全文获取类型
收费全文 | 68026篇 |
免费 | 15487篇 |
国内免费 | 6528篇 |
专业分类
化学 | 64371篇 |
晶体学 | 752篇 |
力学 | 2618篇 |
综合类 | 463篇 |
数学 | 6041篇 |
物理学 | 15796篇 |
出版年
2024年 | 60篇 |
2023年 | 689篇 |
2022年 | 821篇 |
2021年 | 1312篇 |
2020年 | 2612篇 |
2019年 | 3771篇 |
2018年 | 2133篇 |
2017年 | 1786篇 |
2016年 | 4810篇 |
2015年 | 4995篇 |
2014年 | 5268篇 |
2013年 | 6432篇 |
2012年 | 5963篇 |
2011年 | 5441篇 |
2010年 | 5123篇 |
2009年 | 5054篇 |
2008年 | 4795篇 |
2007年 | 3881篇 |
2006年 | 3459篇 |
2005年 | 3312篇 |
2004年 | 2802篇 |
2003年 | 2414篇 |
2002年 | 3103篇 |
2001年 | 2275篇 |
2000年 | 2058篇 |
1999年 | 1147篇 |
1998年 | 656篇 |
1997年 | 623篇 |
1996年 | 535篇 |
1995年 | 461篇 |
1994年 | 401篇 |
1993年 | 317篇 |
1992年 | 247篇 |
1991年 | 231篇 |
1990年 | 211篇 |
1989年 | 145篇 |
1988年 | 145篇 |
1987年 | 125篇 |
1986年 | 94篇 |
1985年 | 75篇 |
1984年 | 49篇 |
1983年 | 43篇 |
1982年 | 47篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 11篇 |
1976年 | 7篇 |
1975年 | 12篇 |
1959年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
991.
992.
Study on the Phase Diagram of CsCl-CeCl3-HCl(11%)-H2O System and the Properties of the Compounds 总被引:2,自引:0,他引:2
The equilibrium solubility of CsCl-CeCl3-HCl(11%)-H2O qua-ternary system at 25℃ has been determined by the physicchemical analysis method ,and the phase diagram was plotted, Two new double salts 3CsCl.CeCl3.3H2O and CsCl.CeCl3.4H2O obtained from the complicated system were identified and characterized by XRD,TG-DTA ,DSC,UV and fluorescence spectroscopy, Studies on the fluorescence excitation and emission show that 3CsCl.CeCl3.3H2O and CsCl.CeCl3.4H2O have upconversion luminescence of infrared-visible range,and the upconversion emission intensity increases with the increase of ratio of CeCl3 in CsCl. 相似文献
993.
The high-performance liquid chromatographic behavior of some sulfonamides and quinolones was studied on a p-tert-butyl-calix[6]arene-bonded silica gel stationary phase. The effect of mobile phase variables such as methanol content, ionic strength and pH on their chromatographic behavior was investigated. The retention behavior of sulfonamides on the stationary phase was compared with that on both Zorbax C18-bonded silica gel and γ-(ethylenediamino)propyltriethoxylsilane-bonded silica gel (diamino-bonded phase). The retention mechanism of sulfonamides and quinolones on the stationary phase was also discussed. The results indicate that the stationary phase behaves as a reversed-phase packing and its separation selectivity is much better than that of not only Zorbax C18 phase but also diamino-bonded phase. Some sulfonamides and quinolones were separated on the stationary phase, but the separation of sulfonamides is far more successful. 相似文献
994.
Hans‐Ruedi Mürner Rosario Scopelliti Jean‐Claude G. Bünzli 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):m434-m435
In the title compound, [TbCl(C27H35N3)2(H2O)](ClO4)2·2C2H6O, the TbIII ion has a coordination number of eight, composed of two tridentate substituted‐terpyridine ligands, a water molecule and a bound Cl? anion. The first coordination shell can be described as a distorted bicapped trigonal prism. The dihedral angles between pyridine rings belonging to the same tpy ligand range from 5.2 (5) to 16.8 (5)°. 相似文献
995.
Two new esters, methyl 4‐(prenyloxy)dihydrocinnamate and methyl 4‐(geranyloxy)dihydrocinnamate, together with fourteen known compounds have been isolated from the stem bark of Zanthoxylum pistaciiflorum. The structures of two new compounds were determined through spectral analyses. Among the isolates, four compounds exhibited effective cytotoxicities against P‐388 and HT‐29 cell lines in vitro. 相似文献
996.
利用大分子单体技术合成接枝共聚物 总被引:9,自引:0,他引:9
大分子单体和小分子共单体共聚是合成接枝共聚物的重要途径之一。本文综述了大分子单体通过各种聚合方式(自由基共聚、离子型共聚、配位共聚、基团转移共聚和逐步共聚)和普通小分子单体的共聚反应,详细讨论了大分子单体和小分子单体的自由基共聚反应动力学,并简要介绍了接枝共聚物的应用背景。 相似文献
997.
The relaxation properties of water saturated in porous core are discussed and the distribution of proton transverse relaxation time and bi-exponential model of longitudiual relaxation time are obtained, which provide an illustration for two-model of fluids saturated in porous media. The cutoff value of T_1 based on relaxation specific property of fluids in porous core is adopted to improve the correlation between permeability and ?4T1b2. 相似文献
998.
用X-射线衍射方法测定了μ-氧-双(三苄基锡)的晶体结构,该化合物晶体属三方晶系,空间群为R3,晶体学参数:a=b=c=0.9646 nm,α=β=γ=83.99(1)°,V=0.8840 nm3, Z=1, Dx=1.503 g·cm-3, μ=14.473 cm-1, F(000)=402, R 相似文献
999.
1000.
The cover picture shows a typical building within the Campus of Xiamen University displaying Chen Jiageng (Tan Kah Kee)'s style. Just like many beautiful buildings designed and constructed by human, Nature “designs and constructs” a huge number of useful molecules with fascinating structures called natural products. Many natural products possess a fused six or seven‐membered carbocyclic unity. On page 315–322, the Huang's group disclosed a three‐step “[2+n]” annulation method for the construction of fused six and seven‐membered carbocyclic enimines and enones. The method starts from simple cyclic ketones and terminal olefinic amides, and relies on both the Suzuki coupling reaction and the olefin‐amide based Friedel‐Crafts type acylating reaction, a method developed by Huang and coworkers.