全文获取类型
收费全文 | 72715篇 |
免费 | 13735篇 |
国内免费 | 3585篇 |
专业分类
化学 | 70371篇 |
晶体学 | 1048篇 |
力学 | 2031篇 |
综合类 | 265篇 |
数学 | 7383篇 |
物理学 | 8937篇 |
出版年
2024年 | 69篇 |
2023年 | 232篇 |
2022年 | 1015篇 |
2021年 | 1066篇 |
2020年 | 1605篇 |
2019年 | 3055篇 |
2018年 | 2745篇 |
2017年 | 3243篇 |
2016年 | 3810篇 |
2015年 | 5935篇 |
2014年 | 5784篇 |
2013年 | 7879篇 |
2012年 | 6311篇 |
2011年 | 5848篇 |
2010年 | 4833篇 |
2009年 | 4609篇 |
2008年 | 4902篇 |
2007年 | 4251篇 |
2006年 | 3916篇 |
2005年 | 3645篇 |
2004年 | 3049篇 |
2003年 | 2791篇 |
2002年 | 3800篇 |
2001年 | 1791篇 |
2000年 | 1655篇 |
1999年 | 777篇 |
1998年 | 251篇 |
1997年 | 188篇 |
1996年 | 172篇 |
1995年 | 119篇 |
1994年 | 134篇 |
1993年 | 99篇 |
1992年 | 78篇 |
1991年 | 60篇 |
1990年 | 70篇 |
1989年 | 45篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 37篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1977年 | 8篇 |
1975年 | 5篇 |
1967年 | 1篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Summary Adsorption properties of activated carbon cloth were investigated by gas-solid chromatography. Retention of several organic
compounds was measured in the temperature range from 200 to 250°C. The gas/solid distribution coefficients and the related
thermodynamic function of adsorption at zero surface coverage were determined. The obtained experimental data were used to
explain the adsorbent-adsorbate interaction. 相似文献
992.
Yoshitaka Uenoyama Takahide Fukuyama Keisuke Morimoto Osamu Nobuta Hidefumi Nagai Ilhyong Ryu 《Helvetica chimica acta》2006,89(10):2483-2494
The carbonylation of alkanes 1 under radical‐reaction conditions was examined by using ethynyl triflone A as the unimolecular chain‐transfer (UMCT) reagent. Good to moderate yields of ethynyl ketones 2 were prepared by means of this three‐component coupling reaction. Higher CO pressures as well as lower concentrations of triflone A improved the efficiency of the reaction over the direct addition, the latter leading to alkylated ethynes 3 . In contrast to the reaction with A , the reaction of cyclohexane ( 1a ) with allyl triflone B (= ethyl 2‐methylene‐3‐[(trifluoromethyl)sulfonyl]propanoate) in the presence of CO gave a mixture of carbonylation products, including 8a formed from two molecules each of cyclohexane, CO, and allyl triflone B . 相似文献
993.
《Electroanalysis》2003,15(19):1567-1570
Application of thin colloidal Au multilayers on glass substrates as optically transparent electrodes is reported herein. Evaluation of the electrode by scanning electron microscopy and as an optically transparent thin layer electrode (OTTLE) illustrate its use for spectroelectrochemical applications. A spectroelectrochemical Nernst plot acquired for the oxidation of o‐tolidine yielded a value of E°=0.605 V (vs. Ag/AgCl) and n=1.88. Both of these values are in excellent agreement with previously published values obtained using a traditional Au minigrid OTTLE. The colloidal Au multilayer electrode is expected to offer many advantages over the minigrid OTTLE in specific applications. These advantages include direct control over microscopic surface topography, large electrochemical surface area, applicability to many different electrode geometries, and increased microscopic surface roughness for SERS and SPR applications. 相似文献
994.
星状四芳胺类空穴传输材料的合成 总被引:1,自引:0,他引:1
有机电致发光器件 (OELD)是继阴极射线管平板显示器 (CRT)和液晶显示器 (LCD)之后的第三代平板显示器。它具有主动发光、驱动电压低(2伏左右 )、发光亮度高 (1 3 0 0 0cd m2 以上 ) ,无软X 射线污染 ,响应速度快 (1 0 -6 ~ 1 0 -8秒 )等优点。从 1 987年美藉华人邓清云等提出多层结构的OELD的器件结构以来的十多年间 ,OELD以及其材料的研究已成为显示技术以及显示材料等方面的研究热点 ,发展很快[1~ 3] 。在 1 999年日本先锋公司已开发出了单色的汽车用OEL平板显示器商品 ,今年东芝公司又开发出了 2 .7英寸的彩… 相似文献
995.
