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   2670篇
  免费   142篇
  国内免费   247篇
化学   15篇
力学   80篇
综合类   47篇
数学   2833篇
物理学   84篇
  2023年   16篇
  2022年   14篇
  2021年   27篇
  2020年   39篇
  2019年   52篇
  2018年   45篇
  2017年   70篇
  2016年   70篇
  2015年   57篇
  2014年   91篇
  2013年   140篇
  2012年   132篇
  2011年   97篇
  2010年   88篇
  2009年   142篇
  2008年   150篇
  2007年   168篇
  2006年   169篇
  2005年   144篇
  2004年   137篇
  2003年   120篇
  2002年   117篇
  2001年   100篇
  2000年   132篇
  1999年   96篇
  1998年   102篇
  1997年   109篇
  1996年   56篇
  1995年   47篇
  1994年   43篇
  1993年   44篇
  1992年   31篇
  1991年   27篇
  1990年   27篇
  1989年   14篇
  1988年   17篇
  1987年   12篇
  1986年   8篇
  1985年   14篇
  1984年   14篇
  1983年   5篇
  1982年   11篇
  1981年   13篇
  1980年   9篇
  1979年   9篇
  1978年   10篇
  1977年   9篇
  1976年   3篇
  1975年   2篇
  1974年   6篇
排序方式: 共有3059条查询结果,搜索用时 218 毫秒
1.
We investigate the value of an optimal transportation problem with the maximization objective as a function of costs and vectors of production and consumption. The value is concave in production. For generic costs, the numbers of linearity domains and peak points are independent of costs and consumption. The peak points are determined by an auxiliary assignment problem. The volumes of the linearity domains are independent of costs while their dependence on consumption can be expressed via the multinomial distribution.  相似文献   
2.
In this paper, we define interval‐valued left‐sided and right‐sided generalized fractional double integrals. We establish inequalities of Hermite‐Hadamard like for coordinated interval‐valued convex functions by applying our newly defined integrals.  相似文献   
3.
4.
The pyrolysis of propane plays an important role in determining the combustion properties of natural gas mixtures and offers insight into the cracking patterns of larger fuels. This work investigates propane pyrolysis behind reflected shock waves with a multiwavelength laser-absorption speciation technique. Nine laser wavelengths, sensitive to key pyrolysis species, were used to measure absorbance time histories during the decomposition of 2% propane in argon between 1022 and 1467 K, 3.7-4.3 atm. Absorbance models were developed at each diagnostic wavelength to interrogate common initial conditions, and time histories of all major species are reported at 1250, 1290, 1330, 1370, and 1410 K. Nearly complete carbon recovery observed at lower temperatures enabled the inference of hydrogen formation from atomic conservation, while decaying carbon recovery at high temperatures suggests the formation of allene and 1-butene. The results show systematically faster pyrolysis than predicted by kinetic modeling and motivate further study into the kinetics of propane pyrolysis.  相似文献   
5.
For wide classes of locally convex spaces, in particular, for the space C p ( X ) of continuous real‐valued functions on a Tychonoff space X equipped with the pointwise topology, we characterize the existence of a fundamental bounded resolution (i.e., an increasing family of bounded sets indexed by the irrationals which swallows the bounded sets). These facts together with some results from Grothendieck's theory of ( D F ) ‐spaces have led us to introduce quasi‐ ( D F ) ‐spaces, a class of locally convex spaces containing ( D F ) ‐spaces that preserves subspaces, countable direct sums and countable products. Regular ( L M ) ‐spaces as well as their strong duals are quasi‐ ( D F ) ‐spaces. Hence the space of distributions D ( Ω ) provides a concrete example of a quasi‐ ( D F ) ‐space not being a ( D F ) ‐space. We show that C p ( X ) has a fundamental bounded resolution if and only if C p ( X ) is a quasi‐ ( D F ) ‐space if and only if the strong dual of C p ( X ) is a quasi‐ ( D F ) ‐space if and only if X is countable. If X is metrizable, then C k ( X ) is a quasi‐ ( D F ) ‐space if and only if X is a σ‐compact Polish space.  相似文献   
6.
7.
Let K and S be locally compact Hausdorff spaces and let X be a strictly convex Banach space of finite dimension at least 2. In this paper, we prove that if there exists an isomorphism T from onto satisfying then K and S are homeomorphic. Here denotes the Schäffer constant of X. Even for the classical cases , and , this result is the X‐valued Banach–Stone theorem via isomorphism with the largest distortion that is known so far, namely . On the other hand, it is well known that this result is not true for , even though K and S are compact Hausdorff spaces.  相似文献   
8.
In this article, we prove the existence and multiplicity of non-trivial solutions for an indefinite fractional elliptic equation with magnetic field and concave–convex nonlinearities. Our multiplicity results are based on studying the decomposition of the Nehari manifold.  相似文献   
9.
水火联合调度问题是电力系统中一类复杂的优化问题。合理安排调度周期内的水火电出力,确定一个最优发电计划,可以带来巨大的经济效益。在实际系统中,汽轮机调汽阀开启时出现的拔丝现象会使机组耗量特性产生阀点效应。忽略阀点效应,在一定程度上降低求解的精度。本文考虑带阀点效应的水火联合调度问题。该问题非凸非光滑,且带有非线性约束,直接使用确定性全局优化方法求解是相当困难的。本文使用高效的半定规划求解此问题。首先用耗量特性函数的初始周期代替其余有限的周期,并对其进行二次拉格朗日插值拟合。再通过引进0-1变量,得到整个耗量特性函数的近似,进而把问题松弛为半定规划模型。最后,采用凸规划应用软件包CVX求解一个仿真算例,得到一个近似全局最优解。  相似文献   
10.
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