全文获取类型
收费全文 | 295106篇 |
免费 | 4498篇 |
国内免费 | 1233篇 |
专业分类
化学 | 164927篇 |
晶体学 | 4306篇 |
力学 | 12176篇 |
综合类 | 12篇 |
数学 | 31772篇 |
物理学 | 87644篇 |
出版年
2020年 | 2059篇 |
2019年 | 2049篇 |
2018年 | 1958篇 |
2017年 | 1890篇 |
2016年 | 4061篇 |
2015年 | 3263篇 |
2014年 | 4238篇 |
2013年 | 12830篇 |
2012年 | 10312篇 |
2011年 | 12898篇 |
2010年 | 7940篇 |
2009年 | 7817篇 |
2008年 | 11684篇 |
2007年 | 11601篇 |
2006年 | 11333篇 |
2005年 | 10658篇 |
2004年 | 9505篇 |
2003年 | 8166篇 |
2002年 | 8108篇 |
2001年 | 8976篇 |
2000年 | 6979篇 |
1999年 | 5535篇 |
1998年 | 4414篇 |
1997年 | 4416篇 |
1996年 | 4298篇 |
1995年 | 3999篇 |
1994年 | 3711篇 |
1993年 | 3561篇 |
1992年 | 3991篇 |
1991年 | 3887篇 |
1990年 | 3574篇 |
1989年 | 3577篇 |
1988年 | 3585篇 |
1987年 | 3517篇 |
1986年 | 3320篇 |
1985年 | 4810篇 |
1984年 | 4849篇 |
1983年 | 3939篇 |
1982年 | 4396篇 |
1981年 | 4168篇 |
1980年 | 4130篇 |
1979年 | 4076篇 |
1978年 | 4286篇 |
1977年 | 4138篇 |
1976年 | 4057篇 |
1975年 | 3985篇 |
1974年 | 3774篇 |
1973年 | 4035篇 |
1972年 | 2390篇 |
1971年 | 1755篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2 下载免费PDF全文
Stefan Kissling Peter T. Altenbuchner Dr. Maximilian W. Lehenmeier Dr. Eberhardt Herdtweck Dr. Peter Deglmann Dr. Uwe B. Seemann Prof. Dr. Bernhard Rieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8148-8157
The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO2 revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO2 co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion. 相似文献
36.
37.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated. 相似文献
38.
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
39.
40.