全文获取类型
收费全文 | 1526篇 |
免费 | 40篇 |
国内免费 | 13篇 |
专业分类
化学 | 953篇 |
晶体学 | 2篇 |
力学 | 45篇 |
数学 | 352篇 |
物理学 | 227篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 37篇 |
2020年 | 28篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 17篇 |
2016年 | 58篇 |
2015年 | 32篇 |
2014年 | 34篇 |
2013年 | 83篇 |
2012年 | 72篇 |
2011年 | 126篇 |
2010年 | 66篇 |
2009年 | 51篇 |
2008年 | 93篇 |
2007年 | 95篇 |
2006年 | 81篇 |
2005年 | 57篇 |
2004年 | 47篇 |
2003年 | 42篇 |
2002年 | 37篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1986年 | 9篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1858年 | 7篇 |
排序方式: 共有1579条查询结果,搜索用时 15 毫秒
911.
Mujeebur R. Khan Katharina M. Fromm Tanveer F. Rizvi Bernd Giese Faheem Ahamad Raymond J. Turner Michael Füeg Enrico Marsili 《Particle & Particle Systems Characterization》2020,37(5):1900419
Metal nanoparticles (NPs), chalcogenides, and carbon quantum dots can be easily synthesized from whole microorganisms (fungi and bacteria) and cell-free sterile filtered spent medium. The particle size distribution and the biosynthesis time can be somewhat controlled through the biomass/metal solution ratio. The biosynthetic mechanism can be explained through the ion-reduction theory and UV photoconversion theory. Formation of biosynthetic NPs is part of the detoxification strategy employed by microorganisms, either in planktonic or biofilm form, to reduce the chemical toxicity of metal ions. In fact, most reports on NP biosynthesis show extracellular metal ion reduction. This is important for environmental and industrial applications, particularly in biofilms, as it allows in principle high biosynthetic rates. The antimicrobial and antifungal effect on biosynthetic NPs can be explained in terms of reactive oxygen species and can be enhanced by the capping agents attached to the NP during the biosynthesis process. Industrial applications of NP biosynthesis are still lagging, due to the difficulty of controlling NP size and low titer. Further, the environmental assessment of biosynthetic NPs has not yet been carried out. It is expected that further advancements in biosynthetic NP research will lead to applications, particularly in environmental biotechnology. 相似文献
912.
Enrico Bergamaschi Dr. Frédéric Beltran Dr. Christopher J. Teskey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(23):5180-5184
While the use of visible light in conjunction with transition metal catalysis offers powerful opportunities to switch between on/-off states of catalytic activity, the next frontier would be the ability to switch the actual function of the catalyst and resulting products. Here we report such an example of multi-dimensional catalysis. Featuring an easily prepared, bench-stable cobalt(I) hydride complex in conjunction with pinacolborane, we can switch the reaction outcome between two widely employed transformations, olefin migration and hydroboration, with visible light as the trigger. 相似文献
913.
Aequationes mathematicae - It is well known that Heron’s equality provides an explicit formula for the area of a triangle, as a symmetric function of the lengths of its edges. It has been... 相似文献
914.
Dr. Denise Medeiros Selegato Dr. Cesare Bracco Prof. Carlotta Giannelli Prof. Giacomo Parigi Prof. Claudio Luchinat Dr. Luca Sgheri Dr. Enrico Ravera 《Chemphyschem》2021,22(1):127-138
Conformational variability and heterogeneity are crucial determinants of the function of biological macromolecules. The possibility of accessing this information experimentally suffers from severe under-determination of the problem, since there are a few experimental observables to be accounted for by a (potentially) infinite number of available conformational states. Several computational methods have been proposed over the years in order to circumvent this theoretically insurmountable obstacle. A large share of these strategies is based on reweighting an initial conformational ensemble which arises from, for example, molecular simulations of different qualities and levels of theory. In this work, we compare the outcome of three reweighting approaches based on radically different views of the conformational heterogeneity problem, namely Maximum Entropy, Maximum Parsimony and Maximum Occurrence, and we do so using the same experimental data. In this comparison we find both expected as well as unexpected similarities. 相似文献
915.
