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   8390篇
  免费   745篇
  国内免费   657篇
化学   2119篇
晶体学   23篇
力学   860篇
综合类   146篇
数学   4862篇
物理学   1782篇
  2024年   9篇
  2023年   73篇
  2022年   95篇
  2021年   113篇
  2020年   194篇
  2019年   185篇
  2018年   197篇
  2017年   232篇
  2016年   232篇
  2015年   206篇
  2014年   332篇
  2013年   502篇
  2012年   298篇
  2011年   353篇
  2010年   375篇
  2009年   457篇
  2008年   573篇
  2007年   602篇
  2006年   515篇
  2005年   480篇
  2004年   356篇
  2003年   384篇
  2002年   350篇
  2001年   319篇
  2000年   278篇
  1999年   244篇
  1998年   277篇
  1997年   191篇
  1996年   194篇
  1995年   174篇
  1994年   134篇
  1993年   127篇
  1992年   106篇
  1991年   92篇
  1990年   59篇
  1989年   56篇
  1988年   45篇
  1987年   47篇
  1986年   42篇
  1985年   49篇
  1984年   33篇
  1983年   19篇
  1982年   39篇
  1981年   45篇
  1980年   30篇
  1979年   25篇
  1978年   19篇
  1977年   6篇
  1976年   10篇
  1973年   6篇
排序方式: 共有9792条查询结果,搜索用时 15 毫秒
61.
Historical textiles in the Topkap? Museum, which are called silk kaftans and brocades by art historians from the sixteenth and nineteenth were characterized by scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) and high-performance liquid chromatography with diode array detection for identification of metal threads and dyestuffs. In the most Ottoman textiles, metal threads, especially belonging to the sultans, were used as the gold gild. Although the chemical composition of the samples on the surface may easily be obtained by SEM–EDX, the thickness of the thin gold layer on metal threads cannot be obtained directly. Hence, the goal of this project is to describe whether metal threads are gilded or not and to measure coating thickness. A new method was developed for measuring the thickness of gold layer, and the modeling was reformed. The SEM–EDX results were interpreted in accordance with the theoretical models. The coating thickness of metal threads was subsequently measured in ancient textiles. The thickness, depth, and valuable metal composition in the threads of the artistic objects were obtained by this approach. Dye analysis was used to characterize the presence of indigotin, carminic acid, ellagic acid, and luteolin in the historical textiles.  相似文献   
62.
Natural rubber/polycaprolactone (NR/PCL) bio-based blends with different organic peroxides were prepared using an internal batch mixer and subsequently cross-linked at 170 °C. Two types of commonly used organic peroxides, dicumyl peroxide and di(tert-butylperoxyisopropyl)benzene peroxide, were applied as free-radical initiator. Cross-linking efficiency of NR/PCL blends were investigated using oscillating disc rheometer measurements, followed by infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Total volatile organic compounds (TVOCs) emissions were determined using headspace analysis integrated with gas chromatography with flame ionization detector. Determined TVOCs emissions varying in range 21.6–52.1 μg/g and generally value of this parameter decreased with increasing content of PCL phase in studied blends or with application of more efficient di(tert-butylperoxyisopropyl)benzene peroxide as cross-linking agent. It was found that increasing of TVOCs parameter indicated deterioration of mechanical properties of NR/PCL blends, which corresponded with the changes in chemical structure and thermal properties of cross-linked NR/PCL. This confirms that evaluation of TVOCs parameter is interesting alternative for “conventional methods” to characterization of the studied bio-based blends.  相似文献   
63.
复杂网络广泛存在于日常生活,首先,给出几类标准的网络模型;然后,利用稳定性控制方法设计并实现了具有时滞与非时滞耦合的复杂网络模型快速控制;最后,通过构造优化Lyapunov函数,讨论其模型的射影同步问题,得到了系统全局稳定的条件和有效的控制器,以实例数值验证其方法的可行性。  相似文献   
64.
65.
In this paper we provide conditions under which automorphism-coinvariant modules over a right perfect ring are quasi-projective.  相似文献   
66.
67.
We consider a linear parabolic problem in a thick junction domain which is the union of a fixed domain and a collection of periodic branched trees of height of order 1 and small width connected on a part of the boundary. We consider a three‐branched structure, but the analysis can be extended to n‐branched structures. We use unfolding operator to study the asymptotic behavior of the solution of the problem. In the limit problem, we get a multi‐sheeted function in which each sheet is the limit of restriction of the solution to various branches of the domain. Homogenization of an optimal control problem posed on the above setting is also investigated. One of the novelty of the paper is the characterization of the optimal control via the appropriately defined unfolding operators. Finally, we obtain the limit of the optimal control problem. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
68.
A class of inverse problems for restoring the right‐hand side of a fractional heat equation with involution is considered. The results on existence and uniqueness of solutions of these problems are presented.  相似文献   
69.
In this paper, we study the existence of a positive ground state solution to the following coupled system of nonlinear Schrödinger equations: where the nonlinearities f1(x,s) and f2(x,s) are superlinear at infinity and have exponential critical growth of the Trudinger‐Moser type. The potentials V1(x) and V2(x) are nonnegative and satisfy a condition involving the coupling term λ(x), namely, λ(x)2<δ2V1(x)V2(x) for some 0<δ<1. For this purpose, we use the minimization technique over the Nehari manifold and strong maximum principle to get a positive ground state solution. Moreover, by using a bootstrap argument and Lq‐estimates, we get regularity and asymptotic behavior.  相似文献   
70.
In this study, first, a formula for regularized sums of eigenvalues of a Sturm‐Liouville problem with retarded argument at 2 points of discontinuity which contains a spectral parameter in the boundary conditions is obtained. After that, oscillation properties of the related problem is investigated. Finally, under the condition that a subset of nodal points is dense in definition set, the potential function is determined.  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