全文获取类型
收费全文 | 576篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 469篇 |
晶体学 | 8篇 |
力学 | 7篇 |
数学 | 25篇 |
物理学 | 91篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2016年 | 13篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 25篇 |
2012年 | 23篇 |
2011年 | 28篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 34篇 |
2007年 | 32篇 |
2006年 | 35篇 |
2005年 | 39篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 13篇 |
2001年 | 24篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 13篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有600条查询结果,搜索用时 15 毫秒
501.
We developed hollow fibers with polycarbonate (PC) capillaries for use as a supporting tube. The PC capillaries were prepared by using a glass-drawing technique. Hollow PC fibers are safer and more flexible than hollow glass fibers because no fragments are released when the fibers are broken in various applications. Inner coating layers of silver and cyclic olefin polymer (COP) enhanced the reflection rate at the Er:YAG laser light wavelength. Using these fibers, we attained low loss for Er:YAG laser light transmission. By adjusting the drawing temperature in the fabrication of the PC capillaries, we created a smooth inner surface and uniform PC capillaries. We also demonstrated low-loss properties for visible pilot beams. 相似文献
502.
Doi T Fukuyama T Minamino S Husson G Ryu I 《Chemical communications (Cambridge, England)》2006,(17):1875-1877
When primary unsaturated alcohols were treated with a catalytic amount of RuHCl(CO)(PPh3)3 in benzene under reflux, dimerization reactions took place to give alpha-hydroxymethyl ketones as major product. 相似文献
503.
The Pd(0)-mediated rapid coupling of methyl iodide with an excess of alkenyltributylstannane was examined with the aim of incorporating a short-lived 11C-labeled methyl group into a biologically significant organic compound with a 1-methylalkene unit for the synthesis of a PET tracer. Four sets of reaction conditions (A-D) were used, all performed in DMF at 60 degrees C for 5 min. Condition B, using CH3I/stannane/Pd2(dba)3/P(o-tolyl)3/CuCl/K2CO3 (1:40:0.5:4-6:2:5), works well in almost all cases. Condition D, using CH3I/stannane/Pd2(dba)3/P(o-tolyl)3/CuX (X = Br, Cl, or I)/CsF (1:40:0.5-5:2-20:2-20:5-50), shows the best results with regard to general applicability to tin substrates, affording the corresponding methylated product in >90% yield based on consumption of methyl iodide. P(t-Bu)2Me was less effective than P(o-tolyl)3, particularly for alpha,beta-unsaturated carbonyl substrates. No regio- or stereoisomerization occurred under these reaction conditions. The efficiency of the protocol was demonstrated by synthesis of an 11C-methylated compound. 相似文献
504.
We develop a 3-dimensional mechanical model which describes cavity expansions in a viscoelastic solid medium during the debonding
phase of the probe-tack test. The stress-strain curves are in good agreement with experiments for the typical pressure-sensitive
adhesives. We also show that the separation speed dependence can be explained by viscous dissipations due to large strain
rates around the cavities. 相似文献
505.
Takahiro Shimada Daisuke Shirasaki Yusuke Doi Takayuki Kitamura 《Physica D: Nonlinear Phenomena》2010,239(8):407-413
Excitation of intrinsic localized modes (ILMs) in carbon nanotubes (CNTs) with different chiral structures was investigated by molecular dynamics simulations. For CNTs with a chiral angle less than or equal to 30°, energy concentration that continued for more than 200 fs was found in a localized area, where a pair of neighboring atoms strongly oscillated with a higher vibrational frequency than the upper bound of phonon bands. This evidently indicates excitation of the ILM. On the other hand, the ILM was not excited in CNTs with a chiral angle greater than or equal to 41°. Analyzing the nonlinearity of the interaction between excited atoms in the ILM vibration mode, we elucidated that nonlinearity predominates the selective ILM excitation. Furthermore, stronger nonlinearity excites ILMs with both higher frequency and longer lifetime. 相似文献
506.
DNA oligomers possessing a 2-nitrobenzyl (NB) protected thiol group have been prepared. The photo-remove of the NB to generate a free thiol group in DNA has been analyzed by using reverse-phase HPLC and denaturing gel electrophoresis. The photo-triggered generation of the thiol function in DNA was applicable in the light-initiated ligation of thiol-modified DNA oligomers and Au–DNA conjugation. 相似文献
507.
A Muppidi K Doi S Edwardraja EJ Drake AM Gulick HG Wang Q Lin 《Journal of the American Chemical Society》2012,134(36):14734-14737
Direct chemical modifications provide a simple and effective means to "translate" bioactive helical peptides into potential therapeutics targeting intracellular protein-protein interactions. We previously showed that distance-matching bisaryl cross-linkers can reinforce peptide helices containing two cysteines at the i and i+7 positions and confer cell permeability to the cross-linked peptides. Here we report the first crystal structure of a biphenyl-cross-linked Noxa peptide in complex with its target Mcl-1 at 2.0 ? resolution. Guided by this structure, we remodeled the surface of this cross-linked peptide through side-chain substitution and N-methylation and obtained a pair of cross-linked peptides with substantially increased helicity, cell permeability, proteolytic stability, and cell-killing activity in Mcl-1-overexpressing U937 cells. 相似文献
508.
Observations of clean Si(111) and gold-deposited Si(111) surfaces have been performed using micro-probe reflection high-energy electron diffraction. It was found that many atomic steps on a Si(111) surface run in nearly the same direction, about 9° off the [1̄1̄2] direction. When gold was deposited on this surface at a substrate temperature of about 800°C, 5 × 1, diffuse √3 × √3R30°, sharp √3 × √3 R30° structures and Au clusters appeared on the surface with continuation of the deposition. During the deposition process, it was found that one kind of Si(111) 5 × 1 Au domain grew selectively along these atomic steps and nearly covered the entire surface. A phenomenon of gold clusters moving during the deposition was also observed. These clusters all moved in nearly the same direction so as to climb the atomic steps. 相似文献
509.
The reaction of alcohols with ethyl nitroacetate, diethyl azodicarboxylate, and triphenylphosphine gave the corresponding aldehydes or ketones in 52–85% yields. 相似文献
510.
Wave propagation in a step-index optical fibre with a curved section is treated theoretically. Mode conversion and radiation take place. The mode coupling coefficients which depend on the polarization of the incident mode are calculated. Radiation losses at the transition between a straight and a curved fibre section and total losses including the continuous radiation loss due to a uniform bend are evaluated. Comparisons are also made between singly and doubly clad fibres. It is shown that the doubly clad fibre can tolerate a sharper bend.Requests for reprints should be sent to Professor G. L. Yip. 相似文献