全文获取类型
收费全文 | 16856篇 |
免费 | 629篇 |
国内免费 | 8篇 |
专业分类
化学 | 9581篇 |
晶体学 | 52篇 |
力学 | 295篇 |
数学 | 2425篇 |
物理学 | 5140篇 |
出版年
2023年 | 126篇 |
2021年 | 134篇 |
2020年 | 203篇 |
2019年 | 135篇 |
2018年 | 169篇 |
2017年 | 171篇 |
2016年 | 394篇 |
2015年 | 369篇 |
2014年 | 363篇 |
2013年 | 718篇 |
2012年 | 662篇 |
2011年 | 873篇 |
2010年 | 382篇 |
2009年 | 332篇 |
2008年 | 753篇 |
2007年 | 750篇 |
2006年 | 714篇 |
2005年 | 620篇 |
2004年 | 491篇 |
2003年 | 460篇 |
2002年 | 406篇 |
2001年 | 380篇 |
2000年 | 313篇 |
1999年 | 260篇 |
1998年 | 215篇 |
1997年 | 218篇 |
1996年 | 228篇 |
1995年 | 211篇 |
1994年 | 206篇 |
1993年 | 231篇 |
1992年 | 226篇 |
1991年 | 193篇 |
1990年 | 154篇 |
1989年 | 155篇 |
1988年 | 145篇 |
1987年 | 157篇 |
1986年 | 176篇 |
1985年 | 194篇 |
1984年 | 224篇 |
1983年 | 196篇 |
1982年 | 219篇 |
1981年 | 232篇 |
1980年 | 204篇 |
1979年 | 181篇 |
1978年 | 213篇 |
1977年 | 199篇 |
1976年 | 174篇 |
1975年 | 151篇 |
1974年 | 153篇 |
1973年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Photoelectrochemical Hydrogen Production in Alkaline Solutions Using Cu2O Coated with Earth‐Abundant Hydrogen Evolution Catalysts 下载免费PDF全文
Carlos G. Morales‐Guio Laurent Liardet Dr. Matthew T. Mayer Dr. S. David Tilley Prof. Dr. Michael Grätzel Prof. Dr. Xile Hu 《Angewandte Chemie (International ed. in English)》2015,54(2):664-667
The splitting of water into hydrogen and oxygen molecules using sunlight is an attractive method for solar energy storage. Until now, photoelectrochemical hydrogen evolution is mostly studied in acidic solutions, in which the hydrogen evolution is more facile than in alkaline solutions. Herein, we report photoelectrochemical hydrogen production in alkaline solutions, which are more favorable than acidic solutions for the complementary oxygen evolution half‐reaction. We show for the first time that amorphous molybdenum sulfide is a highly active hydrogen evolution catalyst in basic medium. The amorphous molybdenum sulfide catalyst and a Ni–Mo catalyst are then deposited on surface‐protected cuprous oxide photocathodes to catalyze sunlight‐driven hydrogen production in 1 M KOH. The photocathodes give photocurrents of ?6.3 mA cm?2 at the reversible hydrogen evolution potential, the highest yet reported for a metal oxide photocathode using an earth‐abundant hydrogen evolution reaction catalyst. 相似文献
952.
Enzyme‐ and Ruthenium‐Catalyzed Enantioselective Transformation of α‐Allenic Alcohols into 2,3‐Dihydrofurans 下载免费PDF全文
Bin Yang Dr. Can Zhu Dr. Youai Qiu Prof. Dr. Jan‐E. Bäckvall 《Angewandte Chemie (International ed. in English)》2016,55(18):5568-5572
An efficient one‐pot method for the enzyme‐ and ruthenium‐catalyzed enantioselective transformation of α‐allenic alcohols into 2,3‐dihydrofurans has been developed. The method involves an enzymatic kinetic resolution and a subsequent ruthenium‐catalyzed cycloisomerization, which provides 2,3‐dihydrofurans with excellent enantioselectivity (up to >99 % ee). A ruthenium carbene species was proposed as a key intermediate in the cycloisomerization. 相似文献
953.
