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   19753篇
  免费   2748篇
  国内免费   1701篇
化学   8911篇
晶体学   234篇
力学   1944篇
综合类   30篇
数学   3042篇
物理学   10041篇
  2024年   34篇
  2023年   955篇
  2022年   761篇
  2021年   871篇
  2020年   1098篇
  2019年   639篇
  2018年   742篇
  2017年   984篇
  2016年   1002篇
  2015年   1026篇
  2014年   1194篇
  2013年   1203篇
  2012年   1429篇
  2011年   1182篇
  2010年   1089篇
  2009年   1078篇
  2008年   744篇
  2007年   854篇
  2006年   953篇
  2005年   590篇
  2004年   391篇
  2003年   400篇
  2002年   397篇
  2001年   587篇
  2000年   274篇
  1999年   535篇
  1998年   354篇
  1997年   268篇
  1996年   166篇
  1995年   147篇
  1994年   97篇
  1993年   105篇
  1992年   110篇
  1991年   84篇
  1990年   78篇
  1989年   104篇
  1988年   484篇
  1987年   798篇
  1986年   349篇
  1985年   12篇
  1984年   5篇
  1983年   2篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1971年   7篇
  1963年   1篇
  1959年   1篇
  1957年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
In this paper we consider minimizers of the functionalmin{λ1(Ω)++λk(Ω)+Λ|Ω|,:ΩD open} where DRd is a bounded open set and where 0<λ1(Ω)λk(Ω) are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets Ω have finite perimeter and that their free boundary ΩD is composed of a regular part, which is locally the graph of a C1,α-regular function, and a singular part, which is empty if d<d, discrete if d=d and of Hausdorff dimension at most dd if d>d, for some d{5,6,7}.  相似文献   
3.
4.
Annals of the Institute of Statistical Mathematics - In this paper, a model averaging approach is developed for the linear regression models with response missing at random. It is shown that the...  相似文献   
5.
Herein, we propose the construction of a sandwich-structured host filled with continuous 2D catalysis–conduction interfaces. This MoN-C-MoN trilayer architecture causes the strong conformal adsorption of S/Li2Sx and its high-efficiency conversion on the two-sided nitride polar surfaces, which are supplied with high-flux electron transfer from the buried carbon interlayer. The 3D self-assembly of these 2D sandwich structures further reinforces the interconnection of conductive and catalytic networks. The maximized exposure of adsorptive/catalytic planes endows the MoN-C@S electrode with excellent cycling stability and high rate performance even under high S loading and low host surface area. The high conductivity of this trilayer texture does not compromise the capacity retention after the S content is increased. Such a job-synergistic mode between catalytic and conductive functions guarantees the homogeneous deposition of S/Li2Sx, and avoids thick and devitalized accumulation (electrode passivation) even after high-rate and long-term cycling.  相似文献   
6.
The accumulation of material degradation under contact with aggressive aqueous environments could lead to reduced structural reliability. In terms of hydrated cementitious materials, such interactions often result in the chemo-physical-mechanical (CPM) degradation, which represents a multiphysics process of high non-linearity and complexity. By further considering the inevitable uncertainties associated with both the materials and the serving conditions, solving such a process requires novel probabilistic approaches. This paper presents a stochastic chemo-physical-mechanical (SCPM) degradation analysis on the hydrated cement under acidic environment. The SCPM analysis consists of modelling the stochastic chemophysical degradation by finite element method, and assessing the mechanical deterioration through analytical micromechanics. The proposed modelling framework couples the conventional Monte Carlo Simulation with a novel support vector regression algorithm. The present method is able to not only address the detailed degradation mechanisms, but also ensure low computational costs for an accurate SCPM degradation assessment.  相似文献   
7.
Novel pyrene‐fused unsymmetrical phthalocyanine derivatives 2,3,9,10,16,17‐hexakis(2,6‐dimethylphenoxy)‐22,25‐diaza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc complex Zn[Pc(Pz‐pyrene)(OC8H9)6] ( 1 ) and 2,3,9,10‐tra(2,6‐dimethylphenoxy)‐15,18,22,25‐traza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc compound Zn[Pc(Pz‐pyrene)2(OC8H9)4] ( 2 ) were isolated for the first time. These unsymmetrical pyrene‐fused phthalocyanine derivatives have been characterized by a wide range of spectroscopic and electrochemical methods. In particular, the pyrene‐fused phthalocyanine structure was unambiguously revealed on the basis of single crystal X‐ray diffraction analysis of 1 , representing the first structurally characterized phthalocyanine derivative fused with an aromatic moiety larger than benzene.  相似文献   
8.
Field-effect transistors (FETs) are one of the most widely-used electronic sensors for continuous monitoring and detection of contaminants such as pharmaceuticals and endocrine-disrupting compounds at low concentrations. FETs have been successfully utilized for the rapid analysis of these environmental pollutants due to their advantageous material properties like the disposability, rapid responses and simplicity. This paper presented an up-to-date overview of applied strategies with different bio-based materials in order to enhance the analytical performances of the designed sensors. Comparison and discussion were made between characteristics of recently engineered FET bio-sensors used for the detection of famous and selected pharmaceutical compounds in the literature. The recent progress in environmental research applications, comments on interesting trends, current challenge for future research in endocrine-disrupting chemicals’ (EDCs) detection using FETs biosensors were highlighted.  相似文献   
9.
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics.  相似文献   
10.
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