全文获取类型
收费全文 | 11586篇 |
免费 | 1019篇 |
国内免费 | 1639篇 |
专业分类
化学 | 8936篇 |
晶体学 | 67篇 |
力学 | 260篇 |
综合类 | 77篇 |
数学 | 2603篇 |
物理学 | 2301篇 |
出版年
2024年 | 18篇 |
2023年 | 198篇 |
2022年 | 278篇 |
2021年 | 345篇 |
2020年 | 424篇 |
2019年 | 375篇 |
2018年 | 300篇 |
2017年 | 427篇 |
2016年 | 530篇 |
2015年 | 446篇 |
2014年 | 625篇 |
2013年 | 980篇 |
2012年 | 751篇 |
2011年 | 829篇 |
2010年 | 694篇 |
2009年 | 869篇 |
2008年 | 848篇 |
2007年 | 921篇 |
2006年 | 661篇 |
2005年 | 576篇 |
2004年 | 450篇 |
2003年 | 403篇 |
2002年 | 269篇 |
2001年 | 310篇 |
2000年 | 213篇 |
1999年 | 217篇 |
1998年 | 184篇 |
1997年 | 196篇 |
1996年 | 143篇 |
1995年 | 125篇 |
1994年 | 93篇 |
1993年 | 104篇 |
1992年 | 100篇 |
1991年 | 64篇 |
1990年 | 31篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 18篇 |
1986年 | 28篇 |
1985年 | 28篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 24篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Meritxell Vinyals Andrea Giovannucci Jesús Cerquides Pedro Meseguer Juan A. Rodriguez-Aguilar 《Journal of Algorithms in Cognition, Informatics and Logic》2008,63(1-3):130
Mixed Multi-Unit Combinatorial Auctions extend and generalize all the preceding types of combinatorial auctions. In this paper, we try to make headway on the practical application of MMUCAs by: (1) providing an algorithm to generate artificial data that is representative of the sort of scenarios a winner determination algorithm is likely to encounter; and (2) subsequently assessing the performance of an Integer Programming implementation of MMUCA in CPLEX. 相似文献
993.
Hugh Chaffey‐Millar Gene Hart‐Smith Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2008,46(5):1873-1892
A mass spectrometry analysis has been performed on complex architecture polymeric material produced during reversible addition fragmentation chain transfer (RAFT) polymerizations yielding star polymers. Para‐acetoxystyrene (AcOSty) has been polymerized at 60 °C, using azobisisobutyronitrile (AIBN) as the thermally decomposing initiator, in the presence of the R‐group approach tetrafunctional RAFT agent (1,2,4,5‐tetrakis‐(2‐phenyl‐thioacetyl‐sulfanylmethyl)‐benzene). In addition to ideal star material, a variety of products unique to this mode of polymerization have been identified. These include star–star couples, stars terminated with initiator fragments, star–star couples terminated with initiator fragments and linear polymers, supporting the notion that these species are responsible for the structured molecular‐weight distributions measured for these systems when analyzed via gel permeation chromatography. The analysis begins with a study of AcOSty polymerizing (i) in the absence of any mediating agent and (ii) in the presence of a monofunctional RAFT agent, revealing the mode of termination of propagating poly(AcOSty) radicals as combination and that some ionization biases exist among variants of poly (AcOSty). The interpretation of the mass spectrometry data has been aided by a novel kinetic model of star polymerizations, allowing the rationalization of experimental observations with theoretical expectations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1873–1892, 2008 相似文献
994.
分散化供应链的自组织演化机制建模与仿真 总被引:1,自引:0,他引:1
供应链是一个复杂适应系统.提出了分散化供应链演化的自组织机制.在开放结构下,多企业主体为了适应外部环境,在非线性互动中涌现出供应链协作结构和协调模式.借鉴生物系统环境适应能力思想,建立了分散化供应链自组织演化模型,并采用Multi-agent技术进行仿真,证明了分散化供应链的自组织演化机制.外部环境和企业内部机制因素控制着分散化供应链的演化,其演化对初始条件高度敏感,存在着锁定、路径依赖和混沌等自组织系统特性. 相似文献
995.
