全文获取类型
收费全文 | 2429篇 |
免费 | 106篇 |
国内免费 | 9篇 |
专业分类
化学 | 1748篇 |
晶体学 | 11篇 |
力学 | 35篇 |
数学 | 296篇 |
物理学 | 454篇 |
出版年
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 26篇 |
2020年 | 40篇 |
2019年 | 53篇 |
2018年 | 26篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 71篇 |
2014年 | 83篇 |
2013年 | 113篇 |
2012年 | 181篇 |
2011年 | 214篇 |
2010年 | 90篇 |
2009年 | 62篇 |
2008年 | 154篇 |
2007年 | 151篇 |
2006年 | 152篇 |
2005年 | 153篇 |
2004年 | 100篇 |
2003年 | 104篇 |
2002年 | 59篇 |
2001年 | 44篇 |
2000年 | 36篇 |
1999年 | 35篇 |
1998年 | 25篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 26篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 27篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 23篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 20篇 |
1973年 | 29篇 |
1969年 | 9篇 |
排序方式: 共有2544条查询结果,搜索用时 15 毫秒
161.
Jayaprakash KN Gillepsie AM Gunnoe TB White DP 《Chemical communications (Cambridge, England)》2002,(4):372-373
Deprotonation of [TpRu(CO)(PPh3)(NHPh)][OTf]2 yields the thermally unstable d4 imido complex [TpRu-(CO)(PPh3)(NPh)][OTf]; a computational study of the bonding of the imido complex provides a foundation for discussion of its instability in terms of pi-conflict. 相似文献
162.
[formula: see text] Apoptolidin (1) is a novel oncolytic lead that induces apoptosis in transformed cell lines with exceptional selectivity. We report the isolation and characterization of a ring-expanded macrolide isomer of apoptolidin: isoapoptolidin (2). The solution conformation of isoapoptolidin is described. The rate of isomerization was measured under biologically relevant conditions and found to approach equilibrium within the time frame of most cell-based assays. Isoapoptolidin's ability to inhibit mitochondrial F0F1-ATPase is over 10-fold less than that of apoptolidin. 相似文献
163.
In this paper we present an algorithm for recursively generating orthogonal bivariate polynomials on a discrete set S 2. For this purpose we employ commuting pairs of real symmetric matrices H, K
n×n
to obtain, in a certain sense, a two dimensional Hermitian Lanczos method. The resulting algorithm relies on a recurrence having a slowly growing length. Practical implementation issues an applications are considered. The method can be generalized to compute orthogonal polynomials depending on an arbitrary number of variables. 相似文献
164.
The dendrobatid alkaloid (-)-251F was synthesized. The key steps of the synthesis were (1) an asymmetric Diels-Alder reaction to establish four of the necessary stereocenters in the target, (2) a ring-opening/ring-closing metathesis reaction to establish a key [3.3.0] bicyclic intermediate, and (3) an intramolecular Schmidt reaction. 相似文献
165.
Bearden IG Beavis D Besliu C Blyakhman Y Budick B Bøggild H Chasman C Christensen CH Christiansen P Cibor J Debbe R Enger E Gaardhøje JJ Hagel K Hansen O Holm A Holme AK Ito H Jakobsen E Jipa A Jørdre JI Jundt F Jørgensen CE Karabowicz R Keutgen T Kim EJ Kozik T Larsen TM Lee JH Lee YK Løvhøiden G Majka Z Makeev A McBreen B Mikelsen M Murray M Natowitz J Nielsen BS Norris J Olchanski K Olness J Ouerdane D Płaneta R Rami F Ristea C Röhrich D Samset BH Sandberg D Sanders SJ Sheetz RA Staszel P 《Physical review letters》2002,88(20):202301
We present charged-particle multiplicities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at square root[s(NN)] = 200 GeV. For the 5% most central events we obtain dN(ch)/deta/(eta = 0) = 625+/-55 and N(ch)/(-4.7< or =eta < or =4.7) = 4630 +/- 370, i.e., 14% and 21% increases, respectively, relative to square root[s(NN)] = 130 GeV collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around midrapidity. These results constrain current models of particle production at the highest RHIC energy. 相似文献
166.
