全文获取类型
收费全文 | 1914篇 |
免费 | 215篇 |
国内免费 | 180篇 |
专业分类
化学 | 1418篇 |
晶体学 | 43篇 |
力学 | 80篇 |
综合类 | 19篇 |
数学 | 187篇 |
物理学 | 562篇 |
出版年
2024年 | 9篇 |
2023年 | 30篇 |
2022年 | 59篇 |
2021年 | 75篇 |
2020年 | 63篇 |
2019年 | 62篇 |
2018年 | 59篇 |
2017年 | 50篇 |
2016年 | 69篇 |
2015年 | 81篇 |
2014年 | 94篇 |
2013年 | 138篇 |
2012年 | 141篇 |
2011年 | 163篇 |
2010年 | 93篇 |
2009年 | 84篇 |
2008年 | 125篇 |
2007年 | 105篇 |
2006年 | 87篇 |
2005年 | 90篇 |
2004年 | 85篇 |
2003年 | 62篇 |
2002年 | 56篇 |
2001年 | 49篇 |
2000年 | 58篇 |
1999年 | 38篇 |
1998年 | 27篇 |
1997年 | 26篇 |
1996年 | 35篇 |
1995年 | 24篇 |
1994年 | 21篇 |
1993年 | 25篇 |
1992年 | 28篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有2309条查询结果,搜索用时 15 毫秒
1.
Chunxia Zhao Guowang Xu Xianzhe Shi Jianmei Ma Yan Zhang Shen Lv Qianfeng Weng Qing Yang 《Analytical sciences》2004,20(7):1001-1005
Fluorescent-based single-strand conformation polymorphism (F-SSCP) analysis with capillary electrophoresis (CE) is the most common method for the detection of mutation because of its high sensitivity and resolution. In this study, we prepared an inexpensive linear polyacrylamide (LPA), and successfully applied it to CE-SSCP analysis and tandem CE-SSCP/heteroduplex analysis (HA) of the P53 gene on an ABI capillary genetic analyzer. A comparison of the sieving capabilities of a homemade LPA and commercial polydimethylacrylamide (PDMA) demonstrates that the homemade LPA has a higher resolution, a shorter analysis time, and is more suitable for tandem SSCP/HA than commercial PDMA. To show the usefulness, mutations of P53 gene exon 7 - 8 in 37 tumor samples were investigated by using homemade LPA. The results indicate that 10 mutations were found in 9 of 37 cases; the majority of P53 mutations were missense mutations, and 70% were located in exon 7, which plays an important role in neoplastic progression in human tumorigenesis. 相似文献
2.
O. Maksimov P. Fisher M. Skowronski P.A. Salvador M. Snyder J. Xu X. Weng 《Journal of Crystal Growth》2008,310(11):2760-2766
MgO films were grown on (0 0 1) yttria-stabilized zirconia (YSZ) substrates by molecular beam epitaxy (MBE). The crystalline structures of these films were investigated using X-ray diffraction and transmission electron microscopy. Growth temperature was varied from 350 to 550 °C, with crystalline quality being improved at higher temperatures. The MgO films had a domain structure: (1 1 1)[1 1 2¯]MgO(0 0 1)[1 0 0]YSZ with four twin variants related by a 90° in-plane rotation about the [1 1 1]MgO axis. The observed epitaxial orientation was compared to previous reports of films grown by pulsed laser deposition and sputtering and explained as resulting in the lowest interface energy. 相似文献
3.
ToF-SIMS analysis of the organometallic cluster Os3(μ-H)(CO)10(μ-SCH2CH2SH) chemically attached onto a silver or gold surface, and of the cluster fragment Os3(μ-H)(CO)10(μ-OSi) on a silica surface, allows for identification of the surface organometallic species, and also gives information on its reactivity. 相似文献
4.
