全文获取类型
收费全文 | 1857篇 |
免费 | 232篇 |
国内免费 | 143篇 |
专业分类
化学 | 807篇 |
晶体学 | 21篇 |
力学 | 75篇 |
综合类 | 17篇 |
数学 | 144篇 |
物理学 | 1168篇 |
出版年
2023年 | 13篇 |
2022年 | 29篇 |
2021年 | 41篇 |
2020年 | 40篇 |
2019年 | 42篇 |
2018年 | 30篇 |
2017年 | 45篇 |
2016年 | 54篇 |
2015年 | 40篇 |
2014年 | 70篇 |
2013年 | 125篇 |
2012年 | 95篇 |
2011年 | 102篇 |
2010年 | 72篇 |
2009年 | 115篇 |
2008年 | 121篇 |
2007年 | 127篇 |
2006年 | 113篇 |
2005年 | 107篇 |
2004年 | 87篇 |
2003年 | 75篇 |
2002年 | 85篇 |
2001年 | 84篇 |
2000年 | 89篇 |
1999年 | 76篇 |
1998年 | 77篇 |
1997年 | 26篇 |
1996年 | 25篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 24篇 |
1992年 | 8篇 |
1991年 | 19篇 |
1990年 | 15篇 |
1989年 | 3篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有2232条查询结果,搜索用时 31 毫秒
991.
1 Introduction ThematchedspatialfilteringproposedbyVanderlugt[1] hasreceivedconsiderableattentionbecauseithasinherentadvantageofshiftinvariance ,butthistechniquesuffersfromsensitivitytorotationandscaledeformation .Theinvarianceisthekeytopatternrecogniti… 相似文献
992.
Yousuke Konno Atsushi Kameyama Tadatomi Nishikubo Takabumi Nagai 《Journal of polymer science. Part A, Polymer chemistry》2001,39(16):2683-2690
A donor–acceptor norbornadiene derivative, 5‐(4‐methoxyphenyl)‐1,4,6,7,7‐pentamethyl‐2,5‐norbornadiene‐2,3‐dicarboxylic acid diglycidyl ester (D–A NDGE), was synthesized by the reaction of the cesium salt of 5‐(4‐methoxyphenyl)‐1,4,6,7,7‐pentamethyl‐2,5‐norbornadiene‐2,3‐dicarboxylic acid with epibromohydrin in N‐methyl‐ pyrrolidone (NMP). The polyaddition reactions of D–A NDGE with certain dicarboxylic acids were carried out with tetrabutylammonium bromide as a catalyst in NMP, producing corresponding polyesters containing D–A norbornadiene (NBD) residues in the main chain in fair to good yields. The photoisomerization of the D–A NBD residues in the polyesters proceeded very smoothly, forming the corresponding quadricyclane groups. The photoreactivities of the D–A NBD residues in the polymer were 50 times higher than those of the NBD residues in the film state and 60 times higher than those in a tetrahydrofuran solution. The stored energy in the quadricyclane groups of the polymers was about 45–55 kJ/mol according to differential scanning calorimetry analysis of the irradiated polymer films. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2683–2690, 2001 相似文献
993.
994.
Wim Klopper Claire C. M. Samson Gyrgy Tarczay Attila G. Csszr 《Journal of computational chemistry》2001,22(13):1306-1314
The basis‐set convergence of singlet and triplet pair energies of coupled‐cluster theory including single and double excitations is accelerated by means of extrapolations based on the distinct convergence behaviors of these pairs. The new extrapolation procedure predicts a nonrelativistic Born–Oppenheimer inversion barrier of 1767±12 cm?1 for NH3. An effective one‐dimensional, vibrationally averaged barrier of 2021±20 cm?1 is obtained when relativistic effects (+20 cm?1), Born–Oppenheimer diagonal corrections (?10 cm?1), and zero‐point vibrations (+244 cm?1) are accounted for. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1306–1314, 2001 相似文献
995.
M. Weiszflog G. de Angelis A. Axelsson D. Bazzacco F. Becker M. De Poli J. Eberth C. Fahlander A. Gadea S. Lunardi D.R. Napoli J. Nyberg C. Rossi Alvarez B. Rubio D. Rudolph S. Skoda H.G. Thomas R. Wyss 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):25-38
High-spin states in the nuclei 63Ga and 65Ga were studied following the reaction 32S + 40Ca at a reaction energy of 125 MeV and using the GASP γ-ray spectrometer in combination with the ISIS charged-particle detector
system. In addition to low-lying negative-parity states with single-particle character, rotational-like cascades built on
the 9/2+ and 19/2- states have been observed in both nuclei. Sidebands with negative parity in 63Ga and positive parity in 65Ga could be established. The experimental results are compared with Total Routhian Surface calculations which describe the
nuclei as moderately deformed (β2≈ 0.25) and γ soft at low rotational frequencies. The highest experimentally observed positive-parity state in 65Ga (41/2+) is in good agreement with the calculated crossing of the collective band with a non-collective one terminating at this spin.
