全文获取类型
收费全文 | 997篇 |
免费 | 169篇 |
国内免费 | 107篇 |
专业分类
化学 | 654篇 |
晶体学 | 9篇 |
力学 | 44篇 |
综合类 | 4篇 |
数学 | 114篇 |
物理学 | 448篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 48篇 |
2021年 | 59篇 |
2020年 | 50篇 |
2019年 | 37篇 |
2018年 | 28篇 |
2017年 | 41篇 |
2016年 | 54篇 |
2015年 | 37篇 |
2014年 | 64篇 |
2013年 | 63篇 |
2012年 | 106篇 |
2011年 | 105篇 |
2010年 | 50篇 |
2009年 | 52篇 |
2008年 | 33篇 |
2007年 | 64篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 18篇 |
2003年 | 24篇 |
2002年 | 28篇 |
2001年 | 22篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有1273条查询结果,搜索用时 578 毫秒
41.
42.
Xiaojuan Liu Qingqing Wen Prof. Dr. Li Xiang Dr. Xuebing Leng Prof. Dr. Yaofeng Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(24):5494-5499
The synthesis and catalytic applications of trivalent rare-earth metal alkyl complexes have been well developed, but the chemistry of divalent rare-earth metal alkyl complexes lagged much behind. Herein, we report the synthesis, structure, and catalytic applications of a samarium(II) monoalkyl complex supported by a β-diketiminato-based tetradentate ligand, [LSmCH(SiMe3)2] (L=[MeC(NDipp)CHC(Me)NCH2CH2N(Me)CH2CH2NMe2]−, Dipp=2,6-(iPr)2C6H3). This complex is synthesized by the salt metathesis reaction of samarium iodide [LSm(μ-I)]2 and KCH(SiMe3)2 in 63 % yield. Its structure is characterized by single-crystal X-ray diffraction, showing a distorted square-pyramid coordination geometry. This samarium(II) monoalkyl complex exhibits high catalytic activity in the hydrosilylation of aryl and methyl-substituted unsymmetrical internal alkynes with secondary hydrosilanes, selectively providing the α-(E) products in high yields. 相似文献
43.
Taniya M. S. K. Pathiranage Dushanthi S. Dissanayake Crystal N. Niermann Yixin Ren Michael C. Biewer Mihaela C. Stefan 《Journal of polymer science. Part A, Polymer chemistry》2017,55(20):3327-3346
Semiconducting polythiophenes display electroactive properties which make them excellent candidates for applications as electroactive materials. Ability to undergo doping and to switch between different oxidation states allow tuning the chemical and physical properties of polythiophenes. Furthermore, the ability to integrate polythiophenes into copolymers, hybrid composites with metals and inorganic materials make them useful in electronic and biomedical applications. The capability to vary the properties of the final material with low production cost and high processability into thin films makes polythiophenes desirable materials for many applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3327–3346 相似文献
44.
Combined effect of modified zeolite 13X and β-nucleating agent on improving β-crystal content and toughening polypropylene random copolymer 总被引:1,自引:0,他引:1
Although addition of β-NUCLEATING agent directly into homo-polypropylene(PPH) is a useful method to improve β-CRYSTAL content and toughen PPH, polypropylene random copolymer(PPR) makes this method powerless due to its random structure and low crystallinity. In this study, the-nucleated PPR with high β-CRYSTAL content was prepared by a novel high effective β-NUCLEATING system which consists of-nucleation agent(TMB-5) and modified zeolite 13X(M13X). It was found that M13X and TMB-5 had a synergistic influence on improving β-CRYSTAL content and toughening PPR. The content of β-CRYSTAL in PPR/M13X/TMB-5 was significantly larger than the sum of that in PPR/M13X and PPR/TMB-5. Besides,fracture behavior, phase morphology and relaxation of matrix chain segments were also investigated. The results showed that M13X and TMB-5 improved the mobility of amorphous chain segments at low temperature and contributed to much energy dissipation. This work provides a powerful method to modify PPR. 相似文献
45.
