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   853篇
  免费   29篇
  国内免费   1篇
化学   670篇
晶体学   17篇
力学   17篇
数学   39篇
物理学   140篇
  2023年   7篇
  2022年   4篇
  2021年   9篇
  2020年   9篇
  2019年   18篇
  2018年   11篇
  2017年   6篇
  2016年   22篇
  2015年   16篇
  2014年   18篇
  2013年   50篇
  2012年   54篇
  2011年   62篇
  2010年   41篇
  2009年   23篇
  2008年   52篇
  2007年   54篇
  2006年   52篇
  2005年   45篇
  2004年   41篇
  2003年   30篇
  2002年   30篇
  2001年   15篇
  2000年   18篇
  1999年   8篇
  1998年   6篇
  1997年   11篇
  1996年   8篇
  1995年   9篇
  1994年   8篇
  1993年   4篇
  1992年   14篇
  1991年   21篇
  1990年   8篇
  1989年   8篇
  1988年   6篇
  1987年   9篇
  1986年   5篇
  1985年   8篇
  1984年   7篇
  1983年   4篇
  1982年   6篇
  1980年   6篇
  1979年   8篇
  1978年   6篇
  1977年   5篇
  1976年   4篇
  1974年   7篇
  1973年   2篇
  1969年   2篇
排序方式: 共有883条查询结果,搜索用时 343 毫秒
121.
122.
We present a Bayesian approach to pricing longevity risk under the framework of the Lee-Carter methodology. Specifically, we propose a Bayesian method for pricing the survivor bond and the related survivor swap designed by Denuit et al. (2007). Our method is based on the risk neutralization of the predictive distribution of future survival rates using the entropy maximization principle discussed by Stutzer (1996). The method is illustrated by applying it to Japanese mortality rates.  相似文献   
123.
Successive differential and integral sorptions of water vapor into the polyelectrolyte complex of poly (sty renesulfonic acid) / poly(4-vinyl-N-ethylpyridinum bromide) have been measured; films of stoichiometric (1/1 molar ratio) and nonstoichiometric (2/1 molar ratio) complex were employed in the experiments. Sorption isotherms have been also determined by using the values obtained from integral sorption experiments. The sorption data have suggested the following. (i) The rearrangement of polymer chains plays a relatively unimportant role in sorption of water. (ii) The relaxation motion of network chains is suppressed. (iii) The change of morphological structure caused by vapor sorption is obscure. (iv) The ionic character of the 1/1 complex is higher than that of 2/1 complex. (v) A small amount of water can be dispersed on specific polymer sites, but the sorption of a large amount of water is accompanied by an expansion of network structure. Points (i)-(v) have been consistently interpreted on the basis of the network structure and ionic character of this complex.  相似文献   
124.
Abstract

The microstructure of milled mesophase pitch-based carbon fibers (mMPCFs) that have been developed as an anode material for Li ion batteries have been studied as a function of heat treatment temperature (HTT), by SEM, X-ray diffraction, and Raman spectroscopy. And the results obtained are compared with those by X-ray diffraction (XRD) and SEM observations, for the characterization of specific structural features of mMPCFs as a promising anode material.  相似文献   
125.
Electric-discharge nitrogen comprises three main types of excited nitrogen species-atomic nitrogen (Natom), excited nitrogen molecules (N2*), and nitrogen ions (N2+) – which have different lifetimes and reactivities. In particular, the interfacial reaction locus between the discharged nitrogen and the water phase produces nitrogen compounds such as ammonia and nitrate ions (denoted as N-compounds generically); this is referred to as the plasma/liquid interfacial (P/L) reaction. The Natom amount was analyzed quantitatively to clarify the contribution of Natom to the P/L reaction. We focused on the quantitative relationship between Natom and the produced N-compounds, and found that both N2* and N2+, which are active species other than Natom, contributed to P/L reaction. The production of N-compounds from N2* and N2+ was enhanced upon UV irradiation of the water phase, but the production of N-compounds from Natom did not increase by UV irradiation. These results revealed that the P/L reactions starting from Natom and those starting from N2* and N2+ follow different mechanisms.  相似文献   
126.
We report the measurements of the heat capacity of (4)He confined in nanoporous Gelsil glass that has nanopores of 2.5-nm diameter at pressures up to 5.3 MPa. The heat capacity has a broad peak at a temperature much higher than the superfluid transition temperature obtained using the torsional oscillator technique. The peak provides definite thermodynamic evidence for the formation of localized Bose-Einstein condensates on nanometer length scales. The temperature dependence of the heat capacity is described well by the excitations of phonons and rotons, supporting the existence of localized Bose-Einstein condensates.  相似文献   
127.
Abstract

The reaction of 2-t-Bu-germabenzenylpotassium with Me2(t-Bu)SiCl (TBDMSCl) resulted in the coupling among two TBDMS-substituted germabenzenes and the germabenzenylpotassium. The structure of the product was determined by X-ray crystallographic analysis. Its formation mechanism was proposed with the help of theoretical calculations.  相似文献   
128.
We present a systematic analysis of electron transport characteristics of carbon nanotube (CNT) intramolecular heterojunctions with peptide linkages, MM, SS, SM1, and SM2 where M and S stand for metallic and semiconducting CNT electrodes, respectively. Our theoretical investigations show that the incorporation of peptide linkages and their associated dipole moments play an important role in determining the electron transport characteristics and lead to materials with unique properties, such as Schottky-like behavior. Furthermore, we show that the Schottky-like behavior is observed in our SM1 junction but not in the SM2 junction because of the different effects that arise from both the direction and strength of their dipole moments. We believe that our results will pave the way towards the design and implementation of various electronic logic functions based on carbon nanotubes for applications in the field of nanoelectronics.  相似文献   
129.
The heterotrich ciliate Blepharisma japonicum produces red pigment blepharismins, which function as self-defense toxin against predators and as a photoreceptor for step-up photonegativity. The dibenzoperylenequinone moiety of blepharismins was shown to be biosynthesized via the polyketide pathway. In this paper, the starter units of the biosynthetic pathway of blepharismins were determined to be isovaleryl-CoA and butyryl-CoA by HPLC, LC/ESI-MS, and 1H and 2H NMR analyses of the pigments obtained from feeding experiment of l-leucine or sodium butyrate in excess and deuterium-labeled l-leucine.  相似文献   
130.
A sensitive liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) method for the simultaneous determination of five 3-oxo-4-ene-neuroactive steroids, i.e. androstenedione, testosterone (T), progesterone (PROG), 20alpha-dihydroprogesterone and 20beta-dihydroprogesterone, in rat brain has been developed and validated. The brain steroids were extracted with methanol-acetic acid, purified using solid-phase extraction cartridges and subjected to LC-ESI-MS/MS. The method does not require derivatization. Deuterium-labeled T and PROG were used as the internal standards, and quantification was based on the selected reaction monitoring mode. This method allowed the reproducible and accurate quantification of the brain neuroactive steroids using 100 mg of tissue; the intra- and inter-assay relative standard deviations were below 4.7 and 4.3%, respectively, and the accuracy values were 97.6-103.2% for all the steroids. The limits of quantitation were 0.1 ng/g tissue for all the steroids. The application of this developed method for the analysis of changes in the brain neuroactive steroid levels by immobilization stress is also presented.  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