全文获取类型
收费全文 | 27170篇 |
免费 | 645篇 |
国内免费 | 714篇 |
专业分类
化学 | 5198篇 |
晶体学 | 952篇 |
力学 | 436篇 |
综合类 | 51篇 |
数学 | 17572篇 |
物理学 | 4320篇 |
出版年
2023年 | 68篇 |
2022年 | 89篇 |
2021年 | 176篇 |
2020年 | 198篇 |
2019年 | 547篇 |
2018年 | 589篇 |
2017年 | 381篇 |
2016年 | 385篇 |
2015年 | 422篇 |
2014年 | 790篇 |
2013年 | 1980篇 |
2012年 | 796篇 |
2011年 | 2041篇 |
2010年 | 1798篇 |
2009年 | 1753篇 |
2008年 | 1959篇 |
2007年 | 1978篇 |
2006年 | 1477篇 |
2005年 | 1165篇 |
2004年 | 1022篇 |
2003年 | 821篇 |
2002年 | 781篇 |
2001年 | 580篇 |
2000年 | 539篇 |
1999年 | 561篇 |
1998年 | 497篇 |
1997年 | 404篇 |
1996年 | 448篇 |
1995年 | 512篇 |
1994年 | 468篇 |
1993年 | 355篇 |
1992年 | 342篇 |
1991年 | 228篇 |
1990年 | 229篇 |
1989年 | 215篇 |
1988年 | 134篇 |
1987年 | 150篇 |
1986年 | 140篇 |
1985年 | 215篇 |
1984年 | 168篇 |
1983年 | 95篇 |
1982年 | 141篇 |
1981年 | 159篇 |
1980年 | 133篇 |
1979年 | 89篇 |
1978年 | 138篇 |
1977年 | 111篇 |
1976年 | 108篇 |
1975年 | 45篇 |
1974年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Hiromichi Kurosu Mizuyo Kikuchi Isao Ando 《Journal of Polymer Science.Polymer Physics》1995,33(5):769-775
The solid-state 15N CP/MAS NMR spectra and 15N spin-lattice relaxation times (T1) of doped and dedoped 15N-labeled polypyrroles prepared by electrochemical polymerization, have been measured by means of high-resolution solid-state 15N NMR. The 15N signal of polypyrrole consists of four peaks decomposed by line shape analysis. The four peaks obtained have been assigned to the various structures of polypyrrole. Further, the half-width of the 15N NMR spectra of polypyrroles is discussed as related to the electrical conductivity. © 1995 John Wiley & Sons, Inc. 相似文献
92.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献
93.
94.
Oleg Borodin 《Combinatorica》1993,13(1):121-125
The weight of an edge in a graph is the sum of the degrees of its end-vertices. It is proved that in each 3-polytope there exists either an edge of weight at most 13 for which both incident faces are triangles, or an edge of weight at most 10 which is incident with a triangle, or else an edge of weight at most 8. All the bounds 13, 10, and 8 are sharp and attained independently of each other. 相似文献
95.
A self-avoiding polygon (SAP) on a graph is an elementary cycle. Counting SAPs on the hypercubic lattice ℤ
d
withd≥2, is a well-known unsolved problem, which is studied both for its combinatorial and probabilistic interest and its connections
with statistical mechanics. Of course, polygons on ℤ
d
are defined up to a translation, and the relevant statistic is their perimeter.
A SAP on ℤ
d
is said to beconvex if its perimeter is “minimal”, that is, is exactly twice the sum of the side lengths of the smallest hyper-rectangle containing
it. In 1984, Delest and Viennot enumerated convex SAPs on the square lattice [6], but no result was available in a higher
dimension.
We present an elementar approach to enumerate convex SAPs in any dimension. We first obtain a new proof of Delest and Viennot's
result, which explains combinatorially the form of the generating function. We then compute the generating function for convex
SAPs on the cubic lattice. In a dimension larger than 3, the details of the calculations become very cumbersome. However,
our method suggests that the generating function for convex SAPs on ℤ
d
is always a quotient ofdifferentiably finite power series. 相似文献
96.
97.
Sans résumé
相似文献
相似文献
98.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4]. 相似文献
99.
The main aim of this paper is the calculation of the dimension of certain atomic amalgams. These consist of finite Boolean algebras (blocks) pasted together in such a way that a pair of blocks intersects either trivially in the bounds, or the intersection consists of the bounds, an atom, and its complement. 相似文献
100.
The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min−1 was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L−1, respectively. 相似文献