全文获取类型
收费全文 | 1684篇 |
免费 | 240篇 |
国内免费 | 1208篇 |
专业分类
化学 | 2321篇 |
晶体学 | 10篇 |
力学 | 91篇 |
综合类 | 10篇 |
数学 | 147篇 |
物理学 | 553篇 |
出版年
2022年 | 17篇 |
2021年 | 25篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 275篇 |
2012年 | 243篇 |
2011年 | 234篇 |
2010年 | 99篇 |
2009年 | 230篇 |
2008年 | 72篇 |
2007年 | 40篇 |
2006年 | 49篇 |
2005年 | 118篇 |
2004年 | 464篇 |
2003年 | 314篇 |
2002年 | 286篇 |
2001年 | 76篇 |
2000年 | 34篇 |
1999年 | 49篇 |
1998年 | 74篇 |
1997年 | 52篇 |
1996年 | 30篇 |
1995年 | 8篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1970年 | 7篇 |
排序方式: 共有3132条查询结果,搜索用时 15 毫秒
51.
Cerebrosterol (2 4S hydroxycholesterol,1)formedinsmallamountsinhumanandanimalbrain1fromcholes terolisimportantforcholesterolhomeostasisinthisorgan .Theexcesscholesterolisconvertedinto 2 4S hydroxy cholesterolbyauniquebrain specific 2 4S hydroxylase ,whichcouldber… 相似文献
52.
The organic nanoparticles of a blue-light-emitting molecule, 1,3-diphenyl-5-(9-anthryl)-2-pyrazuline, were prepared by reprecipitation method using acetonitrile as the solvent for the molecular precursor. Three morphologies, spherical, doughnut-shaped and cubic, could be observed on the silicon substrate forthe nanoparfides by the volume-controlled addition of acetonitrile. The evolution of particle morphology as a function of acetonitrile addition was attributed to the variation of the growth habits of the particles in the different environment. The nanoparticles exhibit the novel photoluminescence spectra as compared to those of monomer and the bulk crystals. 相似文献
53.
54.
Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at ?0.74 V vs. SCE, in 0.1M EDTA solution: 10?1M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10?2M and 10?5M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between ?0.50 and ?0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium. 相似文献
55.
The native oxide layers on Si(100) surface were irradiated under UHV conditions by an ArF excimer laser pulses with energy density varied between melting and evaporating thresholds. The resulting changes were studied by LEED, AES and UPS. The increase of the energy density up to evaporation threshold results in the recrystallisation of native oxide layer. The pulses with energy densities just above the evaporation threshold ablate the top layer leaving an ordered and atomicaly clean surface. The observed (1x1) surface reconstruction is probably stabilised by strains introduced during rapid melting and quenching of the topmost layers. The surface electronic structure is dominated by random satisfaction of dangling bonds swearing a well defined surface states observed on (2x1)Si(100) surface. 相似文献
56.
Rapid Synthesis of Lead Oxide Nanorods by One-step Solid-state Chemical Reaction at Room Temperature
A simple and facile method was reported to synthesize lead oxide nanorods. Nanorods of lead oxide were obtained directly from grinding solid metal salt and sodium hydroxide in agate mortar with the assistance of a suitable nonionic surfactant in only one step, which is different from the result of hydroxide in solution. The product has been characterized by XRD, TEM and SEM. The formation mechanism of rod-like morphology is discussed and the surfactant plays an important soft-template role in modifying the interface of solid-state reaction and according process of rod-formation. 相似文献
57.
58.
以正庚烷的转化为探针反应 ,研究了添加元素锆对铂重整催化剂性能的影响规律。结果表明 ,在 4 50℃和连续流动条件下 ,Pt/γ -Al2 O3催化剂中引入锆不仅能够提高铂催化剂的稳定性和芳构化产率、抑制氢解和异构化 ,而且能使铂催化剂保持初活性。锆含量在 0 .56%左右 ,其调变作用最为显著。 相似文献
59.
Two guanidino acid oxovanadium(Ⅳ) complexes have been synthesized. Preliminary tests in vivo have shown that the two title complexes all display lowering glucose activity in vivo to STZ-rats. The effect of glucose-lowering of guanidino acetic acid oxovanadium(Ⅳ) complex in vivo is higher than that of guanidino propanoic acid oxovanadium(Ⅳ) complex. 相似文献
60.