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   1744篇
  免费   30篇
  国内免费   4篇
化学   920篇
晶体学   9篇
力学   45篇
数学   198篇
物理学   606篇
  2021年   13篇
  2020年   12篇
  2019年   17篇
  2017年   13篇
  2016年   27篇
  2015年   15篇
  2014年   27篇
  2013年   87篇
  2012年   57篇
  2011年   82篇
  2010年   58篇
  2009年   29篇
  2008年   78篇
  2007年   98篇
  2006年   67篇
  2005年   58篇
  2004年   60篇
  2003年   29篇
  2002年   57篇
  2001年   45篇
  2000年   38篇
  1999年   17篇
  1998年   22篇
  1997年   19篇
  1996年   18篇
  1995年   30篇
  1994年   36篇
  1993年   39篇
  1992年   32篇
  1991年   26篇
  1990年   21篇
  1989年   16篇
  1988年   28篇
  1987年   14篇
  1986年   19篇
  1985年   32篇
  1984年   17篇
  1983年   17篇
  1982年   24篇
  1981年   20篇
  1980年   27篇
  1979年   24篇
  1978年   31篇
  1977年   21篇
  1976年   32篇
  1975年   34篇
  1974年   20篇
  1973年   33篇
  1972年   14篇
  1971年   15篇
排序方式: 共有1778条查询结果,搜索用时 0 毫秒
71.
We report the first observation of an excited singly charmed baryon Omega c* (css) in the radiative decay Omega c0gamma, where the Omega c0 baryon is reconstructed in the decays to the final states Omega(-)pi+, Omega(-)pi+pi0, Omega(-)pi+pi(-)pi+, and Xi(-)K(-)pi+pi+. This analysis is performed using a data set of 230.7 fb(-1) collected by the BABAR detector at the PEP-II asymmetric-energy B factory at the Stanford Linear Accelerator Center. The mass difference between the Omega c* and the Omega c0 baryons is measured to be 70.8+/-1.0(stat)+/-1.1(syst) MeV/c2. We also measure the ratio of inclusive production cross sections of Omega c* and Omega c0 in e+e(-) annihilation.  相似文献   
72.
Quantum error-correcting codes can protect multipartite quantum states from errors on some limited number of their subsystems (usually qubits). We construct a family of Bell inequalities which inherit this property from the underlying code and exhibit the violation of local realism, without any quantum information processing (except for the creation of an entangled state). This family shows no reduction in the size of the violation of local realism for arbitrary errors on a limited number of qubits. Our minimal construction requires preparing an 11-qubit entangled state.  相似文献   
73.
Single-crystal X-ray diffraction structures of the 5-amino-2-methylpyridinium hydrogen fumarate salt have been solved at 150 and 300 K (CCDC 1952142 and 1952143). A base–acid–base–acid ring is formed through pyridinium-carboxylate and amine-carboxylate hydrogen bonds that hold together chains formed from hydrogen-bonded hydrogen fumarate ions. 1H and 13C chemical shifts as well as 14N shifts that additionally depend on the quadrupolar interaction are determined by experimental magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) and gauge-including projector-augmented wave (GIPAW) calculation. Two-dimensional homonuclear 1H-1H double-quantum (DQ) MAS and heteronuclear 1H-13C and 14N-1H spectra are presented. Only small differences of up to 0.1 and 0.6 ppm for 1H and 13C are observed between GIPAW calculations starting with the two structures solved at 150 and 300 K (after geometry optimisation of atomic positions, but not unit cell parameters). A comparison of GIPAW-calculated 1H chemical shifts for isolated molecules and the full crystal structures is indicative of hydrogen bonding strength.  相似文献   
74.
A preliminary LEED theory experiment comparison for the InP(110) surface has been performed using experimental I(V) data recorded in the authors' laboratory from a clean, UHV-cleaved, single crystal specimen. A range of model surface geometries including both lateral and vertical displacements of the top layer In and P atoms have been examined. The results clearly demonstrate that the structure of this surface is substantially different from a simple termination of the bulk lattice and that the disturbance extends more than one layer into the real crystal. The possibility of extending the analysis to include second layer distortions is considered.  相似文献   
75.
The lifetimes of positrons annihilating in cholesterol and in cholesteryl oleate have been measured as a function of temperature in the vicinity of a previously reported solid-solid transition in each compound. The observed changes in lifetime parameters are discussed in terms of structural changes occurring in these two compounds.  相似文献   
76.
Bulk Poly(N-isopropylacrylamide) (PNIPAm) hydrogels are thermally responsive polymers that undergo a sharp volumetric phase transition around its lower critical solution temperature of 33 °C. The physical characteristics of bulk, micro-, and nano-form PNIPAm hydrogel have been well-studied, and have applications ranging from biomedical devices to mechanical actuators. An important physical characteristics which reveals lack of available information is speed of sound. Prior studies have utilized Brillouin scattering, multi-echo reflection ultrasound spectroscopy, the sing-around method, and others in measuring the speed of sound. We use a planar resonant cavity with bulk PNIPAm hydrogel in aqueous solution to determine the temperature dependent speed of sound around the lower critical solution temperature. The results show sharp nonmonotonic behavior of the sound velocity in vicinity of the phase transition.  相似文献   
77.
Microwave plasmas at atmospheric pressure are used for surface treatments like for example cleaning, sterilization or decontamination purposes, for a pre‐treatment to increase the adhesion of lacquer, paint, or glue, and for the deposition of different kind of layers and coatings. Micro plasma jets can also be applied for biomedical applications and for treatment of small and complex geometries like for example the inside of capillaries. Larger plasma torches which exhibit higher gas temperatures can also be used for chemical syntheses like waste gas decomposition, methane pyrolysis, or carbon dioxide dissociation and for plasma spraying purposes. In the present publication an overview on the development and the investigation of the operating principle of two atmospheric pressure microwave plasma torches at frequencies of 2.45 GHz and 915 MHz will be presented. The plasma sources are based on a cylindrical resonator combined with coaxial structures. To explain how these plasma sources work, simulations of the electric field distribution will be discussed. Furthermore, some physical characteristics of an air and an Ar/H2 atmospheric plasma like gas temperatures, excitation temperatures and densities as well as the heating of the plasma by the microwave will be investigated. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
78.
In this Letter, we report a novel approach to the preparation of 3-anilino-pyrazin-2(1H)-ones and 3-anilino-quinoxalin-2(1H)-ones from the corresponding 3-halo pyrazin-2-amines and 3-haloquinoxalin-2-amines, using a microwave-mediated Smiles rearrangement.  相似文献   
79.
An hydrophobic interaction chromatography step was developed for the large-scale production of an Fc-fusion biologic. Two abundant product-related impurities were separated from the active monomer using a Butyl resin and a simple step-wash and step-elution strategy. Capacity and resolution of the HIC step was optimal when sodium sulfate was employed as the lyotropic salt and pore size of the Butyl resin was 750A. Factorial analysis identified critical parameters for the Butyl chromatography and an operating window capable of delivering high product quality and yield over a broad column loading range.  相似文献   
80.
Abstract— Two simple methods of phototaxis measurements have been applied to study the effects of ionophores on the negative phototactic response in Stentor coeruleus. The inhibitory effects of Ca2+-ionophore (A23187), Ca2+-blocking agent (Ruthenium Red), and K+ -ionophore (valinomycin) on photo-taxis have been determined. Results suggest that the influx of Ca2+ plays a transducing role in the phototaxis of Stentor.  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