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   105329篇
  免费   1370篇
  国内免费   388篇
化学   42068篇
晶体学   1082篇
力学   7182篇
数学   36510篇
物理学   20245篇
  2023年   178篇
  2022年   240篇
  2021年   363篇
  2020年   457篇
  2019年   481篇
  2018年   10842篇
  2017年   10643篇
  2016年   7100篇
  2015年   1729篇
  2014年   1304篇
  2013年   2376篇
  2012年   5470篇
  2011年   11999篇
  2010年   6648篇
  2009年   6937篇
  2008年   8102篇
  2007年   10178篇
  2006年   1651篇
  2005年   2575篇
  2004年   2671篇
  2003年   2836篇
  2002年   1768篇
  2001年   838篇
  2000年   834篇
  1999年   544篇
  1998年   488篇
  1997年   415篇
  1996年   540篇
  1995年   370篇
  1994年   340篇
  1993年   318篇
  1992年   276篇
  1991年   296篇
  1990年   262篇
  1989年   259篇
  1988年   249篇
  1987年   243篇
  1986年   239篇
  1985年   345篇
  1984年   342篇
  1983年   218篇
  1982年   224篇
  1981年   245篇
  1980年   244篇
  1979年   197篇
  1978年   171篇
  1977年   153篇
  1976年   136篇
  1975年   134篇
  1973年   123篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
21.
22.
23.
Journal of Thermal Analysis and Calorimetry - The work concerns the alumina–graphene materials sintered by two different pressure methods. The different particle sizes of graphene were used....  相似文献   
24.
25.
Algebras and Representation Theory - We introduce and study the category of twisted modules over a triangular differential graded bocs. We show that in this category idempotents split, that it...  相似文献   
26.
Journal of Thermal Analysis and Calorimetry - Buckwheat starch is an alternative source to supply the high global demand for starch. The properties of starch can be modified through chemical and...  相似文献   
27.
The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria), and its structure and action is related to human neurotransmitter γ-aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear 1H and 13C nuclear magnetic resonance (NMR) experiments supported by density functional theory molecular modeling. The structures of three forms of free muscimol molecule both in the gas phase and in the presence of water solvent, modeled by polarized continuous model, and nuclear magnetic isotropic shieldings, the corresponding chemical shifts, and indirect spin–spin coupling constants were calculated. Several J-couplings observed in proton and carbon NMR spectra, not available before, are reported. The obtained experimental spectra, supported by theoretical calculations, favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in dimethyl sulfoxide (DMSO) solution. In addition, positions of signals C3 and C5 are reversed in both solvents.  相似文献   
28.
Metabolomics is a potential tool for the discovery of new biomarkers in the early diagnosis of diseases. An ultra-fast gas chromatography system equipped to an electronic nose detector (FGC eNose) was used to identify the metabolomic profile of Volatile Organic Compounds (VOCs) in type 2 diabetes (T2D) urine from Mexican population. A cross-sectional, comparative, and clinical study with translational approach was performed. We recruited twenty T2D patients and twenty-one healthy subjects. Urine samples were taken and analyzed by FGC eNose. Eighty-eight compounds were identified through Kovats's indexes. A natural variation of 30% between the metabolites, expressed by study groups, was observed in Principal Component 1 and 2 with a significant difference (p < 0.001). The model, performed through a Canonical Analysis of Principal coordinated (CAP), allowed a correct classification of 84.6% between healthy and T2D patients, with a 15.4% error. The metabolites 2-propenal, 2-propanol, butane- 2,3-dione and 2-methylpropanal, were increased in patients with T2D, and they were strongly correlated with discrimination between clinically healthy people and T2D patients. This study identified metabolites in urine through FGC eNose that can be used as biomarkers in the identification of T2D patients. However, more studies are needed for its implementation in clinical practice.  相似文献   
29.
30.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  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