全文获取类型
收费全文 | 120716篇 |
免费 | 1467篇 |
国内免费 | 414篇 |
专业分类
化学 | 65771篇 |
晶体学 | 1232篇 |
力学 | 4891篇 |
综合类 | 5篇 |
数学 | 11796篇 |
物理学 | 38902篇 |
出版年
2016年 | 1231篇 |
2015年 | 943篇 |
2014年 | 1278篇 |
2013年 | 4720篇 |
2012年 | 3323篇 |
2011年 | 4307篇 |
2010年 | 2666篇 |
2009年 | 2451篇 |
2008年 | 3858篇 |
2007年 | 3883篇 |
2006年 | 3979篇 |
2005年 | 3900篇 |
2004年 | 3394篇 |
2003年 | 3062篇 |
2002年 | 2740篇 |
2001年 | 3374篇 |
2000年 | 2417篇 |
1999年 | 1906篇 |
1998年 | 1583篇 |
1997年 | 1702篇 |
1996年 | 1627篇 |
1995年 | 1696篇 |
1994年 | 1491篇 |
1993年 | 1456篇 |
1992年 | 1682篇 |
1991年 | 1661篇 |
1990年 | 1603篇 |
1989年 | 1616篇 |
1988年 | 1615篇 |
1987年 | 1614篇 |
1986年 | 1523篇 |
1985年 | 2085篇 |
1984年 | 2220篇 |
1983年 | 1841篇 |
1982年 | 2159篇 |
1981年 | 1985篇 |
1980年 | 2023篇 |
1979年 | 2029篇 |
1978年 | 2149篇 |
1977年 | 2043篇 |
1976年 | 2075篇 |
1975年 | 2024篇 |
1974年 | 1859篇 |
1973年 | 2082篇 |
1972年 | 1264篇 |
1971年 | 965篇 |
1970年 | 898篇 |
1969年 | 920篇 |
1968年 | 1047篇 |
1967年 | 1101篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Ukrainian Mathematical Journal - Two determinants of Wronskian matrices are evaluated for the case where the matrix rows are partitioned into n blocks. Similar formulae are derived for the matrices... 相似文献
2.
Journal of Applied Spectroscopy - With the COVID-19 outbreak, many challenges are posed before the scientific world to curb this pandemic. The diagnostic testing, treatment, and vaccine development... 相似文献
3.
Experimental Mechanics - Ratcheting is an important mechanical behavior of metals and alloys, which is caused by the repeated accumulations of tensile and compressive strain in circle load.... 相似文献
4.
The energy spectra of three types of two-dimensional potentials(we will call them‘Davidson-like potentials’(DLPs)),characterized by four minima separated by barriers,are investigated.The predictions for spectra and wave functions are obtained by using the nine-point finite-difference method.For these potentials,with the existence of a single configuration,a transition of spectra,as a function of barrier height,is covered from tunneling splitting modes to fluctuations phenomena,with equal peaks wave functions,crossing to the spectra of purely anharmonic oscillator potentials(AOPs).A different type of phase transition occurs when two(or more)configurations coexist.With the change of the parameters,a transition of spectra is covered from coexistence phenomena of two distinct quantum tunneling modes to fluctuations phenomena,with unequal peaks wave functions,crossing to the spectra of purely AOPs.Using DLPs,a particular application of the coherent quadropole-octupole model to describe energy bands with alternating parity of the nuclei100Mo,146,148Nd,148,150Sm,220Ra,220,222Rn,and220,222Th is presented.The global parametrization of the model for the selected nuclei is achieved. 相似文献
5.
