全文获取类型
收费全文 | 9437篇 |
免费 | 224篇 |
国内免费 | 11篇 |
专业分类
化学 | 5611篇 |
晶体学 | 136篇 |
力学 | 122篇 |
数学 | 1438篇 |
物理学 | 2365篇 |
出版年
2022年 | 80篇 |
2021年 | 97篇 |
2020年 | 124篇 |
2019年 | 137篇 |
2018年 | 171篇 |
2017年 | 186篇 |
2016年 | 274篇 |
2015年 | 259篇 |
2014年 | 266篇 |
2013年 | 566篇 |
2012年 | 432篇 |
2011年 | 533篇 |
2010年 | 390篇 |
2009年 | 335篇 |
2008年 | 429篇 |
2007年 | 327篇 |
2006年 | 355篇 |
2005年 | 266篇 |
2004年 | 260篇 |
2003年 | 210篇 |
2002年 | 216篇 |
2001年 | 154篇 |
2000年 | 161篇 |
1999年 | 156篇 |
1998年 | 114篇 |
1997年 | 98篇 |
1996年 | 137篇 |
1995年 | 105篇 |
1994年 | 118篇 |
1993年 | 106篇 |
1992年 | 99篇 |
1991年 | 88篇 |
1990年 | 99篇 |
1989年 | 73篇 |
1988年 | 68篇 |
1987年 | 61篇 |
1985年 | 97篇 |
1984年 | 103篇 |
1983年 | 87篇 |
1982年 | 96篇 |
1981年 | 88篇 |
1980年 | 85篇 |
1979年 | 77篇 |
1978年 | 83篇 |
1977年 | 82篇 |
1976年 | 102篇 |
1975年 | 83篇 |
1974年 | 70篇 |
1973年 | 68篇 |
1957年 | 62篇 |
排序方式: 共有9672条查询结果,搜索用时 375 毫秒
101.
Summary High-molecular-weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. The molecular weight of hyaluronate and its polydispersity was determined by gel-permeation chromatography. During 75-min treatment the molecular weight value decreased from 1.39×106 Da to 2.25×105 Da while the polydispersity of the molecular weight increased from 1.29 to 2.36. The reciprocal value of the square of the hyaluronate's molecular weight was linearly proportional to the time of ultrasonication. 相似文献
102.
Summary A high molecular weight sodium hyaluronate isolated from rooster combs was degraded by ultrasonication. High-performance size exclusion chromatography allowed rapid and accurate determination of molecular weight parameters (Mz, Mw, Mn) and distributions. The time dependence of hyaluronan ultrasonication to the molecular characteristics of the polymer was investigated. A non-random nature of the degradation process was demonstrated and the reciprocal Mn value was found to be linearly proportional to the time of ultrasonication. 相似文献
103.
The applicability of an approach to establish the sequence of oligopeptides involving on-probe-tip enzymatic fragmentation and subsequent direct fast atom bombardment (FAB) mass spectrometry (MS) and FAB-MS/MS of the subpeptide mixture was tested using two model peptides consisting of 19 and 25 amino acid residues. The method was found to be both time and sample sparing and flexible enough to use even subsequent digests, if necessary, with enzymes of different specificity. It provided in both cases complete information, not only for the sequence of enzymic fragments but also for their order in the original oligopeptide. Consequently, this approach to the sequence analysis of oligopeptides can be a method of choice when the FAB-MS/MS technique itself is unsuitable for obtaining detailed structural information. The method seems to be applicable to enzymically digestible peptides with an upper mass limit of about 3500. 相似文献
104.
E. Makrlík P. Vaňura P. Selucký 《Journal of Radioanalytical and Nuclear Chemistry》2006,267(3):533-535
Summary Extraction of microamounts of calcium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of 18-crown-6 (18C6, L) has been investigated. The equilibrium data have been explained assuming that the
complexes HL+, CaL2+and CaL are extracted into the organic phase. The values of extraction and stability constants of the complex species in nitrobenzene
saturated with water have been determined. 相似文献
105.
