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   1595篇
  免费   3篇
  国内免费   2篇
化学   1051篇
晶体学   15篇
力学   33篇
数学   298篇
物理学   203篇
  2014年   14篇
  2013年   27篇
  2012年   36篇
  2011年   42篇
  2010年   32篇
  2009年   23篇
  2008年   47篇
  2007年   37篇
  2006年   44篇
  2005年   41篇
  2004年   39篇
  2003年   42篇
  2002年   35篇
  2001年   22篇
  2000年   22篇
  1999年   30篇
  1998年   16篇
  1996年   19篇
  1994年   13篇
  1993年   18篇
  1992年   15篇
  1991年   20篇
  1990年   21篇
  1989年   24篇
  1988年   18篇
  1987年   16篇
  1986年   26篇
  1985年   19篇
  1984年   31篇
  1983年   22篇
  1982年   34篇
  1981年   37篇
  1980年   21篇
  1979年   30篇
  1978年   19篇
  1977年   18篇
  1976年   22篇
  1975年   21篇
  1971年   17篇
  1969年   13篇
  1938年   15篇
  1937年   17篇
  1934年   21篇
  1933年   19篇
  1931年   24篇
  1930年   19篇
  1929年   20篇
  1928年   29篇
  1927年   18篇
  1926年   19篇
排序方式: 共有1600条查询结果,搜索用时 15 毫秒
11.
Generation of low-timing-jitter 150 fs pulse trains at 1560 nm with 2 GHz repetition rate is demonstrated by locking a 200 MHz fundamental polarization additive-pulse mode-locked erbium fiber laser to high-finesse external Fabry-Perot cavities. The timing jitter and relative intensity noise of the repetition-rate multiplied pulse train are investigated.  相似文献   
12.
13.
14.
15.
We study lattice models of charged particles in uniform magnetic fields. We show how longer range hopping can be engineered to produce a massively degenerate manifold of single-particle ground states with wave functions identical to those making up the lowest Landau level of continuum electrons in a magnetic field. We find that in the presence of local interactions, and at the appropriate filling factors, Laughlin's fractional quantum Hall wave function is an exact many-body ground state of our lattice model. The hopping matrix elements in our model fall off as a Gaussian, and when the flux per plaquette is small compared to the fundamental flux quantum one only needs to include nearest and next-nearest neighbor hoppings. We suggest how to realize this model using atoms in optical lattices, and describe observable consequences of the resulting fractional quantum Hall physics.  相似文献   
16.
The relation between sample mass andDSC-amplitude was investigated under various experimental conditions for vitreous quartz, both as discs and powders. Contrary to other authors3 proportionality has been found up to the highest masses (75 mg) used. A statistical analysis of the data indicates that the accuracy of directC p-measurements byDSC can be increased by determining the blank value by extrapolation of the amplitudes for several masses to zero mass instead of using the usual procedure, which involves a run with the empty pans. The overall error ofC p due to instrument errors is estimated not to exceed 2%.  相似文献   
17.
The self-consistent mean field model of Scheutjens and Fleer is used to model spherical aggregates of homopolymers and monomer—polymer particles in solution. For homopolymer aggregates we found that the chain ends are preferentially located at the exterior side of the polymer/solvent interface. The distribution of the end segments may be an important parameter in latex film formation. For monomer—polymer particles a “core-shell” structure is found with an extended core containing a monomer—polymer mixture and a thin shell a few nanometres thick strongly enriched with monomer. The monomer-enriched shell seems to function as a solvating envelope for the dangling chain ends. These results are compared with other simulations based on a single chain in a spherical-cavity model.  相似文献   
18.
19.
Jäntti introduced a method to reduce the time required for the stepwise measurement of adsorption isotherms (Jäntti et al., Progress in Vacuum Microbalance Techniques, Vol. 1, Heyden, London, pp. 345–353, 1972). After a pressure change he measured the adsorbed mass three times and calculated its equilibrium value for the new pressure. In the present paper we discuss the applicability of this method in a broader scope (without starting from a single combination of gas and solid adsorbent) and also discuss the influence of measurement inaccuracies. It is shown that the method can serve as an early warning system, which decides whether an improvement of the adsorption model is necessary.  相似文献   
20.
The reaction of trimethylammonium acetic acid betaine (1) with trifluoroaceticanhydride (TFA) yielding trifluoroacetyl-N-methylide can be extended to triethylammonium acetic acid betaine (2), 2-pyridiniumpropionic acid betaine (9) andN,N-dimethyl-piperidinium-2-carboxylate betaine (14). Trigonelline and 3-pyridiniumpropionic acid betaine (11), however, do not react in this way. It follows that the formation of such ylides is only possible if the methylene or methine group of the betaines are flanked by ammonium and carboxylate group.
Herrn emer. o. Univ.-Prof. Dr. techn. Dr. hc.Otto Kratky, Institut für Feinstrukturforschung der Österr. Akademie der Wissenschaften und Forschungszentrum Graz, zur Vollendung des 80. Lebensjahres gewidmet.  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