全文获取类型
收费全文 | 1258篇 |
免费 | 12篇 |
国内免费 | 11篇 |
专业分类
化学 | 323篇 |
晶体学 | 7篇 |
力学 | 185篇 |
数学 | 486篇 |
物理学 | 280篇 |
出版年
2022年 | 33篇 |
2021年 | 17篇 |
2020年 | 37篇 |
2019年 | 17篇 |
2018年 | 29篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 42篇 |
2013年 | 66篇 |
2012年 | 52篇 |
2011年 | 79篇 |
2010年 | 58篇 |
2009年 | 49篇 |
2008年 | 54篇 |
2007年 | 50篇 |
2006年 | 52篇 |
2005年 | 37篇 |
2004年 | 30篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 34篇 |
2000年 | 21篇 |
1999年 | 29篇 |
1998年 | 19篇 |
1997年 | 7篇 |
1996年 | 24篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1990年 | 10篇 |
1987年 | 10篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 19篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1971年 | 7篇 |
1968年 | 10篇 |
1967年 | 6篇 |
1956年 | 6篇 |
排序方式: 共有1281条查询结果,搜索用时 15 毫秒
71.
We consider stochastic equations in Hilbert spaces with singular drift in the framework of [G. Da Prato, M. Röckner, Singular dissipative stochastic equations in Hilbert spaces, Probab. Theory Related Fields 124 (2) (2002) 261-303]. We prove a Harnack inequality (in the sense of [F.-Y. Wang, Logarithmic Sobolev inequalities on noncompact Riemannian manifolds, Probab. Theory Related Fields 109 (1997) 417-424]) for its transition semigroup and exploit its consequences. In particular, we prove regularizing and ultraboundedness properties of the transition semigroup as well as that the corresponding Kolmogorov operator has at most one infinitesimally invariant measure μ (satisfying some mild integrability conditions). Finally, we prove existence of such a measure μ for noncontinuous drifts. 相似文献
72.
For a general class of divergence type quasi-linear degenerate parabolic equations with measurable coefficients and lower order terms from nonlinear Kato-type classes, we prove local boundedness and continuity of solutions, and the intrinsic Harnack inequality for positive solutions. 相似文献
73.
《Stochastic Processes and their Applications》2019,129(11):4576-4596
The asymptotic log-Harnack inequality is established for several kinds of models on stochastic differential systems with infinite memory: non-degenerate SDEs, neutral SDEs, semi-linear SPDEs, and stochastic Hamiltonian systems. As applications, the following properties are derived for the associated segment Markov semigroups: asymptotic heat kernel estimate, uniqueness of the invariant probability measure, asymptotic gradient estimate (hence, asymptotically strong Feller property), as well as asymptotic irreducibility. 相似文献
74.
《Physics letters. [Part B]》2004,578(1-2):23-32
We show that antihydrogen production is the dominant process when mixing antiprotons and positrons in the ATHENA apparatus, and that the initial production rate exceeds 300 Hz, decaying to 30 Hz within 10 s. A fraction of 65% of all observed annihilations is due to antihydrogen. 相似文献
75.
Stefaan J. Soenen Bella B. Manshian Abuelmagd M. Abdelmonem José‐María Montenegro Sisareuth Tan Lieve Balcaen Frank Vanhaecke Alain R. Brisson Wolfgang J. Parak Stefaan C. De Smedt Kevin Braeckmans 《Particle & Particle Systems Characterization》2014,31(7):794-800
Poly(ethylene glycol) (PEG) is frequently used to coat various medical nanoparticles (NPs). As PEG is known to minimize NP interactions with biological specimens, the question remains whether PEGylated NPs are intrinsically less toxic or whether this is caused by reduced NP uptake. In the present work, the effect of gold NP PEGylation on uptake by three cell types is compared and evaluated the effect on cell viability, oxidative stress, cell morphology, and functionality using a multiparametric methodology. The data reveal that PEGylation affects cellular NP uptake in a cell‐type‐dependent manner and influences toxicity by different mechanisms. At similar intracellular NP numbers, PEGylated NPs are found to yield higher levels of cell death, mostly by induction of oxidative stress. These findings reveal that PEGylation significantly reduces NP uptake, but that at similar functional (= cell‐associated) NP levels, non‐PEGylated NPs are better tolerated by the cells. 相似文献
76.
E. Lodi-Rizzini V. Mascagna L. Venturelli N. Zurlo M. Charlton 《Hyperfine Interactions》2014,228(1-3):53-60
Antihydrogen is now routinely produced at CERN by overlapping clouds of positrons and antiprotons. The mechanisms responsible for antihydrogen formation (radiative capture and the three-body reaction) are both dependent on the temperature of the positrons (T e ), though with a different weight. Here we present a simple model of the behavior of the positron temperature based on the main processes involved during antihydrogen synthesis, namely: antiproton–positron collisions, positron heating due to plasma expansion and cooling via the emission of synchrotron radiation. The time evolution of T e has been simulated by changing the relevant parameters of the mechanisms involved in order to highlight the importance of the different (competing) effects. 相似文献
77.
《ournal of non Newtonian Fluid Mechanics》2002,102(1):97-107
It is shown that steady channel, simple shear and Couette flows of a Bingham fluid come to rest in a finite amount of time, if either the applied pressure falls below a critical value, or the moving boundaries are brought to rest. An explicit formula for a bound on the finite stopping time in each case is derived. This bound depends on the density, the viscosity, the yield stress, a new geometric constant, and the least eigenvalue of the second order linear differential operator for the interval under consideration. 相似文献
78.
《Solid State Communications》2002,121(9-10):493-496
The CuGaS2 crystallites with different morphologies were prepared at 160 °C through hydrothermal process by using CuCl, GaCl3 solution, and thiourea as source materials. The samples were characterized by means of X-ray powder diffraction, element analysis, transmission electron microscopy, and photoluminescence (PL). In present route, as-prepared CuGaS2 crystallites displayed spherical and whisker-like nanoparticles and snowflake-like micrometer particles. Room temperature PL spectrum of the snowflake-like crystallites exhibits a weak emission band at 540 nm and a broad strong emission band at 735 nm. The role that the reaction media played in the morphologies of the CuGaS2 crystallites was investigated, and a possible reaction mechanism was proposed. 相似文献
79.
《Superlattices and Microstructures》2000,28(1):35-45
We have theoretically investigated the subband structure of single Si δ -doped GaAs inserted into a quantum well at T = 0 K. We will discuss the influence of the δ -doping concentration, the δ -layer thickness and diffusion of donor impurities. The spread of the impurities are taken into account in two different models: (i) a uniform distribution and (ii) a nonuniform distribution. In this paper, the nonuniform distribution is different from the Gaussian distribution use of other authors. The electronic structures have been calculated by solving the Schrödinger and Poisson equations self-consistently. We thus find the confining potential, the subband energies and their eigen envelope functions, the subband occupations and Fermi energy. 相似文献
80.
Sergio Albeverio Yeneng Sun Jiang-Lun Wu 《Transactions of the American Mathematical Society》2007,359(2):517-527
It is shown that for a large collection of independent martingales, the martingale property is preserved on the empirical processes. Under the assumptions of independence and identical finite-dimensional distributions, it is proved that a large collection of stochastic processes are martingales essentially if and only if the empirical processes are also martingales. These two results have implications on the testability of the martingale property in scientific modeling. Extensions to submartingales and supermartingales are given.