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   2451篇
  免费   168篇
  国内免费   155篇
化学   358篇
晶体学   17篇
力学   74篇
综合类   7篇
数学   840篇
物理学   1478篇
  2023年   10篇
  2022年   12篇
  2021年   35篇
  2020年   19篇
  2019年   36篇
  2018年   25篇
  2017年   33篇
  2016年   29篇
  2015年   31篇
  2014年   43篇
  2013年   57篇
  2012年   58篇
  2011年   149篇
  2010年   155篇
  2009年   331篇
  2008年   309篇
  2007年   247篇
  2006年   236篇
  2005年   142篇
  2004年   78篇
  2003年   102篇
  2002年   109篇
  2001年   77篇
  2000年   79篇
  1999年   82篇
  1998年   58篇
  1997年   13篇
  1996年   26篇
  1995年   22篇
  1994年   18篇
  1993年   15篇
  1992年   21篇
  1991年   12篇
  1990年   4篇
  1989年   4篇
  1988年   6篇
  1987年   7篇
  1985年   12篇
  1984年   7篇
  1983年   3篇
  1982年   4篇
  1981年   7篇
  1980年   7篇
  1979年   9篇
  1978年   2篇
  1977年   7篇
  1976年   7篇
  1975年   2篇
  1974年   4篇
  1973年   9篇
排序方式: 共有2774条查询结果,搜索用时 15 毫秒
961.
The problem of the existence of a decomposition of the complete graph ey:10638539:media:jcd21340:jcd21340-math-0001" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/d6fc7852-26a2-4447-ab7b-0388b9650a52/jcd21340-math-0001.png"> into disjoint copies of ey:10638539:media:jcd21340:jcd21340-math-0002" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/9074b2e7-9cfc-4c66-90e8-027b5805086e/jcd21340-math-0002.png"> has been solved for all admissible orders n, except for 27, 36, 54, 64, 72, 81, 90, 135, 144, 162, 216, and 234. In this paper, I eliminate 4 of these 12 unresolved orders. Let Γ be a ey:10638539:media:jcd21340:jcd21340-math-0003" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/a61e6418-7e5a-4dea-b2a8-2c025bb1ed46/jcd21340-math-0003.png">‐design. I show that ey:10638539:media:jcd21340:jcd21340-math-0004" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/a8ed2ff0-bd29-4fed-a250-632f8aef179c/jcd21340-math-0004.png"> divides 2k3 for some ey:10638539:media:jcd21340:jcd21340-math-0005" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/f4ddfec9-7db3-4ab7-bd0e-582b95093971/jcd21340-math-0005.png"> and that ey:10638539:media:jcd21340:jcd21340-math-0006" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/f252b987-f05c-4c1e-a031-be3ffe4227ea/jcd21340-math-0006.png">. I construct ey:10638539:media:jcd21340:jcd21340-math-0007" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/7d6ffd14-136b-4c3c-8887-df2a6684e70a/jcd21340-math-0007.png">‐designs by prescribing ey:10638539:media:jcd21340:jcd21340-math-0008" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/1aee69fe-af32-4924-8ccb-5a574f4f4c71/jcd21340-math-0008.png"> as an automorphism group, and show that up to isomorphism there are exactly 24 ey:10638539:media:jcd21340:jcd21340-math-0009" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/842957cf-160d-45ff-a840-dd2cf8ad6899/jcd21340-math-0009.png">‐designs with ey:10638539:media:jcd21340:jcd21340-math-0010" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/173d172c-ba9c-4ca9-8148-26036172426c/jcd21340-math-0010.png"> as an automorphism group. Moreover, I show that the full automorphism group of each of these designs is indeed ey:10638539:media:jcd21340:jcd21340-math-0011" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/aa34ce76-7813-424d-9b4d-23c6a28303df/jcd21340-math-0011.png">. Finally, the existence of ey:10638539:media:jcd21340:jcd21340-math-0012" class="section_image" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/a9993ac3-c5ea-4ee9-9de1-57fc45570ff6/jcd21340-math-0012.png">‐designs of orders 135, 162, and 216 follows immediately by the recursive constructions given by G. Ge and A. C. H. Ling, SIAM J Discrete Math 21(4) (2007), 851–864.  相似文献   
962.
