全文获取类型
收费全文 | 4879篇 |
免费 | 221篇 |
国内免费 | 5篇 |
学科分类
工业技术 | 5105篇 |
出版年
2023年 | 25篇 |
2022年 | 36篇 |
2021年 | 83篇 |
2020年 | 62篇 |
2019年 | 96篇 |
2018年 | 91篇 |
2017年 | 82篇 |
2016年 | 110篇 |
2015年 | 88篇 |
2014年 | 116篇 |
2013年 | 293篇 |
2012年 | 226篇 |
2011年 | 304篇 |
2010年 | 236篇 |
2009年 | 208篇 |
2008年 | 270篇 |
2007年 | 255篇 |
2006年 | 223篇 |
2005年 | 182篇 |
2004年 | 155篇 |
2003年 | 133篇 |
2002年 | 127篇 |
2001年 | 101篇 |
2000年 | 83篇 |
1999年 | 73篇 |
1998年 | 116篇 |
1997年 | 92篇 |
1996年 | 81篇 |
1995年 | 78篇 |
1994年 | 66篇 |
1993年 | 71篇 |
1992年 | 83篇 |
1991年 | 31篇 |
1990年 | 58篇 |
1989年 | 56篇 |
1988年 | 50篇 |
1987年 | 44篇 |
1986年 | 35篇 |
1985年 | 40篇 |
1984年 | 51篇 |
1983年 | 42篇 |
1982年 | 45篇 |
1981年 | 46篇 |
1980年 | 41篇 |
1979年 | 29篇 |
1978年 | 31篇 |
1976年 | 33篇 |
1975年 | 28篇 |
1974年 | 27篇 |
1972年 | 23篇 |
排序方式: 共有5105条查询结果,搜索用时 31 毫秒
91.
Gregory B. Furman Shaul D. Goren Victor M. Meerovich Vladimir L. Sokolovsky 《Quantum Information Processing》2014,13(12):2759-2768
We study behavior of quantum discord, a kind of quantum correlation, in systems of dipole–dipole interacting spins in an external magnetic field in the whole temperature range ( \(-\infty ). It was shown that negative temperatures, which are introduced to describe inversions in the population in a finite level system, provide more favorable conditions for emergence of quantum correlations including entanglement. We show that at negative temperature, the correlations become more intense and discord exists between remote spins being in separated states. 相似文献
92.
Michael D. Dahlberg Richard L. Rohrer Daniel J. Fauth Richard Sprecher Gregory J. Olson 《Fuel》1993,72(12):1645-1649
A bacterium identified as Arthrobacter sp. was grown on dibenzothiophene (DBT) sulfone as a sole source of sulfur, producing sulfite and sulfate. Sulfur in DBT sulfone (1.0 mM) was nearly quantitatively converted to sulfate by the organism. The organism could also use DBT sulfone as a sole source of carbon and energy. There was evidence for transient accumulation of benzoic acid in the culture medium after growth of the cells slowed. The DBT sulfoxide analogue 9-fluorenone was converted by resting cells to a product identified as 1,10-dihydroxy-1,10-dihydrofluoren-9-one, suggesting that DBT sulfone may be metabolized via an angular hydroxylation resulting in carbon- sulfur bond cleavage. This strain of Arthrobacter showed no ability to desulfurize oxidized Illinois No. 6 coal. 相似文献
93.
Gregory S. Corman 《Journal of the American Ceramic Society》1992,75(12):3421-3424
The compressive creep behavior of single-crystal 6H α-SiC was measured for orientations parallel to and at 45° to [0001]. Deformation of the 45° orientation was dominated by basal slip. Steady-state creep rates above 10-7 /s were measured at temperatures as low as 800°C. An activation energy of 277 kJ/mol and a stress exponent of 3.32 were determined. Creep testing with applied stresses parallel to [0001] was performed at 1650°C to 1850°C, yielding a stress exponent and activation energy of 4.93 and 180 kJ/mol, respectively. The occurrence of basal slip in the [0001] specimens suggested that significant off-axis stresses were present during testing. 相似文献
94.
Unoccupied beaver (Castor canadensis) sites in New York State were for two years experimentally scented with a mixture of beaver castoreum and anal gland secretion. These sites were colonized less often than unscented control sites. The beaver is the first mammal to have been shown experimentally to use intraspecific odor cues when settling in vacant habitat. Territorial pheromones may be useful as repellents for beaver or other rodents. 相似文献
95.
Garrett BC Dixon DA Camaioni DM Chipman DM Johnson MA Jonah CD Kimmel GA Miller JH Rescigno TN Rossky PJ Xantheas SS Colson SD Laufer AH Ray D Barbara PF Bartels DM Becker KH Bowen KH Bradforth SE Carmichael I Coe JV Corrales LR Cowin JP Dupuis M Eisenthal KB Franz JA Gutowski MS Jordan KD Kay BD Laverne JA Lymar SV Madey TE McCurdy CW Meisel D Mukamel S Nilsson AR Orlando TM Petrik NG Pimblott SM Rustad JR Schenter GK Singer SJ Tokmakoff A Wang LS Wettig C Zwier TS 《Chemical reviews》2005,105(1):355-390
96.
