全文获取类型
收费全文 | 770篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 521篇 |
晶体学 | 2篇 |
力学 | 16篇 |
数学 | 58篇 |
物理学 | 193篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 23篇 |
2011年 | 60篇 |
2010年 | 24篇 |
2009年 | 10篇 |
2008年 | 40篇 |
2007年 | 49篇 |
2006年 | 51篇 |
2005年 | 52篇 |
2004年 | 41篇 |
2003年 | 33篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1969年 | 4篇 |
1939年 | 4篇 |
排序方式: 共有790条查询结果,搜索用时 0 毫秒
51.
The reaction of glycosyl acetates with allyltrimethylsilane in the presence of zinc bromide has been investigated as a new method for -glycoside construction. 相似文献
52.
J. Bartke M. Deutschmann H.G. Kirk P. Sixel L. Becker H. Vogt R. Hartmann H. Plothow D. Kocher D.R.O. Morrison P. Porth K. Eskreys K. Olkiewicz K. Doroba T. Hofmokl 《Nuclear Physics B》1977,120(1):1-13
Interactions in which the baryon is emitted forwards in the c.m.s. are studied in 8 and 16 GeV/cπ+p collisions. These interactions are interpreted as representing baryon exchange. The properties of such off-shell N annihilation events are studied. It is found that the multiplicity distribution of the multi-pion system as a function of the effective mass for events with |upp| < 1 GeV2 is the same as for real annihilations. 相似文献
53.
54.
H.F. Chambers R.W. Kirk J.K. Thompson M.J. Warner P.M. Wilt 《Journal of Molecular Spectroscopy》1975,58(1):76-86
The infrared spectrum of HC13F3 is reported for the first time. Fundamental frequency shifts due to carbon-13 substitution have been measured and rotational analyses of several of the fundamental and combination bands are given. Coriolis x-y and Fermi perturbations are evident in several of the bands. Table VI summarizes the data obtained in this study. 相似文献
55.
Ooms KJ Feindel KW Willans MJ Wasylishen RE Hanna JV Pike KJ Smith ME 《Solid state nuclear magnetic resonance》2005,28(2-4):125-134
Results from a solid-state 139La NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX3; X=F, Cl, Br, I) at applied magnetic fields of 7.0, 9.4, 11.7, 14.1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The 139La quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl3 and LaI3, respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from −135 ppm for LaF3 to 700 ppm for LaI3, which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF3 through LaI3. DFT calculations of the 139La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally. 相似文献
56.
Kirk JG 《Physical review letters》2004,92(18):181101
Relativistic current sheets have been proposed as the sites of dissipation in pulsar winds, jets in active galaxies, and other Poynting flux dominated flows. It is shown that the steady versions of these structures differ from their nonrelativistic counterparts because they do not permit transformation to a de Hofmann-Teller frame with zero electric field. Instead, their generic form is that of a true neutral sheet with no linking magnetic field component normal to the sheet. The maximum energy to which such structures can accelerate particles is derived, and used to compute the maximum frequency of the subsequent synchrotron radiation. This can be substantially in excess of standard estimates. In the magnetically driven gamma-ray burst scenario, acceleration of electrons is possible to energies sufficient to enable photon-photon pair production after an inverse Compton scattering event. 相似文献
57.
Ahmad SI Hargreaves A Taiwo FA Kirk SH 《Journal of photochemistry and photobiology. B, Biology》2004,77(1-3):55-62
Compared with ultraviolet B and C, UVA is considered to have little direct effects on biological systems. However, damaging effects of UVA on biological systems are often synergistically enhanced in the presence of sensitizers. Production of reactive oxygen species (ROS) has been implicated in the process. Several ROS have been identified but their involvement in inducing cellular damage is yet to be fully evaluated. Although membranes and proteins are affected, DNA is an important target and a variety of types of damage have been reported. Here, we present evidence that L-mandelate can act as a near UV (NUV) sensitizer, when activated by a lamp emitting 99% UVA and 1% UVB. Although evidence is available that H(2)O(2) and a small amount of *OH are produced, an alternative effect of the sensitization reaction may involve direct electron transfer. Studies have shown that NUV photolysis of mandelate can inactivate phage T7. Employment of tetrazolium blue test to detect superoxide anion may not be sufficient evidence as this agent may be reduced by alternative routes. 相似文献
58.
Induction of decision trees via evolutionary programming 总被引:1,自引:0,他引:1
Decision trees have been used extensively in cheminformatics for modeling various biochemical endpoints including receptor-ligand binding, ADME properties, environmental impact, and toxicity. The traditional approach to inducing decision trees based upon a given training set of data involves recursive partitioning which selects partitioning variables and their values in a greedy manner to optimize a given measure of purity. This methodology has numerous benefits including classifier interpretability and the capability of modeling nonlinear relationships. The greedy nature of induction, however, may fail to elucidate underlying relationships between the data and endpoints. Using evolutionary programming, decision trees are induced which are significantly more accurate than trees induced by recursive partitioning. Furthermore, when assessed on previously unseen data in a 10-fold cross-validated manner, evolutionary programming induced trees exhibit a significantly higher accuracy on previously unseen data. This methodology is compared to single-tree and multiple-tree recursive partitioning in two domains (aerobic biodegradability and hepatotoxicity) and shown to produce less complex classifiers with average increases in predictive accuracy of 5-10% over the traditional method. 相似文献
59.
Himpel Benjamin; Kirk Paul; Lesch Matthias 《Proceedings London Mathematical Society》2004,89(1):241-272
The existence and continuity for the Calderón projectorof the perturbed odd signature operator on a 3-manifold is established.As an application we give a new proof of a result of Taubesrelating the modulo 2 spectral flow of a family of operatorson a homology 3-sphere with the difference in local intersectionnumbers of the character varieties coming from a Heegard decomposition.2000 Mathematics Subject Classification 57M27 (primary), 58J32(secondary). 相似文献
60.
De Nicola A Liu Y Schanze KS Ziessel R 《Chemical communications (Cambridge, England)》2003,(2):288-289
A facile and original synthesis of four 2,2'-bipyridine (bipy) ligands grafted with thiophene subunits is described using phase transfer experimental conditions: related Ru(II) complexes exhibit well-defined redox and photophysical properties which were probed by cyclic voltammetry, UV-vis, steady-state emission and transient absorption spectroscopy. 相似文献