全文获取类型
收费全文 | 57386篇 |
免费 | 1861篇 |
国内免费 | 3070篇 |
专业分类
化学 | 35104篇 |
晶体学 | 40篇 |
力学 | 1447篇 |
综合类 | 51篇 |
数学 | 2509篇 |
物理学 | 16450篇 |
综合类 | 6716篇 |
出版年
2023年 | 188篇 |
2022年 | 220篇 |
2021年 | 194篇 |
2020年 | 171篇 |
2019年 | 148篇 |
2018年 | 247篇 |
2017年 | 147篇 |
2016年 | 262篇 |
2015年 | 290篇 |
2014年 | 521篇 |
2013年 | 397篇 |
2012年 | 5037篇 |
2011年 | 6591篇 |
2010年 | 1434篇 |
2009年 | 533篇 |
2008年 | 4779篇 |
2007年 | 5018篇 |
2006年 | 5004篇 |
2005年 | 5153篇 |
2004年 | 4121篇 |
2003年 | 3283篇 |
2002年 | 2697篇 |
2001年 | 2028篇 |
2000年 | 2340篇 |
1999年 | 1009篇 |
1998年 | 407篇 |
1997年 | 297篇 |
1996年 | 795篇 |
1995年 | 712篇 |
1994年 | 738篇 |
1993年 | 924篇 |
1992年 | 808篇 |
1991年 | 439篇 |
1990年 | 480篇 |
1989年 | 454篇 |
1988年 | 418篇 |
1987年 | 428篇 |
1986年 | 443篇 |
1985年 | 452篇 |
1984年 | 260篇 |
1983年 | 188篇 |
1982年 | 184篇 |
1981年 | 129篇 |
1975年 | 122篇 |
1959年 | 117篇 |
1958年 | 177篇 |
1957年 | 188篇 |
1956年 | 140篇 |
1955年 | 142篇 |
1954年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
163.
The reference [4] proved the consistency of S1 and S2 among Lewis' five strict implication systems in the modal logic by using the method of the Boolean-valued model. But, in this method, the consistency of S3, S4 and S5 in Lewis' five strict implication systems is not decided. This paper makes use of the properties: (1) the equivalence of the modal systems S3 and P3, S4 and P4; (2) the modal systems P3 and P4 all contained the modal axiom T(□p → p); (3) the modal axiom T is correspondence to the reflexive property in VB. Hence, the paper proves: (a) ‖As31‖ = 1; (b) ‖AS41‖ = 1; (c) ‖AS5l‖ = 1 in the model (where B is a complete Boolean algebra, R is reflexive property in VB). Therefore, the paper finally proves that the Boolean-valued model VB of the ZFC axiom system in set theory is also a Boolean-valued model of Lewis' the strict implication system S3, S4 and S5. 相似文献
164.
§1 IntroductionAt present,boundary value problems (BVPs) are widely investigated with variousmethods and techniques. BVPs with integral boundary conditions constitute a veryinteresting class of problems such as multipoint,three-point,four-point and nonlocalboundary value problems which are considered by many authors.And the existence ofpositive solutions for these problems becomes the subjectof many papers[1—6] .In a recentpaper[7] ,the authors have studied the existence of positive solut… 相似文献
165.
The present paper establishes sufficient conditions for the uniformly bounded of any solution of (1.1) and which tend to zero as t → ∞. 相似文献
166.
M.I.Gil' 《Annals of Differential Equations》2004,20(2):145-154
The nonlocal initial problem for nonlinear nonautonomous evolution equati-ons in a Banach space is considered. It is assumed that the nonlinearities havethe local Lipschitz properties. The existence and uniqueness of mild solutionsare proved. Applications to integro-differential equations are discussed.The main tool in the paper is the normalizing mapping (the generalizednorm). 相似文献
167.
Let 0 < p < 1. In this paper we prove that the Bergman norm on the p-th Bergman space bp(H) is equivalent to certain "normal direction norm" as well as certain "tangential direction norm", where H = Rn-1 × R is the upper half space. As an application, we get the boundedness of harmonic conjugation operators on bp(H). 相似文献
168.
1 Results Amphiphilic block copolymers are capable of forming supramolecular assemblies resembling those observed in nature,such as spherical micelles,worm micelles,and vesicles.Changing the solvent composition,ionic strength or pH of the polymer solution may induce the self-assembly of block copolymers or trigger the transition between the geometries of noncovalent assemblies.In the current work,we have synthesised starlike amphiphilic block copolymers having hydrophobic poly(methyl methacrylate),PMMA,core,and hydrophilic poly(acrylic acid),PAA,shell.The self-assembling characteristics of these polymers have been investigated in aqueous solutions by light scattering and direct visualisation by cryo-transmission electron microscopy (cryoTEM)[1]. Computer simulations along with the theoretical predictions made for the star-like system based on mean-field theory have been used to support the experimental observations[2]. The association of the starlike macromolecules resembles that of charged biopolymers,such as actin,since a balance between attractive and repulsive forces is required for the formation of cylindrical assemblies and can be manipulated by changing the pH or the ionic strength of the solvent[3]. 相似文献
169.
Confined thin film melt polymerization (CTFMP) of naphthalene chloride/hydroquinone (NCMQ, 1/1, molar)mixtures at polymerization temperatures (T_p) below ca. 300℃ resulted in relatively thick, elongated crystals. Polymerizationof NC/HQ above 300℃ between glass yielded well-formed lamellar crystals ca. 100 A thick. Phase Ⅰ and Ⅱ [001] EDpatterns were obtained for all T_p, the relative amount of phase Ⅰ increasing with T_p. Polymerization of naphthalenedicarboxylic acid/hydroquinione diacetate 1/1 mixtures at high T_p also yielded lamellar crystals that "curled up" off of thesubstrate. When the high temperature CTFMP polymerization was conducted between mica, aggregates of lamellae on-edgedeveloped but epitaxial growth did not occur. Epitaxial growth of lamellae between mica could be obtained, however, byconfined thin film solution polymerization, with both of the latter samples yielding apparently related ED patterns from adifferent unit cell than phase Ⅰ or Ⅱ. Fiber patterns, obtained from sheared samples, indicated considerably greater crystaldisorder than in the nascent crystals. Refinement of the phase Ⅰ unit cell parameters, based on the [001] and [01 1] EDpatterns, with modeling based on Cerius~2, suggests a monoclinic phase Ⅰ unit cell with a = 7.76, b = 5.71, c = 14.99 A, α = γ= 90°, β= 99.7°, ρ = 1.47 g/cm~3, space group P12_1/al. 相似文献
170.
Y. G. Ma 《复旦学报(自然科学版)》2007,46(1):33-40
Progress on nuclear liquid gas phase transition (LGPT) or critical behavior has been simply reviewed and some signals of LGPT in heavy ion collisions, especially in NIMROD data, are focused. These signals include the power-law charge distribution, the largest fluctuation of the fragment observables, the nuclear Zipf law, caloric curve and critical exponent analysis etc. 相似文献