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   972篇
  免费   129篇
化学   915篇
晶体学   4篇
力学   10篇
数学   39篇
物理学   85篇
无线电   48篇
  2024年   2篇
  2023年   18篇
  2022年   19篇
  2021年   38篇
  2020年   42篇
  2019年   51篇
  2018年   35篇
  2017年   24篇
  2016年   59篇
  2015年   74篇
  2014年   63篇
  2013年   68篇
  2012年   96篇
  2011年   92篇
  2010年   53篇
  2009年   35篇
  2008年   61篇
  2007年   46篇
  2006年   40篇
  2005年   30篇
  2004年   15篇
  2003年   14篇
  2002年   12篇
  2001年   8篇
  2000年   21篇
  1999年   10篇
  1998年   7篇
  1997年   5篇
  1996年   3篇
  1995年   7篇
  1994年   2篇
  1993年   6篇
  1992年   2篇
  1991年   4篇
  1990年   5篇
  1988年   2篇
  1987年   3篇
  1985年   3篇
  1983年   2篇
  1981年   2篇
  1978年   2篇
  1977年   2篇
  1969年   2篇
  1959年   2篇
  1958年   1篇
  1957年   1篇
  1943年   1篇
  1937年   2篇
  1936年   2篇
  1925年   1篇
排序方式: 共有1101条查询结果,搜索用时 15 毫秒
31.
32.
33.
A new stream of research indicates that framing effects are based on emotional as well as cognitive processes. However, it is not entirely clear whether emotions mediate framing effects and what the moderators of emotional mediation processes are. To address these questions, we conducted an experiment in which the framing of responsibility for a social problem was manipulated (ambivalent vs. high‐responsibility frame). We find that the high‐responsibility frame increased the preference for punitive measures by increasing responsibility beliefs and eliciting anger. Furthermore, we find that trait anger moderates the framing effect on anger and that responsibility beliefs are positively associated with anger intensity. The significance of these findings for framing research and suggestions for future studies are discussed.  相似文献   
34.
Motivated by the possibility of modifying energy levels of a molecule without substantially changing its band gap, the impact of gradual fluorination on the optical and structural properties of zinc phthalocyanine (FnZnPc) thin films and the electronic characteristics of FnZnPc/C60 (n = 0, 4, 8, 16) bilayer cells is investigated. UV–vis measurements reveal similar Q‐ and B‐band absorption of FnZnPc thin films with n = 0, 4, 8, whereas for F16ZnPc a different absorption pattern is detected. A correlation between structure and electronic transport is deduced. For F4ZnPc/C60 cells, the enhanced long range order supports fill factors of 55% and an increase of the short circuit current density by 18%, compared to ZnPc/C60. As a parameter being sensitive to the organic/organic interface energetics, the open circuit voltage is analyzed. An enhancement of this quantity by 27% and 50% is detected for F4ZnPc‐ and F8ZnPc‐based devices, respectively, and is attributed to an increase of the quasi‐Fermi level splitting at the donor/acceptor interface. In contrast, for F16ZnPc/C60 a decrease of the open circuit voltage is observed. Complementary photoelectron spectroscopy, external quantum efficiency, and photoluminescence measurements reveal a different working principle, which is ascribed to the particular energy level alignment at the interface of the photoactive materials.  相似文献   
35.
The nonlinear properties and the photophysical behavior of two π‐conjugated chromophores that incorporate an electron‐deficient pyrimidine core (A) and γ‐methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes’ scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end‐groups. This latter structural parameter also has a strong influence on the excited‐state dynamics, which leads to a very efficient fluorescence quenching.  相似文献   
36.
The content of tenuazonic acid in human urine was determined by a stable isotope dilution assay (SIDA) that was recently developed for the analysis of food commodities and extensively re-validated for urine matrix in this study. Linearity of the response curve was proven between molar ratios n(labeled standard)/n(analyte) of 0.02–100. The limits of detection and determination were 0.2 and 0.6 μg/L, respectively. The mean recovery of the stable isotope dilution assay was 102?±?3 % in the range between 1.0 and 100 μg/L. Interassay precision was 6.7 % (relative standard deviation of three triplicate analyses of a human urine sample during 3 weeks). The method was applied to two studies dealing with urinary excretion of tenuazonic acid: In the first study, tenuazonic acid was quantified in the 24-h urine of six volunteers from Germany (three female, three male) in a concentration range of 1.3–17.3 μg/L or 2.3–10.3 ng/mg?1 creatinine, respectively. In the second study, two volunteers (one female, one male) ingested 30 μg tenuazonic acid by consumption of naturally contaminated whole meal sorghum infant cereals and tomato juice, respectively. The urinary excretion of the ingested tenuazonic acid was 54–81 % after 6 h, depending on matrix and volunteer. After 24 h, 87–93 % of the ingested amount of tenuazonic acid was excreted, but the fate of the remaining about 10 % is open. Thus, it is not possible to exclude potential health hazards for the consumer, completely.
Figure
Urinary excretion of tenuazonic acid (TA) by two volunteers (A and B) after ingestion of sorghum infant cereals [1] and tomato juice [2]  相似文献   
37.
38.
Artificial implants and biomaterials lack the natural defense system of our body and, thus, have to be protected from bacterial adhesion and biofilm formation. In addition to the increasing number of implanted objects, the resistance of bacteria is also an important problem. Silver ions are well‐known for their antimicrobial properties, yet not a lot is known about their mode of action. Silver is expected to interact on many levels, thus the development of silver resistance is very difficult. Nevertheless, some bacteria are able to resist silver, even at higher concentrations. One such defense mechanism of bacteria against heavy‐metal intoxication includes an efflux system. SilE, a periplasmic silver‐binding protein that is involved in this defense mechanism, has been shown to possess numerous histidine functions, which strongly bind to silver atoms, as demonstrated by ourselves previously. Herein, we address the question of how histidine binds to silver ions as a function of pH value. This property is important because the local proton concentration in cells varies. Thus, we solved the crystal structures of histidine–silver complexes at different pH values and also investigated the influence of the amino‐acid configuration. These results were completed by DFT calculations on the binding strength and packing effects and led to the development of a model for the mode of action of SilE.  相似文献   
39.
The synthesis of base‐stabilized boryl and borylene complexes is reported. An N‐heterocyclic carbene (NHC)‐stabilized iron–dihydroboryl complex was prepared by two different routes including methane liberation and salt elimination. A range of base‐stabilized iron–dichloroboryl complexes was prepared by addition of Lewis bases to boryl complexes. Base‐stabilized, cationic monochloroborylene complexes were synthesized from these boryl complexes by halide abstraction by using weakly coordinating anions.  相似文献   
40.
Versatile ruthenium(II) complexes allow for site‐selective C H oxygenations with weakly‐coordinating aldehydes. The challenging C H functionalizations proceed with high chemoselectivity by rate‐determining C H metalation. The new method features an ample substrate scope, which sets the stage for the step‐economical preparation of various bioactive heterocycles.  相似文献   
[首页] « 上一页 [1] [2] [3] 4 [5] [6] [7] [8] [9] [10] [11] 下一页 » 末  页»
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