全文获取类型
收费全文 | 35535篇 |
免费 | 454篇 |
国内免费 | 378篇 |
专业分类
化学 | 15617篇 |
晶体学 | 298篇 |
力学 | 1757篇 |
综合类 | 12篇 |
数学 | 9623篇 |
物理学 | 9060篇 |
出版年
2023年 | 56篇 |
2022年 | 220篇 |
2021年 | 371篇 |
2020年 | 382篇 |
2019年 | 380篇 |
2018年 | 1547篇 |
2017年 | 1778篇 |
2016年 | 1171篇 |
2015年 | 881篇 |
2014年 | 905篇 |
2013年 | 1452篇 |
2012年 | 3711篇 |
2011年 | 2806篇 |
2010年 | 2128篇 |
2009年 | 1858篇 |
2008年 | 864篇 |
2007年 | 864篇 |
2006年 | 769篇 |
2005年 | 4567篇 |
2004年 | 3992篇 |
2003年 | 2388篇 |
2002年 | 559篇 |
2001年 | 310篇 |
2000年 | 102篇 |
1999年 | 192篇 |
1998年 | 124篇 |
1997年 | 86篇 |
1996年 | 62篇 |
1995年 | 49篇 |
1994年 | 55篇 |
1992年 | 181篇 |
1991年 | 162篇 |
1990年 | 143篇 |
1989年 | 113篇 |
1988年 | 103篇 |
1987年 | 70篇 |
1986年 | 46篇 |
1985年 | 48篇 |
1984年 | 41篇 |
1979年 | 35篇 |
1978年 | 32篇 |
1976年 | 84篇 |
1975年 | 39篇 |
1974年 | 41篇 |
1973年 | 51篇 |
1972年 | 39篇 |
1970年 | 34篇 |
1969年 | 38篇 |
1968年 | 37篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The electrochemical reduction of 1-([(4-halophenyl)imino]methyl)-2-naphthols on graphite electrodes was studied using cyclic voltammetry, chronoamperometry, constant-potential coulometry and preparative constant-potential electrolysis techniques. The data revealed that the reduction on graphite was irreversible and followed an EC mechanism. The diffusion coefficients and the number of electrons transferred were determined using the chronoamperometric Cottrell slope and the ultramicro disc Pt-electrode steady-state current. The number of electrons was also determined by bulk electrolysis. The compounds were subjected to constant-potential preparative electrolysis and the electrolysis products were purified and identified by spectroscopic methods. Based on these findings, a mechanism for the electro-reduction process is proposed. 相似文献
42.
Ghodratollah Absalan Mohammad Soleimani Mozaffar Asadi Mohammad Bagher Ahmadi 《Analytical sciences》2004,20(10):1433-1436
A new ammonia optical sensor was designed using bis(acetylacetoneethylendiamine)tributylphosphin cobalt(III) tetraphenylborate complex, coated on transparent triacetylcellulose film as membrane. The change in the absorbance of the optode at the maximum wavelength of 408 nm was related to ammonia concentration in aqueous samples. A buffer solution with a pH of 9 (sodium borate-HCl) was used. The optode was fully regenerated in pH 2. The linear dynamic range for determination of ammonia was 3.3 x 10(-4) to 6.9 x 10(-3) mol l(-1) with a detection limit of 5.0 x 10(-5) mol l(-1) and a response time range of 4 - 6 min. This membrane was successfully applied for determination of ammonia in drinking water. 相似文献
43.
Hamid R Zare Masoud Salavati-Niassary Farkhondeh Memarzadeh Mohammad Mazloum Navid Nasirizadeh 《Analytical sciences》2004,20(5):815-819
A novel membrane coated platinum-wire electrode (MCPWE) based on N,N'-bis(2-thienylmethylene)-1,2-diaminobenzene (BTMD) for highly selective determination of Ag+ ion has been developed. The influences of membrane composition and pH on the potentiometric responses of electrode were investigated. The potentiometric responses are independent of the pH of the test solution in the range of 5.0 - 9.0. The electrode shows a linear response for Ag+ ion over the concentration range of 1.0 x 10(-60 to 1.0 x 10(-1) M with a lower detection limit of 6.0 x 10(-7) M. The electrode possesses a Nernstian slope of 59.7 mV decade(-1) and a fast response time of < or = 17 s and can be used for at least 2 months without any observable deviation. The proposed electrode displayed very good selectivity for Ag+ ion with respect to NH4+ and alkali, alkaline earth and some common transition metal ions. The practical utility of the electrode has been demonstrated by its use as the indicator electrode in the potentiometric titration of an AgNO3 solution with a NaI solution and in determination of the silver content of a developed radiological film. 相似文献
44.
JingXiaWANG ChengYouKAN DeShanLIU 《中国化学快报》2004,15(10):1161-1163
Two novel polymerizable dyes with anthraquinone residue have been prepared, and their structures were characterized by FTIR, ^1HNMR and EA. 相似文献
45.
46.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents. 相似文献
47.
48.
LetP(z) be a polynomial of degreen which does not vanish in |z|<1. In this paper, we estimate the maximum and minimum moduli of thekth polar derivative ofP(z) on |z|=1 and thereby obtain compact generalizations of some known results, which among other results, yields interesting refinements of Erdos-Lax theorem and a theorem of Ankeny and Rivlin. 相似文献
49.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
50.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献