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   1406篇
  免费   74篇
  国内免费   17篇
化学   919篇
晶体学   3篇
力学   55篇
数学   247篇
物理学   273篇
  2023年   19篇
  2022年   18篇
  2021年   48篇
  2020年   48篇
  2019年   47篇
  2018年   21篇
  2017年   31篇
  2016年   83篇
  2015年   55篇
  2014年   61篇
  2013年   74篇
  2012年   93篇
  2011年   105篇
  2010年   63篇
  2009年   64篇
  2008年   80篇
  2007年   66篇
  2006年   87篇
  2005年   86篇
  2004年   68篇
  2003年   48篇
  2002年   44篇
  2001年   26篇
  2000年   19篇
  1999年   11篇
  1998年   4篇
  1997年   5篇
  1996年   16篇
  1995年   9篇
  1994年   11篇
  1993年   10篇
  1992年   7篇
  1991年   5篇
  1990年   7篇
  1988年   7篇
  1987年   3篇
  1986年   4篇
  1985年   6篇
  1984年   6篇
  1983年   3篇
  1982年   5篇
  1981年   2篇
  1980年   6篇
  1979年   7篇
  1977年   1篇
  1976年   1篇
  1966年   1篇
  1908年   2篇
  1900年   1篇
  1870年   1篇
排序方式: 共有1497条查询结果,搜索用时 15 毫秒
1.
The reduction of high-dimensional systems to effective models on a smaller set of variables is an essential task in many areas of science. For stochastic dynamics governed by diffusion processes, a general procedure to find effective equations is the conditioning approach. In this paper, we are interested in the spectrum of the generator of the resulting effective dynamics, and how it compares to the spectrum of the full generator. We prove a new relative error bound in terms of the eigenfunction approximation error for reversible systems. We also present numerical examples indicating that, if Kramers–Moyal (KM) type approximations are used to compute the spectrum of the reduced generator, it seems largely insensitive to the time window used for the KM estimators. We analyze the implications of these observations for systems driven by underdamped Langevin dynamics, and show how meaningful effective dynamics can be defined in this setting.  相似文献   
2.
Proton acceleration using high-intensity laser pulses, at 1016 W/cm2 was studied irradiating different types of thin metal and plastic targets having 1-micron thickness. The maximization of the proton energy process was investigated optimizing the laser parameters, the irradiation conditions and the target properties. Employing 600–700 J laser pulse energy, a focalization inducing self-focusing effects and using targets with optimized thickness, it was possible to accelerate protons up to energies of above 8 MeV. The time-of-flight diagnostics has allowed to monitor the plasma properties and to control the ion acceleration process.  相似文献   
3.
4.
The most basic function of synthetic microenvironments for tissue engineering is to act as a physical substrate for cell attachment, migration, and proliferation, similar to the natural cell environment. Functionalization of supramolecular materials with guest compounds that display the same recognition moieties is a common strategy to introduce biofunctionality. However, besides a robust interaction with the material, a certain level of dynamics needs to be conserved for an adaptive interface toward the living environment. A balance between robust material functionalization and dynamic cell interaction needs to be met. The detailed analysis hereof using a ureido‐pyrimidinone (UPy) poly(ethylene glycol) system in dilute and transient network regime is demonstrated. Monovalent and bivalent UPy‐functionalized guest molecules are designed and their interaction with UPy‐host fibers is evaluated. Analysis of guest interaction in the dilute state by microfluidics, and in the gel state, by fluorescence recovery after photobleaching and fluorescence resonance energy transfer is proven to be suitable to quantify the local and ensemble guest mobility. The results demonstrate that the interaction of bioactive moieties through supramolecular host–guest chemistry yields a dynamic system, which is stronger for divalent guests but risks unintended leakage in the case of functional monomeric units.  相似文献   
5.
The new ligand HPDO3MA [(R,R,R,R)-10-(2-hydroxypropyl)-α,α′,α′′-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] was designed to combine and optimize the chemical properties of the macrocyclic ligands HPDO3A and DOTMA. The presence of the methyl groups on the acetic pendant arms of HPDO3A is expected to rigidify the structure of the ligand and favor an increase of the kinetic inertness of the Ln complexes. 1H NMR spectra of Eu(HPDO3MA) displayed the presence of two pairs of diastereoisomers: SAP (square antiprismatic) and TSAP (twisted square antiprismatic) isomers (56 and 44 %, respectively). In addition, 1H and 17O relaxometric NMR studies of Gd(HPDO3MA) showed approximately a 10 % increase in relaxivity and a faster water exchange rate with respect to Gd(HPDO3A). Moreover, a detailed chemical exchange saturation transfer (CEST) characterization of Yb(HPDO3MA) displayed a sensitivity about two times larger than that of Yb(HPDO3A) both in phantom and in cell labeling experiments. Finally, the kinetic inertness of Yb(HPDO3MA) was measured to be twice as high as that of Yb(HPDO3A), with a dissociation half-life at physiological pH of about 2500 years.  相似文献   
6.
Semigroup Forum - Recently, S. Kanti Patra and Md. Moid Shaikh proved the existence of monochromatic solutions to systems of polynomial equations near zero for particular dense...  相似文献   
7.
Aequationes mathematicae - In this work we provide the mathematical framework of !FTL, a new gesture recognition algorithm. This allows us to algebraically quantify the notion of shape for a smooth...  相似文献   
8.
Introduction of atropisomeric axes into a bent bispyridine ligand leads to the quantitative formation of a complex mixture of atropisomeric M2L4 cages upon treatment with metal ions. Whereas the isomer ratio of the obtained cage mixture, consisting of up to 42 isomers, is insensitive to temperature and solvent, the quantitative convergence from the mixture to a single isomer is accomplished upon encapsulation of a large spherical guest, namely fullerene C60. The observed isomerization with other guests depends largely on their size and shape (e.g., <10 and 82% convergence with planar triphenylene and bowl-shaped corannulene guests, respectively). Besides the unusual guest-induced convergence, the present cage mixture displays the strongest guest emission (ΦF = 68%) among previously reported MnLm cages and capsules, upon encapsulation of a BODIPY dye in water.

A complex mixture of atropisomeric M2L4 cages is shown to undergo perfect convergence to a single isomer upon encapsulation of spherical C60 in water. Moreover, the cage mixture displays very strong guest emission upon encapsulation of a BODIPY dye.  相似文献   
9.
10.
The structural and energetic features of the C?H???π interaction and the internal dynamics of the CHF3 group change drastically in going from benzene?CHF3 to indan?CHF3, according to the analysis of the rotational spectrum of the latter complex generated in a supersonic expansion.  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