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   671篇
  免费   59篇
  国内免费   56篇
化学   164篇
晶体学   5篇
力学   61篇
综合类   41篇
数学   303篇
物理学   212篇
  2025年   1篇
  2024年   11篇
  2023年   10篇
  2022年   21篇
  2021年   31篇
  2020年   17篇
  2019年   10篇
  2018年   14篇
  2017年   22篇
  2016年   23篇
  2015年   19篇
  2014年   39篇
  2013年   48篇
  2012年   33篇
  2011年   33篇
  2010年   25篇
  2009年   26篇
  2008年   36篇
  2007年   49篇
  2006年   28篇
  2005年   28篇
  2004年   36篇
  2003年   32篇
  2002年   34篇
  2001年   29篇
  2000年   25篇
  1999年   25篇
  1998年   16篇
  1997年   18篇
  1996年   15篇
  1995年   7篇
  1994年   4篇
  1993年   4篇
  1992年   2篇
  1991年   5篇
  1990年   2篇
  1988年   1篇
  1986年   1篇
  1985年   4篇
  1977年   1篇
  1957年   1篇
排序方式: 共有786条查询结果,搜索用时 0 毫秒
1.
介绍了克劳修斯方法对可逆和不可逆过程(循环)的处理,提出了处理不可逆过程的方法,论证了处理方法与克劳修斯方程的一致性,论述了克劳修斯方法的实质和意义;简单介绍了熵的另一个导出方法,比较了两种方法对绝热过程的处理,指出克劳修斯方法存在一个假设条件.  相似文献   
2.
The concept of weighted discrepancy of sequences was introduced by Sloan and Woniakowski when they proved a general form of a Koksma–Hlawka inequality for the numerical integration of functions. This version takes imbalances in the importance of the projections of the integrand into account.In this paper we give estimates for the weighted discrepancy of several important point sets. Further we carry out various (high-dimensional) numerical integration experiments and we compare the results with the error bounds provided by the generalized Koksma–Hlawka inequality and by the estimates for the weighted discrepancy. Finally we discuss various consequences.  相似文献   
3.
    
Two coordination polymers (CPs), namely, [Zn(BPDC)(3-bpdb)0.5(H2O)2]n ( 1 ), and [Ni(BPDC)(3-bpdb)(H2O)2]n ( 2 ) (where H2BPDC = 4,4'-biphenyldicarboxylic acid, 3-bpdb = 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene) have been solvothermally synthesized and characterized by single-crystal X-ray diffraction, IR, elemental analyses, PXRD, and SEM. CP 1 possesses a 2D 3-connected hcb net, and weak hydrogen bonding and π ··· π stacking contacts further link the 2D networks to form 3D supramolecular structure. The structure of 2 presents a 4-connected threefold interpenetrated cds framework. Through structural analysis, it is found that the coordination geometry of metal ions significantly affects the binding behaviors of the ligands and the resultant extended networks of the CPs. Besides, the Hirshfeld surface analyses detailed the surface characteristics of the two CPs. In addition, the thermal stabilities and photoluminescent properties were also investigated.  相似文献   
4.
5.
1 INTRODUCTIONHeterometalpolynuclearcomplexeshavebeenthesubjectofmanyrecentstudiestoelucidatethemechanismofspincouplingbetweenthemetalions〔1,2〕,mimickingtheactivesiteofsomemetalenzymescontainingdissimilarmetalions,suchascytochromeoxidaseandsuperoxi…  相似文献   
6.
许多金属元素对于生物体是必需的,Na、K、Mg、Ca、Mn、Fe、Co、Cu、Mo和Zn在人体中的含量约3%;各种金属离子在生物体中具有不同的作用,其功能是很复杂的.铜在生物体内主要是进行氧化还原反应,起输送氧气和电子载体的作用.如果人体内缺乏铜,则...  相似文献   
7.
含间苯基聚醚酮醚酮酮的合成和性能研究   总被引:12,自引:0,他引:12  
自英国ICI公司开发聚醚醚酮(PEEK)并于八十年代初期商品化以来[1],聚芳醚酮作为一类新型结构的高性能特种工程塑料得到了惊人的发展,不同结构的聚芳醚酮相继出现.Janson[2]等以对苯二甲酰氯(TPC)和4,4′ 二苯氧基二苯酮(DPBP)为单...  相似文献   
8.
Two d10 metal coordination polymers, [Zn(µ-Me2biim)Cl2] n (1) and [Cd3(MeHbiim)2(1,4-BDC)3] n (2) (Me2biim?=?N,N′-dimethyl-2,2′-biimidazole, MeHbiim?=?N-methyl-2,2′-biimidazole, 1,4-BDC?=?1,4-benzenedicarboxylate), were synthesized under hydrothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal X-ray crystallography. Complex 1 features an infinite neutral zigzag 1-D chain. Interchain hydrogen-bonding interactions further extend the 1-D arrangement to generate a 2-D supramolecular architecture. Complex 2 features a 3-D coordination polymer with α-Po net topology, based on linear trinuclear {Cd3O14N4} clusters. Both complexes have high thermal stability and exhibit strong luminescence at room temperature.  相似文献   
9.
    
A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid–structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests.  相似文献   
10.
    
A useful set of expressions that allow the analytical use of the stereographic Wulff net, e.g. for orientation in the Laue method, for 1‐, 2‐ and 3‐rotated cuts of single crystals fastened on a two‐axis goniometric holder are derived. Application of the derived expressions in everyday crystallographic practice is illustrated by examples. The results of lattice‐parameter measurements, the choice of planes suitable for diffractometric orientation, and the values of their Bragg angles, useful for orientation in the Laue and diffractometric methods, are described for Ca4GdO(BO3)3:Nd and CsLiB6O10 single crystals.  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