全文获取类型
收费全文 | 2207篇 |
免费 | 60篇 |
国内免费 | 8篇 |
专业分类
化学 | 1595篇 |
晶体学 | 20篇 |
力学 | 51篇 |
数学 | 268篇 |
物理学 | 341篇 |
出版年
2023年 | 9篇 |
2021年 | 27篇 |
2020年 | 36篇 |
2019年 | 27篇 |
2018年 | 28篇 |
2017年 | 15篇 |
2016年 | 38篇 |
2015年 | 28篇 |
2014年 | 27篇 |
2013年 | 119篇 |
2012年 | 96篇 |
2011年 | 123篇 |
2010年 | 82篇 |
2009年 | 49篇 |
2008年 | 103篇 |
2007年 | 119篇 |
2006年 | 131篇 |
2005年 | 99篇 |
2004年 | 99篇 |
2003年 | 65篇 |
2002年 | 84篇 |
2001年 | 45篇 |
2000年 | 50篇 |
1999年 | 32篇 |
1998年 | 31篇 |
1997年 | 32篇 |
1996年 | 29篇 |
1995年 | 39篇 |
1994年 | 29篇 |
1993年 | 25篇 |
1992年 | 16篇 |
1991年 | 32篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 30篇 |
1981年 | 16篇 |
1980年 | 31篇 |
1979年 | 31篇 |
1978年 | 21篇 |
1977年 | 29篇 |
1976年 | 14篇 |
1975年 | 22篇 |
1974年 | 20篇 |
1973年 | 17篇 |
排序方式: 共有2275条查询结果,搜索用时 640 毫秒
91.
A reliable computational method for the prediction of organoselenium geometries and bond dissociation energies (BDEs) has been determined on the basis of the performance of density functional theory (DFT: B3LYP and B3PW91) and ab initio molecular orbital procedures (Hartree-Fock (HF)) in conjunction with various Pople basis sets including (but not limited to) the 6-31G(d), 6-31G(d,p), 6-311G(d), 6-311G(d,p), 6-311G(2df,p), and 6-311G(3df,3pd) sets. Predicted geometries and BDEs are compared with available experimental data and quadratic configuration interaction including single and double substitutions (QCISD) results. The B3PW91/6-311G(2df,p) level of theory is recommended for the prediction of the geometries and energetics of organoselenium compounds. 相似文献
92.
Lin JF Militzer B Struzhkin VV Gregoryanz E Hemley RJ Mao HK 《The Journal of chemical physics》2004,121(17):8423-8427
The melting curve of H(2)O has been measured by in situ Raman spectroscopy in an externally heated diamond anvil cell up to 22 GPa and 900 K. The Raman-active OH-stretching bands and the translational modes of H(2)O as well as optical observations are used to directly and reliably detect melting in ice VII. The observed melting temperatures are higher than previously reported x-ray measurements and significantly lower than recent laser-heating determinations. However, our results are in accord with earlier optical determinations. The frequencies and intensities of the OH-stretching peaks change significantly across the melting line while the translational mode disappears altogether in the liquid phase. The observed OH-stretching bands of liquid water at high pressure are very similar to those obtained in shock-wave Raman measurements. 相似文献
93.
Singh SB Zink DL Heimbach B Genilloud O Teran A Silverman KC Lingham RB Felock P Hazuda DJ 《Organic letters》2002,4(7):1123-1126
[structure: see text] HIV-1 integrase is a critical enzyme for viral replication, and its inhibition is an emerging target for potential antiviral chemotherapy. We have discovered a novel inhibitor, integramycin, from screening of fermentation extracts using an in vitro assay. Integramycin possesses a hexacyclic ring system and exhibited an IC50 value of 4 microM against HIV-1 integrase (strand transfer). The isolation, structure elucidation, stereochemistry, conformation, and biological activity has been described. 相似文献
94.
Lijun Zhang Xun Hu Chengzhong Yu Russell Crawford 《International journal of environmental analytical chemistry》2013,93(12):1274-1285
A new solid phase extractant, sinapinaldehyde (SA) modified SBA-15 mesoporous silica, was developed for selective extraction and preconcentration of trace Pb(II) from aqueous solutions. The successful immobilization of SA on SBA-15 and the strong interaction between SA-SBA-15 and Pb(II) were characterized and confirmed by FTIR spectroscopy and scanning electron microscopy. Parameters such as solution pH, shaking time, eluent condition and sample volume were optimized so that the maximum removal of Pb(II) from solution could be achieved. At pH 4.0, the maximum adsorption capacity of the sorbent for Pb(II) was found to be 33.6?mg?g?1 and the adsorbed Pb(II) could be completely eluted using a mixed solution of 2?M HCl and 5% CS(NH2)2. Some common metal ions such as K(I), Na(I), Mg(II), Ca(II), Cr(III), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) did not interfere with the adsorption of trace Pb(II). The detection limit of the present method was found to be 1.3?ng?mL?1 and the relative standard deviation was less than 2.0% (n?=?8). These results suggested that this new sorbent is very efficient and selective for the removal of trace Pb(II) in water samples. 相似文献
95.
96.
97.
Russell Merris 《Linear and Multilinear Algebra》2013,61(2-3):287-289
Matrix Analysis, by Rajendra Bhatia, Graduate Texts in Mathematics, 169, Springer, New York, 1997, 347 + xi pages. ISBN 0-387-94846-5 相似文献
98.
99.
Johannes Barth Michael Buback Christopher Barner‐Kowollik Thomas Junkers Gregory T. Russell 《Journal of polymer science. Part A, Polymer chemistry》2012,50(22):4740-4748
The termination of model mid‐chain radicals (MCRs), which mimic radicals that occur in acrylate polymerization over a broad range of reaction conditions, has been studied by single‐pulse pulsed laser polymerization (SP‐PLP) in conjunction with electron paramagnetic resonance spectroscopy. The model radicals were generated by initiator‐fragment addition to acrylic macromonomers that were preformed prior to the kinetic experiments, thus enabling separation of termination from the propagation reaction, for these model radicals propagate sparingly, if at all, on the timescale of SP‐PLP experiments. Termination rate coefficients of the MCRs were determined in the temperature range of 0–60°C in acetonitrile and butyl propionate solution as well as in bulk macromonomer over the range of 0–100 °C. Termination rate coefficients slightly below those of the corresponding secondary radicals were deduced, demonstrating the relatively high termination activity of this species, even when undergoing MCR–MCR termination. For chain length of 10, a reduction by a factor of 6 is observed. Unusually high activation energies were found for the termination rate coefficient in these systems, with 35 kJ mol?1 being determined for bulk macromonomer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
100.
Abstract The results of an evaluation of polymers as cryogenic adhesives are presented. It was observed that polyether-based polyurethanes provided the most attractive capability as adhesives for use at liquid hydrogen temperatures. 相似文献