全文获取类型
收费全文 | 3586篇 |
免费 | 71篇 |
国内免费 | 40篇 |
专业分类
化学 | 194篇 |
晶体学 | 7篇 |
力学 | 30篇 |
综合类 | 1篇 |
数学 | 3013篇 |
物理学 | 452篇 |
出版年
2023年 | 9篇 |
2022年 | 26篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 81篇 |
2018年 | 88篇 |
2017年 | 42篇 |
2016年 | 28篇 |
2015年 | 36篇 |
2014年 | 83篇 |
2013年 | 201篇 |
2012年 | 103篇 |
2011年 | 247篇 |
2010年 | 254篇 |
2009年 | 224篇 |
2008年 | 307篇 |
2007年 | 319篇 |
2006年 | 253篇 |
2005年 | 137篇 |
2004年 | 120篇 |
2003年 | 94篇 |
2002年 | 69篇 |
2001年 | 63篇 |
2000年 | 69篇 |
1999年 | 75篇 |
1998年 | 67篇 |
1997年 | 53篇 |
1996年 | 93篇 |
1995年 | 98篇 |
1994年 | 61篇 |
1993年 | 69篇 |
1992年 | 53篇 |
1991年 | 32篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 12篇 |
1987年 | 20篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有3697条查询结果,搜索用时 15 毫秒
151.
152.
By applying the L2-estimate of the scalar curvature of a Riemannian 3-manifold with a Seiberg–Witten monopole class to a collapsing sequence of metrics, we obtain conditions to be a monopole class on certain 3-manifolds. This also gives a relation between a maximizing sequence of the Yamabe constants and the collapsing on a 3-manifold with a non-torsion monopole class. 相似文献
153.
154.
By referring to theorems of Donaldson and Hitchin, we exhibit a rigorous AdS/CFT-type correspondence between classical 2+1-dimensional vacuum general relativity theory on Σ×R and SO(3) Hitchin theory (regarded as a classical conformal field theory) on the spacelike past boundary Σ, a compact, oriented Riemann surface of genus greater than 1. Within this framework we can interpret the 2+1-dimensional vacuum Einstein equation as a decoupled “dual” version of the two-dimensional SO(3) Hitchin equations. 相似文献
155.
Poly(D,L‐lactide‐co‐glycolide) 50:50 (PLGA)/graphene oxide (GO) nanocomposite films were prepared with various GO weight fractions. A significant enhancement of mechanical properties of the PLGA/GO nanocomposite films was obtained with GO weight fractions. The incorporation of only 5 wt% of GO resulted in an ~2.5‐fold and ~4.7‐fold increase in the tensile strength and Young's modulus of PLGA, respectively. The thermomechanical behaviors of composite films were investigated by dynamic mechanical analysis. Results indicated that the values of Tg and storage moduli of the PLGA/GO composites were higher than those of the pristine PLGA. The improvement in oxygen barrier properties of composites was presumably attributed to the filler effect of the randomly dispersed GO throughout the PLGA matrix. In this work, we also studied in vitro biodegradation behavior. PLGA/GO composite films were hydrolyzed at 37°C for periods up to 49 days. Because of the presence of GO nanosheets, degradation of composite films took place more slowly with increasing GO amounts. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
156.
Ming Zhang Fengqi Zhao Yanjing Yang Hui Li Jiankan Zhang Wenzhe Ma Hongxu Gao Na Li 《物理化学学报》2020,36(6):1904027-0
Energy components used in solid rocket propellants are beneficial for improving the energy performance, and their thermal decomposition characteristics significantly affect the combustion properties of the propellants. As a kind of energetic material with both high energy and low sensitivity (impact and friction), 5, 5'-bistetrazole-1, 1'-diolate (TKX-50) can effectively improve the energy and safety characteristics of solid propellants. Burning catalyst is another important component of solid propellants, which can significantly improve the burning rate of the propellant and reduce the pressure exponent. Among various burning catalysts, nanoscale transition metal oxides can promote the thermal decomposition of the energetic component, thus enhancing the combustion properties of the solid propellant. However, the catalytic effects of nanoscale transition metal oxides with different morphologies on the thermal decomposition of TKX-50 have rarely been studied. Based on the excellent catalytic activity of Fe2O3 for TKX-50 thermal decomposition, nano-Fe2O3 particles with spherical and tubular microstructures were used for TKX-50 thermal decomposition. The Fe2O3 nanoparticles were successfully fabricated via the solvothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. The XRD, FT-IR, and XPS results confirmed the successful fabrication of spherical and tubular Fe2O3 samples. The SEM and TEM images showed that the spherical Fe2O3 samples are composed of agglomerated Fe2O3 nanoparticles with an average particle size of 110 nm. In addition, the average diameter and length of hollow tubular Fe2O3 nanoparticles are 120 nm and 200 nm, respectively. The catalytic activities of spherical and tubular Fe2O3 for TKX-50 decomposition were studied by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) methods. The DSC and TG-DTG curves showed that both tubular and spherical Fe2O3 could effectively promote TKX-50 thermal decomposition. The first thermal decomposition peak temperature (TFDP) of TKX-50 was reduced by 36.5 K and 26.3 K in the presence of tubular and spherical Fe2O3, respectively, at 10 K·min−1. The activation energy (Ea) of TKX-50, determined by the iso-conversional method, was significantly reduced in the presence of both tubular and spherical Fe2O3. The results indicated that the microstructure of the catalyst has a significant effect on its catalytic performance for TKX-50 thermal decomposition, and that tubular Fe2O3 with hollow microstructure possesses better catalytic activity than spherical Fe2O3. The excellent catalytic activity of tubular Fe2O3 can be attributed to the hollow microstructure, which has more active sites for TKX-50 thermal decomposition. 相似文献
157.
