全文获取类型
收费全文 | 3397篇 |
免费 | 466篇 |
国内免费 | 336篇 |
专业分类
化学 | 2635篇 |
晶体学 | 44篇 |
力学 | 152篇 |
综合类 | 16篇 |
数学 | 317篇 |
物理学 | 1035篇 |
出版年
2024年 | 6篇 |
2023年 | 40篇 |
2022年 | 42篇 |
2021年 | 102篇 |
2020年 | 107篇 |
2019年 | 123篇 |
2018年 | 100篇 |
2017年 | 80篇 |
2016年 | 148篇 |
2015年 | 172篇 |
2014年 | 199篇 |
2013年 | 258篇 |
2012年 | 321篇 |
2011年 | 295篇 |
2010年 | 202篇 |
2009年 | 213篇 |
2008年 | 259篇 |
2007年 | 202篇 |
2006年 | 173篇 |
2005年 | 177篇 |
2004年 | 121篇 |
2003年 | 109篇 |
2002年 | 112篇 |
2001年 | 65篇 |
2000年 | 46篇 |
1999年 | 48篇 |
1998年 | 42篇 |
1997年 | 27篇 |
1996年 | 30篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1980年 | 24篇 |
1978年 | 19篇 |
1977年 | 46篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1974年 | 11篇 |
1973年 | 5篇 |
1970年 | 5篇 |
1968年 | 5篇 |
1943年 | 10篇 |
排序方式: 共有4199条查询结果,搜索用时 15 毫秒
51.
纳米级金膜微电极的制作,表征及异相催化反应 总被引:1,自引:0,他引:1
报道了纳米级金膜微电极的制作方法,用XPS及SEM对电极表面进行了表征,考察了该电极的循环伏安及计时电流特性,在聚吡咯修饰微带金电极上成功地实现了葡萄糖氧化酶和电子传递媒体Fe(CN)6^3-的同时固定,并研究了GOD/Fe(CN)6^3-/PPy微酶电极对葡萄糖的响应,稳态响应电流与葡萄糖浓度之间存在Michealis-Menten动力学特征。 相似文献
52.
53.
Ja. L. Goldfarb Ju. B. Volkentein L. I. Belenkij 《Angewandte Chemie (International ed. in English)》1968,7(7):519-529
Under normal conditions, thiophene and furan derivatives are substituted in the α position, and no convenient alternative methods for the preparation of β-substitution products have been available until now. The present article describes a method that permits the synthesis of many β-substituted thiophenes and furans. In this method, the carbonyl group in α-aldehydes or ketones of the thiophene and furan series is blocked by complex formation with an excess of aluminum chloride, so that electrophilic substitution takes place in position 4. In another useful method, the carbonyl group is blocked by acetalization. The acetals can be metalated in the ring by organolithium compounds. 相似文献
54.
"Click chemistry" 1,3-dipolar cycloaddition between alkynyl 6-carboxyfluorescein (FAM) and azido-labeled single-stranded (ss) DNA was carried out under aqueous conditions to produce FAM-labeled ssDNA in quantitative yield. The FAM-labeled ssDNA was successfully used as a primer to produce DNA sequencing products with single-base resolution in a capillary electrophoresis DNA sequencer with laser-induced fluorescence detection. 相似文献
55.
56.
The repression of glucose oxidase (GOD) biosynthesis by catabolites during fermentation can be alleviated through membrane dialysis fermentation (MDF). The results show that the volumetric enzyme productivity of MDF was two times higher than that of the control (fermentation without dialysis), and its total enzyme activity was increased by 30–50%. The operation conditions of MDF, such as pore size of the membrane, initiating time for membrane dialysis, and volume of dialysate used, were optimized. The content of amino acids and organic acids in the fermentation broth and the dialysate in the reservoir were assessed by amino acid analyzer and ionic chromatography, respectively. The relationship among the contents of pyruvic acid, gluconic acid, and enzyme activity during fermentation was analyzed quantitatively. Furthermore, the effect of membrane dialysis technology applied to the low-yield strain was found to be more effective than that applied to the high-yield strain. 相似文献
57.
Wieczorek-Ciurowa K. Gamrat K. Shirokov Ju. G. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):323-328
A catalytic action of the mechanochemical products of copper hydroxocarbonate with calcium carbonate was investigated in n-butyl
alcohol oxidation tests. The solid products of high-energy milling were identified using thermogravimetry supplemented by
X-ray diffraction method. It was shown that the mechanical activation induces more effective tested catalyst because it promotes
the alcohol conversion at lower temperatures than that unmilled one.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
58.
Ju Wang Zuo Yin Yang Xiu Li Wang Jing Chang Zhang Wei Liang Cao State Key Laboratory of Chemical Resource Engineering Faculty of Science Beijing University of Chemical Technology Beijing China 《中国化学快报》2007,18(2):244-246
The conformational conversion of 1,3-dioxane guest encapsulated inside a cylindrical capsular host was investigated with PM3 method and single point energies were evaluated by B3LYP method. When entrapped in the capsule, the guest tumbles were slower than that in the free condition. The influences of the inner phase of the capsule on the guest conformational conversion were discussed in detail. 相似文献
59.
Hong-Wen Hu Xu-Dong Wei Cun Li Hong-Zhe Sun Yi-Ming Yao Zhong-Yuan Zhou Kai-Bei Yu 《中国化学》1992,10(3):278-284
The reaction of m-chlorobenzaldoxime dehydrodimer with styrene gives two 1:1 adducts.The main product 7 is a bisnitrone. The minor product 8 has been shown by X-ray diffraction anal-ysis to possess the structure: ArCH(N=O)CH_2CH (Ph)O--N=CHAr. The two C=N bonds areall in Z configuration. The structure of the adducts from benzaldoxime dehydrodimer and styrene isalso assigned. 相似文献
60.
Asymmetric silyl nitronate cycloadditions with N-acryloyl (2R)-bornane-10,2-sultam, N-acryloyl (2S)-bornane-10,2-sultam, and N-methacryloyl (2R)-bornane-10,2-sultam have been studied. The asymmetric silyl nitronate cycloaddidon/elimination methodology provides a general route for the asymmetric synthesis of 2-isoxazolines. 相似文献