Immunoassay methods for paralytic shellfish poisoning toxins 总被引:1,自引:0,他引:1
Usleber E Dietrich R Bürk C Schneider E Märtlbauer E 《Journal of AOAC International》2001,84(5):1649-1656
The current status of immunochemical techniques for analysis of paralytic shellfish poisoning (PSP) toxins is summarized. Important aspects regarding production of the biological reagents necessary for immunochemical methods, the characteristics of polyclonal and monoclonal antibodies against saxitoxin and neosaxitoxin, and the importance of test sensitivity and specificity are discussed. Applications of immunochemical techniques for PSP toxins include microtiter plate enzyme immunoasays and enzyme-linked immunofiltration assays for toxin detection, and immunoaffinity chromatography (IAC) for sample extract cleanup. A major advantage of enzyme immunoassay (EIA) is simplicity and rapidity of the test procedure, and higher sensitivity than other methods. However, quantitative agreement between EIA and mouse bioassay is dependent on antibody specificity and the toxin profile in the shellfish; thus, both over- and underestimation of total toxicity may occur. For screening purposes, however, EIAs offer major advantages over the mouse bioassay, which is criticized in Europe because of animal welfare. A major application of antibodies against PSP toxins is their use for extract cleanup by IAC, which gives highly purified extracts, thereby enhancing determination of PSP toxins by conventional physicochemical methods such as liquid chromatography. IAC can also be used to isolate PSP toxins for preparation of analytical standard solutions. 相似文献
954.
955.
956.
Prediction of the ageing of rubber using the chemiluminescence approach and isoconversional kinetics
A common scepticism towards the application of many product formulations results from the fact that their long-term stability
is difficult to predict. In the present study we report on a new approach of kinetic analysis of the oxidation reactions of
natural rubbers with and without stabiliser in an oxygen atmosphere at moderate temperatures using CL measurements carried
out on a newly-developed instrumentation. The kinetic parameters of the oxidation process, calculated from the chemiluminescence’s
signals by means of the differential isoconversional method of Friedman, were subsequently applied for the simulation of the
rubber aging under different temperature profiles. The presented results are the first stage of research by using the chemiluminescence
method to measure the oxidative aging of rubber and predicting the life time of rubber items. 相似文献
957.
Kami K. Thoen Diane Tutko Thilini D. Ranatunga Hilkka I. Kenttämaa 《Journal of the American Society for Mass Spectrometry》1996,7(11):1138-1143
The usefulness of CH3OBOCH 3 + as a chemical ionization reagent was examined by allowing the ion to react with carboxylic esters of various chain lengths in a small Fourier-transform ion cyclotron resonance mass spectrometer equipped with a permanent magnet. CH3OBOCH 3 + is a strong electrophile and readily abstracts an oxygen-containing group from the carboxylic esters. Long-chain esters exclusively lose the alkoxide moiety to give the acylium ion. The same reaction was observed for saturated, unsaturated, branched and cyclic esters. In each case, the acylium ion reacts further with a neutral ester molecule by proton transfer to yield the protonated ester as a secondary product. This remarkably simple product distribution reveals the molecular weight of the ester, the chain length of its acid moiety, and the degree of unsaturation in the acid and alcohol moieties. 相似文献
958.
959.
960.
Cappelluti E Ciuchi S Grimaldi C Pietronero L Strässler S 《Physical review letters》2002,88(11):117003
The evidence for the key role of the sigma bands in the electronic properties of MgB2 points to the possibility of nonadiabatic effects in the superconductivity of these materials. These are governed by the small value of the Fermi energy due to the vicinity of the hole doping level to the top of the sigma bands. We show that the nonadiabatic theory leads to a coherent interpretation of T(c) = 39 K and the boron isotope coefficient alphaB = 0.30 without invoking very large couplings and it naturally explains the role of the disorder on T(c). It also leads to various specific predictions for the properties of MgB2 and for the material optimization of these types of compounds. 相似文献