全文获取类型
收费全文 | 3317篇 |
免费 | 282篇 |
国内免费 | 336篇 |
专业分类
化学 | 2947篇 |
晶体学 | 39篇 |
力学 | 6篇 |
综合类 | 25篇 |
数学 | 1篇 |
物理学 | 917篇 |
出版年
2024年 | 6篇 |
2023年 | 25篇 |
2022年 | 84篇 |
2021年 | 75篇 |
2020年 | 70篇 |
2019年 | 80篇 |
2018年 | 80篇 |
2017年 | 102篇 |
2016年 | 112篇 |
2015年 | 116篇 |
2014年 | 135篇 |
2013年 | 309篇 |
2012年 | 193篇 |
2011年 | 208篇 |
2010年 | 170篇 |
2009年 | 202篇 |
2008年 | 179篇 |
2007年 | 255篇 |
2006年 | 214篇 |
2005年 | 195篇 |
2004年 | 144篇 |
2003年 | 144篇 |
2002年 | 123篇 |
2001年 | 93篇 |
2000年 | 94篇 |
1999年 | 84篇 |
1998年 | 61篇 |
1997年 | 51篇 |
1996年 | 38篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 21篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有3935条查询结果,搜索用时 343 毫秒
91.
Guihua Huang Yipeng Huang Wei Xu Qiuhong Yao Xiaofang Liu Caifeng Ding Xi Chen 《中国化学快报》2019,30(5):1021-1023
Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)_3, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)_3 nanocrystals are well dispersed in the ethyl cellulose(EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl_2 Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)_3 film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)_3 based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters 相似文献
92.
Frank?WendlerEmail author Gerhard?Grane? Thomas?Heinze 《Cellulose (London, England)》2005,12(4):411-422
The thermal stability of cellulose/N-methylmorpholine-N-oxide (NMMO) solutions were investigated using UV/VIS spectrometry with a temperature programming cuvette and caloric measurements
by means of the Systag calorimeter RADEX (mini-autoclave). Both analytical methods allow to characterize the influences of
stabilizers and additives. With the temporal course of the optical density, temperature and pressure thermal runaway reactions
with gas evolution and accumulation of chromophoric degradation products were recognized. Kinetic model calculations compared
with UV/VIS measurements demonstrate the existence of autocatalytic reactions in cellulose/NMMO solutions. Varying the heating
rate autocatalysis can be proved by dynamic caloric measurements as well. 相似文献
93.
94.
Chandra S Kumar R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):1050-1057
Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO3, SCN and SO4) with macrocyclic ligands L1, L2 and L3 having N2S2, N4 and N5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru-N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L1 is more effective electron donors to ruthenium than of L2 and L3. Electronic spectral properties also show that the sulphur donor atom of L1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal-ligand bonds tend to be weaker than third-row transition metal-ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to pi-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism. 相似文献
95.
Guodong Feng Yanfu Huan Yanbo Cao Shuhua Wang Xinghua Wang Jie Jiang Aimin Yu Qinhan Jin Hongmei Yu 《Microchemical Journal》2004,76(1-2):17
An unique miniature simultaneous microwave plasma torch (MPT) atomic emission spectrometer employing linear UV intensified charge-coupled device (ICCD) array detector has been developed and studied preliminarily. The detection limits and precisions of the spectrometer for Ag, Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Sr and V by using different CCD exposure times have been determined. An analysis of a practical sample has been carried out. The preliminary results demonstrate that such simultaneous spectrometer has advantages of saving sample and time, especially suitable for use as detector for chromatography and in combination with flow injection systems. Taking analytical figures of merit and portability into accounts, the miniature simultaneous MPT system will have extended application areas and greater competition potential as compared with commercialized scanning MPT spectrometers. 相似文献
96.
