全文获取类型
收费全文 | 1850篇 |
免费 | 49篇 |
国内免费 | 7篇 |
专业分类
化学 | 1358篇 |
晶体学 | 3篇 |
力学 | 37篇 |
数学 | 284篇 |
物理学 | 224篇 |
出版年
2021年 | 23篇 |
2020年 | 36篇 |
2019年 | 29篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 41篇 |
2014年 | 45篇 |
2013年 | 70篇 |
2012年 | 80篇 |
2011年 | 96篇 |
2010年 | 57篇 |
2009年 | 64篇 |
2008年 | 87篇 |
2007年 | 72篇 |
2006年 | 67篇 |
2005年 | 63篇 |
2004年 | 73篇 |
2003年 | 60篇 |
2002年 | 63篇 |
2001年 | 42篇 |
2000年 | 26篇 |
1999年 | 27篇 |
1998年 | 18篇 |
1997年 | 38篇 |
1996年 | 28篇 |
1995年 | 13篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 27篇 |
1986年 | 25篇 |
1985年 | 34篇 |
1984年 | 26篇 |
1983年 | 21篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 27篇 |
1978年 | 27篇 |
1977年 | 28篇 |
1976年 | 38篇 |
1975年 | 16篇 |
1974年 | 18篇 |
1973年 | 25篇 |
1972年 | 16篇 |
1970年 | 13篇 |
排序方式: 共有1906条查询结果,搜索用时 15 毫秒
41.
In a systematic study of the transfer process to sulphur dioxide, in seven different H2 + SO2 gas mixtures, the time spectra of the muonic sulphur X-rays yield muon transfer rates to the SO2 molecule, deduced from the lifetimes of the p atoms, which agree all well with each other. The muonic oxygen time spectra show an additional structure as if p atoms of another kind were present. Reduced transfer ratesO are reproducible if one uses the model of ephemeral p atoms. The intensity ratios between the different kinds of p atoms are also discussed in the framework of this model and the one of black and white p atoms. 相似文献
42.
Hubert Delange 《Monatshefte für Mathematik》1993,116(3-4):175-196
Let (n) be the number of prime divisors ofn, counted with multiplicity. We denote byS(x, k) the set of thenx for which (n)=k, and byV
p(n) the exponent of the primep in the factorization ofn. In a previous paper we proved a result which implies that, ify=x/2
k
tends to infinity withk>2loglogx where >1, then the distribution of the numbers
on the setS(x, k) converges to the normal distribution of Gauss. Here, besides a slight improvement of that result, we give, for the moment of orderq of the above mentioned distribution, a formula which holds uniformly for 2loglogxklog (x/3)/log2 where 1<<3/2. 相似文献
43.
Jagoda M Warzeska S Pritzkow H Wadepohl H Imhof P Smith JC Krämer R 《Journal of the American Chemical Society》2005,127(43):15061-15070
For a number of phosphoryltransfer enzymes, including the exonuclease subunit of DNA polymerase I, a mechanism involving two-metal ions and double Lewis-acid activation of the substrate, combined with leaving group stabilization, has been proposed. Inspired by the active site structure of this enzyme, we have designed as a synthetic phosphoryl transfer catalyst the dicopper(II) macrocyclic complex LCu(2). Crystal structures of complexes [(L)Cu(2)(mu-NO(3))(NO(3))](NO(3))(2) (1), [(L)Cu(2)(mu-CO(3))(CH(3)OH)](BF(4))(2) (2), and [(L)Cu(2)(mu-O(2)P(OCH(3))(2))(NO(3))](NO(3))(2) (3) illustrate various possibilities for the interaction of oxoanions with the dicopper(II) site. 1 efficiently promotes the transesterification of dimethyl phosphate (DMP) in CD(3)OD, k(cat) = 2 x 10(-)(4) s(-)(1) at 55 degrees C. 1 is the only available catalyst for the smooth transesterification of highly inert simple dialkyl phosphates. From photometric titrations and the pH dependence of reactivity, we conclude that a complex [(L)Cu(2)(DMP)(OCH(3))](2+) is the reactive species. Steric bulk at the -OR substituents of phosphodiester substrates O(2)P(OR)(2)(-) drastically reduces the reactivity of 1. This is explained with -OR leaving group stabilization by Cu coordination, an interaction which is sensitive to steric crowding at the alpha-C-atom of substituent R. A proposed reaction mechanism related to that of the exonuclease unit of DNA polymerase I is supported by DFT calculations on reaction intermediates. The complex [(L)Cu(3)(mu(3)-OH)(mu-CH(3)O)(2)(CH(3)CN)(2)](ClO(4))(3) (4) incorporates a [Cu(OH)(OCH(3))(2)(CH(3)CN)(2)](-) complex anion, which might be considered as an analogue of the [PO(2)(OCH(3))(2)(OCD(3))](2)(-) transition state (or intermediate) of DMP transesterification catalyzed by LCu(2). 相似文献
44.
