全文获取类型
收费全文 | 4138篇 |
免费 | 157篇 |
国内免费 | 23篇 |
专业分类
化学 | 2861篇 |
晶体学 | 43篇 |
力学 | 105篇 |
数学 | 473篇 |
物理学 | 572篇 |
无线电 | 264篇 |
出版年
2023年 | 21篇 |
2022年 | 27篇 |
2021年 | 47篇 |
2020年 | 64篇 |
2019年 | 60篇 |
2018年 | 53篇 |
2017年 | 44篇 |
2016年 | 118篇 |
2015年 | 96篇 |
2014年 | 99篇 |
2013年 | 226篇 |
2012年 | 272篇 |
2011年 | 311篇 |
2010年 | 130篇 |
2009年 | 116篇 |
2008年 | 290篇 |
2007年 | 299篇 |
2006年 | 277篇 |
2005年 | 280篇 |
2004年 | 193篇 |
2003年 | 175篇 |
2002年 | 158篇 |
2001年 | 57篇 |
2000年 | 58篇 |
1999年 | 42篇 |
1998年 | 41篇 |
1997年 | 46篇 |
1996年 | 61篇 |
1995年 | 39篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 36篇 |
1991年 | 32篇 |
1990年 | 39篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 43篇 |
1983年 | 33篇 |
1982年 | 40篇 |
1981年 | 34篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1978年 | 25篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1974年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有4318条查询结果,搜索用时 15 毫秒
51.
Philemon E. Tyllianakis Sotiris E. Kakabakos Gregory P. Evangelatos Dionyssis S. Ithakissios 《Applied biochemistry and biotechnology》1993,38(1-2):15-25
The several factors that could affect the sensitivity and the accuracy of the determination of solid-supported amino groups using 2-iminothiolane (Traut's reagent) and 5,5′-dithiobis-(2-nitrobenzoic acid) (Ellman's reagent) are described. The authors found that by using 0.1M phosphate buffer, pH 8.0, instead of ethanol as solvent for the reaction of the solid supports with the 2-iminothiolane, using 0.1M phosphate buffer adjusted at pH 7.27 instead of 8.0 as diluent of 5,5′-dithiobis-(2-nitrobenzoic acid), and selecting carefully the concentration of the latter reagent, it was possible to produce a very sensitive assay capable of quantitatively determining the surface amino groups of very different types of samples. The assay is well adapted for quantitative determination of amino-carrying plastic beads, permitting the determination of nanomolar quantities. In addition, the assay is well suited for microparticulated solid supports (e.g., AH-Sepharose). 相似文献
52.
Vapor to liquid multicomponent nucleation is a dynamical process governed by a delicate interplay between condensation and evaporation. Since the population of the vapor phase is dominated by monomers at reasonable supersaturations, the formation of clusters is governed by monomer association and dissociation reactions. Although there is no intrinsic barrier in the interaction potential along the minimum energy path for the association process, the formation of a cluster is impeded by a free energy barrier. Dynamical nucleation theory provides a framework in which equilibrium evaporation rate constants can be calculated and the corresponding condensation rate constants determined from detailed balance. The nucleation rate can then be obtained by solving the kinetic equations. The rate constants governing the multistep kinetics of multicomponent nucleation including sensitivity analysis and the potential influence of contaminants will be presented and discussed. 相似文献
53.
We construct a rigid-body (five-dimensional) potential-energy surface for the water-hydrogen complex using scaled perturbation theory (SPT). An analytic fit of this surface is obtained, and, using this, two minima are found. The global minimum has C2v symmetry, with the hydrogen molecule acting as a proton donor to the oxygen atom on water. A local minimum with Cs symmetry has the hydrogen molecule acting as a proton acceptor to one of the hydrogen atoms on water, where the OH bond and H2 are in a T-shaped configuration. The SPT global minimum is bound by 1097 microEh (Eh approximately 4.359744 x 10(-18) J). Our best estimate of the binding energy, from a complete basis set extrapolation of coupled-cluster calculations, is 1076.1 microEh. The fitted surface is used to calculate the second cross virial coefficient over a wide temperature range (100-3000 K). Three complementary methods are used to quantify quantum statistical mechanical effects that become significant at low temperatures. We compare our results with experimental data, which are available over a smaller temperature range (230-700 K). Generally good agreement is found, but the experimental data are subject to larger uncertainties. 相似文献
54.
