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   1234篇
  免费   62篇
  国内免费   26篇
化学   923篇
晶体学   12篇
力学   46篇
数学   89篇
物理学   252篇
  2024年   11篇
  2023年   11篇
  2022年   26篇
  2021年   84篇
  2020年   66篇
  2019年   58篇
  2018年   46篇
  2017年   36篇
  2016年   66篇
  2015年   39篇
  2014年   59篇
  2013年   77篇
  2012年   98篇
  2011年   96篇
  2010年   50篇
  2009年   47篇
  2008年   61篇
  2007年   61篇
  2006年   45篇
  2005年   45篇
  2004年   21篇
  2003年   22篇
  2002年   20篇
  2001年   10篇
  2000年   7篇
  1999年   3篇
  1997年   12篇
  1996年   9篇
  1995年   7篇
  1994年   7篇
  1993年   8篇
  1992年   5篇
  1991年   7篇
  1989年   3篇
  1988年   4篇
  1987年   4篇
  1986年   4篇
  1985年   6篇
  1984年   13篇
  1983年   3篇
  1982年   11篇
  1981年   4篇
  1980年   4篇
  1979年   2篇
  1978年   7篇
  1977年   4篇
  1976年   6篇
  1975年   8篇
  1973年   6篇
  1972年   5篇
排序方式: 共有1322条查询结果,搜索用时 312 毫秒
1.
It is pointed out that the observation of the electrostatic ion acoustic wave frequency can be a suitable check to determine whether the produced plasma is a pure pair-ion plasma or whether it comprises some concentration of electrons. A theoretical model for the pair-ion plasma dynamics is presented along with a new electrostatic mode which can exist only in such systems. It can become unstable in the presence of shear flow and it can give rise to vortex structures in the nonlinear regime. The possibility of shocks and solitons, due to nonlinear drift waves in a pair-ion plasma comprising electrons, is also discussed. The relevance of this investigation to both laboratory and astrophysical plasmas is pointed out.  相似文献   
2.
A closed-form expression is presented to find the location of solid-liquid interface motion in convection-dominated solidification and melting problems. In this regard, the solutions are expressed in terms of the generalized representations of error functions,E (u, v) andF (u, v), which are useful to heat-conduction problems with convective-type boundary conditions. It is demonstrated that for constant surface temperature, the interface solution reduces to the classical Neumann solution.  相似文献   
3.
The solubility and diffusion coefficient of carbon dioxide in intermediate‐moisture starch–water mixtures were determined both experimentally and theoretically at elevated pressures up to 16 MPa at 50 °C. A high‐pressure decay sorption system was assembled to measure the equilibrium CO2 mass uptake by the starch–water system. The experimentally measured solubilities accounted for the estimated swollen volume by Sanchez–Lacombe equation of state (S‐L EOS) were found to increase almost linearly with pressure, yielding 4.0 g CO2/g starch–water system at 16 MPa. Moreover, CO2 solubilities above 5 MPa displayed a solubility increase, which was not contributed by the water fraction in the starch–water mixture. The solubilities, however, showed no dependence on the degree of gelatinization (DG) of starch. The diffusion coefficient of CO2 was found to increase with concentration of dissolved CO2, which is pressure‐dependent, and decrease with increasing DG in the range of 50–100%. A free‐volume‐based diffusion model proposed by Areerat was employed to predict the CO2 diffusivity in terms of pressure, temperature, and the concentration of dissolved CO2. S‐L EOS was once more used to determine the specific free volume of the mixture system. The predicted diffusion coefficients showed to correlate well with the measured values for all starch–water mixtures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 607–621, 2006  相似文献   
4.
5.
6.
Fluorotricyanomethane is prepared from potassium tricyanomethanide and perchlorylfluoride. The crystal structure of this compound (orthorhombic, space group P212121, with a=6.270, b=6.734, c=11.776 Å) has been determined by X-ray analysis. The results are discussed in relation to those of (NC)3C? X (X=? CH3, ? Cl, ? Br or ? CN).  相似文献   
7.
In view of the attributed medicinal properties of beta-carboline alkaloids, some new O-acyl derivatives of beta-carboline alkaloid--harmol, were prepared and tested for possible antimycobacterial activity against Mycobacterium tuberculosis H37Rv.  相似文献   
8.
Summary A parametric study of catalytic reforming process in a pilot plant was carried out by varying the pressure, H2/HC ratio, and space velocity. The results show that lower aromatics and higher hydrogen yields can be accomplished by increasing the space velocity in existing reformers, which will also result in better C5+yield.  相似文献   
9.
The volatile products from the γ irradiation of samples of poly(vinyl chloride) prepared under different conditions and reduced to the corresponding polyethylenes have been measured quantitatively and compared with those for low- and high-density polyethylenes and copolymers of ethylene with small amounts of α-olefins. The presence of methyl branches is clearly demonstrated and there is also evidence for ethyl and butyl branches, although these had not been considered significant in previous [13C] NMR studies. The method is shown to be extremely sensitive to small quantities of residual trialkyl tin hydride reductant occluded in, and possibly also reacted with, the polymer, and to residual chlorine (<0.5%). The yields of alkanes are higher than expected from the branch frequencies determined by i.r. and [13C] NMR and results for ethylene-α-olefin copolymers. This difference is apparently due to sensitisation of the radiation degradation by residual chlorine and reductant. Quantitative determinations of branch frequencies by the radiolytic method are unlikely to be obtained until these problems are overcome.  相似文献   
10.
Desloratadine (DES) is an antihistamine used in the treatment of allergies and chronic urticaria. 1H NMR spectroscopic study of varying ratios of DES and β-Cyclodextrin (β-CD) in D2O suggests the formation of a 1:1 inclusion complex formed by the penetration of Cl-substituted aromatic ring into the β-CD cavity. The stoichiometry and binding constant of the complex were determined by Scott’s method.  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