全文获取类型
收费全文 | 7715篇 |
免费 | 141篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 44篇 |
综合类 | 12篇 |
化学工业 | 456篇 |
金属工艺 | 51篇 |
机械仪表 | 59篇 |
建筑科学 | 81篇 |
矿业工程 | 6篇 |
能源动力 | 108篇 |
轻工业 | 262篇 |
水利工程 | 33篇 |
石油天然气 | 57篇 |
武器工业 | 2篇 |
无线电 | 190篇 |
一般工业技术 | 318篇 |
冶金工业 | 5915篇 |
原子能技术 | 5篇 |
自动化技术 | 283篇 |
出版年
2023年 | 28篇 |
2022年 | 66篇 |
2021年 | 120篇 |
2020年 | 119篇 |
2019年 | 115篇 |
2018年 | 137篇 |
2017年 | 108篇 |
2016年 | 128篇 |
2015年 | 72篇 |
2014年 | 105篇 |
2013年 | 174篇 |
2012年 | 133篇 |
2011年 | 106篇 |
2010年 | 90篇 |
2009年 | 69篇 |
2008年 | 46篇 |
2007年 | 51篇 |
2006年 | 38篇 |
2005年 | 34篇 |
2004年 | 26篇 |
2003年 | 22篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 202篇 |
1998年 | 1954篇 |
1997年 | 1122篇 |
1996年 | 714篇 |
1995年 | 396篇 |
1994年 | 286篇 |
1993年 | 368篇 |
1992年 | 48篇 |
1991年 | 48篇 |
1990年 | 59篇 |
1989年 | 58篇 |
1988年 | 46篇 |
1987年 | 44篇 |
1986年 | 41篇 |
1985年 | 55篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 41篇 |
1980年 | 57篇 |
1978年 | 16篇 |
1977年 | 131篇 |
1976年 | 295篇 |
1975年 | 15篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1955年 | 4篇 |
排序方式: 共有7882条查询结果,搜索用时 421 毫秒
21.
C Montixi C Langlet AM Bernard J Thimonier C Dubois MA Wurbel JP Chauvin M Pierres HT He 《Canadian Metallurgical Quarterly》1998,17(18):5334-5348
T-cell receptors (TCRs) upon binding to peptide-MHC ligands transduce signals in T lymphocytes. Tyrosine phosphorylations in the cytoplasmic domains of the CD3 (gammadeltaepsilon) and zeta subunits of the TCR complex by Src family kinases initiate the signaling cascades via docking and activation of ZAP-70 kinase and other signaling components. We examined the role of the low-density detergent-insoluble membranes (DIMs) in TCR signaling. Using mouse thymocytes as a model, we characterized the structural organization of DIMs in detail. We then demonstrated that TCR engagement triggered an immediate increase in the amount of TCR/CD3 present in DIMs, which directly involves the engaged receptor complexes. TCR/CD3 recruitment is accompanied by the accumulation of a series of prominent tyrosine-phosphorylated substrates and by an increase of the Lck activity in DIMs. Upon TCR stimulation, the DIM-associated receptor complexes are highly enriched in the hyperphosphorylated p23 zeta chains, contain most of the TCR/CD3-associated, phosphorylation-activated ZAP-70 kinases and seem to integrate into higher order, multiple tyrosine-phosphorylated substrate-containing protein complexes. The TCR/CD3 recruitment was found to depend on the activity of Src family kinases. We thus provide the first demonstration of recuitment of TCR/CD3 to DIMs upon receptor stimulation and propose it as a mechanism whereby TCR engagement is coupled to downstream signaling cascades. 相似文献
22.
23.
