全文获取类型
收费全文 | 1691篇 |
免费 | 117篇 |
国内免费 | 27篇 |
专业分类
化学 | 1140篇 |
晶体学 | 11篇 |
力学 | 70篇 |
综合类 | 2篇 |
数学 | 300篇 |
物理学 | 312篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 33篇 |
2020年 | 48篇 |
2019年 | 44篇 |
2018年 | 32篇 |
2017年 | 28篇 |
2016年 | 82篇 |
2015年 | 58篇 |
2014年 | 79篇 |
2013年 | 118篇 |
2012年 | 120篇 |
2011年 | 141篇 |
2010年 | 73篇 |
2009年 | 98篇 |
2008年 | 102篇 |
2007年 | 88篇 |
2006年 | 65篇 |
2005年 | 76篇 |
2004年 | 71篇 |
2003年 | 68篇 |
2002年 | 52篇 |
2001年 | 13篇 |
2000年 | 23篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1984年 | 20篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 5篇 |
排序方式: 共有1835条查询结果,搜索用时 15 毫秒
1.
Nguyen Van Hung Vo Minh Tam Dumitru Baleanu 《Mathematical Methods in the Applied Sciences》2020,43(7):4614-4626
In this paper, we consider a class of split mixed vector quasivariational inequality problems in real Hilbert spaces and establish new gap functions by using the method of the nonlinear scalarization function. Further, we obtain some error bounds for the underlying split mixed vector quasivariational inequality problems in terms of regularized gap functions. Finally, we give some examples to illustrate our results. The results obtained in this paper are new. 相似文献
2.
Extraordinary transport behavior of gases in isothermally annealed poly(4‐methyl‐1‐pentene) membranes 下载免费PDF全文
Ywu‐Jang Fu Cheng‐Lee Lai Chien‐Chieh Hu Yi‐Ming Sun Shuan‐Ying Wu Jung‐Tsai Chen Shu‐Hsien Huang Wei‐Song Hung Kueir‐Rarn Lee 《Journal of Polymer Science.Polymer Physics》2016,54(22):2368-2376
Poly(4‐methyl‐1‐pentene) (PMP) membranes were modified through isothermal annealing to investigate the change of their crystalline structure and rigid and mobile amorphous fractions (RAF and MAF), assuming a three‐phase model, affected the gas transport behavior. The crystalline structure was characterized by wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering (SAXS) techniques, and the free volume properties were analyzed by positron annihilation lifetime spectroscopy. Compared with the pristine membrane, the annealed membranes show higher crystallinity; the crystals undergo partial structural change from form III to form I. The lamellar crystal thickness, rigid amorphous fraction thickness, and long period in the lamellar stacks increase with crystallinity. The annealed PMP membranes exhibit higher permeability due to the increase in larger size free volumes in MAF and higher selectivity due to the increase in smaller size free volumes in RAF, respectively. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2368–2376 相似文献
3.
Identification and formation mechanism of individual degradation products in lithium‐ion batteries studied by liquid chromatography/electrospray ionization mass spectrometry and atmospheric solid analysis probe mass spectrometry 下载免费PDF全文
4.
