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   30914篇
  免费   4934篇
  国内免费   3503篇
化学   22828篇
晶体学   373篇
力学   1615篇
综合类   169篇
数学   2908篇
物理学   11458篇
  2024年   110篇
  2023年   582篇
  2022年   1052篇
  2021年   1115篇
  2020年   1263篇
  2019年   1248篇
  2018年   1134篇
  2017年   966篇
  2016年   1476篇
  2015年   1473篇
  2014年   1818篇
  2013年   2374篇
  2012年   2753篇
  2011年   2796篇
  2010年   1953篇
  2009年   1842篇
  2008年   2056篇
  2007年   1870篇
  2006年   1665篇
  2005年   1469篇
  2004年   1146篇
  2003年   969篇
  2002年   986篇
  2001年   697篇
  2000年   593篇
  1999年   555篇
  1998年   470篇
  1997年   416篇
  1996年   380篇
  1995年   307篇
  1994年   322篇
  1993年   237篇
  1992年   229篇
  1991年   198篇
  1990年   158篇
  1989年   141篇
  1988年   82篇
  1987年   60篇
  1986年   68篇
  1985年   63篇
  1984年   42篇
  1983年   27篇
  1982年   29篇
  1981年   24篇
  1980年   26篇
  1979年   9篇
  1976年   14篇
  1975年   13篇
  1974年   14篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
基于EPP协议的便携机数据采集系统   总被引:1,自引:0,他引:1  
韩松  芦汉生  徐宁 《光学技术》2002,28(3):273-274
设计了基于EPP协议的便携机数据采集系统 ,给出了技术解决方案。方案具有软硬件设计简捷、无需插卡等优点 ,可使外设工作于PC并行口的多种模式下。解决了线阵CCD图像采集系统与笔记本电脑之间的数据通讯 ,达到了便携数据采集的目的。  相似文献   
93.
Ranked-set sampling is useful when measurements are destructive or costly to obtain but ranking of the observations is relatively easy. The Wilcoxon signed rank test statistic based on the ranked-set sample is considered. We compared the asymptotic relative efficiencies of the RSS Wilcoxon signed rank test statistic with respect to the SRS Wilcoxon signed rank test statistic and the RSS sign test statistic. Throughout the ARE’s, the proposed test statistic is superior to the SRS Wilcoxon signed rank test statistic and the RSS sign test statistic.  相似文献   
94.
Chemisorption of polybenzimidazole on silver and copper etched with nitric acid has been observed by surface-enhanced Raman scattering (SERS). The polymer is found to react chemically with silver, forming a complexed film on the surface. The SERS spectra show that polybenzimidazole film inhibits oxidation of the metal at high temperature, unlike chemisorbed benzimidazole, benzotriazole, and poly(4-vinyl pyridine). © 1992 John Wiley & Sons, Inc.  相似文献   
95.
中国西南武陵山区跳蛛新种记述(蜘蛛目:跳蛛科)   总被引:2,自引:0,他引:2  
本文记述跳蛛科13个新种,采自西南武陵山地区。暗跳蛛Asemonea、列锡蛛Lycidas和法老蛛Pharacocerus 3属为我国新记录属。  相似文献   
96.
The use of Cu-doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 as self-pumped phase conjugators using internal reflection is reported. Reflectivities as high as 63% at 5145.5 nm and 60% at 632.8 nm were realized. It was found that the photorefractive response changes significantly at different doping concentration. The responses of the crystals to the laser wavelength, incident angle and dopant concentration are studied.  相似文献   
97.
In this article, the linear and nonlinear shear rheological behaviors of polylactide (PLA)/clay (organophilic‐montmorillonite) nanocomposites (PLACNs) were investigated by an Advanced Rheology Expanded System rheometer. The nanocomposites were prepared by master batch method using a twin‐screw extruder with poly(ε‐caprolactone) (PCL) as a compatibilizer. The presence of org‐MMT leads to obvious pseudo‐solid‐like behaviors of nanocomposite melts. The behaviors caused by the formation of a “percolating network” derived from the reciprocity among the strong related sheet particles. Therefore, the storage moduli, loss moduli, and dynamic viscosities of PLACNs show a monotonic increase with MMT content. Nonterminal behaviors exists in PLACNs nanocomposites. Besides the PLACNs melts show a greater shear thinning tendency than pure PLA melt because of the preferential orientation of the MMT layers. Therefore, PLACNs have higher moduli but better processibility compared with pure PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3189–3196, 2007  相似文献   
98.
The crystallization behavior of miscible syndiotactic polystyrene (sPS) and atactic polystyrene (aPS) blends with different sPS/aPS weight ratios was investigated in supercritical CO2 by using Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and wide‐angle X‐ray diffraction. Supercritical CO2 and aPS exhibited different effects on the conformational change of sPS and competed with each other. Increasing the content of amorphous aPS in the blends made its effect on the conformational change of sPS gradually surpass that of supercritical CO2. Supercritical CO2 favored the formation of the helical conformation of sPS in lower temperature range and the all trans planar conformation in higher temperature range, instead of forming the latter one only in higher temperature range in ambient atmosphere. However, increasing aPS content in the blends pushed the range for forming the helical conformation to lower temperature and made the all trans planar conformation dominant in aPS/sPS 25/75 blend after treating in supercritical CO2 above 60 °C. The all trans planar zigzag conformation was more favorable than the helical conformation after mixing aPS in sPS in supercritical CO2. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1755–1764, 2007  相似文献   
99.
In the title centrosymmetric binuclear complex, [Cd2(C17H11N3O)4(H2O)2](ClO4)4, the CdII ion assumes a distorted octahedral geometry. There are π–π stacking interactions between the pyridine and 1,10‐phenanthroline ring systems of adjacent ligands at the same CdII centre. Intermolecular hydrogen bonds between the coordinated aqua ligand and the O atom of a keto group connect adjacent complex cations into extended chains. Hydrogen bonds also exist between the complex cations and the perchlorate anions. Compared with the fluorescence spectrum of the organic ligand, the complex displays strong fluorescent emission and an ipsochromic shift of the emission peaks, which may be attributed to the structural character.  相似文献   
100.
冠状动脉支架为圆柱形微型网状结构,直径1mm,厚度0.1mm,长度10~16mm。在经皮冠状动脉介入PCI治疗中由球囊充气撑开到直径为2.5~3.5mm的支架,在血管内承受血管壁回弹压力。为了保持血液流通支架必须保持其几何圆形。这是一个结构弹塑性稳定性问题。但是目前国际上对于支架的力学性能质量指标主要以强度性能评定而不涉及支架屈曲性能是不妥的。本文对于支架的强度和屈曲性能进行了全面的理论分析和实验研究,自行研制了智能式电子检测仪成功地对微型网状结构支架的强度和屈曲性能实现了实测实验研究。由于微型支架的离散型网状结构的特点,在实验中出现一些特殊的屈曲现象。本文研究结果对于支架的形状与性能设计的改进和力学性能质量标准规范的制订具有重要意义。  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