全文获取类型
收费全文 | 8823篇 |
免费 | 367篇 |
国内免费 | 156篇 |
专业分类
化学 | 4300篇 |
晶体学 | 153篇 |
力学 | 256篇 |
综合类 | 24篇 |
数学 | 1842篇 |
物理学 | 2771篇 |
出版年
2023年 | 183篇 |
2022年 | 219篇 |
2021年 | 333篇 |
2020年 | 371篇 |
2019年 | 223篇 |
2018年 | 304篇 |
2017年 | 304篇 |
2016年 | 322篇 |
2015年 | 288篇 |
2014年 | 498篇 |
2013年 | 790篇 |
2012年 | 531篇 |
2011年 | 590篇 |
2010年 | 544篇 |
2009年 | 538篇 |
2008年 | 406篇 |
2007年 | 430篇 |
2006年 | 445篇 |
2005年 | 303篇 |
2004年 | 245篇 |
2003年 | 202篇 |
2002年 | 146篇 |
2001年 | 214篇 |
2000年 | 103篇 |
1999年 | 147篇 |
1998年 | 91篇 |
1997年 | 85篇 |
1996年 | 49篇 |
1995年 | 24篇 |
1994年 | 29篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 18篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 28篇 |
1985年 | 28篇 |
1984年 | 40篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1973年 | 15篇 |
1971年 | 8篇 |
排序方式: 共有9346条查询结果,搜索用时 725 毫秒
11.
12.
The paper presents the synthesis and catalytic activity of CuFe2O4 nanoparticles. The CuFe2O4 nanoparticles have been prepared by sonochemical route under low power ultrasonic irradiation (UI) and using silent stirring at room temperature only (ST) along with co-precipitation method, without using any additive/capping agent. The synthesized magnetic nanoparticles were successfully used and compared for the synthesis of 4H-chromene-3-carbonitrile derivatives. The CuFe2O4 nanoparticles obtained by sonochemical route exhibit higher catalytic activity because of small size (0.5–5 nm), high surface area (214.55 m2/g), high thermal stability up to 700 °C, recyclability and reusability due to its magnetic characteristics than CuFe2O4 nanoparticles obtained by room temperature silent stirring. The synthesized CuFe2O4 nanoparticles were characterized by FT-IR, SEM–EDX, HR-TEM, XRD, TGA/DTA/DTG, BET, VSM techniques. The present method is of great interest due to its salient features such as environmentally compatible, efficient, short reaction time, chemoselectivity, high yield, cheap, moisture insensitive, green and recyclable catalyst which make it sustainable protocol. 相似文献
13.
Mei Xueqing Li Zhixiong Bagherzadeh Seyed Amin Karimipour Aliakbar Bahrami Mehrdad Karimipour Arash 《Journal of Thermal Analysis and Calorimetry》2021,145(4):2123-2128
Journal of Thermal Analysis and Calorimetry - Artificial neural network/kriging interpolation method optimization method which is evaluated concerned the hybrid nanofluid composed of iron oxide... 相似文献
14.
15.
Pure and 0.1 mol% Xylenol orange (XO) doped Imidazolium L-tartrate (IMLT) nonlinear optical (NLO) single crystals were grown using Sankaranarayanan–Ramasamy (SR) method of uniaxial solution crystallization technique. The pure IMLT crystal is 100 mm in length and 15 mm in diameter. The doped IMLT crystal is 25 mm in length and 10 mm in diameter. UV–Vis-NIR spectrum shows that the pure and XO doped IMLT crystals' cut off wavelength is 235 nm. High-resolution X-ray diffraction (HRXRD) measurement and birefringence interferometry confirm that the SR method grown crystal has good crystalline perfection and optical homogeneity. The wavelength dependent refractive index and piezoelectric d33 coefficient were measured. The difference refractive index (Δn) of (100) plane in parallel and perpendicular directions shows a strong dependence on wavelength. The dielectric constant, hardness and SHG conversion efficiency were also increased as a result of XO dye doping in IMLT crystal. 相似文献
16.
Michael Dickson 《Foundations of Physics》2015,45(10):1330-1340
17.
18.
19.
《European Journal of Operational Research》2006,175(3):1798-1817
Workflow systems provide means and techniques for modelling, designing, performing and controlling repetitive (business) processes. The quality of commercial workflow systems is usually determined to a large extent by their versatility and multi-purpose application. One of the current trends in improving workflow systems lies in enriching modelling methods and techniques in order to enlarge design alternatives.The need for such advanced methods is particularly apparent in those fields in which the process duration can be determined only vaguely, but whose completion schedules are at the same time strictly enforced by a highly competitive market by means of fines and penalties. The risk of an overrun has to be weighed against the expected costs and benefits of certain measures reducing turn-around time and their combinations. Because they can help to avoid such penalties—or, at least, keep any potential losses low by identifying critical subprocesses and evaluate appropriate measures—modelling and evaluation techniques are becoming essential features of workflow systems.Methodologically, we use Stochastic Branch-and-Bound as a technique for finding “optimal” bundles of measures. A numerical study shows the benefits of this meta-approach by means of five stepwise-developed decision scenarios requiring rich modelling. Petri nets as a modelling tool and Stochastic Branch-and-Bound as an optimization technique determine for multi-mode resource constrained workflows of varying complexity an optimal workforce strategy with respect to the number of workers and their qualification. 相似文献
20.