探讨了应用光波导光模光谱(Optical waveguide lightmode spectroscopy,OWLS)技术研究DNA-DNA结合蛋白相互作用的可行性和灵敏性。以固定在传感器芯片表面的DNA探针为捕捉分子,溶液中同时含有探针结合序列和NF—κB结合位点序列的寡核苷酸与NF-κB亚单位p50同源二聚体形成的DNA-蛋白质复合物为检测分子,用光波导光模光谱检测技术建立非标记DNA-DNA结合蛋白相互作用检测研究体系。利用这一体系对不同样品中NF-κB p50浓度和具不同NF-κB结合位点序列的寡核苷酸与NF-κB p50亲合和力进行检测。样品中低至0.33 nmol/1的NF-κB p50被光波导光模光谱检测出,不同的NF-κB结合序列与NF-κB p50亲合力有显著的差异。研究发现,光波导光模光谱技术可以用于DNA-DNA结合蛋白相互作用研究,所建立的非标记检测研究体系可以进行样品中结合蛋白含量高灵敏检测和核酸序列与结合蛋白的亲合力的检测研究。 相似文献
158.
In this paper, the so-called approximate convexity and concavity properties of generalized Groetzsch ring function μa (r) by studying the monotonieity,convexity or concavity of certain composites of μa(r) are obtained. 相似文献
159.
Han-Qing Fang Jie Zeng Shou-Kai Wang Xiao Wang Fang Chen Bo Li Jie Liu Zhen Jin Ya-Hong Liu You-Zhi Tang 《Molecules (Basel, Switzerland)》2022,27(3)
A series of novel pleuromutilin derivatives containing nitrogen groups on the side chain of C14 were synthesized under mild conditions. Most of the synthesized derivatives displayed potent antibacterial activities. Compound 9 was found to be the most active antibacterial derivative against MRSA (MIC = 0.06 μg/mL). Furthermore, the result of time-kill curves showed that compound 9 had a certain inhibitory effect against MRSA in vitro. Moreover, according to a surface plasmon resonance (SPR) study, compound 9 (KD = 1.77 × 10−8 M) showed stronger affinity to the 50S ribosome than tiamulin (KD = 2.50 × 10−8 M). The antibacterial activity of compound 9 was further evaluated in an MRSA-infected murine thigh model. Compared to the negative control group, tiamulin reduced MRSA load (~0.7 log10 CFU/mL), and compound 9 performed a treatment effect (~1.3 log10 CFU/mL). In addition, compound 9 was evaluated in CYP450 inhibition assay and showed only moderate in vitro CYP3A4 inhibition (IC50 = 2.92 μg/mL). 相似文献
160.
Signless Laplacians of finite graphs 总被引:4,自引:0,他引:4
We survey properties of spectra of signless Laplacians of graphs and discuss possibilities for developing a spectral theory of graphs based on this matrix. For regular graphs the whole existing theory of spectra of the adjacency matrix and of the Laplacian matrix transfers directly to the signless Laplacian, and so we consider arbitrary graphs with special emphasis on the non-regular case. The results which we survey (old and new) are of two types: (a) results obtained by applying to the signless Laplacian the same reasoning as for corresponding results concerning the adjacency matrix, (b) results obtained indirectly via line graphs. Among other things, we present eigenvalue bounds for several graph invariants, an interpretation of the coefficients of the characteristic polynomial, a theorem on powers of the signless Laplacian and some remarks on star complements. 相似文献