全文获取类型
收费全文 | 57808篇 |
免费 | 2938篇 |
国内免费 | 6330篇 |
专业分类
化学 | 49030篇 |
晶体学 | 425篇 |
力学 | 545篇 |
综合类 | 812篇 |
数学 | 6516篇 |
物理学 | 9748篇 |
出版年
2023年 | 475篇 |
2022年 | 1652篇 |
2021年 | 2071篇 |
2020年 | 1336篇 |
2019年 | 1456篇 |
2018年 | 1113篇 |
2017年 | 1301篇 |
2016年 | 1625篇 |
2015年 | 1617篇 |
2014年 | 1960篇 |
2013年 | 3981篇 |
2012年 | 2901篇 |
2011年 | 2684篇 |
2010年 | 2458篇 |
2009年 | 3141篇 |
2008年 | 3386篇 |
2007年 | 3625篇 |
2006年 | 3029篇 |
2005年 | 2346篇 |
2004年 | 2159篇 |
2003年 | 1968篇 |
2002年 | 4303篇 |
2001年 | 1822篇 |
2000年 | 1371篇 |
1999年 | 1114篇 |
1998年 | 1012篇 |
1997年 | 863篇 |
1996年 | 921篇 |
1995年 | 806篇 |
1994年 | 775篇 |
1993年 | 759篇 |
1992年 | 744篇 |
1991年 | 510篇 |
1990年 | 433篇 |
1989年 | 412篇 |
1988年 | 368篇 |
1987年 | 266篇 |
1986年 | 250篇 |
1985年 | 350篇 |
1984年 | 276篇 |
1983年 | 179篇 |
1982年 | 319篇 |
1981年 | 489篇 |
1980年 | 439篇 |
1979年 | 483篇 |
1978年 | 390篇 |
1977年 | 286篇 |
1976年 | 241篇 |
1974年 | 109篇 |
1973年 | 191篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
以4-N,N-二乙基氨基水杨醛为原料,制备了2-(苯并噻唑-2-基)-5-(N,N-二乙基氨基)苯酚衍生物(探针L),并对其结构进行了表征。在DMSO/PBS(体积比3∶7,pH=7.4)溶液中,探针L具有高选择性并可荧光"关-开"识别H_2S,在365nm紫外灯照射下,由无荧光变成蓝色荧光。实验表明,探针L识别H_2S的检测限为2.05×10~(-6)mol/L,pH适用范围为6~9,可用于检测实际水样中的H_2S。 相似文献
972.
聚吡咯水杨酸修饰电极的电化学行为及水杨酸含量测定 总被引:10,自引:0,他引:10
本用电化学方法制备了聚吡咯-水杨酸修饰电极;并进行了电化学行为的研究,经电化学处理该是电极对水杨酸根具有选择性响应,响应线性范围在1.0×10^-^5-1.0×10^-^3mol/L之间。电极斜率为40mV/pC,该电极具有较好的稳定性,响应时间在180-300s之间;电极寿命可达60d。 相似文献
973.
V. V. Nikitenko A. I. Martynenko S. A. Ostrovsky V. V. Rusak V. V. Kryuchkov D. A. Topchiev 《Russian Chemical Bulletin》1993,42(2):378-380
3-Methyl-l-vinylpyrazole (M3VP) and 5-methyl-1-vinylpyrazole (M5VP) were isolated as individual substances by vacuum rectification of their mixture (M3VP: M5VP 60 40). For each of them the kinetics of free-radical polymerization in MeOH were measured at low conversions. In both cases the rate of polymerization is proportional to 0.5 order with respect to the initiator (AIBN) concentration. On the other hand, a first order of reaction with respect to monomer concentration is observed only when the latter is relatively low (3M). At higher initial concentrations of monomers the order of reaction becomes less than unity. The overall rate of polymerization for M5VP was higher than for M3VP, whereas the initiation rate remained constant in the whole range of monomer concentrations and did not depend on the exact structure of the monomer. The difference in the rates of polymerization observed for M3VP and M5VP is probably connected with the difference in the key parameterk
p/k
t
1/2
for each of the two isomers. It is concluded that the correct kinetic information about homo- and co-polymerization of M3VP and M5VP cannot be obtained without their adequate separation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 413–415, February, 1993. 相似文献
974.
