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   76818篇
  免费   5936篇
  国内免费   7059篇
化学   26621篇
晶体学   319篇
力学   6665篇
综合类   1427篇
数学   33349篇
物理学   21432篇
  2023年   594篇
  2022年   1013篇
  2021年   1388篇
  2020年   1476篇
  2019年   1765篇
  2018年   1461篇
  2017年   1824篇
  2016年   2104篇
  2015年   1746篇
  2014年   2720篇
  2013年   5039篇
  2012年   3077篇
  2011年   3522篇
  2010年   3065篇
  2009年   4274篇
  2008年   4720篇
  2007年   4935篇
  2006年   4548篇
  2005年   3898篇
  2004年   3567篇
  2003年   3602篇
  2002年   3326篇
  2001年   2813篇
  2000年   2705篇
  1999年   2422篇
  1998年   2280篇
  1997年   1868篇
  1996年   1657篇
  1995年   1480篇
  1994年   1377篇
  1993年   1160篇
  1992年   1108篇
  1991年   868篇
  1990年   723篇
  1989年   616篇
  1988年   571篇
  1987年   447篇
  1986年   380篇
  1985年   469篇
  1984年   453篇
  1983年   230篇
  1982年   361篇
  1981年   425篇
  1980年   314篇
  1979年   306篇
  1978年   233篇
  1977年   215篇
  1976年   157篇
  1974年   109篇
  1973年   105篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We determine the limiting density of the zeroes of Heine–Stieltjes polynomials (or of any set of points satisfying the conclusion of Heine–Stieltjes Theorem) in the thermodynamic limit and use this to prove a strong law of large numbers for the zeroes.  相似文献   
992.
It is generally in a firm’s interest for its supply chain partners to invest in innovations. To the extent that these innovations either reduce the partners’ variable costs or stimulate demand for the end product, they will tend to lead to higher levels of output for all of the firms in the chain. However, in response to the innovations of its partners, a firm may have an incentive to opportunistically increase its own prices. The possibility of such opportunistic behavior creates a hold-up problem that leads supply chain partners to underinvest in innovation. Clearly, this hold-up problem could be eliminated by a pre-commitment to price. However, by making an advance commitment to price, a firm sacrifices an important means of responding to demand uncertainty. In this paper we examine the trade-off that is faced when a firm’s channel partner has opportunities to invest in either cost reduction or quality improvement, i.e. demand enhancement. Should it commit to a price in order to encourage innovation, or should it remain flexible in order to respond to demand uncertainty. We discuss several simple wholesale pricing mechanisms with respect to this trade-off.  相似文献   
993.
Valuable insights into the problem of how to fund defined benefitpension schemes can be obtained by analysis using the standardBlack–Scholes/Merton option pricing model, consideringthe pension fund finances jointly with those of the sponsoringcompany. The nature of the fund assets and liabilities is completelydifferent, and this lies behind current controversies aboutthe appropriate discount rate, valuation, financial accountingand preferential status for pension fund claimants in insolvency.  相似文献   
994.
基于突变论的林火蔓延分析   总被引:8,自引:0,他引:8  
在对森林火灾进行能量和质量守恒分析的基础上,把尖点突变模型应用于森林火灾蔓延的预测,使突变理论在 森林火灾的模型中从理论上有了初步的应用。文中计算了林火发生突变时的一些分歧点,分析了林火突变的特点和变化规 律。  相似文献   
995.
We consider a discretized volume V consisting of finite, congruent and attached copies of a tile t. We find a group L V the orbit of which, when applied to t, is just V. We show the connection between the structural matrixQ in the formal solution of a boundary value problem formulated for volume V and the so called auxiliary matrix of the graph Γ v associated with V. We show boundary value problems to be isomorphic if the graphs associated with the volumes are isomorphic, or, if the covering groups are Sunada pairs.  相似文献   
996.
The purpose of this paper is to review the mechanisms and available theoretical methods for modeling the strength and failure of thin film/substrate systems  相似文献   
997.
We exhibit a general class of interactive decision situations in which all the agents benefit from more information. This class includes as a special case the classical comparison of statistical experiments à la Blackwell. AMS 2000 Subject Classification:Primary 91A35.The work of Bruno Bassan and Marco Scarsini was partially supported by MIUR-COFIN. The authors express their thanks to Sylvain Sorin for enlightening comments.  相似文献   
998.
We give asymptotic formulas for the multiplicities of weights and irreducible summands in high-tensor powers VλN of an irreducible representation Vλ of a compact connected Lie group G. The weights are allowed to depend on N, and we obtain several regimes of pointwise asymptotics, ranging from a central limit region to a large deviations region. We use a complex steepest descent method that applies to general asymptotic counting problems for lattice paths with steps in a convex polytope.  相似文献   
999.
从患罗氏沼虾幼苗肌肉白浊病的幼虾体内分离到两种病毒颗粒,诺达病毒(MrNV)和直径只有15nm的小病毒颗粒(extrasmallvirus,XSV),本文通过建立病毒cDNA文库获得XSV基因组的部分序列,在此基础上合成探针,用从病虾组织中提取的总PNA进行Northern杂交,结果表明XSV基因组至少包括两条RNA片段.利用不同的方法对XSV的两端序列进行克隆和测定,分别得到了872、831和662bp3个相互重叠的序列片段,这3个序列的阅读框编码一个相同的大小在17×103左右的蛋白.  相似文献   
1000.
The authors give error estimates, a Voronovskaya-type relation, strong converse results and saturation for the weighted approximation of functions on the real line with Freud weights by Bernstein-type operators.  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