全文获取类型
收费全文 | 95642篇 |
免费 | 17574篇 |
国内免费 | 8481篇 |
专业分类
化学 | 81034篇 |
晶体学 | 1074篇 |
力学 | 4217篇 |
综合类 | 458篇 |
数学 | 9162篇 |
物理学 | 25752篇 |
出版年
2024年 | 216篇 |
2023年 | 1311篇 |
2022年 | 2423篇 |
2021年 | 2728篇 |
2020年 | 3670篇 |
2019年 | 4726篇 |
2018年 | 3051篇 |
2017年 | 2685篇 |
2016年 | 6088篇 |
2015年 | 6307篇 |
2014年 | 6791篇 |
2013年 | 8348篇 |
2012年 | 8357篇 |
2011年 | 7603篇 |
2010年 | 6544篇 |
2009年 | 6287篇 |
2008年 | 6071篇 |
2007年 | 5038篇 |
2006年 | 4423篇 |
2005年 | 4142篇 |
2004年 | 3408篇 |
2003年 | 2935篇 |
2002年 | 3618篇 |
2001年 | 2703篇 |
2000年 | 2372篇 |
1999年 | 1637篇 |
1998年 | 1113篇 |
1997年 | 992篇 |
1996年 | 952篇 |
1995年 | 858篇 |
1994年 | 726篇 |
1993年 | 606篇 |
1992年 | 517篇 |
1991年 | 459篇 |
1990年 | 384篇 |
1989年 | 279篇 |
1988年 | 207篇 |
1987年 | 182篇 |
1986年 | 178篇 |
1985年 | 154篇 |
1984年 | 110篇 |
1983年 | 110篇 |
1982年 | 62篇 |
1981年 | 54篇 |
1980年 | 35篇 |
1979年 | 25篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1972年 | 20篇 |
1957年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
T′相R2CuO4稀土铜氧化合物由于尺度效应而产生弱铁磁性行为已经被人们关注,报导了通过高温高氧压(6GPa,1000℃)合成稀土T′相R2CuO4(R=Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er和Tm)化合物的结构和磁学性能。磁化率曲线显示,在低温下所有的高压增氧R2CuO4样品都出现新的低温弱铁磁性反常行为,转变温度在28K附近。新的低温弱铁磁性行为是由于CuO2面上微量氧空穴的掺入,使处于反铁磁有序CuO2面形成局域化的铁磁性团簇造成。实验证明新发现的低温弱铁磁性行为与尺度效应产生弱铁磁性行为属于完全不同的物理机制。结果还预示T′相R2CuO4稀土铜氧化合物很难通过空穴掺杂而实现超导。 相似文献
63.
LiAlO2 single crvstals doped with Ti at concentration 0.2at.% are grown by the Czochralskl technique with dimensions φ42×55mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the VLi and Vo absorptions, respectively: The peaks at 716nm and 798nm may stem from the VLi^+ and absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti^4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals. 相似文献
64.
65.
Jensen and Toft 8 conjectured that every 2‐edge‐connected graph without a K5‐minor has a nowhere zero 4‐flow. Walton and Welsh 19 proved that if a coloopless regular matroid M does not have a minor in {M(K3,3), M*(K5)}, then M admits a nowhere zero 4‐flow. In this note, we prove that if a coloopless regular matroid M does not have a minor in {M(K5), M*(K5)}, then M admits a nowhere zero 4‐flow. Our result implies the Jensen and Toft conjecture. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
66.
报道了KDP晶体中的三倍频产生的实验研究,计算了比较了直接三倍频过程和级联过程对KDP晶体三阶有效非线性系数的贡献,并探讨了KDP作为非线性晶体材料三阶非线性系数测量基准的可行性。 相似文献
67.
68.
By constructing close-one-cochain density Ω^12n in the gauge group space we get the Wess-Zumino-Witten (WZW) effective Lagrangian on high-dimensional noncommutative space.Especially consistent anomalies derived from this WZW effective action in noncommutative four-dimensional space coincide with those obtained by L.Bonora etc.(het-th/0002210). 相似文献
69.
70.
In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of TChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation. 相似文献