The direct reactions of (C5H5)2LnCl with LiN=C(NMe2)2 proceeded at room temperature in THF under pure nitrogen to yield the lanthanocene guanidinate complexes [(C5H5)2Ln(mu-eta1:eta2-N=C(NMe2)2)]2 (Ln = Gd (1), Er (2)). Treatment of phenyl isocyanate with complexes 1 and 2 results in monoinsertion of phenyl isocyanate into the Ln-N(mu-Gua) bond to yield the corresponding insertion products [(C5H5)2Ln(mu-eta1:eta2-OC(N=C(NMe2)2)NPh)]2 (Ln = Gd (3), Er (4)), presenting the first example of unsaturated organic small molecule insertion into the metal-guanidinate ligand bond. Further investigations indicate that N,N'-diisopropylcarbodiimide does not react with complexes 1 and 2 under the same conditions; however, it readily inserts into the lithium-guanidinate ligand bond of LiN=C(NMe2)2. As a synthon of the insertion product Li[(iPrN)2C(N=C(NMe2)2)], its reaction with (C5H5)2LnCl gives the novel organolanthanide complexes containing the guanidinoacetamidinate ligand, (C5H5)2Ln[(iPrN)2C(N=C(NMe2)2)] (Ln = Yb (5), Er (6), Dy (7)). All complexes were characterized by elemental analysis and spectroscopic properties. The structures of complexes 1, 3, 5 and 7 were determined through X-ray single-crystal diffraction analysis. 相似文献
5.
Chiral chromanone lactones are a class of natural products with important biological activity. We report a direct diastereo- and enantioselective vinylogous conjugate addition of butenolide to 2-ester substituted chromones. The transformation proceeded well in the presence of as low as 1 mol% of a chiral N,N′-dioxide/ScIII complex, 3 Å MS and a catalytic amount of hexafluoroisopropanol (HFIP). The scope of Michael acceptors includes a variety of substituted chromones at different positions, and the desired chromanone lactones upon reduction are afforded in good yield and diastereoselectivity, and excellent enantioselectivity (up to 99% ee). The strategy could be used in the concise synthesis of blennolide C and gonytolide A, C and G.We report a direct, diastero- and enantioselective vinylogous 1,4-addition of butanolide to 2-ester chromones. A chiral ScIII complex enabled the reaction to proceed smoothly to give a variety of chraomanone lactones. 相似文献
6.
7.
Reported herein is the FeCl3-promoted intermolecular sulfoesterification of o-(1-alkynyl)benzoates with disulfides, which provides a convenient and efficient method for synthesis of 4-sulfenylisocoumarins. Various functional groups such as methoxy, halides, ester, cyano and silicon groups in the substrates are tolerated, and heterocycle-fused chalcogenylpyrones are also successfully achieved directly from the corresponding heterocyclic precursors under the same reaction conditions. In addition, starting from diynylbenzoate, this reaction sequence can be combined with a bicyclization step leading to the tetracyclic (E)-3-(2-phenyl-3-phenylchalcogenylinden-1-ylidene)isobenzofuranone frameworks with high regiospecificity and exclusive trans stereoselectivity. 相似文献
8.
9.
Otto F. Sankey Gary B. Adams Xudong Weng John D. Dow Yin-Min Huang J. C. H. SpenceD. A. Drabold Wei-Min Hu R. P. WangStefan KlemmPeter A. Fedders 《Superlattices and Microstructures》1991,10(4)
The technique of quantum molecular dynamics is reviewed, and a simplified approach based on a first-principles tight-binding implementation of local density theory is discussed. Several illustrations and applications of the theory are presented. Applying it to amorphous materials, we have developed a procedure for producing amorphous Si networks with small defect concentrations. Benchmark checks are made for atomic geometries at Si(111)-(2×1) and Si(001)-(2×1), p(2×2), and c(4×2) reconstructed surfaces. A simulation of a Scanning Tunneling Microscope tip interacting with a reconstructed surface is performed, and it is shown how the tip can alter the reconstruction of the surface. Simulation of a kinked Si(001) surface step and comparison to an unkinked step are also presented. 相似文献
10.
GM(1,1)的周期修正模型及其在泉水流量预测中的应用 总被引:4,自引:2,他引:4
本文阐述了 GM( 1 ,1 )的残差周期修正模型 ,并将它应用于山西神头泉的流量预测中 ,建立了神头泉流量的 GM( 1 ,1 )周期修正模型 ,对其流量进行了预测 ,为神头泉域岩溶水资源开发利用和保护提供了科学依据 相似文献