We model the detection and crosstalk probability of orbital angular momentum (OAM) states of the entangled signal photon in the Kolmogorov channels of the low-order turbulence aberrations and by the Rytov approximation. The results show that lower OAM mode number of signal photons and larger sub-beam number of multi-Gaussian Schell-model pump beam, the less susceptible of the detection probability of the signal photon to spatial coherence of source and turbulence aberrations is achieved. The maximum crosstalk probability is decrease as the decreasing of the sub-beam number of multi-Gaussian Schell-model. Enlarging OAM difference value or decreasing sub-beam number of multi-Gaussian Schell-model pump beam results in a lower crosstalk probability of the OAM of entangled signal photons. 相似文献
46.
Cheng Wang Yuxin Leng Chuang Li Baozhen Zhao Zhizhan Xu 《Optics & Laser Technology》2010,42(4):657-661
A decentered grating stretcher for chirped pulse amplification systems is analyzed with oblique meridional ray tracing. Several formulae and conclusions are developed to design and optimize the stretcher. On basis of an analytical phase expression with an explicit significance, the expressions of the second-, third- and approximate fourth-order phases at the central wavelength are presented with only independent variables. These simplify the parameter design for this kind of stretcher and the phase compensation design of the whole amplifier system, which has been demonstrated with a practical example. 相似文献
47.
48.
A simulation-based approach for fleet design in a technician dispatch problem with stochastic demand
C E Cortés M Gendreau D Leng A Weintraub 《The Journal of the Operational Research Society》2011,62(8):1510-1523
We address the problem of developing policies for selecting the proper number of technicians to hire (fleet size) for an on-call repair service operating over a yearly planning horizon in an environment where the number of requests to be serviced each day can vary significantly from day to day and on a seasonal basis. We propose a new approach based on the simulation of a large number of sampled weekly instances and the application of a previously developed optimization procedure for the daily dispatch of technicians. The sampled instances are derived from an extensive statistical analysis of demand data with respect to several key parameters. The results of the simulations are utilized to adjust performance curves in function of fleet size that are then used in an economic analysis of the trade-offs between service quality and cost. Efficient policies for fleet design are then deducted from this analysis. 相似文献
49.
4,4′-Methylene diphenyl diisocyanate (MDI) is one of the most important isocyanates in the industrial production of polyurethane and other MDI-based synthetics. Because of its high reactivity, it is known as a sensitizing agent, caused by protein adducts. Analysis of MDI is routinely done by determination of the nonspecific 4,4′-methylenedianiline as a marker for MDI exposure in urine and blood. Since several publications have reported specific adducts of MDI and albumin or hemoglobin, more information about their existence in humans is necessary. Specific adducts of MDI and hemoglobin were only reported in rats after high-dose MDI inhalation. The aim of this investigation was to detect the hemoglobin adduct 5-isopropyl-3-[4-(4-aminobenzyl)phenyl]hydantoin (ABP-Val-Hyd) in human blood for the first time. We found values up to 5.2 ng ABP-Val-Hyd/g globin (16 pmol/g) in blood samples of workers exposed to MDI. Because there was no information available about possible amounts of this specific MDI marker, the analytical method focused on optimal sensitivity and selectivity. Using gas chromatography–high-resolution mass spectrometry with negative chemical ionization, we achieved a detection limit of 0.02 ng ABP-Val-Hyd/g globin (0.062 pmol/g). The robustness of the method was confirmed by relative standard deviations between 3.0 and 9.8 %. Combined with a linear detection range up to 10 ng ABP-Val-Hyd/g globin (31 pmol/g), the enhanced precision parameter demonstrates that the method described is optimized for screening studies of the human population. 相似文献
50.
Shi‐Zhao Kang Zhizhen Xu Yixin Song 《Journal of Dispersion Science and Technology》2013,34(6):857-859
In this article, TiO2 nanorods (aspect ratio >20) were prepared through a polyol process and doped with metal ions (Cu2+, Ni2+, Fe3+, and Cr3+). Compared with TiO2 nanoparticles, the TiO2 nanorods displayed relatively higher photocatalytic activity for the degradation of copper sulfophthalocyanine. Moreover, the photocatalytic activity was greatly enhanced when the metal ions were doped in the TiO2 nanorods. 相似文献