Gregory L. Eyink 《Journal of statistical physics》1995,78(1-2):353-375
Parisi and Frisch proposed some time ago an explanation for multiscaling of turbulent velocity structure functions in terms of a multifractal hypothesis, i.e., they conjecture that the velocity field has local Hölder exponents in a range [h
min,h
max], with exponents <h occurring on a setS(h) with a fractal dimensionD(h). Heuristic reasoning led them to an expression for the scaling exponentz
p
ofpth order as the Legendre transform of the codimensiond-D(h). We show here that a part of the multifractal hypothesis is correct under even weaker assumptions: namely, if the velocity field hasL
p
-mean Hölder indexs, i.e., if it lies in the Besov spaceB
p
s,
, then local Hölder regularity is satisfied. Ifs<d/p, then the hypothesis is true in a generalized sense of Hölder space with negative exponents and we discuss the proper definition of local Hölder classes of negative index. Finally, if a certain box-counting dimension exists, then the Legendre transform of its codimension gives the scaling exponentz
p
, and, more generally, the maximal Besov index of order,p, ass
p
=z
p
/p. Our method of proof is derived from a recent paper of S. Jaffard using compactly-supported, orthonormal wavelet bases and gives an extension of his results. We discuss implications of the theorems for ensemble-average scaling and fluid turbulence. 相似文献
55.
56.
57.
Yong Ryun Kim Oskar J. Sandberg Stefan Zeiske Gregory Burwell Drew B. Riley Paul Meredith Ardalan Armin 《Advanced functional materials》2023,33(16):2300147
Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been one of the most established hole transport layers (HTL) in organic solar cells (OSCs) for several decades. However, the presence of PSS− ions is known to deteriorate device performance via a number of mechanisms including diffusion to the HTL-active layer interface and unwanted local chemical reactions. In this study, it is shown that PSS− ions can also result in local p-doping in the high efficiency donor:non-fullerene acceptor blends – resulting in photocurrent loss. To address these issues, a facile and effective approach is reported to improve the OSC performance through a two-component hole transport layer (HTL) consisting of a self-assembled monolayer of 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) and PEDOT:PSS. The power conversion efficiency (PCE) of 17.1% using devices with PEDOT:PSS HTL improved to 17.7% when the PEDOT:PSS/2PACz two-component HTL is used. The improved performance is attributed to the overlaid 2PACz layer preventing the formation of an intermixed p-doped PSS− ion rich region (≈5–10 nm) at the bulk heterojunction-HTL contact interface, resulting in decreased recombination losses and improved stability. Moreover, the 2PACz monolayer is also found to reduce electrical shunts that ultimately yield improved performance in large area devices with PCE enhanced from 12.3% to 13.3% in 1 cm2 cells. 相似文献
58.
Gregory JC 《Radiation measurements》1996,26(6):841-850
The radioactive isotope 7Be was discovered on the forward-facing side of the LDEF satellite in amounts far exceeding that expected from direct cosmic ray activation of the spacecraft material. This prompted an examination of the production of cosmogenic isotopes in the atmosphere and of the processes by which they may be transported to orbital altitudes and absorbed by a spacecraft. 7Be is only one of several atmospheric cosmogenic isotopes that might be detectable at orbital altitudes and that might prove to be as useful as tracers of atmosphere ciculation processes in the mesosphre and thermosphere as they have been in the lower layers of the atmosphere. 相似文献
59.
60.