Klára Melánová Ludvík Beneš Vítězslav Zima Jan Svoboda Miroslava Trchová Jiří Dybal 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):95-101
Intercalation compounds of α-Zr(HPO4)2 · H2O with 1,2-alkanediols (from C3 to C16) have been prepared by replacing 1-propanol in α-Zr(HPO4)2 · 2C3H7OH with the desired 1,2-alkanediols by a treatment in a microwave field. It was found that the intercalates contain 1.5 molecules
of diol per formula unit. The diol molecules are placed between the host layers in a bimolecular way with their aliphatic
chains tilted at an angle of 51°. The diol molecules are anchored in the interlayer space by H-bonds. A mixed intercalate,
containing 1,2-butanediol and 1,2-decanediol in a roughly equimolar ratio, is formed when the α-Zr(HPO4)2 · 2C3H7OH intercalate, suspended in a mixture of 1,2-butanediol and 1,2-decanediol, is exposed to microwave radiation. No new phase
containing both types of the guest molecules was observed when the 1-propanol intercalate, suspended in a mixture of 1-propanol
and 1,2-octanediol, is exposed to microwave radiation. 相似文献
106.
The effect of substituted hydroxybenzophenone, benzotriazole and organic metal complexes on the photooxidation of PP films has been studied. It has been established that NiDBTC added in 1.0 wt. % is the most effective photostabilizer.While in the case of other stabilizers there is a slight increase in the Co content even during the induction period, with the application of NiDBTC practically no oxidation can be observed before the stabilizer completely disappears. This means that NiDBTC inhibits the photooxidation of the polymer even in low concentration.
, - . , Ni, 1,0 . %. . , Ni , . , Ni .相似文献
107.
An efficient synthesis of 6-azapregnane derivatives and their biological activity is described. The nitrogen was introduced into the B ring using Beckmann rearrangement of the (E)-oxime of 6-oxo-B-nor-5α-pregnane derivatives. The required 3α-hydroxyl was produced either by solvolysis of the corresponding 3β-mesyloxy group or by the Meerwein-Ponndorf-Verley reduction of the 3-oxo group; this reduction could be carried out selectively with an unprotected 3,20-dioxo derivative. The binding of the 6-aza-steroids to the γ-aminobutyric acid receptor (GABAA) was measured using [35S]-tert-butyl-bicyclo[2.2.2]phosphorothionate (TBPS) and [3H]flunitrazepam. The only analogue to be slightly active was that lacking any oxygen function in position 3. 相似文献
108.
B. Hlavőček J. Šestők L. Koudelka P. Mošner J. J. Mareš 《Journal of Thermal Analysis and Calorimetry》2005,80(2):271-283
Summary The forms of vibrations and displacements of particles in amorphous structures have been investigated. The particles, moving on highly non-linear amplitude, are responsible for the creation of disordered structures of amorphous bodies. The non-linear oscillators, even if 'few' in concentration, are characterized by unpredictable trajectories in phase space. The non-linear oscillators are fully developed in the liquid state above the crossover temperature Tcr and between Tcr and Tg their number decreases. Under Tg they completely disappear. The interconnection between the linear oscillators in blocks plays the most important role in the characteristic time spectra in liquid state. Using the additive properties of elements polarizibilities, the number of acoustical units in individual blocks at Tcr is estimated to be about 600 units. The diameter of blocks at Tcr was estimated to be about 1.8 nm. Even if the non-linear high amplitude motions disappear at solidification, the remnants of structural irregularity remain and the disordered structure of glass is formed. 相似文献
109.
The mass spectrometric behaviour of nine azidomorphine derivatives have been studied. These compounds proved to have surprisingly specific and selective fragmentation under electron-impact. For 6-deoxy-6-azido-dihydro-isomorphine derivatives (I to V) the main decomposition pathway involves the loss of an N2 molecule followed by a very rapid and selective fragmentation process. On the other hand, the molecular ions of 6-deoxy-8-azido-pseudomorphine derivatives (VI to VIII) and 6-deoxy-6-azido-14-hydroxy-isocodein (IX) primarily decompose by loss of the N3 radical. This is due to the allylic effect of the double bond in ring C, corresponding to the chemical behaviour of these compounds. 相似文献
110.
P. Rajec L'. Mátel J. Orechovská J. Šúcha I. Novák 《Journal of Radioanalytical and Nuclear Chemistry》1996,208(2):477-486
Inorganic sorbents are often used in separation of metals and radionuclides in radioanalytical application and they were also used in technological scale for separation of radionuclides in cleanup of Three Mile Island NPP. Inorganic sorbents become popular in the last years because no problem with organic contamination, there are stable against radiation, sorption efficiency can be tailor made for selective separation of chosen metal. Contrary to the organic sorbents they have usually lower capacity and chemical stability is limited to narrower pH. Nevertheless of some problems, many good properties of inorganic sorbents make them very attractive for sorption study. 相似文献