Yujie Tao Ahren W. Jasper Yuri Georgievskii Stephen J. Klippenstein Raghu Sivaramakrishnan 《Proceedings of the Combustion Institute》2021,38(1):515-522
Recent theoretical studies have shown that termolecular chemistry can be facilitated through reactions of flame radicals (H, O, and OH) or O2 with highly-energized collision complexes (either radical or stable species) formed in exothermic reactions. In this work, radical-radical recombination reaction induced termolecular chemistry and its impact on combustion modeling was studied. Two recombination reactions, H + CH3 + M → CH4 + M and H + OH + M → H2O + M, were analyzed using ab-initio master equation analyses guided by quasiclassical trajectory results. The dynamics results and the master equation calculations indicate that CH4? and H2O? (formed in the two radical-radical reactions outlined above) react rapidly with flame radicals and O2 at rates that are competitive with collisional cooling. The addition of these processes into conventional combustion modeling requires two modifications: the inclusion of the new nonthermal termolecular reaction rates and the simultaneous reduction of the competing recombination reaction rates. The former is described with newly derived Arrhenius expressions based on quasiclassical trajectories, and the latter is achieved by perturbing the recombination reaction rate during the simulation. Kinetic modeling was used to gauge the impact of including this nonthermal chemistry for H2/CH4-air laminar flames speeds. Inclusion of this nonthermal chemistry has a noticeable impact on simulated flame speeds. The procedure developed here can be utilized to properly quantify the effects of such nonthermal reactions in macroscopic kinetic models. 相似文献
6.
7.
Prof. Dr. Samih A. Halawy Dr. Ahmed I. Osman Dr. Adel Abdelkader Mahmoud Nasr Prof. Dr. David W. Rooney 《ChemistryOpen》2022,11(3):e202200021
Measuring the Lewis-acidic surface sites in catalysis is problematic when the material‘s surface area is very low (SBET ≤1 m2 ⋅ g−1). For the first time, a quantitative assessment of total acidic surface sites of very small surface area catalysts (MoO3 as pure and mixed with 5–30 % CdO (wt/wt), as well as CdO for comparison) was performed using a smart new probe molecule, tetrahydrofuran (THF). The results were nearly identical compared to using another commonly used probe molecule, pyridine. This audition is based on the limited values of the surface area of these samples that likely require a relatively moderate basic molecule as THF with pKb=16.08, rather than strong basic molecules such as NH3 (pKb=4.75) or pyridine (pKb=8.77). We propose mechanisms for the interaction of vapour phase molecules of THF with the Lewis-cationic Mo and Cd atoms of these catalysts. Besides, dehydration of isopropyl alcohol was used as a probe reaction to investigate the catalytic activity of these catalysts to further support our findings in the case of THF in a temperature range of 175–300 °C. A good agreement between the obtained data of sample MoO3-10 % CdO, which is characterised by the highest surface area value, the population of Lewis-acidic sites and % selectivity of propylene at all the applied reaction temperatures was found. 相似文献
8.
Candle soot (CS) is a desirable carbon nanomaterial for sensors owing to its highly porous nanostructure and large specific surface area. CS is advantageous in its low-cost and facile preparation compared to graphene and carbon nanotubes, but its pristine nanostructure is susceptible to collapse, hampering its application in electronic devices. This article reports conformal coating of nanoscale crosslinked hydrophilic polymer on CS film using initiated chemical vapor deposition, which well preserved the CS nanostructure and obtained nanoporous CS@polymer composites. Tuning coating thickness enabled composites with different morphologies and specific surface areas. Surprisingly, the humidity sensor made from composite with the lowest filling degree, thus largest specific surface area, showed relatively low sensitivity, which is likely due to its discontinuous structure, thus insufficient conductive channels. Composite sensor with optimum filling degree shows excellent sensing response of more than 103 with the linearity of R2 = 0.9400 within a broad relative humidity range from 11% to 96%. The composite sensor also exhibits outstanding sensing performance compared to literature with low hysteresis (3.00%), a satisfactory response time (28.69 s), and a fast recovery time (0.19 s). The composite sensor is fairly stable and durable even after 24 h soaking in water. Furthermore, embedding a humidity sensor into a face mask realizes real-time monitoring of human breath and cough, suggesting promising applications in respiratory monitoring. 相似文献
9.
Restricted testing conditions were considered recently. For the maximal operator, Hytönen, Li and Sawyer [8] first obtained parental testing condition. Later, they [9] showed that it suffices to restrict testing to doubling cubes. Chen and Lacey [3] gave a similar restricted testing condition. In our paper, we discuss a version of the latter in the multilinear setting.
相似文献10.
Maschler Tobias Strmer-Stephan Bastian Morhard Jrg Stegmaier Thomas Tilebein Meike Griepentrog Hans W. 《Annals of Operations Research》2022,314(2):577-600
Annals of Operations Research - Selecting a vegetation layer design goes along with determining its future irrigation need. Therefore, it is essential to take a design decision that is minimising... 相似文献