全文获取类型
收费全文 | 4463篇 |
免费 | 742篇 |
国内免费 | 415篇 |
专业分类
化学 | 3150篇 |
晶体学 | 42篇 |
力学 | 271篇 |
综合类 | 46篇 |
数学 | 424篇 |
物理学 | 1687篇 |
出版年
2024年 | 14篇 |
2023年 | 125篇 |
2022年 | 171篇 |
2021年 | 177篇 |
2020年 | 211篇 |
2019年 | 162篇 |
2018年 | 145篇 |
2017年 | 126篇 |
2016年 | 207篇 |
2015年 | 180篇 |
2014年 | 252篇 |
2013年 | 279篇 |
2012年 | 394篇 |
2011年 | 359篇 |
2010年 | 266篇 |
2009年 | 265篇 |
2008年 | 282篇 |
2007年 | 272篇 |
2006年 | 270篇 |
2005年 | 182篇 |
2004年 | 126篇 |
2003年 | 110篇 |
2002年 | 98篇 |
2001年 | 86篇 |
2000年 | 86篇 |
1999年 | 99篇 |
1998年 | 90篇 |
1997年 | 89篇 |
1996年 | 65篇 |
1995年 | 90篇 |
1994年 | 74篇 |
1993年 | 44篇 |
1992年 | 58篇 |
1991年 | 45篇 |
1990年 | 40篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有5620条查询结果,搜索用时 15 毫秒
81.
消旋反式菊酸α—氰基—4—氟—3—苯氧基苄酯的合成 总被引:1,自引:0,他引:1
含氟拟除虫菊酯的合成是近年来新型高效拟除虫菊酯研究工作的方向之一。该类化合物由于具有高效、低毒、广谱、低残留、无致癌、致畸作用,有的还具有低鱼毒,杀螨的特性,因此倍受注目。西德拜尔公司开发的百治菊酯(Baythroid)(1)便是其中一种高效杀虫剂。 相似文献
82.
建立了分离测定萘普生和溴代萘普生的反相键合相高效液相色谱法。采用ODS柱,以添加50mmol/L乳酸并用高氯酸调节pH为2.5的80%甲醇-水溶液作为流动相,以苯甲酸为内标物,测定了不对称合成工艺产物中萘普生和溴代萘普生的含量。方法的准确度分别为99.83%~102.07%(萘普生)和99.0%~100.83%(溴代萘普生),相对标准偏差分别小于2.58%(萘普生)和3.64%(溴代萘普生)。方法可用于工艺条件的选择和质量检测。 相似文献
83.
Zou Jianzhong Wu Yong Duan Chunyin Liu Yongjiang Xu Zheng 《Transition Metal Chemistry》1998,23(3):305-308
Three binuclear copper(II) complexes bridged by three different bridging ligands: μ-TPHA (terephthalato), μ-PHTA (phthalato)
and μ-TCB (tetracarboxylatobenzene) have been synthesized. The crystal structure of [{Cu(dipn)}2(μ-TPHA)](ClO4)2 where dipn = N-(3-aminopropyl)-1,3-propanediamine was solved at room temperature. The [{Cudipn}2(μ-TPHA)](ClO4)2 complex consists of a μ-terephthalato bridging binuclear copper(II) cationic unit and two non-coordinated perchlorate anions.
The TPHA ligand bridges in a bismonodentate fashion. The environment of the copper(II) ion is a distorted plane-square-planar coordination sphere. The magnetic
properties of the three complexes have been investigated in the 75–300 K range, and show that the geometry of the CuII atom is the important factor for magnetic interactions in the terephthalato bridging binuclear copper(II) complexes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
84.
Pan A Yang H Liu R Yu R Zou B Wang Z 《Journal of the American Chemical Society》2005,127(45):15692-15693
High-quality CdSxSe1-x nanobelts of variable composition (0 = x = 1) were fabricated by a simple one-step thermal evaporation route. Photoluminescence measurements showed that all the CdSxSe1-x nanobelts have a single near-bandedge emission band, and their spectral maximum positions can be tuned from approximately 508 nm (for pure CdS) to approximately 705 nm (for pure CdSe). These kinds of nanobelts may have potential applications in adjustable nano/micro photoelectric devices in the visible region. 相似文献
85.
Xiang Pu Hanguang Wang Ping Zou Guangtu Wang Guizhou Yue Kuan Liu Li Cheng Juhua Feng Huixian Zhang Qianming Huang Hanbing Rao 《大学化学》1986,36(1):2002053-0
The crop science of Sichuan Agricultural University is an authorized first-class discipline. As the strategic supporting department for innovative talent cultivation in agriculture and forestry major, we are facing a long-term challenge in reforming the teaching mode for basic course-organic chemistry and cultivating talented students with solid basic knowledge and strong sense of innovation. Herein a thorough survey was performing to establish the executable teaching programs for this course during the "Double-First Class Universities Plan" period. A multidimensional teaching resource library for organic chemistry course was also constructed. The new classroom teaching mode "Interest cultivation-Creative thought development-Autonomous and Cooperative learning", along with a stepwise practice teaching mode "Foundation skills-Integrated application-Innovative trial" was proposed and practiced among thirty-five majors including agriculture, forestry and veterinary, to improve the quality for innovative talent cultivation and support our first-class discipline construction. This research could probably serve as a reference for congeneric agricultural university. 相似文献
86.