AE Speckens AM Van Hemert JH Bolk HG Rooijmans MW Hengeveld 《Canadian Metallurgical Quarterly》1996,26(4):745-752
BACKGROUND: Measurement of intracardiac hemodynamic parameters has been limited to brief periods in the acute care setting. We developed and evaluated an implantable hemodynamic monitor that is capable of measuring chronic right ventricular oxygen saturation and pulmonary artery pressure. METHODS AND RESULTS: The device consists of an electronic controller placed subcutaneously and two transvenous leads placed in the right ventricle (reflectance oximeter) and pulmonary artery (variable capacitance pressure sensor). Implantation was performed in 10 patients with severe left ventricular dysfunction. Average implant pulmonary artery pressures were systolic, 52 +/- 16 mm Hg; diastolic, 29 +/- 11 mm Hg; and mean, 40 +/- 12 mm Hg. The mean right ventricular oxygen saturation at implant was 51%. Provocative maneuvers, including postural changes, sublingual nitroglycerin, and bicycle exercise, demonstrated expected changes in measured oxygen saturation and pulmonary artery pressures over time. At follow-up of 0.5 to 15.5 months, there were no significant differences between pulmonary artery pressures or oxygen saturation values transmitted from the device and simultaneous measurement with balloon flotation catheters. Four of the pulmonary artery leads dislodged and three demonstrated sensor drift, whereas two of the oxygen saturation sensors failed. Four patients died and four received transplants. Pathological study did not demonstrate injury to the right ventricular outflow tract or pulmonic valve. CONCLUSIONS: Chronic measurement of hemodynamic parameters in the outpatient setting with implantable sensor technology appears to be feasible. The devices are well tolerated without significant untoward effects, and the sensors generally function well over time, providing reliable information. Clinical usefulness remains to be established. 相似文献
24.
25.
26.
Novel polyurethane insulating coatings were prepared from the reaction of glycerin‐terminated polyurethane prepolymers (GPUPs) and a blocked isocyanate curing agent (BIC). The GPUPs were prepared from the reaction of one equivalent of polycaprolactone polyol (CAPA 210) with an excess amount of 4,4′‐methylene bis(phenyl isocyanate) (MDI) and subsequent reaction of the NCO‐terminated polyurethane with glycerin. The BIC was prepared from the reaction of trimethylol propane (TMP), toluene diisocyanate (TDI) and N‐methylaniline (NMA). The polyols and curing agent were characterized by conventional methods while the curing condition was optimized via gel content measurements. The curing kinetics of the polyurethane coating were investigated and the kinetic parameters derived. The crosslink densities of the samples were determined via the equilibrium swelling method, using the Flory–Rehner equation. The relationships between the crosslink density and the electrical, physical, mechanical and dynamic mechanical properties of the coatings were also studied. Copyright © 2005 Society of Chemical Industry 相似文献
27.
28.
29.
30.
The three-dimensional solution structure of des-[Phe(B25)] human insulin has been determined by nuclear magnetic resonance spectroscopy and restrained molecular dynamics calculations. Thirty-five structures were calculated by distance geometry from 581 nuclear Overhauser enhancement-derived distance constraints, ten phi torsional angle restraints, the restraints from 16 helical hydrogen bonds, and three disulfide bridges. The distance geometry structures were optimized using simulated annealing and restrained energy minimization. The average root-mean-square (r.m.s.) deviation for the best 20 refined structures is 1.07 angstroms for the backbone and 1.92 angstroms for all atoms if the less well-defined N and C-terminal residues are excluded. The helical regions are more well defined, with r.m.s. deviations of 0.64 angstroms for the backbone and 1.51 angstroms for all atoms. It is found that the des-[Phe(B25)] insulin is a monomer under the applied conditions (4.6 to 4.7 mM, pH 3.0, 310 K), that the overall secondary and tertiary structures of the monomers in the 2Zn crystal hexamer of native insulin are preserved, and that the conformation-averaged NMR solution structure is close to the structure of molecule 1 in the hexamer. The structure reveals that the lost ability of des-[Phe(B25)] insulin to self-associate is caused by a conformational change of the C-terminal region of the B-chain, which results in an intra-molecular hydrophobic interaction between Pro(B28) and the hydrophobic region Leu(B11)-Leu(B15) of the B-chain alpha-helix. This interaction interferes with the inter-molecular hydrophobic interactions responsible for the dimerization of native insulin, depriving the mutant of the ability to dimerize. Further, the structure displays a series of features that may explain the high potency of the mutant on the basis of the current model for the insulin-receptor interaction. These features are: a change in conformation of the C-terminal region of the B-chain, the absence of strong hydrogen bonds between this region and the rest of the molecule, and a relatively easy accessibility to the Val(A3) residue. 相似文献