全文获取类型
收费全文 | 43105篇 |
免费 | 3537篇 |
国内免费 | 3263篇 |
专业分类
化学 | 29086篇 |
晶体学 | 222篇 |
力学 | 528篇 |
综合类 | 718篇 |
数学 | 6781篇 |
物理学 | 12570篇 |
出版年
2023年 | 306篇 |
2022年 | 585篇 |
2021年 | 1594篇 |
2020年 | 1043篇 |
2019年 | 1232篇 |
2018年 | 864篇 |
2017年 | 944篇 |
2016年 | 1267篇 |
2015年 | 1320篇 |
2014年 | 1623篇 |
2013年 | 2885篇 |
2012年 | 2016篇 |
2011年 | 2021篇 |
2010年 | 2009篇 |
2009年 | 2485篇 |
2008年 | 2574篇 |
2007年 | 2793篇 |
2006年 | 2235篇 |
2005年 | 1506篇 |
2004年 | 1406篇 |
2003年 | 1385篇 |
2002年 | 3772篇 |
2001年 | 1357篇 |
2000年 | 935篇 |
1999年 | 653篇 |
1998年 | 670篇 |
1997年 | 505篇 |
1996年 | 549篇 |
1995年 | 535篇 |
1994年 | 497篇 |
1993年 | 542篇 |
1992年 | 521篇 |
1991年 | 366篇 |
1990年 | 282篇 |
1989年 | 244篇 |
1988年 | 262篇 |
1987年 | 218篇 |
1986年 | 213篇 |
1985年 | 330篇 |
1984年 | 240篇 |
1983年 | 144篇 |
1982年 | 288篇 |
1981年 | 467篇 |
1980年 | 430篇 |
1979年 | 466篇 |
1978年 | 370篇 |
1977年 | 280篇 |
1976年 | 237篇 |
1974年 | 78篇 |
1973年 | 153篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Kang Yang Chang-Shan Yang Xing-Xian Dong Dr. Yu-Hui Tan Prof. Yun-Zhi Tang Dr. Wen-Juan Wei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(26):5887-5892
Smart multifunctional molecular ferroelectrics bearing high Curie temperatures and diverse excellent physical properties, such as second harmonic generation (SHG) responses, luminescence, and semiconductivity, among others, have significant applications but have seldom been documented. Herein, the rare-earth metals Nd and Pr are introduced into a simple molecular system (nBu4N )3[M(NO3)x(SCN)y] (nBu4N=tetrabutyl ammonium, M=rare-earth metal, nBu=CH3CH2CH2CH2), and two new multifunctional molecular ferroelectrics are obtained: (nBu4N )3[Nd(NO3)4(SCN)2] ( 1 ) and (nBu4N )3[Pr(NO3)4(SCN)2] ( 2 ). Their distinct heat and dielectric anomaly dependence on temperature verifies that compounds 1 and 2 experience high-temperature para-ferroelectric phase transitions at 408 and 413 K, respectively. Strikingly, both molecular ferroelectrics possess large spontaneous polarization with Ps values of 9.05 and 8.50 μC cm−2, respectively, and are further characterized by the appearance of multiple intersecting non-180° domains and polarization switching behavior. In particular, compounds 1 and 2 show good stability with only a small decrease in SHG intensity after switching cycles, suggesting that they have great potential for application in nonlinear optical (NLO) switches. Simultaneously, the rare-earth compounds 1 and 2 present bright yellow–red and bright green fluorescence, respectively, at room temperature. 相似文献
102.
Dr. Jinghui Zhang Lei Gong Xiaoshuang Zhang Dr. Mengliang Zhu Chaorui Su Qing Ma Dr. Dongdong Qi Prof. Yongzhong Bian Prof. Hongwu Du Prof. Jianzhuang Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(61):13842-13848
Two-photon excited fluorescent (TPEF) materials are highly desirable for bioimaging applications owing to their unique characteristics of deep-tissue penetration and high spatiotemporal resolution. Herein, by connecting one, two, or three electron-deficient zinc porphyrin units to an electron-rich triazatruxene core via ethynyl π-bridges, conjugated multipolar molecules TAT-(ZnP) n (n=1–3) were developed as TPEF materials for cell imaging. The three new dyes present high fluorescence quantum yields (0.40–0.47) and rationally improved two-photon absorption (TPA) properties. In particular, the peak TPA cross section of TAT-ZnP (436 GM) is significantly larger than that of the ZnP reference (59 GM). The δTPA values of TAT-(ZnP)2 and TAT-(ZnP)3 further increase to 1031 and up to 1496 GM, respectively, indicating the effect of incorporated ZnP units on the TPA properties. The substantial improvement of the TPEF properties is attributed to the formation of π-conjugated quadrapole/octupole molecules and the extension of D -π-A-D systems, which has been rationalized by density function theory (DFT) calculations. Moreover, all of the three new dyes display good biocompatibility and preferential targeting ability toward cytomembrane, thus can be superior candidates for TPEF imaging of living cells. Overall, this work demonstrated a promising strategy for the development of porphyrin-based TPEF materials by the construction and extension of D -π-A-D multipolar array. 相似文献
103.
