全文获取类型
收费全文 | 1683篇 |
免费 | 300篇 |
国内免费 | 158篇 |
专业分类
化学 | 1321篇 |
晶体学 | 20篇 |
力学 | 88篇 |
综合类 | 5篇 |
数学 | 132篇 |
物理学 | 575篇 |
出版年
2024年 | 5篇 |
2023年 | 36篇 |
2022年 | 25篇 |
2021年 | 69篇 |
2020年 | 68篇 |
2019年 | 67篇 |
2018年 | 67篇 |
2017年 | 40篇 |
2016年 | 83篇 |
2015年 | 79篇 |
2014年 | 84篇 |
2013年 | 109篇 |
2012年 | 161篇 |
2011年 | 164篇 |
2010年 | 104篇 |
2009年 | 86篇 |
2008年 | 118篇 |
2007年 | 101篇 |
2006年 | 99篇 |
2005年 | 100篇 |
2004年 | 59篇 |
2003年 | 40篇 |
2002年 | 45篇 |
2001年 | 31篇 |
2000年 | 28篇 |
1999年 | 31篇 |
1998年 | 26篇 |
1997年 | 28篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 21篇 |
1990年 | 18篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1947年 | 1篇 |
1946年 | 1篇 |
排序方式: 共有2141条查询结果,搜索用时 15 毫秒
991.
We study the problem of wear of a rotationally symmetric profile subjected to oscillations with small amplitude. Under these conditions, sliding occurs at the boundary of the contact area while the inner parts of the contact area may still stick. In a recent paper, Dimaki with colleagues proposed a numerically exact simulation procedure based on the method of dimensionality reduction (MDR). This drastically reduced the simulation time compared with conventional finite element simulations. The proposed simulation procedure requires carrying out the direct and the inverse MDR transformations in each time step. This is the main time consuming operation in the proposed method. However, solutions obtained with this method showed a remarkable simplicity of the development of wear profiles in the MDR space. In the present paper, we utilize these results to formulate an approximate model, in which the wear is simulated directly in the one-dimensional space without using integral transformations. This speeds up the simulations of wear by further several orders of magnitude. 相似文献
992.
The effect of k-cubic Dresselhaus spin–orbit coupling on the decay time of persistent spin helix states in semiconductor two-dimensional electron gases 下载免费PDF全文
We study the theoretical effect of k-cubic (i.e, cubic-in-momentum) Dresselhaus spin-orbit coupling on the decay time of persistent spin helix states in semiconductor two-dimensional electron gases. We show that the decay time of persistent spin helix states may be suppressed substantially by k-cubic Dresselhaus spin-orbit coupling, and after taking the effect of k-cubic Dresselhaus spin-orbit interaction into account, the theoretical results obtained accord both qualitatively and quantitatively with other recent experimental results. 相似文献
993.
A novel Lagrangian relaxation approach for a hybrid flowshop scheduling problem in the steelmaking-continuous casting process 总被引:1,自引:0,他引:1
One of the largest bottlenecks in iron and steel production is the steelmaking-continuous casting (SCC) process, which consists of steel-making, refining and continuous casting. The SCC scheduling is a complex hybrid flowshop (HFS) scheduling problem with the following features: job grouping and precedence constraints, no idle time within the same group of jobs and setup time constraints on the casters. This paper first models the scheduling problem as a mixed-integer programming (MIP) problem with the objective of minimizing the total weighted earliness/tardiness penalties and job waiting. Next, a Lagrangian relaxation (LR) approach relaxing the machine capacity constraints is presented to solve the MIP problem, which decomposes the relaxed problem into two tractable subproblems by separating the continuous variables from the integer ones. Additionally, two methods, i.e., the boundedness detection method and time horizon method, are explored to handle the unboundedness of the decomposed subproblems in iterations. Furthermore, an improved subgradient level algorithm with global convergence is developed to solve the Lagrangian dual (LD) problem. The computational results and comparisons demonstrate that the proposed LR approach outperforms the conventional LR approaches in terms of solution quality, with a significantly shorter running time being observed. 相似文献
994.
Cathay Chai Au-Yeung Lok-Kwan Li Man-Chung Tang Shiu-Lun Lai Wai-Lung Cheung Maggie Ng Mei-Yee Chan Vivian Wing-Wah Yam 《Chemical science》2021,12(27):9516
Here, we report the design and synthesis of a new class of fused heterocyclic alkynyl ligand-containing gold(iii) complexes, which show tunable emission colors spanning from the yellow to red region in the solid state and exhibit thermally activated delayed fluorescence (TADF) properties. These complexes display high photoluminescence quantum yields of up to 0.87 and short excited-state lifetimes in sub-microsecond timescales, yielding high radiative decay rate constants on the order of up to 106 s−1. The observation of the drastic enhancement in the emission intensity of the complexes with insignificant change in the excited-state lifetime upon increasing the temperature from 200 to 360 K indicates an increasing radiative decay rate. The experimentally estimated energy splitting between the lowest-lying singlet excited state (S1) and the lowest-lying triplet excited state (T1), ΔES1–T1, is found to be as small as ∼0.03 eV (250 cm−1), comparable to the value of ∼0.05 eV (435 cm−1) obtained from computational studies. The delicate choice of the cyclometalating ligand and the fused heterocyclic ligand is deemed the key to induce TADF through the control of the energy levels of the intraligand and the ligand-to-ligand charge transfer excited states. This work represents the realization of highly emissive yellow- to red-emitting gold(iii) TADF complexes incorporated with fused heterocyclic alkynyl ligands and their applications in organic light-emitting devices.We report the design of a new class of fused heterocyclic alkynyl ligand-containing gold(iii) complexes, which shows tunable emission colors spanning yellow to red region and exhibits thermally activated delayed fluorescence (TADF) properties. 相似文献
995.
