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   394篇
  免费   9篇
  国内免费   1篇
化学   252篇
晶体学   6篇
力学   11篇
数学   39篇
物理学   96篇
  2022年   3篇
  2021年   4篇
  2020年   9篇
  2019年   4篇
  2018年   3篇
  2017年   2篇
  2016年   9篇
  2015年   12篇
  2014年   6篇
  2013年   23篇
  2012年   17篇
  2011年   40篇
  2010年   11篇
  2009年   14篇
  2008年   20篇
  2007年   21篇
  2006年   21篇
  2005年   12篇
  2004年   13篇
  2003年   17篇
  2002年   12篇
  2001年   8篇
  2000年   9篇
  1999年   3篇
  1998年   4篇
  1997年   6篇
  1996年   5篇
  1995年   3篇
  1994年   4篇
  1993年   2篇
  1992年   4篇
  1991年   3篇
  1990年   7篇
  1989年   6篇
  1988年   16篇
  1987年   11篇
  1986年   5篇
  1985年   7篇
  1984年   3篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1977年   3篇
  1975年   2篇
  1971年   1篇
  1969年   2篇
  1968年   1篇
  1967年   2篇
  1962年   1篇
排序方式: 共有404条查询结果,搜索用时 31 毫秒
331.
This paper is concerned with the melting of a packed snow heated by the radiative energy which is the blackbody radiation having source temperature of 3200 °K and short radiative energy. A transfer of the radiation in snow is significantly affected by both the porosity of snow and water saturation. The internal melting in snow is greatly characteristic for radiative heating which is to be produced by absorbing of a comparatively short wave radiation. In this study, an analysis is attempted to predict the variation of snow density, the moving rate of dry-wet interface of snow due to percolation of melt water, and the transient temperature distribution in dry snow zone located under wet snow zone.  相似文献   
332.
An experimental investigation has been conducted for exploring a possibility to improve the heat transfer of tube banks of in-line arrangement, in which the first cylinder was roughened with pyramids. Measured were the heat transfer characteristics of the first cylinder for several cylinder spacings. It is found that there exists the critical Reynolds numberRe c , beyond which the heat transfer rate increases drastically by about 30 to 50% as compared with that for the smooth cylinder, though the increasing rate is small for the case of very narrow spacing such asC y /d×C x /d =1.2×1.2. In the region ofRe>Re c , the separation point shifts downstream to θ=120° to 130° from the forward stagnation point, and it results in the decrease of the form drag.  相似文献   
333.
To date, the majority of zeolites have been prepared by the solvothermal route using organic structure directing agents. Two new zeolites with structural codes PCR and OKO were recently prepared from UTL germanosilicate by removal of the double‐four ring (D4R) connecting the dense two‐dimensional layers [Nature Chem. 2013 , 5, 628]. The corresponding experimental protocol, Assembly–Disassembly–Organization–Reassembly (ADOR), is explored in this contribution with an in silico investigation. The structure and properties of hypothetical zeolites that could be obtained from zeolites with IWW, IWV, IWR, ITR, and ITH topologies using the ADOR protocol are reported based on a computational investigation. A total of 20 new structures are presented together with their characteristics.  相似文献   
334.
Heterogeneous ReOx–Pd/CeO2 catalyst showed excellent performance for simultaneous hydrodeoxygenation of vicinal OH groups. High yield (>99 %), turnover frequency (300 h?1), and turnover number (10 000) are achieved in the reaction of 1,4‐anhydroerythritol to tetrahydrofuran. This catalyst can be applied to sugar alcohols, and mono‐alcohols and diols are obtained in high yields (≥85 %) from substrates with even and odd numbers of OH groups, respectively. The high catalytic performance of ReOx–Pd/CeO2 can be assigned to rhenium species with +4 or +5 valence state, and the formation of this species is promoted by H2/Pd and the ceria support.  相似文献   
335.
Measurements have been made by the comparison method for the effective thermal conductivity of dispersed materials which consist of substances with different thermal conductivities. The applicability of existing predicting formulae is discussed in detail as comparing their predicted values with the present data. A new predicting formula is proposed through analyzing the experimental data, the numerical results, and also the data obtained with the electrolytic-bath. It is found that the proposed formula has a wider range of applicability than that of previously reported ones.  相似文献   
336.
Y Ota  I Ohba 《Pramana》2002,59(2):409-412
The classical Duffing oscillator is a dissipative chaotic system, and so there is not a definite Hamiltonian. We quantize the Duffing oscillator on the basis of quantum state diffusion (QSD) which is a formulation for open quantum systems and a useful tool for analyzing nonlinear problems and classical limits. We can define a ‘Lyapunov exponent’, which corresponds to the classical one in the proper limit, and investigate the behavior of the system by varying the Planck constant effectively. We show that there exists a critical stage, where the behavior of the system crosses over from classical to quantum one.  相似文献   
337.
Let ? be a set of connected graphs. An ?‐factor of a graph is its spanning subgraph such that each component is isomorphic to one of the members in ?. Let Pk denote the path of order k. Akiyama and Kano have conjectured that every 3‐connected cubic graph of order divisible by 3 has a {P3}‐factor. Recently, Kaneko gave a necessary and sufficient condition for a graph to have a {P3, P4, P5}‐factor. As a corollary, he proved that every cubic graph has a {P3, P4, P5}‐factor. In this paper, we prove that every 2‐connected cubic graph of order at least six has a {Pkk ≥ , 6}‐factor, and hence has a {P3, P4}‐factor. © 2002 Wiley Periodicals, Inc. J Graph Theory 39: 188–193, 2002; DOI 10.1002/jgt.10022  相似文献   
338.
Targeting cancer with small molecule prodrugs should help overcome problems associated with conventional cancer‐targeting methods. Herein, we focused on lysine‐specific demethylase 1 (LSD1) to trigger the controlled release of anticancer drugs in cancer cells, where LSD1 is highly expressed. Conjugates of the LSD1 inhibitor trans‐2‐phenylcyclopropylamine (PCPA) were used as novel prodrugs to selectively release anticancer drugs by LSD1 inhibition. As PCPA‐drug conjugate (PDC) prototypes, we designed PCPA‐tamoxifen conjugates 1 a and 1 b , which released 4‐hydroxytamoxifen in the presence of LSD1 in vitro. Furthermore, 1 a and 1 b inhibited the growth of breast cancer cells by the simultaneous inhibition of LSD1 and the estrogen receptor without exhibiting cytotoxicity toward normal cells. These results demonstrate that PDCs provide a useful prodrug method that may facilitate the selective release of drugs in cancer cells.  相似文献   
339.
Dynamic and efficient inversion of peptide helices by an achiral NO3- anion was programmed in terms of time scale from milliseconds to hours.  相似文献   
340.
XH/pi hydrogen bonds have been predicted to make important contributions to protein structure and function. NMR evidence is presented for an OH/pi interaction between a highly conserved threonine and phenylalanine pair found specifically in CAP-Gly domains associated with mictrotubule plus ends. The functional contribution of this nonclassical hydrogen bond in target peptide recognition is demonstrated via subtle point mutagenesis. The OH/pi interaction is part of a TxFxxxxW motif that comprises a conserved "threonine clasp" that defines function in CAP-Gly domains.  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