全文获取类型
收费全文 | 2012篇 |
免费 | 65篇 |
国内免费 | 12篇 |
专业分类
化学 | 1338篇 |
晶体学 | 23篇 |
力学 | 57篇 |
数学 | 386篇 |
物理学 | 285篇 |
出版年
2023年 | 15篇 |
2022年 | 46篇 |
2021年 | 52篇 |
2020年 | 60篇 |
2019年 | 60篇 |
2018年 | 70篇 |
2017年 | 39篇 |
2016年 | 82篇 |
2015年 | 58篇 |
2014年 | 86篇 |
2013年 | 153篇 |
2012年 | 144篇 |
2011年 | 159篇 |
2010年 | 101篇 |
2009年 | 80篇 |
2008年 | 112篇 |
2007年 | 89篇 |
2006年 | 97篇 |
2005年 | 91篇 |
2004年 | 64篇 |
2003年 | 41篇 |
2002年 | 49篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 17篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 21篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1971年 | 4篇 |
排序方式: 共有2089条查询结果,搜索用时 15 毫秒
961.
Jae Wook Song Han Do Ghim Jin Hyun Choi Sohk-Won Ko Won Seok Lyoo 《Journal of polymer science. Part A, Polymer chemistry》2001,39(10):1810-1816
To provide sodium alginate (SA) with an antimicrobial property, we introduced chito-oligosaccharide (COS) via chemical bonding in a two-step procedure. We reacted COS with N-methylol acrylamide (NMA) with N-methylol groups to prepare acrylamidomethyl chito-oligosaccharide (COS–NMA). SA with COS side chains (SA–COS) was produced through a subsequent reaction of SA with COS–NMA. The chemical structure of SA–COS was confirmed by IR spectroscopy and 1H NMR spectroscopy. With a two-step method, we successfully prevented insoluble-complex formation due to electrostatic attraction between chitosan and alginate. SA–COS showed excellent antimicrobial activity, with the growth of microorganisms completely suppressed by a small amount of COS (1.8 wt %). © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1810–1816, 2001 相似文献
962.
We have examined the unusual behavior of wave propagation in the BrO3
- - 1,4- cyclohexanedione - ferroin reaction system. Two patterns of traveling wave have been induced spontaneously with long
time lag in the reaction process. A new wave has been induced as a concentric pattern after an initially induced wave has
disappeared. The initially induced wave shows an irregular spiral pattern with a high wave frequency. The two waves show very
different behavior in the pattern and in other wave characteristics as well. We compared the behavior of the two waves and
suggested an appropriate reaction process for unusual behavior of wave propagation in the system by considering the reaction
intermediates of the organic compounds.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
963.
Jindong Kim Jeong-Wook Hwang Youngjo Kim Min Hyung Lee Yonggyu Han Youngkyu Do 《Journal of organometallic chemistry》2001,620(1-2):1-7
Mixed ketoiminate/ketoimine/pentamethylcyclopentadienyl (Cp*) complex of zirconium, [(η5-Cp*){CH3C(O)CHC(NHR)CH3}{CH3C(O)CHC(NR)CH3}ZrCl2] (R=4-CF3Ph) (3) has been prepared in high yield by the reaction of one equivalent of 4-CF3-phenyl-β-ketoimine (1a) and one equivalent of lithium 4-CF3-phenyl-β-ketoiminate (2a) with one equivalent of Cp*ZrCl3 in Et2O. Bis(ketoiminate)zirconium dichloride complexes, 4 and 6, have been also prepared in high yield by the reaction of amine elimination of ketoimine ligands, respectively 1a and 1b, with Zr(NMe2)4 and followed by chlorination reaction with TMSCl. The X-ray crystallography reveals that the compound 3 is based on distorted octahedral geometry containing a ketoimine and a ketoiminate. The ketoiminate ligand coordinates to the zirconium as a bidentate ligand, leaving the metal center coordinatively unsaturated and thus leading to an additional binding of a ketoimine ligand to the metal to stabilize the complex 3. The zirconium complexes 3, 4 and 6 provide the moderate activity for the polymerization of ethylene in the presence of MMAO cocatalyst. Low molecular weight and high density polyethylene was obtained. 相似文献
964.
In this paper, we describe a method for fuzzy polynomial regression analysis for fuzzy input-output data using shape preserving
operations based on Tanaka’s approach. Shape preserving operations simplifies the computation of fuzzy arithmetic operations.
