全文获取类型
收费全文 | 17567篇 |
免费 | 2648篇 |
国内免费 | 2231篇 |
专业分类
化学 | 13507篇 |
晶体学 | 277篇 |
力学 | 948篇 |
综合类 | 188篇 |
数学 | 1744篇 |
物理学 | 5782篇 |
出版年
2024年 | 23篇 |
2023年 | 262篇 |
2022年 | 335篇 |
2021年 | 513篇 |
2020年 | 623篇 |
2019年 | 625篇 |
2018年 | 479篇 |
2017年 | 491篇 |
2016年 | 793篇 |
2015年 | 768篇 |
2014年 | 926篇 |
2013年 | 1274篇 |
2012年 | 1546篇 |
2011年 | 1635篇 |
2010年 | 1165篇 |
2009年 | 1022篇 |
2008年 | 1169篇 |
2007年 | 988篇 |
2006年 | 990篇 |
2005年 | 937篇 |
2004年 | 757篇 |
2003年 | 664篇 |
2002年 | 729篇 |
2001年 | 494篇 |
2000年 | 443篇 |
1999年 | 396篇 |
1998年 | 296篇 |
1997年 | 269篇 |
1996年 | 262篇 |
1995年 | 250篇 |
1994年 | 193篇 |
1993年 | 175篇 |
1992年 | 167篇 |
1991年 | 143篇 |
1990年 | 126篇 |
1989年 | 103篇 |
1988年 | 92篇 |
1987年 | 62篇 |
1986年 | 62篇 |
1985年 | 65篇 |
1984年 | 33篇 |
1983年 | 29篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1957年 | 6篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
以TiO2纳米粒子为主催化剂, 采用“浸渍-还原法”构筑了铜、镍共负载的二氧化钛基光催化系统。以苯为起始原料, H2O2为氧化剂, 研究了Cu/Ni助催化剂对TiO2可见光催化制取苯酚性能的影响并对Cu/Ni助催化剂的作用机制进行了探讨。结果表明, 在可见光照射下, 纯TiO2纳米粒子对苯氧化制取苯酚反应没有催化活性。铜、镍的引入可以明显地增强TiO2可见光催化制取苯酚的活性。当使用负载有铜、镍的TiO2作为催化剂时, 苯酚的产率可达到18%。结果还表明Cu、Ni之间存在着很强的协同作用。在该协同作用下, Cu、Ni共负载的TiO2纳米粒子表现出了较单一金属负载的TiO2纳米粒子高得多的光催化活性。 相似文献
962.
为了对海水痕量营养盐与重金属进行测定,基于FCS的设计思想,采用流动注射分光光度法研制了具有自适应外界设备、快速组建多种仪器及全数字化通信等特点的软硬件一体化的通用测定平台。平台以ARM(S3C2416)处理器为核心,Linux为操作系统,LCD作为人机交互显示,触摸屏或者USB鼠标完成输入控制,构成完整的嵌入式工控机系统;采用CAN总线并制定CAN应用层协议管理设备,提高了系统的可靠性及抗干扰能力。实际测试和应用证明,该平台自动化程度高,通用性、重用性及可扩展性均较强,可组建成亚硝氮、硝氮、氨氮、活性磷、铁等多种痕量元素的实验室、船载和原位分析系统,检测限为nmol/L级别。平台对样品的测试准确度与商品专用仪器无显著性差异。 相似文献
963.
针对仿真可视化系统开发时间长、开发费用高的问题,提出了一种利用Unity3D引擎进行实时仿真可视化系统开发的模块式设计方法。首先,对武器仿真可视化系统进行了分析,提出了智能弹药实时仿真可视化系统的五大模块;然后,通过在3ds Max下建立智能弹药模型和Unity3D下的二次开发,构建了智能弹药仿真可视化系统的仿真环境,以C#为编程工具,设计了仿真驱动、串口数据通讯和仿真输出模块;最终,实现了智能弹药实时仿真可视化系统。实验证明,该系统可以有效地在监视器上实时显示出智能弹药的飞行姿态、飞行参数和飞行轨迹。 相似文献
964.
Little theoretical work has been done on edge flips in surface meshes despite their popular usage in graphics and solid modeling to improve mesh equality. We propose the class of \((\varepsilon ,\alpha )\)-meshes of a surface that satisfy several properties: the vertex set is an \(\varepsilon \)-sample of the surface, the triangle angles are no smaller than a constant \(\alpha \), some triangle has a good normal, and the mesh is homeomorphic to the surface. We believe that many surface meshes encountered in practice are \((\varepsilon ,\alpha )\)-meshes or close to being one. We prove that flipping the appropriate edges can smooth a dense \((\varepsilon ,\alpha )\)-mesh by making the triangle normals better approximations of the surface normals and the dihedral angles closer to \(\pi \). Moreover, the edge flips can be performed in time linear in the number of vertices. This helps to explain the effectiveness of edge flips as observed in practice and in our experiments. A corollary of our techniques is that, in \(\mathbb {R}^2\), every triangulation with a constant lower bound on the angles can be flipped in linear time to the Delaunay triangulation. 相似文献
965.
