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   445篇
  免费   32篇
  国内免费   4篇
化学   334篇
晶体学   4篇
力学   1篇
数学   47篇
物理学   95篇
  2023年   2篇
  2022年   2篇
  2021年   7篇
  2020年   13篇
  2019年   9篇
  2018年   11篇
  2017年   5篇
  2016年   21篇
  2015年   20篇
  2014年   11篇
  2013年   18篇
  2012年   26篇
  2011年   31篇
  2010年   12篇
  2009年   13篇
  2008年   22篇
  2007年   30篇
  2006年   30篇
  2005年   18篇
  2004年   21篇
  2003年   13篇
  2002年   17篇
  2001年   11篇
  2000年   10篇
  1999年   8篇
  1998年   7篇
  1997年   7篇
  1996年   8篇
  1995年   6篇
  1994年   2篇
  1993年   2篇
  1992年   6篇
  1991年   4篇
  1988年   7篇
  1987年   3篇
  1986年   12篇
  1985年   3篇
  1984年   4篇
  1982年   2篇
  1980年   3篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1974年   1篇
  1969年   1篇
  1968年   3篇
  1967年   3篇
  1966年   1篇
  1964年   1篇
排序方式: 共有481条查询结果,搜索用时 15 毫秒
91.
We present a measurement of the standard model CP violation parameter sin2 phi(1) based on a 29.1 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is fully reconstructed as a J/psi K(S), psi(2S)K(S), chi(c1)K(S), eta(c)K(S), J/psi K(L), or J/psi K(*0) decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin2 phi(1) = 0.99+/-0.14(stat)+/-0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.  相似文献   
92.
Angiotensin I‐converting enzyme (ACE) inhibitory peptide was isolated from the hen ovotransferrin hydrolysate using chymotryptic hydrolysis by two steps of reverse‐phase high‐performance liquid chromatography. The amino sequence of this novel peptide was identified as Lys‐Val‐Arg‐Glu‐Gly‐Thr‐Thr‐Tyr that inhibited ACE activity in vitro in a concentration‐dependent manner with an effective concentration (IC50) of 102.8 μM. Also, this inhibition was identified as noncompetitive using the Lineweaver‐Burk plot. Moreover, the antihypertensive action of this novel peptide was investigated by an intravenous injection into spontaneously hypertensive rats (SHR). A dose‐dependent reduction of systolic blood pressure by this peptide was observed after 40 min of treatment and it decreased the blood pressure markedly at the maximal dose (1 nmol/mL/kg). The maximal blood pressure lowering activity of this peptide was calculated as 163% of captopril (10 pmol/mL/kg) that was used as positive control. In conclusion, the obtained data suggests that Lys‐Val‐Arg‐Glu‐Gly‐Thr‐Thr‐Tyr has an ability to inhibit ACE activity and decrease the systolic blood pressure in hypertensive animals.  相似文献   
93.
We report a determination of the B(0)(d)-&B_(0)(d) mixing parameter Deltam(d) based on the time evolution of dilepton yields in Upsilon(4S) decays. The measurement is based on a 5.9 fb(-1) data sample collected by the Belle detector at KEKB. The proper-time difference distributions for same-sign and opposite-sign dilepton events are simultaneously fitted to an expression containing Deltam(d) as a free parameter. Using both muons and electrons, we obtain Deltam(d) = 0.463+/-0.008 (stat)+/-0.016 (syst) ps(-1). This is the first determination of Deltam(d) from time evolution measurements at the Upsilon(4S). We also place limits on possible CPT violations.  相似文献   
94.
A new xenicane diterpenoid, 15-deoxy-isoxeniolide-A (1) along with four known compounds 9-deoxy-isoxeniolide-A (2), isoxeniolide-A (3), xeniolide-A (4) and coraxeniolide-B (5) were isolated from the Bornean soft coral Xenia sp. The structures of these metabolites were elucidated on the basis of spectral analysis, NMR and HRESIMS. Compound 5 showed cytotoxic activity against ATL cell line, S1T.  相似文献   
95.
