全文获取类型
收费全文 | 13717篇 |
免费 | 1474篇 |
国内免费 | 1033篇 |
专业分类
化学 | 9499篇 |
晶体学 | 122篇 |
力学 | 535篇 |
综合类 | 110篇 |
数学 | 1791篇 |
物理学 | 4167篇 |
出版年
2023年 | 187篇 |
2022年 | 294篇 |
2021年 | 318篇 |
2020年 | 385篇 |
2019年 | 376篇 |
2018年 | 315篇 |
2017年 | 343篇 |
2016年 | 581篇 |
2015年 | 526篇 |
2014年 | 666篇 |
2013年 | 934篇 |
2012年 | 1026篇 |
2011年 | 1120篇 |
2010年 | 732篇 |
2009年 | 621篇 |
2008年 | 822篇 |
2007年 | 712篇 |
2006年 | 630篇 |
2005年 | 494篇 |
2004年 | 466篇 |
2003年 | 408篇 |
2002年 | 427篇 |
2001年 | 337篇 |
2000年 | 248篇 |
1999年 | 262篇 |
1998年 | 172篇 |
1997年 | 140篇 |
1996年 | 159篇 |
1995年 | 143篇 |
1994年 | 136篇 |
1993年 | 125篇 |
1992年 | 112篇 |
1991年 | 105篇 |
1990年 | 76篇 |
1989年 | 91篇 |
1988年 | 68篇 |
1987年 | 70篇 |
1986年 | 83篇 |
1985年 | 91篇 |
1984年 | 69篇 |
1983年 | 58篇 |
1982年 | 59篇 |
1978年 | 55篇 |
1976年 | 51篇 |
1968年 | 65篇 |
1966年 | 49篇 |
1965年 | 57篇 |
1964年 | 54篇 |
1962年 | 52篇 |
1961年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Chen Hou Rongjun Qu Chunnuan Ji Chunhua Wang Chengguo Wang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):219-225
FeCl3 coordinated by isophthalic acid was first used as a catalyst in the azobisisobutyronitrile‐initiated reverse atom transfer radical polymerization of acrylonitrile. N,N‐Dimethylformamide was used as a solvent to improve the solubility of the ligand. An FeCl3‐to‐isophthalic acid ratio of 0.5 not only gave the best control of the molecular weight and its distribution but also provided rather a rapid reaction rate. The effects of different solvents on the polymerization of acrylonitrile were also investigated. The rate of the polymerization in N,N‐dimethylformamide was faster than that in propylene carbonate and toluene. The molecular weight of polyacrylonitrile agreed reasonably well with the theoretical molecular weight in N,N‐dimethylformamide. The rate of polymerization increased with increasing polymerization temperature, and the apparent activation energy was calculated to be 59.9 kJ mol?1. Reverse atom transfer radical polymerization was first used to successfully synthesize acrylonitrile polymers with a molecular weight higher than 80,000 and a narrow polydispersity as low as 1.22. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 219–225, 2006 相似文献
92.
Many sets of the soliton and periodic travelling wave solutions for the quadratic χ^(2) nonlinear system are obtained by the Backlund transformation and the trial method. The property of the propagation for some travelling waves is investigated. 相似文献
93.
The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH2)2C6H3OH (LH) revealed compounds L3Al ( 1 ) and L2AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 ( 3 ), rather 2 together with Me3Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
94.
热效应对光折变晶体两波耦合的特性影响的理论分析 总被引:3,自引:1,他引:2
用一种模型对两波耦合进行了分析,导出了强度相位的解析式,对影响两波耦合的参数进行了理论分析。分析了对BaTiO3光折变晶体的两波耦合的测量结果。 相似文献
95.
从实验上探讨了掺Nd^3+的氟化物玻璃光纤正向双程超荧光基本特性,包括输入-输出特性、输出-带宽特性以及输出-波长(激发)特性。并给出了理论上的拟合公式,实验表明利用氟化物玻璃光纤有望获得性能优异的有应用前景的低相干度集成化光源。 相似文献
96.
This paper presents some results of the relation between wavelet transform and fractal transform. The wavelet transform of the attractor of fractal transform posseses translational and scale invariance. So we speed the fractal image encoding by testing the invariance of the wavelet transform appropriate for image encoding. The classfication scheme of range blocks by wavelet transform is given in this paper. 相似文献
97.
98.
JiŘí Kvapil Josef Kvapil Bohumil Perner Michal Košelja Helena Jelínková 《Czechoslovak Journal of Physics》1990,40(11):1283-1287
The methods of growing YAG:Nd crystals with a flat interface and YAP:Nd crystals with a sharp conical interface are described. The form of the interface was controlled by the He and H2O content in the reducing atmosphere composed mainly of Ar and H2 as well as by axial temperature gradient above the melt level. The crystals of 120–180 mm in length were machined to the high-quality slabs. 相似文献
99.
I. R. Gulamov A. A. Karakhodzhaev A. M. Mukhamedzhanov G. K. Nie E. A. Pak R. Yarmukhamedov V. Burjan J. Cejpek V. Kroha J. Křemének M. Kurka 《Czechoslovak Journal of Physics》1990,40(8):875-894
The angular distributions of the (p, d), (d, t) and(3He, ) reactions on13C have been analysed within the framework of DWBA in which additional information on nuclear vertex constants was introduced. Although all these reactions seem to be similar single nucleon transfer, their mechanism is shown to be quite different and so is the information extracted thereof. While from the (p, d) reactions spectroscopic factors may be extracted unambiguously, from the (d, t) reactions it is possible to obtain directly the values of vertex constants only, which in turn are consistent with those determined by extrapolation of the experimental cross sections of the (p, d) reactions to the pole.In the case of (3He, ) reactions, however, the analysis indicates inadequacy of the DWBA concerning the calculations of central partial amplitudes. For a more reliable extraction of structural information, besides the correct normalization of peripheral amplitudes, a contribution of more complex mechanisms must be taken into account. 相似文献
100.
J. Novotný 《Czechoslovak Journal of Physics》1990,40(2):151-163
The dependence of the on-shellS-matrix on the change of the Lagrangian induced by a nonlinear substitutionF() is investigated by means of a graphical analysis. A cancellation mechanism is found and used to show that the tree approximation of theS-matrix is independent of such a substitution and that the Jacobian of the substitution has to be introduced in order to cancel a new class of singular one-loop graphs and to recover the primaryS-matrix at the one-loop level. 相似文献