全文获取类型
收费全文 | 1936篇 |
免费 | 58篇 |
国内免费 | 12篇 |
专业分类
化学 | 1301篇 |
晶体学 | 13篇 |
力学 | 41篇 |
数学 | 174篇 |
物理学 | 477篇 |
出版年
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 22篇 |
2020年 | 42篇 |
2019年 | 39篇 |
2018年 | 33篇 |
2017年 | 29篇 |
2016年 | 58篇 |
2015年 | 33篇 |
2014年 | 34篇 |
2013年 | 79篇 |
2012年 | 125篇 |
2011年 | 131篇 |
2010年 | 76篇 |
2009年 | 55篇 |
2008年 | 81篇 |
2007年 | 100篇 |
2006年 | 84篇 |
2005年 | 83篇 |
2004年 | 58篇 |
2003年 | 75篇 |
2002年 | 44篇 |
2001年 | 28篇 |
2000年 | 35篇 |
1999年 | 16篇 |
1997年 | 22篇 |
1996年 | 43篇 |
1995年 | 36篇 |
1994年 | 22篇 |
1993年 | 37篇 |
1992年 | 36篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 21篇 |
1988年 | 12篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 16篇 |
1974年 | 12篇 |
1973年 | 9篇 |
1972年 | 10篇 |
排序方式: 共有2006条查询结果,搜索用时 15 毫秒
1.
2.
Indermeet Kohli Taylor L. Braunberger Amanda F. Nahhas Fatima N. Mirza Mohsen Mokhtari Alexis B. Lyons Nikiforos Kollias Eduardo Ruvolo Henry W. Lim Iltefat H. Hamzavi 《Photochemistry and photobiology》2020,96(1):208-214
Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm−2): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm−2 of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range. 相似文献
3.
4.
William J. Letts Bambi L. Bailey Kathryn Scantlebury 《School science and mathematics》1997,97(4):192-199
With recent national calls for the reform of science education have come standards that delineate not only science content but also assessment, pedagogy, and teachers’ professional development. If teachers must teach science differently, then teacher preparation must change. This study asked 31 inservice secondary science teachers to complete a survey about topics for inclusion in a secondary science methods course. Respondents ranked a list of prespecified topics and had an opportunity to suggest other topics for inclusion in the course. Results showed that the majority of prespecified potential topics were judged important enough by these teachers to warrant inclusion in a methods course, though no individual added topic appeared on more than two surveys. Results demonstrate that these teachers believe teaching many of the traditional topics in science methods courses is still needed. In addition, they advocated the inclusion of several topics that either represent recent technological and theoretical advances, or longstanding ideas that have recently received considerable attention. 相似文献
5.
6.
The identification of incomplete signal re-setting of optically stimulated luminescence signals in sedimentary quartz is a vitally important step in the continued improvement of optical dating. It is shown that narrow spectrum (blue-green) laboratory partial bleaching of aliquots of natural sedimentary quartz has a significant effect on equivalent dose (measured using a single aliquot procedure) calculated as a function of measurement time (De(t)). The blue-green stimulation spectrum mimics that found underwater and the results suggest that incomplete re-setting of waterlain sediments may be possible using the De(t) method. 相似文献
7.
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
8.
Design theory crosses the boundary between mathematics and statistics, and includes a wide range of disparate types of design. In this paper we present a classification scheme which aims to include as many important types as possible, based on a balance among concept, representation and use. 相似文献
9.
Partially supported by NSF grant DMS-8701746 相似文献