全文获取类型
收费全文 | 15983篇 |
免费 | 2691篇 |
国内免费 | 2382篇 |
专业分类
化学 | 8952篇 |
晶体学 | 139篇 |
力学 | 803篇 |
综合类 | 144篇 |
数学 | 1317篇 |
物理学 | 9701篇 |
出版年
2024年 | 27篇 |
2023年 | 212篇 |
2022年 | 304篇 |
2021年 | 363篇 |
2020年 | 424篇 |
2019年 | 331篇 |
2018年 | 349篇 |
2017年 | 425篇 |
2016年 | 555篇 |
2015年 | 621篇 |
2014年 | 764篇 |
2013年 | 1295篇 |
2012年 | 923篇 |
2011年 | 1140篇 |
2010年 | 920篇 |
2009年 | 1087篇 |
2008年 | 1108篇 |
2007年 | 1201篇 |
2006年 | 1081篇 |
2005年 | 994篇 |
2004年 | 805篇 |
2003年 | 810篇 |
2002年 | 753篇 |
2001年 | 664篇 |
2000年 | 583篇 |
1999年 | 557篇 |
1998年 | 403篇 |
1997年 | 391篇 |
1996年 | 299篇 |
1995年 | 298篇 |
1994年 | 227篇 |
1993年 | 171篇 |
1992年 | 156篇 |
1991年 | 138篇 |
1990年 | 80篇 |
1989年 | 104篇 |
1988年 | 66篇 |
1987年 | 59篇 |
1986年 | 31篇 |
1985年 | 64篇 |
1984年 | 49篇 |
1983年 | 22篇 |
1982年 | 46篇 |
1981年 | 30篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 20篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
41.
A highly selective solid phase extraction sorbent for pre-concentration of sameridine made by molecular imprinting 总被引:5,自引:0,他引:5
Summary A novel approach to solid phase extraction, based on the use of a highly selective molecularly imprinted polymer, is presented.
The versatility of this type of sorbent for solid phase extraction was demonstrated in a model batch-wise pre-concentration
of sameridine prior to gas chromatography. Problems associated with leakage of remaining imprint molecules during the desorption
phase could be eliminated by the use of a close structural analogue of sameridine as the imprint species. It was found that
a major benefit of the imprinted polymer was its specificity, which lead to distinctly cleaner chromatographic traces and
ability to improve sensitivity by extracting sameridine from larger sample volumes. 相似文献
42.
与q形变玻色算符逆算符相关的相干态及其量子统计性质 总被引:1,自引:1,他引:0
讨论了q形变玻色算符的广义逆算符作用于q-相干态所得到的两类量子态的数学及量子统计性质。结果表明,q-相干态的光子激发态不存在压缩但呈现反聚束效应,而q-相干态的光子湮灭态却存在压缩但不呈现反聚束效应。 相似文献
43.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
44.
45.
The 2D Rancieite type manganic acid was prepared by reduction of KMnO4 in acidic medium. Its ion exchange behavior allows to prepare alkali derivatives. All compounds were characterized with use of a combination of X-ray diffraction, chemical analyses, TGA, magnetic measurements and spectroscopic techniques. The evolution of their chemical composition versus temperature was studied between 180 and 400 °C. It shows that the dehydration process is partly reversible in these compounds whereas the weak reduction is irreversible. The 2D Rancieite-type manganic acid is readily different from a Birnessite-type phyllomanganate, as shown by several features: the interlayer distance, the ion exchange capacity, the thermal behavior, the interlayer cation content, the manganese average oxidation state, the magnetic behavior and the IR spectrum. 相似文献
46.
采用MSDI严格角动量投影46Ti、48Cr形变HF谱 总被引:1,自引:1,他引:0
采用修正的表面δ相互作用(MSDI),以球形壳模型单粒子态作基矢,对fp壳层区偶偶核46Ti、48Cr进行形变Hartree–Fock(HF)计算,并用形变HF单粒子态构造Slater行列式波函数,即形变HF内禀态,然后对其实施严格角动量投影程序,得到比较合理的结果. 相似文献
47.
The direct growth of ZnSe–CdSe solid solution onto metallic cathodes by electrodeposition from acidic aqueous sulphate solutions
is described. The plating process is studied by simple voltammetry, while the structure and composition of the electrolytic
deposits are investigated by X-ray diffraction. The experimental d-spacing values of the as-grown mixed lattice are compared to data from reference Zn
x
Cd1-x
Se pellets of standard composition, produced by a sintering method. The findings are supplemented with energy-dispersive X-ray
(EDX) elemental analysis. Thereupon, the variation of the mole fraction x in Zn
x
Cd1-x
Se, and the solid phase constitution of the electrodeposits are determined and correlated to the electrochemical conditions
of growth. The resulting films contain admixtures of CdSe compound and metallic Cd. 相似文献
48.
采用固相反应合成了四羟基苯基卟啉与与Fe^2+,Co^2+金属离子的配合物,在室温下,将其与分子O2作用,提纯后得到两种固态氧合配合物.通过元素分析、红外光谱(IR)、核磁共振氢谱(^1HNMR)、电导、热分析(TG/DTA)、紫外光谱(UV)等测试手段确定了氧合配合物的组成为[Co·THPP·O2](NO3)2·2H2O、[Fe·THPP·O2]Cl2·2H2O],可知1mol配合物吸收了1molO2,采用失重法测定了氧合配合物中的配位氧,确定1mol金属配合物吸收1molO2形成超氧配合物. 相似文献
49.
Wilson A. Cañas-Marín Julián D. Ortiz-Arango Uriel E. Guerrero-Aconcha Claudia P. Soto-Tavera 《Fluid Phase Equilibria》2007
The ability of Soave–Redlich–Kwong cubic equation of state (SRK EoS) to predict densities and thermodynamic derivative properties such as thermal expansivity, isothermal compressibility, calorific capacity, and Joule–Thompson coefficients, for two gas condensates over a wide range of pressures (up to 110 MPa) was studied. The predictions of the EoS were compared to Monte Carlo simulation data obtained by Lagache et al. [M.H. Lagache, P. Ungerer, A. Boutin, Fluid Phase Equilibr. 220 (2004) 221]. Two completely different alpha functions for the SRK EoS attractive term were used and their respective effects on the predictions of such properties were analyzed. Also, two different forms of the crossed terms of the attractive parameter, aij, and three expressions of the crossed terms of the repulsive parameter, bij, were combined in different ways, and predictions were carried out. Little sensitivity of the properties on the chosen alpha function, except for the calorific capacities, was found in the systems studied. The most commonly used combination rules to model phase behavior of reservoir fluids, i.e. geometric and arithmetic forms of aij and bij, respectively, predicted very deficient results for these fluids at extreme conditions, specially for density calculations. 相似文献
50.