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   204458篇
  免费   1716篇
  国内免费   593篇
化学   102552篇
晶体学   3345篇
力学   9290篇
综合类   5篇
数学   22514篇
物理学   69061篇
  2021年   1658篇
  2020年   1798篇
  2019年   2003篇
  2018年   2700篇
  2017年   2602篇
  2016年   3772篇
  2015年   2308篇
  2014年   3619篇
  2013年   9090篇
  2012年   7248篇
  2011年   8744篇
  2010年   6043篇
  2009年   5919篇
  2008年   7928篇
  2007年   8098篇
  2006年   7732篇
  2005年   6905篇
  2004年   6436篇
  2003年   5660篇
  2002年   5499篇
  2001年   6429篇
  2000年   4937篇
  1999年   3798篇
  1998年   3043篇
  1997年   3053篇
  1996年   2794篇
  1995年   2618篇
  1994年   2474篇
  1993年   2342篇
  1992年   2696篇
  1991年   2678篇
  1990年   2607篇
  1989年   2398篇
  1988年   2459篇
  1987年   2452篇
  1986年   2285篇
  1985年   2968篇
  1984年   3219篇
  1983年   2632篇
  1982年   2803篇
  1981年   2773篇
  1980年   2644篇
  1979年   2732篇
  1978年   2824篇
  1977年   2824篇
  1976年   2890篇
  1975年   2675篇
  1974年   2648篇
  1973年   2777篇
  1972年   1764篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
942.
Lyoluminescence of luminol induced by -irradiated NaCl has been studied in aqueous amines. The emission spectra of lyoluminescence are recorded on 400 ASA Kodak film using a Fuess spectrograph. A broad continuous emission band appears in the visible region from 390 to 500 nm. The emission band showed two peaks centered at 430 and 470 nm. The 430 nm peak is more intense in secondary amines while the 470 nm band is more intense in primary amines. The mechanism of light emission is based on the comparative study of lyoluminescence, fluorescence and chemiluminescence of luminol in aqueous amines.  相似文献   
943.
The electrochemical production and doping of soluble, as well as the physicochemical properties of a soluble electrically conducting polymer based on 3-methyl-4-phenylthiophene were studied.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 29, No. 2, pp. 143–148, March–April, 1993.The authors would like to express gratitude to the State Committee of the Ukraine on questions of science and technology for financial support for this work within the framework of the State Scientific and Technical Program 7.1. Materials for Electronic Technology, as well as to V. P. Kandilenko and V. Ya. Chernov for aid in recording the fluorescence spectra of the P3M4PT films.  相似文献   
944.
Electroanalytical methods based on biosensor technology and differential pH measurement for the determination of l-lactic and l-malic acids in wine were developed. Lactic acid was determined according to two procedures consisting of the use of two lactate electrochemical biosensors, one based on a Clark O(2) probe and the other based on the H(2)O(2) probe. The two probes were assembled employing a polymeric membrane where the enzyme lactate oxidase was previously immobilized. Both sensors exhibited high storage and operational stabilities, and good reproducibility when used in wine matrix. Measurement of lactate was carried out using two different flow-through cells assembled with the lactate probes. The low detection limit of these probes and the relatively high concentration of lactate in wine samples required a serial dilution in the range 1:100 to 1:200, thus eliminating all potential electrochemical or enzyme interferences present in the sample. Malic acid was determined using a differential commercially available pH-meter and an enzymatic procedure. For this analysis, we employed the malic enzyme (EC 1.1.1.40) and the NADP(+) cofactor. The pH variation due to the action of this enzyme on malic acid was found to be proportional to the malic acid present in the sample. Experimental parameters such as pH, temperature, and co-factor concentration were optimized, resulting in malate determination in less than 1 min with good reproducibility. Various samples of wine and wine musts were assayed for lactate with the two biosensor procedures, and for malate with differential pH-metry. The results when compared with those obtained with the commonly used spectrophotometric procedure correlated well.  相似文献   
945.
We formulate a series of conjectures (and a few theorems) on the quotient of the polynomial ring in two sets of variables by the ideal generated by all S n invariant polynomials without constant term. The theory of the corresponding ring in a single set of variables X = {x 1, ..., x n} is classical. Introducing the second set of variables leads to a ring about which little is yet understood, but for which there is strong evidence of deep connections with many fundamental results of enumerative combinatorics, as well as with algebraic geometry and Lie theory.  相似文献   
946.
In the spirit of work of Kerman and Sawyer, a condition is given that is necessary and sufficient for the Fourier transform norm inequality $\Big(\int_{{\Bbb R}_d} \vert\hat{f}\vert^q d\mu\Big)^{1/q} \leq C\Big(\int_{{\Bbb R}_d} \vert f\vert^p v\Big)^{1/p}$ provided v is a radial weight for which v?1/p is convexly decreasing and μ is a suitable measure. We also establish alternative conditions for such inequalities by proving corresponding trace type inequalities and maximal function inequalities that underlie the Fourier transform estimates. Our conditions are relatively simple to compute. Among applications we give extensions of a Sobolev restriction theorem.  相似文献   
947.
948.
LetG R be the graph obtained by joining all sites ofZ d which are separated by a distance of at mostR. Let (G R ) denote the connective constant for counting the self-avoiding walks in this graph. Let (G R ) denote the coprresponding constant for counting the trees embedded inG R . Then asR, (G R ) is asymptotic to the coordination numberk R ofG R , while (G R ) is asymptotic toek R. However, ifd is 1 or 2, then (G R )-k R diverges to –.Dedicated to Oliver Penrose on this occasion of his 65th birthday.  相似文献   
949.
The devices and systems for EHF therapy and diagnosis of the BAYuR series are examined and compared with known analogs.Scientific-Research Measuring-Systems Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 1, pp. 155–157, January, 1994.  相似文献   
950.
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