全文获取类型
收费全文 | 46172篇 |
免费 | 4426篇 |
国内免费 | 3220篇 |
专业分类
化学 | 19504篇 |
晶体学 | 157篇 |
力学 | 2026篇 |
综合类 | 897篇 |
数学 | 19215篇 |
物理学 | 12019篇 |
出版年
2023年 | 352篇 |
2022年 | 528篇 |
2021年 | 1383篇 |
2020年 | 1071篇 |
2019年 | 1211篇 |
2018年 | 978篇 |
2017年 | 1065篇 |
2016年 | 1319篇 |
2015年 | 1383篇 |
2014年 | 1883篇 |
2013年 | 3477篇 |
2012年 | 2174篇 |
2011年 | 2449篇 |
2010年 | 2266篇 |
2009年 | 2851篇 |
2008年 | 2977篇 |
2007年 | 3102篇 |
2006年 | 2516篇 |
2005年 | 1803篇 |
2004年 | 1668篇 |
2003年 | 1662篇 |
2002年 | 1591篇 |
2001年 | 1434篇 |
2000年 | 1169篇 |
1999年 | 961篇 |
1998年 | 899篇 |
1997年 | 748篇 |
1996年 | 698篇 |
1995年 | 630篇 |
1994年 | 586篇 |
1993年 | 581篇 |
1992年 | 575篇 |
1991年 | 369篇 |
1990年 | 334篇 |
1989年 | 257篇 |
1988年 | 274篇 |
1987年 | 230篇 |
1986年 | 253篇 |
1985年 | 370篇 |
1984年 | 296篇 |
1983年 | 170篇 |
1982年 | 336篇 |
1981年 | 505篇 |
1980年 | 469篇 |
1979年 | 510篇 |
1978年 | 400篇 |
1977年 | 316篇 |
1976年 | 264篇 |
1974年 | 87篇 |
1973年 | 158篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Stochastic equations indexed by negative integers and taking values in compact groups are studied. Extremal solutions of the equations are characterized in terms of infinite products of independent random variables. This result is applied to characterize several properties of the set of all solutions in terms of the law of the driving noise. 相似文献
992.
Ravi P. Agarwal 《Nonlinear Analysis: Theory, Methods & Applications》2010,72(6):2859-124
We consider a differential equation of fractional order with uncertainty and present the concept of solution. It extends, for example, the cases of first order ordinary differential equations and of differential equations with uncertainty. Some examples are presented. 相似文献
993.
<正>A novel polyester containing ferrocenyl was prepared by low-temperature interface polycondensation of 1,1'-ferrocenedicarboxylic acid chloride with 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one(DHPZ),which is a twisted non-coplanar heterocyclic bisphenol-like monomer.The newly generated polymer was evaluated based on characterization of its solubility,viscosity measurements,elemental analysis,FTIR spectroscopy,differential scanning calorimetric and thermogravimetric studies. 相似文献
994.
995.
996.
Zhi HuLi Chen Bin ZhaoYuan Luo De-Yi WangYu-Zhong Wang 《Polymer Degradation and Stability》2011,96(3):320-327
A novel silicon- and phosphorus-containing flame retardant, poly (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide siloxane), P(DOPO-VTES) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) and vinyltriethoxy silane(VTES). Its chemical structure was confirmed by FTIR. The thermal gravimetrical analysis (TGA) showed that P(DOPO-VTES) had good thermal stability and a high of char yield (86.31%) at 700 °C in nitrogen atmosphere. Its XRD patterns showed that this compound had a certain ordered structure. P(DOPO-VTES) was blended with polycarbonate (PC) together with montmorillonite(MMT) to prepare a series of organic-inorganic hybrids of flame retardant (PC)/P(DOPO-VTES)/MMT via melt blending. The thermal degradation behavior and flame retardancy of those hybrids were investigated with TGA, limiting oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter. The LOI value of the flame-retardant PC systems could reach a maximal value of 32.8 when the content of P(DOPO-VTES) was 5 wt%. When 2 wt% MMT was added into the PC/5%P(DOPO-VTES) system, the UL-94 rating reached V-0. The possible flame retardant mode of MMT was studied via the dynamic rheological properties of the systems and the morphology of the chars remaining after the LOI test and the cone calorimeter test. 相似文献
997.
Determination of halogenated flame retardants by liquid chromatography coupled to mass spectrometry 总被引:1,自引:0,他引:1
We present an overview of current analytical methods for selected halogenated flame retardants (HFRs), focusing on instrumental determination using liquid chromatography coupled to mass spectrometry. We based the strategy for literature search on recent articles published in peer-reviewed scientific journals or conference proceedings. We report on selected HFRs and some metabolites and transformation products, and on the analytical performances of different ionization modes, with emphasis on selectivity and sensitivity. Moreover, we compare these parameters with those obtained by gas chromatography. 相似文献
998.
Changing ocean-carbonate chemistry caused by oceanic uptake of anthropogenic atmospheric carbon dioxide leads to the formation of carbonic acid, thus lowering the pH of the sea with predictions of a decrease from current levels at 8.15 to 7.82 by the end of the century. The exact measurement of subtle pH changes in seawater over time presents significant analytical challenges, as the equilibrium constants are governed by water temperature and pressure, salinity effects, and the existence of other ionic species in seawater.Here, we review these challenges and how pH also affects dissolved inorganic and organic chemicals that affect biological systems. This includes toxic compounds (xenobiotics) as well as chemicals that are beneficial for marine organisms, such as the chemical signals (i.e. pheromones) that are utilized to coordinate animal behavior. We review how combining analytical, molecular and biochemical tools can lead to the development of biosensors to detect pH effects to enable predictive modeling of the ecological consequences of ocean acidification. 相似文献
999.
In recent years, increasing attention has been paid to “soft” photoionization (PI), which will potentially become a standard, universal ionization method. Tunable synchrotron vacuum ultraviolet (SVUV) light, a quasi-continuous light with good energy resolution and high photon flux, has proved an ideal source for “soft” PI in various research fields (e.g., combustion chemistry and molecular imaging).This review focuses on combinations of SVUV light with commonly used techniques (e.g., molecular-beam sampling, laser desorption, ion desorption, and thermal vaporization). These couplings have successful applications in flame chemistry, organic analysis, chemical imaging and aerosol mass spectrometry. 相似文献
1000.
Cu-catalyzed enantioselective 1,4-conjugate addition of β,γ-unsaturated α-keto ester compound was carried out to afford chiral γ-substituted γ-aryl α-keto ester, which could be conveniently converted to the potential skeleton of new Pril drugs. Up to 81% ee and 99% yield were afforded for the 1,4-conjugate addition using D2-symmetric biphenyl phosphoramidite ligand. 相似文献