全文获取类型
收费全文 | 45071篇 |
免费 | 8343篇 |
国内免费 | 1430篇 |
专业分类
化学 | 45618篇 |
晶体学 | 397篇 |
力学 | 771篇 |
数学 | 3548篇 |
物理学 | 4510篇 |
出版年
2022年 | 115篇 |
2021年 | 257篇 |
2020年 | 1341篇 |
2019年 | 2700篇 |
2018年 | 1130篇 |
2017年 | 742篇 |
2016年 | 3533篇 |
2015年 | 3642篇 |
2014年 | 3563篇 |
2013年 | 4565篇 |
2012年 | 3208篇 |
2011年 | 2482篇 |
2010年 | 3094篇 |
2009年 | 3021篇 |
2008年 | 2648篇 |
2007年 | 2002篇 |
2006年 | 1697篇 |
2005年 | 1848篇 |
2004年 | 1678篇 |
2003年 | 1504篇 |
2002年 | 2201篇 |
2001年 | 1513篇 |
2000年 | 1425篇 |
1999年 | 478篇 |
1998年 | 148篇 |
1997年 | 154篇 |
1996年 | 163篇 |
1995年 | 121篇 |
1994年 | 127篇 |
1993年 | 153篇 |
1992年 | 154篇 |
1991年 | 162篇 |
1990年 | 118篇 |
1989年 | 121篇 |
1988年 | 133篇 |
1987年 | 183篇 |
1986年 | 150篇 |
1985年 | 199篇 |
1984年 | 185篇 |
1983年 | 146篇 |
1982年 | 170篇 |
1981年 | 178篇 |
1980年 | 176篇 |
1979年 | 173篇 |
1978年 | 164篇 |
1977年 | 162篇 |
1976年 | 141篇 |
1975年 | 158篇 |
1974年 | 126篇 |
1973年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Pedro lvarez‐Boo Jos Sergio Casas Alfonso Castieiras María Delfina Couce Eduardo Freijanes Eva Novoa Jos Sordo 《应用有机金属化学》2003,17(9):725-729
Reaction of dichloro‐ and dibromodimethyltin(IV) with 2‐(pyrazol‐1‐ylmethyl)pyridine (PMP) afforded [SnMe2Cl2(PMP)] and [SnMe2Br2(PMP)] respectively. The new complexes were characterized by elemental analysis and mass spectrometry and by IR, Raman and NMR (1H, 13C) spectroscopies. Structural studies by X‐ray diffraction techniques show that the compounds consist of discrete units with the tin atom octahedrally coordinated to the carbon atoms of the two methyl groups in a trans disposition (Sn? C = 2.097(5), 2.120(5) Å and 2.110(6), 2.121(6) Å in the chloro and in the bromo compounds respectively), two cis halogen atoms (Sn? Cl = 2.4908(16), 2.5447(17) Å; Sn? Br = 2.6875(11), 2.7464(9) Å) and the two donor atoms of the ligand (Sn? N = 2.407(4), 2.471(4) Å and 2.360(5), 2.455(5) Å). In both cases, the Sn? N(pyridine) bond length is markedly longer than the Sn? N(pyrazole) distance. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
102.
We give a number of characterizations of bodies of constant width in arbitrary dimension. As an application, we describe a way to construct a body of constant width in dimension n, one of its (n – 1)‐dimensional projection being given. We give a number of examples, like a four‐dimensional body of constant width whose 3D‐projection is the classical Meissner's body. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
103.
In this work, the melting behaviors of nonisothermally and isothermally melt‐crystallized poly(L ‐lactic acid) (PLLA) from the melt were investigated with differential scanning calorimetry (DSC) and temperature‐modulated differential scanning calorimetry (TMDSC). The isothermal melt crystallizations of PLLA at a temperature in the range of 100–110 °C for 120 min or at 110 °C for a time in the range of 10–180 min appeared to exhibit double melting peaks in the DSC heating curves of 10 °C/min. TMDSC analysis revealed that the melting–recrystallization mechanism dominated the formation of the double melting peaks in PLLA samples following melt crystallizations at 110 °C for a shorter time (≤30 min) or at a lower temperature (100, 103, or 105 °C) for 120 min, whereas the double lamellar thickness model dominated the formation of the double melting peaks in those PLLA samples crystallized at a higher temperature (108 or 110 °C) for 120 min or at 110 °C for a longer time (≥45 min). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 466–474, 2007 相似文献
104.
Zhen‐Feng Chen Hong‐Li Zhou Hong Liang Yan Li Ren‐Gen Xiong Xiao‐Zeng You 《应用有机金属化学》2003,17(11):883-884
The centrosymmetric binuclear structure of [Pb2(H‐Norf)2(ONO2)4]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
105.
106.
Paul Van Der Meeren Jan Vanderdeelen Leon Baert 《Particle & Particle Systems Characterization》1994,11(4):320-326
Using a monodisperse PMMA dispersion, it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influcence of reflection on DLS measurements was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from the basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the static and dynamic light scattering technique. 相似文献
107.
Van Kolpin 《International Journal of Game Theory》1993,22(1):43-50
The traditional design of cooperative games implicitly assumes that preferences are continuous. However, if agents implement tie breaking procedures, preferences are effectively lexicographic and thus discontinuous. This rouses concern over whether classic core nonemptiness theorems apply in such settings. We show that balanced NTU games may have empty cores when agents have discontinuous preferences. Moreover, exchange economies may lack coalitionally rational trades when consumers implement tie breaking rules, even if these rules are themselves continuous and convex as are all first order preferences. Results are more positive when “utility” is transferable. We prove that balancedness is necessary and sufficient to ensure a nonempty core in lexicographic TU games. 相似文献
108.
109.
110.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献