全文获取类型
收费全文 | 744934篇 |
免费 | 23824篇 |
国内免费 | 11970篇 |
专业分类
化学 | 400374篇 |
晶体学 | 10697篇 |
力学 | 37215篇 |
综合类 | 552篇 |
数学 | 106173篇 |
物理学 | 225717篇 |
出版年
2022年 | 7104篇 |
2021年 | 8685篇 |
2020年 | 9479篇 |
2019年 | 9858篇 |
2018年 | 19389篇 |
2017年 | 18988篇 |
2016年 | 21320篇 |
2015年 | 12542篇 |
2014年 | 17112篇 |
2013年 | 34622篇 |
2012年 | 32225篇 |
2011年 | 42715篇 |
2010年 | 28236篇 |
2009年 | 28179篇 |
2008年 | 34209篇 |
2007年 | 35263篇 |
2006年 | 26034篇 |
2005年 | 23981篇 |
2004年 | 21594篇 |
2003年 | 19455篇 |
2002年 | 18119篇 |
2001年 | 19098篇 |
2000年 | 14878篇 |
1999年 | 12324篇 |
1998年 | 10333篇 |
1997年 | 9944篇 |
1996年 | 9911篇 |
1995年 | 8715篇 |
1994年 | 8522篇 |
1993年 | 7902篇 |
1992年 | 8839篇 |
1991年 | 8799篇 |
1990年 | 8267篇 |
1989年 | 7904篇 |
1988年 | 7908篇 |
1987年 | 7669篇 |
1986年 | 7279篇 |
1985年 | 9316篇 |
1984年 | 9378篇 |
1983年 | 7457篇 |
1982年 | 7596篇 |
1981年 | 7582篇 |
1980年 | 6980篇 |
1979年 | 7582篇 |
1978年 | 7735篇 |
1977年 | 7693篇 |
1976年 | 7497篇 |
1975年 | 6885篇 |
1974年 | 6839篇 |
1973年 | 6808篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
D. Amutha Rani Y. Yamamoto S. Mohri M. Sivakumar Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2003,41(3):269-273
In this study, a novel stepwise extraction method has been examined. The guest molecules housed between the helices of the clathrate δ form of syndiotactic polystyrene can be removed completely with this method. A systematic study of the preparation of a solvent‐free mesophase (emptied clathrate) membrane, its helical and residual solvent contents, and its structural transformations has been performed. In this first attempt, an enhancement in the TTGG helical content has been observed in the extracted membrane, and a conceptual mechanism is proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 269–273, 2003 相似文献
42.
43.
In previous papers by the present author, a machinery for calculating automorphisms, constructing invariants, and classifying real submanifolds of a complex manifold was developed. The main step in this machinery is the construction of a “nice” model surface. The nice model surface can be treated as an analog of the osculating paraboloid in classical differential geometry. Model surfaces suggested earlier possess a complete list of the desired properties only if some upper estimate for the codimension of the submanifold is satisfied. If this estimate fails, then the surfaces lose the universality property (that is, the ability to touch any germ in an appropriate way), which restricts their applicability. In the present paper, we get rid of this restriction: for an arbitrary type (n,K) (where n is the dimension of the complex tangent plane, and K is the real codimension), we construct a nice model surface. In particular, we solve the problem of constructing a nondegenerate germ of a real analytic submanifold of a complex manifold of arbitrary given type (n,K) with the richest possible group of holomorphic automorphisms in the given class. 相似文献
44.
The title compound is a centrosymmetric dimer with each cadmium in a distorted CdS5 square pyramidal geometry. The Cd–S bond distances range from 2.5626(11) to 2.8459(11) Å. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
45.
The electro-optic and complex dielectric behaviour of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4'-(n-butanoyloxyprop-1-oxy)biphenyl-4-carboxylate, having chiral SmCA* and hexatic smectic phases, have been investigated. Complex dielectric permittivities were measured as a function of frequency, d.c. bias field and temperature. Spontaneous polarization was measured by the current reversal technique; tilt angle was measured under a polarizing microscope using a low frequency electric field. The electro-optic properties and dielectric behaviour of the material are compared with results obtained by DSC and polarizing optical microscopy. Dielectric relaxation processes in SmCA* and hexatic smectic phases were determined. The dielectric strength at the SmCA* to hexatic smectic phase transition is discussed in terms of coupling between the long range bond orientational order and smectic C director. It seems from the results of spontaneous polarization and dielectric relaxation spectroscopy that the material might possess an additional phase between the SmCA* and hexatic smectic I* phases. 相似文献
46.
J. M. Martínez‐Burgos R. Benavente E. Prez M. L. Cerrada 《Journal of Polymer Science.Polymer Physics》2003,41(11):1244-1255
Several composites were prepared on the basis of an ethylene homopolymer and different copolymers of ethylene and 1‐hexene, synthesized with a metallocene catalyst, as matrices and a content of a 5 wt % of short glass fiber. The effect of the fiber incorporation on the structure and mechanical and viscoelastic behaviors was analyzed for the different samples. The glass fibers induced a slightly higher crystallinity, and the crystallite morphology significantly changed (long spacings and crystal orientation). The incorporation of fibers did not reinforce the different matrices under study at this low content; consequently, the mechanical parameters, such as Young's modulus, yielding stress, and microhardness, were lower in the composites as compared with those values found in the neat polyolefins. The location and apparent activation energies of distinct relaxation processes are also discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1244–1255, 2003 相似文献
47.
M. Ohsaki 《Archive of Applied Mechanics (Ingenieur Archiv)》2003,73(3-4):241-251
Summary Characteristics of optimal solutions under nonlinear buckling constraints are investigated by using a bar-spring model. It is demonstrated that optimization under buckling constraints of a symmetric system often leads to a structure with hill-top branching, where a limit point and bifurcation points coincide. A general formulation is derived for imperfection sensitivity of the critical load factor corresponding to a hill-top branching point. It is shown that the critical load is not imperfection-sensitive even for the case where an asymmetric bifurcation point exists at the limit point. 相似文献
48.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献
49.
Herein we report a new method to collect a qualified infrared spectrum of a solute in solution by two solvent cells with different thickness during background single-beam spectrum scanning. By collecting the background spectrum with two cells (two stages), we successfully achieved accurate solvent compensation between a sample and a reference, namely, the solvent amounts in the sample and background measurements could become congruent. Therefore, the solvent bands were thoroughly suppressed in the infrared spectrum and a qualified spectrum of the solute was obtained. 相似文献
50.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224