Josianne Lefebvre Federico Galli Claudia L. Bianchi Gregory S. Patience Daria C. Boffito 《加拿大化工杂志》2019,97(10):2588-2593
X‐ray photoelectron spectroscopy (XPS) is a quantitative surface analysis technique used to identify the elemental composition, empirical formula, chemical state, and electronic state of an element. The kinetic energy of the electrons escaping from the material surface irradiated by an x‐ray beam produces a spectrum. XPS identifies chemical species and quantifies their content and the interactions between surface species. It is minimally destructive and is sensitive to a depth between 1–10nm. The elemental sensitivity is in the order of 0.1 atomic %. It requires ultra high vacuum ( Pa) in the analysis chamber and measurement time varies from minutes to hours per sample depending on the analyte. XPS dates back 50 years ago. New spectrometers, detectors, and variable size photon beams, reduce analysis time and increase spatial resolution. An XPS bibliometric map of the 10 000 articles indexed by Web of Science[1] identifies five research clusters: (i) nanoparticles, thin films, and surfaces; (ii) catalysis, oxidation, reduction, stability, and oxides; (iii) nanocomposites, graphene, graphite, and electro‐chemistry; (iv) photocatalysis, water, visible light, and ; and (v) adsorption, aqueous solutions, and waste water. 相似文献
97.
Torsion and normal force measurements were made during single step stress relaxation experiments on a polymeric glass (PMMA). Isochronal data were analysed using an approach adapted from that developed by Penn and Kearsley1 (for incompressible elastic materials) to determine the derivatives , and of the time dependent strain potential function. and are determined from existing solution to the torsion of an incompressible cylinder. A special solution to the torsion of a compressible cylinder is presented and it is shown that the values of and obtained using this solution to analyse the data do not differ greatly from those obtained using the incompressible solution. It is found from both solutions that is negative and increases towards zero with increasing time and deformation while is positive, greater in magnitude than and decreases towards zero with increasing time and deformation. These results were unexpected and a full understanding of their meaning has yet to be reached. 相似文献
98.
Microcellular foams in polypropylene containing rubber particles were produced in an injection molding process. The foams are generated because of the thermodynamic instability and are controlled by formation process. The effect of processing parameters on microcellular foaming was investigated in the injection molding process. Injection speed and pressure are less important factors but packing pressure plays an important role in controlling the foam density. A critical packing pressure, about 5 × 106 Pa, was found to generate microcellular foams in our polypropylene material system. Rubber particles inside the polypropylene seem to stabilize the microcellular foams. 相似文献
99.
Warren Gregory L.; Petsko Gregory A. 《Protein engineering, design & selection : PEDS》1995,8(9):905-913
We present a statistical comparison of the amino acid compositionin a secondary structure element, the -helix, of proteins stableat high temperatures with those which are less so. This studyhas shown that the temperature-dependent Zimm-Bragg helix propagationvalue s is not a good predictor for the helix-forming tendencyof an amino acid in thermostable proteins. However, we haveshown that s, the change in s from 20 to 60°C, accuratelypredicts the direction of the probability shift for 15 aminoacids in thermostable protein a-helices, although it does notpredict the magnitude of that change. The residues tyrosine,glycine and glutamine show a significant increase in residencyin a-helices for thermostable proteins over their nonthermostablecounterparts. Significant decreases in -helix residency occurfor the residues valine, glutamic acid, histidine, cysteineand aspartic acid in proteins from thermophilic organisms. Aromaticinteractions, hydrogen bonding and a reduction of charge mayexplain the increase observed for tyrosine and glutamine andthe decrease in glutamic acid and aspartic acid, although packingconsiderations cannot be ruled out The only physical explanationfor the increase in glycine would seem to be its positive svalue 相似文献
100.
D. R. Gregory 《应用聚合物科学杂志》1972,16(6):1479-1487
The complete steady-state flow properties of molten poly(ethylene terephthalate) for shear stresses ≦4.14 × 106 dynes/cm2 were determined. A single, complete master curve had been constructed in earlier work by Gregory and Watson; the curve interrelates the shear stress, shear rate, temperature, and molecular weight (inherent viscosity) by using a temperature superposition scheme from the literature and a similar molecular weight superposition scheme. Equations in agreement with theory and with other published experimental data were derived from the master curve. Results presented here make possible the direct calculation of the melt viscosity of poly(ethylene terephthalate) at shear stresses ≦4.14 × 106 dynes/cm2. The effects of a unit temperature change and/or a unit change in inherent viscosity (I. V.) on the melt viscosity were determined. For poly(ethylene terephthalate) with a 0.6 I. V., a 0.0025 change in I. V. accounts for about the same change in melt viscosity as a 1°C change in temperature. 相似文献