全文获取类型
收费全文 | 9770篇 |
免费 | 1863篇 |
国内免费 | 1035篇 |
专业分类
化学 | 6850篇 |
晶体学 | 85篇 |
力学 | 578篇 |
综合类 | 52篇 |
数学 | 1087篇 |
物理学 | 4016篇 |
出版年
2024年 | 47篇 |
2023年 | 234篇 |
2022年 | 357篇 |
2021年 | 412篇 |
2020年 | 403篇 |
2019年 | 381篇 |
2018年 | 380篇 |
2017年 | 311篇 |
2016年 | 525篇 |
2015年 | 460篇 |
2014年 | 593篇 |
2013年 | 782篇 |
2012年 | 940篇 |
2011年 | 898篇 |
2010年 | 618篇 |
2009年 | 604篇 |
2008年 | 621篇 |
2007年 | 531篇 |
2006年 | 498篇 |
2005年 | 403篇 |
2004年 | 310篇 |
2003年 | 232篇 |
2002年 | 199篇 |
2001年 | 172篇 |
2000年 | 198篇 |
1999年 | 221篇 |
1998年 | 171篇 |
1997年 | 162篇 |
1996年 | 183篇 |
1995年 | 143篇 |
1994年 | 119篇 |
1993年 | 92篇 |
1992年 | 99篇 |
1991年 | 56篇 |
1990年 | 74篇 |
1989年 | 54篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 37篇 |
1985年 | 38篇 |
1984年 | 13篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
Adsorption enthalpy and desorption enthalpy during displacement of adsorbate to solvent in a liquid-solid system 总被引:6,自引:0,他引:6
Xinpeng Geng Tongshan Han Chen Cao 《Journal of Thermal Analysis and Calorimetry》1995,45(1-2):157-165
The adsorption heat of the stoichiometric displacement process for the adsorption of a solute in a liquid-solid system was
investigated. On the basis of the SDM-A and the rule of the additivity of energy, an expression which describes the dependence
of the adsorption enthalpy on the nature and concentration of the solute, and on the solvent and adsorbent, was derived. The
adsorption heat determined for the solute with the traditional method can be divided into two independent fractions, relating
to the adsorption of the solute and to the desorption of the solvent. Experimental data on both isotherms from the literatures
and precise calorimetry were used to test the adsorption heat and its fractions computed quantitatively via the equations
presented in this study, and a satisfactory degree of conformity between them was obtained.
Supported by the Natural Science Foundation of Shaanxi Province in China. 相似文献
123.
Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the lowest-energy geometries and electronic structure of neutral gallium clusters containing up to 26 atoms. Harmonic vibrational frequency analysis is undertaken to assure that the lowest-energy geometries are real local minima. With increasing cluster size, we find that the gallium clusters tend to adopt compact structures. The structures comprise triangular units that connect each other with different dihedral angles. The lowest-energy structure can be obtained by capping an atom on the structure of smaller one. The capping site occurs at a site where interactions with more atoms are available. The binding energy evolves monotonically with size, but Ga(8), Ga(14), and Ga(20) exhibit particularly higher stability. Except Ga(2) and Ga(4), all even-numbered gallium clusters we studied are closed-shell singlet states with a substantial highest occupied and lowest unoccupied molecular orbitals gap. The odd-numbered clusters are open shell with a small gap. The size dependence of cluster's ionization potentials and electron affinities is discussed and compared with available experiment. 相似文献
124.
The objective of this study was to develop and evaluate a supported capillary membrane sampling-gas chromatography method for the analysis of trihalomethanes (THMs) in drinking water. The effects of experimental parameters, such as flow rate of carrier gas, water temperature, ionic strengths of solutions and transfer line temperature on the system performance were investigated. The results of method detection limit and accuracy and precision studies are reported. 相似文献
125.
Cao B Wakahara T Tsuchiya T Kondo M Maeda Y Aminur Rahman GM Akasaka T Kobayashi K Nagase S Yamamoto K 《Journal of the American Chemical Society》2004,126(30):9164-9165
A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5). 相似文献
126.
随着激光技术的发展,近年来出现了与散射光频加宽相应的光子相干光谱即准弹性光散射。于是,利用光散射(也称弹性光散射)法不仅能获得高聚物的各种物性参数如分子量(?),第二维利系数A_2和均方旋转半径(),而且还能得到大分子在溶液中的动态参数,即扩散系数D_0。由D_0求得流体力学半径R_H。本文只涉及小角度准弹性光散射(1°<θ<7°)对稀溶液范围的平动扩散系数的测定。与文献比较,表明方法是成功的。 相似文献
127.
钇对2618合金组织及性能的影响 总被引:7,自引:1,他引:7
采用X射线,光学显微镜及扫描电镜等手段研究了2618合金中的组织与相结构,并研究了元素钆在2618合金中的存在形式及其对合金力学性能的影响。结果表明,微量钆元素在铝合金中是以化合物形式存在的;钆对合金中的铸态组织及Al9FeNi仃形态没有影响。由于微量钆的加入,降低了铜与镁在2618合金中的固溶量,减少了时效析出相A2CuMg数量,从而降低2618合金的室温强度帮在250℃的高温瞬时强度;但由于微量钆减少了铜与镁在2618合金中的扩散速度,延缓了时效机的粗化,并由于第二相数量的增多,因此提高了2618合金在250℃经100h高温热暴露后的高温瞬时强度。 相似文献
128.
运用HREELS技术对甲醇在预吸附氯的Ag(111)表面上的吸附氧化行为进行了较细致的研究.结果证明Cl对甲醇氧化的影响缘于它在Ag(111)上的吸附所引起的表面结构的改变进而改变表面氧吸附物种,从而使得甲醇氧化的中间产物发生变化.实验结果说明甲醇在Ag(111)和低暴露量氯吸附的Ag(111)表面上的氧化行为是相似的,检测到了中间产物Ⅰ和Ⅲ;在高暴露量氯吸附的Ag(111)上甲醇氧化时则产生中间产物Ⅰ、Ⅳ和甲醛物种.对上述不同的甲醇氧化行为作了分析,并指出了以前人们在考察甲醇氧化机理时只考虑原子氧作用的片面性. 相似文献
129.
Conjugated linoleic acids (CLA) have been a subject of extensive investigation for their anticarcinogenic, hypolipidemic, antiatherosclerotic and immune-enhancing activities. Stability of CLA in foods has not received much attention by both academics and industry. Although CLA has shown many beneficial effects, its decomposition must be prevented when CLA in foods is processed, stored and transported. However, no study to date has addressed the stability of CLA in foods. The present study was carried out further to examine the stability of CLA in egg yolk during the storage and frying, using gas liquid chromatography (GLC) and silver ion high-performance liquid chromatography (Agt-HPLC). The eggs, containing 4.0% CLA per gramme of egg yolk, were 40s. Either storage for 6 months or frying for 40 s did not significantly change the composition of CLA in egg yolk. However, the degradation of CLA was statistically significant when the CLA components of egg yolk protected CLA from degradation. It is concluded that CLA is well preserved in egg before it is consumed. 相似文献
130.