We derive the solution using general linear program. 相似文献
965.
966.
967.
Control charts with exponentially weighted moving average (EWMA) statistics (mean and variance) are used to jointly monitor the mean and variance of a process. An EWMA cost minimization model is presented to design the joint control scheme based on pure economic or both economic and statistical performance criteria. The pure economic model is extended to the economic-statistical design by adding constraints associated with in-control and out-of-control average run lengths. The quality related production costs are calculated using Taguchi’s quadratic loss function. The optimal values of smoothing constants, sampling interval, sample size, and control chart limits are determined by using a numerical search method. The average run length of the control scheme is computed by using the Markov chain approach. Computational study indicates that optimal sample sizes decrease as the magnitudes of shifts in mean and/or variance increase, and higher values of quality loss coefficient lead to shorter sampling intervals. The sensitivity analysis results regarding the effects of various inputs on the chart parameters provide useful guidelines for designing an EWMA-based process control scheme when there exists an assignable cause generating concurrent changes in process mean and variance. 相似文献
968.
Customer demand is sensitive to the price paid for the service in many service environments. Using queueing theory framework, we develop profit maximization models for jointly determining the price and the staffing level in a service company. The models include constraints on the average waiting time and the blocking probability. We show convexity of the single‐variable subproblem under certain plausible assumptions on the demand and staffing cost functions. Using numerical examples, we investigate the sensitivity of the price and the staffing level to changes in the marginal service cost and the user‐specified constraint on the congestion measure. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
969.
This paper is about equality of proofs in which a binary predicate formalizing properties of equality occurs, besides conjunction
and the constant true proposition. The properties of equality in question are those of a preordering relation, those of an
equivalence relation, and other properties appropriate for an equality relation in linear logic. The guiding idea is that
equality of proofs is induced by coherence, understood as the existence of a faithful functor from a syntactical category
into a category whose arrows correspond to diagrams. Edges in these diagrams join occurrences of variables that must remain
the same in every generalization of the proof. It is found that assumptions about equality of proofs for equality are parallel
to standard assumptions about equality of arrows in categories. They reproduce standard categorial assumptions on a different
level. It is also found that assumptions for a preordering relation involve an adjoint situation.
相似文献
970.
Hwa Kyu Kim Seong Kyun Kim Dr. Jun Ha Park Seung Woong Yoon Min Hyung Lee Dr. Youngkyu Do Prof. Dr. 《化学:亚洲杂志》2008,3(11):1912-1921
A series of ortho or meta Lewis base functionalized unbridged zirconocenes, [{1‐(En‐Ph)‐3,4‐Me2C5H2}2ZrCl2] (E=NMe2, OMe; n=1, 2), and a half‐functionalized zirconocene, [{1‐(p‐Me2NC6H4)‐3,4‐Me2C5H2}{1‐(p‐tolyl)‐3,4‐Me2C5H2}ZrCl2], were prepared. The crystal structures of these compounds determined by X‐ray diffraction revealed the presence of only C2‐symmetric rac‐like isomers in the asymmetric units. In combination with methylaluminoxane (MAO) cocatalyst, the meta‐functionalized complexes afforded mixtures of polymers that exhibit multimelting transition temperatures and broad molecular‐weight distributions (MWDs) in propylene polymerization at atmospheric monomer pressure, whereas the ortho‐functionalized complexes did not give rise to polymerization. Stepwise solvent extraction of the polymer mixtures showed that the polymers consist of amorphous, moderately isotactic, and highly isotactic portions, the weight ratio of which is dependent on the reaction temperature. 13C NMR spectral analysis indicated that the [mmmm] methyl pentad value of the isotactic portion reached around 90 %. Among the meta‐functionalized zirconocenes, the di‐OMe‐substituted one afforded the largest amount of the isotactic portion at all temperatures, and the portion comprised 82 wt % of the crude polymer obtained at 25 °C. In contrast, propylene polymerization with the half‐functionalized unbridged zirconocene resulted in the formation of nearly atactic polypropylene with a narrow MWD of around 2. These results corroborate the proposition that the rigid rac‐like cation–anion ion pair of type [rac‐L2ZrP]+[Me‐MAO]? generated in situ, through Lewis acid–base interactions between the functional groups and [Me‐MAO]?, is responsible for the isospecific propylene polymerization with the given class of functionalized unbridged zirconocenes and further indicate that the formation of such ion pairs can be favored by difunctionalization at the meta position of the phenyl ring with OMe groups. 相似文献