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   1677篇
  免费   63篇
  国内免费   8篇
化学   1327篇
晶体学   31篇
力学   23篇
数学   171篇
物理学   196篇
  2023年   9篇
  2022年   9篇
  2021年   14篇
  2020年   23篇
  2019年   31篇
  2018年   17篇
  2017年   21篇
  2016年   39篇
  2015年   36篇
  2014年   40篇
  2013年   97篇
  2012年   112篇
  2011年   115篇
  2010年   55篇
  2009年   68篇
  2008年   116篇
  2007年   108篇
  2006年   100篇
  2005年   93篇
  2004年   94篇
  2003年   80篇
  2002年   65篇
  2001年   12篇
  2000年   29篇
  1999年   12篇
  1998年   24篇
  1997年   23篇
  1996年   18篇
  1995年   15篇
  1994年   7篇
  1993年   10篇
  1992年   17篇
  1991年   12篇
  1990年   12篇
  1989年   11篇
  1988年   7篇
  1987年   16篇
  1986年   6篇
  1985年   14篇
  1984年   14篇
  1983年   16篇
  1982年   20篇
  1981年   12篇
  1980年   24篇
  1979年   15篇
  1978年   14篇
  1976年   11篇
  1975年   8篇
  1974年   5篇
  1973年   7篇
排序方式: 共有1748条查询结果,搜索用时 15 毫秒
991.
In this paper, we are going to describe the first and second complex interpolations of closed subspaces of Morrey spaces, based on our previous results in [11]. Our results will be general enough because we are going to deal with abstract linear subspaces satisfying the lattice condition only. We also consider the closure in Morrey spaces on bounded domains of the set of smooth functions with compact support. Here, we do not require the smoothness condition on domains.  相似文献   
992.
Germanene is a two-dimensional germanium (Ge) analogous of graphene, and its unique topological properties are expected to make it a material for next-generation electronics. However, no germanene electronic devices have yet been reported. One of the reasons for this is that germanene is easily oxidized in air due to its lack of chemical stability. Therefore, growing germanene at solid interfaces where it is not oxidized is one of the key steps for realizing electronic devices based on germanene. In this study, the behavior of Ge at the solid interface at high temperatures is observed by transmission electron microscopy (TEM). To achieve such in situ heating TEM observation, this work fabricates a graphene/Ge/graphene encapsulated structure. In situ heating TEM experiments reveal that Ge like droplets move and coalesce with other Ge droplets, indicating that Ge remains as a liquid phase between graphene layers at temperatures higher than the Ge melting point. It is also observed that Ge droplets incorporate the surrounding amorphous Ge as Ge nuclei, thereby increasing its size (domain growth). These results indicate that Ge crystals can be grown at the interface of van der Waals materials, which will be important for future germanene growth at solid interfaces.  相似文献   
993.
994.
995.
2,5‐Bis(4‐propyl‐2‐pyrrolyl)thiophene was reacted with aryl aldehydes to afford large porphyrinoids; [24]dithiaamethyrin(1.0.0.1.0.0) and [36]trithianonaphyrin(1.0.0.1.0.0.1.0.0). X‐ray crystallography of the dithiaamethyrin revealed a highly planar ring structure with mean plane deviation (MPD) value of 0.053 Å. A large positive NICS(0) value (+13.9 ppm) calculated for this planar 24π system unambiguously indicates an antiaromatic character that is consistent with a remarkably low field 1H chemical shift of the inner NH proton at 24.0 ppm. The magnitude of the paratropic ring current effect in the 24π amethyrin framework in the free base form and the diprotonated form was discussed on the basis of the MPD value and the NICS value. The present dithiaamethyrin is much more strongly antiaromatic than the dodecaalkylamethyrin in their free base forms, but the order inversed in their diprotonated forms.  相似文献   
996.
Short total syntheses of natural glycosides (ellagitannins) were performed through sequential and regioselective functionalization of the hydroxy groups of unprotected glucose. The key reactions are β‐selective glycosidation of a gallic acid derivative by using unprotected glucose as a glycosyl donor and catalyst‐controlled regioselective introduction of a galloyl group into the inherently less reactive hydroxy group of the glucoside.  相似文献   
997.
The first total syntheses of multifidosides A–C have been achieved. The synthetic strategy is characterized by catalytic site‐selective acylation of unprotected glycoside precursors in the final stage of the synthesis. High functional‐group tolerance of the site‐selective acylation, promoted by an organocatalyst, enabled the conventionally difficult molecular transformation in a predictable and reliable manner. An advantage of this strategy is to avoid the risks of undesired side reactions during the removal of the protecting groups at the final stage of the total synthesis.  相似文献   
998.
We have developed a metabolic flux analysis method that is based on (13)C-labeling patterns of the intracellular metabolites directly measured by capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). The flux distribution of the central carbon metabolism in Escherichia coli was determined by this new approach and the results were compared with findings obtained by conventional GC-MS analysis based on isotopomer of the proteinogenic amino acids. There were some differences in estimation results between new approach using CE-TOFMS and conventional approach using GC-MS. These were thought to be attributable to variations in measured mass distributions between amino acids and the corresponding precursors and to differences in the sensitivity of the exchange coefficients to mass distributions. However, our CE-TOFMS method facilitates high-throughput flux analysis without requiring complicated sample preparation such as hydrolysis of proteins and derivatization of amino acids.  相似文献   
999.
We have developed a bio/chemiluminescence spectrometer with a cooled charge-coupled-device (CCD) detector to obtain a quantitative luminescence spectrum as the absolute number of all emitted photons at each wavelength. The integrated area of the spectrum divided by the number of reacted substrate molecules gives the quantum yield. Calibration of the absolute sensitivity of the CCD-spectrometer system was performed by using lasers and a tungsten lamp with calibrated powers as primary light standards, and calibration of the light-collection efficiency of the spectrometer with several kinds of cells for liquid samples was achieved by introducing a simple reference double-plate cell. The reference cell is not convenient for final bio/chemiluminescence measurements but is useful for the calibration because it has well-defined angular dependence of light emission, allowing accurate calculation of the light-collection efficiency. Using this CCD-spectrometer system, we re-examined the quantum yield of aqueous luminol chemiluminescence with H2O2 catalyzed by horseradish peroxidase. The quantum yield was constant for a wide range of luminol concentrations, whereas it changed and had an optimum against H2O2 concentrations. The optimum quantum yield was 1.23(+/-0.20)%, which is in good agreement with previously reported values.  相似文献   
1000.
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