全文获取类型
收费全文 | 97196篇 |
免费 | 5590篇 |
国内免费 | 4652篇 |
专业分类
化学 | 55265篇 |
晶体学 | 1200篇 |
力学 | 5528篇 |
综合类 | 329篇 |
数学 | 11823篇 |
物理学 | 33293篇 |
出版年
2022年 | 1197篇 |
2021年 | 1826篇 |
2020年 | 2297篇 |
2019年 | 2485篇 |
2018年 | 2852篇 |
2017年 | 2792篇 |
2016年 | 3456篇 |
2015年 | 2346篇 |
2014年 | 3430篇 |
2013年 | 4875篇 |
2012年 | 5042篇 |
2011年 | 5370篇 |
2010年 | 4264篇 |
2009年 | 4271篇 |
2008年 | 4466篇 |
2007年 | 4186篇 |
2006年 | 3817篇 |
2005年 | 3393篇 |
2004年 | 3038篇 |
2003年 | 2687篇 |
2002年 | 2672篇 |
2001年 | 2503篇 |
2000年 | 1943篇 |
1999年 | 1554篇 |
1998年 | 1497篇 |
1997年 | 1301篇 |
1996年 | 1255篇 |
1995年 | 1078篇 |
1994年 | 1155篇 |
1993年 | 1093篇 |
1992年 | 1052篇 |
1991年 | 1115篇 |
1990年 | 1110篇 |
1989年 | 1027篇 |
1988年 | 906篇 |
1987年 | 908篇 |
1986年 | 870篇 |
1985年 | 910篇 |
1984年 | 908篇 |
1983年 | 815篇 |
1982年 | 797篇 |
1979年 | 797篇 |
1978年 | 809篇 |
1977年 | 805篇 |
1976年 | 917篇 |
1975年 | 811篇 |
1974年 | 839篇 |
1973年 | 843篇 |
1972年 | 751篇 |
1971年 | 739篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Herein we report a novel visible-light-mediated external reductant-free reductive cross coupling for the construction of C sp~2–C sp~3 bonds. A variety of benzylammonium salts underwent selective coupling with(hetero)aryl nitriles to deliver important diarylmethanes under mild reaction conditions. Importantly, photocatalysts can be omitted for many cases, which might involve the electron donor acceptor(EDA) complex. Mechanistic studies indicated benzylic radicals might be involved as the key intermediates. Moreover, the in situ generated NMe_3 via cleavage of C–N bond in ammonium salts acts as the electron donor,thus avoiding the use of external-reductant. 相似文献
102.
103.
Stolpovskaya N. V. Kruzhilin A. A. Zorina A. V. Shikhaliev Kh. S. Ledeneva I. V. Kosheleva E. A. Vandyshev D. Yu. 《Russian Journal of Organic Chemistry》2019,55(9):1322-1328
Russian Journal of Organic Chemistry - A procedure has been proposed for the synthesis of a series of substituted N-(1,3-thiazol-2-yl)-pyrimidin-2-amines and N-(pyrimidin-2-yl)thioureas by... 相似文献
104.
Bowen Yang Feng Cai Shuai Huang Prof. Dr. Haifeng Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(10):4064-4071
Imprinting nanopatterns on flexible substrates has diverse applications in advanced fabrication. However, the traditional thermal nanoimprint lithography (T-NIL) often causes shrinkage upon cooling. Here, a simple yet versatile method is introduced to fabricate multiple nanopatterns on a flexible substrate coated with an azopolymer by combining athermal nanoimprint lithography (AT-NIL) and photolithography. The azopolymer has various mechanical properties upon photoirradiation: 1) phototunable glass-transition temperatures (Tg) and concomitantly photoinduced switch from glassy plastic to viscoplastic polymer; 2) prominent modulation of viscoplasticity under light illumination at different wavelengths. Regionally selective multiple nanopatterns are conveniently fabricated, presenting angle-dependent structural color images on poly(ethylene terephthalate) (PET) substrates. The flexible, athermal and multiple nanopatterning method has the potential for on-demand fabrication of complex nanopatterns. 相似文献
105.
Nonlinear Dynamics - The problem of self-sustained oscillations in excitable complex networks is the central issue under investigation, among which the exploration of the key factors in determining... 相似文献
106.
107.
Optics and Spectroscopy - The temperature dependence of the selective emission intensity of the R1 line upon laser-thermal heating of ruby is studied and explained by competition of radiative and... 相似文献
108.
Sample preparation methods used for genetically modified organisms (GMOs) analysis are often time consuming, require extensive manual manipulation, and result in limited amounts of purified protein, which may complicate the detection of low‐abundance GM protein. A robust sample pretreatment method prior to mass spectrometry (MS) detection of the transgenic protein (5‐enolpyruvylshikimate‐3‐phosphate synthase [CP4 EPSPS]) present in Roundup Ready soya is investigated. Liquid chromatography‐multiple reaction monitoring tandem MS (nano LC‐MS/MS‐MRM) was used for the detection and quantification of CP4 EPSPS. Gold nanoparticles (AuNPs) and concanavalin A (Con A)‐immobilized Sepharose 4B were used as selective probes for the separation of the major storage proteins in soybeans. AuNPs that enable the capture of cysteine‐containing proteins were used to reduce the complexity of the crude extract of GM soya. Con A‐sepharose was used for the affinity capture of β‐conglycinin and other glycoproteins of soya prior to enzymatic digestion. The methods enabled the detection of unique peptides of CP4 EPSPS at a level as low as 0.5% of GM soya in MRM mode. Stable‐isotope dimethyl labeling was further applied to the quantification of GM soya. Both probes exhibited high selectivity and efficiency for the affinity capture of storage proteins, leading to the quantitative detection at 0.5% GM soya, which is a level below the current European Union's threshold for food labeling. The square correlation coefficients were greater than 0.99. The approach for sample preparation is very simple without the need for time‐consuming protein prefractionation or separation procedures and thus presents a significant improvement over existing methods for the analysis of the GM soya protein. 相似文献
109.
Markin G. V. Ketkov S. Yu. Lopatin M. A. Kuropatov V. A. Shavyrin A. S. Belikov A. A. 《Russian Chemical Bulletin》2020,69(4):751-757
Russian Chemical Bulletin - The sodium and bis(arene)chromium salts of monosubstituted hydrofullerides, containing bis(3,4-dimethoxyphenyl)phenylmethane, 2,6-bis(4-methoxyphenyl)-4-phenylpyridine,... 相似文献
110.
International Applied Mechanics - The plane contact problem of the transfer of a horizontal load from a weakly inhomogeneous infinite stringer to a prestressed elastic strip clamped at one edge is... 相似文献