全文获取类型
收费全文 | 173040篇 |
免费 | 2067篇 |
国内免费 | 724篇 |
专业分类
化学 | 93268篇 |
晶体学 | 2473篇 |
力学 | 7654篇 |
综合类 | 7篇 |
数学 | 17976篇 |
物理学 | 54453篇 |
出版年
2021年 | 1057篇 |
2020年 | 1157篇 |
2019年 | 1175篇 |
2018年 | 1198篇 |
2017年 | 1193篇 |
2016年 | 2397篇 |
2015年 | 1980篇 |
2014年 | 2551篇 |
2013年 | 7815篇 |
2012年 | 6393篇 |
2011年 | 8071篇 |
2010年 | 4971篇 |
2009年 | 5110篇 |
2008年 | 7419篇 |
2007年 | 7369篇 |
2006年 | 7088篇 |
2005年 | 6611篇 |
2004年 | 5924篇 |
2003年 | 5086篇 |
2002年 | 5007篇 |
2001年 | 6057篇 |
2000年 | 4587篇 |
1999年 | 3507篇 |
1998年 | 2645篇 |
1997年 | 2641篇 |
1996年 | 2589篇 |
1995年 | 2301篇 |
1994年 | 2185篇 |
1993年 | 2048篇 |
1992年 | 2365篇 |
1991年 | 2327篇 |
1990年 | 2034篇 |
1989年 | 2014篇 |
1988年 | 2047篇 |
1987年 | 1968篇 |
1986年 | 1880篇 |
1985年 | 2789篇 |
1984年 | 2767篇 |
1983年 | 2215篇 |
1982年 | 2416篇 |
1981年 | 2283篇 |
1980年 | 2239篇 |
1979年 | 2176篇 |
1978年 | 2250篇 |
1977年 | 2208篇 |
1976年 | 2135篇 |
1975年 | 2122篇 |
1974年 | 2030篇 |
1973年 | 2111篇 |
1972年 | 1202篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
821.
822.
Aurora González-Portal F. Bermejo-Martínez C. Baluja-Santos María Cristina Diez-Rodríguez 《Microchemical Journal》1985,31(3):368-374
A new method for the Spectrophotometric determination of bismuth using N-(2-acetamido)iminodiacetic acid as complexometric agent is proposed. The complex is formed in a wide pH range, 5.5–7.5, and has a maximum absorption at 265 nm. Beer's law is obeyed in the interval 3.8–17.9 μg of bismuth(III)/ml, with a minimum photometric error of 2.3. The molar absorptivity is 9.1 × 103 liters/cm mol. The stoichiometry of the reaction takes place in the metal-to-ligand ratio 1:2. The interferences produced by the more common ions are studied. The method has been successfully applied to the determination of bismuth in pharmaceutical formulations. 相似文献
823.
The nuclear coordinate dependence of electronic transtion moments has been investigated for the purpose of finding new interpretations of deuterium isotope effects on spectral intensities and radiative decay rates in orbitally forbidden electronic transitions. By using “AO following nuclei” wavefunctions as the building block for the electronic wavefunction in the adiabatic BO vibronic wavefunction, the spin-free hamiltonian is diagonalized to generate eigenfunctions and eigen-energies. It is found that the electronic transtion moments based on these eigenfunctions show dependences upon the vibrational modes which are not directly involved in vibronic coupling. This leads to interpretations of the deuterium isotope effects in T1 → S0 radiative transitions of aromatic hydrocarbons and S0 → S1 absorption in pyrazine which are not based on the conventional Herzberg—Teller or non-BO coupling. 相似文献
824.
The synthesis and thermal decomposition of a series of 3-azido-4-benzylideneamino-s-triazoles are described. The decompositions resulted in a loss of nitrogen and intra-molecular cyclization at the carbon atom of the azomethine linkage to produce 1H-2-aryl-s-triazolo-[3,2-c]-s-triazoles. 相似文献
825.
Fietzek C Hermle T Rosenstiel W Schurig V 《Fresenius' Journal of Analytical Chemistry》2001,371(1):58-63
The enantiomeric composition of the chiral flavoring agent limonene was analyzed by means of a quartz-crystal microbalance (QCM) sensor. As chiral selectors three different modified beta-cyclodextrins were investigated. The selector molecules were applied as mixtures in different polysiloxane matrices. The chiral separation factors alpha for limonene obtained at 30 degrees C by gas chromatography and by use of the QCM sensor were comparable. Evaluation of sensor data was performed by use of an artificial neuronal network (ANN); this enabled prediction of the enantiomeric composition of the gas mixtures. 相似文献
826.
Empore disks were used to successfully extract herbicide residues from a difficult-to-analyze surface water source and deionized water. Herbicide recoveries were lower in surface water at 7,14, or 21 days after fortification and storage at 4 degrees C, presumably due to chemical sorption onto precipitated organic particulates. The addition of acid to the samples, as recommended in EPA Method 525.2, did not affect recoveries of alachlor and metolachlor, but reduced recoveries of atrazine, simazine, and cyanazine. Treatment of water samples with sodium hypochlorite did not affect alachlor or metolachlor recoveries, but greatly reduced the recovery of all triazine herbicides. This indicates that addition of acid or sodium hypochlorite to water samples may be detrimental to triazine analysis. 相似文献
827.
828.
The photoelectron spectrum of HCP has been obtained, Ionization potentials are found at 10.79 ± 0.01 eV (X2 Π) and 12.86 ± 0.01 eV (A 2 Σ). By comparison with HCP, a new interpretation of the first photoelectron band of HCN has been proposed which involves a Renner-Teller interaction in the Σ+ vibronic states of the molecular ion. 相似文献
829.
C. Schnier 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(2):209-216
Many unexplained phenomena associated with the radioactive halos in very old minerals are described in the literature. In this paper these phenomena are enumerated. The new hypothesis that a primordial superheavy element (SHE) survived in the earth"s crust can help to solve the problems. According to this hypothesis, the SHE decays by spontaneous fission into fragments of very different mass. The heavy fragments, assumed to lie in the region of the natural decay series, exhibit many indications for a SHE. Additionally, the alpha decay of SHE may occur. Applying the methods of mass spectrometry and X-ray fluorescence can probably prove the existence of SHE. 相似文献
830.