-antagonistic activity upon hydrolysis by STS. We synthesized a series of compounds and evaluated their biological activities by means of STS-inhibitory activity assay and ER reporter gene assay. Among them, silicon-containing compound 16a showed strong STS-inhibitory activity (IC50 = 0.17 μM). Further, its putative metabolite (12a) exhibited potent ERα-antagonistic activity (IC50 = 29.7 nM). 相似文献
7.
Steve W. Blecker Stagg L. King Louis A. Derry Oliver A. Chadwick James A. Ippolito Eugene F. Kelly 《Biogeochemistry》2007,86(2):189-199
Slight differences in the chemical behavior of germanium (Ge) and silicon (Si) during soil weathering enable Ge/Si ratios
to be used as a tracer of Si pathways. Mineral weathering and biogenic silicon cycling are the primary modifiers of Ge/Si
ratios, but knowledge of the biogenic cycling component is based on relatively few studies. We conducted two sets of greenhouse
experiments in order to better quantify the range and variability in Ge discrimination by plants. Graminoid species commonly
found in North American grassland systems, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii were grown under controlled hydroponic environmental conditions. Silicon leaf contents were positively correlated with solution
Si and ambient temperature but not with nutrient solution pH, electrical conductivity, or species. The Ge/Si ratio incorporated
into phytoliths shows a distribution coefficient [(Ge/Si)phytolith/(Ge/Si)solution] of about 0.2 and is remarkably invariant between species, photosynthetic pathway, and solution temperature. Ge seems to
be discriminated against during the uptake and translocation of Si to the opal deposition sites by about a factor of five.
In the second experiment, a wider range of graminoid species (Agropyron smithii, Bouteloua gracilis, Buchloe dactyloides, Oryzopsis hymenoides, Schizachyrium scoparium and Andropogon gerardii) were grown in two different soil mediums. Plant phytoliths showed a distribution factor of about 0.4 for field grown grasses,
and 0.6 for potting soil grown grasses with no clear trends among the species. Evidence of the direction and degree of biological
Ge discrimination during plant uptake provides a geochemical finger print for plants and improves the utility of Ge/Si ratios
in studies of terrestrial weathering and links between Si cycles in terrestrial and marine systems. 相似文献
8.
Whisker-mediated transformation of embryogenic callus of maize 总被引:4,自引:0,他引:4
The present study was designed to establish embryogenic callus as a target tissue for whisker-mediated transformation of maize (Zea mays L.). Silicon carbide whiskers were used to deliver the bar and uidA (GUS) genes into embryogenic maize callus. Samples of osmotically-treated Type II callus were vigorously agitated in the presence of whiskers and plasmid DNA using a standard laboratory vortex or a modified dental amalgamator. On average, three transgenic callus lines were obtained per 100 samples treated. Plants were regenerated from several GUS-expressing callus lines and DNA analyses confirmed stable integration and inheritance. As with other direct DNA delivery methods involving embryogenic maize callus, integration patterns of the inserted DNA appeared to be complex. Although currently less efficient than microparticle bombardment on a per target basis, whisker-mediated transformation of embryogenic callus represents a viable method for transgenic maize production. Received: 14 May 1999 / Revision received: 11 October 1999 / Accepted: 11 October 1999 相似文献
9.
S.J. Lugowski D.C. Smith H. Bonek J. Lugowski W. Peters J. Semple 《Journal of trace elements in medicine and biology》2000,14(1):31-42
The increase, in the last two decades, in the application of silicones (polysiloxanes) and inorganic silicon compounds in medicine and the food industry, has exposed the human body to extensive contacts with these substances. Most silicone breast implants contain a gel consisting of a crosslinked silicone elastomer swollen by silicone oil (PDMS). Diffusion of PDMS through the silicone elastomer envelope and rupture of the envelope with release of the gel contents both occur clinically. The amount and distribution of silicone compounds in various tissues are key issues in the assessment of health problems connected with silicone implants. We have measured by GFAAS the Si content of tissues from normal and implant patients and the organic solvent extractable Si levels (assumed to be silicone), using careful control of sample collection and preparation. Whole blood levels were: implant patients mean 38.8 (SD 25.6) (microg/kg), controls mean 24.2 (SD 26.7) (microg/kg) in one study and subsequently 103.8 (SD 112.1) and 74.3 (SD 86.5) (microg/kg) in another study. Capsular tissue levels were: gel implants 25047 (SD 39313) (mg/kg of dry tissue), saline implants 20.0 (SD 27.3) (mg/kg of dry tissue) and controls 0.24 (SD 0.39) (mg/kg of dry tissue). Breast milk levels were: implant patients mean 58.7 (SD 33.8) (microg/kg), controls mean 51.1 (SD 31.0) (microg/kg); infant formula mean was 4.40 (mg/kg). Various precautions were undertaken to avoid Si contamination in this work, the most important being a) the use of a Class 100 laboratory for sample preparation and b) application of strict and elaborate washing procedure for specimen collection tools and laboratory plasticware. This data demonstrated that to properly interpret the importance of these numbers for human health, a larger study of \"normal\" levels of Si in human tissues should be undertaken and factors such as diet, water, race and geographical location should be considered. 相似文献
10.
Joji Ohshita Hidekazu Arase Nobuhisa Mimura Yosuke Tada Yutaka Harima 《Inorganica chimica acta》2005,358(14):4156-4162
UV irradiation of poly(organosilanylene-2,5-diethynylenesiloles) in benzene with an excess of Fe(CO)5 led to the formation of Fe(CO)3-coordinated silole units in the polymer backbone. The Fe(CO)3-coordinated polymers exhibited suppressed π-conjugation, relative to the parent non-coordinated polymers. Hole-transporting properties of poly(organosilanylene-2,5-diethynylenesiloles) were examined by the performance of EL devices containing the polymer layer as the hole-transport and Alq3 layer as the electron-transporting emitter. 相似文献