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31.
改性聚苯乙烯微球的制备及其胶体晶体的组装 总被引:10,自引:0,他引:10
采用甲基丙烯酸改性的无皂乳液聚合方法制备了尺寸为210 nm、含羧基的聚苯乙烯(PS)微球,用红外光谱、透射电子显微镜和粒度分析仪对其形状和结构进行分析,结果表明,经甲基丙烯酸改性后得到了表面为高密度电荷的单分散性PS微球.用垂直沉积法快速制备出在较大范围(大于1 cm2)呈现很好有序性的密排结构聚苯乙烯胶体晶体薄膜,其在590 nm波长处存在光子带隙.在电子显微镜下,观察到这种胶体晶体是面心立方(fcc)密排结构. 相似文献
32.
33.
The synthesis of a series of novel acetylenic cyclophanes is described. X-ray crystallographic analysis of the core structure revealed a twisted conformation with helical chirality. Preliminary results suggest that these cyclophanes, with appropriate functionality, have the potential to act as unique liquid crystalline materials. 相似文献
34.
Tayebani M Feghali K Gambarotta S Yap GP Thompson LK 《Angewandte Chemie (International ed. in English)》1999,38(24):3659-3661
In spite of the short Nb-Nb distance (2.268 ?) and the presumable existence of an Nb identical withNb bond, the paddle-wheel-shaped diniobium(II) complex 1 is paramagnetic. Theoretical calculations indicate that the presence of LiCl moieties on the intermetallic axis lowers the Nb-Nb bond order and is responsible for the observed paramagnetism. 相似文献
35.
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37.
Graham LA Fout AR Kuehne KR White JL Mookherji B Marks FM Yap GP Zakharov LN Rheingold AL Rabinovich D 《Dalton transactions (Cambridge, England : 2003)》2005,(1):171-180
The manganese(I) tricarbonyl complexes (Bm(R))Mn(CO)3(R = Me, Bz, But, p-Tol) and (PhBmMe)Mn(CO)3, the first bis(mercaptoimidazolyl)borate derivatives for this metal, have been readily prepared and fully characterized. In particular, the presence of three-center-two-electron Mn...H-B interactions in these species, both in solution and in the solid state, has been investigated using a combination of IR and NMR spectroscopies and, in the case of the methyl-, tert-butyl- and para-tolyl-substituted derivatives, by X-ray crystallography. To complement these synthetic and structural studies, the tris(mercaptoimidazolyl)borate complexes (TmMe)Mn(CO)3(R = Me, Bz, But, p-Tol) and (PhTm(Me))Mn(CO)3, as well as the related pyrazolylbis(mercaptoimidazolyl)borate (pzBmMe)Mn(CO)3, have also been synthesized and characterized by a combination of analytical and spectroscopic techniques. 相似文献
38.
We introduce a technique for computing approximate
solutions to optimization problems. If $X$ is the set
of feasible solutions, the standard goal
of approximation algorithms is to compute $x\in X$ that is an
$\varepsilon$-approximate solution in the following sense:
$$d(x) \leq (1+\varepsilon)\, d(x^*),$$
where $x^* \in X$ is an optimal solution,
$d\colon\ X\rightarrow {\Bbb R}_{\geq 0}$ is
the optimization function to be minimized, and
$\varepsilon>0$ is an input parameter.
Our approach is first to devise algorithms that
compute pseudo $\varepsilon$-approximate solutions
satisfying the bound
$$d(x) \leq d(x_R^*) + \varepsilon R,$$
where $R>0$ is a new input parameter.
Here $x^*_R$ denotes an optimal solution in the space $X_R$ of
$R$-constrained feasible solutions. The parameter $R$ provides
a stratification of $X$ in the sense that (1) $X_R \subseteq X_{R}$ for
$R < R$ and (2) $X_R = X$ for $R$ sufficiently large.
We first describe a highly efficient scheme
for converting a pseudo $\varepsilon$-approximation
algorithm into a true $\varepsilon$-approximation algorithm.
This scheme is useful because
pseudo approximation algorithms seem to be
easier to construct than $\varepsilon$-approximation algorithms.
Another benefit is that our algorithm is
automatically precision-sensitive.
We apply our technique to two problems in robotics:
(A) Euclidean Shortest Path (3ESP), namely
the shortest path for a point robot amidst polyhedral obstacles in
three dimensions, and
(B) $d_1$-optimal motion for a rod moving amidst
planar obstacles (1ORM).
Previously, no polynomial time $\varepsilon$-approximation algorithm
for (B) was known. For (A), our new solution
is simpler than previous solutions and has
an exponentially smaller complexity in terms
of the input precision. 相似文献
39.
Bis(guanidinate) titanium imido complexes [{(Me2N)C(NiPr)2}2TiNAr'] (Ar' = 2,6-Me2C6H3 (1a); C6F5 (1b)) are competent catalysts for the guanylation of a variety of arylamines with carbodiimide. The reversible [2 + 2] addition of iPrN=C=NiPr to 1b is demonstrated and is proposed to be part of the catalytic cycle. Compounds 1a and 1b are also effective precatalysts for the transamination of trialkylguanidines with arylamines to yield aryldialkylguanidines. 相似文献
40.
本文基于一种并行高精度的静动交接面处理方法,采用了SA模型及基于SA的分离涡模拟DES方法,进行了某压气机静动干涉流动的计算.研究表明对本文算例,在微小分离处,如20%到80%叶高处,DES与SA计算出的流动损失相差很小;而在大分离处,如叶根叶顶处,DES结果与SA差别较大,并且DES可更好地描述涡结构.在叶顶处,DES计算出比SA更强的泄漏流动,导致更大的损失.在叶根处,DES计算出了明显的静叶动态尾迹涡脱落现象,这一现象导致了与SA不一样的损失机理,即脱落涡与动叶头部相撞而产生时序效应,从而使计算损失较小.同时,本文研究结果与之前对孤立静叶的研究是相互验证的. 相似文献