全文获取类型
收费全文 | 7849篇 |
免费 | 1402篇 |
国内免费 | 812篇 |
专业分类
化学 | 5523篇 |
晶体学 | 45篇 |
力学 | 486篇 |
综合类 | 49篇 |
数学 | 998篇 |
物理学 | 2962篇 |
出版年
2024年 | 23篇 |
2023年 | 170篇 |
2022年 | 265篇 |
2021年 | 311篇 |
2020年 | 366篇 |
2019年 | 304篇 |
2018年 | 260篇 |
2017年 | 251篇 |
2016年 | 375篇 |
2015年 | 420篇 |
2014年 | 446篇 |
2013年 | 560篇 |
2012年 | 699篇 |
2011年 | 733篇 |
2010年 | 468篇 |
2009年 | 433篇 |
2008年 | 476篇 |
2007年 | 445篇 |
2006年 | 430篇 |
2005年 | 309篇 |
2004年 | 275篇 |
2003年 | 181篇 |
2002年 | 199篇 |
2001年 | 133篇 |
2000年 | 145篇 |
1999年 | 165篇 |
1998年 | 161篇 |
1997年 | 160篇 |
1996年 | 140篇 |
1995年 | 127篇 |
1994年 | 115篇 |
1993年 | 106篇 |
1992年 | 78篇 |
1991年 | 75篇 |
1990年 | 63篇 |
1989年 | 42篇 |
1988年 | 36篇 |
1987年 | 37篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1959年 | 1篇 |
1916年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
892.
采用以表面具有贯穿大孔的二氧化硅空心微球为载体制备的负载型钯催化剂(Pd/SHMs),对聚苯乙烯(PS)在非均相加氢催化剂上的吸附及加氢反应行为进行了系统研究,得到了吸附和反应动力学模型,并对部分加氢产物进行了详细分析.结果表明随着温度的升高,PS吸附量逐渐增加,且达到饱和吸附时间也随之增长,确定了PS非均相加氢为1级反应,活化能为58.3 kJ·mol-1.将不同加氢度的样品进行分离提纯分析,结果显示PS的部分加氢产物都是由较高加氢转化率(85%左右)和较低加氢转化率(25%左右)的PS组成,证明PS非均相加氢存在二次吸附和竞争吸附加氢的现象,即服从“Blocky”机理.此工作为PS催化加氢吸附及反应过程的研究奠定基础,也为理解其他聚合物在非均相催化剂上的吸附及反应行为提供帮助. 相似文献
893.
894.
We investigate numerically the effects of scatterer sizes on backscattered polarization patterns using the third-order scattering model developed. The calculated results show that both parallel and cross polarization patterns from water suspensions of polystyrene spheres have four-lobe structures of the azimuth dependence of intensities. Particularly, the parallel polarization pattern is sensitive to scatterer sizes, exhibiting good agreement with prior experimental measurements. Furthermore, the polarization patterns from the dysplastic and normal cells with different size distribution widths are calculated and analyzed. The results show that the polarization patterns of dysplastic and normal cells have distinct differences, which might be used for identification of the morphological structure changes of cancer, dysplasia, and regeneration cells. 相似文献
895.
Polymerization of hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) complex of methyl methacrylate (MMA) (MMA/HP‐β‐CD) was carried out under UV irradiation in aqueous solution with Irgacure 2959 (4‐(2‐hydroxyethoxy)phenyl‐(2‐hydroxy‐2‐propyl)ketone) as a photoinitiator at room temperature. The effects of some principal factors, including UV irradiation intensity, initiator concentration, and the ratio of HP‐β‐CD to MMA, on the polymerization were investigated in detail. Compared to the corresponding thermal polymerization, photo‐induced polymerization of the MMA/HP‐β‐CD complex could be accomplished at a higher speed; the polymerization conversion in photo‐induced polymerization reached 94% within 30 min, while it was only 62% for the thermal polymerization of 16 hr at 70°C. The number‐average molecular weight (Mn) and polymerization conversion decreased with the increase in UV intensity and initiator concentration. The resulting PMMA precipitated spontaneously from the solution during polymerization in the absence of any precipitator. About 95 wt% of the HP‐β‐CD remained in the solution after polymerization and the reusability of the residual HP‐β‐CD was experimentally demonstrated. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
896.
