全文获取类型
收费全文 | 1857篇 |
免费 | 111篇 |
国内免费 | 6篇 |
专业分类
化学 | 1496篇 |
晶体学 | 15篇 |
力学 | 23篇 |
数学 | 86篇 |
物理学 | 354篇 |
出版年
2023年 | 9篇 |
2022年 | 22篇 |
2021年 | 57篇 |
2020年 | 47篇 |
2019年 | 52篇 |
2018年 | 24篇 |
2017年 | 29篇 |
2016年 | 70篇 |
2015年 | 68篇 |
2014年 | 74篇 |
2013年 | 123篇 |
2012年 | 166篇 |
2011年 | 181篇 |
2010年 | 109篇 |
2009年 | 93篇 |
2008年 | 130篇 |
2007年 | 104篇 |
2006年 | 93篇 |
2005年 | 93篇 |
2004年 | 88篇 |
2003年 | 59篇 |
2002年 | 69篇 |
2001年 | 37篇 |
2000年 | 27篇 |
1999年 | 30篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1974条查询结果,搜索用时 109 毫秒
131.
We have found that it is possible to preserve the temporal waveform of the reflected wave generated from stimulated Brillouin scattering (SBS) by using a prepulse technique. The waveform of the SBS wave usually shows a steep rising edge in the ordinary SBS process. It has been found that the waveform of the reflected wave depends on both the prepulse energy and the time delay between the main pulse and the prepulses. A prepulse energy of 5 mJ and a time delay of 5 ns have been measured to be the optimum values under the experimental conditions. This prepulse method is useful in developing a multistage system employing several SBS cells in series for high-power laser applications. 相似文献
132.
133.
134.
135.
Kim IW Morse DE Evans JS 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11664-11673
The AP7 protein is one of several mollusk shell proteins which are responsible for aragonite polymorph formation and stabilization within the nacre layer of the Pacific red abalone, H. rufescens. Previously, we demonstrated that the 30-AA N-terminal domain of AP7, denoted as AP7-1, exists as an unfolded sequence and possesses the capability of inhibiting calcium carbonate crystal growth in vitro via growth step frustration or interruption. However, very little is known with regard to the interactive capabilities of this sequence with Ca(II) and with calcium carbonates. Using multidisciplinary techniques, we determine that the AP7-1 polypeptide interacts with Ca(II) ions at the -DD- sequence clusters, yet retains its unfolded, conformationally labile structure in the presence of Ca(II) ions. Further, NMR experiments reveal that the extended structured sequence blocks, -GNGM-, -SVRTQG-, and -ISYL, exhibit motional, chemical exchange, and/or backbone geometry perturbations in response to Ca(II) interactions with AP7-1. Solid-state NMR magic angle spinning studies verify that during the course of in vitro calcium carbonate crystal growth, AP7-1 becomes bound to calcite fragments and cannot be entirely displaced from the mineral fragments using competitive Ca(II) washing. Finally, using a scrambled sequence version of the AP7-1 polypeptide, we observe that sequence scrambling does not adversely affect the crystal growth inhibitory activity of AP7-1, suggesting that the amino acid composition of AP7-1 may be more critical to growth step inhibition than the linear ordering of amino acids. 相似文献
136.
Choi WJ Moon HR Kim HO Yoo BN Lee JA Shin DH Jeong LS 《The Journal of organic chemistry》2004,69(7):2634-2636
The preparative and stereoselective synthesis (45-50% overall yields) of the target compound 17 has been accomplished from D-ribose. The bulky protecting groups such as TBDPS and Trityl enforced the facial selectivity during Grignard reaction to give the tertiary beta-allylic alcohol 16 as the sole product, which was oxidatively rearranged to the key molecule 17 in excellent yield. 相似文献
137.
A high-density array of vertically aligned ZnGa(2)O(4) nanowires has been synthesized on Si substrates via CVD of ZnO-Ga at 1000 degrees C consisting of a single-crystalline cubic spinel structure grown in a [111] direction and exhibiting strong photoluminescence and cathodoluminescence in the blue wavelength region. 相似文献
138.
Sim TB Kang SH Lee KS Lee WK Yun H Dong Y Ha HJ 《The Journal of organic chemistry》2003,68(1):104-108
5-Funtionalized enantiomerically pure oxazolidin-2-ones were prepared in one pot from commercially available chiral aziridines bearing an electron-withdrawing group at C-2 with retention of the configuration in high yields by regioselective aziridine ring-opening followed by intramolecular cyclization. 相似文献
139.
Song HY Joo JM Kang JW Kim DS Jung CK Kwak HS Park JH Lee E Hong CY Jeong S Jeon K Park JH 《The Journal of organic chemistry》2003,68(21):8080-8087
The proposed structure of lasonolide A was synthesized employing radical cyclization reactions of beta-alkoxyacrylates for preparation of the tetrahydropyranyl units A and B, but the spectroscopic data did not match those of the natural product. Both enantiomers of a revised structure featuring 17E,25Z double bonds were synthesized, and the (-)-isomer was found to be the biologically active enantiomer. 相似文献
140.
Lee CH Na HK Yoon DW Won DH Cho WS Lynch VM Shevchuk SV Sessler JL 《Journal of the American Chemical Society》2003,125(24):7301-7306
Three calix[4]pyrroles bearing m-orcinol-derived diether straps of different lengths on one side of the tetrapyrrolic core have been synthesized and characterized. Structural information for an analogous diester bridged strapped system reported previously (Yoon, D. W.; Hwang, H.; Lee, C. H. Angew. Chem., Int. Ed. Engl. 2002, 41, 1757-1759) is also provided as are bromide and chloride anion affinities for all four systems determined by Isothermal Titration Calorimetry (ITC) in acetonitrile. Although both sets of the strapped calix[4]pyrroles displayed enhanced affinities for chloride and bromide anion, differences were seen among the various receptors that support the conclusion that the anion binding ability of calixpyrrole-type systems can be effectively tuned by modifying the length and nature of the bridging straps. In the specific case of the diether systems, the largest chloride affinity was seen with the shortest strap, whereas the largest affinity for bromide anion was recorded in the case of the longest strap. On the basis of these findings, as well as supporting (1)H NMR spectroscopic studies, it is postulated that not only cavity size per se, but also the ability of the aryl portion of the strap to serve as a CH hydrogen bond donor site are important in regulating the observed anion affinities. 相似文献