全文获取类型
收费全文 | 3833篇 |
免费 | 105篇 |
国内免费 | 34篇 |
专业分类
化学 | 2559篇 |
晶体学 | 36篇 |
力学 | 91篇 |
数学 | 723篇 |
物理学 | 563篇 |
出版年
2022年 | 41篇 |
2021年 | 43篇 |
2020年 | 33篇 |
2019年 | 45篇 |
2018年 | 42篇 |
2017年 | 33篇 |
2016年 | 66篇 |
2015年 | 81篇 |
2014年 | 71篇 |
2013年 | 190篇 |
2012年 | 185篇 |
2011年 | 275篇 |
2010年 | 120篇 |
2009年 | 110篇 |
2008年 | 222篇 |
2007年 | 219篇 |
2006年 | 227篇 |
2005年 | 185篇 |
2004年 | 170篇 |
2003年 | 154篇 |
2002年 | 169篇 |
2001年 | 61篇 |
2000年 | 51篇 |
1999年 | 77篇 |
1998年 | 53篇 |
1997年 | 60篇 |
1996年 | 76篇 |
1995年 | 40篇 |
1994年 | 47篇 |
1993年 | 62篇 |
1992年 | 39篇 |
1991年 | 43篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 31篇 |
1986年 | 20篇 |
1985年 | 37篇 |
1984年 | 51篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 48篇 |
1980年 | 31篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 32篇 |
1976年 | 35篇 |
1975年 | 25篇 |
1974年 | 34篇 |
1973年 | 19篇 |
排序方式: 共有3972条查询结果,搜索用时 0 毫秒
1.
Aequationes mathematicae - In this paper, we establish a new class of dynamic inequalities of Hardy’s type which generalize and improve some recent results given in the literature. More... 相似文献
2.
3.
We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given. 相似文献
4.
Douglas Bridges 《Indagationes Mathematicae》2003,14(2):163-168
Two surprising constructive lemmas of Ishihara, with extremely useful proof techniques, are placed in a general setting. This both clarifies the ideas underlying those lemmas and raises the possibility that some other applications of their proof techniques in constructive analysis are, in fact, corollaries of our general results. 相似文献
5.
Douglas R. White Jason Owen-Smith James Moody Walter W. Powell 《Computational & Mathematical Organization Theory》2004,10(1):95-117
Social action is situated in fields that are simultaneously composed of interpersonal ties and relations among organizations, which are both usefully characterized as social networks. We introduce a novel approach to distinguishing different network macro-structures in terms of cohesive subsets and their overlaps. We develop a vocabulary that relates different forms of network cohesion to field properties as opposed to organizational constraints on ties and structures. We illustrate differences in probabilistic attachment processes in network evolution that link on the one hand to organizational constraints versus field properties and to cohesive network topologies on the other. This allows us to identify a set of important new micro-macro linkages between local behavior in networks and global network properties. The analytic strategy thus puts in place a methodology for Predictive Social Cohesion theory to be developed and tested in the context of informal and formal organizations and organizational fields. We also show how organizations and fields combine at different scales of cohesive depth and cohesive breadth. Operational measures and results are illustrated for three organizational examples, and analysis of these cases suggests that different structures of cohesive subsets and overlaps may be predictive in organizational contexts and similarly for the larger fields in which they are embedded. Useful predictions may also be based on feedback from level of cohesion in the larger field back to organizations, conditioned on the level of multiconnectivity to the field. 相似文献
6.
Scott T. Knauert Jack F. Douglas Francis W. Starr 《Journal of Polymer Science.Polymer Physics》2007,45(14):1882-1897
Nanoparticles can influence the properties of polymer materials by a variety of mechanisms. With fullerene, carbon nanotube, and clay or graphene sheet nanocomposites in mind, we investigate how particle shape influences the melt shear viscosity η and the tensile strength τ, which we determine via molecular dynamics simulations. Our simulations of compact (icosahedral), tube or rod‐like, and sheet‐like model nanoparticles, all at a volume fraction ? ≈ 0.05, indicate an order of magnitude increase in the viscosity η relative to the pure melt. This finding evidently can not be explained by continuum hydrodynamics and we provide evidence that the η increase in our model nanocomposites has its origin in chain bridging between the nanoparticles. We find that this increase is the largest for the rod‐like nanoparticles and least for the sheet‐like nanoparticles. Curiously, the enhancements of η and τ exhibit opposite trends with increasing chain length N and with particle shape anisotropy. Evidently, the concept of bridging chains alone cannot account for the increase in τ and we suggest that the deformability or flexibility of the sheet nanoparticles contributes to nanocomposite strength and toughness by reducing the relative value of the Poisson ratio of the composite. The molecular dynamics simulations in the present work focus on the reference case where the modification of the melt structure associated with glass‐formation and entanglement interactions should not be an issue. Since many applications require good particle dispersion, we also focus on the case where the polymer‐particle interactions favor nanoparticle dispersion. Our simulations point to a substantial contribution of nanoparticle shape to both mechanical and processing properties of polymer nanocomposites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1882–1897, 2007 相似文献
7.
8.
We consider the minimum number of edges in ak-edge-connected graph of ordern with chromatic number at leastc, obtaining the optimal bounds in most cases. 相似文献
9.
Problems associated with interferences in the analysis of serum for polychlorinated biphenyls 总被引:2,自引:0,他引:2
V W Burse M P Korver P C McClure J S Holler D M Fast S L Head D T Miller D J Buckley J Nassif R J Timperi 《Journal of chromatography. A》1991,566(1):117-125
During a recent survey to determine serum concentrations of polychlorinated biphenyls (PCBs) among people living around New Bedford, MA, U.S.A., an unidentified contaminant precluded the quantification of some early eluting Webb and McCall peaks. Loss of data is estimated to have reduced reported serum levels by 12%. Efforts to identify the contaminant by gas chromatography with an electron-capture detector, a Hall electrolytic condutivity detector, and mass spectrometer were not successful. Researchers ascertained, however, that the contaminant is not a PCB, it does not contain halogens, but it may contain phthalates. Vacutainer tubes and closures for serum storage bottles are suspected sources of contamination. 相似文献
10.
Renewal systems are symbolic dynamical systems originally introduced by Adler. IfW is a finite set of words over a finite alphabetA, then the renewal system generated byW is the subshiftX
W ⊂A
Z formed by bi-infinite concatenations of words fromW. Motivated by Adler’s question of whether every irreducible shift of finite type is conjugate to a renewal system, we prove
that for every shift of finite type there is a renewal system having the same entropy. We also show that every shift of finite
type can be approximated from above by renewal systems, and that by placing finite-type constraints on possible concatenations,
we obtain all sofic systems.
The authors were supported in part by NFS grants DMS-8706284, DMS-8814159 and DMS-8820716. 相似文献