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   1152篇
  免费   39篇
  国内免费   4篇
化学   781篇
晶体学   50篇
力学   20篇
数学   67篇
物理学   277篇
  2023年   12篇
  2022年   25篇
  2021年   33篇
  2020年   29篇
  2019年   37篇
  2018年   33篇
  2017年   21篇
  2016年   38篇
  2015年   25篇
  2014年   37篇
  2013年   79篇
  2012年   69篇
  2011年   66篇
  2010年   52篇
  2009年   49篇
  2008年   68篇
  2007年   51篇
  2006年   35篇
  2005年   33篇
  2004年   28篇
  2003年   25篇
  2002年   21篇
  2001年   29篇
  2000年   46篇
  1999年   57篇
  1998年   13篇
  1997年   9篇
  1996年   9篇
  1995年   6篇
  1994年   8篇
  1993年   9篇
  1992年   7篇
  1991年   9篇
  1990年   6篇
  1989年   7篇
  1987年   5篇
  1986年   8篇
  1985年   14篇
  1984年   8篇
  1983年   5篇
  1982年   6篇
  1981年   3篇
  1980年   6篇
  1979年   8篇
  1977年   12篇
  1976年   5篇
  1975年   4篇
  1974年   5篇
  1973年   4篇
  1972年   4篇
排序方式: 共有1195条查询结果,搜索用时 15 毫秒
51.
Ojha  Minita  Bansal  Raj K. 《Structural chemistry》2020,31(6):2179-2187
Structural Chemistry - A theoretical investigation of the model diazotization/dediazotization of N-aminopiperidine and N-aminomorpholine at the DFT (B3LYP/6-31+G(d)) level indicated that the...  相似文献   
52.
A protein''s adaptive response to its substrates is one of the key questions driving molecular physics and physical chemistry. This work employs the recently developed structure-mechanics statistical learning method to establish a mechanical perspective. Specifically, by mapping all-atom molecular dynamics simulations onto the spring parameters of a backbone-side-chain elastic network model, the chemical moiety specific force constants (or mechanical rigidity) are used to assemble the rigidity graph, which is the matrix of inter-residue coupling strength. Using the S1A protease and the PDZ3 signaling domain as examples, chains of spatially contiguous residues are found to exhibit prominent changes in their mechanical rigidity upon substrate binding or dissociation. Such a mechanical-relay picture thus provides a mechanistic underpinning for conformational changes, long-range communication, and inter-domain allostery in both proteins, where the responsive mechanical hotspots are mostly residues having important biological functions or significant mutation sensitivity.

Protein residues exhibit specific routes of mechanical relay as the adaptive responses to substrate binding or dissociation. On such physically contiguous connections, residues experience prominent changes in their coupling strengths.  相似文献   
53.
The title compounds 3 and 7 are novel heterocyclic systems incorporating two-coordinate phosphorus. They are obtained in reasonable to good yields from the condensation of suitable 2-ethyl-3-alkylthiazolinium and -benzothiazolium bromides 2 and 6 with phosphorus trichloride in the presence of triethylamine in an aprotic solvent. Intermediate dichlorophosphino-substituted N-ylides can be observed or isolated in some cases. From a 2-methyl-3-alkylthiazolinium bromide ( 2a ), a 1-(dichlorophosphino) substituted 1, 3-azaphospholo[5,1-b]thiazoline ( 4 ) was obtained. The chemical shift of the two-coordinate phosphorus in 1,3-azaphosphole derivatives clearly reflects the influence of the heterocyclic system annulated to its 1,5-bond and of the substituents in its 2-and 4-positions.  相似文献   
54.
Background: Ponciri Fructus, a crude drug consisting of the dried immature fruits of Poncirus trifoliata (L.) Raf., is a popular folk medicine used for the treatment of allergy and gastrointestinal disorders in Korea and China. In this study, the anti-adipogenic activity of extracts and isolated compounds were evaluated using 3T3-L1 preadipocytes. Methods: Dried immature fruits were extracted and fractionated into n-hexane, ethyl acetate (EtOAc), n-butanol and water-soluble fractions. The ethanol extract and fractions were tested for anti-adipogenic activity in the 3T3-L1 cell line. The active fractions (n-hexane and EtOAc fractions) were further subjected to chromatographic techniques to isolate and identify active compounds. Furthermore, the isolated compounds were evaluated for their anti-adipogenic activity. Results: Altogether, seven compounds, including two flavonoids, one phytosteroid and four coumarin derivatives, were isolated. Ethanol extract, n-hexane fraction, EtOAc fraction and three isolated compounds (phellopterin, oxypeucedanin and poncirin) showed significant anti-adipogenic activity as observed by reduced lipid deposition in differentiated 3T3-L1 cells. Further, oxypeucedanin downregulated the key adipogenic markers, such as peroxisome proliferator-activated receptors proteins γ (PPAR-γ), sterol response element binding proteins-1 (SREBP-1), CCAAT/enhancer binding proteins-α (C/EBP-α), adipocyte-specific lipid binding proteins (FABP-4), adipocyte fatty acid binding proteins (aP2), lipoprotein lipase (LPL) and leptin. Conclusion: This study indicated that the ethanol extract, hexane fraction and ethyl acetate fraction of P. trifoliata fruits possess strong anti-adipogenic activity, containing the active compounds such as phellopterin, oxypeucedanin and poncirin. Further research is recommended to explore their efficacy and safety in animal and clinical models.  相似文献   
55.
56.
57.
This paper presents an analysis of diffraction effects taking place at different Schlieren diffracting elements. Two types of diffraction effects are prominent in the Schlieren schemes. One is diffraction of direct light (source image) at the Schlieren element, which limits the sensitivity and resolution of Schlieren systems. The second type is the diffraction of light deflected from the test object at the Schlieren-diffracting element. This second type of diffraction degrades the quality of Schlieren results. Experimental results showing the effect of diffraction of light deflected from the test object at a phase knife-edge, corner of a square phase aperture and an optical fiber tip as Schlieren diffracting elements have been presented and discussed.   相似文献   
58.
We study spectral distortions of diffuse ultra-high energy (UHE) neutrino flavour fluxes resulting due to physics beyond the Standard Model (SM). Even large spectral differences between flavours at the source are massaged into a common shape at earth by SM oscillations, thus, any significant observed spectral differences are an indicator of new physics present in the oscillation probability during propagation. Lorentz symmetry violation (LV) and neutrino decay are examples, and result in significant distortion of the fluxes and of the well-known bounds on them, which may allow UHE detectors to probe LV parameters, lifetimes and the mass hierarchy over a broad range.  相似文献   
59.
60.
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