全文获取类型
收费全文 | 47514篇 |
免费 | 7920篇 |
国内免费 | 5455篇 |
专业分类
化学 | 26199篇 |
晶体学 | 487篇 |
力学 | 2093篇 |
综合类 | 223篇 |
数学 | 3710篇 |
物理学 | 14246篇 |
无线电 | 13931篇 |
出版年
2024年 | 155篇 |
2023年 | 1277篇 |
2022年 | 1523篇 |
2021年 | 2136篇 |
2020年 | 2158篇 |
2019年 | 2033篇 |
2018年 | 1667篇 |
2017年 | 1590篇 |
2016年 | 2271篇 |
2015年 | 2369篇 |
2014年 | 2978篇 |
2013年 | 3531篇 |
2012年 | 4210篇 |
2011年 | 4279篇 |
2010年 | 2955篇 |
2009年 | 2931篇 |
2008年 | 3235篇 |
2007年 | 2723篇 |
2006年 | 2596篇 |
2005年 | 2090篇 |
2004年 | 1534篇 |
2003年 | 1228篇 |
2002年 | 1258篇 |
2001年 | 1039篇 |
2000年 | 808篇 |
1999年 | 925篇 |
1998年 | 785篇 |
1997年 | 711篇 |
1996年 | 714篇 |
1995年 | 590篇 |
1994年 | 502篇 |
1993年 | 389篇 |
1992年 | 375篇 |
1991年 | 296篇 |
1990年 | 249篇 |
1989年 | 181篇 |
1988年 | 113篇 |
1987年 | 91篇 |
1986年 | 112篇 |
1985年 | 82篇 |
1984年 | 48篇 |
1983年 | 52篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1959年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
991.
Xinbo Zhang Danzi Sun Wenya Yin Yujun Chai Minshou Zhao 《Journal of Solid State Electrochemistry》2006,10(4):236-242
This paper presents results concerning structure and electrochemical characteristics of the La0.67Mg0.33 (Ni0.8Co0.1Mn0.1)
x
(x=2.5–5.0) alloy. It can be found from the result of the Rietveld analyses that the structures of the alloys change obviously
with increasing x from 2.5 to 5.0. The main phase of the alloys with x=2.5–3.5 is LaMg2Ni9 phase with a PuNi3-type rhombohedral structure, but the main phase of the alloys with x=4.0–5.0 is LaNi5phase with a CaCu5-type hexagonal structure. Furthermore, the phase ratio, lattice parameter and cell volume of the LaMg2Ni9phase and the LaNi5 phase change with increasing x. The electrochemical studies show that the maximum discharge capacity increases from 214.7 mAh/g
(x=2.5) to 391.1 mAh/g (x=3.5) and then decreases to 238.5 mAh/g (x=5.0). As the discharge current density is 1,200 mA/g, the high rate dischargeability (HRD) increases from 51.1% (x=2.5) to 83.7% (x=3.5) and then decreases to 71.6% (x=5.0). Moreover, the exchange current density (I
0) of the alloy electrodes first increases and then decrease with increasing x from 2.5 to 5.0, which is consistent with the variation of the HRD. The cell volume reduces with increasing x in the alloys, which is detrimental to hydrogen diffusion and accordingly decreases the low-temperature dischargeability
of the alloy electrodes. 相似文献
992.
Feng Zhao Yu-Kou Du Ping Yang Ji’an Tang Xing-Chang Li 《Colloid and polymer science》2005,283(12):1361-1365
In the present study, the structure and morphology of single sodium poly(styrenesulfonate) (PSS) molecules adsorbed to mica
surface from the natural aqueous solution is investigated using atomic force microscopy technique. Results show that single
PSS molecules are observed which show a morphology of wormlike coils. Meanwhile, single sodium poly(styrenesulfonate) (PSS)/Hexadecyltrimethylammonium
bromide (CTAB) complexes deposited on mica from the air–water interface are also observed. However, the PSS/CTA+ complexes show different conformations by appearing in the morphology of circular patches. Experimental data are in fair
agreement with the theoretical analysis. 相似文献
993.
Amphiphilic phthalocyanines with one crown ether and three alkyl chain substitutions can form stable monolayers on a water surface. This monolayer can be transferred to a substrate by a vertical dipping method. The arrangement of phthalocyanine molecules in LB films was affected by the length of alkyl chains and the coordination of alkali ions in crown ether. Davydov splitting was observed in the absorption spectra of the LB films of phthalocyanine with the shortest alkyl chain substitutions, and this splitting was affected by the alkali ions in the subphase. 相似文献
994.
