首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   232篇
  免费   19篇
  国内免费   6篇
  2024年   1篇
  2023年   8篇
  2022年   3篇
  2021年   6篇
  2020年   5篇
  2019年   7篇
  2018年   6篇
  2017年   3篇
  2016年   9篇
  2015年   5篇
  2014年   12篇
  2013年   18篇
  2012年   8篇
  2011年   8篇
  2010年   9篇
  2009年   19篇
  2008年   11篇
  2007年   12篇
  2006年   5篇
  2005年   9篇
  2004年   12篇
  2003年   6篇
  2002年   5篇
  2001年   6篇
  2000年   5篇
  1999年   1篇
  1998年   2篇
  1997年   6篇
  1996年   4篇
  1995年   3篇
  1994年   6篇
  1993年   4篇
  1992年   1篇
  1991年   5篇
  1990年   1篇
  1989年   1篇
  1987年   1篇
  1986年   2篇
  1985年   4篇
  1984年   6篇
  1983年   4篇
  1982年   1篇
  1980年   1篇
  1978年   1篇
  1976年   2篇
  1975年   3篇
排序方式: 共有257条查询结果,搜索用时 31 毫秒
21.
Using vanadate, poly(1H-pyrazol-1-yl)borate and pyrazole as starting materials, two new neutral peroxovanadium(V) complexes with poly(1H-pyrazol-1-yl)borate, VO(O(2))(pzH)(HB(pz)(3))(1) and VO(O(2))(pzH)(B(pz)(4))(2), were synthesized successfully. Both complexes were characterized by elemental analysis, IR, UV-vis and NMR spectra. And the structure of complex 1 was determined by X-ray diffraction, which is somewhat relevant for haloperoxidase enzymes. Cytotoxic effects also are discussed on 3T3 cell proliferation. In the concentration range (0.1-100mumol), both complexes have an inhibiting cellular proliferation effect. When the cells cultivated with the complexes at high dose, the toxicity effect of both complexes is more and more predominant.  相似文献   
22.
Auxin is essential for plant growth and development, this makes it difficult to study the biological function of auxin using auxin‐deficient mutants. Chemical genetics have the potential to overcome this difficulty by temporally reducing the auxin function using inhibitors. Recently, the indole‐3‐pyruvate (IPyA) pathway was suggested to be a major biosynthesis pathway in Arabidopsis thaliana L. for indole‐3‐acetic acid (IAA), the most common member of the auxin family. In this pathway, YUCCA, a flavin‐containing monooxygenase (YUC), catalyzes the last step of conversion from IPyA to IAA. In this study, we screened effective inhibitors, 4‐biphenylboronic acid (BBo) and 4‐phenoxyphenylboronic acid (PPBo), which target YUC. These compounds inhibited the activity of recombinant YUC in vitro, reduced endogenous IAA content, and inhibited primary root elongation and lateral root formation in wild‐type Arabidopsis seedlings. Co‐treatment with IAA reduced the inhibitory effects. Kinetic studies of BBo and PPBo showed that they are competitive inhibitors of the substrate IPyA. Inhibition constants (Ki) of BBo and PPBo were 67 and 56 nm , respectively. In addition, PPBo did not interfere with the auxin response of auxin‐marker genes when it was co‐treated with IAA, suggesting that PPBo is not an inhibitor of auxin sensing or signaling. We propose that these compounds are a class of auxin biosynthesis inhibitors that target YUC. These small molecules are powerful tools for the chemical genetic analysis of auxin function.  相似文献   
23.
Acrocarpous mosses present on stonewalls in urban areas may be used for monitoring purposes. Therefore for this investigation we selected Tortula muralis expecting that this species with an ability to colonise buildings in polluted agglomerations where other species have vanished may provide important information to monitor environmental quality. Concentrations of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn in T. muralis, in dust deposited on sandstone surfaces, and in the sandstones on which the moss grew were measured. T. muralis appeared to be a good bioindicator of airborne pollution which accumulated especially extremely high Cu, Fe and Zn concentrations reaching values much higher than harmful for plants. There was no relation between metal concentrations in underlying sandstones and T. ruralis. There was a relation between metal concentrations in dust and T. muralis. Cd, Co, Cr, Mn and V concentrations in T. muralis were higher than in dust. The Self-Organizing Feature Map identifying groups of sampling sites with similar concentrations of metals in mosses was able to classify the pollution level by distinguishing groups of highly, medium and less polluted sites. Once trained, SOFM can be applied in ecological investigations and could form a future basis for recognizing e.g. the type of pollution in urban environments by analysing the concentrations of elements in T. muralis.  相似文献   
24.
