全文获取类型
收费全文 | 13726篇 |
免费 | 1225篇 |
国内免费 | 4407篇 |
专业分类
化学 | 14253篇 |
晶体学 | 423篇 |
力学 | 515篇 |
综合类 | 146篇 |
数学 | 1717篇 |
物理学 | 2304篇 |
出版年
2024年 | 111篇 |
2023年 | 147篇 |
2022年 | 342篇 |
2021年 | 357篇 |
2020年 | 395篇 |
2019年 | 317篇 |
2018年 | 335篇 |
2017年 | 407篇 |
2016年 | 472篇 |
2015年 | 397篇 |
2014年 | 632篇 |
2013年 | 1072篇 |
2012年 | 1423篇 |
2011年 | 755篇 |
2010年 | 630篇 |
2009年 | 846篇 |
2008年 | 973篇 |
2007年 | 1046篇 |
2006年 | 968篇 |
2005年 | 953篇 |
2004年 | 865篇 |
2003年 | 719篇 |
2002年 | 626篇 |
2001年 | 497篇 |
2000年 | 500篇 |
1999年 | 468篇 |
1998年 | 406篇 |
1997年 | 359篇 |
1996年 | 350篇 |
1995年 | 340篇 |
1994年 | 302篇 |
1993年 | 217篇 |
1992年 | 272篇 |
1991年 | 201篇 |
1990年 | 159篇 |
1989年 | 117篇 |
1988年 | 88篇 |
1987年 | 64篇 |
1986年 | 67篇 |
1985年 | 48篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1972年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
讨论了激光在等效折射率横向分布为二次及高次型复折射率介质中的传输问题。数值计算结果表明,在二次及高次型介质中,无论是否考虑饱和效应,均存在特征距离,当激光传输距离大于特征距离后,将出现光导现象,其传输参数(光斑半径与曲率半径)只与介质有关。折射率的空间分布与增益的空间分布对光导的形成均有贡献。 相似文献
22.
文章将从非平衡态统计物理发展和应用的角度,介绍德国科学家哈塞尔曼荣获2021年诺贝尔物理学奖的研究工作——基于布朗运动理论,建立了描述气象(天气)影响气候长期演化的随机气候学模型,并建立了寻求影响气候主因的最优指纹方法,从而能够分辨出人类活动和自然界局部改变对气候这一复杂系统的影响。哈塞尔曼的工作本质上是理论物理在实际复杂系统领域的成功应用,他采用的基础物理方法——布朗运动理论是我国杰出女物理学家王明贞和其导师乌伦贝克在20世纪40年代基于爱因斯坦的工作发展起来的[1,2]。文章将介绍布朗运动理论的发展及其相关的非平衡统计物理思想的当代发展,以展示哈塞尔曼如何把相关的物理理论巧妙地用于气候长期预测的实际应用研究:(1)建立了快变的局部“气象”变量涨落通过耗散涨落关系影响缓变的整体气候变量的基础理论;(2)通过最优指纹方法,寻找局部“噪音”和外驱动力影响气候演化的关键要素。 相似文献
23.
24.
25.
26.
We propose a low-density discharge plasma model that takes into account the impact of oxygen admixture in typical conditions of complex (dusty) plasmas. Numerical simulations based on this model show that the concentration of negative ions turns out to be very high, and they play an important role in the overall kinetics in this particular range of plasma conditions. The ambipolar diffusion electric field drags these negative ions into the center of the plasma. The density of negative ions is high enough to push the negatively charged dust component out of the center, both by weakening the radial electric field and by increasing the thermophoretic force. This phenomenon was observed in the published experiment and qualitatively supports the proposed model. Additionally, the proposed model allows an alternative explanation of the experiment. 相似文献
27.
利用苯妥英,二(3-氨基丙基)胺与醋酸铜反应合成了一种新的铜三元配合物[Cu(pht)2(bapa)](CH3OH)[Hpht:苯妥英(5,5-Diphenylhydantion);bapa:二(3-氨基丙基)胺(bis(3-aminopropyl)amine)].通过元素分析、红外光谱和X射线单晶衍射确定了其组成和结构.配合物属于三斜晶系,空间群为Pī.晶胞参数:a=0.84190(10)nm,b=1.37540(15)nm,c=1.5622(2)nm,α=86.038(3)°,β=82.542(2)°,γ=83.904(2)°;V=1.7807(4)nm3,Mr=729.32,Z=2,F(000)=766,Dc=1.360 g/cm3,μ=0.666 mm-1,R1=0.0692,wR2=0.1430.配合物中铜离子配位数为5,处于变形三角双锥配位环境中.测试了配合物、配体和铜盐的抑菌活性,结果表明,它们对4种细菌均有一定的活性. 相似文献
28.