Qunying Jiang Min Pan Jialing Hu Junlin Sun Lei Fan Zhiqiao Zou Jianshuang Wei Xiaoquan Yang Xiaoqing Liu 《Chemical science》2021,12(1):148
Many cancer treatments including photodynamic therapy (PDT) utilize reactive oxygen species (ROS) to kill tumor cells. However, elevated antioxidant defense systems in cancer cells result in resistance to the therapy involving ROS. Here we describe a highly effective phototherapy through regulation of redox homeostasis with a biocompatible and versatile nanotherapeutic to inhibit tumor growth and metastasis. We systematically explore and exploit methylene blue adsorbed polydopamine nanoparticles as a targeted and precise nanocarrier, oxidative stress amplifier, photodynamic/photothermal agent, and multimodal probe for fluorescence, photothermal and photoacoustic imaging to enhance anti-tumor efficacy. Remarkably, following the glutathione-stimulated photosensitizer release to generate exogenous ROS, polydopamine eliminates the endogenous ROS scavenging system through depleting the primary antioxidant, thus amplifying the phototherapy and effectively suppressing tumor growth in vitro and in vivo. Furthermore, this approach enables a robust inhibition against breast cancer metastasis, as oxidative stress is a vital impediment to distant metastasis in tumor cells. Innovative, safe and effective nanotherapeutics via regulation of redox balance may provide a clinically relevant approach for cancer treatment.Amplified oxidative stress achieved by modulating redox homeostasis with PDA–MB for highly effective synergistic phototherapy to inhibit primary tumors and metastases. 相似文献
87.
88.
The effects of molecular structure on the solute-micelle and solute-stationary phase binding constants in micellar liquid chromatography (MLC) have been investigated. The following points have been observed. (1) There is quite a good linear relationship between the solute-micelle and solute-stationary phase binding constants in MLC with the cationic (CTAB) and anionic surfactants as the additives, which means that the contribution of physico-chemical properties of solutes on the solute-micelle and solute-stationary phase binding constants acts in a parallel way. (2) Good quantitative relationships between the solute-micelle and solute-stationary phase binding constants and the solvatochromic parameters have been obtained, which indicates that the distribution mechanism of the neutral solutes in MLC is determined via their molecular interactions. Both the cavity process and the hydrogen bond interaction play a very important role in the retention of neutral solutes in MLC. The contribution of the hydrogen bond interaction, especially the hydrogen donor ability of the solutes on those binding constants in anionic and cationic surfactant MLC, is determined in a different way. (3) Linear regression analysis of the solute-micelle and solute-stationary phase binding constants between the cationic and anionic surfactant MLC has been carried out. The obtained results suggest that the transfer of the non-polar solutes from the aqueous phase to the anionic and cationic surfactant micelles acts in a parallel way, but that of the polar solutes in a different way. A model of micelles with three different sites of solubilization, i.e., (1) the core of the micelle, (2) the surface of the micelle and (3) the palisade layer of the micelle, has been used to successfully explain the observed results. Finally, the retention behavior of solutes in MLC is compared with that in reversed-phase liquid chromatography (RP-LC). It has been observed that there is no difference in separation selectivity for the non-polar solutes between MLC and RP-LC; however, for the polar solutes, MLC provides a different separation selectivity compared to that in RP-LC. 相似文献
89.
Tao He Ying‐Fang Zou Cai‐Yuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3367-3378
Comb‐shaped graft copolymers with poly(methyl methacrylate) as a handle were synthesized by the macromonomer technique in two steps. First, polytetrahydrofuran acrylate (A‐PTHF), prepared by the living cationic ring‐opening polymerization of tetrahydrofuran, underwent homopolymerization with 1‐(ethoxycarbonyl)prop‐1‐yl dithiobenzoate as an initiator under 60Co γ irradiation at room temperature; Second, the handle of the comb‐shaped copolymers was prepared by the block copolymerization of methyl methacrylate with P(A‐PTHF) as a macroinitiator under 60Co γ irradiation. The two‐step polymerizations were proved to be controlled with the following evidence: the straight line of ln[M]0/[M] versus the polymerization time, the linear increase in the number‐average molecular weight with the conversion, and the relatively narrow molecular weight distribution. The structures of the P(A‐PTHF) and final comb‐shaped copolymers were characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3367–3378, 2002 相似文献
90.
Yaping Zou 《Tetrahedron letters》2007,48(27):4781-4784
A series of new diphosphite ligands have been easily prepared from BINOL derivatives; moderate enantioselectivities (up to 80% ee) and excellent regioselectivities (b/l up to 98/2) have been achieved in the Rh-catalyzed asymmetric hydroformylation of vinyl acetate. 相似文献