描述了一件象属( Elephas) 的右上臼齿化石。标本产自查谟紧靠上西瓦立克亚群巨砾岩组( Boulder Conglomerate Formation) 之上的砂质、粉砂质泥岩夹砾石层中,化石地点位于查谟市南10 km,Kharian 村北约500 m 处。根据齿板数、齿脊频率、釉质层厚度、冠高指数、绝对大小和齿长/齿高指数等牙齿形态参数,暂时将之归为 Elephas cf. E. maximus indicus。还简短讨论了象属的地理分布和地质时代。  相似文献   
25.
Goal, Scope and Background The disposal phase of a product’s life cycle in LCA is often neglected or based on coarse indicators like ‘kilogram waste’. The goal of report No. 13 of the ecoinvent project (Doka 2003) is to create detailed Life Cycle Inventories of waste disposal processes. The purpose of this paper is to give an overview of the models behind the waste disposal inventories in ecoinvent, to present exemplary results and to discuss the assessment of long-term emissions. This paper does not present a particular LCA study. Inventories are compiled for many different materials and various disposal technologies. Considered disposal technologies are municipal incineration and different landfill types, including sanitary landfills, hazardous waste incineration, waste deposits in deep salt mines, surface spreading of sludges, municipal wastewater treatment, and building dismantling. The inventoried technologies are largely based on Swiss plants. Inventories can be used for assessment of the disposal of common, generic waste materials like paper, plastics, packaging etc. Inventories are also used within the ecoinvent database itself to inventory the disposal of specific wastes generated during the production phase. Inventories relate as far as possible to the specific chemical composition of the waste material (waste-specific burdens). Certain expenditures are not related to the waste composition and are inventoried with average values (process-specific burdens). Methods The disposal models are based on previous work, partly used in earlier versions of ecoinvent/ETH LCI data. Important improvements were the extension of the number of considered chemical elements to 41 throughout all disposal models and new landfill models based on field data. New inventories are compiled for waste deposits in deep salt mines and building material disposal. Along with the ecoinvent data and the reports, also Excel-based software tools were created, which allow ecoinvent members to calculate waste disposal inventories from arbitrary waste compositions. The modelling of long-term emissions from landfills is a crucial part in any waste disposal process. In ecoinvent long-term emissions are defined as emissions occurring 100 years after present. They are reported in separate emission categories. The landfill inventories include long-term emissions with a time horizon of 60’000 years after present. Results and Discussion As in earlier studies, the landfills prove to be generally relevant disposal processes, as also incineration and wastewater treatment processes produce landfilled wastes. Heavy metals tend to concentrate in landfills and are washed out to a varying degree over time. Long-term emissions usually represent an important burden from landfills. Comparisons between burdens from production of materials and the burdens from their disposal show that disposal has a certain relevance. Conclusion The disposal phase should by default be included in LCA studies. The use of a material not only necessitates its production, but also requires its disposal. The created inventories and user tools facilitate heeding the disposal phase with a similar level of detail as production processes. The risk of LCA-based decisions shifting burdens from the production or use phase to the disposal phase because of data gaps can therefore be diminished. Recommendation and Perspective Future improvements should include the modelling of metal ore refining waste (tailings) which is currently neglected in ecoinvent, but is likely to be relevant for metals production. The disposal technologies considered here are those of developed Western countries. Disposal in other parts of the World can differ distinctly, for logistic, climatic and economic reasons. The cross-examination of landfill models to LCIA soil fate models could be advantageous. Currently only chemical elements, like copper, zinc, nitrogen etc. are heeded by the disposal models. A possible extension could be the modelling of the behaviour of chemical compounds, like dioxins or other hydrocarbons.  相似文献   
26.
In this paper we propose a new fast free zone capillary electrophoresis method for the simultaneous determination of ascorbic acid (AA) and uric acid (UA) in human plasma. We investigated the effect of analytical parameters, such as concentration and pH of borate running buffer, cartridge temperature, and sample treatment, on resolution, migration times, corrected peak areas, and efficiency. A good separation was achieved using a 60.2-cmx75-microm uncoated silica capillary and 100 mmol/L sodium borate buffer, pH 8, when metaphosphoric acid was employed as protein precipitant, in less than 4 min. These conditions gave a good reproducibility of migration times (CV 0.35 and 0.34%) and peak areas (CV 3.2 and 3.1%) for ascorbate and urate, respectively. The limit of detection was 0.5mg/L for both analytes when the detection was performed at 254 nm for AA and at 292 nm for UA. We compared the present method with a validated capillary electrophoresis assay by measuring plasma urate and ascorbate in 32 normal subjects and the obtained data were analyzed by the Passing and Bablok regression.  相似文献   
27.
