全文获取类型
收费全文 | 3193篇 |
免费 | 492篇 |
国内免费 | 1444篇 |
专业分类
化学 | 3412篇 |
晶体学 | 25篇 |
力学 | 166篇 |
综合类 | 14篇 |
数学 | 390篇 |
物理学 | 1122篇 |
出版年
2023年 | 48篇 |
2022年 | 63篇 |
2021年 | 87篇 |
2020年 | 107篇 |
2019年 | 76篇 |
2018年 | 65篇 |
2017年 | 72篇 |
2016年 | 106篇 |
2015年 | 93篇 |
2014年 | 99篇 |
2013年 | 378篇 |
2012年 | 379篇 |
2011年 | 362篇 |
2010年 | 167篇 |
2009年 | 320篇 |
2008年 | 180篇 |
2007年 | 140篇 |
2006年 | 117篇 |
2005年 | 188篇 |
2004年 | 505篇 |
2003年 | 346篇 |
2002年 | 320篇 |
2001年 | 119篇 |
2000年 | 78篇 |
1999年 | 80篇 |
1998年 | 94篇 |
1997年 | 74篇 |
1996年 | 65篇 |
1995年 | 39篇 |
1994年 | 36篇 |
1993年 | 32篇 |
1992年 | 29篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1970年 | 5篇 |
1931年 | 3篇 |
排序方式: 共有5129条查询结果,搜索用时 16 毫秒
81.
82.
Prefractionation of protein samples prior to two-dimensional electrophoresis (2-DE) has the potential to increase the dynamic detection range for proteomic analysis. We evaluated a membrane-based electrophoretic separation technique (Gradiflow) for its ability to fractionate an exoproteome sample from the filamentous fungus Trichoderma reesei. The sample was separated on the basis of size and charge. Buffer optimization was found to be necessary for successful size fractionation. Fractionation by charge was used to resolve the sample into four fractions that were subjected to analysis by two-dimensional electrophoresis (2-DE). Enhanced detection of low-abundance proteins with selective removal of high-abundance species was achieved. Fractionated and unfractionated samples were examined for differences in the ability to identify proteins following 2-DE using trypsin in-gel digestion followed by peptide mass fingerprinting using matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). Fractionated samples showed marked improvement in protein identification ability and sequence coverage. This study demonstrates the utility of the Gradiflow for fractionation, resulting in an enhancement of resolution and characterization of a moderately complex proteome. 相似文献
83.
Cerebrosterol (2 4S hydroxycholesterol,1)formedinsmallamountsinhumanandanimalbrain1fromcholes terolisimportantforcholesterolhomeostasisinthisorgan .Theexcesscholesterolisconvertedinto 2 4S hydroxy cholesterolbyauniquebrain specific 2 4S hydroxylase ,whichcouldber… 相似文献
84.
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
85.
86.
含钼化合物及其配合物的抗癌抗肿瘤活性 总被引:4,自引:0,他引:4
钼是生命体所必需的微量元素。本文介绍了钼在人体中的作用,钼缺乏和钼过量对人体的影响,并介绍了含钼化合物以及配合物的抗癌抗肿瘤研究情况。 相似文献
87.
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
88.
Nd—Al双金属活性体的组成及其对共轭双烯烃的聚合 总被引:1,自引:0,他引:1
稀土Ziegler-Natta催化剂活性体对双烯烃配位聚合的研究已有很多报道。作者曾从NdCl_3·3P_(350)~(**)-Al(i-Bu)_3体系分离出Nd-Al双金属活性体。本文从NdCl_3·3P_(350)-HAl(i-Bu)_2和Al(C_2H_5)_3反应体系中分离出一系列Nd-Al双金属活性体,用元素分析方法研究了这些活性体的组成,并综合考察了在无助催化剂AlR_3存在下从不同烷基铝获得的活性体本身对共轭双烯烃的定向聚合能力。 单体、溶剂、HAl(i-Bu)_2、Al(C_2H_5)_5及活性体的合成,聚合方法,聚合物表征均按文献[4]。 相似文献
89.
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
90.