全文获取类型
收费全文 | 15252篇 |
免费 | 1294篇 |
国内免费 | 422篇 |
专业分类
电工技术 | 713篇 |
综合类 | 511篇 |
化学工业 | 2710篇 |
金属工艺 | 568篇 |
机械仪表 | 727篇 |
建筑科学 | 778篇 |
矿业工程 | 154篇 |
能源动力 | 493篇 |
轻工业 | 1467篇 |
水利工程 | 219篇 |
石油天然气 | 279篇 |
武器工业 | 75篇 |
无线电 | 2134篇 |
一般工业技术 | 2190篇 |
冶金工业 | 1700篇 |
原子能技术 | 204篇 |
自动化技术 | 2046篇 |
出版年
2024年 | 66篇 |
2023年 | 257篇 |
2022年 | 515篇 |
2021年 | 737篇 |
2020年 | 525篇 |
2019年 | 470篇 |
2018年 | 535篇 |
2017年 | 532篇 |
2016年 | 541篇 |
2015年 | 574篇 |
2014年 | 730篇 |
2013年 | 909篇 |
2012年 | 954篇 |
2011年 | 1088篇 |
2010年 | 811篇 |
2009年 | 744篇 |
2008年 | 761篇 |
2007年 | 618篇 |
2006年 | 526篇 |
2005年 | 422篇 |
2004年 | 370篇 |
2003年 | 323篇 |
2002年 | 354篇 |
2001年 | 292篇 |
2000年 | 234篇 |
1999年 | 258篇 |
1998年 | 601篇 |
1997年 | 388篇 |
1996年 | 306篇 |
1995年 | 174篇 |
1994年 | 181篇 |
1993年 | 144篇 |
1992年 | 107篇 |
1991年 | 100篇 |
1990年 | 73篇 |
1989年 | 89篇 |
1988年 | 52篇 |
1987年 | 52篇 |
1986年 | 48篇 |
1985年 | 48篇 |
1984年 | 42篇 |
1983年 | 42篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 31篇 |
1979年 | 27篇 |
1978年 | 17篇 |
1977年 | 46篇 |
1976年 | 70篇 |
1975年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
931.
L Peyrin H Simon JM Cottet-Emard N Bruneau M Le Moal 《Canadian Metallurgical Quarterly》1982,235(2):363-369
Free and conjugated catecholamines (dopamine, noradrenaline, adrenaline) and their methoxylated and/or deaminated metabolites were studied in rat urine after the bilateral destruction of the A10 dopaminergic cell group. Two months after the lesion, dopamine (DA) loss reached 91% in the nucleus accumbens, and was greater than 80% in olfactory tubercles, lateral septum and frontal cortex. At the same time urinary conjugated dihydroxyphenylacetic acid (DOPAC) was decreased by 45% whilst homovanillic acid (HVA) was increased only in its sulfated form (+62%). In contrast, no changes were observed in the free and conjugated forms of urinary DA, 3-methoxytyramine noradrenaline, normetanephrine, adrenaline, vanylmandelic acid, 3-methoxy-4-hydroxyphenylglycol and in the free forms of DOPAC and HVA. The present report confirms and extends our previous findings on the relationships between central dopaminergic activity and urinary deaminated metabolites of DA in the rat. It emphasizes the interest of urinary assays which could provide in vivo information on CNS functions. 相似文献
932.
Energy transfer from the Ce3+ to the Tb3+ ion has been studied in a host GdAlO3 structure. The maximum fluorescence intensity of Tb3+ is observed for the composition Gd0.96Ce0.02Tb0.02AlO3. The energy transfer from Ce3+ to Tb3+ is explained by a dipole-dipole type coulombic interaction. 相似文献
933.
C. Delmas J.C. Viala R. Olazcuaga G. Le Flem P. Hagenmuller F. Cherkaoui R. Brochu 《Materials Research Bulletin》1981,16(1):83-90
Ionic conductivity measurements in the solid solution Na1+xZr2?xLx(PO4)3 (L = Cr, Yb) have been carried out. The materials have a Nasicon-type structure in a 0 ? x ? xmax.L range (xmax.Cr = 2.0 and xmax.Yb = 1.9). A small monoclinic distortion appears at low temperature for Na3Cr2(PO4)3. As in the Na1+xZr2P3?xSixO12 system a strong increase of the conductivity with rising x has been observed. The results are discussed in connection with temperature and structural parameters. 相似文献
934.
