全文获取类型
收费全文 | 2462篇 |
免费 | 340篇 |
国内免费 | 260篇 |
专业分类
化学 | 1107篇 |
晶体学 | 37篇 |
力学 | 344篇 |
综合类 | 38篇 |
数学 | 708篇 |
物理学 | 828篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 33篇 |
2021年 | 50篇 |
2020年 | 78篇 |
2019年 | 114篇 |
2018年 | 93篇 |
2017年 | 137篇 |
2016年 | 133篇 |
2015年 | 163篇 |
2014年 | 153篇 |
2013年 | 180篇 |
2012年 | 121篇 |
2011年 | 153篇 |
2010年 | 109篇 |
2009年 | 113篇 |
2008年 | 107篇 |
2007年 | 108篇 |
2006年 | 102篇 |
2005年 | 110篇 |
2004年 | 94篇 |
2003年 | 131篇 |
2002年 | 113篇 |
2001年 | 99篇 |
2000年 | 95篇 |
1999年 | 81篇 |
1998年 | 82篇 |
1997年 | 63篇 |
1996年 | 49篇 |
1995年 | 36篇 |
1994年 | 29篇 |
1993年 | 16篇 |
1992年 | 18篇 |
1991年 | 21篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3062条查询结果,搜索用时 31 毫秒
31.
32.
多级轴流压气机全工况特性计算 总被引:1,自引:0,他引:1
本文使用三维粘性流动计算软件Fine/Numeca,对某十五级轴流压气机进行了内流流场和全工况特性的数值计算尝试。分析了该压气机在设计工况和非设计工况的性能,同时把整机计算结果和前七级叶片的计算结果进行了比较。计算结果表明,当计算的级数较少时,目前的软件和硬件平台可以比较合理地预测压气机的全工况特性;而当计算的级数较多时,准确的数值模拟仍需要更为准确的多级模型和数值方法。 相似文献
33.
这篇文章讨论边值问题-(| u′|p-2u′)′=λf(t ,u) ,t∈(0,1) ,p >1,u(0) =u(1) =0,其中f(t ,u)≥-M( M是正常数) ,对(t ,u)∈0,1×0,∞) .我们利用度理论和锥上的不动点定理得到方程存在两个正解. 相似文献
34.
电子自旋共振准三维图象的重建方法 总被引:3,自引:0,他引:3
根据投影切片原理, 设计了一个简单而有效的ESR图象重建算法和程序, 可利用样品的一集ESR谱, 方便地绘制出样品在某截面的自旋密度立体轮廓图、等值图和散点密度分布图等, 为分析和研究自旋密度的分布及其性质, 提供了直观依据。作为应用, 文中给出了石英杜瓦受紫外光辐照后产生的局部晶格缺陷——F心的空间分布图, 图中清楚表明, F心的浓度与辐照方向和辐照强度的密切关系, 与试验结果完全相符。 相似文献
35.
本文报道了一种新型三维亚磷酸锌[HO(CH2)2NH3]2•[Zn3(HPO3)4]的合成和晶体结构。在它的结构中,ZnO4和HPO3严格按照顶点连接的方式交替相连。骨架结构存在两个沿着不同方向无限延伸的由ZnO4和HPO3组成的四元环链,在[0 1 0]、[0 4 15]和[0 -4 15]三个方向形成了三个交叉8元环孔道,有机胺阳离子起着平衡电荷和稳定骨架的结构。它的晶体数据为:[HO(CH2)2NH3]2•[Zn3(HPO3)4],M=640.21, 正交晶系, Fdd2空间群, a=2.8528, b=0.8426, c=1.6159nm, Z=8, V=3.884nm3, R1=0.0219, wR2=0.0544。 相似文献
36.
《Electroanalysis》2006,18(6):533-550
We review recent advances in biosensors based on one‐dimensional (1‐D) nanostructure field‐effect transistors (FET). Specifically, we address the fabrication, functionalization, assembly/alignment and sensing applications of FET based on carbon nanotubes, silicon nanowires and conducting polymer nanowires. The advantages and disadvantages of various fabrication, functionalization, and assembling procedures of these nanosensors are reviewed and discussed. We evaluate how they have been used for detection of various biological molecules and how such devices have enabled the achievement of high sensitivity and selectivity with low detection limits. Finally, we conclude by highlighting some of the challenges researchers face in the 1‐D nanostructures research arena and also predict the direction toward which future research in this area might be directed. 相似文献
37.
The novel complex [K(18-C-6)]2[Cd(mnt)2][18-C-6-18-crown-6,nmt=1,2-dicyanoethene-1,2-dithiolate,C2S2-(CN)2^2-] was synthesized and characterized by elemental analysis,IR spectrum and X-ray diffraction analysis.The complex displays two-dimensional network structure of [K(18-C-6)] complex segments and [Cd(nmt)2] complex segment bridged by S-K-S,S-K-N and N-K-N interactions between adjacent[K(18-C-6)] and [Cd(mnt)2]units. 相似文献
38.
Study of the development of thermoresistance in human pancreatic carcinoma cell lines using proteome analysis 总被引:3,自引:0,他引:3
In order to find candidate proteins that are potentially associated with the thermoresistant phenotype in combination with drug resistance, we analyzed the differential protein expression in vitro in the human pancreatic cancer cell line EPP85-181-P and classical and atypical multidrug-resistant variants and their thermoresistant counterparts using proteomics. This study identifies sets of proteins that may lead to the development of thermoresistance. These results provide a fundamental basis to elucidate the molecular mechanism of thermoresistance and chemoresistance phenomena that may assist the therapy of inoperable cancers. 相似文献
39.
Davis JM 《Journal of separation science》2005,28(4):347-359
The low prediction by statistical-overlap theory of the numbers of singlets and peaks in two-dimensional separations containing zones represented by either circles of small number or eccentric ellipses of any number is shown to result from use of probability expressions for unbound spaces of infinite extent. An exact theory is derived for the probability of singlet formation in a reduced two-dimensional space of unit length, width, and area. The probability is a weighted sum of the probabilities of singlet formation in the interior, edge, and corner regions of the space, which depend only on saturation. The weighting factors are the fractions of area associated with each region and depend on the number of zones, the aspect ratio, the saturation, and the ellipse's spatial orientation. The average numbers of doublets, triplets, and peaks in the space are approximated by combining these results with Roach's equations describing the clustering of circles in an unbound two-dimensional space. Simulations show that theory predicts the number of singlets, doublets, triplets, and peaks, when the number of zones is 25 or more, the aspect ratio is 100 or less, and the saturation is 2 or less. The relationship is derived between the aspect ratios of ellipses in the reduced space and actual separation space. Calculations are presented for comprehensive two-dimensional gas chromatography. 相似文献
40.
《Journal of separation science》2005,28(13):1457-1466
Comprehensive 2‐D size‐exclusion chromatography (SEC×SEC) has been realized. SEC×SEC is not a useful technique for characterizing complex polymers. However, it is potentially an elegant tool to study band‐broadening phenomena. If narrow fractions can be collected from the first dimension, the band broadening in the second dimension is only due to chromatographic dispersion. This would allow a clear distinction to be made between chromatographic band broadening (column and extra‐column) and SEC selectivity (band broadening due to sample polydispersity). In comparison with MALDI‐MS, SEC×SEC allows the study of polymers across a much broader molar‐mass range. 相似文献