96.
Simulation study on microstructure formations in magnetic fluids   总被引:3,自引:0,他引:3  
We propose the Langevin-type microscopic equations of motion for magnetic fluids. Magnetic fluids are modeled as an ensemble of interacting ferromagnetic nanoparticles suspended in a viscous fluid. The present model is described in terms of position vectors of nanoparticles and orientation vectors of their magnetic dipole moments. In this model, forces and torques arising from the magnetic origin and the surrounding fluid flow are included. Effects of non-spherical particle shape are also taken into account. From the Brownian dynamics simulations of the model, it is found that the present model exhibits various microstructure formation processes in magnetic fluids.  相似文献   
97.
We investigate the dynamics of phase separations in quenched binary mixtures, such as binary alloys and polymer blends with low mobilities, at higher volume fractions. Computer simulations are performed using simple model equations in the presence of encounters of droplets. Four characteristics stages with three crossovers, including dynamical scaling behavior and temporal power laws, are found beyond a volume fraction of approximately 0.14, where each crossover is attributed to a transition from one growth mechanism to the other. The encounter effect is thus shown to strongly influence a transition from the diffusion-controlled (t1/2) stage to the coarsening (t1/3) stage. A simple analytical argument for the simulation results is also presented.  相似文献   
98.
99.
Summary Deuteration technique was applied to study the micro structures of copolymer series VDC/VC by infrared spectroscopy and high resolution NMR. The CH2 bending modes of chlorine atom containing polymers assigned as follows; –CCl2CH2CCl2– 1405 cm–1 (cryst.) and 1410 cm–1 (amorph.), –CHClCH2CCl2– 1422 cm–1, –CHClCH2CHCl– 1428 cm–1 (cryst.) and 1432 cm–1 (amorph.) –CHClCH2CH2CHCl– 1445 cm–1 and –CCl2CH2CH2CCl2– 1448 cm–1. This infrared interpretation shows that only the head to tail addition occurs in the copolymerisation. Nine peaks of the methylene protons were observed clearly in the NMR spectra of the copolymers. The study of the deuterated copolymers revealed that the effects of the chemical groups until the third at both sides from the marked methylene and the stereo configuration of long VC part should be considered to assign the NMR spectra. The CCl2 group made the chemical shift of the methylene proton to appear at lower magnetic field and the CHCl group gave the opposite behavior.
Zusammenfassung Mit deuterierten Monomeren wurde die Mikrostruktur der Copolymerenserie Vinyliden-Chlorid/Vinyl-Chlorid im Infraroten und mit hochauflösender Kernresonanz untersucht. Für die Biegeschwingung der Chloratome enthaltenden Polymeren der Methylengruppe ergeben sich folgende Werte: –CCl2CH2CCl2– 1405 cm–1 (krist.) und 1410 cm–1 (amorph.), –CHClCH2CCl2– 1422 cm–1, –CHClCH2CHCl– 1428 cm–1 (krist.) und 1432 cm–1 (amorph.), –CHClCH2CH2CHCl– 1445 cm–1 und –CCl2CH2CH2CCl2– 1448 cm–1.Diese Interpretation des Infraroten zeigt, daß nur die Kopf-Schwanz-Addition bei der Copolymerisation stattfindet. Neun Maxima des Methylenprotons wurden deutlich in den NMR-Spektren der Copolymeren beobachtet. Die Untersuchungen an den deuterierten Copolymeren zeigen, daß die Effekte der chemischen Gruppen bis zur dritten nach beiden Seiten vom markierten Methylen und die Stereokonfiguration von langen Vinyl-Chlorid-Anteilen betrachtet werden müssen, um die NMR-Spektren zu beschreiben. Die CCl2-Gruppe läßt die chemische Verschiebung des Methylen-protons bei geringeren magnetischen Feldern und die CHCl-Gruppe bei höheren erscheinen.


With 5 figures in 13 details and 4 tables  相似文献   
100.
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