The SCED code solves the equilibrium equations for a Tokamak axisymmetric configuration and the plasma diffusion equations. The equilibrium system takes into account the presence of a magnetic circuit made of iron, the currents in the poloidal coils and the plasma pressure and toroidal field profiles. The plasma boundary is a free boundary defined by its contact with a limiter. A variational formulation of the problem is written and the equations of the poloidal flux ψ are solved by a finite element method; the Picard and the Newton algorithms are tested for the treatment of the non-linearities and compared on TFR and JET equilibrium configurations. The variation of the plasma position with respect to the currents in the coils is then studied by a continuation method and the link between the convergence of the Picard method and the stability of the plasma motions is proved. The evolution problem takes into account the induction of the primary coils and the penetration of the eddy currents in the vacuum vessel. The 2D diffusion equations for the electronic and ionic densities and temperatures and for the poloidal flux are written in terms of the toroidal flux by averaging over the magnetic surfaces. These equations are solved by an implicit scheme in time and by a finite difference scheme in space; the non-linearities are treated by the Newton method. The coupling between the equilibrium system and the diffusion equations enables one to follow the evolution of the plasma boundary. The study of the plasma motions in TFR, in the presence or absence of a feedback system, has been performed with this code and compared with the experimental observations. 相似文献
935.
936.
Viola A Nicoli F Denis B Confort-Gouny S Le Fur Y Ranjeva JP Viout P Cozzone PJ 《Magma (New York, N.Y.)》2004,17(1):47-61
Cerebral metabolic changes that concur to motor and/or cognitive disorders in actively drinking alcoholics are not well established. We tested the hypothesis that chronic alcoholics exhibit profound alterations in the cerebral metabolism of scyllo-inositol. Brain metabolism was explored in nine actively drinking and 11 recently detoxified chronic alcoholics by in vivo brain 1H-MRS and in vitro 1H-MRS of blood serum and cerebrospinal fluid. The cohort was composed of individuals with acute, subacute or chronic encephalopathy or without any clinical encephalopathy. Chronic alcoholism is associated with a hitherto unrecognized accumulation of brain scyllo-inositol. Our results suggest that scyllo-inositol is produced within the central nervous system and shows a diffuse but heterogenous distribution in brain where it can persist several weeks after detoxification. Its highest levels were observed in subjects with a clinically symptomatic alcohol-related encephalopathy. When detected, brain scyllo-inositol takes part in a metabolic encephalopathy since it is associated with reduced N-acetylaspartate and increased creatine. High levels of cerebral scyllo-inositol are correlated with altered glial and neuronal metabolism. Our findings suggest that the accumulation of scyllo-inositol may precede and take part in the development of symptomatic alcoholic metabolic encephalopathy. 相似文献
937.
Salmain M Caro B Le Guen-Robin F Blais JC Jaouen G 《Chembiochem : a European journal of chemical biology》2004,5(1):99-109
Study of the reaction between the transition organometallic complex 4-ruthenocenyl 2,6-dimethylpyrylium tetrafluoroborate and the enzyme hen egg white lysozyme (HEWL) in solution and by diffusion in crystals was performed by use of a combination of spectroscopic and chromatographic methods. Conjugation involving the lysine residues of lysozyme appeared to occur readily, yielding very stable ruthenocenyl pyridinium adducts with average degrees of incorporation ranging from 0.2 to 1.8 metal complexes per protein molecule, depending on reaction conditions. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) revealed that the protein conjugates were in fact mixtures of unmodified, mono-, di- and sometimes tripyridinium adducts. In combination with reversed-phased HPLC, we were able to show that six different monoruthenocenyl pyridinium adducts were formed in solution. This result was confirmed by trypsin digestion of a ruthenocenyl pyridinium conjugate and MALDI-TOF MS analysis of the peptide mixture, which showed that lysines 1, 13, 33, 96, 97 and 116 were involved in the reaction with the pyrylium complex, lysines 13, 33 and 116 being the major binding sites. In the tetragonal crystal state, no binding of the ruthenium complex was shown to occur at lysine 116, owing to steric hindrance at this particular position. 相似文献
938.
