全文获取类型
收费全文 | 2447篇 |
免费 | 63篇 |
国内免费 | 16篇 |
专业分类
化学 | 1631篇 |
晶体学 | 16篇 |
力学 | 44篇 |
数学 | 469篇 |
物理学 | 366篇 |
出版年
2022年 | 24篇 |
2021年 | 29篇 |
2020年 | 26篇 |
2019年 | 36篇 |
2018年 | 23篇 |
2017年 | 25篇 |
2016年 | 38篇 |
2015年 | 31篇 |
2014年 | 42篇 |
2013年 | 111篇 |
2012年 | 85篇 |
2011年 | 135篇 |
2010年 | 81篇 |
2009年 | 64篇 |
2008年 | 118篇 |
2007年 | 98篇 |
2006年 | 112篇 |
2005年 | 109篇 |
2004年 | 122篇 |
2003年 | 105篇 |
2002年 | 90篇 |
2001年 | 23篇 |
2000年 | 36篇 |
1999年 | 23篇 |
1997年 | 20篇 |
1996年 | 53篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 21篇 |
1985年 | 42篇 |
1984年 | 34篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1978年 | 33篇 |
1977年 | 31篇 |
1976年 | 21篇 |
1975年 | 31篇 |
1974年 | 37篇 |
1973年 | 29篇 |
1970年 | 20篇 |
1968年 | 19篇 |
排序方式: 共有2526条查询结果,搜索用时 15 毫秒
1.
An Application of Branch and Cut to Open Pit Mine Scheduling 总被引:5,自引:0,他引:5
The economic viability of the modern day mine is highly dependent upon careful planning and management. Declining trends in average ore grades, increasing mining costs and environmental considerations will ensure that this situation will remain in the foreseeable future. The operation and management of a large open pit mine having a life of several years is an enormous and complex task. Though a number of optimization techniques have been successfully applied to resolve some important problems, the problem of determining an optimal production schedule over the life of the deposit is still very much unresolved. In this paper we will critically examine the techniques that are being used in the mining industry for production scheduling indicating their limitations. In addition, we present a mixed integer linear programming model for the scheduling problems along with a Branch and Cut solution strategy. Computational results for practical sized problems are discussed. 相似文献
2.
Summary In the present paper we study truncated projections for the fanbeam geometry in computerized tomography. First we derive consistency conditions for the divergent beam transform. Then we study a singular value decomposition for the case where only the interior rays in the fan are provided, as for example in region-of-interest tomography. We show that the high angular frequency components of the searched-for densities are well determined and we present reconstructions from real data where the missing information is approximated based on the singular value decomposition.The work of the authors was supported by the Deutsche Forschungsgemeinschaft under grant Lo 310/2-4 相似文献
3.
We prove that there is no functorial universal finite type invariant for braids in Σ×I if the genus of Σ is positive. To cite this article: P. Bellingeri, L. Funar, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
4.
Partially supported by NSF Grant DMS-9004123 and ARO through MSI Cornell (DAAG 29-85-C-0018) 相似文献
5.
Louis Block James Keesling Shihai Li Kevin Peterson 《Journal of statistical physics》1989,55(5-6):929-939
A new algorithm is presented for computing the topological entropy of a unimodal map of the interval. The accuracy of the algorithm is discussed and some graphs of the topological entropy which are obtained using the algorithm are displayed. 相似文献
6.
Jean-Jacques Jutier Even Lemieux Robert E. Prud'homme 《Journal of Polymer Science.Polymer Physics》1988,26(6):1313-1329
The miscibility of polyester/nitrocellulose blends was investigated by differential scanning calorimetry and Fourier-transform infrared (FTIR) spectroscopy. Two nitrocelluloses (NC) derived from wood and having different nitrogen contents (12.62 and 13.42%) were used. On the basis of the glass transition temperature criterion, poly(?-caprolactone) (PCL), poly(valerolactone), poly(ethylene adipate), and poly(butylene adipate) are miscible with nitrocellulose, whereas poly(α-methyl α-propyl β-propiolactone) and poly(α-methyl β-proiolactone) are immiscible. The Tg versus composition curves of PCL/NC blends do not follow a monotone function but exhibit a singular point at a critical PCL volume fraction of 0.51 for NC-1342 and 0.45 for NC-1262 in agreement with Kovacs' theory. A shift of 17 cm-1 of the carbonyl stretching band was observed with PCL/NC blends and is taken as evidence for hydrogen bonding interaction between the PCL carbonyl group and NC hydroxyl group. The frequency difference between the free hydroxyl absorbance and the absorbances of the hydrogen-bonded species was found to be 85 cm-1 in pure NC and 125 cm-1 in PCL/NC blends; it indicates that the average strength of this interaction is stronger than the corresponding self-associated hydrogen bonding in pure NC. The presence of a dipole-dipole interaction between the nitrate-ester groups of NC and the carbonyl groups of the polyesters is reported. The relative strength of the hydrogen bonding and dipole-dipole interactions is discussed and correlated with polymer miscibility. 相似文献
7.
Anne Boutet De Monvel-Berthier Louis Boutet De Monvel Gilles Lebeau 《Journal d'Analyse Mathématique》1992,58(1):39-60
Sans résumé
Dedicated to Professor Shmuel Agmon 相似文献
8.
The determination of doxazosin by high-performance liquid chromatography with fluorescence detection is described. Propanolol was used as the internal standard. Plasma samples were treated with methanol to precipitate the proteins. Doxazosin was isolated with C18 reversed-phase extraction columns. The determination limit is 1 ng/ml of plasma, while the extraction columns can be reused frequently. The method is applied to clinical trial samples. 相似文献
9.
We prove that simply connected open manifolds of bounded geometry, linear growth and sublinear filling growth (e.g. finite filling area) are simply connected at infinity. 相似文献
10.