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   2628篇
  免费   60篇
  国内免费   19篇
化学   1608篇
晶体学   26篇
力学   57篇
数学   390篇
物理学   626篇
  2021年   18篇
  2020年   22篇
  2019年   32篇
  2017年   22篇
  2016年   39篇
  2015年   48篇
  2014年   56篇
  2013年   142篇
  2012年   100篇
  2011年   131篇
  2010年   75篇
  2009年   67篇
  2008年   122篇
  2007年   127篇
  2006年   130篇
  2005年   114篇
  2004年   119篇
  2003年   90篇
  2002年   71篇
  2001年   53篇
  2000年   35篇
  1999年   32篇
  1998年   37篇
  1997年   28篇
  1996年   52篇
  1995年   39篇
  1994年   28篇
  1993年   42篇
  1992年   33篇
  1991年   25篇
  1990年   26篇
  1989年   42篇
  1988年   33篇
  1987年   35篇
  1986年   19篇
  1985年   51篇
  1984年   48篇
  1983年   24篇
  1982年   41篇
  1981年   33篇
  1980年   34篇
  1979年   30篇
  1978年   47篇
  1977年   40篇
  1976年   32篇
  1975年   30篇
  1974年   42篇
  1973年   27篇
  1972年   17篇
  1971年   18篇
排序方式: 共有2707条查询结果,搜索用时 128 毫秒
1.
Transport in Porous Media - In the original publication of the article, Table 2 was published incorrectly.  相似文献   
2.
A fundamental question in random matrix theory is to quantify the optimal rate of convergence to universal laws. We take up this problem for the Laguerre β ensemble, characterized by the Dyson parameter β, and the Laguerre weight , in the hard edge limit. The latter relates to the eigenvalues in the vicinity of the origin in the scaled variable . Previous work has established the corresponding functional form of various statistical quantities—for example, the distribution of the smallest eigenvalue, provided that . We show, using the theory of multidimensional hypergeometric functions based on Jack polynomials, that with the modified hard edge scaling , the rate of convergence to the limiting distribution is , which is optimal. In the case , general the explicit functional form of the distribution of the smallest eigenvalue at this order can be computed, as it can for and general . An iterative scheme is presented to numerically approximate the functional form for general .  相似文献   
3.
4.
Bionized nanoferrite (BNF) particles with high specific power absorption rates were synthesized in the size range of 20–100 nm by high-pressure homogenization for targeted cancer therapy with alternating magnetic fields. Several strategies were used to conjugate antibodies to the BNF particles. These strategies were compared using an immunoassay to find optimal conditions to reach a high immunoreactivity of the final antibody–particle conjugate.  相似文献   
5.
In this paper, we extend the oscillation criteria that have been established by Hille [E. Hille, Non-oscillation theorems, Trans. Amer. Math. Soc. 64 (1948) 234-252] and Nehari [Z. Nehari, Oscillation criteria for second-order linear differential equations, Trans. Amer. Math. Soc. 85 (1957) 428-445] for second-order differential equations to third-order dynamic equations on an arbitrary time scale T, which is unbounded above. Our results are essentially new even for third-order differential and difference equations, i.e., when T=R and T=N. We consider several examples to illustrate our results.  相似文献   
6.
7.
A new algorithm is presented for computing the topological entropy of a unimodal map of the interval. The accuracy of the algorithm is discussed and some graphs of the topological entropy which are obtained using the algorithm are displayed.  相似文献   
8.
The Sommerfeld diffraction theory is extended to the case of extremely short pulses. It is shown that a simple qualitative analysis and a quantitative solution of a wide class of diffraction problems are possible for pulses with durations of the order of the period of the light oscillations and an arbitrary initial distribution of the light field. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 323–326 (10 September 1997) Deceased  相似文献   
9.
A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18 adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma.  相似文献   
10.
Improved reaction conditions for the preparation of poly(p‐phenylene sulfide) (PPS) directly from bis(4‐bromophenyl) disulfide (BBD) have been established. Heating BBD with magnesium metal afforded only a low molecular weight polymer. PPS with a melting temperature around 280 °C was obtained from BBD in the presence of sodium carbonate or zinc metal. The best results were obtained with the addition of a catalytic amount of KI to the zinc–BBD mixture. Polymers prepared by the above methods are semicrystalline and dissolve in 1‐chloronaphthalene and have properties comparable to commercial PPS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 900–904, 2006  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