全文获取类型
收费全文 | 1134篇 |
免费 | 43篇 |
国内免费 | 20篇 |
专业分类
化学 | 611篇 |
晶体学 | 2篇 |
力学 | 59篇 |
数学 | 340篇 |
物理学 | 185篇 |
出版年
2023年 | 12篇 |
2022年 | 39篇 |
2021年 | 44篇 |
2020年 | 50篇 |
2019年 | 46篇 |
2018年 | 49篇 |
2017年 | 39篇 |
2016年 | 57篇 |
2015年 | 26篇 |
2014年 | 48篇 |
2013年 | 92篇 |
2012年 | 64篇 |
2011年 | 60篇 |
2010年 | 46篇 |
2009年 | 35篇 |
2008年 | 56篇 |
2007年 | 52篇 |
2006年 | 28篇 |
2005年 | 29篇 |
2004年 | 29篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1987年 | 7篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1197条查询结果,搜索用时 15 毫秒
871.
Pham Tien Dung 《Analysis Mathematica》2009,35(4):289-299
The result of Golubov [5, Theorem 2] on the boundedness of the Hardy-Littlewood operator $$ \mathcal{B}f(x): = \frac{1} {x}\int_0^x {f(t)} dt $$ in the space BMO(?) is well known. The author of the present paper solves the analogous problem in the weighted space BMO on the semi-axis ?+ for the operator $$ T_w f(x): = \frac{1} {{W(x)}}\int_0^x {f(t)w(t)} dt $$ and also in the classical space BMO(?+) for a class of integral operators involving, for example, the Riemann-Liouville fractional integral. 相似文献
872.
In this paper, we consider the case of downside risk measures with cardinality and bounding constraints in portfolio selection.
These constraints limit the amount of capital to be invested in each asset as well as the number of assets composing the portfolio.
While the standard Markowitz’s model is a convex quadratic program, this new model is a NP-hard mixed integer quadratic program.
Realizing the computational intractability for this class of problems, especially large-scale problems, we first reformulate
it as a DC program with the help of exact penalty techniques in Difference of Convex functions (DC) programming and then solve
it by DC Algorithms (DCA). To check globality of computed solutions, a global method combining the local algorithm DCA with
a Branch-and-Bound algorithm is investigated. Numerical simulations show that DCA is an efficient and promising approach for
the considered problem.
相似文献
873.
The value-at-risk is an important risk measure that has been used extensively in recent years in portfolio selection and in
risk analysis. This problem, with its known bilevel linear program, is reformulated as a polyhedral DC program with the help
of exact penalty techniques in DC programming and solved by DCA. To check globality of computed solutions, a global method
combining the local algorithm DCA with a well adapted branch-and-bound algorithm is investigated. An illustrative example
and numerical simulations are reported, which show the robustness, the globality and the efficiency of DCA. 相似文献
874.
2-Methylarsino-ethanol Synthesis and reactions of 2-methylarsino-ethanol MeAs(H)? CH2CH2? OH are described. These reactions result in the formation of bifunctional arsanes of the general formula MeAs(CH2CH2? X)2 and MeAs(CH2CH2? X)CH2CH2? Y, respectively, with different groups X and Y. 相似文献
875.
876.
Methods for the preparation of geometrically defined enoxy(trichlorosilanes) derived from ethyl ketone enolates have been developed. The addition of enoxy(trichlorosilanes) (trichlorosilyl enolates) to aldehydes proceeds with good yields in the presence of catalytic amounts of chiral phosphoramides. The reaction of Z-trichlorosilyl enolates to aryl aldehydes affords aldol products with good to excellent diastereo- and enantioselectivities. Phosphoramide-catalyzed aldol additions lacked substrate generality providing modest selectivities with unsaturated and aliphatic aldehydes. In all cases, the phosphoramide-catalyzed aldol addition of E-trichlorosilyl enolates to aldehydes provided good yields with moderate to good stereoselectivities. 相似文献
877.
Minh PT Ngoc PH Quang DN Hashimoto T Takaoka S Asakawa Y 《Chemical & pharmaceutical bulletin》2003,51(5):590-591
A novel ent-kaurane diterpenoid, ent-1alpha-acetoxy-7beta,14alpha-dihydroxy-kaur-16-en-15-on has been isolated from leaves of Croton tonkinensis GAGNEP. Its structure was determined by a combination of spectroscopy, X-ray crystallographic analysis and the chemical reaction acetylation. 相似文献
878.
Pham Anh Minh 《Proceedings of the American Mathematical Society》2003,131(2):363-368
Let be an odd prime number. The purpose of this paper is to provide a -group whose mod- cohomology ring has a nilpotent element satisfying .
879.
Pham Anh Minh 《Transactions of the American Mathematical Society》2001,353(5):1937-1957
Let be an odd prime number and let be an extraspecial -group. The purpose of the paper is to show that has no non-zero essential mod- cohomology (and in fact that is Cohen-Macaulay) if and only if and .
880.
Complexes of the Ni2+ and Co2+ Ions with Sulfides and Selenides of di-, tri-, and tetratertiary Arsanes The reaction of the sulfides (selenides) of di-, tri- and tetra-tertiary arsanes with the salts CoCl2 · 6 H2O respectively Ni(ClO4)2 · 6 H2O results in the formation of chelat complexes, in which the metal ions are tetrahedrally surrounded by the ligands. The UV spectra of the complexes are discussed. 相似文献