We employ density functional and quantum Monte Carlo calculations to show that significant changes occur in the gap of fully hydrogenated nanoclusters when the surface contains passivants other than hydrogen, in particular atomic oxygen. In the case of oxygen, the gap reduction computed as a function of the nanocluster size provides a consistent interpretation of several recent experiments. Furthermore, we predict that other double bonded groups also significantly affect the optical gap, while single bonded groups have a minimal influence. 相似文献
167.
We present a model of leptogenesis that preserves lepton number. The model maintains the important feature of more traditional leptogenesis scenarios: The decaying particles that provide the CP violation necessary for baryogenesis also provide the explanation for the smallness of the neutrino Yukawa couplings. This model clearly demonstrates that, contrary to conventional wisdom, neutrinos need not be Majorana in nature in order to help explain the baryon asymmetry of the universe. 相似文献
168.
Jean-Jacques Aaron Zouhair Mechbal Alain Adenier Cyril Parkanyi Vaclav Kozmik Jiri Svoboda 《Journal of fluorescence》2002,12(2):231-239
The structural and solvent effects on the electronic absorption and fluorescence spectra, and fluorescence quantum yields, of four new fused benzothiophene derivatives, including benzothieno[3,2b]-thiophene (BTT), benzothieno[3,2-b]benzothiophene (BTBT), 6-methoxy[1]benzothieno[3,2b]-thiophene (MeOBTT), and benzothieno[3,2-b]indole (BTI) were investigated at 295 K. The luminescence properties of the corresponding conductive oligomers, poly(BTT) and poly (MeOBTT), electrosynthesized in acetonitrile, were also studied. Satisfactory McRae, Suppan, and Kawski-Chamma-Viallet solvatochromic correlations were established for the four monomers in most solvents. A weak negative solvatochromic behavior was found for these compounds, indicating that their dipole moments are slightly lower in the excited singlet state than in the ground state. Kamlet-Abboud-Taft multiparametric correlations were also obtained for absorption and fluorescence wave numbers and quantum yields, demonstrating the existence of specific solute-solvent interactions. In the case of the oligomers, important red-shifts of the fluorescence emission maxima ( 90–110 nm) relative to the corresponding monomers were observed, which shows the extent of conjugated segments in the oligomer chains. 相似文献
169.
Jack B. Brown Udayan B. Darji Eric P. Larsen 《Proceedings of the American Mathematical Society》1999,127(1):173-182
We investigate the relationships between the notions of a continuous function being monotone on no interval, monotone at no point, of monotonic type on no interval, and of monotonic type at no point. In particular, we characterize the set of all points at which a function that has one of the weaker properties fails to have one of the stronger properties. A theorem of Garg about level sets of continuous, nowhere monotone functions is strengthened by placing control on the location in the domain where the level sets are large. It is shown that every continuous function that is of monotonic type on no interval has large intersection with every function in some second category set in each of the spaces , and .
170.
Yao-Yi Cheng Peggy Cebe Malcolm Capel Heidi Schreuder-Gibson Aaron Bluhm Walter Yeomans 《Journal of Polymer Science.Polymer Physics》1995,33(17):2331-2341
Crystallization and melting behavior are studied by small-angle X-ray scattering (SAXS) for a series of recently synthesized monotropic liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene flexible spacer. The one-dimensional electron density correlation function is used to obtain long period, crystal thickness, and linear crystallinity from the Lorentz-corrected SAXS intensity. Changes in these parameters during nonisothermal crystallization and melting are explained by a model of dual crystal populations. The primary crystals form first using the liquid crystalline phase as crystal nuclei, while smaller and less perfect crystals form later from the isotropic phase at low temperature. The results of the real-time SAXS study of isothermal crystallization also support the view that the nematic phase serves as crystal nuclei for fast crystallization. An odd-even effect in crystal thickness and linear crystallinity is observed in all the SAXS experiments mentioned above. The results of this study and our complementary wide-angle X-ray scattering (WAXS) investigation show clearly that the difference in the position of the neighboring carbonate dipoles on a chain affects structural organization both at the unit cell level and at the level of the crystal in these monotropic LCPs. © 1995 John Wiley & Sons, Inc. 相似文献