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   6916篇
  免费   979篇
  国内免费   552篇
化学   4857篇
晶体学   32篇
力学   367篇
综合类   16篇
数学   807篇
物理学   2368篇
  2024年   23篇
  2023年   153篇
  2022年   217篇
  2021年   286篇
  2020年   287篇
  2019年   242篇
  2018年   223篇
  2017年   179篇
  2016年   296篇
  2015年   286篇
  2014年   378篇
  2013年   465篇
  2012年   614篇
  2011年   622篇
  2010年   415篇
  2009年   351篇
  2008年   428篇
  2007年   380篇
  2006年   351篇
  2005年   270篇
  2004年   206篇
  2003年   159篇
  2002年   129篇
  2001年   133篇
  2000年   125篇
  1999年   135篇
  1998年   107篇
  1997年   92篇
  1996年   123篇
  1995年   103篇
  1994年   70篇
  1993年   64篇
  1992年   69篇
  1991年   57篇
  1990年   74篇
  1989年   53篇
  1988年   34篇
  1987年   29篇
  1986年   24篇
  1985年   18篇
  1984年   17篇
  1983年   17篇
  1982年   15篇
  1981年   10篇
  1979年   20篇
  1978年   15篇
  1977年   14篇
  1976年   10篇
  1975年   13篇
  1973年   13篇
排序方式: 共有8447条查询结果,搜索用时 15 毫秒
81.
The aim of this study was to investigate the feasibility of the inverse micelles (IM) technique in producing protein-loaded calcium phosphate nanoparticles (CaP NPs), and to compare this technique with the conventional co-precipitation (co-ppt) technique. In this study, bovine serum albumin and lysozyme were used as model proteins. The results show that CaP NPs produced by IM were shown to be spherical and homogenous in size of ~50 nm. Protein loading efficiency of the IM technique was shown to be much higher than CaP NPs synthesized through co-ppt technique. X-ray photoelectron spectroscopy shows that proteins were not adsorbed onto the surface of IM-synthesized CaP NPs, which suggested that the proteins were entrapped within the particle matrix. Release studies show that protein release was more rapid at lower pH conditions (pH 5 and 6) than at physiological pH of 7.4. A burst release was observed for co-ppt CaP NPs, while a continuous release of protein was observed for IM-produced CaP NPs. This study shows the superiority of the IM technique in preparing pH responsive CaP NPs as nano-carriers.  相似文献   
82.
亚波长金属线栅的设计、制备及偏振成像实验研究   总被引:3,自引:0,他引:3       下载免费PDF全文
针对红外偏振成像系统,运用等效介质理论,在氟化钙基底上设计了周期为200 nm,深度为100 nm的金属铝栅.模拟计算结果表明,设计的金属铝栅在中红外(3—5 μm)和远红外(8—12 μm)双波段范围内,以及±20°的视场范围内能够提供大于35dB的消光比.利用电子束曝光、反应离子束刻蚀、等离子去胶等工艺完成了金属铝栅的制作.将金属铝栅放在中波红外热像仪前,得到了目标轮廓清晰的偏振图像. 关键词: 亚波长衍射光栅 偏振成像 等效介质理论  相似文献   
83.
提出一种海洋溢油近红外光谱特征提取与种类鉴别新方法.海面溢油种类鉴别对现场应急处置方案的制定和可疑溢油源的追踪具有重要意义.采用傅里叶变换近红外光谱仪测定汽油、柴油、煤油三类模拟海洋溢油样本的近红外光谱,基于稀疏非负矩阵分解算法对光谱进行特征提取,采用五重交义检验,对210个样本进行训练,建立基于支持向量机的溢油光谱定...  相似文献   
84.
We investigate the entanglement dynamics of the two-qubit entanglement quantum system when they transmitted through the Pauli channels and the depolarizing channel both independently or collectively. Making use of the concurrence we found that the entanglement of a kind of mixed two-qubit system defined in this paper can be preserved in the collective Pauli σ y noise channel, but the entanglement of the other kind of mixed two-qubit system can be preserved in the collective Pauli σ z noise channel. Meanwhile, our quantum systems will undergoing the entanglement sudden death (ESD) in collective depolarizing channel when they return to the maximally entangled Bell states. The reason is the Landblad operators in depolarizing channel are non-commuting operators and this finding is in accord with the previous study.  相似文献   
85.
We present a new graded-index photonic crystal (GRIN PhC) structure which can be made by laser interference lithography (LIL). It can be applied as miniaturized focusing lens. Numerical simulations are carried out on the structures with different widths, lengths, and modulations. In the qualitative analysis of the focal length, focusing of a GRIN PhC was proved to originate from both the graded sizes of the rods and multimode interference. Multimode interference dominates the focusing effect when a GRIN PhC has a small length or a small difference in the rod sizes. Intensity distributions in different cases were given to support the conclusion.  相似文献   
86.
We have performed theoretical investigations on the structure, equation of state (EOS), elasticity, and mechanical properties of 2, 4, 6, 8, 10, 12-Hexanitrohexaazaisowurzitane (HNIW) energetic material by molecular dynamics (MD) simulations. The lattice parameters and equations of state of the four polymorphs (ε-, γ-, β-, and α-HNIW) under high pressure are calculated. Our calculated results agree with the previous experiments and theoretical calculations. Meanwhile, the elastic constants and some other mechanical properties of the most stable ε-HNIW under high pressure and temperature are predicted successfully.  相似文献   
87.
A high average power, high-repetition-rate TEA CO2 laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps. Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated.  相似文献   
88.
采用密度泛函理论中的广义梯度近似(generalized gradient approximation, 简称GGA),对内掺氢分子富勒烯H2@C60及其二聚体的几何结构和电子结构进行了计算研究.发现无论是在H2@C60单体,还是在其二聚体中,氢倾向以分子形式存在于碳笼中心处,且在室温下氢分子可以做自由旋转.电子结构分析表明,氢分子掺入到C60和C120中,仅对距离费米能级以下-8eV至-5eV能级处有一定的贡献,其他能级的分布和能隙几乎没有变化.  相似文献   
89.
Neutral spin texture (ST) excitations at nu=1/3 are directly observed for the first time by resonant inelastic light scattering. They are determined to involve two simultaneous spin flips. At low magnetic fields, the ST energy is below that of the magnetoroton minimum. With increasing in-plane magnetic field these mode energies cross at a critical ratio of the Zeeman and Coulomb energies of eta(c)=0.020+/-0.001. Surprisingly, the intensity of the ST mode grows with temperature in the range in which the magnetoroton modes collapse. The temperature dependence is interpreted in terms of a competition between coexisting phases supporting different excitations. We consider the role of the ST excitations in activated transport at nu=1/3.  相似文献   
90.
In this paper, we developed a new kind of substrate, the silver-coated anodic aluminum oxide (AAO), to investigate the characters of surface-enhanced resonant Raman scattering (SERRS) of the dilute single-walled carbon nanotubes. Homogeneous Ag-coated AAO substrate was obtained by decomposing the AgNO3 on the surface of AAO. single-walled carbon nanotubes (SWNTs) were directly grown onto this substrate through floating catalyst chemical vapor deposition method (CVD). SERRS of SWNTs was carried out using several different wavelength lasers. The bands coming from metallic SWNTs were significantly enhanced. The two SERRS mechanisms, the “electromagnetic” and “chemical” mechanism, were mainly responsible for the experiment results.  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