Crosslinkable high dielectric constant polymer dielectrics for low voltage organic field‐effect transistor memory devices 下载免费PDF全文
Chih‐Chien Hung Hung‐Chin Wu Yu‐Cheng Chiu Shih‐Huang Tung Wen‐Chang Chen 《Journal of polymer science. Part A, Polymer chemistry》2016,54(19):3224-3236
I n this study, we successfully synthesized water/methanol soluble random copolymers with a high dielectric constant, poly(n‐(hydroxymethyl) acrylamide‐co‐5‐(9‐(5‐(diethylamino)pentyl)?2‐(4‐vinylphenyl)?9H‐fluorene(P(NMA‐co‐F6NSt)), which contained chemical crosslinkable segment (NMA) and hole trapping building block (F6NSt). The feeding molar ratios of two monomers (NMA:F6NSt) were set as 100:0, 95:5, 80:20, and 67:33 for the copolymers of P1 , P2 , P3, and P4 , respectively. The crosslinked P(NMA‐co‐F6NSt) thin film could serve as both dielectric and charge storage layers in organic field‐effect transistor (OFET) memory device and exhibited high k (i.e., 4.91–6.47) characteristics, leading to a low voltage operation and a small power consumption. Devices based on the P1 ‐ P4 dielectrics showed excellent insulating properties and good charge storage performance under a low operating voltage in a range of ±5V because of tightly network structures and well‐dispersed trapping cites. In particular, P3 ‐based memory device exhibited a large memory window of 4.13 V with stable data retention stability over 104 s, a large on/off ratio of 104, and good endurance characteristics as high as 200 cycles. The above results suggested that a high‐performance OFET memory device could be facilely achieved using the novel crosslinkable high‐k copolymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3224–3236 相似文献
5.
This study describes the development of a simple, enzyme-free, label-free, sensitive, and selective system for detecting adenosine based on the use of Tween 20-stabilized gold nanoparticles (Tween 20-AuNPs) as an efficient fluorescence quencher for boron dipyrromethene-conjugated adenosine 5′-triphosphate (BODIPY-ATP) and as a recognition element for adenosine. BODIPY-ATP can interact with Tween 20-AuNPs through the coordination between the adenine group of BODIPY-ATP and Au atoms on the NP surface, thereby causing the fluorescence quenching of BODIPY-ATP through the nanometal surface energy transfer (NSET) effect. When adenosine attaches to the NP surface, the attached adenosine exhibits additional electrostatic attraction to BODIPY-ATP. As a result, the presence of adenosine enhances the efficiency of AuNPs in fluorescence quenching of BODIPY-ATP. The AuNP-induced fluorescence quenching of BODIPY-ATP progressively increased with an increase in the concentration of adenosine; the detection limit at a signal-to-noise ratio of 3 for adenosine was determined to be 60 nM. The selectivity of the proposed system was more than 1000-fold for adenosine over any adenosine analogs and other nucleotides. The proposed system combined with a phenylboronic acid-containing column was successfully applied to the determination of adenosine in urine. 相似文献
6.
7.
8.
9.
10.
Sample preparation methods used for genetically modified organisms (GMOs) analysis are often time consuming, require extensive manual manipulation, and result in limited amounts of purified protein, which may complicate the detection of low‐abundance GM protein. A robust sample pretreatment method prior to mass spectrometry (MS) detection of the transgenic protein (5‐enolpyruvylshikimate‐3‐phosphate synthase [CP4 EPSPS]) present in Roundup Ready soya is investigated. Liquid chromatography‐multiple reaction monitoring tandem MS (nano LC‐MS/MS‐MRM) was used for the detection and quantification of CP4 EPSPS. Gold nanoparticles (AuNPs) and concanavalin A (Con A)‐immobilized Sepharose 4B were used as selective probes for the separation of the major storage proteins in soybeans. AuNPs that enable the capture of cysteine‐containing proteins were used to reduce the complexity of the crude extract of GM soya. Con A‐sepharose was used for the affinity capture of β‐conglycinin and other glycoproteins of soya prior to enzymatic digestion. The methods enabled the detection of unique peptides of CP4 EPSPS at a level as low as 0.5% of GM soya in MRM mode. Stable‐isotope dimethyl labeling was further applied to the quantification of GM soya. Both probes exhibited high selectivity and efficiency for the affinity capture of storage proteins, leading to the quantitative detection at 0.5% GM soya, which is a level below the current European Union's threshold for food labeling. The square correlation coefficients were greater than 0.99. The approach for sample preparation is very simple without the need for time‐consuming protein prefractionation or separation procedures and thus presents a significant improvement over existing methods for the analysis of the GM soya protein. 相似文献