全文获取类型
收费全文 | 3406篇 |
免费 | 150篇 |
国内免费 | 54篇 |
专业分类
化学 | 1873篇 |
晶体学 | 51篇 |
力学 | 166篇 |
综合类 | 16篇 |
数学 | 740篇 |
物理学 | 764篇 |
出版年
2023年 | 28篇 |
2022年 | 49篇 |
2021年 | 62篇 |
2020年 | 92篇 |
2019年 | 89篇 |
2018年 | 133篇 |
2017年 | 120篇 |
2016年 | 173篇 |
2015年 | 134篇 |
2014年 | 165篇 |
2013年 | 356篇 |
2012年 | 216篇 |
2011年 | 219篇 |
2010年 | 231篇 |
2009年 | 145篇 |
2008年 | 206篇 |
2007年 | 186篇 |
2006年 | 129篇 |
2005年 | 93篇 |
2004年 | 77篇 |
2003年 | 71篇 |
2002年 | 98篇 |
2001年 | 80篇 |
2000年 | 54篇 |
1999年 | 35篇 |
1998年 | 42篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1964年 | 8篇 |
排序方式: 共有3610条查询结果,搜索用时 15 毫秒
991.
Mahmure ü. ?zgür Abdürrezzak Bozdo?an Ay?e Er?a? ?kbal Koyuncu 《Monatshefte für Chemie / Chemical Monthly》2001,1(3):669-673
Two methods for the simultaneous determination of anthocyanin and ponceau 4R in drink powders by second derivative spectrophotometry and by partial least-squares multivariate spectrophotometric calibration are described. The procedures do not require any separation step. The methods were applied to determine both colorants in commercial gelatin powders; the results obtained are compared. 相似文献
992.
Jana Bludská Ivo Jakubec Dušan Nohavica Ladislav Pekárek 《Czechoslovak Journal of Physics》1999,49(5):775-781
We report on preparation of p-In1−x
Ga
x
P polycrystalline, p-In0.5 Ga0.5P/p-GaAs, and p-In0.5 Ga0.5P/n-GaAs/n-InP tandem-type cathodes. The photovoltaic efficiency of InGaP tandem type epitaxial electrodes is two times higher
than that of polycrystalline photocathodes. The most significant advantage of epitaxial electrodes is in their markedly better
corrosion resistance in comparison with polycrystalline photocatodes.
Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17,
1998. 相似文献
993.
994.
995.
Cemil Aydoğan Fatma Yılmaz Duygu Çimen Lokman Uzun Adil Denizli 《Electrophoresis》2013,34(13):1908-1914
A new type of polymethacrylate‐based monolithic column with chiral stationary phase was prepared for the enantioseparation of aromatic amino acids, namely d ,l ‐phenylalanine, d ,l ‐tyrosine, and d ,l ‐tryptophan by CEC. The monolithic column was prepared by in situ polymerization of butyl methacrylate (BMA), N‐methacryloyl‐l ‐histidine methyl ester (MAH), and ethylene dimethacrylate (EDMA) in the presence of porogens. The porogen mixture included DMF and phosphate buffer. MAH was used as a chiral selector. FTIR spectrum of the polymethacrylate‐based monolith showed that MAH was incorporated into the polymeric structure via in situ polymerization. Some experimental parameters including pH, concentration of the mobile phase, and MAH concentration with regard to the chiral CEC separation were investigated. Single enantiomers and enantiomer mixtures of the amino acids were separately injected into the monolithic column. It was observed that l ‐enantiomers of aromatic amino acids migrated before d ‐enantiomers. The reversal enantiomer migration order for tryptophan was observed upon changing of pH. Using the chiral monolithic column (100 μm id and 375 μm od), the best chiral separation was performed in 35:65% ACN/phosphate buffer (pH 8.0, 10 mM) with an applied voltage of 12 kV in CEC. SEM images showed that the chiral monolithic column has a continuous polymeric skeleton and large through‐pore structure. 相似文献
996.
The particulate emission caused by welding of steel plates covered with 29 diversified shop primers has been investigated. The investigation includes the determination of particle mass, particle size distribution, and of the contents of heavy metals such as lead and cadmium. The results show that all investigated primers except those with high concentration of zinc pigment produce mass emissions which are very low in comparison to manual arc welding with covered electrode and CO2-welding on uncoated steel. The emitted particles of the primers are smaller than 1 μm particle diameter and therefore respirable. Lead and cadmium was found in particles emitted during the welding process of all investigated primers. The highest amount was found in particles of primers with high contents of zinc and ferric oxide. 相似文献
997.
Some properties of unsteady unidirectional flows of a fluid of second grade are considered for flows produced by the sudden application of a constant pressure gradient or by the impulsive motion of one or two boundaries. Exact analytical solutions for these flows are obtained and the results are compared with those of a Newtonian fluid. It is found that the stress at the initial time on the stationary boundary for flows generated by the impulsive motion of a boundary is infinite for a Newtonian fluid and is finite for a second grade fluid. Furthermore, it is shown that initially the stress on the stationary boundary, for flows started from rest by sudden application of a constant pressure gradient is zero for a Newtonian fluid and is not zero for a fluid of second grade. The required time to attain the asymptotic value of a second grade fluid is longer than that for a Newtonian fluid. It should be mentioned that the expressions for the flow properties, such as velocity, obtained by the Laplace transform method are exactly the same as the ones obtained for the Couette and Poiseuille flows and those which are constructed by the Fourier method. The solution of the governing equation for flows such as the flow over a plane wall and the Couette flow is in a series form which is slowly convergent for small values of time. To overcome the difficulty in the calculation of the value of the velocity for small values of time, a practical method is given. The other property of unsteady flows of a second grade fluid is that the no-slip boundary condition is sufficient for unsteady flows, but it is not sufficient for steady flows so that an additional condition is needed. In order to discuss the properties of unsteady unidirectional flows of a second grade fluid, some illustrative examples are given. 相似文献
998.
999.
We begin by a short survey of various attempts in selection theory to avoid the closedness assumption for values of multivalued mappings. We collect special cases when Michael's Gδ-problem admits an affirmative solution and we prove some unified theorems of such type. We also show that in general this problem has a negative solution. In comparison with a recent result of Filippov, we work directly in the Hilbert cube rather than in the space of all probabilistic measures endowed with different topologies. 相似文献
1000.
Abstract In this paper, we introduce new difference sequence spaces combining with de la Vallee-Poussin mean using by a sequence of
modulus functions and ϕ -functions. We also studied connections between statistically convergence related with this space.
Keywords Difference sequence, Modulus function, ϕ -function, De la Vallee-Poussin means, Statistical convergence
Mathematics Subject Classification (2000) 46A45, 40F05, 46A80 相似文献