The effect of bias voltage on electron tunneling across a junction with a ferroelectric-ferromagnetic composite barrier is investigated theoretically. Because of the inversion symmetry breaking of the spontaneous ferroelectric polarization, bias voltage dependence of the electron tunneling shows significant differences between the positive bias and the negative one. The differences of spin filtering or tunnel magnetoresistance increase with the increasing absolute value of bias voltage. Such direction preferred electron tunneling is found intimately related with the unusual asymmetry of the electrical potential profile in two-phase composite barrier and provides a unique change to realize rectifying functions in spintronics.  相似文献   
963.
Let P = E G be a Zappa-Szp product of a semilattice E with an identity and a group G. In this paper, we first introduce the concept of congruence pairs for P , and then prove that every congruence on P can be described by such a congruence pair. In fact the congruence lattice on P is lattice-isomorphic to the set of all congruence pairs for P . Finally,we characterize group congruences on P .  相似文献   
964.
The standard distorted wave Born approximation(DWBA) method has been extended to second-order Born amplitude in order to describe the multiple interactions between the projectile and the atomic target.Second-order DWBA calculations have been preformed to investigate the triple differential cross sections(TDCS) of coplanar doubly symmetric(e,2e) collisions for the alkali target potassium at excess energies of 6 eV-60 eV.Compared with the previous first-order DWBA calculations,the present theoretical model improves the degree of agreement with experiments,especially for the backward scattering angle region of TDCS.This indicates that the present second-order Born term is capable of giving a reasonable correction to the DWBA model in studying coplanar symmetric(e,2e) problems in low and intermediate energy ranges.  相似文献   
965.
In this article, we introduce the concept of lacunary <em>Iem>-convergent sequence of fuzzy real numbers and study some basic properties.  相似文献   
966.
Following the line of recent works of Das et al. (2011) [15] and Savas and Das (2011) [19] we apply the notion of ideals to strong matrix summability, and in this note, we introduce the notion of strong <em>Aem><em>Iem>-summability with respect to an Orlicz function. We make certain investigations on the classes of sequences arising out of this new summability method.  相似文献   
967.
文中采用氨原子的三种近似波函数,计算了入射电子能量为5599 eV时,敲出电子共面等能分享几何安排下,氦原子双电离He(e,3e)反应全微分截面.结果表明三种波函数的理论计算结果,在误差范围内都与实验数据基本吻合,其中采用Pluvinage波函数所得到的理论数据更接近实验数据.  相似文献   
968.
In this study the adsorption geometry of aspirin molecule on a hydroxylated (0 0 1) α-quartz surface has been investigated using DFT calculations. The optimized adsorption geometry indicates that both, adsorbed molecule and substrate are strongly deformed. Strong hydrogen bonding between aspirin and surface hydroxyls, leads to the breaking of the original hydroxyl–hydroxyl hydrogen bonds (Hydrogenbridges) on the surface. In this case new hydrogen bonds on the hydroxylated (0 0 1) α-quartz surface appear which significantly differ from those at the clean surface. The 1.11 eV adsorption energy reveals that the interaction of aspirin with α-quartz is an exothermic chemical interaction.  相似文献   
969.
In this paper, we design resonant reflection grating filters employing the second diffracted orders as the leaky modes, then analyze the bandwidth of the reflection peak and the electric field distributions inside the waveguide under resonance. The numeric calculation confirms that ultra-narrow resonant reflection peaks can be observed in these structures. At the same time, strong electric field enhancement appears under resonance. It provides a new approach to diversify the resonant reflection filters and may open a new way to the realization of ultra-narrow bandwidth filters.  相似文献   
970.
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