The content of thisreview consists of recent developments covering an advancedtreatment of multiple crack problems in plane elasticity. Severalelementary solutions are highlighted, which are the fundamentalsfor the formulation of the integral equations. The elementarysolutions include those initiated by point sources or by adistributed traction along the crack face. Two kinds of singularintegral equations, three kinds of Fredholm integral equations,and one kind of hypersingular integral equation are suggested forthe multiple crack problems in plane elasticity. Regularizationprocedures are also investigated. For the solution of the integralequations, the relevant quadrature rules are addressed. A varietyof methods for solving the multiple crack problems is introduced.Applications for the solution of the multiple crack problems arealso addressed. The concept of the modified complex potential(MCP) is emphasized, which will extend the solution range, forexample, from the multiple crack problem in an infinite plate tothat in a circular plate. Many multiple crack problems areaddressed. Those problems include: (i) multiple semi-infinitecrack problem, (ii) multiple crack problem with a general loading,(iii) multiple crack problem for the bonded half-planes, (iv)multiple crack problem for a finite region, (v) multiple crackproblem for a circular region, (vi) multiple crack problem inantiplane elasticity, (vii) T-stress in the multiple crackproblem, and (viii) periodic crack problem and many others. Thisreview article cites 187 references. 相似文献
29.
Two new ternary complexes [Zn(3-aba)2(phen)](2.58H2O 1 and {[Cd(3-aba)- (phen)2]·(NO3)·(1.5H2O)}n 2 (3-aba = 3-aminobenzoic acid anion, phen = 1,10-phenanthroline) were synthesized and characterized by elemental analysis, IR, UV spectrum and X-ray diffraction. Complex 1 crystallizes in the rhombohedral system, space group R with a = 3.5733(3), b = 3.5733(3), c = 1.1231(2) nm, V = 12.419(3) nm3, C26H25.17N4O6.58Zn, Mr = 564.37, Z = 18, F(000) = 5253, μ = 0.937 mm-1, Dc = 1.358 g/cm3, R = 0.0668 and wR = 0.1690 for 2424 observed reflections (I > 2σ(I)). Complex 2 belongs to the tetragonal system, space group P4/ncc with a = 2.88451(10), b = 2.88451(10), c = 1.55571(11) nm, V = 12.9441(11) nm3, C31H25CdN6O6.50, Mr = 697.97, Z = 16, F(000) = 5648, μ = 0.727 mm-1, Dc = 1.433 g/cm3, R = 0.0607 and wR = 0.1742 for 3468 observed reflections (I > 2σ(I)). Complex 1 displays a mononuclear structure. The carboxylate group of 3-aminobenzoic acid anion coordinates to Zn(Ⅱ) in a chelating bidentate mode, and the nitrogen atom of the ligand does not involve in coordination. Complex 2 exhibits a one-dimensional chain structure with 3-aminobenzoic acid anion coordinating to Cd(Ⅱ) in a μ2-bridging mode through its nitrogen atom and one of its oxygen atoms. 相似文献
30.
Qi Nie Hao Jiang Si-Dong Zhong Qiang Wang Juan-Juan Wang Hao Wang Li-Hua Wu 《Entropy (Basel, Switzerland)》2022,24(7)
Community detection and structural hole spanner (the node bridging different communities) identification, revealing the mesoscopic and microscopic structural properties of complex networks, have drawn much attention in recent years. As the determinant of mesoscopic structure, communities and structural hole spanners discover the clustering and hierarchy of networks, which has a key impact on transmission phenomena such as epidemic transmission, information diffusion, etc. However, most existing studies address the two tasks independently, which ignores the structural correlation between mesoscale and microscale and suffers from high computational costs. In this article, we propose an algorithm for simultaneously detecting communities and structural hole spanners via hyperbolic embedding (SDHE). Specifically, we first embed networks into a hyperbolic plane, in which, the angular distribution of the nodes reveals community structures of the embedded network. Then, we analyze the critical gap to detect communities and the angular region where structural hole spanners may exist. Finally, we identify structural hole spanners via two-step connectivity. Experimental results on synthetic networks and real networks demonstrate the effectiveness of our proposed algorithm compared with several state-of-the-art methods. 相似文献