全文获取类型
收费全文 | 40298篇 |
免费 | 6616篇 |
国内免费 | 4482篇 |
专业分类
化学 | 27532篇 |
晶体学 | 540篇 |
力学 | 2552篇 |
综合类 | 299篇 |
数学 | 4586篇 |
物理学 | 15887篇 |
出版年
2024年 | 145篇 |
2023年 | 807篇 |
2022年 | 1346篇 |
2021年 | 1414篇 |
2020年 | 1544篇 |
2019年 | 1471篇 |
2018年 | 1334篇 |
2017年 | 1232篇 |
2016年 | 1885篇 |
2015年 | 1860篇 |
2014年 | 2256篇 |
2013年 | 2873篇 |
2012年 | 3410篇 |
2011年 | 3537篇 |
2010年 | 2462篇 |
2009年 | 2419篇 |
2008年 | 2606篇 |
2007年 | 2353篇 |
2006年 | 2244篇 |
2005年 | 1731篇 |
2004年 | 1378篇 |
2003年 | 1189篇 |
2002年 | 1098篇 |
2001年 | 871篇 |
2000年 | 909篇 |
1999年 | 849篇 |
1998年 | 756篇 |
1997年 | 701篇 |
1996年 | 712篇 |
1995年 | 625篇 |
1994年 | 546篇 |
1993年 | 441篇 |
1992年 | 433篇 |
1991年 | 338篇 |
1990年 | 310篇 |
1989年 | 250篇 |
1988年 | 209篇 |
1987年 | 180篇 |
1986年 | 158篇 |
1985年 | 158篇 |
1984年 | 108篇 |
1983年 | 76篇 |
1982年 | 63篇 |
1981年 | 42篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1977年 | 8篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
气相色谱质谱联用仪与微机的数据传输和处理 总被引:1,自引:0,他引:1
报道了一种用于气相色谱质谱联用仪和微机之间实现数据传输和处理的方法。方法可更有效地利用质谱仪采集的数据,解决了工作站处理数据的局限性。经数据格式转换,原始数据可以在微机上实现色谱峰再现,从而为色谱条件的优化和定量数据处理创造了条件。 相似文献
212.
A fluorogenic probe for bacteria imaging was reported. The binding with anionic bacterial surfaces disassembled the self-assembly probe to turn-on the fluorescence and shift pyrene monomer/excimer ratiometric signals. 相似文献
213.
The secondary reduction in the direct and oxazaborolidine‐catalyzed asymmetric borane reduction of ketones was investigated by the use of GC/MS tracing titration and control experiments. The results indicate that the secondary reduction affects the enantioselectivity only in noncoordinated solvents at low temperature and not under the usual catalytic reduction conditions because the intermediate alkoxyborane is unstable and quickly converts to borane and dialkoxyborane. The function of an alcohol additive in the asymmetric borane reduction of ketones is to consume excess borane in the reduction system thus inhibiting noncatalytic reduction, which leads to increased enantioselectivity in the catalytic reduction. 相似文献
214.
The covalent binding of acrylonitrile (CH(2)=CH-C triple bond N) and the formation of a C=C-C=N structure on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. For chemisorbed acrylonitrile, the absence of nu(C triple bond N) at 2245 cm(-1) and the appearance of nu(C=N) at 1669 cm(-1) demonstrate that the cyano group directly participates in the interaction with Si(100), which is further supported by XPS and UPS observations. Our experimental results and DFT calculations unambiguously demonstrate a [2 + 2] cycloaddition mechanism for acrylonitrile chemisorption on Si(100) through the binding of C triple bond N to Si dimers. The resulting chemisorbed monolayer with a C=C-C=N skeleton can serve as a precursor for further chemical syntheses of multilayer organic thin films in a vacuum and surface functionalization for in situ device fabrication. 相似文献
215.
Lizhuang Zou Buxing Han Haike Yan K.L. Kasperski Yuming Xu L.G. Hepler 《Journal of colloid and interface science》1997,190(2):472
The enthalpies of adsorption and the isotherms for adsorption of naphthenic acid onto Na-montmorillonite, Na-kaolinite, and Na-illite were studied by means of calorimetry and the static method at 298.15 K. The results show that the enthalpies of adsorption and saturated adsorption amounts of naphthenic acid on different clays change in the order Na-montmorillonite > Na-illite > Na-kaolinite. The interaction between naphthenic acid and clays is discussed. 相似文献
216.
硫酸颜色反应用于荧光法测定利血平研究 总被引:6,自引:1,他引:6
提出了硫酸颜色反应用于利血平的荧光分析新方法。利用血平与浓硫酸反应,生成强荧光物质,所得产物的荧光强度与利血平的浓度在0-0.6μg/mL范围内有良好的线性关系。检测限为0.2ng/mL。本法可直接用于尿液中利血平的定量分析,回收率为82.5%-84.2%。 相似文献
217.
218.
Chengfu Xu 《Tetrahedron》2004,60(17):3883-3892
A novel and enzymatic approach to α-chloro-δ-hydroxy-β-ketoalkanephosphonates was developed via enantioselective CALB-catalyzed acetylation and CRL-catalyzed hydrolysis. The resultant optically active compounds provide, via Horner-Wadsworth-Emmons (HWE) reaction, chiral α,β-unsaturated ketones that are building block with potential application in organic synthesis. 相似文献
219.
A Minor New Flavone from Scutellaria baicalensis Georgi 总被引:1,自引:0,他引:1
A new flavone,6,2′-dihydroxy-5,7,8,6′-tetramethoxyflavone,was isolated from the roots of Scutellaria baicalensis. Its structure was established on the basis of spectral evidences. 相似文献
220.
An easily prepared and highly efficient monodentate phosphoramidite ligand derived from BINOL, (S)-2,2'-O,O-(1,1'-binaphthyl)-dioxo-N,N-diethylphospholidine, was examined in the hydrogenation of both enamides and alpha-dehydroamino acid derivatives. The catalyst provided remarkably high enantioselectivities (up to 99.6% ee for enamides and >99.9% ee for alpha-dehydroamino acid derivatives). 相似文献