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   719848篇
  免费   6424篇
  国内免费   1977篇
化学   354142篇
晶体学   10594篇
力学   37531篇
综合类   18篇
数学   103409篇
物理学   222555篇
  2021年   5842篇
  2020年   6409篇
  2019年   7286篇
  2018年   13724篇
  2017年   14016篇
  2016年   15610篇
  2015年   7988篇
  2014年   12762篇
  2013年   30075篇
  2012年   25122篇
  2011年   33868篇
  2010年   23859篇
  2009年   23882篇
  2008年   30942篇
  2007年   32825篇
  2006年   23636篇
  2005年   24009篇
  2004年   21037篇
  2003年   19415篇
  2002年   18311篇
  2001年   18940篇
  2000年   14794篇
  1999年   11449篇
  1998年   9827篇
  1997年   9602篇
  1996年   9196篇
  1995年   8291篇
  1994年   8250篇
  1993年   8053篇
  1992年   8527篇
  1991年   8993篇
  1990年   8571篇
  1989年   8447篇
  1988年   8336篇
  1987年   8087篇
  1986年   7679篇
  1985年   10018篇
  1984年   10479篇
  1983年   8679篇
  1982年   9086篇
  1981年   8665篇
  1980年   8284篇
  1979年   8820篇
  1978年   9076篇
  1977年   8893篇
  1976年   8895篇
  1975年   8409篇
  1974年   8291篇
  1973年   8629篇
  1972年   6236篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Optics and Spectroscopy - 10.1134/S0030400X17050095  相似文献   
92.
Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the...  相似文献   
93.
The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF4 are mediated by the side chains on the receptor (100 s−1<kex<5000 s−1), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method.  相似文献   
94.
95.
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.  相似文献   
96.
97.
98.
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526  相似文献   
99.
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   
100.
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained...  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