全文获取类型
收费全文 | 17228篇 |
免费 | 538篇 |
国内免费 | 112篇 |
专业分类
化学 | 10900篇 |
晶体学 | 82篇 |
力学 | 393篇 |
综合类 | 2篇 |
数学 | 3606篇 |
物理学 | 2895篇 |
出版年
2023年 | 102篇 |
2022年 | 282篇 |
2021年 | 371篇 |
2020年 | 324篇 |
2019年 | 296篇 |
2018年 | 665篇 |
2017年 | 464篇 |
2016年 | 523篇 |
2015年 | 411篇 |
2014年 | 463篇 |
2013年 | 930篇 |
2012年 | 955篇 |
2011年 | 1594篇 |
2010年 | 687篇 |
2009年 | 665篇 |
2008年 | 941篇 |
2007年 | 942篇 |
2006年 | 850篇 |
2005年 | 797篇 |
2004年 | 613篇 |
2003年 | 568篇 |
2002年 | 479篇 |
2001年 | 286篇 |
2000年 | 328篇 |
1999年 | 216篇 |
1998年 | 167篇 |
1997年 | 167篇 |
1996年 | 189篇 |
1995年 | 135篇 |
1994年 | 139篇 |
1993年 | 134篇 |
1992年 | 122篇 |
1991年 | 108篇 |
1990年 | 117篇 |
1989年 | 100篇 |
1988年 | 83篇 |
1987年 | 81篇 |
1986年 | 82篇 |
1985年 | 100篇 |
1984年 | 123篇 |
1983年 | 88篇 |
1982年 | 100篇 |
1981年 | 94篇 |
1980年 | 73篇 |
1979年 | 56篇 |
1978年 | 76篇 |
1977年 | 62篇 |
1976年 | 64篇 |
1975年 | 54篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We present here an improved version of the method introduced by the first author to derive
pointwise gradient estimates for the solutions of one-dimensional parabolic problems. After considering
a general qualinear equation in divergence form we apply the method to the case of a nonlinear
diffusion-convection equation. The conclusions are stated first for classical solutions and then for
generalized and mild solutions. In the case of unbounded initial datum we obtain several regularizing
effects for t > 0. Some unilateral pointwise gradient
estimates are also obtained. The case of
the Dirichlet problem is also considered. Finally, we collect, in the last section, several comments
showing the connections among these estimates and the study of the free boundaries
associated to the solutions of the diffusion-convection equation. 相似文献
82.
We give three formulas expressing the Smale invariant of an immersion f of a (4k−1)-sphere into (4k+1)-space. The terms of the formulas are geometric characteristics of any generic smooth map g of any oriented 4k-dimensional manifold, where g restricted to the boundary is an immersion regularly homotopic to f in (6k−1)-space.The formulas imply that if f and g are two non-regularly homotopic immersions of a (4k−1)-sphere into (4k+1)-space then they are also non-regularly homotopic as immersions into (6k−1)-space. Moreover, any generic homotopy in (6k−1)-space connecting f to g must have at least ak(2k−1)! cusps, where ak=2 if k is odd and ak=1 if k is even. 相似文献
83.
84.
85.
86.
István Szilágyi László. Horváth Imre Labádi Klara Hernadi István Pálinkó Tamás Kiss 《Central European Journal of Chemistry》2006,4(1):118-134
An imidazolate-bridged copper(II)-zinc(II) complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(2-aminoethyl)amine perchlorate (denoted as “Cu,Zn complex”) and a simple copper(II) complex (Cu(II)-tris(2-aminoethyl)
amine chloride (“Cu-tren”) were prepared and immobilised on silica gel (by hydrogen or covalent bonds) and montmorillonite
(by ion exchange). The immobilised substances were characterised by FT-IR spectroscopy and their thermal characteristics were
also studied. The obtained materials were tested in two probe reactions: catalytic oxidation of 3,5-di-tert-butyl catechol (DTBC) (catecholase activity) and the decomposition of hydrogen peroxide (catalase activity). It was found
that the catecholase activity of the Cu,Zn complex increased considerably upon immobilization on silica gel via hydrogen bonds and intercalation by ion exchange among the layers of montmorillonite. The imidazolate-bridged copper(II)-zinc(II)
complex and its immobilised versions were inactive in hydrogen peroxide decomposition. The Cu(II)-tris(2-aminoethyl)amine
chloride complex displayed good catalase activity; however, immobilisation could not improve it. 相似文献
87.
D. Kaptás T. Kemény J. Balogh L. F. Kiss L. Gránásy I. Vincze 《Hyperfine Interactions》1994,94(1):1861-1865
The temperature dependence of the iron hyperfine field distribution is reported in melt-quenched amorphous Fe-Zr alloys. The most remarkable feature is the compositinal change in the shape of the average hyperfine field versus temperature curves. The unusual increase in the average hyperfine field below about 85 K is a characteristic feature of the RSG systems; however, no anomaly is observed in the width of the hyperfine field distribution as a function of temperature. The results cannot be properly explained in the framework of the existing spin glass models. 相似文献
88.
E. Manova C. Estournès D. Paneva J.-L. Rehspringer T. Tsoncheva B. Kunev I. Mitov 《Hyperfine Interactions》2005,165(1-4):215-220
Iron–nickel spinel oxide NiFe2O4 nanoparticles have been prepared by the combination of chemical precipitation and subsequent mechanical milling. For comparison, their analogue obtained by thermal synthesis is also studied. Phase composition and structural properties of iron–nickel oxides are investigated by X-ray diffraction and Mössbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. An influence of the preparation method on the reduction and catalytic properties of iron–nickel samples is established. 相似文献
89.
Rodrigo París Jos Luis de la Fuente 《Journal of polymer science. Part A, Polymer chemistry》2006,44(18):5304-5315
Functional spontaneous gradient copolymers of allyl methacrylate (A) and butyl acrylate (B) were synthesized via atom transfer radical polymerization. The copolymerization reactions were carried out in toluene solutions at 100 °C with methyl 2‐bromopropionate as the initiator and copper bromide with N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst system. Different aspects of the statistical reaction copolymerizations, such as the kinetic behavior, crosslinking density, and gel fraction, were studied. The gel data were compared with Flory's gelation theory, and the sol fractions of the synthesized copolymers were characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. The copolymer composition, demonstrating the gradient character of the copolymers, and the microstructure were analyzed. The experimental data agreed well with data calculated with the Mayo–Lewis terminal model and Bernoullian statistics, with monomer reactivity ratios of 2.58 ± 0.37 and 0.51 ± 0.05 for A and B, respectively, an isotacticity parameter for A of 0.24, and a coisotacticity parameter of 0.33. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5304–5315, 2006 相似文献
90.
We evaluate the financial performance of most of the branch offices of a large European savings bank for a recent accounting
period. We employ a complementary pair of nonparametric techniques to evaluate their financial performance, in terms of their
ability to conserve on the expenses they incur in building their customer bases and providing customer services. We find variation
in the ability of branch offices to perform this task, and agreement on the identity of the laggard branches. We then employ
parametric techniques to determine that the list of indicators on which their financial performance is evaluated can be reduced
without statistically significant loss of information to bank management. Both findings suggest ways in which the bank can
increase the profitability of its branch network.
A previous version of this paper was presented at CORE, Université Catholique de Louvain, Louvain-la-Neuve, Belgium, where
we received many helpful comments from the audience. We are grateful to three referees for their helpful comments as well. 相似文献