A new simple receptor 1 based on aminosalicylimine was prepared. It exhibited an ‘off–on fluorescence type’ mode with high sensitivity in the presence of Zn2+. In particular, this chemosensor could clearly distinguish Zn2+ from Cd2+. Also, it could be a reusable chemosensor because the addition of EDTA quenched the fluorescence of the Zn2+-2·1 complex. Furthermore, receptor 1 had a sufficiently low detection limit (68 nM) in aqueous solutions, which implies that 1 could sense the nanomolar concentration of Zn2+. Therefore, this sensor has the ability to be a practical system for the monitoring of Zn2+ concentrations in aqueous samples. 相似文献
966.
The palladium-catalyzed cyclization–allylation reaction of ortho-azido propynylbenzenes 1 and allyl methyl carbonate 2d gives the corresponding allylated quinolines in moderate to good yields. The reaction of 1-azido-2-(2-propynyl)benzene 1a proceeds smoothly with 10 mol % Pd(PPh3)4 and 5 equiv K3PO4 or NaOAc in DMF at 100 °C to afford 3,4-diallylquinoline 3a in 69% yield in the case of R2 = H and 3-allylquinoline 4 in 67% yield in the case of R2 ≠ H. 相似文献
967.
Mingxia Zhao Liqin Xiong Shilei Li Jin Chang Hongyu Ning Chuanmin Qi 《无机化学与普通化学杂志》2014,640(1):159-167
Four complexes with supramolecular architectures, namely, MZCA · 3H2O ( 1 ), [Zn(H2O)6]2+ · [MZCA]2 · [H2O]6 ( 2 ), [Mn(MZCA)2(H2O)4] · 2H2O ( 3 ), and [Ni(MZCA)2(H2O)4] · 2H2O ( 4 ) [MZCA = 3‐(carboxymethyl)‐2, 7‐dimethyl‐3H‐benzo[d]imidazole‐5‐carboxylic acid], were synthesized and characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. Complexes 1 and 2 display a remarkable 3D network with 1D hydrophilic channels. Complexes 3 and 4 are isostructural and exhibit a 3D structure encapsulating 1D 24‐membered ring microporous channels. The UV/Vis and fluorescent spectra were measured to characterize complexes 1 – 4 . The thermal stability of complexes 2 – 4 were also examined. 相似文献
968.
The TbIII compound [Tb(tci)(H2O)]n · n(DMF) ( 1 ) [H3tci = tri(2‐carboxythyl)isocyanurate, DMF = N,N′‐dimethylformamide] was synthesized by the reaction of terbium oxide, H3tci, and two drops of concentrated nitric acid in the presence of DMF and H2O. Single crystal X‐ray analysis reveals that it features a three‐dimensional (3D) framework based on infinite –Tb–COO–Tb– chains. The tci ligand in 1 links six different TbIII ions with its two carboxylate groups in μ2‐κ1O;κ2O,O′ mode and the third in μ2‐κ1O;κ1O′ mode. Thermal analysis reveals that it remains high thermal stability until 390 °C. Luminescence investigation shows that it emits characteristic green light of TbIII ions. 相似文献
969.
Yan‐Xue Chen Kang‐Kang Tang Xin Wang Bing‐Yi Chen Guo‐Qiang Qin Jin‐Hui Yang 《无机化学与普通化学杂志》2014,640(11):2292-2295
The zinc(II) coordination polymer [Zn3(BPT)2(μ2‐H2O)2(H2O)2]n · n(DMA) ( 1 ) (H3BPT = biphenyl‐3,4′,5‐tricarboxylic acid, DMA = N,N′‐dimethylactamide) was obtained by the solvothermal reaction of H3BPT with Zn(NO3)2 in DMA/H2O mixed solvent. Single crystal X‐ray analysis reveals that compound 1 has a complicated 3D framework containing linear trinuclear [Zn3(COO)4(μ2‐H2O)2] clusters as building subunits, which can be simplified into a (3,6)‐connected rtl topological network with the Schläfli symbol {4.62}2{42.610.83}. The calculated results of total and partial density of states (DOS) indicate that the luminescence of 1 mainly originates from intraligand charge transfer. 相似文献
970.
Jae Cheol Lee Yong Koo Kyoung In Yong Song Jae Woo Lee Young Sik Shin Jin Seok Kim Shin‐ichi Iida 《Surface and interface analysis : SIA》2014,46(7):429-432
We have developed a simple and powerful method, which is called ‘angled sample holder method’, to characterize a topographic structured sample such as microsized via hole of ball grid array using time‐of‐flight SIMS. The diameter of via holes was 100 µm and the depth was 70 µm. To remove the shaded area by incidence primary ion beam and to extract secondary ions from the bottom of a via hole, several types of angled sample holders with compensation steering plate were applied on the basis of simulation results using SIMION code. And the analyses using angled sample holder method enabled us to characterize the bottom and side wall of a via hole in clear. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献