An indirect UV photometric detection technique is described in which a low concentration of a UV-absorbing compound (UVAC) is added to the mobile phase in reversed phase liquid chromatography, thereby making it possible for non UV-absorbing compounds such as the lower alcohols to be detected by the UV detector. This happens because the injected analyte may extract a portion of the UV absorbing compound from the mobile and/or stationary phase and the complex is co-eluted as a positive peak at the retention time of the analyte. Alternatively, the injected analyte may appear as a negative peak if the UV-absorbing compound is transferred to the mobile and stationary phases. In any case, the injected compound appears either as a positive or negative peak depending on the relative polarities and concentrations of all the compounds in the system. In addition, the resulting excess or deficiency of detection agent in the stationary phase is eluted separately as a positive or negative peak, indicating that the system has returned to equilibrium. In the work described herein, the chromatographic conditions and variables of the indirect photometric technique were studied to develop a quantitative HPLC method for UV-transparent compounds. It was found that under optimal conditions it is possible to determine some analytes quantitatively at concentrations as low as 0.05%. 相似文献
97.
通过自由基共聚合合成了含有高二阶非线性光学活性偶氮单元的侧链液晶共聚物。共聚物的液晶转变温度为DSC测定,实验证明当偶氮单元含量超过40mol%时,共聚物的液晶性消失。通过高压电场对该聚合物膜进行针尖电晕极化取向,并由紫外测试给出了聚合物膜的取向参数及其稳定性,对液晶聚合物的非线性光学性质进行了初步的研究。 相似文献
98.
J. Aupiais 《Chromatographia》1997,44(5-6):303-312
Summary The indirect UV detection of cations by capillary zone electrophoresis gives peaks of very different height or area between
cations. We show that the height depends on the electrophoretic mobility of the cation compared with the electrophoretic mobility
of the chromophore used. Moreover, the limit of detection can be easily improved by about 4-fold by adjusting the concentration
of complexing agent or by using a chromophore with the same velocity as the studied cation. Using a new parameter termedsensitization power we can optimize the limit of detection and have determined the best chromophores for each family of cations.Sensitization power is a maximum for: alkali metals and alkali earths with imidazole and UV Cat 2?, for transition metal with pyridine, for light rare earth with ephedrine and UV Cat 1?, for heavy lanthanides with 1-naphthylamine and phenyl-trimethyl-ammonium bromide. Corrected areas of all cations studied
have normal distributions directly proportional to their ionic charge. Certain behaviour can be predicted for elements such
as actinides. Detection can also be enhanced because the relation of proportionality between ionic charge and corrected area
allows comparison of the performance of all chromophores. 相似文献
99.
Summary A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.Deceased July 31, 1996 相似文献
100.
M. Jayakannan Paul A. Van Hal Ren A. J. Janssen 《Journal of polymer science. Part A, Polymer chemistry》2002,40(14):2360-2372
Novel alternating conjugated copolymers ( P1–P6 ) consisting of an electron‐deficient benzothiadiazole and a variety of electron‐rich thiophene‐arene‐thiophene units were synthesized by palladium‐catalyzed polycondensations (Stille and Suzuki reactions), aiming at processable materials with a reduced optical band gap. The structures of P1–P6 were confirmed by 1H NMR and 13C NMR, and their molecular weights were determined by size exclusion chromatography. In the Suzuki polycondensation, the role of the catalyst [Pd(PPh3)4 and Pd(OAc)2] on the resulting molecular weight was investigated. Pd(OAc)2 enhances the molecular weight of the polymers for both thiophene and phenylene bis‐boronic esters as compared with Pd(PPh3)4. The optical properties of the polymers were examined in solution and the solid state. The polymers with n‐octyl substituents ( P1 , P4 , P5 , and P6 ) on the thiophene rings possessed less‐planar structures as a result of torsional steric hindrance, and their absorption spectra appeared blueshifted as compared with their unsubstituted analogues ( P2 and P3 ). The electrochemical properties of the polymers were studied using cyclic voltammetry. Although the alkyl substitution affects the oxidation potential, only marginal differences in the reduction potentials were observed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2360–2372, 2002 相似文献