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   201486篇
  免费   2244篇
  国内免费   494篇
化学   110262篇
晶体学   3358篇
力学   7994篇
综合类   11篇
数学   19203篇
物理学   63396篇
  2020年   1722篇
  2019年   1921篇
  2018年   2238篇
  2017年   2356篇
  2016年   3518篇
  2015年   2194篇
  2014年   3547篇
  2013年   9089篇
  2012年   6514篇
  2011年   8014篇
  2010年   5698篇
  2009年   5657篇
  2008年   7161篇
  2007年   7071篇
  2006年   6703篇
  2005年   6059篇
  2004年   5526篇
  2003年   5106篇
  2002年   4871篇
  2001年   6143篇
  2000年   4625篇
  1999年   3524篇
  1998年   2747篇
  1997年   2705篇
  1996年   2595篇
  1995年   2443篇
  1994年   2335篇
  1993年   2168篇
  1992年   2832篇
  1991年   2736篇
  1990年   2674篇
  1989年   2692篇
  1988年   2714篇
  1987年   2725篇
  1986年   2592篇
  1985年   3308篇
  1984年   3318篇
  1983年   2602篇
  1982年   2714篇
  1981年   2703篇
  1980年   2477篇
  1979年   2825篇
  1978年   2827篇
  1977年   2952篇
  1976年   2790篇
  1975年   2535篇
  1974年   2478篇
  1973年   2444篇
  1972年   1680篇
  1968年   1702篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
An experimental scheme of the spin detailed balance in polarized neutron transmission through a polarized nuclear target is discussed for the T-violation test. The value of the spin detailed balance is estimated by using the data of the scattering amplitudes. The nuclear polarizations of proton,3He and139La are discussed for the T-violation experiment.  相似文献   
992.
A two-dimensional self consistent model of the Beam-Plasma-Discharge (BPD) has been developed to calculate the discharge ignition of a bandlike electron beam in a discharge chamber. The discharge was considered in Argon with an initial concentration of 1014 cm?3. The model allows calculation of the time evolution of perpendicular profiles of electron density, temperature and the potential.  相似文献   
993.
Summary A method of joining two metal cylindrical shafts with adhesive coupling is proposed. Two cylindrical shafts with the same diameter are connected by bonding through a cylindrical coupling with epoxy resin. The strength of the shaft joint under tensile loading and torsional loading is investigated analytically and experimentally. The stress and strain distributions of the shaft joint is analyzed by the finite element method. The analyzed strain distributions in the joint are compared with experimental values. The joint strength is predicted by applying the strength laws of shafts, coupling, adhesive layer and adhesive interface between shaft and adhesive coupling. The effects of the coupling dimension on the joint strength are examined. It is shown that the adhesive shaft joint can transfer the load by which the cylindrical shafts are plastically deformed.This paper was refined by the author, K. Ikegami, during statying at Technische Universität München under the support of Deutscher Akademischer Austauschdients. The author is grateful to Professor Lippmann of Technische Universität München who is the host professor of the support.  相似文献   
994.
Book reviews     
Ohne Zusammenfassung
Book reviews
  相似文献   
995.
Two extensions of the univariate Gini index are considered:RD, based on expected distance between two independent vectors from the same distribution with finite meanμ d; andRV, related to the expected volume of the simplex formed fromd+1 independent such vectors. A new characterization ofRDas proportional to a univariate Gini index for a particular linear combination of attributes relates it to the Lorenz zonoid. TheLorenz zonoidwas suggested as a multivariate generalization of the Lorenz curve.RVis, up to scaling, the volume of the Lorenz zonoid plus a unit cube of full dimension. Whend=1, bothRDandRVequal twice the area between the usual Lorenz curve and the line of zero disparity. Whend>1, they are different, but inherit properties of the univariate Gini index and are related via the Lorenz zonoid:RDis proportional to the average of the areas of some two-dimensioned projections of the lift zonoid, whileRVis the average of the volumes of projections of the Lorenz zonoid over all coordinate subspaces.  相似文献   
996.
997.
Summary A new approach to cancer treatment using low-energy gamma-rays is discussed. Cultures of bone marrow mononuclear cells collected from normal donors and patients with chronic myelogenous leukaemia have been studied after the addition of hematin, at different concentrations, and irradiation by a M?ssbauer gamma-ray source. Growth stimulation has been observed when hematin is added to normal bone marrow cultures, while growth inhibition is observed when hematin is added to leukaemic cultures. The effect becomes then more pronounced when hematin is used in combination with M?ssbauer gamma-rays.  相似文献   
998.
999.
Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates.  相似文献   
1000.
A simple High performance liquid chromatographic (HPLC) method for the specific determination of the molecular weight and concentration of hyaluronic acid (HA) in complex mixtures has been developed. Hyaluronate-binding proteins isolated from bovine cartilage labelled by 125I or fluoresceinisothiocyanate were used as specific markers. The specific binding affinities of the markers were compared and were found to have association constants of 1.6 x 10(7) M-1 and 1.2 x 10(7) M-1 respectively. The HA levels and molecular weight distributions can be easily determined in the range 10-500 ng/mL in complex mixtures by the use of markers, molecular sieving HPLC columns and appropriate detectors. It has been demonstrated clearly that the method is useful for the highly specific determination of the parameters in complex biological samples such as serum and synovial fluids and is recommended for clinical applications.  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