全文获取类型
收费全文 | 1897篇 |
免费 | 51篇 |
国内免费 | 1篇 |
专业分类
化学 | 1380篇 |
晶体学 | 19篇 |
力学 | 33篇 |
数学 | 174篇 |
物理学 | 343篇 |
出版年
2023年 | 10篇 |
2022年 | 24篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 37篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 42篇 |
2015年 | 47篇 |
2014年 | 28篇 |
2013年 | 99篇 |
2012年 | 89篇 |
2011年 | 112篇 |
2010年 | 60篇 |
2009年 | 63篇 |
2008年 | 105篇 |
2007年 | 113篇 |
2006年 | 107篇 |
2005年 | 110篇 |
2004年 | 93篇 |
2003年 | 73篇 |
2002年 | 59篇 |
2001年 | 28篇 |
2000年 | 33篇 |
1999年 | 32篇 |
1998年 | 14篇 |
1997年 | 14篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 20篇 |
1993年 | 31篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 23篇 |
1979年 | 8篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有1949条查询结果,搜索用时 15 毫秒
1.
2.
Brian R. Holder Colleen A. McNaney David Luchetti Eric Schaeffer Dieter M. Drexler 《Biomedical chromatography : BMC》2015,29(9):1375-1379
Acetyl‐l ‐carnitine (ALCAR) is a potential biomarker for the modulation of brain neurotransmitter activity, but is also present in cerebrospinal fluid (CSF). Recent studies have utilized hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC‐MS/MS) based assays to detect and quantify ALCAR within biofluids such as urine, plasma and serum, using various sample pretreatment procedures. In order to address the need to quantify ALCAR in CSF on a high‐throughput scale, a new and simple HILIC‐MS/MS assay has been successfully developed and validated. For rapid analysis, CSF sample pretreatment was performed via ‘dilute and shoot’ directly onto an advanced HILIC column prior to MS/MS detection. This newly developed HILIC‐MS/MS assay shows good recoveries of ALCAR without the need for chemical derivatization and multistep sample extraction procedures. The employment of this assay is suitable for the high‐throughput bioanalysis and quantification of ALCAR within the CSF of various animal models and human clinical studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
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
4.
5.
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
6.
A method for calculating the number of rotamers of a linear alkane and of the number of rotamers with a given number of gauche conformations along the chain as a function of the total number of atoms in the chain, using general equations, is presented. A graphical method for generating individual rotamers was applied to the homologs up to decane, which has 1134 rotamers. The steric energies calculated by molecular mechanics (MM2 force field) were used as measures of the heat of formation for the coiled conformations relative to the anti conformer for each molecule, whereas the statistical entropy differences were calculated for classes of coiled rotamers grouped by the number of gauche bonds and steric energy. The free energy values calculated from these components show that already at 400 K hexane exists preferentially in conformations containing gauche bonds. For larger chains the free energy advantage for the coiled chains increases very steeply. The implications for the question of reactions of linear alkanes occurring on the surface or inside the channels of small- and medium-pore zeolites are briefly examined. 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.
A review of the analysis of petroleum fuels, oils, tars and engine exhaust particulate extracts by on-line coupled LC-GC is presented. 相似文献
10.
An overview is given on the stepwise learning programmes undertaken to identify the main sources of error associated with the determination of the mandatory organic contaminants in the marine monitoring programmes. Details are given on the preparation and use of LRMs and CRMs to maintain analytical control and quantify the laboratory errors in relation to the measurement of changes in the environment. 相似文献