Qing‐Xiang Liu Feng‐Bo Xu Qing‐Shan Li Xian‐Shun Zeng Xue‐Bing Leng Zheng‐Zhi Zhang 《中国化学》2002,20(9):878-883
Dinuclear silver (I) six‐membered ring complex [Ag2 (bta)2 ‐(hmbta)2] (ClO4)2 (3) has been synthesized by the reaction of benzotriazole (bta) (1) and 1‐hydroxymethyl benzotriazole (hmbta) (2) with Ag (CH3CN)4ClO4. The structures of compound 2 and Complex 3 have been studied by single crystal X‐ray diffraction analysis. The change of luminescent intensity of 1, 2 and 3 was reported. Compound 2 crystallizes in the monoclinic system with space group P2 (1)/c, a = 0.7655 (10) nm, b = 1.0126 (14) nm, c =0.9502 (13) nm, β = 95.07 (2)°, V = 0.7337 (17) nm3 and Z = 4. Complex 3 crystallizes in the triclinic system with space group P1, a = 0.73611 (18) nm, b = 0.9152 (2) nm, c = 1.2277 (3) nm, β = 87.170 (5)°, V = 0.8221 (3) nm3 and Z = 1. The main structural feature of complex 3 is a symmetric dinuclear six‐membered ring formed by two silver (I) atoms and four N‐atoms from two benzotriazoles. The second structural feature of complex 3 is the τ‐τ stacking interaction between two adjacent molecular planes, which forms the two‐dimentional layer structure. Besides, compared with 2, the luminescent intensity of complex 3 shows a remarkable enhancement. 相似文献
996.
The intergrowth of 1,10-decanedicarboxylic acid and urea give infinite hydrogen-bonded chains of the guest included in the hexagonal urea host. A deuterium high-resolution solid-state NMR study of the selectively deuterated intergrowth compound 1,10-decanedicarboxylic acid/hydrogenated urea at variable temperature in the range 90 < or = T < or = 300 K was performed on a single crystal. The analysis of the second moment as a function of temperature is shown to be compatible with the known phase transition occurring near T(c) = 203 K. Moreover, the spectra indicate that the orientational disorder is strong, and is compared to an axial uniform disorder. For this purpose, the general equation for the second moment of a system with uniform two-dimensional axial orientational disorder is given, and a method to take into account the non-uniform excitation of the pulse sequence is proposed. 相似文献
997.
Enkhtsetseg Dashjav Guido Kreiner Walter Schnelle Frank R. Wagner Rüdiger Kniep 《无机化学与普通化学杂志》2004,630(5):689-696
Carbometalates: Complex Anions equation/tex2gif-stack-4.gif [MoC4/26—] in the Crystal Structure of Pr equation/tex2gif-stack-5.gif [MoIIC2] Criteria for the existence of carbometalates are established and discussed in a broader context. The concept is then applied to the novel compound Pr2[MoC2], which is characterized by chemical analyses, X‐ray diffraction and metallography. The crystal structure (tetragonal, P42/mnm, Z = 4, a = 581.29(8) pm, c = 1032.53(14) pm) consists of layered polyanions equation/tex2gif-stack-6.gif[MoC4/26—] of distorted vertex and edge sharing MoC4 tetrahedra. Praseodymium is also in a distorted tetrahedral coordination by carbon. The physical properties show “bad metal” behaviour and localized magnetic 4f‐moments in agreement with the existence of Pr3+‐species. A detailed bonding analysis using both the electron localization function ELF and the COHP method justifies the interpretation of the title compound as a carbomolybdate(II). 相似文献
998.
Quantitative analysis of docetaxel in human plasma using liquid chromatography coupled with tandem mass spectrometry 总被引:2,自引:0,他引:2
Kuppens IE van Maanen MJ Rosing H Schellens JH Beijnen JH 《Biomedical chromatography : BMC》2005,19(5):355-361
An assay for the quantitative determination of docetaxel in human plasma is described. Docetaxel was extracted from the matrix using liquid-liquid extraction with ter-butylmethylether, followed by high-performance liquid chromatographic analysis using an alkaline eluent. Paclitaxel was used as internal standard. Positive ionization electrospray tandem mass spectrometry was performed for selective and sensitive detection. The method was validated according to the FDA guidelines on bioanalytical method validation. The validated range for docetaxel was from 0.25--1000 ng/mL using 200 microL plasma aliquots. The method requires only a limited volume (200 microL) of human plasma and the method can be applied in studies requiring a low lower limit of quantitation of 0.25 ng/mL. The assay was applied successfully in several clinical and pharmacological studies with docetaxel. 相似文献
999.
A number of aldehydes and ketones were prepared by oxidation of alcohol by N,N‐dichloro‐4‐methylbenzenesulfonamide under mild and neutral conditions in good to high yield in dichloromethane at room temperature. 相似文献
1000.