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   2480篇
  免费   94篇
  国内免费   10篇
化学   1836篇
晶体学   51篇
力学   82篇
数学   144篇
物理学   471篇
  2023年   22篇
  2022年   40篇
  2021年   51篇
  2020年   42篇
  2019年   76篇
  2018年   60篇
  2017年   46篇
  2016年   73篇
  2015年   55篇
  2014年   65篇
  2013年   192篇
  2012年   119篇
  2011年   188篇
  2010年   99篇
  2009年   72篇
  2008年   99篇
  2007年   116篇
  2006年   100篇
  2005年   84篇
  2004年   77篇
  2003年   60篇
  2002年   86篇
  2001年   47篇
  2000年   41篇
  1999年   19篇
  1998年   20篇
  1997年   21篇
  1996年   25篇
  1995年   17篇
  1994年   21篇
  1993年   21篇
  1992年   34篇
  1991年   16篇
  1990年   16篇
  1989年   16篇
  1988年   19篇
  1987年   24篇
  1986年   22篇
  1985年   23篇
  1984年   24篇
  1983年   27篇
  1980年   23篇
  1978年   15篇
  1976年   13篇
  1975年   13篇
  1966年   25篇
  1965年   18篇
  1964年   14篇
  1963年   16篇
  1962年   43篇
排序方式: 共有2584条查询结果,搜索用时 15 毫秒
1.
New aromatic (co)polyesters containing pendant propargyloxy groups were synthesized by phase transfer‐catalyzed interfacial polycondensation of 5‐(propargyloxy)isophthaloyl chloride (P‐IPC) and various compositions of P‐IPC and isophthaloyl chloride with bisphenol A. FTIR and NMR spectroscopic data, respectively, revealed successful incorporation of pendant propargyloxy groups into (co)polyesters and formation of (co)polyesters with desired compositions. (Co)polyesters exhibited good solubility in common organic solvents such as chloroform, dichloromethane, and tetrahydrofuran and could be cast into transparent, flexible, and tough films from chloroform solution. Inherent viscosities and number average molecular weights of (co)polyesters were in the range 0.77–1.33 dL/g and 43,600–118,000 g/mol, respectively, indicating the achievement of reasonably high‐molecular weights. The 10% weight loss temperatures of (co)polyesters were in the range 390–420 °C, demonstrating their good thermal stability. (Co)polyesters exhibited Tg in the range 146–170 °C and Tg values decreased with increase in mol % incorporation of P‐IPC. The study of non‐isothermal curing by DSC indicated thermal crosslinking of (co)polyesters via propargyloxy groups. The utility of pendant propargyloxy group was demonstrated by post‐modification of the selected copolyester with 1‐(4‐azidobutyl)pyrene, 9‐(azidomethyl)anthracene, and azido‐terminated poly(ethyleneglycol) monomethyl ether via copper(I)‐catalyzed Huisgen 1,3‐dipolar cycloaddition reaction. FTIR and 1H NMR spectra confirmed that click reaction was quantitative. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 588–597  相似文献   
2.
Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO5 samples doped with CeO2 and co-doped with CeO2 and Sm2O3. On gamma-irradiation at room temperature, BO3 2–, O2 and O radicals were produced. It was seen that the O radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O radical ions results in transfer of recombination energy to the impurity centre Ce3+ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce3+ to Sm3+ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work.  相似文献   
3.
Summary We introduce nonparametric estimators of the autocovariance of a stationary random field. One of our estimators has the property that it is itself an autocovatiance. This feature enables the estimator to be used as the basis of simulation studies such as those which are necessary when constructing bootstrap confidence intervals for unknown parameters. Unlike estimators proposed recently by other authors, our own do not require assumptions such as isotropy or monotonicity. Indeed, like nonparametric function estimators considered more widely in the context of curve estimation, our approach demands only smoothness and tail conditions on the underlying curve or surface (here, the autocovariance), and moment and mixing conditions on the random field. We show that by imposing the condition that the estimator be a covariance function we actually reduce the numerical value of integrated squared error.  相似文献   
4.
This is the report of the subgroup QCD of Working Group-4 at WHEPP-9. We present the activities that had taken place in the subgroup and report some of the partial results arrived at following the discussion at the working group meetings.  相似文献   
5.
Satya Prakash 《Pramana》1989,33(1):109-131
This article summarizes the recent radiochemical investigations on mass, charge kinetic energy and fragment angular distributions in low energy fission of actinides.  相似文献   
6.
Over the last two decades many strategies have been planned to design specific drugs for rare diseases to target their action at the DNA level. Advancements in our understanding of the interactions of small nonpeptide molecules with DNA have opened the doors for “rational” drug design. Special methods have now been developed to give accurate account of the precise location of ligand-DNA adducts on target DNA. We are now in a position to think of designing ligands that recognize particular sequences of base pairs. This work will allow us to enter into a new era of gene therapy for diseases like Cystic fibrosis, Alzheimer’s disease and many related disorders at genetic level. These ligands can also be employed in the treatment of various types of cancers. They may also be useful as highly specific probes to locate particular sequences in the genomic DNA.  相似文献   
7.
8.
9.
We demonstrate a technique to measure hyperfine structure using a frequency-stabilized diode laser and an acousto-optic modulator locked to the frequency difference between two hyperfine peaks. We use this technique to measure hyperfine intervals in the 5 P 3/2 state of 85Rb and obtain a precision of 20 kHz. We extract values for the magnetic-dipole coupling constant A = 25.038(5) MHz and the electric-quadrupole coupling constant B = 26.011(22) MHz. These values are a significant improvement over previous results. Received 6 March 2003 Published online 15 April 2003  相似文献   
10.
Themaximal minor polytope Π m, n is the Newton polytope of the product of all maximal minors of anm×n matrix of indeterminates. The family of polytopes {Π m, n } interpolates between the symmetric transportation polytope (form=n−1) and the permutohedron (form=2). Both transportation polytope and the permutohedron aresimple polytopes but in general Π m, n is not simple. The main result of this paper is an explicit construction of a class of simple vertices of Π m, n for generalm andn. We call themvertices of diagonal type. For every such vertexv we explicitly describe all the edges and facets of Π m, n which containv. Simple vertices of Π m, n have an interesting algebro-geometric application: they correspond tononsingular extreme toric degenerations of the determinantal variety ofm×n matrices not of full rank. Andrei Zelevinsky was partially supported by the NSF under Grant DMS-9104867.  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