Calculations of electron energy near edge structures (ELNES) are compared with experimental data obtained in a high-resolution transmission electron microscope. This study concerns small precipitates of aluminium nitride in low carbon steel. The ELNES technique allows to clearly establish that these precipitates crystallize in a cubic rather than in a hexagonal crystallographic cell. The influence on simulated spectra of different parameters are investigated: the size of the atomic shell and its relation with the electron inelastic mean free path. We also examine the influence of the core hole and the sensitivity to cell parameters. We particularly examine the Al L(23) near edge structure and features relating to the different transition channels (A(1g), E(g) and T(2g)). Results of a multiple scattering and band structure calculations using ICXANES and WIEN97 codes, respectively, are compared in the region from 0 to 30 eV above the edge onsets. Both calculations are in a rather good agreement. 相似文献
939.
Structural diversity of sphingomyelin microdomains 总被引:2,自引:0,他引:2
In cells plasma membrane, sphingomyelin (SM) plays a key role in the formation of a category of lipid microdomains enriched in cholesterol (Chl) often referred to as rafts. Atomic force microscopy (AFM) was used to analyze the mesoscopic topography of enriched SM microdomains in supported bilayers made of SM/dioleoylphosphatidylcholine (SM/DOPC) and SM/palmitoyl-oleoyl-phosphatidylcholine (SM/POPC) equimolar mixtures, in buffer, at room temperature. Gel–fluid phase separation occurs in both SM/DOPC and SM/POPC bilayers. The gel phase SM-enriched microdomains adopt a variety of size, shape and mesoscopic structure, from homogeneous flat domains of a few hundreds of nanometer in diameter to domains of several micrometers made of closely packed globular structures. Gel–gel phase separation in SM domains is also observed which gives rise to different structures for the diunsaturated and the mixed-saturated PC species. These differences could also extend to the interactions with Chl. This suggests that studies on rafts formation commonly performed using SM/DOPC mixture as a model should also include the physiologically more relevant POPC species. 相似文献
940.
Nabhan MA Girardet JM Campagna S Gaillard JL Le Roux Y 《Journal of dairy science》2004,87(11):3614-3622
Raw skim milk was submitted to high pressure (300 to 600 MPa) and temperature (4 to 70 degrees C) treatments for 2 or 5 min. The combined effects of pressure and temperature on milk proteins induced structural changes and polymer and copolymer formation characterized by anion-exchange and size-exclusion fast protein liquid chromatography and electrophoretic techniques. Approximately half of the beta-lactoglobulin formed polymers, and the other half formed large copolymers, mainly with kappa-casein, alpha-lactalbumin via intermolecular disulfide bond exchange, and alpha(s1)-casein via physicochemical interactions, in proportions of 1.0:0.7:0.3:0.1, respectively. Minor whey proteins (serum albumin, immunoglobulins, and lactoferrin) also participated in the formation of the copolymers but to a lesser extent. Two populations of the copolymers were found with apparent molecular masses ranging from 440 to 2000 kDa for the first and more than 2000 kDa for the second. On the contrary, for heated milks the aggregation kinetics obtained by combination of high pressure and thermal treatment were very fast, as no intermediates such as dimers and small size oligomers were observed after pressurization, whatever the temperature studied. Lactosylation of proteins as well as proteolysis were very limited. A beta-casein amino-terminal peptide of 22 kDa was specifically recovered in milk samples treated under the more drastic conditions (500 MPa/55 degrees C per 5 min and 600 MPa/70 degrees C per 5 min) and might have been generated by neutral proteases such as elastase released from somatic cells present in milk. No casein was released from the micelle whatever the combination of high pressure and temperature studied. 相似文献