用停止-流动分光光度法研究了Eu~(2+)与二甲酚橙(XO)间快速电子转移反应的动力学规律。求得了速控步骤的动力学参数。如反应级数(n=2)、几个不同温度下的速率常数(k_(278 K)=5.7×10~8 L·mol~-·s~(-1), k_(s38 K)=1.01×10~9 L·mol~(-1)·s~(-1))、活化能(E=7.6×10~3 J·mol~(-1)), 以及指前因子(A=1.5×10~(10) L·mol~(-1)·s~(-1)), 并判断出其为溶液中扩散控制型反应。根据实验现象与测试结果, 提出了Eu~(2+)与XO的反应分别在Eu~(2+)相对过量和在XO过量时的反应机理, 并判断了各反应步骤速率常数之间的相对关系。 相似文献
975.
高效液相色谱法测定小麦幼苗中植物生长调节剂 总被引:3,自引:0,他引:3
介绍了高效液相色谱法测定麦苗中植物生长调节剂(赤霉素GA3),3-吲哚乙酸(IAA)的方法,用国产预处理小柱处理样品,并以甲醇:1%,冰乙酸=12:88(V/V)为流动相,色谱柱为ZorbaxC18,在210nm紫外检测。 相似文献
976.
对苯乙烯-丙烯腈-二乙烯基苯(S/AN/DVB)交联共聚机理研究曾发现,丙烯腈作为第三单体,可使DVB竞聚率比在S/DVB共聚体系中降低,相互分离显著,从而有利于合成性能较好的离子交换树脂;本文在此基础上,将S/AN/DVB共聚体中的氰基水解成羧基来合成含磺酸、羧酸双功能基树脂,解决了前人研究中仅有50%的氰基水解成羧基的问题,并首次将这种树脂应用于混合氨基酸的分离。 相似文献
977.
The transferability of the first and second order electric moments of localized orbitals have been shown. Some moment characteristics have also been investigated. The standard deviation of first order localized moments is less than 2.0%. The standard deviation of second order electric moment components are larger: although they do not exceed 4.0% for bond orbitals, for lone pair ones they vary about 1.5–10.1%. 相似文献
978.
H. Thielemann 《Fresenius' Journal of Analytical Chemistry》1978,292(3):237
Ohne Zusammenfassung
Separation and identification of the HCH ointment antiskabiosum using ready-made foils for thin-layer chromatography (purity test)
Verwendet wurden Silufol Fertigfolien UV 254 (Herstellerfirma: Sklárny Kavalier, SSR). Sorptionsmittel: Silpearl — weitporiges Silicagel nach Pitra mit Leuchtstoff für UV 254, Unterlage — Aluminiumfolie, Bindemittel — Stärke 相似文献
979.
As an extension of previous reports, the barium carbonate procedure has been optimized in detail for the preparation of apolar columns. The aim was to produce optimum overall column characteristics, and to maintain them unchanged under the prolonged influence of the highest possible temperature. The main parameters under optimization were glass variety, leaching of glass surface with aqueous HCl, and amount of barium carbonate deposited, while deactivation and coating were kept constant. The basic column characteristics were adsorption properties and thermostability of deactivation, acid/base behaviour and separation efficiency. They were determined by a new, quantitative testing procedure. Intense leaching was able to eliminate almost totally the differences between glass varieties and to create a well-defined glass surface. While untreated glass, leached glass, and barium carbonate treated glass showed specific weak points in the respective column quality, the combination of leaching and barium carbonate treatment yielded the highest and most stable quality. Some technical modifications of the preparation procedure are described, including deactivation in the gas phase, and use of pentane as a solvent for static coating. 相似文献
980.
W. Zielenkiewicz B. Golankiewicz G. L. Perlovich M. Koźbiał 《Journal of solution chemistry》1999,28(6):731-745
Solubilities of tricyclic analogs of acyclovir have been determined in water at 25, 35, and 45°C and in octanol, water-saturated octanol, and octanol-saturated water at 25°C. Octanol-water partition coefficients were determined at 25°C. Melting temperatures and molar enthalpies of fusion were measured. Activity coefficients in water, octanol, and in aqueous octanol solutions were determined and are discussed. The effect of hydrophilic and hydrophobic substituents in the tricyclic analogs on their thermodynamic properties are discussed. The standard Gibbs energy of transfer between the saturated phases were found to correlate with known values of the melting point of the solvents and the solubilities of the solute. For a number of the compounds examined, correlations between the minimum inhibitory concentration against the herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV), thymidine kinase-deficient (TK–) strains of VZV and
were established. Detailed conclusions have been derived concerning the relationships between the structure and the thermodynamic parameters of the compounds examined. 相似文献