Received: 20 December 2000 / Accepted: 2 May 2001 相似文献
996.
J. Wrzesiński K.H. Maier R. Broda B. Fornal W. Królas T. Pawłat D. Bazzacco S. Lunardi C. Rossi Alvarez G. de Angelis A. Gadea J. Gerl M. Rejmund 《The European Physical Journal A - Hadrons and Nuclei》2001,10(3):259-265
High-spin states in 208Pb have been studied by γ-ray-spectroscopy methods in deep inelastic reactions induced by beams of 208Pb, 136Xe and 76Ge beams on a thick 208Pb target. The 11+
2 state and new γ-transitions between the one-particle one-hole states of highest spin have been found and electromagnetic
matrix elements verified. High-spin states of two-particle two-hole structure have been detected for the first time. The results
are compared to shell model calculations with realistic interactions in the complete Kuo-Herling space.
Received: 31 October 2000 / Accepted: 26 March 2001 相似文献
997.
S. Hofmann F.P. Heßberger D. Ackermann S. Antalic P. Cagarda S. Ćwiok B. Kindler J. Kojouharova B. Lommel R. Mann G. Münzenberg A.G. Popeko S. Saro H.J. Schött A.V. Yeremin 《The European Physical Journal A - Hadrons and Nuclei》2001,10(1):5-10
The even-even nucleus 270110 was synthesized using the reaction 64Ni + 207Pb. A total of eight α-decay chains was measured during an irradiation time of seven days. Decay data were obtained for the
ground-state and a high-spin K isomer. The new nuclei 266Hs and 262Sg were identified as daughter products after α-decay. Spontaneous fission of 262Sg terminates the decay chain. The measured data are in agreement with calculations using the macroscopic-microscopic model
and with self-consistent HFB calculations with Skyrme-Sly4 interaction.
Received: 27 November 2000 / Accepted: 16 January 2001 相似文献
998.
R. Parajuli S. Matt O. Echt A. Stamatovic P. Scheier T.D. Märk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):69-72
We have carried out measurements on metastable fragmentation of mass selected argon cluster ions which are produced by electron
impact ionization of a neutral argon cluster beam. From the shape of the fragment ion peaks (MIKE scan technique) one can
deduce information about the distribution of kinetic energy that is released in the decay reaction. In this study, for Ar
5
+ to Ar
15
+, it is Gaussian and thus we can calculate from the peak width the mean kinetic energy release 〈KER〉 of the corresponding
decay reactions. Using finite heat bath theory we calculate from these data the binding energies of the decaying cluster ions.
Received 20 November 2000 相似文献
999.
Wedad Hussein Christopher G. Walker Zenaida Peralta‐Inga Jane S. Murray 《International journal of quantum chemistry》2001,82(4):160-169
The electrostatic potentials and average local ionization energies computed on the molecular surfaces of four tetracyclines have been investigated with the objective of identifying common features as well as subtle differences that may be related to their biological activities. The four are the parent molecule tetracycline, chlortetracycline, oxytetracycline, and doxycyline. The calculations were carried out at the HF/STO‐3G*//STO‐3G* level. Our electrostatic potential results show that each molecule has a large negative region that extends along its lower portion, consistent with its ability to complex Ca2+ and Mg2+ ions. Although the surface electrostatic potentials of the four tetracyclines show many similarities, our statistical measure of local polarity allows us to label doxycycline as the one with the lowest degree of local polarity, consistent with its longer half‐life in vivo. The regions in the tetracyclines with the most reactive electrons are the amide nitrogen lone pairs and certain carbons of the outermost rings. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 160–169, 2001 相似文献
1000.
外调制光纤有线电视发射机中一般采用预失真补偿技术以提高其复合三阶差拍失真指标。分析了在此情形下入射偏振对发射机复合三阶差拍失真补偿特性的影响 ,分析计算显示 :入射光偏振态模式为TE模时系统复合三阶差拍失真补偿特性最佳。对入射偏振态偏离TE模的情形的理论分析与实验研究表明 :为保证发射机的复合三阶差拍失真性能 ,入射光偏离TE模的角度应小于 15° 相似文献