全文获取类型
收费全文 | 32791篇 |
免费 | 1093篇 |
国内免费 | 249篇 |
专业分类
化学 | 22748篇 |
晶体学 | 223篇 |
力学 | 769篇 |
数学 | 5445篇 |
物理学 | 4948篇 |
出版年
2022年 | 284篇 |
2021年 | 420篇 |
2020年 | 517篇 |
2019年 | 488篇 |
2018年 | 376篇 |
2017年 | 372篇 |
2016年 | 838篇 |
2015年 | 738篇 |
2014年 | 810篇 |
2013年 | 1739篇 |
2012年 | 1875篇 |
2011年 | 2363篇 |
2010年 | 1152篇 |
2009年 | 1007篇 |
2008年 | 2020篇 |
2007年 | 2027篇 |
2006年 | 2006篇 |
2005年 | 1873篇 |
2004年 | 1596篇 |
2003年 | 1385篇 |
2002年 | 1282篇 |
2001年 | 406篇 |
2000年 | 391篇 |
1999年 | 363篇 |
1998年 | 337篇 |
1997年 | 361篇 |
1996年 | 486篇 |
1995年 | 347篇 |
1994年 | 299篇 |
1993年 | 270篇 |
1992年 | 269篇 |
1991年 | 238篇 |
1990年 | 202篇 |
1989年 | 203篇 |
1988年 | 232篇 |
1987年 | 198篇 |
1986年 | 180篇 |
1985年 | 349篇 |
1984年 | 339篇 |
1983年 | 242篇 |
1982年 | 313篇 |
1981年 | 324篇 |
1980年 | 299篇 |
1979年 | 282篇 |
1978年 | 258篇 |
1977年 | 228篇 |
1976年 | 206篇 |
1975年 | 212篇 |
1974年 | 212篇 |
1973年 | 211篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
François Loiseau Jean-Mary Simone David Carcache Pavel Bobal Reinhard Neier 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):121-129
Summary. Free radical couplings from furan, as cheap starting material, were studied in view of developing a rapid strategy en route to the synthesis of derivatives of nonactin. The chain containing the alcohol function was introduced in one or two steps
in 86% yield. For the introduction of the second chain with the ester function two different coupling methods were tested.
Starting from the advanced intermediates obtained nonactin derivatives can be prepared by catalytic hydrogenation of the furan
ring. 相似文献
102.
David Worthington 《The Journal of the Operational Research Society》1991,42(10):833-843
This paper describes work carried out with hospital consultants in Lancaster District Health Authority to develop and use computerized waiting list management models. The ‘what if?’ models produced have been found to be a very useful tool in the constructive debate about problems faced by consultants and managers, and of the options available to them. 相似文献
103.
104.
We analyze an infinite horizon, single product, continuous review model in which pricing and inventory decisions are made simultaneously and ordering cost includes a fixed cost. We show that there exists a stationary (s,S) inventory policy maximizing the expected discounted or expected average profit under general conditions. 相似文献
105.
David L. Applegate 《Operations Research Letters》2007,35(6):693-699
The use of floating-point calculations limits the accuracy of solutions obtained by standard LP software. We present a simplex-based algorithm that returns exact rational solutions, taking advantage of the speed of floating-point calculations and attempting to minimize the operations performed in rational arithmetic. Extensive computational results are presented. 相似文献
106.
We give a new independent self-dual 3-basis for the trivial variety with two binary operations.
Received October 24, 2006; accepted in final form January 25, 2007. 相似文献
107.
108.
109.
David Loffreda 《Surface science》2006,600(10):2103-2112
Adsorption thermodynamics based on density functional theory (DFT) calculations are exposed for the interaction of several multifunctional molecules with Pt and Au(1 1 0)-(1 × 2) surfaces. The Gibbs free adsorption energy explicitly depends on the adsorption internal energy, which is derived from DFT adsorption energy, and the vibrational entropy change during the chemisorption process. Zero-point energy (ZPE) corrections have been systematically applied to the adsorption energy. Moreover the vibrational entropy change has been computed on the basis of DFT harmonic frequencies (gas and adsorbed phases, clean surfaces), which have been extended to all the adsorbate vibrations and the metallic surface phonons. The phase diagrams plotted in realistic conditions of temperature (from 100 to 400 K) and pressure (0.15 atm) show that the ZPE corrected adsorption energy is the main contribution. When strong chemisorption is considered on the Pt surface, the multifunctional molecules are adsorbed on the surface in the considered temperature range. In contrast for weak chemisorption on the Au surface, the thermodynamic results should be held cautiously. The systematic errors of the model (choice of the functional, configurational entropy and vibrational entropy) make difficult the prediction of the adsorption-desorption phase boundaries. 相似文献
110.
We present an algorithm which calculates the monopole number of anSU
2-valued lattice gauge field, together with a lattice Higgs field, on a simplicial lattice of dimension ≧3. The calculation
is gauge invariant. The expected value of the monopole density (for a fixed Higgs field) does not depend on the Higgs field.
Partially supported by NSF grants DMS 8607168 and DMS 8907753
Partially supported by PSC-CUNY and by NSF grant DMS 8805485 相似文献