全文获取类型
收费全文 | 3865篇 |
免费 | 80篇 |
国内免费 | 3篇 |
专业分类
化学 | 2432篇 |
晶体学 | 32篇 |
力学 | 85篇 |
数学 | 452篇 |
物理学 | 947篇 |
出版年
2022年 | 28篇 |
2021年 | 34篇 |
2020年 | 31篇 |
2019年 | 59篇 |
2018年 | 46篇 |
2017年 | 25篇 |
2016年 | 78篇 |
2015年 | 67篇 |
2014年 | 60篇 |
2013年 | 186篇 |
2012年 | 156篇 |
2011年 | 172篇 |
2010年 | 95篇 |
2009年 | 79篇 |
2008年 | 167篇 |
2007年 | 177篇 |
2006年 | 165篇 |
2005年 | 188篇 |
2004年 | 159篇 |
2003年 | 141篇 |
2002年 | 122篇 |
2001年 | 87篇 |
2000年 | 91篇 |
1999年 | 77篇 |
1998年 | 35篇 |
1997年 | 54篇 |
1996年 | 71篇 |
1995年 | 56篇 |
1994年 | 47篇 |
1993年 | 62篇 |
1992年 | 66篇 |
1991年 | 53篇 |
1990年 | 70篇 |
1989年 | 62篇 |
1988年 | 63篇 |
1987年 | 37篇 |
1986年 | 41篇 |
1985年 | 62篇 |
1984年 | 64篇 |
1983年 | 38篇 |
1982年 | 51篇 |
1981年 | 39篇 |
1980年 | 52篇 |
1979年 | 29篇 |
1978年 | 43篇 |
1977年 | 45篇 |
1976年 | 30篇 |
1975年 | 39篇 |
1974年 | 30篇 |
1973年 | 41篇 |
排序方式: 共有3948条查询结果,搜索用时 0 毫秒
1.
Kelly R. Kirker Glenn D. Prestwich 《Journal of Polymer Science.Polymer Physics》2004,42(23):4344-4356
The chemical composition of glycosaminoglycan (GAG) hydrogels was found to have a profound effect on the physical properties of gels. Hyaluronan (HA) and chondroitin sulfate (CS) were each modified with adipic dihydrazide (ADH) with carbodiimide chemistry. The resulting polymer was crosslinked with various concentrations of poly(ethylene glycol) dialdehyde (PEG‐diald) to produce a series of hydrogels. The physical properties of these GAG hydrogels varied in a concentration‐dependent fashion. Maximal crosslinking was observed at a theoretical crosslinking of 50% for the HA‐ADH‐PEG‐diald hydrogels and 75% for the CS‐ADH‐PEG‐diald hydrogels. Adding PEG‐diald beyond the optimum for crosslinking prolonged the in vitro enzymatic degradation time of the hydrogels. The swelling of the crosslinked GAG hydrogels was correlated with the amount of PEG‐diald used rather than with the crosslinking density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4344–4356, 2004 相似文献
2.
3.
Although the most important use of nuclear magnetic resonance imaging (MRI) continues to be for diagnostic medicine, recognition is being gained for many nonmedical applications. Examples include the following areas: petrogeology, food, agriculture, polymers and polymer-composites, and pharmaceuticals. These areas all involve studies of species that have short spin-spin relaxation times, and consequently need far fast gradient switching. These technical details are discussed and typical applications given. 相似文献
4.
Properties of nonparametric estimators of autocovariance for stationary random fields 总被引:1,自引:0,他引:1
Summary We introduce nonparametric estimators of the autocovariance of a stationary random field. One of our estimators has the property that it is itself an autocovatiance. This feature enables the estimator to be used as the basis of simulation studies such as those which are necessary when constructing bootstrap confidence intervals for unknown parameters. Unlike estimators proposed recently by other authors, our own do not require assumptions such as isotropy or monotonicity. Indeed, like nonparametric function estimators considered more widely in the context of curve estimation, our approach demands only smoothness and tail conditions on the underlying curve or surface (here, the autocovariance), and moment and mixing conditions on the random field. We show that by imposing the condition that the estimator be a covariance function we actually reduce the numerical value of integrated squared error. 相似文献
5.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
6.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
7.
We give a new independent self-dual 3-basis for the trivial variety with two binary operations.
Received October 24, 2006; accepted in final form January 25, 2007. 相似文献
8.
S. M. J. Kelly 《Optics Communications》1989,70(6):495-501
The effect of incorporating an empty external cavity into the feedback loop of a mode-locked laser is investigated. Particular attention is paid to the response of the mode-locking as the external cavity is detuned by a fraction of a wavelength from the round trip transit time associated with the laser. The results for two regimes of operation are presented. In the first case a series of short lived transients develop whereas the other case leads to a persistent intermittent Q-switching scenario, where mode-locking fails. The role of coupling between the cavities and the laser's memory time in relation to the results is discussed. A mechanism for the improved mode-locking observed with non-linear external cavities is suggested. 相似文献
9.
Soluble catalysts for the Juliá-Colonna asymmetric epoxidation reaction have been constructed in three different ways, using NH2-PEG-OMe as the support system: suitable solvents have been identified and it is shown that the degree of helicity of the conjugates correlates with the extent of conversion and (to a lesser extent) the enantioselectivity of epoxidation. 相似文献
10.
J. I. Hall 《Combinatorica》1987,7(1):77-85
Within the Johnson schemeI(m, d) we find the graphK(m, d) ofd-subsets of anm-set, two such adjacent when disjoint. Among all connected graphs,K(m, d) is characterized by the isomorphism type of its vertex neighborhoods providedm is sufficiently large compared tod.
Partial support provided by NSF (USA), SERC (UK), ZWO (NL). 相似文献