全文获取类型
收费全文 | 2106篇 |
免费 | 374篇 |
国内免费 | 531篇 |
专业分类
化学 | 1244篇 |
晶体学 | 11篇 |
力学 | 156篇 |
综合类 | 19篇 |
数学 | 770篇 |
物理学 | 811篇 |
出版年
2024年 | 3篇 |
2023年 | 54篇 |
2022年 | 86篇 |
2021年 | 84篇 |
2020年 | 120篇 |
2019年 | 88篇 |
2018年 | 85篇 |
2017年 | 67篇 |
2016年 | 71篇 |
2015年 | 85篇 |
2014年 | 128篇 |
2013年 | 250篇 |
2012年 | 256篇 |
2011年 | 234篇 |
2010年 | 191篇 |
2009年 | 201篇 |
2008年 | 175篇 |
2007年 | 184篇 |
2006年 | 179篇 |
2005年 | 106篇 |
2004年 | 60篇 |
2003年 | 53篇 |
2002年 | 56篇 |
2001年 | 44篇 |
2000年 | 24篇 |
1999年 | 33篇 |
1998年 | 23篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有3011条查询结果,搜索用时 15 毫秒
101.
Hui Wang Rui Luo Shijun Liao Julian Key Shan Ji Rongfang Wang 《Journal of Solid State Electrochemistry》2013,17(7):2009-2015
Pt nanoparticles deposited on a low-cost, surfacial, carbonized palygorskite (Pt/C-PLS) prepared by carbonizing sucrose were evaluated as a methanol oxidation catalyst for direct methanol fuel cells. Transmission electron microscopy and Fourier transfrom infrared spectrophotometry analyses revealed that carbon was formed on the surface of PLS and that free silica presented in the C-PLS support. The catalytic activity of methanol oxidation of Pt/C-PLS was higher than that of Pt/C, and the former catalyst had better CO tolerance. 相似文献
102.
通过二水乙酸锌(Ⅱ)和双Salamo型四肟配体6,6''-二乙氧基-双(2,2''-(乙二氧双(氮次甲基)))四酚(H4L)的配位反应,合成了2种锌(Ⅱ)配合物即:[Zn3(L)(OAc)2(H2O)](1)和[Zn3(L)(OAc)2(H2O)]·[Zn3(L)(OAc)2(CH3OH)(H2O)]·3CH3OH·H2O(2)。该类配合物含有2个Salamo型L4-配体和3个锌(Ⅱ)离子,其中2个锌(Ⅱ)原子位于Salamo型螯合单元的N2O2空腔内。[Zn(L)]螯合物中桥联的酚氧原子进一步和中心的锌(Ⅱ)原子配位。这类结构能通过2个桥联的乙酸根配体稳定,从而使配合物1和2达到电荷平衡。配合物有2种不同的几何构型即扭曲的三角双锥和四方锥(配合物1)或三角双锥和八面体(配合物2)。另外,配合物1和2在激发波长为340和337 nm时能发出强的绿光,其最大发射波长分别为531和536 nm。 相似文献
103.
A novel copper selective sensor 2 based on hydrazide and salicylaldehyde has been designed and prepared. Sensor 2 behaves a single selectivity and sensitivity in the recognition for Cu2+ over other metal ions such as Fe3+, Hg2+, Ag+, Ca2+, Zn2+, Pb2+, Cd2+, Ni2+, Co2+, Cr3+ and Mg2+ in DMSO. The distinct color change and the rapid changement of fluorescence emission provide naked‐eyes detection for Cu2+. The UV‐vis data indicate that 1:2 stoichiometry complex is formed by sensor 2 and Cu2+. The association constant Ks was 3.51×104 mol?1·L. The detection limitation of Cu2+ with the sensor 2 was 2.2×10?7 mol·L?1. The sensing of Cu2+ by this sensor was found to be reversible, with the Cu2+‐induced color being lost upon addition of EDTA. 相似文献
104.
A Cu(I) generated in situ from CuSO4·5H2O/sodium ascorbate catalyzed cross‐coupling reaction of aryl halides with aqueous ammonia for the synthesis of primary aromatic amines has been developed. Key to the success included the application of aqueous ammonia under a homogeneous condition. 相似文献
105.
