全文获取类型
收费全文 | 235篇 |
免费 | 36篇 |
国内免费 | 42篇 |
专业分类
化学 | 170篇 |
晶体学 | 2篇 |
力学 | 16篇 |
综合类 | 3篇 |
数学 | 44篇 |
物理学 | 78篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 13篇 |
2012年 | 27篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 15篇 |
2003年 | 3篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有313条查询结果,搜索用时 15 毫秒
71.
Nonlinear Dynamics - This paper investigates the problem of attitude synchronization tracking of multiple spacecraft in the presence of limited inter-spacecraft communication, model uncertainties... 相似文献
72.
73.
本研究探讨腹部彩超联合糖类抗原125(CA125)诊断卵巢浆液性肿瘤的价值。选取卵巢浆液性肿瘤患者80例,其中卵巢浆液性囊腺瘤患者23例,浆液性交界性肿瘤患者30例,浆液性癌患者27例,比较各组超声特征及血清CA125差异。浆液性交界性肿瘤、浆液性癌患者囊实性回声、有血流分布、腹水比例明显高于卵巢浆液性囊腺瘤患者(P<0.05),形态规则、边界清晰比例明显低于卵巢浆液性囊腺瘤患者(P<0.05);浆液性癌患者血清CA125为(301.45±104.42)U/mL,明显高于浆液性交界性肿瘤和卵巢浆液性囊腺瘤患者(P<0.05);浆液性交界性肿瘤患者血清CA125为(210.10±98.28)U/mL,明显高于卵巢浆液性囊腺瘤患者(P<0.05);超声联合血清CA125诊断浆液性癌的特异性、准确率和阳性预测值分别为90.57%、87.50%和81.48%,明显高于超声检查(P<0.05)。腹部彩超联合CA125鉴别诊断卵巢浆液性肿瘤有较好的价值。 相似文献
74.
Zhang X Wang Y Ma Y Ye Y Wang Y Wu K 《Langmuir : the ACS journal of surfaces and colloids》2006,22(1):344-348
A stable organic sol of solvent-stabilized oxovanadium phthalocynine (VOPc) nanoparticles with excellent photoconductivity was successfully prepared by ultrasonificating a prepared nanoscopic VOPc powder in1,2-dichloroethane (C(2)H(4)Cl(2)) without any additive. These solvent-stabilized VOPc nanoparticles have a size distribution from 2 to 20 nm with an average diameter of 4.6 nm. The VOPc concentration of these organic sols could be as high as 100 g/L. The nanoscopic VOPc particles were well-dispersed in an insulating polycarbonate (PC) resin, resulting in single-layered photoreceptors with high surface charge durability in the dark and excellent photoconductivity. Based on the light-assisted scanning tunneling microscopy (STM) measurements, the charge transport mechanism of these photoreceptors was ascribed to light-induced enhancement of electron tunneling through the VOPc-nanoparticle/insulator junctions. 相似文献
75.
Hermann JC Ghanem E Li Y Raushel FM Irwin JJ Shoichet BK 《Journal of the American Chemical Society》2006,128(49):15882-15891
With the emergence of sequences and even structures for proteins of unknown function, structure-based prediction of enzyme activity has become a pragmatic as well as an interesting question. Here we investigate a method to predict substrates for enzymes of known structure by docking high-energy intermediate forms of the potential substrates. A database of such high-energy transition-state analogues was created from the KEGG metabolites. To reduce the number of possible reactions to consider, we restricted ourselves to enzymes of the amidohydrolase superfamily. We docked each metabolite into seven different amidohydrolases in both the ground-state and the high-energy intermediate forms. Docking the high-energy intermediates improved the discrimination between decoys and substrates significantly over the corresponding standard ground-state database, both by enrichment of the true substrates and by geometric fidelity. To test this method prospectively, we attempted to predict the enantioselectivity of a set of chiral substrates for phosphotriesterase, for both wild-type and mutant forms of this enzyme. The stereoselectivity ratios of the six enzymes considered for those four substrate enantiomer pairs differed over a range of 10- to 10,000-fold and underwent 20 switches in stereoselectivities for favored enantiomers, compared to the wild type. The docking of the high-energy intermediates correctly predicted the stereoselectivities for 18 of the 20 substrate/enzyme combinations when compared to subsequent experimental synthesis and testing. The possible applications of this approach to other enzymes are considered. 相似文献
76.
77.
The Ramanujan Journal - Let $$2< c < \frac{52}{25}$$. In this paper, it is proved that for any sufficiently large real number N, the Diophantine inequality $$|p_1^{c} + p_2^{c} +... 相似文献
78.
LetN be a sufficiently large even integer and $$\begin{gathered} q \geqslant 1, (l_i ,q) = 1 (i = 1, 2), \hfill \\ l_1 + l_2 \equiv N(\bmod q). \hfill \\ \end{gathered} $$ . It is proved that the equation $$N = p + P_2 ,p \equiv l_1 (\bmod q), P_2 \equiv l_2 (\bmod q)$$ has infinitely many solutions for almost all $q \leqslant N^{\frac{1}{{37}}} $ , wherep is a prime andP 2 is an almost prime with at most two prime factors. 相似文献
79.
The first nonthiolic, odorless 1,3-propanedithiol equivalent and its application in thioacetalization 总被引:1,自引:0,他引:1
Liu Q Che G Yu H Liu Y Zhang J Zhang Q Dong D 《The Journal of organic chemistry》2003,68(23):9148-9150
2-[2-Chloro-1-(1-chlorovinyl)allylidene]-1,3-dithiane 1 was synthesized by the chlorination of 3-(1,3)-dithianylidenepentane-2,4-dione 2 using the Vilsmeier-Haack reagent in 99% yield. As a novel nonthiolic, odorless 1,3-propanedithiol equivalent, 1 was investigated in the thioacetalization reaction. Various types of aldehydes and ketones 3 were converted to the corresponding dithianes 4 in the presence of 1 in high yields (79-97%). Moreover, 1 exhibited obvious chemoselectivity between aldehyde and ketone in this thioacetalization reaction. A mechanism for this thioacetalization reaction is proposed. 相似文献
80.
Yingchun CAI 《数学年刊B辑(英文版)》2008,(6)
Let p denote a prime and P2 denote an almost prime with at most two prime factors. The author proves that for suffciently large x,sum from p≤x p 2=P2 1>(1.13Cx)/(log~2x), where the constant 1.13 constitutes an improvement of the previous result 1.104 due to J. Wu. 相似文献