全文获取类型
收费全文 | 1552篇 |
免费 | 48篇 |
国内免费 | 11篇 |
专业分类
化学 | 969篇 |
晶体学 | 40篇 |
力学 | 65篇 |
数学 | 209篇 |
物理学 | 328篇 |
出版年
2023年 | 12篇 |
2022年 | 32篇 |
2021年 | 39篇 |
2020年 | 45篇 |
2019年 | 31篇 |
2018年 | 32篇 |
2017年 | 36篇 |
2016年 | 53篇 |
2015年 | 33篇 |
2014年 | 54篇 |
2013年 | 113篇 |
2012年 | 93篇 |
2011年 | 110篇 |
2010年 | 67篇 |
2009年 | 54篇 |
2008年 | 56篇 |
2007年 | 78篇 |
2006年 | 73篇 |
2005年 | 57篇 |
2004年 | 48篇 |
2003年 | 46篇 |
2002年 | 31篇 |
2001年 | 15篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有1611条查询结果,搜索用时 15 毫秒
181.
Manoj Kumar Chandra Mohan Sang Kyun Shim June Key Lee Nakwon Jang Naesung Lee Wael Z. Tawfik 《Molecules (Basel, Switzerland)》2021,26(13)
The far ultraviolet C (UVC) light sources based on carbon nanotube (CNT) field emitters as excitation sources have become promising light sources for sterilization, disinfection, and water purification. However, the low light extraction efficiency of UVC–CNT light sources still hinders the practical application of these structures. Herein, we report an optimized aluminum (Al) reflector to enhance the light extraction efficiency of UVC–CNT light sources. Optical analysis of UVC-CNT light sources covered by the Al reflectors with various thicknesses ranging from 30 to 150 nm was performed to realize the optimized reflector. The UVC-CNT light sources exhibit the highest light extraction efficiency when the Al reflector layer has an optimized thickness of 100 nm. For comparison, the cathodoluminescence (CL) spectra were recorded for UVC–CNT light sources with and without the optimized Al reflector. The measured light output power and the estimated power efficiency of the UVC–CNT light-source-tube with Al reflector were enhanced by about 27 times over the reference. This enhancement is mainly attributed to the outstanding reflection effect of the Al reflector. 相似文献
182.
A. Kandasamy R. Mohan M. Lydia Caroline S. Vasudevan 《Crystal Research and Technology》2008,43(2):186-192
Nucleation parameters such as solubility, induction period, interfacial energy and metastable zone width have been investigated for the aqueous solution growth of a semi‐organic nonlinear optical (NLO) material of L‐Proline cadmium chloride monohydrate (L‐PCCM) single crystal. Metastable zone width and induction period values were determined experimentally in order to optimize the growth parameters. The grown crystals are transparent (dimensions: 16 x 8 x 5 mm3) and characterized by powder X‐Ray Diffraction and dielectric studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
183.
The excited-state photophysical properties of curcumin in the presence of bovine serum albumin (BSA) have been studied. The absorption and fluorescence changes in curcumin on binding to BSA have been followed at varying concentrations of either curcumin or BSA to determine the binding constant, which has been found to be approximately 10(4) to 10(5) M(-1). Stopped-flow kinetics studies suggested at least two distinct kinetic steps for the binding of curcumin to BSA. The photophysical properties of the singlet-excited state of the curcumin-BSA complex have also been studied. Whereas the absorption spectrum of curcumin is redshifted, the fluorescence spectrum of curcumin was blueshifted in the presence of BSA. The fluorescence quantum yield of curcumin on complexing with BSA was approximately 0.05. Steady-state fluorescence anisotropy studies showed a significant increase in the anisotropy value of 0.37 in BSA-bound curcumin. The fluorescence decay of the curcumin-BSA complex followed a biexponential decay with fluorescence lifetimes of 413 ps (33%) and 120 ps (67%). On the basis of these complementary results, it has been concluded that curcumin shows very high binding to BSA, probably at the hydrophobic cavities inside the protein. 相似文献
184.
E. Rajanarendar P. Ramesh G. Mohan E. Kalyan Rao 《Journal of heterocyclic chemistry》2007,44(2):483-486
An efficient and modified Biginelli one‐pot synthesis of new‐isoxazole substituted 3,4‐dihydropyrimidin‐2(1H)‐ones and thiones from aromatic aldehydes, ketoamide and urea/thiourea in acetonitrile using VCl3 as the catalyst is described. 相似文献
185.
Jing He Mohan Yu Maofu Pang Yanqing Fan Zhe Lian Dr. Ying Wang Prof. Wenguang Wang Prof. Yajun Liu Prof. Hua Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202103832
Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]paracyclophane ([2.2]PCP) lead to optical-active chiral macrocycles with intriguing properties. X-ray crystal analysis revealed aesthetic necklace-shaped structures and size-dependent packages with long-range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82 %, and the fluorescent color varies with ring size. In addition, size-dependent chiroptical properties with moderately large CPL dissymmetry factor of 10−3 and CPL brightness in the range of 30–40 M−1 cm−1 were observed. 相似文献
186.
187.
Prakash TP Püschl A Lesnik E Mohan V Tereshko V Egli M Manoharan M 《Organic letters》2004,6(12):1971-1974
[structure: see text] Oligonucleotides with a novel 2'-O-[2-(guanidinium)ethyl] (2'-O-GE) modification have been synthesized using a novel protecting group strategy for the guanidinium group. This modification enhances the binding affinity of oligonucleotides to RNA as well as duplex DNA (DeltaT(m) 3.2 degrees C per modification). The 2'-O-GE modified oligonucleotides exhibited exceptional resistance to nuclease degradation. The crystal structure of a palindromic duplex formed by a DNA oligonucleotide with a single 2'-O-GE modification was solved at 1.16 A resolution. 相似文献
188.
A selective Spectrophotometric method has been developed for the trace determination of copper after adsorption of its 1-phenyl-4,4,6-trimethyl(1H, 4H)-pyrimidine-2-thiol (PTPT) complex onto microcrystalline naphthalene. The complex is quantitatively adsorbed on naphthalene in the pH range 7.5–11.5, separated by filtration, dissolved in dimethylformamide (DMF) and determined spectrophotometrically at 400 nm. Beer's law is obeyed in the concentration range 2.5–37.5 g of copper in 10 ml of DMF. The molar absorptivity and Sandell's sensitivity are 1.30 × 1041 · mol–1 · cm–1 and 0.0048g cm–2, respectively. Ten replicate analyses of a solution containing 20.0 g of copper gave a mean absorbance of 0.410 with a relative standard deviation of 0.91 %. The interferences of various ions have been studied and the method has been validated by the determination of copper in various standard reference materials, beers, wines, human hair, goat liver and environmental samples.On leave from St. Stephen's College, Delhi 110 007, India 相似文献
189.
In this paper we consider abstract equations of the typeK
ν
ν +ν =w
0, in a closed convex subset of a separable Hilbert spaceH. For eachv in the closed convex subset,K
v :H →H is a bounded linear map. As an application of our abstract result we obtain an existence result for nonlinear integral equations
of the typeν(s)+ν(s)∫
0
1
k(s,t)ν(t)dt =W
0(s) in the spaceL
2 [0,1]. 相似文献
190.
A copper(II)-catalyzed conversion of bisaryloxime ethers to 2-arylbenzoxazoles has been developed. The reaction involves a cascade C-H functionalization and C-N/C-O bond formation under oxygen atmosphere. 相似文献