Xian Zhao Daren Guan Xizhang Yi Guibao Xu Minhua Jiang 《International journal of quantum chemistry》2003,93(5):335-343
A dynamic Lie algebraic (DLA) formulation is applied to the study of nonlinear optical properties of the substituted benzenes. We have described the generation of the dynamic Lie algebra for the model Hamiltonian used in the present study. In terms of these elements of the dynamic algebra we express the evolution operator as a function of the group parameters, which can be determined by means of solving a system of coupled nonlinear differential equations. Thus, in terms of the density matrix operator formalism in statistical mechanics we obtain the statistical averages of the electric polarization and then derive readily an expression for the hyperpolarizability of the paradisubstituted benzenes. Comparisons with experimental observations and other quantum calculations of the hyperpolarizabilities for the paradisubstituted benzenes are made qualitatively and quantitatively. These results imply that the DLA method appears useful in describing the nonlinear optical phenomena in the substituted benzene molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 335–343, 2003 相似文献
995.
Substituted carbazoles are readily prepared in good yields by the palladium-catalyzed cross-coupling of alkynes and N-(3-iodophenyl)anilines. This process proceeds by carbopalladation of the alkyne, heteroatom-directed vinylic to aryl palladium migration, and ring closure involving two consecutive C-H activation processes. The process has also been expanded to the synthesis of an indole. [Structure: see text] 相似文献
996.
The rheological properties of the aqueous mixtures of cationic-anionic surfactants, both in single-phase systems and in aqueous two-phase systems, have been studied. Bizarre rheological properties —negative thixotropy, viscoelasticity and hihg viscosity of shear rate dependent at relatively low concentration — have been observed. An unusual viscosity change, that is, viscosity lowering with increasing concentration, was obtained. The negative thixotropy might be due to the existence of lamellar or sheet-like micelles, viscoelasticity might be induced by rodlike and lamellar or sheet-like micelles, the high viscosity might be a consequence of the formation of network by long rodlike micelles and the concentration-induced viscosity lowering could be interpreted in terms of the decrease of micellar dimensions with concentration. 相似文献
997.
报道A-β-M'xHy-[GeWOM3(H2O)3O37].nH2O(M=Cr^3^+,Co^2^+,Ni^2^+,Cu^2^+;M'=Bu4N^+,K^+)的立体有择合成法制备及红外和远红外光谱,紫外和可见光谱和循环伏安,磁化率和磁矩,XPS,ESR以及催化活性等研究结果。 相似文献
998.
以过氧化二苯甲酰为引发剂,使丙烯睛在涤沦(PET)纤维上接枝共聚。接枝纤维在含铜化合物,含硫还原剂溶液中反应,制备PET导电纤维。讨论了影响接枝共聚的各种因素,选择出最佳聚合条件。对该纤维的导电成份和结构以及性能进行了研究。 相似文献
999.
Determination of DNA using sodium 9,10-anthraquinone-2-sulfonate as an in situ photochemical fluorescence probe 总被引:2,自引:0,他引:2
Wen-You Li Xiang-Qun Guo Jin-Gou Xu Qing-Zhi Zhu Yi-Bing Zhao 《Analytica chimica acta》1997,340(1-3):291-296
An in situ photochemical fluorescence probe method for the determination of DNA with sodium 9,10-anthraquinone-2-sulfonate (AQS) as a photochemical fluorescence probe was developed. It was based on the conversion of AQS into an intensively fluorescent product by irradiating with UV radiation. The photochemical reaction is retarded by DNA. The determination can be carried out by measuring the fluorescence intensity at a fixed time. The calibration graph was linear in the range 0–80 ng ml−1 calf thymus (CT) DNA (r = 0.9991), the limit of detection was 3.2 ng ml−1 CT DNA (n = 9). The kinetic behaviour of the photochemical reaction and the effects of experimental conditions were investigated and discussed in detail. The results of absorption spectra and competitive binding experiments suggested the interaction between AQS and DNA to be intercalative. 相似文献
1000.
Liu H Zhang S Nie S Zhao X Sun X Yang X Pan W 《Chemical & pharmaceutical bulletin》2005,53(6):631-633
Methylacrylic acid/styrene cross-linked with divinylbenzene is a novel pH-sensitive ion exchange resin. Microspheres of this resin were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The microspheres showed a pulsatile swelling behavior when the pH of the media changed. The pH-sensitive microspheres were loaded with salbutamol sulfate and the drug-release characteristics were studied under both simulated gastric and intestinal pH conditions. The results obtained showed that the drug release also depended on the pH of the release media. 相似文献