A genetic algorithm for the two-stage supply chain distribution problem associated with a fixed charge 总被引:1,自引:0,他引:1
This paper considers a two-stage distribution problem of a supply chain that is associated with a fixed charge. Two kinds of cost are involved in this problem: a continuous cost that linearly increases with the amount transported between a source and a destination, and secondly, a fixed charge, that incurs whenever there exists a transportation of a non-zero quantity between a source and a destination. The objective criterion is the minimisation of the total cost of distribution. A genetic algorithm (GA) that belongs to evolutionary search heuristics is proposed and illustrated. The proposed methodology is evaluated for its solution quality by comparing it with the approximate and lower bound solutions. Thus, the comparison reveals that the GA generates better solution than the approximation method and is capable of providing solution either equal or closer to the lower bound solution of the problem. 相似文献
996.
997.
Let X1,X2,...,Xk be k disjoint subsets of S with the same cardinality m.Define H(m,k) = {X (C) S: X (C) Xi for 1 ≤I ≤k} and P(m,k) = {X (C) S : X ∩ Xi ≠φ for at least two Xi's}.Suppose S = Uki=1 Xi,and let Q(m,k,2) be the collection of all subsets K of S satisfying|K ∩ Xi|≥ 2 for some 1 ≤ I ≤ k.For any two disjoint subsets Y1 and Y2 of S,we define F1,j = {X (C) S : either |X ∩ Y1|≥ 1 or |X ∩ Y2|≥ j}.It is obvious that the four posers are graded posets ordered by inclusion.In this paper we will prove that the four posets are nested chain orders. 相似文献
998.
This paper contributes to the supply chain contracts literature in economics and operations by performing qualitative sensitivity analysis of a wholesale price contract in a two-echelon supply chain setting. Order-theory tools are used to derive sufficient conditions for monotonicity of contract parameters.The upstream supplier is modeled as a Stackelberg leader. The supplier is assumed to have complete information about the costs and revenue function of the downstream retailer. It is shown that an equilibrium wholesale price weakly increases with an increase in the supplier production cost rate, but it may increase or decrease with an increase in the retailer cost rate. As either the supplier production cost or the retailer cost increases, the supplier profit decreases weakly. Additional sensitivity analysis is performed assuming certain properties of the retailer revenue function.Several well-known results in the supply chain contracting literature can be considered as special cases of the more general theorems developed here. In particular, this paper reexamines the analysis of a newsvendor supply chain problem by Lariviere and Porteus [Lariviere, M.A., Porteus, E.L., 2001. Selling to the newsvendor: An analysis of price-only contracts. Manufacturing & Service Operations Management 3, 293–305]. This paper generalizes and extends their work, by establishing properties of the newsvendor demand distribution that guarantee monotonicity of the contract parameters, without requiring a unique contract solution. 相似文献
999.
In pH 5.5 phosphate buffer solution,N-n-undecyl-N'-(sodium-p-amino-benzenesulfonate)thiourea(UPT)produced a pair of redox peaks on the bare glassy carbon electrode.At the multi-walled carbon nanotube(MWNT)modified electrode,the electrochemical behavior of UPT enhanced greatly.In the presence of bovine serum albumin (BSA),the peak currents of UPT decreased linearly due to the formation of a super-molecular complex.This method was successfully applied to the determination of BSA in a bovine serum sample. 相似文献
1000.
Chemical reactions are often carried out in nano-structured materials, which can enhance reactions due to their large specific
surface area, their interactions with the reacting mixture and confinement effects. In this work, we present a systematic
study of the effect that the geometrical restrictions imposed by the pore walls can have on reactions that involve a three
dimensional rearrangement of the atoms in a molecule. In particular, we consider the isomerization of three 4-membered hydrocarbons—n-butane,
1-butene and 1,3-butadiene confined in carbon nanopores of slit geometry. Our results illustrate the fact that, in the molecular
sieving limit, the reaction rates change as the double exponential of the pore size (Santiso et al., in J. Chem. Phys., 2007a, submitted), and therefore the transition rates in nanopores can be many orders of magnitude different from the corresponding
bulk values. These results can be used as a guideline for the molecular-level design of improved catalytic materials. 相似文献