全文获取类型
收费全文 | 6873篇 |
免费 | 1209篇 |
国内免费 | 1206篇 |
专业分类
化学 | 5235篇 |
晶体学 | 157篇 |
力学 | 358篇 |
综合类 | 123篇 |
数学 | 819篇 |
物理学 | 2596篇 |
出版年
2024年 | 22篇 |
2023年 | 180篇 |
2022年 | 301篇 |
2021年 | 342篇 |
2020年 | 385篇 |
2019年 | 361篇 |
2018年 | 284篇 |
2017年 | 327篇 |
2016年 | 379篇 |
2015年 | 403篇 |
2014年 | 492篇 |
2013年 | 597篇 |
2012年 | 643篇 |
2011年 | 632篇 |
2010年 | 478篇 |
2009年 | 471篇 |
2008年 | 464篇 |
2007年 | 429篇 |
2006年 | 381篇 |
2005年 | 278篇 |
2004年 | 249篇 |
2003年 | 160篇 |
2002年 | 197篇 |
2001年 | 176篇 |
2000年 | 135篇 |
1999年 | 100篇 |
1998年 | 72篇 |
1997年 | 45篇 |
1996年 | 43篇 |
1995年 | 27篇 |
1994年 | 37篇 |
1993年 | 27篇 |
1992年 | 19篇 |
1991年 | 26篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1974年 | 4篇 |
1965年 | 6篇 |
1962年 | 3篇 |
1961年 | 3篇 |
1957年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有9288条查询结果,搜索用时 156 毫秒
71.
The nitro group in tertiary or secondary aliphatic nitro compounds is replaced by hydrogen or deuterium on treatment with tributyltin hydride or tributyltin deuteride, respectively. 相似文献
72.
吸热碳氢燃料裂解镧改性混合型催化剂的研究 总被引:3,自引:0,他引:3
制备了吸热型碳氢燃料NNJ-150和镧离子交换改性的USY、ZSM-5分子重申及混合分子筛,考察了NNJ-150在USHY、HZSM-5和两者混合物以及镧改性单分子筛和混合分子筛催化剂上的裂解反应。结果表明,ZSM-5分子筛中添加镧,对NNJ-150的单分子裂解反应有明显影响;混合分子两种分子筛之间存在协同作用,低温(500℃)下,LaUSY LaZSM-5(75:25)混合分子筛对低碳烯烃的选择性较高(41.48%),催化剂寿命较长(35min以上),能有效提高吸热型碳氢燃料NNJ-150的吸热能效。 相似文献
73.
用峰鉴别技术反相高效液相色谱法测定火锅汤料中微量吗啡 总被引:3,自引:0,他引:3
本文报道了以峰鉴别技术为定性依据的测定火锅汤料中微量吗啡的反相高效液相色谱法。本法采用改良的Stas-otto法分离提取复杂样品中的微量吗啡。由于采用峰鉴别技术,增加了定性参数,大大提高了定性方法的准确性。本法简便、快速。最低检出浓度为0.04mg/L。在数十例样品分析中,与其它仪器分析结果比照,非常符合。 相似文献
74.
Dehydroluciferyl-coenzyme A (L-CoA) was chemically synthesized and characterized by MS, UV-vis spectrometry and RP-HPLC. The identity of the chemically synthesized compound with the one that was produced by firefly luciferase was confirmed. Moreover, the reversibility of the enzymatic conversion of dehydroluciferin ? dehydroluciferyl-adenylate ? L-CoA was also confirmed. The chemical synthesis of L-CoA, described here, may help the clarification of the activator effect of CoA on luciferase bioluminescent assays, in which the enzyme catalyzed formation of L-CoA and the consequent destruction of L-AMP is one of the possible explanations for that effect. 相似文献
75.
Detection of single molecules, particles, and rapid redox events is a challenge of electrochemical investigations and requires either an amplification strategy or significant averaging for the electrochemical current to exceed the noise level. We consider the minimum number of electrons required to reach the limit of quantification in these electrochemical measurements. A survey of the literature indicates that the state-of-the-art limit in current detection for different types of measurements (e.g. voltammetry, single-molecule redox cycling, ion channel recordings of single molecules, metal nanoparticle collision, and phase nucleation) is independent of the nature of the measurement and increases linearly with reciprocal response time, Δt?1, over ~5 orders of magnitude (from ~10 to ~106 s?1). We demonstrate that the practical limit of quantification requires cumulative measurement of ~2100 electrons during Δt and is determined by statistics of counting electrons, that is, the shot noise in the current. 相似文献
76.
Amorphous poly(ethylene terephthalate) was annealed at temperatures around the glass transition temperature and then heated up in differential scanning calorimeter at 20 °C min−1. It was found that the annealing favored the subsequent cold crystallization and this effect became stronger with increasing annealing temperature. The experimental results were explained by considering the structural change during the annealing. 相似文献
77.
采用密度泛函理论, 对在Ru(II)催化剂存在下, 有机叠氮化合物和末端炔的反应机理作了深入理论研究. 在B3LYP/LANL2DZ水平上, 对该反应体系中势能面各驻点的几何构型进行了全优化计算, 并经振动频率分析确定了过渡态和中间体, 通过内禀反应坐标(IRC)的计算, 确认了反应物、中间体、过渡态和产物的相关性. 对多个反应通道的协同反应以及分步反应进行了研究. 结果表明: 协同反应通道Ic和分步反应通道IIc是反应能垒较低的反应通道, 活化自由能较其它反应通道低, 有利于1,5-二取代1,2,3-三唑的生成, 具有特定的区域选择性, 与实验结果吻合. 相似文献
78.
Li Ting Chai Yang Zhou Li Wei Wei Wang Quan Rui Wang Feng Gang Tao 《中国化学快报》2007,18(12):1460-1462
Nation-Teflon bimembrane was used as an efficient support for the preparation and application of heterogeneous palladium catalysts.The supported palladium catalysts exhibit high activity and stability in the Suzuki cross-coupling of aryl bromides with arylboronic acids to afford the corresponding biaryls in good to excellent yields,and can be readily recovered and reused several times without significant loss of activity. 相似文献
79.
Valerio Magnasco Massimo Ottonelli Giuseppe Figari Marina Rui Camilla Costa 《Journal of Molecular Structure》1998,430(1-3):231-239
The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angle-dependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (l, l′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, C10, and numerical results are presented for H2-H2 using two-term reduced spectra values from the Kaiserlautern group. 相似文献
80.