YiHua Deng 《Mathematische Nachrichten》2015,288(10):1122-1126
In this note, we get a necessary and sufficient condition such that the scalar curvature of generalized m‐quasi‐Einstein manifold with is constant. In particular, we discuss a class of generalized quasi‐Einstein manifolds which are more general than ‐quasi‐Einstein manifolds and prove that these manifolds with dimension four are either Einstein or locally conformally flat under some suitable conditions. 相似文献
897.
The paper is concerned with the uniform time stability in the Lebesgue space \({L^{p}(\mathbb{R}^{3} \times \mathbb{R}^{3})}\) of solutions to the Boltzmann equation near vacuum. Precisely, for the soft potential case \({-2 < \gamma < 0}\), there exists \(p_{\gamma} > 1\) such that the nonnegative solution with algebraic decay rate in x, v at infinity is stable with respect to small initial data uniformly in time in \({L^{p}}\) with \({1 \leq p < p_{\gamma}}\). 相似文献
898.
Deng Y Wang Y Holtz B Li J Traaseth N Veglia G Stottrup BJ Elde R Pei D Guo A Zhu XY 《Journal of the American Chemical Society》2008,130(19):6267-6271
As drug delivery, therapy, and medical imaging are becoming increasingly cell-specific, there is a critical need for high fidelity and high-throughput screening methods for cell surface interactions. Cell membrane-mimicking surfaces, i.e., supported lipid bilayers (SLBs), are currently not sufficiently robust to meet this need. Here we describe a method of forming fluidic and air-stable SLBs through tethered and dispersed cholesterol groups incorporated into the bottom leaflet. Achieving air stability allows us to easily fabricate SLB microarrays from direct robotic spotting of vesicle solutions. We demonstrate their application as cell membrane-mimicking microarrays by reconstituting peripheral as well as integral membrane components that can be recognized by their respective targets. These demonstrations establish the viability of the fluidic and air-stable SLB platform for generating content microarrays in high throughput studies, e.g., the screening of drugs and nanomedicine targeting cell surface receptors. 相似文献
899.
Two new zinc(II) complexes have been synthesized and studied by single crystal X-ray diffraction method: [Zn(L1)Cl2]·2DMF (1) and [Zn(L2)Cl2]·DMF (2) (L1 = 3,3′-bis(2-benzimidazolyl)-2,2′-dipyridine, L2 = 3,3′-bis[2-bis(2-ethylbenzimidazolyl)]-2,2′-dipyridine). Compound
1 is monoclinic, C2/c, a = 23.142(3) ?, b = 11.845(1) ?, c = 14.735(3) ?; compound 2 is orthorhombic, C2221, a = 12.140(7) ?, b = 16.283(9) ?, c = 16.51(1) ?. In both compounds, Zn(II) cations are coordinated by two chlorine atoms and two benzimidazole nitrogen atoms
in a slightly distorted tetrahedron fashion. Structural features responsible for fluorescent properties of the complexes are
discussed. 相似文献
900.
Peiyu Wang Qinglong Wang Guoheng Zhang Haiyan Jiao Xiaoyan Deng Liwei Liu 《Journal of Solid State Electrochemistry》2016,20(2):319-325
In this paper, cabbage leaves (CLs) were used to synthesize porous activated carbon by the carbonization and activation processes. The material for CLs were carbonized at 600 °C and activated at 800 °C with the KOH/C-600 mass ratio 4 (denoted as AC-800) show typical amorphous character and display porous structures with high specific surface areas 3102 m2/g via XRD and BET measurements. As the electro-active material, AC-800 electrode exhibit ideal capacitive behaviors in aqueous electrolytes and the maximal specific capacitance is as high as 336 F/g at the current density of 1 A/g. Furthermore, AC-800 electrode shows excellent electrochemical cycle stability with ~95 % initial capacitance being retained after 2000 cycles. The desirable capacitive performances enable the CLs to act as a new biomass source of carbonaceous materials for high-performance supercapacitors and low-cost electrical energy storage devices. 相似文献