The largest risk factor for age-related macular degeneration (ARMD) is advanced age. With aging, there is a striking accumulation of neutral lipids in Bruch''s membrane (BrM) of normal eye that continues through adulthood. This accumulation has the potential to significantly impact the physiology of the retinal pigment epithelium (RPE). It also ultimately leads to the creation of a lipid wall at the same locations where drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD, subsequently form. Here, we summarize evidence obtained from light microscopy, ultrastructural studies, lipid histochemistry, assay of isolated lipoproteins, and gene expression analysis. These studies suggest that lipid deposition in BrM is at least partially due to accumulation of esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles produced by the RPE. Furthermore, we suggest that the formation of ARMD lesions and their aftermath may be a pathological response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (Tabas, I., K. J. Williams, and J. Borén. 2007. Subendothelial lipoprotein retention as the initiating process in atherosclerosis: update and therapeutic implications. Circulation. 116:1832–1844). This view provides a conceptual basis for the development of novel treatments that may benefit ARMD patients in the future.  相似文献   
28.
Tris(triazolyl)borate (Ttz) ligands are sterically similar to tris(pyrazolyl)borate (Tp) but complexes of Ttz show improved solubility in water and alcohols due to their propensity for forming hydrogen bonds. Recently developed bulky tris(triazolyl)borate ligands can produce four and five coordinate transition metal complexes and serve as models for enzyme active sites in an aqueous environment. Herein we report the synthesis of such complexes, i.e. (TtztBu,Me)ZnCl, (TtztBu,Me)ZnBr, (TtztBu,Me)NiCl, and (TtztBu,Me)CuCl, which were analyzed by X-ray crystallographic and spectroscopic methods [TtztBu,Me = tris(3-t-butyl-5-methyl-1,2,4-triazolyl)borate]. (TtztBu,Me)ZnCl crystallizes as two different polymorphs with cubic and monoclinic symmetry. Both polymorphs of (TtztBu,Me)ZnCl and (TtztBu,Me)ZnBr have tetrahedral zinc atoms whereas the geometries at the metal in (TtztBu,Me)NiCl and (TtztBu,Me)CuCl are distorted tetrahedral. All complexes are methanol soluble and they also dissolve in methanol/water mixtures with up to 60% water.  相似文献   
29.
The potentials of a series of one-electron oxidation and reduction reactions have been determined for manganese group half-sandwich complexes of the tricarbadecaboranyl ligand PhC3B7H9 and the penta-organo fullerene ligand C60Bn2PhH2 (Bn = benzyl). The anodic processes were studied in CH2Cl2 and the cathodic processes were studied in both CH2Cl2 and THF, the supporting electrolyte being [NBu4][B(C6F5)4]. The manganese complex Mn(CO)2(PMe3)(PhC3B7H9) (1) is a member of a three-electron transfer series which includes oxidation to 1+ (0.51 V versus ferrocene) and successive reductions to 1 (−1.66 V) and 12− (−1.77 V). Both the oxidation and reduction of the closely-related complex Mn(CO)2(PPh3)(PhC3B7H9) (2) are chemically irreversible under slow-scan cyclic voltammetry conditions. The rhenium complex Re(CO)2(PPh3)(PhC3B7H9) (3) oxidizes (E1/2 = 0.82 V versus ferrocene) to a radical cation which, unlike its cyclopentadienyl analogue, shows no evidence of dimerization. Oxidation of the fullerene-based complex Re(CO)3(C60Bn2PhH2) is more facile than that of its cyclopentadienyl analogue, in contrast to previous findings in this class of metal-fullerene derivatives. An electrochemical ligand factor, EL, of 0.63 is calculated for the PhC3B7H9 ligand in manganese group half-sandwich complexes.  相似文献   
30.
It has been established that relict fungi Penicillium variabile Sopp can synthesize clavine alkaloids, rugulovasines A and B, which are revealed in this species for the first time. Submerged cultivation of the strain-producer revealed several microcycles of conidia formation. The synthesis of alkaloids was also of a cyclic character. The synchronism of cyclic rugulovasine biosynthesis and conidia formation was revealed. Zinc ions stimulated fungal growth but had a negative effect on the biosynthesis of rugulovasines.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号