全文获取类型
收费全文 | 11529篇 |
免费 | 2121篇 |
国内免费 | 1346篇 |
专业分类
化学 | 7948篇 |
晶体学 | 162篇 |
力学 | 802篇 |
综合类 | 105篇 |
数学 | 1250篇 |
物理学 | 4729篇 |
出版年
2024年 | 22篇 |
2023年 | 268篇 |
2022年 | 458篇 |
2021年 | 482篇 |
2020年 | 488篇 |
2019年 | 494篇 |
2018年 | 409篇 |
2017年 | 371篇 |
2016年 | 602篇 |
2015年 | 560篇 |
2014年 | 673篇 |
2013年 | 810篇 |
2012年 | 1053篇 |
2011年 | 1024篇 |
2010年 | 799篇 |
2009年 | 730篇 |
2008年 | 714篇 |
2007年 | 631篇 |
2006年 | 647篇 |
2005年 | 564篇 |
2004年 | 368篇 |
2003年 | 309篇 |
2002年 | 311篇 |
2001年 | 231篇 |
2000年 | 211篇 |
1999年 | 212篇 |
1998年 | 177篇 |
1997年 | 202篇 |
1996年 | 180篇 |
1995年 | 162篇 |
1994年 | 138篇 |
1993年 | 97篇 |
1992年 | 88篇 |
1991年 | 79篇 |
1990年 | 78篇 |
1989年 | 69篇 |
1988年 | 53篇 |
1987年 | 29篇 |
1986年 | 44篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
本文引进发生函数矩阵与同构向量两个概念,利用它们讨论了与Scheffè单纯形—中心设计有关的0-1矩阵的一些性质。在I_(λ-)最优观测配置的分块算法的基础上,本文给出了q分量n阶广义单纯形—中心设计I_(λ-)最优观测频数的一般解析表达式。 相似文献
992.
993.
Homodesmotic reactions were designed for the computation of strain energies (SE) for four nitro-substituted 1,3,5,7-tetraazacubane
derivatives. Total energies of the optimized geometric structures at the DFT-B3LYP/6-31G* and DFT-B3LYP/6-311G** levels were
used to derive the SE. The variation of SE with respect to the number of substituents is similar with both basis sets. The
SE value is 237.32 kcal/mol at the B3LYP/6-311G** level for 2,4,6,8-tetranitro-1,3,5,7-tetraazacubane, which is unexpectedly
much larger than that of its cubane analogue. The SE increases remarkably with more nitro groups being attached to the cage
skeleton of tetraazacubane. The ‘bending’ of the bonds within the cubic skeleton attributes to the increase of strains as
the attached number of nitro groups increases. 相似文献
994.
995.
本文报导了在透明的CaF2衬底上采用气相外延(VPE)方法生长的高质量CdS薄膜。通过对其发射和吸收光谱以及光双稳特性的研究,表明这种外延膜的性质与体单晶相似。 相似文献
996.
997.
A connected graph is said to be unoriented Laplacian maximizing if the spectral radius of its unoriented Laplacian matrix attains the maximum among all connected graphs with the same number of vertices and the same number of edges. A graph is said to be threshold (maximal) if its degree sequence is not majorized by the degree sequence of any other graph (and, in addition, the graph is connected). It is proved that an unoriented Laplacian maximizing graph is maximal and also that there are precisely two unoriented Laplacian maximizing graphs of a given order and with nullity 3. Our treatment depends on the following known characterization: a graph G is threshold (maximal) if and only if for every pair of vertices u,v of G, the sets N(u)?{v},N(v)?{u}, where N(u) denotes the neighbor set of u in G, are comparable with respect to the inclusion relation (and, in addition, the graph is connected). A conjecture about graphs that maximize the unoriented Laplacian matrix among all graphs with the same number of vertices and the same number of edges is also posed. 相似文献
998.
Chang‐Ying Yang Zhong‐Xu Dai Xin Li Fan‐Chong Rong 《Surface and interface analysis : SIA》2009,41(5):366-370
The gold electrode was modified by noisomes, prepared by sonicating the mixed solution of PEG 6000/Tween 80/Span 80/H2O. Electrochemical cyclic voltammetry (CV) and impedance spectroscopy (EIS) were performed for characterizing the modification. The construction of multilayer films of octadecanethiol (ODT)‐niosomes had almost no pinholes, which elicited that niosomes‐coated electrode through ODT assembly was more effective immobilization compared to direct modification method. A large semicircle formation in the entire range of frequency indicated the complete electron‐transfer control for the redox reaction, implying a perfect blocking behavior. The Nyquist plot was consisting of two depressed semicircles after storage for 36 h in air, which implied a progressive and uniform construction manner, as expected for porous coatings. The modified electrode was used to investigate the interaction between 1‐anilino‐8‐naphthalene‐sulfonate (ANS) and noisomes. It was found that the low‐frequency semicircular arcs increase in diameter, indicating that the increase in the resistance Rp attributed mainly to the niosomes/solution interface. It was due to the binding of ANS to the niosomes‐modified electrode surface, exhibited against diffusing species through the pores. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
999.
The first phytochemical investigation on stems of Mitrephora thorelii led to the isolation of three new lignanamides, thoreliamides A–C ( 1 – 3 ), and a new sesquiterpenoid, thorelinin ( 4 ), together with ten known compounds. The structures of the new compounds were established on the basis of extensive spectroscopic analyses. Thoreliamide C is the first trimer derived from cinnamic acid amide units. 相似文献
1000.
采用热重-差式扫描量热法(TG—DSC)分析了不同酸度的盐酸-水合氯化铈饱和溶液中生成的CeCl3·nH2O晶体在空气氛围热分解脱水的过程,热分析表明酸度对CeCl3·nH2O晶体结晶形式有影响,氯化铈饱和溶液在盐酸中生成的CeCl3·nH2O晶体较商品CeCl3·nH2O晶体的热分解多一个恒温脱水失重的过程.X射线粉末衍射(XRD)结果表明此商品CeCl3·nH2O晶体为CeCl3·7H2O,盐酸-水合氯化铈饱和溶液中生成的CeCl3·nH2O晶体为含有不同个数结晶水的混合物. 相似文献