全文获取类型
收费全文 | 177395篇 |
免费 | 1998篇 |
国内免费 | 560篇 |
专业分类
化学 | 92087篇 |
晶体学 | 3088篇 |
力学 | 7260篇 |
综合类 | 3篇 |
数学 | 20807篇 |
物理学 | 56708篇 |
出版年
2021年 | 1365篇 |
2020年 | 1512篇 |
2019年 | 1723篇 |
2018年 | 2171篇 |
2017年 | 2226篇 |
2016年 | 3424篇 |
2015年 | 2092篇 |
2014年 | 3322篇 |
2013年 | 8112篇 |
2012年 | 6137篇 |
2011年 | 7363篇 |
2010年 | 5378篇 |
2009年 | 5294篇 |
2008年 | 6920篇 |
2007年 | 6805篇 |
2006年 | 6410篇 |
2005年 | 5828篇 |
2004年 | 5373篇 |
2003年 | 4821篇 |
2002年 | 4635篇 |
2001年 | 5302篇 |
2000年 | 3943篇 |
1999年 | 3064篇 |
1998年 | 2554篇 |
1997年 | 2432篇 |
1996年 | 2314篇 |
1995年 | 2161篇 |
1994年 | 2137篇 |
1993年 | 2045篇 |
1992年 | 2343篇 |
1991年 | 2272篇 |
1990年 | 2207篇 |
1989年 | 2138篇 |
1988年 | 2126篇 |
1987年 | 2132篇 |
1986年 | 2030篇 |
1985年 | 2644篇 |
1984年 | 2695篇 |
1983年 | 2398篇 |
1982年 | 2505篇 |
1981年 | 2320篇 |
1980年 | 2289篇 |
1979年 | 2433篇 |
1978年 | 2473篇 |
1977年 | 2399篇 |
1976年 | 2442篇 |
1975年 | 2370篇 |
1974年 | 2331篇 |
1973年 | 2509篇 |
1972年 | 1627篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
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
33.
34.
35.
36.
Cheriha Hassen Gati Yousra Kostov Vladimir Petrov 《Lithuanian Mathematical Journal》2020,60(4):456-469
Lithuanian Mathematical Journal - For sequences of d + 1 signs + and ? beginning with a + and having exactly two variations of sign, we give some sufficient conditions for the (non)existence... 相似文献
37.
38.
Enantiomeric Cyclic Peptides with Different Caco‐2 Permeability Suggest Carrier‐Mediated Transport
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
B. Sc. Eduard Puig Prof. Dr. Beat Ernst Prof. Dr. Horst Kessler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8023-8027
Recently, oral absorption of cyclic hexapeptides was improved by N‐methylation of their backbone amides. However, the number and position of N‐methylations or of solvent exposed NHs did not correlate to intestinal permeability, measured in a Caco‐2 model. In this study, we investigate enantiomeric pairs of three polar and two lipophilic peptides to demonstrate the participation of carrier‐mediated transporters. As expected, all the enantiomeric peptides exhibited identical lipophilicity (logD7.4) and passive transcellular permeability determined by the parallel artificial membrane permeability assay (PAMPA). However, the enantiomeric polar peptides exhibited different Caco‐2 permeability (Papp) in both directions a–b and b–a. The same trend was observed for one of the lipophilic peptide, whereas the second lipophilic enantiomer pair showed identical Caco‐2 permeability (within the errors). These findings provide the first evidence for the involvement of carrier‐mediated transport for peptides, especially for those of polar nature. 相似文献
39.
40.
Dapeng Liu Binod R. Giri Milán Szőri Béla Viskolcz Et-touhami Es-sebbar Aamir Farooq 《Proceedings of the Combustion Institute》2021,38(1):967-976
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000–1252 K and pressure range of 1.5–5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H5I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO → products (R1) and C3H5 + NO2 → products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5–5.0 bar, indicating that the measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm3/molecule/s):To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions. The reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels. 相似文献