全文获取类型
收费全文 | 346534篇 |
免费 | 4943篇 |
国内免费 | 1179篇 |
专业分类
化学 | 185183篇 |
晶体学 | 4381篇 |
力学 | 14611篇 |
综合类 | 10篇 |
数学 | 41637篇 |
物理学 | 106834篇 |
出版年
2021年 | 2292篇 |
2020年 | 2790篇 |
2019年 | 2837篇 |
2018年 | 3356篇 |
2017年 | 3415篇 |
2016年 | 6000篇 |
2015年 | 4246篇 |
2014年 | 6051篇 |
2013年 | 16203篇 |
2012年 | 12410篇 |
2011年 | 15165篇 |
2010年 | 10030篇 |
2009年 | 10033篇 |
2008年 | 14196篇 |
2007年 | 14102篇 |
2006年 | 13301篇 |
2005年 | 12166篇 |
2004年 | 10959篇 |
2003年 | 9656篇 |
2002年 | 9414篇 |
2001年 | 10698篇 |
2000年 | 8196篇 |
1999年 | 6279篇 |
1998年 | 5045篇 |
1997年 | 4953篇 |
1996年 | 4896篇 |
1995年 | 4459篇 |
1994年 | 4286篇 |
1993年 | 4133篇 |
1992年 | 4578篇 |
1991年 | 4422篇 |
1990年 | 4165篇 |
1989年 | 4028篇 |
1988年 | 4063篇 |
1987年 | 3961篇 |
1986年 | 3769篇 |
1985年 | 5376篇 |
1984年 | 5423篇 |
1983年 | 4547篇 |
1982年 | 4806篇 |
1981年 | 4554篇 |
1980年 | 4476篇 |
1979年 | 4559篇 |
1978年 | 4716篇 |
1977年 | 4602篇 |
1976年 | 4583篇 |
1975年 | 4445篇 |
1974年 | 4353篇 |
1973年 | 4578篇 |
1972年 | 2796篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
V. A. Bespalov V. M. Glazov E. A. Il’ichev Yu. A. Klimov S. V. Kuklev A. E. Kuleshov R. M. Nabiev G. N. Petrukhin B. G. Potapov G. S. Rychkov D. S. Sokolov V. V. Fandeev E. A. Fetisov S. S. Yakushov 《Technical Physics》2015,60(4):553-560
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied. 相似文献
52.
53.
Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides 下载免费PDF全文
Anna Ulmer Dr. Maciej Stodulski Stefanie V. Kohlhepp Christoph Patzelt Dr. Alexander Pöthig Dr. Wolfgang Bettray Dr. Tanja Gulder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1444-1448
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
54.
55.
Unexpected benzimidazole ring formation from a quinoneimide species in the presence of ammonium acetate as supporting electrolyte used in the coupling of electrochemistry with mass spectrometry 下载免费PDF全文
56.
57.
ABSTRACTThis study was to investigate the piezotolerance and diversity indices of microflora of Indian white prawn (Fenneropenaeus indicus) after high pressure (HP)-treatment. Indian white prawns subjected to HP-treatments and its effect was studied up to species level and compared with unpressurized samples. The bacterium was identified by using bacterial identification schemes, biochemical tests and API kits (bioMérieux, Marcyl’Etoile, France). Diversity analysis was performed using PRIMER (Plymouth Routines in Multivariate Research) software v 5.2.2. The significant elimination of microflora was found to be proportional with the pressure level. In the case of spore formers, mere destruction was noticed after HP-treatment. Arthrobacter spp., Listeria grayi and Corynebacterium spp. were the most piezotolerant bacteria in HP-treated samples. Diversity indices revealed a significant reduction of microflora of Indian white prawn. The apparent reduction of microflora with pressure level was clearly evident from the diversity indices; moreover a diminished piezotolerance of Gram negative spoilage bacteria was also observed. 相似文献
58.
Timm Bergholz Dr. Benjamin Oelkers Dr. Benedikt Huber Prof. Bernhard Roling Prof. Dr. Jörg Sundermeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2613-2620
New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C2N5]? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries. 相似文献
59.
60.
Ahmed Waqar Chowdhury Z. Z. Kazi S. N. Johan MR. Akram Naveed Oon C. S. Abdelrazek Ali H. 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1517-1534
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers... 相似文献