全文获取类型
收费全文 | 11029篇 |
免费 | 538篇 |
国内免费 | 562篇 |
专业分类
化学 | 5940篇 |
晶体学 | 184篇 |
力学 | 322篇 |
综合类 | 51篇 |
数学 | 3138篇 |
物理学 | 2494篇 |
出版年
2023年 | 48篇 |
2022年 | 185篇 |
2021年 | 138篇 |
2020年 | 176篇 |
2019年 | 218篇 |
2018年 | 207篇 |
2017年 | 207篇 |
2016年 | 214篇 |
2015年 | 185篇 |
2014年 | 238篇 |
2013年 | 413篇 |
2012年 | 313篇 |
2011年 | 550篇 |
2010年 | 447篇 |
2009年 | 801篇 |
2008年 | 636篇 |
2007年 | 618篇 |
2006年 | 584篇 |
2005年 | 560篇 |
2004年 | 690篇 |
2003年 | 587篇 |
2002年 | 579篇 |
2001年 | 398篇 |
2000年 | 352篇 |
1999年 | 276篇 |
1998年 | 233篇 |
1997年 | 226篇 |
1996年 | 247篇 |
1995年 | 198篇 |
1994年 | 243篇 |
1993年 | 189篇 |
1992年 | 175篇 |
1991年 | 98篇 |
1990年 | 76篇 |
1989年 | 73篇 |
1988年 | 65篇 |
1987年 | 75篇 |
1986年 | 62篇 |
1985年 | 54篇 |
1984年 | 51篇 |
1983年 | 21篇 |
1982年 | 40篇 |
1981年 | 48篇 |
1980年 | 53篇 |
1979年 | 74篇 |
1978年 | 55篇 |
1977年 | 56篇 |
1976年 | 40篇 |
1974年 | 14篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
10,10′-二烃基-9, 9′-联二吖啶盐有很强的荧光, 在光学材料[1]和重金属离子的分析[2]中有重要的应用价值。 相似文献
962.
Summary A sensitive LC method for the detection of amino acids and oligopeptides with pre-column fluorescence derivatization has been
developed. Glycine, glycylglycine, triglycine, glutathione, glutamic acid, and cysteine were separated on a reversed-phase
C18 column with methanol-water-triethylamine eluent, derivatization and chromatographic conditions were optimized. The six derivatives
were eluted in 20 min with good reproducibility. The relative standard derviations (n=6) at an analytical concentration of
2×10−6 M are <5%. Detection limits (signal-to-noise ratio=3) for the six derivatives are 23–68 fmol. 相似文献
963.
Zhongliang Zhang Fuming Liu Manhong Liu Zhenzhen Wang Faping Zhong Feng Wu 《Journal of Thermal Analysis and Calorimetry》1997,50(1-2):89-103
Calorimetric measurements were carried out on the electrorefining of copper using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (Q
m orW
m) to the input electric energy (Q
in orW
in) and the excess heat (Q
ex orW
ex), i.e. the difference betweenQ
m (orW
m) andQ
in (orW
in) during the electrorefining process were discussed in terms of general thermodynamics. It was found thatR andQ
ex were related to the current density employed in the experiment and varied as a logarithmic function. The results obtained here indicate that the heat generation under different conditions, such as different currents or voltages, may be caused partially by the irreversibility of the process or by some unknown processes.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThe authors would like to acknowledge the extreme encouragements and help of Professor Shuyi Liu (University of Science and Technology of China) and Professors Fu Tan and Guoquan Liu (Institute of Chemistry, Academia Sinica).This study was supported by the National Nature Science Foundation of China. 相似文献
964.
Hoebbel Dagobert Reinert Thomas Schmidt Helmut Arpac Ertugrul 《Journal of Sol-Gel Science and Technology》1997,10(2):115-126
The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated -diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and -ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and 13 C NMR spectroscopy and were found to be L:M 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H2O : OR) = 0.5–2.0 decreases with increasing H
965.