916.
Cover Picture: Light‐Induced Porphyrin‐Based Spectroscopic Ruler for Nanometer Distance Measurements (Chem. Eur. J. 48/2016)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
917.
Erika Simona Cozza Orietta Monticelli Ornella Cavalleri Enrico Marsano 《先进技术聚合物》2012,23(9):1252-1257
Nanostructered nanofibers based on poly(vinylidene fluoride) (PVDF) and polyhedral oligomeric silsesquioxane (POSS) have been prepared by electrospinning process. The starting solutions were prepared by dissolving both the system components in the mixture N,N‐dimethylacetamide/acetone. The characteristics of the fiber prepared, studied by scanning electron microscopy, atomic force microscopy, and wide angle X‐ray diffraction, have been compared with those of PVDF fibers. Morphological characterization has demonstrated the possibility to obtain defect‐free PVDF/POSS nanofibers by properly choosing the electrospinning conditions, such as voltage, polymer concentration, humidity, etc. Conversely, in the case of fibers based on the neat polymer, it was not possible to attain the complete elimination of beads in the electrospun nanofibers. The different behavior of the two types of solutions has been ascribed to silsesquioxane molecules, which, without influencing the solution viscosity or conductivity, favor the formation of uniform structures by decreasing the system surface tension. Concerning POSS distribution in the fibers, the morphological characterization of the electrospun films has shown a submicrometric dispersion of the silsesquioxane. It is relevant to underline that cast films, prepared by the same solutions, have been found to be characterized by POSS aggregation, thus demonstrating a scarce affinity between the two‐system components. Indeed, the peculiar solvent evaporation of the electrospun solution, which is much faster than that occurring during the cast process, prevents POSS aggregation, thus leading to the formation of nanofibers characterized by a silsesquioxane dispersion similar to that present in solution. Finally, the presence of POSS improves the electrospun film mechanical properties. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
918.
I Fratoddi ES Bronze-Uhle A Batagin-Neto DM Fernandes E Bodo C Battocchio I Venditti F Decker MV Russo G Polzonetti CF Graeff 《The journal of physical chemistry. A》2012,116(34):8768-8774
The effect of (60)Co gamma rays irradiation on the polymetallayne [-Pt(PBu(3))-C≡C-C(6)H(4)-C(6)H(4)-C≡C-](n) (Pt-DEBP) of defined chain length corresponding to 10 repeat units, has been studied in detail. The UV-vis absorption spectra of Pt-DEBP have been recorded in solution upon exposure of the polymetallayne at increasing radiation doses in the range up to 90 Gy, with special care to the features related to low doses. Complex modifications of the chemical structure of Pt-DEBP could be accessed through NMR, FTIR, GPC, and XPS characterizations, which support the attack of Cl and H radicals coming from the radiolysis of the solvent, CHCl(3), to the triple C≡C bonds of the backbone, leading to the formation of chlorinated double and single C-C bonds, with a concomitant increase of the molecular weight due to a recombinant effect of oligomer fragments upon irradiation. The presence of vinyl and single chlorinated moieties has been sustained from the simulation of the UV-vis spectra based on theoretical calculations. 相似文献
919.
920.
We address the exact resolution of a Mixed Integer Non Linear Programming model where resources can be activated in order to satisfy a demand (a covering constraint) while minimizing total cost. For each resource, there is a fixed activation cost and a variable cost, expressed by means of latency functions. We prove that this problem is ${\mathcal {N} \mathcal {P}}$ -hard even for linear latency functions. A branch and bound algorithm is devised, having two important features. First, a dual bound (equal to that obtained by continuous relaxation) can be computed very efficiently at each node of the enumeration tree. Second, to break symmetries resulting in improved efficiency, the branching scheme is n-ary (instead of binary). These features lead to a successful comparison against two popular commercial and open-source solvers, CPLEX and Bonmin. 相似文献