Yuqing Li Prof. Dr. Juewen Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(60):13644-13651
Purines and their derivatives are highly important molecules in biology for nucleic acid synthesis, energy storage, and signaling. Although many DNA aptamers have been obtained for binding adenine derivatives such as adenosine, adenosine monophosphate, and adenosine triphosphate, success for the specific binding of guanosine has been limited. Instead of performing new aptamer selections, we report herein a base-excision strategy to engineer existing aptamers to bind guanosine. Both a Na+-binding aptamer and the classical adenosine aptamer have been manipulated as base-excising scaffolds. A total of seven guanosine aptamers were designed, of which the G16-deleted Na+ aptamer showed the highest bindng specificity and affinity for guanosine with an apparent dissociation constant of 0.78 mm . Single monophosphate difference in the target molecule was also recognizable. The generality of both the aptamer scaffold and excised site were systematically studied. Overall, this work provides a few guanosine binding aptamers by using a non-SELEX method. It also provides deeper insights into the engineering of aptamers for molecular recognition. 相似文献
104.
Dr. Antonio Sánchez-Ruiz Dr. Julián Rodríguez-López Dr. Andrés Garzón-Ruiz Dr. Sonia B. Jiménez-Pulido Dr. Nuria A. Illán-Cabeza Dr. Amparo Navarro Dr. Joaquín C. García-Martínez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(61):13990-14001
Different molecular strategies have been carefully evaluated to produce solid-state luminescence enhancement (SLE) in compounds that show dark states in solution. A set of α-phenylstyrylarene derivatives with a butterfly shape have been designed and synthesised, for the first time, with the aim of improving the solid-state fluorescence emission of their parent styrylarene compounds. Although these butterfly molecules are not fluorescent in solution, one of them (1,2,4,5-tetra(α-phenylstyryl)benzene) exhibits a fluorescence quantum yield as high as 68 % in a drop-cast sample and 31 % in its crystalline form. In contrast, 1,3,5-tris(α-phenylstyryl)benzene and 4,6-bis(α-phenylstyryl)pyrimidine do not show SLE. A range of fluorescence spectroscopy experiments and DFT calculations were carried out to unravel the origin of different photophysical behaviour of these compounds in the solid state. The results indicate that a rational strategy to control the SLE effect in luminogens depends on a delicate balance between molecular properties and inter-/intramolecular interactions in the solid state. 相似文献
105.
Philipp Rietsch Dr. Sebastian Sobottka Dr. Katrin Hoffmann Dr. Alexey A. Popov Pascal Hildebrandt Prof. Dr. Biprajit Sarkar Dr. Ute Resch-Genger Prof. Dr. Siegfried Eigler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(72):17361-17365
Reversibly switching the light absorption of organic molecules by redox processes is of interest for applications in sensors, light harvesting, smart materials, and medical diagnostics. This work presents a symmetrical benzothiadiazole (BTD) derivative with a high fluorescence quantum yield in solution and in the crystalline state and shows by spectroelectrochemical analysis that reversible switching of UV absorption in the neutral state, to broadband Vis/NIR absorption in the 1st oxidized state, to sharp band Vis absorption in the 2nd oxidized state, is possible. For the one-electron oxidized species, formation of a delocalized radical is confirmed by electron paramagnetic resonance spectroelectrochemistry. Furthermore, our results reveal an increasing quinoidal distortion upon the 1st and 2nd oxidation, which can be used as the leitmotif for the development of BTD based redox switches. 相似文献
106.
107.
108.
Manon Catherin Olatz Uranga-Barandiaran Arnaud Brosseau Dr. Rémi Métivier Dr. Gabriel Canard Dr. Anthony D'Aléo Dr. David Casanova Prof. Frédéric Castet Dr. Elena Zaborova Prof. Frédéric Fages 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3818-3828
We describe the synthesis of a series of covalently linked dimers of quadrupolar curcuminoid-BF2 dyes and the detailed investigation of their solvent-dependent spectroscopic and photophysical properties. In solvents of low polarity, intramolecular folding induces the formation of aggregated chromophores, the UV/Vis absorption spectra of which display the optical signature characteristic of weakly-coupled H-aggregates. The extent of folding and, in turn, of ground-state aggregation is strongly dependent on the nature of the flexible linker. Steady-state and time-resolved fluorescence emission spectroscopies show that the Frenkel exciton relaxes into a fluorescent symmetrical excimer state with a long lifetime. Furthermore, our in-depth studies show that a weakly emitting excimer lies on the pathway toward a photocyclomer. Two-dimensional 1H NMR spectroscopy and density functional theory (DFT) allowed the structure of the photoproduct to be established. To our knowledge, this represents the first example of a [2π+2π] photodimerization of the curcuminoid chromophore. 相似文献
109.
肝损伤是影响公众健康的重大问题之一, 已经引起了人们越来越多的关注. 而过表达的过氧化亚硝酸盐(ONOO?)在肝损伤等疾病的发病机制中起着重要作用, 被认为是一种与早期肝损伤密切相关的生物活性分子. 因此, 为了探究ONOO?在肝损伤过程中的作用, 开发可以实现肝损伤过程中ONOO?高选择性和实时检测的分析方法具有重要意义. 本文报道了一种具有大斯托克斯位移的远红光至近红外(FR-NIR)ONOO?荧光探针. 由于该探针具有大的斯托克斯位移, 可以有效消除光谱重叠和自吸收的干扰, 从而显著提高成像的信噪比. 此外, 该探针对ONOO?具有高的灵敏度(检出限为25.8 nmol/L)和良好的选择性, 被成功用于药物诱导肝损伤过程中ONOO?信号的成像检测. 相似文献
110.