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101.
4‐Hydrazino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 4 ) were cyclocondensed with formic acid or triethyl orthoformate to give 7H‐1,2,4‐triazolo[1,5‐c]pyrrolo[3,2‐e]pyrimidines ( 5 ) and 7H‐1,2,4‐triazolo[4,3‐c]pyrrolo‐[3,2‐e]pyrimidines ( 6 ) respectively. The [4,3‐c]‐isomers ( 6 ) were rearranged into thermodynamically more stable [1,5‐c]‐isomers ( 5 ). The identical compounds ( 5 ) were prepared using another route by reacting 3‐amino‐4‐imino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 3 ) with formic acid or triethylorthoformate. Reaction of 2‐amino‐3‐cyanopyrroles ( 1 ) with triethyl orthoformate followed by hydrazinolysis afforded ( 3 ) via the formation of N‐ethoxymethylene‐2‐amino‐3‐cyanopyrroles ( 2 ). 相似文献
102.
Cara N. Gannett Jaehwan Kim Dave Tirtariyadi Phillip J. Milner Hctor D. Abrua 《Chemical science》2022,13(32):9191
Organic electrode materials offer unique opportunities to utilize ion-electrode interactions to develop diverse, versatile, and high-performing secondary batteries, particularly for applications requiring high power densities. However, a lack of well-defined structure–property relationships for redox-active organic materials restricts the advancement of the field. Herein, we investigate a family of diimide-based polymer materials with several charge-compensating ions (Li+, Na+, K+) in order to systematically probe how redox-active moiety, ion, and polymer flexibility dictate their thermodynamic and kinetic properties. When favorable ion-electrode interactions are employed (e.g., soft K+ anions with soft perylenediimide dianions), the resulting batteries demonstrate increased working potentials and improved cycling stabilities. Further, for all polymers examined herein, we demonstrate that K+ accesses the highest percentage of redox-active groups due to its small solvation shell/energy. Through crown ether experiments, cyclic voltammetry, and activation energy measurements, we provide insights into the charge compensation mechanisms of three different polymer structures and rationalize these findings in terms of the differing degrees of improvements observed when cycling with K+. Critically, we find that the most flexible polymer enables access to the highest fraction of active sites due to the small activation energy barrier during charge/discharge. These results suggest that improved capacities may be accessible by employing more flexible structures. Overall, our in-depth structure–activity investigation demonstrates how variables such as polymer structure and cation can be used to optimize battery performance and enable the realization of novel battery chemistries.Organic electrode materials offer unique opportunities to utilize ion-electrode interactions to develop diverse, versatile, and high-performing secondary batteries, particularly for applications requiring high power densities. 相似文献
103.
Robert W. Haas Dennis Brest Harry Mueggenburg Lee Lang Dave Heimlich 《International Journal of Infrared and Millimeter Waves》1993,14(11):2289-2294
Future spaceborne millimeter and sub-millimeter wave sensing systems will require the sensitivity and resolution only achievable with large focal plane array receiving systems. A technique has been developed for the low cost fabrication of large arrays of millimeter and sub-millimeter wave corrugated feed horns. These arrayed horns exhibit high efficiency and symmetrical receiving patterns and are compatible with integrated receivers. W-band test results of a 3×3 array are presented. 相似文献
104.
The extraordinary opportunities offered by integrating solution chemistry of molecular entities with the solid-state nature of the gel provide the basis for designing a number of novel molecular materials. Herein, we present a strategy based on encapsulation of suitable response active species to impart useful optical properties to sol–gel glasses. The basic concept of this molecular programming approach is based on deliberate incorporation of response-active species in the silica gel framework to elicit specific optical responses. Design of molecular materials for device applications depends on selection of molecules which exhibit well-defined electronic or optical response, and assembly of these molecular components into a geometric structure that retains the rigidity, addressability, and stability necessary for practical applications. The approach is based on using molecules as active species and sol–gel glass as structural matrix in which the molecules are selectively integrated. A designer approach that employs specific molecules for generating optical signals is described. As such the properties of these silica-based glasses can be tuned by varying the composition of encapsulated species. These modified glasses exhibit substantially altered optical properties as compared to pristine silica sol–gels. The optical response of these materials provide initial examples toward designing novel materials whose optical and/or photonic responses can be modulated by structural integration of specific dopant entities. 相似文献
105.
106.
Dave Powell Max A. Migliorato Anthony G. Cullis 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):270
We report on the use of the Tersoff empirical potential applied to GaAs. Cohesive and elastic properties, as well as phonon frequencies and Grüneisen parameters at the Γ and X points, are calculated and compared to experimental data. The limitations of the potential and its existing parametrisations are discussed. 相似文献
107.
108.
Let G = SL(n, ?) (or, more generally, let G be a connected, noncompact, simple Lie group). For any compact Lie group K, it is easy to find a compact manifold M, such that there is a volume-preserving, connection-preserving, ergodic action of G on some smooth, principal K-bundle P over M. Can M can be chosen independent of K? We show that if M = H/Λ is a homogeneous space, and the action of G on M is by translations, then P must also be a homogeneous space H′Λ′. Consequently, there is a strong restriction on the groups K that can arise over this particular M. 相似文献
109.
The fundamental group and rational cohomology of the configuration spaces of the Skyrme and Faddeev-Hopf models are computed.
Physical space is taken to be a compact oriented 3-manifold, either with or without a marked point representing an end at
infinity. For the Skyrme model, the codomain is any Lie group, while for the Faddeev-Hopf model it is S2. It is determined when the topology of configuration space permits fermionic and isospinorial quantization of the solitons
of the model within generalizations of the frameworks of Finkelstein-Rubinstein and Sorkin. Fermionic quantization of Skyrmions
is possible only if the target group contains a symplectic or special unitary factor, while fermionic quantization of Hopfions
is always possible. Geometric interpretations of the results are given.
The first author was partially supported by NSF grant DMS-0204651
The second author was partially supported by EPSRC grant GR/R66982/01 相似文献
110.
A procedure for the determination of phenolic pesticides, i.e. the hydroxybenzonitriles bromoxynil and ioxynil and the 2,4-dinitrophenol-derivatives
dinoseb, dinosebacetate, dinoterb, dinoterbacetate, dinobuton, binapacryl and DNOC is presented. The herbicides with a free
phenolic OH-group as well as the corresponding esters are very strongly adsorbed on Carbopack B, a special graphitized carbon
black. In contrast to the esters, which can be removed almost quantitatively, the substances with a free phenolic OH-group
cannot be eluted in any significant amount. This effect was used for the derivatization of the herbicides directly on Carbopack
B, using diazomethane or TMSH as reagents. The derivatives were eluted with ethylacetate and identified and quantified by
GC/MS.
For recovery studies, water samples were spiked with the pesticides in concentrations within the range tolerated by the European
Drinking Water Guideline.
Received: 25 March 1996/Revised: 12 June 1996/Accepted: 17 June 1996 相似文献