全文获取类型
收费全文 | 41119篇 |
免费 | 5382篇 |
国内免费 | 2555篇 |
专业分类
化学 | 10339篇 |
晶体学 | 415篇 |
力学 | 1688篇 |
综合类 | 352篇 |
数学 | 2388篇 |
物理学 | 8318篇 |
无线电 | 25556篇 |
出版年
2024年 | 178篇 |
2023年 | 656篇 |
2022年 | 1329篇 |
2021年 | 1586篇 |
2020年 | 1588篇 |
2019年 | 1080篇 |
2018年 | 951篇 |
2017年 | 1453篇 |
2016年 | 1592篇 |
2015年 | 1667篇 |
2014年 | 2642篇 |
2013年 | 2984篇 |
2012年 | 2780篇 |
2011年 | 2732篇 |
2010年 | 2068篇 |
2009年 | 2138篇 |
2008年 | 2373篇 |
2007年 | 2449篇 |
2006年 | 2265篇 |
2005年 | 1971篇 |
2004年 | 1800篇 |
2003年 | 1716篇 |
2002年 | 1457篇 |
2001年 | 1235篇 |
2000年 | 1166篇 |
1999年 | 949篇 |
1998年 | 742篇 |
1997年 | 661篇 |
1996年 | 600篇 |
1995年 | 483篇 |
1994年 | 421篇 |
1993年 | 345篇 |
1992年 | 258篇 |
1991年 | 140篇 |
1990年 | 134篇 |
1989年 | 96篇 |
1988年 | 84篇 |
1987年 | 43篇 |
1986年 | 40篇 |
1985年 | 39篇 |
1984年 | 36篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
921.
V. V. Semenov N. F. Cherepennikova A. N. Kornev E. V. Naamova N. P. Makarenko S. Ya. Xhorshev G. A. Domrachev O. A. Bochkova 《Russian Chemical Bulletin》1996,45(10):2431-2437
Oligo(phenylcobaltcarbonylsilane) was prepared from oligo(phenylsilane) and dicobalt octacarbonyl. The reaction proceeds with elimination of H2 and CO and insertion of cobalt carbonyl fragments into the silicone backbone of oligosilane. Oligosilane containing cobalt carbonyl groups in side organic substituents was obtained from oligolmethyl(phenylethynyl)Isilane and CO2(CO)8. The reaction of 1,2-bis(phenylethyny1)tetramethyldisilane with Co2(CO)8 proceeds with the sequential attachment of cobalt carbonyl fragments to ethynyl groups to form disilane derivatives [2-CCPhCo2(CO)6] Thermal decomposition of cobalt-containing oligosilanes affords a mixture of paramagnets and ferromagnets.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2561–2567, October, 1996. 相似文献
922.
基因工程技术已经成为研究和生产重组人血清白蛋白(rHSA)替代人血清白蛋白(HSA)的重点技术,而白蛋白的纯化则是该技术的关键。本文主要介绍了从转基因猪血中纯化rHSA的一种新方法,即热乙醇沉淀与多级色谱分离相结合的rHSA纯化方法。热乙醇沉淀法可从猪血浆中获得rHSA粗提取液,此时rHSA的纯度可达69.5%,回收率达51.3%。进一步采用多级色谱分离法,即阴离子交换色谱和反相色谱法进一步纯化,得到rHSA的最终纯度约为100.0%,总回收率为41.1%。该方法为从转基因猪血浆中大规模纯化用于临床和生化研究的高纯度rHSA提供可能,同时也为rHSA替代HSA奠定了基础。 相似文献
923.
Growing environmental concerns and the need for alternatives for oil
and natural gas resulted in intensive researches on ultra clean coal (UCC).
Therefore, the researches related to practice and application of various methods
to produce UCC become more important. Thermal characterization of chemically
demineralized coals by thermogravimetric analysis method is presented in this
study. The aim of the study is to provide thermal data for HF–HNO3
leaching system used for the production of UCC. Coal samples were first physically
enriched by density separation. Then the enriched portion was chemically demineralized
by using HF and HNO3, respectively. Ash content of coal samples were reduced
to a range of 0.12–0.41% by chemical demineralization process. The petrographic,
ultimate and proximate analyses were carried out to determine main features
of samples. Physically and chemically enriched coal samples were then analyzed
in a TG by two different techniques separately. The first technique covered
thermal characterization of samples under non-isothermal conditions. Characteristic
temperatures for each sample were obtained from the TG and DTG data. The second
technique involved the determination of reactivity of in situ produced chars
of each sample. 相似文献
924.
