全文获取类型
收费全文 | 738篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 415篇 |
晶体学 | 8篇 |
力学 | 55篇 |
数学 | 148篇 |
物理学 | 134篇 |
出版年
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 38篇 |
2020年 | 21篇 |
2019年 | 34篇 |
2018年 | 30篇 |
2017年 | 33篇 |
2016年 | 46篇 |
2015年 | 23篇 |
2014年 | 30篇 |
2013年 | 60篇 |
2012年 | 57篇 |
2011年 | 48篇 |
2010年 | 31篇 |
2009年 | 33篇 |
2008年 | 28篇 |
2007年 | 30篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有760条查询结果,搜索用时 15 毫秒
171.
Md. Khalid Anwer Essam A. Ali Muzaffar Iqbal Mohammed Muqtader Ahmed Mohammed F. Aldawsari Ahmed Al Saqr Mohd Nazam Ansari M. Ali Aboudzadeh 《Molecules (Basel, Switzerland)》2022,27(1)
Baricitinib (BTB) is an orally administered Janus kinase inhibitor, therapeutically used for the treatment of rheumatoid arthritis. Recently it has also been approved for the treatment of COVID-19 infection. In this study, four different BTB-loaded lipids (stearin)-polymer (Poly(d,l-lactide-co-glycolide)) hybrid nanoparticles (B-PLN1 to B-PLN4) were prepared by the single-step nanoprecipitation method. Next, they were characterised in terms of physicochemical properties such as particle size, zeta potential (ζP), polydispersity index (PDI), entrapment efficiency (EE) and drug loading (DL). Based on preliminary evaluation, the B-PLN4 was regarded as the optimised formulation with particle size (272 ± 7.6 nm), PDI (0.225), ζP (−36.5 ± 3.1 mV), %EE (71.6 ± 1.5%) and %DL (2.87 ± 0.42%). This formulation (B-PLN4) was further assessed concerning morphology, in vitro release, and in vivo pharmacokinetic studies in rats. The in vitro release profile exhibited a sustained release pattern well-fitted by the Korsmeyer–Peppas kinetic model (R2 = 0.879). The in vivo pharmacokinetic data showed an enhancement (2.92 times more) in bioavailability in comparison to the normal suspension of pure BTB. These data concluded that the formulated lipid-polymer hybrid nanoparticles could be a promising drug delivery option to enhance the bioavailability of BTB. Overall, this study provides a scientific basis for future studies on the entrapment efficiency of lipid-polymer hybrid systems as promising carriers for overcoming pharmacokinetic limitations. 相似文献
172.
Hicham Mahfoz Kotb Mohamad Mahmoud Ahmad Sajid Ali Ansari Tarek S. Kayed Adil Alshoaibi 《Molecules (Basel, Switzerland)》2022,27(3)
In the current study, we report on the dielectric behavior of colossal-dielectric-constant Na1/2La1/2Cu3Ti4O12 (NLCTO) ceramics prepared by mechanochemical synthesis and spark plasma sintering (SPS) at 850 °C, 900 °C, and 925 °C for 10 min. X-ray powder diffraction analysis showed that all the ceramics have a cubic phase. Scanning electron microscope observations revealed an increase in the average grain size from 175 to 300 nm with an increase in the sintering temperature. SPS NLCTO ceramics showed a room-temperature colossal dielectric constant (>103) and a comparatively high dielectric loss (>0.1) over most of the studied frequency range (1 Hz–40 MHz). Two relaxation peaks were observed in the spectra of the electrical modulus and attributed to the response of grain and grain boundary. According to the Nyquist plots of complex impedance, the SPS NLCTO ceramics have semiconductor grains surrounded by electrically resistive grain boundaries. The colossal dielectric constant of SPS NLCTO ceramics was attributed to the internal barrier layer capacitance (IBLC) effect. The high dielectric loss is thought to be due to the low resistivity of the grain boundary of SPS NLCTO. 相似文献
173.
Nowadays, the eye-catching characteristics of boron nitride nanotubes, in particular, the capability of sensing nano-objects, have opened up new prospects to develop the bio-/nano-sensing technologies. This research deals with physically affected single-walled boron nitride nanotubes (SWBNNT) as nano-sensors for sensing attached nanoscale objects. Three different boundary conditions including simply supported at both ends, clamped-free and clamped-clamped are considered to illustrate the vibrational behaviour of SWBNNTs as nano-sensor. The Rayleigh and Timoshenko beam theories are employed to model the SWBNNT. Also, the nonlocal strain gradient model is utilized to capture the size-dependent effects. One of the major factors in the scrutiny of mass nano-sensors is pertinent to the variation in frequency shift magnitudes against the number and mass weight values of attached nanoparticles. Herein, the effects of the nonlocal and material length scale parameters, the number and location of nano-objects, the rotary inertia and mass weight magnitudes of attached nanoparticles, the aspect ratio of SWBNNT, electrical potential and different boundary conditions on the variation in frequency shift and resonant frequency are analysed. 相似文献
174.
Choudhari Dinkar Chakravarty Debamitra Lande Dipali N. Parveen Sana Gejji Shridhar P. Kodam Kisan M. Salunke-Gawali Sunita 《Structural chemistry》2019,30(6):2257-2270
Structural Chemistry - Homologated (N)-n-alkylammonium salts of 2-bromo-3-oxido-1,4-naphthoquinone (BS-1 to BS-8) have been synthesized and characterized from the single crystal X-ray diffraction... 相似文献
175.
176.
Monish Arbaz Ansari Dhananjay Yadav Prof. Maya Shankar Singh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(36):8083-8089
A photocatalyst- and additive-free, visible-light-mediated chemoselective domino protocol was devised to access fully substituted thiazoline derivatives from β-ketothioamides and α-diazo 1,3-diketones at moderate temperature in open air. The reaction proceeds through in situ generation of electrophilic carbenes from α-diazo 1,3-diketones by a low-energy blue LED (448 nm), which undergoes selective coupling with nucleophilic β-ketothioamides to give thiazolines by successive formation of C−S and C−N bonds in one stretch. Notably, the benign and clean conditions, operational simplicity, sustainability, 100 % carbon economy, high yields, and wide functional-group tolerance are further attributes of the strategy. A mechanistic rationale for this cascade reaction sequence is well supported by control experiments. 相似文献
177.
178.
In this paper, we introduce systems of simultaneous generalized vector equilibrium problems and prove the existence of their
solutions. As application of our results, we derive the existence theorems for solutions of systems of vector saddle–point
problems. Consequently, we prove the existence of a solution of systems of generalized minimax inequalities. Further application
of our results is also given to establish the existence of a solution of a Debreu-type equilibrium problem for vector-valued
functions.
The first author thanks the Department of Mathematical Sciences, King Fahd University of Petroleum and Minerals, Dhahran,
Saudi Arabia for providing excellent research facilities. The second and third authors were supported by the National Science
Council of the Republic of China. The authors are grateful to the referees for valuable suggestions and comments. 相似文献
179.
An optical waveguide clad with V2O5 is proposed as a new type of oxygen sensor in ambient air. The presence of gas changes
the light transmission (TE0-polarized mode) through the guide, due to the change in refractive index of the cladding which
changes the effective index of the guide. O2 gas concentration is varied from a few (≈10) ppm to several percent (4%). Sensors
exhibit the same sensitivity at a slightly elevated temperature. The increase in thickness of the cladding causes a reduction
in sensitivity and increase in linearity. It is observed that the sensor exhibits the same performance using the static or
incremental mode.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
180.