通过相界面反应制备了一维卟啉微纳米棒,并通过紫外、红外和X衍射仪等多种表征方法对其进行了表征.结果表明,在无机酸的作用下,卟啉分子通过-,氢键和静电作用等多种相互作用聚集成有序的J-聚集体.将此一维卟啉微纳米棒构筑为微纳米器件,并测试其光电性能.该纳米器件在可见光照射下的光电流很大,关闭光源,电流在40 s内降到最低,再次打开光源,电流又在120 s内升到了最大.经过多次"开"、"关"光源,电导的光响应依旧没有降低.这种具有光电响应的卟啉微纳米棒有望成为微纳电子器件的光电元件. 相似文献
106.
生命活动中用于维持生物体内超氧阴离子自由基动态平衡的超氧化物歧化酶(superoxidedismutase,SOD)是一类金属酶,属于典型的生物大分子金属络合物,因其在生命活动中所起的重要作用而备受关注。目前,有关SOD的模拟已从小分子化合物的模拟,走向大分子环境与活性中心相结合的系统模拟。本文从高分子化合物角度对模拟SOD的研究进展作一综述,以期为设计并开发具有生物相容且高活性的新型高分子抗氧化剂提供新思路。天然大分子有蛋白质与多肽、多糖、分子聚集体,目前所采用的蛋白质(多肽)是性能稳定的天然蛋白质或通过基因重组技术生物合成的蛋白质或多肽,所采用的多糖类物质主要有右旋糖酐、羧甲基纤维素、壳聚糖等。小分子活性化合物(如金属卟啉、新型肟类为配体的同核与异核复合物、salen型金属配合物等)通过与这些天然大分子结合,在提高活性的同时也改善了其稳定性。将活性小分子物质与分子聚集体(如胶束、脂质体)结合制得的SOD模拟物可以模拟天然SOD在体内的环境,提高抗氧化活性和体内循环时间。合成高分子模拟SOD的工作主要集中于高分子接枝金属配合物的研究,其中典型的合成高分子有聚乙二醇(polyethylene glycol,PEG)、聚L-赖氨酸、聚(苯乙烯-马来酸酐)、聚(环己烷-1,4-丙酮二亚甲基缩酮)、氯化聚苯乙烯树脂、聚乳酸和一些嵌段共聚物,其抗氧化活性与金属配体有关,是一类潜在的抗癌药物。 相似文献
107.
Zhihua Wang Jinshu Li Xiaole Liu Jianming Yang Xiaoquan Lu 《Analytical and bioanalytical chemistry》2013,405(8):2525-2533
A sensitive amperometric sensor for norfloxacin (NF) was introduced. The receptor layer was prepared by molecularly imprinted photopolymerization of acrylamide and trimethylolpropane trimethacrylate on the surface of a gold electrode. The binding mechanism of the molecularly imprinted polymer was explored by ultraviolet (UV) and infrared (IR) spectroscopy. The chemosensor was characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance (EI), and scanning electron microscopy (SEM). The electrode prepared by photopolymerization has a better recognition ability to template molecules than that of electropolymerization and NIP. Some parameters affecting sensor response were optimized. Norfloxacin was detected by measurements of an amperometric i–t curve. The linear relationships between current and logarithmic concentration are obtained from 1.0?×?10?9 to 1.0?×?10?3?mol?L?1. The detection limit of the sensor was 1.0?×?10?10?mol?L?1. The proposed method is sensitive, simple, and cheap, and is applied to detect NF in human urine successfully. Figure
Amperometric i-t curves of MIPs electrode 相似文献
108.
A general and efficient synthetic method of 1,3-bis(phenylseleno)-2-propanol by reducing diphenyl diselenides with sodium borohydride in basic environment and then reacting with epichlorohydrin are described. 相似文献
109.
Aluminium powder has been used to reduce titanium tetrachloride to generate the low valent titanium (LVT)reagent which can induce the reductive coupling of aldehydes and ketones to form the corresponding pinacols or olefins. However, arylsulfonyl chlorides will give diaryldisulfides under the same condition. 相似文献
110.
Copper-catalyzed intermolecular C–N bond-forming reactions between aryl iodides and amides are described using sodium ascorbate, which is both cheap and nontoxic, as the additive. A variety of functionalized amides including some practical, unique secondary amides, such as N-arylacrylamides and 4-amido-N-phenylbenzamides, which are difficult to obtain by the classical methods, are prepared. Furthermore, some tertiary amides are prepared by using copper thiophenecarboxylate. 相似文献