全文获取类型
收费全文 | 3615篇 |
免费 | 717篇 |
国内免费 | 631篇 |
专业分类
化学 | 2594篇 |
晶体学 | 58篇 |
力学 | 218篇 |
综合类 | 53篇 |
数学 | 259篇 |
物理学 | 1781篇 |
出版年
2024年 | 10篇 |
2023年 | 71篇 |
2022年 | 112篇 |
2021年 | 168篇 |
2020年 | 190篇 |
2019年 | 160篇 |
2018年 | 142篇 |
2017年 | 172篇 |
2016年 | 207篇 |
2015年 | 227篇 |
2014年 | 271篇 |
2013年 | 292篇 |
2012年 | 349篇 |
2011年 | 343篇 |
2010年 | 258篇 |
2009年 | 260篇 |
2008年 | 316篇 |
2007年 | 211篇 |
2006年 | 196篇 |
2005年 | 179篇 |
2004年 | 143篇 |
2003年 | 104篇 |
2002年 | 137篇 |
2001年 | 96篇 |
2000年 | 104篇 |
1999年 | 49篇 |
1998年 | 27篇 |
1997年 | 40篇 |
1996年 | 12篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1957年 | 1篇 |
1911年 | 4篇 |
排序方式: 共有4963条查询结果,搜索用时 31 毫秒
41.
Controlled growth of calcium carbonate by poly(ethylenimine) at the air/water interface 总被引:1,自引:0,他引:1
Two metastable calcium carbonate polymorphs, hemispherical vaterite and needle-like aragonite, are selectively formed at the air/water interface by the mediation of poly(ethyleneimine)(with molecular weights of 25000 and 2000, respectively) dissolved in supersaturated calcium bicarbonate solution. 相似文献
42.
ZrO2对合成二甲醚双功能催化剂表面结构及催化性能的影响 总被引:5,自引:0,他引:5
采用共沉淀沉积法制备了Cu基双功能催化剂,并进行了合成气一步法制取二甲醚实验.XRD、XPS以及BET表征结果表明,催化剂中ZrO2以无定形状态存在,且随着其含量的增加,Zr^4 逐渐溶进CuO晶格,两者之间的电子交换使得Cu^2 在活化过程中很难被彻底还原为Cu^0,而是以Cu^0/Cu^ 的形式共存.活性评价结果表明,Cu^ 离子表现出优异的CO转化率和DME选择性.同时,ZrO2的存在能有效调节催化剂表面的Cu/Zn摩尔比以及促进Cu元素在表面的富集,从而改善催化剂性能. 相似文献
43.
Two new compounds from Zingiber officinale 总被引:1,自引:0,他引:1
Yu Zhao Qiao Feng Tao Rong Ping Zhang Chang Xin Zhou Hui Dou Shu Yun Shi Ye Cheng Xiao Lian Li Sun Su Zeng Ke Xin Huang Xiao Dong Zhang Xiao Kun Li 《中国化学快报》2007,18(10):1247-1249
A new cyclic diarylheptanoid,1,5-epoxy-3-hydroxy-1-(3-methoxy-4,5-dihydroxyphenyl)-7-(4-hydroxyphenyl)-heptane (1),as well as a new monoterpene,10-O-β-D-glucopyranosyl-hydroxy cineole (2) were isolated from the rhizomes of Zingiber officinale. The structures of compounds 1 and 2 were established based on their spectral data.In addition,the antioxidant activities of these compounds were also measured. 相似文献
44.
Kwak WJ Han CK Chang HW Kim HP Kang SS Son KH 《Chemical & pharmaceutical bulletin》2003,51(3):333-335
A new triterpenoid saponin, loniceroside C was isolated from the aerial parts of Lonicera japonica. Its structure was established to be 3-O-beta-D-glucopyranosyl hederagenin 28-O-alpha-L-rhamnopyranosyl (1-->2)-[beta-D-xylopyranosyl(1-->6)]-beta-D-glucopyranosyl ester by spectroscopic techniques and chemical transformations. Loniceroside C showed in vivo antiinflammatory activity against mouse ear edema provoked by croton oil. 相似文献
45.
