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   46506篇
  免费   4504篇
  国内免费   3108篇
化学   32179篇
晶体学   392篇
力学   1549篇
综合类   77篇
数学   6817篇
物理学   13104篇
  2023年   567篇
  2022年   693篇
  2021年   1181篇
  2020年   1140篇
  2019年   1158篇
  2018年   1213篇
  2017年   1064篇
  2016年   2026篇
  2015年   1651篇
  2014年   1988篇
  2013年   3555篇
  2012年   3590篇
  2011年   3909篇
  2010年   2392篇
  2009年   2485篇
  2008年   2719篇
  2007年   2480篇
  2006年   2230篇
  2005年   1954篇
  2004年   2029篇
  2003年   1463篇
  2002年   1403篇
  2001年   883篇
  2000年   729篇
  1999年   757篇
  1998年   607篇
  1997年   602篇
  1996年   585篇
  1995年   516篇
  1994年   418篇
  1993年   455篇
  1992年   365篇
  1991年   327篇
  1990年   299篇
  1989年   260篇
  1988年   252篇
  1987年   229篇
  1986年   233篇
  1985年   277篇
  1984年   276篇
  1983年   219篇
  1982年   209篇
  1981年   182篇
  1980年   193篇
  1979年   147篇
  1978年   179篇
  1977年   156篇
  1976年   148篇
  1974年   144篇
  1973年   135篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures...  相似文献   
22.
23.
24.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature.  相似文献   
25.
26.
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.  相似文献   
27.
The design and exploration of efficient, stable and environmentally compatible organic emitters for an electrochemiluminescence (ECL) sensor is a promising topic. Herein, a novel environmentally-friendly luminophore, ZnBCBTP@MWCNTs, were fabricated via self-assembly of porphyrin molecules (ZnBCBTP) onto multi-walled carbon nanotubes (MWCNTs). The resulting luminophore ZnBCBTP@MWCNTs displayed not only the highly ECL property and but also the good accelerated electron mobility. Then, a label-free ECL biosensor based ZnBCBTP@MWCNTs was constructed for the ultrasensitive detection of uric acid. Excitingly, this proposed ECL biosensor performed a good linear relationship in the range of 0–300 μM with a low detection limit of 1.4 μM, thus offering another reliable and feasible sensing platform for clinical bioanalysis with good selectivity, stability, and repeatability.  相似文献   
28.
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme.  相似文献   
29.
30.
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