全文获取类型
收费全文 | 60532篇 |
免费 | 1164篇 |
国内免费 | 512篇 |
专业分类
化学 | 32550篇 |
晶体学 | 478篇 |
力学 | 2123篇 |
综合类 | 12篇 |
数学 | 14232篇 |
物理学 | 12813篇 |
出版年
2022年 | 217篇 |
2021年 | 437篇 |
2020年 | 529篇 |
2019年 | 492篇 |
2018年 | 1542篇 |
2017年 | 1788篇 |
2016年 | 1512篇 |
2015年 | 1262篇 |
2014年 | 1249篇 |
2013年 | 2334篇 |
2012年 | 4911篇 |
2011年 | 4586篇 |
2010年 | 2900篇 |
2009年 | 2504篇 |
2008年 | 2524篇 |
2007年 | 2583篇 |
2006年 | 2556篇 |
2005年 | 6188篇 |
2004年 | 5423篇 |
2003年 | 3634篇 |
2002年 | 1745篇 |
2001年 | 680篇 |
2000年 | 474篇 |
1999年 | 524篇 |
1998年 | 441篇 |
1997年 | 422篇 |
1996年 | 527篇 |
1995年 | 383篇 |
1994年 | 341篇 |
1993年 | 290篇 |
1992年 | 434篇 |
1991年 | 389篇 |
1990年 | 335篇 |
1989年 | 309篇 |
1988年 | 330篇 |
1987年 | 254篇 |
1986年 | 221篇 |
1985年 | 384篇 |
1984年 | 370篇 |
1983年 | 268篇 |
1982年 | 332篇 |
1981年 | 341篇 |
1980年 | 310篇 |
1979年 | 310篇 |
1978年 | 281篇 |
1977年 | 245篇 |
1976年 | 285篇 |
1975年 | 245篇 |
1974年 | 250篇 |
1973年 | 257篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
The families index theory for the overlap lattice Dirac operator is applied to derive topological features of the space of SU(N) lattice gauge fields on the 4-torus: the topological sectors, specified by the fermionic topological charge, are shown to contain noncontractible even-dimensional spheres when N3, and noncontractible circles in the N=2 case. We describe how certain obstructions to the existence of gauge fixings without the Gribov problem in the continuum setting correspond on the lattice to obstructions to the contractibility of these spheres and circles. We also point out a canonical connection on the space of lattice gauge fields with monopole-like singularities associated with the spheres. 相似文献
82.
83.
We study the multiplicity of critical points for functionals which are only differentiable along some directions. We extend to this class of functionals the three critical point theorem of Pucci and Serrin and we apply it to a one-parameter family of functionals Jλ, λ∈I⊂R. Under suitable assumptions, we locate an open subinterval of values λ in I for which Jλ possesses at least three critical points. Applications to quasilinear boundary value problems are also given. 相似文献
84.
A tree T is arbitrarily vertex decomposable if for any sequence τ of positive integers adding up to the order of T there is a sequence of vertex-disjoint subtrees of T whose orders are given by τ. An on-line version of the problem of characterizing arbitrarily vertex decomposable trees is completely solved here. 相似文献
85.
Masanobu Haraguchi David F. P. Pile Toshihiro Okamoto Masuo Fukui Dmitri K. Gramotnev 《Optical Review》2006,13(4):228-230
We have numerically shown the existence of coupled wedge plasmons (CWPs) which propagates along a nano gap of a twin metal
wedge. The CWPs are formed by wedge plasmons which can interact with each other. The dispersion relations of the wavenumber,
propagation distance, and beam area of CWPs, are described and show that the characteristics of CWPs are similar to those
of wedge plasmons and of gap plasmons. We also propose a new plasmon waveguide composed of twin metal wedges with a nano gap. 相似文献
86.
Danny E. Akin W. Herbert Morrison III Luanne L. Rigsby Franklin E. Barton II David S. Himmelsbach Kevin B. Hicks 《Applied biochemistry and biotechnology》2006,129(1-3):104-116
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion
to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment
significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf
fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave
up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those
more suitable as residues for soil erosion control. 相似文献
87.
Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1 × 1016 m−3, the electron temperature of about 5.5 eV and the density of neutral oxygen atoms of 8 × 1021 m−3 for 20 s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C-O polar functional group responsible for the increase of the surface energy. 相似文献
88.
Kj?rand Iversen Per Nilsson 《International Journal of Computers for Mathematical Learning》2007,12(2):113-133
This paper focuses on the different ways in which students in lower secondary school (14–16 year olds) experience compound
random events, presented to them in the form of combined junctions. A carefully designed ICT environment was developed enabling
the students to interact with different representations of such structures. Data for the analysis was gathered from two interview
sessions. The analysis of the interaction is based on constructivist principles on learning; i.e. we adopted a student-oriented
perspective, taking into consideration the different ways students try to make sense of chance encounters.
Our results show how some students give priority to geometrical and physical concerns, and we discuss how seeking causal explanations
of random phenomena may have encouraged this. With respect to numerically oriented models a division strategy appears to stand
out as the preferred one. 相似文献
89.
Area,coarea, and approximation in <Emphasis Type="Italic">W</Emphasis><Superscript>1,1</Superscript>
David Swanson 《Arkiv f?r Matematik》2007,45(2):381-399
Let Ω⊂ℝ
n
be an arbitrary open set. We characterize the space W
1,1
loc(Ω) using variants of the classical area and coarea formulas. We use these characterizations to obtain a norm approximation
and trace theorems for functions in the space W
1,1(ℝ
n
). 相似文献
90.