二甲基甲酰胺中四种钕盐的电导 总被引:3,自引:0,他引:3
通过电导测量研究了四种钕盐:Nd(CF3SO3)3、Nd(ClO4)3、Nd(NO3)3和NdCl3在极性非质子溶剂DMF中的电导性质.利用线性拟合方法求得在25 ℃下Nd(CF3SO3)3和Nd(ClO4)3的极限摩尔电导率分别为278.8和 280.7 S•cm2•mol-1.用间接方法求得Nd(NO3)3 与NdCl3 的极限摩尔电导率分别为297.2和287.3 S•cm2 •mol-1.在25~65 ℃温度范围内,Nd(CF3SO3)3和Nd(ClO4)3的电导率随温度呈线性变化. Nd(NO3)3和NdCl3的电导行为表现出明显的离子缔合. 相似文献
46.
Kun Zhao Shuqi Zhuang Zhu Chang Haiyan Songm Liming Dai Pingang He Yuzhi Fang 《Electroanalysis》2007,19(10):1069-1074
A sensitive amperometric glucose biosensor based on platinum nanoparticles (PtNPs) combined aligned carbon nanotubes (ACNTs) electrode was investigated. PtNPs which can enhance the electrocatalytic activity of the electrode for electrooxidating hydrogen peroxide by enzymatic reaction were electrocrystallized on 4‐aminobenzene monolayer‐grafted ACNTs electrode by potential‐step method. These PtNPs combined ACNTs' (PtNPs/ACNTs) surfaces were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The highly dispersed PtNPs on ACNTs can be obtained. The enzyme electrode exhibits excellent response performance to glucose with linear range from 1×10?5–7×10?3 mol L?1 and fast response time within 5 s. Furthermore, this glucose biosensor also has good reproducibility. It is demonstrated that the PtNPs/ACNTs electrode with high electrocatalytic activity is a suitable basic electrode for preparing enzyme electrodes. 相似文献
47.
A strategy for design of bioimprinted proteins with glutathione peroxidase (GPX) activity has been proposed. The proteins imprinted with a glutathione derivative were converted into selenium-containing proteins by chemical modifying the reactive hydroxyl groups of serines followed by sodium hydrogen selenide displacement. These selenium-containing proteins exhibited remarkable GPX activities and the GPX activities of reduction of H2O2 by glutathione (GSH) were found to be 101-817 U μmol−1, which approaches the activity of a selenium-containing catalytic antibody elicited by a hapten similar to our template. The steady state kinetic study for imprinted protein catalysis revealed Michaelis-Menten kinetics for both H2O2 and GSH, e.g. the pesudo-first-order rate constant kcat (H2O2) and the apparent Michaelis constant Km (H2O2) at 1 mM GSH were calculated to be 784 min−1 and 1.24×10−3 M, respectively, and the apparent second-order rate constant kcat (H2O2)/Km (H2O2) was determined to be 6.33×105 (M min)−1. The kinetics and the template inhibition showed that the strategy might be a remarkably efficient one for generating artificial enzyme with GPX activity. 相似文献
48.
Hong J Kim YH Gil JH Cho K Jung JH Han SY 《Rapid communications in mass spectrometry : RCM》2002,16(22):2089-2093
The structural determination of sn-1 and sn-2 hexadecanoic lysophosphatidylcholine (LPC) regioisomers was carried out using fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecules produced diverse product ions due mainly to charge remote fragmentations. Based on the information obtained from the CID spectra of protonated and sodiated molecules, sn-1 and sn-2 hexadecanoic LPC isomers could be discriminated. Especially, the abundance ratio of the diagnostic ion pair [m/z 224/226] in the CID spectra of [M + H](+) ions was shown to be greatly different. Moreover, the CID-MS/MS spectra of sodium-adducted molecules for hexadecanoic LPC isomers showed characteristic product ions such as [M + Na - 103](+), [M + Na - 85](+), and [M + Na - 59](+), by which their regio-specificity can be differentiated. 相似文献
49.
氯化1-乙基-3-甲基烷基咪唑分子结构及其氢键作用能的密度泛函研究 总被引:1,自引:0,他引:1
采用量子化学密度范函方法计算研究了氯化1-乙基-3-甲基咪唑盐([EMIM]C1)正负离子间相互作用的平衡构型和Cl^-离子从不同方位与咪唑阳离子的结合能.计算发现Cl^-可在咪唑环平面上结合形成离子键,其结合能为.368.97kJ/mol,还可与环上的三个H原子形成氢键,其氢键键长和结合能分别为0.2000nm/-378.03kJ/mol、0.2339nm/-344,69kJ/mol和0.2301nm/-346,01kJ/mol.结合能包括氢键作用能和正负离子的静电作用能,后者为主要贡献.从理论上展示了该离子液体的氢键结构. 相似文献
50.