The reaction of acetone-4-chlorophenylhydrazone (6) with bromine in the presence of acetamide yields 2-bromo-2-(4-chlorophenylazo)-propane (7) and 2,2-bis(4-chlorophenylazo)propane (8). The unstable heteroallylic bromide7 was subjected without isolation to nucleophilic displacements with a series of heteronucleophiles thereby affording the corresponding 2-(4-chlorophenylazo)-2-propane derivatives9 with the azo- and heteroelement-functions in a geminal position to each other.
Herrn Prof. Dr. Dr. h. c.K. Kratzl mit den besten Wünschen zum 70. Geburtstag gewidmet. 相似文献
45.
A sensor for measuring adsorption on a substrate has been designed including a contactless detection scheme, called supercapacitive admittance tomoscopy (SCAT). The sensor comprises a thin dielectric layer with two parallel band electrodes on the one side and a chemically modified surface on the other onto which the adsorption of molecules occurs. Upon application of a high frequency ac voltage between the two electrodes, a capacitive coupling is established across the dielectric layer, and the admittance measured depends on the surface state of the chemically modified interface. On the basis of this principle, a flow sensor has been developed to measure sensorgrams to follow the dynamics of the adsorption and has been tested for the adsorption of IgG on the modified surface. 相似文献
46.
47.
48.
N. Balbi J. H. Balbi L. Elegant Y. Girault 《Journal of Thermal Analysis and Calorimetry》1991,37(10):2347-2352
It is possible to study the problems of thermal regulation and energy storage by utilizing chemical reactions. For this purpose, a method of dynamic and global modelling is used to determine the enthalpy of reaction of formic acid and triethylamine. 相似文献
49.
Michael?Sch?ferlingEmail author Michael?Riepl Petra?Pavlickova Hubert?Paul Dev?Kambhampati Bo?Liedberg 《Mikrochimica acta》2003,142(4):193-203
Two different types of -substituted alkanethiol/disulfide compounds have been used to prepare monolayer architectures on gold serving as platforms for the immobilization of receptor probe molecules – antibodies. These are: (i) carboxylic acid alkanethiols post-reacted with amino biotin to generate streptavidin surfaces, and (ii) N-hydroxysuccinimide-terminated disulfide surfaces. The properties of the monolayers, with and without attached receptor probe molecules, were analysed using infrared spectroscopy, ellipsometry, fluorescence scanning and atomic force microscopy. Several experimental parameters, such as condensation reagents, additives, probe and target concentrations and immobilization time, were systematically varied to determine the dynamic range and to optimize the sensitivity and signal-to-noise ratio of the biochip platforms. Fluorescence screening using Cy5-labelled antigens finally demonstrated that both surfaces could be successfully employed to immobilize the antibodies. The pros and cons of the two approaches are also discussed.Received November 15, 2002; accepted March 25, 2003
Published online July 28, 2003 相似文献
50.
Hubert TD Vue C Bernardy JA Van Horsen DL Rossulek MI 《Journal of AOAC International》2001,84(2):392-398
3-Trifluoromethyl-4-nitrophenol (TFM) is a pesticide used for the selective control of sea lampreys (Petromyzon marinus) in stream and river tributaries of the Great Lakes. To determine concentrations of TFM and TFM glucuronide in the edible fillet tissue of fish during sea lamprey control treatments, an analytical method was developed to determine the concentrations of these residues in rainbow trout (Oncorhynchus mykiss; RBT) and channel catfish (Ictalurus punctatis; CCF). Homogenized fillets were extracted with methanol-water (80 + 20). TFM and TFM glucuronide were isolated from coextractives by C18 solid-phase extraction. TFM glucuronide was hydrolyzed to TFM by the addition of beta-glucuronidase to the TFM glucuronide extract. The extracts were analyzed separately by liquid chromatography with UV-visible detection. Recoveries from TFM-fortified CCF and RBT tissues were 84.1 and 96.1%, respectively. The method detection limits (MDLs) are 2.4 ng/g for TFM-fortified tissues of CCF and 3 ng/g for those of RBT. Recoveries were 78.8 and 77% from TFM glucuronide-fortified CCF and RBT tissues, respectively. The MDLs for TFM glucuronide-fortified tissues are 3.5 and 6.9 ng/g for CCF and RBT, respectively. 相似文献