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   27975篇
  免费   4982篇
  国内免费   3817篇
化学   20266篇
晶体学   383篇
力学   1888篇
综合类   284篇
数学   3322篇
物理学   10631篇
  2024年   25篇
  2023年   523篇
  2022年   600篇
  2021年   852篇
  2020年   1159篇
  2019年   1154篇
  2018年   984篇
  2017年   966篇
  2016年   1356篇
  2015年   1353篇
  2014年   1643篇
  2013年   2052篇
  2012年   2688篇
  2011年   2704篇
  2010年   1923篇
  2009年   1788篇
  2008年   2024篇
  2007年   1779篇
  2006年   1635篇
  2005年   1348篇
  2004年   1035篇
  2003年   880篇
  2002年   828篇
  2001年   721篇
  2000年   542篇
  1999年   523篇
  1998年   416篇
  1997年   376篇
  1996年   392篇
  1995年   318篇
  1994年   290篇
  1993年   219篇
  1992年   232篇
  1991年   227篇
  1990年   182篇
  1989年   157篇
  1988年   108篇
  1987年   86篇
  1986年   100篇
  1985年   83篇
  1984年   73篇
  1983年   59篇
  1982年   42篇
  1981年   39篇
  1980年   30篇
  1978年   25篇
  1977年   27篇
  1976年   24篇
  1974年   24篇
  1973年   27篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Journal of Radioanalytical and Nuclear Chemistry - The preparation of C30 concrete for a cavernous waste repository under construction in China and its Cs(I) adsorption performance were...  相似文献   
32.
Given their superior penetration depths, photosensitizers with longer absorption wavelengths present broader application prospects in photodynamic therapy (PDT). Herein, Ag2S quantum dots were discovered, for the first time, to be capable of killing tumor cells through the photodynamic route by near-infrared light irradiation, which means relatively less excitation of the probe compared with traditional photosensitizers absorbing short wavelengths. On modification with polydopamine (PDA), PDA-Ag2S was obtained, which showed outstanding capacity for inducing reactive oxygen species (increased by 1.69 times). With the addition of PDA, Ag2S had more opportunities to react with surrounding O2, which was demonstrated by typical triplet electron spin resonance (ESR) analysis. Furthermore, the PDT effects of Ag2S and PDA-Ag2S achieved at longer wavelengths were almost identical to the effects produced at 660 nm, which was proved by studies in vitro. PDA-Ag2S showed distinctly better therapeutic effects than Ag2S in experiments in vivo, which further validated the enhanced regulatory effect of PDA. Altogether, a new photosensitizer with longer absorption wavelength was developed by using the hitherto-unexplored photodynamic function of Ag2S quantum dots, which extended and enhanced the regulatory effect originating from PDA.  相似文献   
33.
We describe the previously unreported oxygen excess hexagonal antimony tungsten bronze with composition Sb0.5W3O10, in the following denoted as h-SbxWO3+2x with x=0.167, to demonstrate its analogy to classical AxWO3 tungsten bronzes. This compound forms in a relatively narrow temperature range between 580 °C<T<620 °C. It was obtained as a dark-blue polycrystalline powder, and as thin, needle-shaped, blue single crystals. h-SbxWO3+2x crystallizes in the hexagonal space group P6/mmm with the cell parameters a=7.4369(4) Å and c=3.7800(2) Å. The antimony and excess oxygen occupy the hexagonal channels within the network of corner-sharing WO6 octahedra. h-SbxWO3+2x has a resistivity of ρ300 K≈1.28 mΩ cm at room temperature, with little if any temperature-dependence on cooling. DFT calculations on a simplified model for this compound find a metallic-like electronic structure with the Fermi level falling within rather flat bands, especially around the Γ point.  相似文献   
34.
Flexible control of building blocks of photonic crystals enables achieving desirable band structures. Exploration of photonic band extrema has brought many fantastic features to design artificial optical materials, such as Brillouin‐zone‐corner extrema for valley photonic materials and zone‐center extremum for zero‐index metamaterials. However, two such kinds of extrema are always found independently in different photonic crystals. In this work, a kind of valley photonic crystals possessing both zone‐center and zone‐corner band extrema almost at the same frequency is proposed. Inspired by antennas theory, a three‐antenna array (TAA) source is devoted to individually manipulate each extremum. The correlation coefficient is given to determine the coupling efficiency between the TAA source and extrema eigenmodes. By using a source with a high correlation coefficient, these extrema bulk states are selectively excited consistent with their eigenfields. Furthermore, three control cases are shown that multiple extrema points are simultaneously excited, in order to confirm the validity of the correlation coefficient. Finally, a potential application of a beam‐steering device is proposed through selective excitation of ternary extrema. This work develops binary valley states into ternary mix states, rendering more degrees of freedom for on‐chip optical information transport, particularly for beam steering and mode division multiplexing.  相似文献   
35.
Journal of Solid State Electrochemistry - The effects of chemisorbed sulfate on the spatiotemporal dynamics of Na2S in strongly alkaline solutions were investigated via electrochemical measurements...  相似文献   
36.
Science China Chemistry - As bifunctional materials, phenanthrene derivatives 2,7-diphenylphenanthrene and 2,7-di(styryl)phenanthrene (DPPa and DSPa) were designed and studied. Both materials show...  相似文献   
37.
A copper-catalyzed trifunctionalization of alkynes that provides rapid access to oxindoles bearing a geminal diboronate side chain, highlighted by the simultaneous formation of one C−C bond and two C−B bonds, is reported. This new reaction features simple reaction conditions (ligand-free catalysis), a general substrate scope, and excellent chemoselectivity. Mechanistic study revealed a reaction sequence constituted by, in the order, borylation, intramolecular cross-coupling, hydroboration, which has been rarely documented.  相似文献   
38.
39.
Yin  Weidi  Cheng  Songsong  Wei  Yiheng  Shuai  Jianmei  Wang  Yong 《Numerical Algorithms》2019,82(1):201-222
Numerical Algorithms - This paper comes up with a stable bias-compensated fractional order normalized least mean square (BC-FONLMS) algorithm with noisy inputs. This kind of bias-compensated...  相似文献   
40.
[2+2] Photocycloaddition of two olefins is a general method to assemble the core scaffold, cyclobutane, found in numerous bioactive molecules. A new approach to synthesize cyclobutanes through multicomponent cascade reactions by merging aldol reaction and Witting reaction with visible-light-induced [2+2] cycloaddition is reported. An array of cyclobutanes with high selectivity has been achieved from commercially available aldehydes, ketones (or phosphorus ylide), and olefins with visible-light irradiation of a catalytic amount of (fac-tris(2-phenylpyridinato-C2,N)iridium) ([Ir(ppy)3]) at room temperature. Control experiments and spectroscopic studies revealed that the triplet–triplet energy transfer from the excited [Ir(ppy)3]* to enones, generated in situ from aldehyde and ketone or aldehyde and phosphorus ylide, is responsible for these simple and efficient muticomponent transformations.  相似文献   
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