全文获取类型
收费全文 | 353780篇 |
免费 | 2300篇 |
国内免费 | 965篇 |
专业分类
化学 | 149482篇 |
晶体学 | 5086篇 |
力学 | 20805篇 |
综合类 | 5篇 |
数学 | 71474篇 |
物理学 | 110193篇 |
出版年
2021年 | 1665篇 |
2020年 | 1801篇 |
2019年 | 2010篇 |
2018年 | 18805篇 |
2017年 | 19293篇 |
2016年 | 12151篇 |
2015年 | 3766篇 |
2014年 | 3989篇 |
2013年 | 9467篇 |
2012年 | 13942篇 |
2011年 | 27826篇 |
2010年 | 16956篇 |
2009年 | 17261篇 |
2008年 | 22635篇 |
2007年 | 27635篇 |
2006年 | 8070篇 |
2005年 | 14336篇 |
2004年 | 10816篇 |
2003年 | 10443篇 |
2002年 | 7657篇 |
2001年 | 6770篇 |
2000年 | 5461篇 |
1999年 | 3952篇 |
1998年 | 3244篇 |
1997年 | 3185篇 |
1996年 | 3088篇 |
1995年 | 2795篇 |
1994年 | 2608篇 |
1993年 | 2483篇 |
1992年 | 2795篇 |
1991年 | 2782篇 |
1990年 | 2701篇 |
1989年 | 2516篇 |
1988年 | 2580篇 |
1987年 | 2573篇 |
1986年 | 2398篇 |
1985年 | 3086篇 |
1984年 | 3343篇 |
1983年 | 2751篇 |
1982年 | 2920篇 |
1981年 | 2890篇 |
1980年 | 2751篇 |
1979年 | 2847篇 |
1978年 | 2950篇 |
1977年 | 2863篇 |
1976年 | 2958篇 |
1975年 | 2728篇 |
1974年 | 2693篇 |
1973年 | 2866篇 |
1972年 | 1809篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
We provide a characterization of the limit periodic sets for analytic families of vector fields under the hypothesis that the first jet is non-vanishing at any singular point. Also, applying the family desingularization method, we reduce the complexity of some of these sets. 相似文献
122.
Whittum D.H. Ebihara K. Hiramatsu S. Kishiro J.-i. Monaka T. Ozaki T. Takayama K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):136-141
Studies of microwave amplification with an in-focused electron beam drawn from an induction injector are reported. A free-electron laser (FEL) operating at 9.4 GHz and employing ion-focusing within the interaction region has achieved power in excess of 30 MW at 9.4 GHz, with a beam energy of 0.8 MeV and current of 0.7 kA. Peak gain is 20 dB/m, with no saturation after 15 wiggler periods. Also reported are the first evolution and detuning data for an ion-channel laser/maser (ICL). Two shortcomings of the prematurely halted ICL studies are poor frequency discrimination and a large axial plasma gradient. Prospects for operation with an upgraded 1.6 MeV accelerator are discussed 相似文献
123.
S. V. Litvinenko V. I. Savich L. D. Bobrovnik 《Chemistry of Heterocyclic Compounds》1994,30(3):340-344
We have developed a method for synthesis of N-(3-clzloro-2-quinoxalyl)sulfonamides by reaction of 2,3-dichloroquinoxaline with substituted arylsufonamides. Based on the IR spectra, we have established that in the solid state, the synthesized compounds exist in the form of amide tautomers. Alkylation of these compounds leads to N-metliyl-N-(3-chloro-2-quinoxalyl)arylsulfonamides. We demonstrate the possibility of nucleophilic substitution of the halogen upon treatment with O- and N-nucleophiles. The use of bifunctional nucleophiles leads to condensed quinoxalines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 30, No. 3, pp. 387–392, March, 1994. 相似文献
124.
G. D. Krapivan N. I. Val'ter T. Ya. Kaklyugina V. G. Kul'nevich 《Chemistry of Heterocyclic Compounds》1994,30(3):289-295
Halogen in positions 3 and 5 of the furan ring in ftirfurylidenedioxanediones is readily replaced by dithiocarbonate, dithiocarbatnate, dithiophosphate, thiocyanate, and azide anions, and by thiourea, and secondary and tertiary amines. The conformation of the initial halogen derivative is retained in the substitution products.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 327–334, March, 1994. 相似文献
125.
126.
127.
D. Kh. Khalikov M. G. Mukhiddinov M. G. Asoev V. A. Degtyarev 《Chemistry of Natural Compounds》1994,30(6):734-738
Some features of the kinetics of the hydrolysis of apple protopectin have been studied on the basis of an analysis of monosaccharide residues of the pectin substances and determinations of characteristic viscosity. It has been shown that the fine regulation of the physicochemical parameters of the hydrolysis of protopectin leads to the formation of pectin substances with different properties. 相似文献
128.
129.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
130.
The properties of a polymer-concrete composed of polyester matrix and locally available rock aggregate are investigated. The formula of the concrete is found by an experimental-calculation approach in such a way as to attain a closer packing of the aggregate particles on the one hand, and to ensure the needed processing characteristics (placeability) of the mix on the other. It is shown experimentally that the material obtained has a rather high compression strength. Under prolonged compression loads, the polymer-concrete exhibits a noticeable creep behavior with a linear relation between the creep strains and stresses. After the action of half the ultimate load over 3000 h, the total strains exceed the instantaneous ones by 2.0 to 2.2 times. The accumulation of irreversible strains is also observed; however, their contribution to the total strain is small. It is found that the stress-strain relation can be represented by the equation of linear hereditary creep theory.Institute of Polymer Mechanics, University of Latvia, Riga, LV-1006, Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 2, pp. 147–162, March–April, 1999. 相似文献