全文获取类型
收费全文 | 21734篇 |
免费 | 1361篇 |
国内免费 | 1920篇 |
专业分类
化学 | 20685篇 |
晶体学 | 407篇 |
力学 | 744篇 |
综合类 | 78篇 |
数学 | 182篇 |
物理学 | 2919篇 |
出版年
2024年 | 20篇 |
2023年 | 203篇 |
2022年 | 423篇 |
2021年 | 391篇 |
2020年 | 632篇 |
2019年 | 648篇 |
2018年 | 694篇 |
2017年 | 954篇 |
2016年 | 1092篇 |
2015年 | 839篇 |
2014年 | 854篇 |
2013年 | 2190篇 |
2012年 | 1375篇 |
2011年 | 1173篇 |
2010年 | 1064篇 |
2009年 | 1306篇 |
2008年 | 1120篇 |
2007年 | 1188篇 |
2006年 | 1057篇 |
2005年 | 883篇 |
2004年 | 785篇 |
2003年 | 681篇 |
2002年 | 562篇 |
2001年 | 503篇 |
2000年 | 521篇 |
1999年 | 457篇 |
1998年 | 425篇 |
1997年 | 369篇 |
1996年 | 353篇 |
1995年 | 354篇 |
1994年 | 280篇 |
1993年 | 229篇 |
1992年 | 184篇 |
1991年 | 156篇 |
1990年 | 152篇 |
1989年 | 131篇 |
1988年 | 160篇 |
1987年 | 168篇 |
1986年 | 103篇 |
1985年 | 78篇 |
1984年 | 93篇 |
1983年 | 21篇 |
1982年 | 56篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1973年 | 6篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
121.
Epoxy resins toughened with carboxyl-terminated butadieneacrylonitrile copolymers (CTBN) are two-phase thermosets. The network of the in situ formed rubber particles depends upon the curing mechanism of the resin. When a primary polyamine such as triethylene tetramine was used as curing agent, the network of the rubber phase was quite incomplete, whereas a perfect rubber network was formed with 2-ethyl-4-methyl imidazole as the curing agent. 相似文献
122.
123.
A new algorithm/program has been elaborated for simultaneous processing of different sets of vapour–liquid equilibrium data. The program was tested with six binary hexane + isomeric pentanol systems, each of them measured at three different isobaric conditions and one isothermal system of tert-butyl-methyl-ether + 2-methyl-2-propanol measured at three different temperatures. The correlation uses the maximum likelihood method, taking into account real behaviour of vapour phase. The parameters obtained are valid within the whole temperature range of the data, and are consistent in comparison with those obtained from individual correlations of isobars or isotherms. Results are presented for the Wilson and NRTL equations. 相似文献
124.
Xin Ying ZHANG Xue Sen FAN Hong Ying NIU Jian Ji WANGSchool of Chemical Environmental Sciences Henan Normal University Key Laboratory ofEnvironmental Science Engineering of Henan Education Department Xinxiang 《中国化学快报》2003,(10)
a, a'-Bis(substituted benzylidene)cycloalkanones were efficiently prepared from cycloalkanones and benzaldehydes in [bmim][BF4] by using iron(III) chloride hexahydrate as a catalyst. It is shown that [bmim][BF4] and iron(III) chloride hexahydrate can be quantitatively recovered and be reused effectively for many times. Compared with the known methods, this novel process has the advantage of being an envkonmentally benign process together with good yields and mild reaction conditions. 相似文献
125.
V. B. Vol'eva I. S. Belostotskaya O. V. Shishkin Yu. T. Struchkov V. V. Ershov 《Russian Chemical Bulletin》1995,44(8):1489-1491
Anhydrodimers have been synthesized by reactions of salicylaldehyde and 3,5-di-tert-butylsalicylaldehyde with SOCl2 or PCl5. A mechanism of condensation has been proposed, and the molecular structure of dibenzo-2,6,9-trioxabicyclo[3.3.1]nona-3,7-diene has been determined by X-ray structural analysis.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1549–1551, August, 1995.The work was supported by the Russian Foundation for Basic Research (Project No. 94-03-08653). 相似文献
126.
介绍了核磁共振(NMR)波谱,尤其是核磁共振二维谱(2D NMR)在最近几年内的进展。内容包括怎样用NMR测定高聚物的序列分布、共聚物结构、聚合物的混溶性、聚合物液晶的取向度、分子量、短链度和长链支化度、凝聚态高聚物的多相结构等。 相似文献
127.
高效液相色谱法测定精对苯二甲酸中微量杂质 总被引:6,自引:0,他引:6
建立了高效液相色谱法(HPLC)同时测定精对-苯二甲酸(PTA)中微量杂质4-羧基苯甲醛(4-CBA)、对-甲基苯甲酸(P-TOL)和苯甲酸(C7H6O2)含量的方法。采用的色谱柱为Shim-PackWAX-1柱,流动相为0.1mol/L NH3H2PO4 6%CH3OH,(pH4.5),检测波长为254nm。PTA中微量杂质4-CBA、P-TOL和C7H6O2的含量分别为0.59-235.20mg/kg、4.52-392.00mg/kg和0.28-24.55mg/kg时线性关系良好,其线性相关系数分别为0.9998、0.9997和0.9999。苯甲酸加样平均回收率99.03%,RSD0.37%。 相似文献
128.
高效液相色谱法测定细胞分裂素的方法研究 总被引:4,自引:0,他引:4
利用高效液相色谱法测定水稻愈伤组织和微生物发酵产品中的玉米素,二氢玉米素,核糖基玉米素和核糖基二氢玉米素。样品用抽提液抽提,经Bio-Rex70弱阳离子交换柱和XAD-7/Sep-pakC18复合柱净化和富集后,直接用HPLC分析,方法回收率达94%~84%,相对标准偏差小于3.3%。最低检测限达2.0ng。 相似文献
129.
SynthesisandCharacterizationofChiralLiquidCrystalCMPPCDPTIANYan-qing,ZHAOYing-ying,SUFeng-yuandTANGXin-yi(DepartmentofChemist... 相似文献
130.
Simultaneous isolation and determination of esculin and rutin in natural materials using SPE and HPLC 总被引:1,自引:0,他引:1
Summary Esculin (ESC) and rutin (RUT) have been simultaneously isolated from pharmaceutical natural materials by solid phase extraction (SPE). Determination of both substances was performed by reversed phase high performance liquid chromatography (RPHPLC) with UV detection. Optimization of the separation conditions showed that simultaneous isolation and determination of rutin and esculin from pharmaceutical material was possible. The recovery obtained was not lower than 95±2%. 相似文献