Ferrocenyl-doped silica nanoparticles as an immobilized affinity support for electrochemical immunoassay of cancer antigen 15-3 总被引:1,自引:0,他引:1
The aim of this study is to elaborate a simple and sensitive electrochemical immunoassay using ferrocenecarboxylic (Fc-COOH)-doped silica nanoparticles (SNPs) as an immobilized affinity support for cancer antigen 15-3 (CA 15-3) detection. The Fc-COOH-doped SNPs with redox-active were prepared by using a water-in-oil microemulsion method. The use of colloidal silica could prevent the leakage of Fc-COOH and were easily modified with trialkoxysilane reagents for covalent conjugation of CA 15-3 antibodies (anti-CA 15-3). The Fc-COOH-doped SNPs were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The fabrication process of the electrochemical immunosensor was demonstrated by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Under optimal conditions, the developed immunosensor showed good linearity at the studied concentration range of 2.0-240 U mL−1 with a coefficient 0.9986 and a detection limit of 0.64 U mL−1 at S/N = 3. 相似文献
996.
Anyun Zhang Chengliang Xiao Zhifang Chai 《Journal of Radioanalytical and Nuclear Chemistry》2009,280(1):181-191
To separate Sr(II), one of the heat emitting nuclides, from high level liquid waste (HLLW), a macroporous silica-based DtBuCH18C6
polymeric composite, DtOct/SiO2-P, was synthesized by means of molecular modification of 4,4′,(5′)-di(tert-butylcyclohexano)-18-crown-6 (DtBuC H18C6) with a long-chain 1-octanol. It was performed by impregnating and immobilizing
DtBuCH18C6 and 1-octanol molecules into the pores of the SiO2-P particles, the macroporous silica-based support. The adsorption of Sr(II) and some co-existent typical elements Na(I),
K(I), Cs(I), Ru(III), Mo(VI), Pd(II), Ba(II), La(III), and Y(III) contained in highly active liquid waste (HLW) towards DtOct/SiO2-P was investigated at 323 K. The effects of contact time and the concentration of HNO3 in a range of 0.1–5.0M on the adsorption of the tested metals were examined. The macroporous silica-based DtOct/SiO2-P polymeric composite showed strong adsorption ability and high selectivity for Sr(II) over all of the tested metals except
Ba(II). The optimum acidity of Sr(II) adsorption onto DtOct/SiO2-P was determined to be 2.0M HNO3. The bleeding behavior of DtOct/SiO2-P in aqueous phase was evaluated using total organic carbon (TOC) analysis. The content of TOC increased with increasing
the HNO3 concentration and contact time. It resulted from the decrease in the stability of the associated species, C8H17-OH• DtBuCH18C6 formed through hydrogen binding, because of high temperature. 相似文献
997.
Cuimiao Zhang Chunxia Li Chong Peng Ruitao Chai Shanshan Huang Dongmei Yang Ziyong Cheng Jun Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5672-5680
Highly uniform and well‐dispersed CaF2 hollow spheres with tunable particle size (300–930 nm) have been synthesized by a facile hydrothermal process. Their shells are composed of numerous nanocrystals (about 40 nm in diameter). The morphology and size of the CaF2 products are strongly dependent on experimental parameters such as reaction time, pH value, and organic additives. The size of the CaF2 hollow spheres can be controlled from 300 to 930 nm by adjusting the pH value. Nitrogen adsorption–desorption measurements suggest that mesopores (av 24.6 nm) exist in these hollow spheres. In addition, Ce3+/Tb3+‐codoped CaF2 hollow spheres can be prepared similarly, and show efficient energy transfer from Ce3+ to Tb3+ and strong green photoluminescence of Tb3+ (541 nm, 5D4→7F5 transition of Tb3+, the highest quantum efficiency reaches 77 %). The monodisperse CaF2:Ce3+/Tb3+ hollow spheres also have desirable properties as drug carriers. Ibuprofen‐loaded CaF2:Ce3+/Tb3+ samples still show green luminescence of Tb3+ under UV irradiation, and the emission intensity of Tb3+ in the drug‐carrier system varies with the released amount of ibuprofen, so that drug release can be easily tracked and monitored by means of the change in luminescence intensity. The formation mechanism and luminescent and drug‐release properties were studied in detail. 相似文献
998.
A series of novel 7-(4-alkoxyimino-3-hydroxypiperidin-l-yl)quinolone derivatives were designed, synthesized and evaluated for in vitro antibacterial activities. Compounds 8f, 8g, 8i and 8j with the potencies similar to or better than those of levofloxacin and IMB against Staphylococcus aureus and Staphylococcus epidermidis, worth further investigation. 相似文献
999.
1000.
A new type of conductometric probe based on a molecularly imprinted membrane (MIM) for the detection of salbutamol has been designed and fabricated. The probe consists of two parallel screen-printed electrodes (SPE). One of the SPEs was coated with a molecularly imprinted membrane using salbutamol as the template, and the other was modified with a non-molecularly imprinted membrane (N-MIM). Measurements of salbutamol were conducted after the conductometric probe had been connected to a commercial portable conductometer. Multi-sample or successive detections could be easily accomplished by replacing the one-off SPE coated with the salbutamol molecularly imprinted membrane with a new one. The conductometric response of the sensor to the concentration of salbutamol displayed a linear correlation over a range from 50 to 280 nM, with a detection limit of 13.5 nM. The recoveries reached 92.1-98.3% based on pig urine samples. In addition, the sensor based on this new type of probe demonstrated high sensitivity and selectivity for salbutamol. 相似文献