We present an automated conformational analysis program, CAMDAS (Conformational Analyzer with Molecular Dynamics And Sampling). CAMDAS performs molecular dynamics (MD) calculations for a target molecule and samples conformers from the trajectory of the MD. The program then evaluates the similarities between each of the sampled conformers in terms of the root- mean-square deviations of the atomic positions, clusters similar conformers, and finally prints out the clustered conformers. This MD-based conformational analysis is a broadly used method, and CAMDAS is intended to provide a convenient framework for the method. CAMDAS has the ability to find the representative conformers automatically from an arbitrarily given structure of the molecule. The accuracy of the program was examined using N- acetylalanine-N-methylamide, and the obtained result was consistent with that of the systematic search method. In the test calculation of cyclodecane, CAMDAS could identify most of the known conformers and their conformational enantiomers by examining only 5000 conformers. In addition, the potential-scaled method, which we have developed previously as an accelerating technique for MD, could find two additional conformers of cyclodecane that have not been reported. CAMDAS presents a convenient way to find the energetically possible conformers of a molecule, which is needed especially in the early stage of drug design. 相似文献
966.
Monir Uddin Antonis G. Hatzidimitriou Maria Lalia-Kantouri Chris Tsiamis 《Structural chemistry》1997,8(2):131-139
The infrared and electronic excitation spectra of a series of new nickel(II) chelates containing an-diimine (or nitrogenous base, enR) and the anion of a-dione (1,3-ketoenol or 1,3-ketoester,H) were obtained in the solid state and in solution. The composition and the overall structure of the new chelates in the solid state depends on ligand concentration, the substituents within the-dionato moiety and the counterion present. The IR and electronic excitation spectra of [Ni(enR)2
]NO3 and [Ni(enR)(O2NO)] indicate, in conjunction with other physicochemical measurements, bidentate coordination of the ligands, while the spectral shifts reveal replacement of the (O,O)nitrato group by basic solvents. The existence of the nickel(II) in an octahedral environment is confirmed by an X-ray structure analysis of [Ni(dpamH)2acac]NO3 · CH3OH (monoclinic, space groupP2l/n, a=17.296(1),b=7.462(1),c=21.604(3) å,=95.65(1),Z=4, R=0.0534,Rw=0.0600), where dpamH denotes the 2,2-dipyridylamine. 相似文献
967.
Subir Panja Debasish kundu Sabir Ahammed Brindaban C. Ranu 《Tetrahedron letters》2017,58(35):3457-3460
A highly chemoselective reduction of aryl, heteroaryl, acyl and sulfonyl azides to the corresponding amines has been achieved by Fe(0) nanoparticles in water at room temperature in the absence of external hydride source. Several readily reducible functionalities including alkene, alkyne, S-S linkage, OTBDMS remain unaffected during reduction. 相似文献
968.
In this work, acid functionalized multi-wall carbon nanotubes (MWCNTs) were modified with imidazolium-based ionic liquids. The selective oxidation of various alcohols with hydrogen peroxide catalyzed by[PZnMo2W9O39]5-, ZnPOM, supported on ionic liquids-modified with MWCNTs, MWCNTAPIB, is reported. This catalyst[ZnPOM@APIB-MWCNT], was characterized by X-ray diffraction, scanning electron microscopy (SEM) and FT-IR spectroscopic methods. This heterogeneous catalyst exhibited high stability and reusability in the oxidation reaction without loss of its catalytic performance. 相似文献
969.
970.
Summary Capillary electrophoresis has been used for the chiral analysis of two -amino alcohol pharmaceutical compounds. Capillary zone electrophoresis conditions were used with -cyclodextrin as a chiral mobile phase additive. The effects of variation of -cyclodextrin concentration, temperature, pH, background electrolyte composition and concentration have been investigated. Optimum separations were achieved for clenbuterol using -cyclodextrin at its solubility limit (16mM), the lowest practicable temperature (19°C), pH 4.0 and an electrolyte solution with a high ionic strength prepared from 0.1 M citric acid and 0.3 M Na2HPO4. For the development compound picumeterol and its (S)-enationmer, the optimum pH 4.0 buffer was prepared from 0.1 M citric acid and 0.2 M sodium acetate. Baseline separation with resolution greater than 2 was achieved for both compounds.This work was presented in part at the 2nd International Symposium on Chiral Discrimination, Rome, May 27–31, 1991. 相似文献