G. Clouet P. Chaumont P. Corpart 《Journal of polymer science. Part A, Polymer chemistry》1993,31(11):2815-2824
The thermal bulk polymerization of methyl methacrylate (MMA) in a wide range of temperatures has been studied using a dilatometric reactor. It is shown that, irrespective of the care taken to purify the MMA, the evolution of the time-conversion curve can be explained only if we account for the presence of an impurity associated with the monomer acting as a free radical initiator. The activation energy for the decomposition of this impurity has been estimated as 98 kJ/mol. Having accounted for this impurity, the activation energy for the real thermal polymerization of the MMA has been estimated to be 75 kJ/mol. © 1993 John Wiley & Sons, Inc. 相似文献
925.
926.
Thermal studies on some organotin(IV) complexes with piperidine and 2-aminopyridine dithiocarbamates
The complexes of piperidine dithiocarbamate, 2-aminopyridine dithiocarbamate and organotin(IV) of the type R3Sn(L1), R2Sn(L1)2, R3Sn(L2), R2Sn(L2)2, [R=C6H5CH2 (benzyl), p-ClC6H4CH2 (p-chlorobenzyl), L
1=sodium piperidine dithiocarbamate and L
2=sodium 2-aminopyridine dithiocarbamate] have been synthesised and characterised by spectral studies (IR, UV, 1H NMR). Thermogravimetric (TG) and differential thermal analytical (DTA) studies have beeen carried out for these complexes and from the TG curves, the order and apparent activation energy for the thermal decomposition reactions have been elucidated. The various thermal studies have been correlated with some structural aspects of the complexes concerned. From DTA curves, the heat of reaction has been calculated. 相似文献
927.
Torsten Barfels Bernd Schmidt Andreas von Czarnowski Hans-Joachim Fitting 《Mikrochimica acta》2002,139(1-4):11-16
For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary
electron energy E
0 = 2…30 keV. Applying a constant incident power regime (E
0·I
0 = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx.
Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses (0.5–5)1016 ions/cm2. Thus Ge profiles with a concentration maximum of (0.4 – 4) at% at the depth of dm≅240 nm are expected. Afterwards the layers have been partially annealed up to T
a = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (λ = 400 nm) of
the Ge centers is strongly increased but also the luminescent center profiles are shifted from about 250 nm to 170 nm depth
towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster
formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm. 相似文献
928.
《中国化学快报》2020,31(5):1281-1287
Extensive structure-activity relationships (SARs) study of JND3229 was conducted to yield a series of new reversible 2-oxo-3,4-dihydropyrimido[4,5-d]pyrimidine privileged scaffold as EGFRC797S inhibitors. One of the most potent compound 6i potently suppressed EGFRL858R/T790M/C797S kinase with an IC50 value of 3.1 nmol/L, and inhibited the proliferation of BaF3 cells harboring EGFRL858R/T790M/C797S and EGFR19D/T790M/C797S mutants with IC50 values of 290 nmol/L and 316 nmol/L, respectively. Further, 6i dose-dependently induced suppression of the phosphorylation of EGFRL858R/T790M/C797S and EGFR19D/T790M/C797S in BaF3 cells. Compound 6i may serve as a promising lead compound for further drug discovery overcoming the acquired resistance of non-small cell lung cancer (NSCLC) patients. 相似文献
929.
Ru‐Jong Jeng Geng‐Sheng Lo Chih‐Ping Chen Ying‐Ling Liu Ging‐Ho Hsiue Wen‐Chiung Su 《先进技术聚合物》2003,14(2):147-156
Epoxy resins modified by an organosoluble phosphorus‐containing bismaleimide (3,3′‐bis(maleimidophenyl) phenylphosphine oxide; BMPPPO) were prepared by simultaneously curing epoxy/diaminodiphenylmethane (DDM), and BMPPPO. The resulted epoxy resins were found to exhibit glass transition temperatures as high as 212 °C, thermal stability at temperatures over 350 °C, and excellent flame retardancy with Limited oxygen index (LOI) values around 40. Incorporation of BMPPPO into epoxy resins via the thermosetting blend was demonstrated to be an effective way to enhance the thermal properties and flame retardancy simultaneously. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
930.
An investigation of dynamic mechanical, thermal, and electrical properties of housing materials for outdoor polymeric insulators 总被引:1,自引:0,他引:1
The present paper reports the results about a study of mechanical, thermal, dynamic mechanical and electrical properties of housing (weather shed) materials for outdoor polymeric insulators. Silicone rubber, ethylene-propylene-diene monomer (EPDM) and alloys of silicon-EPDM are known polymers for use as housing in high voltage insulators. The result of dynamical mechanical measurement shows that the storage modulus of blends enhances with increase EPDM in formulation. It can be seen from the result of TGA measurement that initial thermal degradation of silicone rubber improves by the effect of EPDM in blends. The blends of silicone-EPDM show good breakdown voltage strength compared to silicone rubber. Surface and volume resistance of silicone rubber improve by EPDM content. The mechanical properties of EPDM such as strength, modulus and elongation at break improve by silicone. 相似文献