全文获取类型
收费全文 | 1933篇 |
免费 | 60篇 |
国内免费 | 7篇 |
专业分类
化学 | 1521篇 |
晶体学 | 17篇 |
力学 | 34篇 |
数学 | 66篇 |
物理学 | 362篇 |
出版年
2023年 | 5篇 |
2021年 | 24篇 |
2020年 | 25篇 |
2019年 | 28篇 |
2018年 | 19篇 |
2017年 | 17篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 33篇 |
2013年 | 76篇 |
2012年 | 100篇 |
2011年 | 112篇 |
2010年 | 59篇 |
2009年 | 61篇 |
2008年 | 102篇 |
2007年 | 99篇 |
2006年 | 116篇 |
2005年 | 113篇 |
2004年 | 86篇 |
2003年 | 89篇 |
2002年 | 89篇 |
2001年 | 48篇 |
2000年 | 38篇 |
1999年 | 27篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 22篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 33篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 27篇 |
1985年 | 31篇 |
1984年 | 36篇 |
1983年 | 18篇 |
1982年 | 33篇 |
1981年 | 25篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 17篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 10篇 |
排序方式: 共有2000条查询结果,搜索用时 31 毫秒
1.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献
2.
J. Fujimoto T. Ishikawa M. Jimbo T. Kaneko T. Kon Y. Kurihara M. Kuroda Y. Shimizu Y. Yasui 《Pramana》2007,69(5):943-946
We report the recent development on the SUSY calculations with the help of GRACE system. GRACE/SUSY/1LOOP is the computer
code which can generate Feynman diagrams in the MSSM automatically and compute one-loop amplitudes in the numerical way. We
present new results of various two-body decay widths and chargino pair production at ILC (international linear collider) at
one-loop level.
相似文献
3.
Hiroto Kudo Nobuhito Ito Keiji Nakajima Masami Ochiai Tadatomi Nishikubo 《Journal of polymer science. Part A, Polymer chemistry》2007,45(19):4421-4429
The polyaddition of fluorine‐containing bis(epoxide)s and fluorine‐containing triazine di(aryl ether)s were examined to give the corresponding fluorine‐containing poly(cyanurate)s. It was observed that the synthesized fluoropolymers had good thermal stabilities and good film‐forming properties. The glass transition temperatures (Tg's) and refractive‐indices (nD's) of synthesized polymers were determined by differential scanning calorimetry and ellipsometry, respectively, and it was found that the values of Tg's and nD's were supported by their fluorine containing ratios and skeletons. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4421–4429, 2007 相似文献
4.
Within the large literature on inter-organizational networks, there has been some discussion of linking-pin organizations and the role they play in integrating these networks. Based on this verbal specification of linking-pin organizations, we construct operational criteria and empirical methods for identifying these structurally important organizations in potentially large and complex inter-organizational networks. These methods are based on ideas drawn from blockmodeling, structural holes, centrality and centralization of networks, and identifying cut-points in networks. These methods are applied to a constructed example and then to real empirical inter-organizational networks. Implications and contrasts with other methods are discussed, together with some open problems. 相似文献
5.
6.
S Watanabe R R Anderson S Brorson G Dalickas J G Fujimoto T J Flotte 《Photochemistry and photobiology》1991,53(6):757-762
Threshold radiant exposures for grossly apparent immediate whitening and ultrastructural alterations of melanosomes in black guinea pig skin were determined for a series of red visible laser pulses ranging from 4 x 10(-4) to 6.5 x 10(-14) s. Threshold exposures for melanosomal injury were found to be independent of pulsewidth when the pulsewidths were below the estimated thermal relaxation time of melanosomes. Threshold radiant exposures for melanosomal injury were found to increase when the pulsewidths were approximately equal to or above the thermal relaxation time of melanosomes. At longer pulse durations, fracturing of melanosomes was not observed despite the longer exposures necessary for injury. Instead, perimelanosomal vacuoles were noted. These findings are consistent with the theory of selective photothermolysis and provide evidence for the thermal initiation of melanosomal disruption. 相似文献
7.
8.
Kenji Hara Keiji Iwahashi Satoru Takakusagi Kohei Uosaki Masaya Sawamura 《Surface science》2007,601(22):5127-5132
Functionalization of self-assembled monolayer (SAM) of alkanethiolate with metal containing unit is one of the versatile methods to obtain functional surfaces such as heterogeneous catalysts. However, organic molecules that strongly bind to transition metals at SAM terminal are limited. Recently N-heterocyclic carbenes (NHCs) such as cyclic diaminocarbenes have emerged as strongly σ-donating ligands forming a robust bond with broad spectrum of transition metals. In the present study, for the purpose of establishment of a new robust basement for heterogeneous metal catalysts, a SAM of the alkanethiolate terminated with NHC-rhodium(I) complex moiety was prepared by utilizing a newly designed disulfide molecule bearing NHC-metal complex terminals. X-ray photoelectron spectroscopy (XPS) analysis and angle resolved XPS measurement revealed successful formation of the Rh-complex-terminated SAM on a gold substrate. Infrared reflection absorption spectroscopy (IRRAS) analysis suggested that the linker methylene chains connecting the rhodium complex moiety and the gold surface are in a loosely packed structure. This unique chemical species, NHC, would be a promising candidate as a basement for the construction of functional surface. 相似文献
9.
13C NMR studies showed that the population of the norcaradiene form of the title systems containing p-CH3O, H, and p-CF3 on the 7-aryl group increases in this order. The result is consistent with the prediction from the π-acceptor strength of the aryl group estimated by INDO calculations. 相似文献
10.
We have proposed a mechanism of nonideality, i.e., the temperature dependence of the ideality factor, in nearly ideal Au/n-Si Schottky barriers. Because of the nature of metal-induced gap states, positively ionized defects close to the interface are considered to cause local lowering of the Schottky barrier height (SBH) due to downward bending of the energy band. These positively charged defects become neutralized in equilibrium with the Fermi level due to the band bending, when they are very close to the interface. However, because the SBH lowering disappears by the neutralization of donor, the energy level of donor with a usual energy level scheme rises above the Fermi level after the neutralization. This contradiction to the equilibrium neutralization is resolved by Si self-interstitial with a large negative-U property, which is generated by the fabrication process. The energy level of the donor estimated from the SBH lowering is in good agreement with that of theoretical calculation of Si self-interstitial. Thus, the defect is concluded to be the Si self-interstitial, which is distributed to more than 10 Å depth from the interface. 相似文献