全文获取类型
收费全文 | 1891篇 |
免费 | 50篇 |
国内免费 | 1篇 |
学科分类
工业技术 | 1942篇 |
出版年
2022年 | 16篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 38篇 |
2018年 | 34篇 |
2017年 | 34篇 |
2016年 | 51篇 |
2015年 | 32篇 |
2014年 | 56篇 |
2013年 | 70篇 |
2012年 | 75篇 |
2011年 | 83篇 |
2010年 | 66篇 |
2009年 | 65篇 |
2008年 | 56篇 |
2007年 | 64篇 |
2006年 | 48篇 |
2005年 | 46篇 |
2004年 | 42篇 |
2003年 | 39篇 |
2002年 | 37篇 |
2001年 | 30篇 |
2000年 | 47篇 |
1999年 | 33篇 |
1998年 | 111篇 |
1997年 | 76篇 |
1996年 | 67篇 |
1995年 | 58篇 |
1994年 | 24篇 |
1993年 | 37篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 14篇 |
1989年 | 18篇 |
1988年 | 33篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 24篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 26篇 |
1974年 | 13篇 |
1972年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有1942条查询结果,搜索用时 15 毫秒
1.
Vladimir Rozenshtein Alexander Berg Haim Levanon Uwe Krueger Dietmar Stehlik Yuri Kandrashkin Art Van Der Est 《Israel journal of chemistry》2003,43(3-4):373-381
Light-induced spin-polarized transient EPR spectra are reported for several water-soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip-doublet to the trip-quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge-transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed. 相似文献
2.
Is there a direct relationship between oral astringency and human salivary protein binding? 总被引:1,自引:0,他引:1
For decades, it is believed that astringency is due to the polyphenol-induced complexation of proline-rich salivary proteins
in the oral cavity. In order to compare for the first time the human sensory threshold concentrations and the salivary protein
binding activity of a series of astringent stimuli, human saliva protein was incubated for 5 min at 37 °C in the presence
of astringent food-derived compounds and, after micro-centrifugation, the amount of the target molecules in the supernatant
was quantitatively determined by HPLC-UV/Vis. Significant protein binding was observed for (−)-epigallocatechin-3-gallate,
(−)-gallocatechin-3-gallate, (+)-gallocatechin, and (−)-catechin-3-gallate, all of which containing at least one galloyl moiety
in the molecule and exhibiting rather high sensory thresholds of more than 200 μmol/L. In comparison, (+)-catechin and procyanidin
B2, both lacking in any galloyl function, showed only comparatively low binding activity and, most interestingly, quercetin-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside and 3-carboxymethyl-indole-1-N-β-d-glucopyranoside did not show any protein binding at all, although the later N- and O-glycosides exhibited extraordinarily low sensory threshold concentrations of less than 0.001 and 0.0003 μmol/L, respectively.
The data give some first evidence that the quantity of the non-bound, “free” astringent stimulus in the saliva liquid might
be more closely related to the sensory perception of astringency than the amount complexed or precipitated by proteins. It
is therefore questionable as to whether oral perception of astringency is related to the complexation and/or precipitation
of salivary proteins. 相似文献
3.
Herzog K. Schulte E. Atmanand M. A. Schwarz W. 《Automation Science and Engineering, IEEE Transactions on》2007,4(2):282-286
Tracked vehicles capable of locomotion in the deep sea are used for manganese nodule mining. This requires specific technical solutions in various respects. Locomotion in the soft sea bed is one of them. For the Crawler to safely maneuver, an automatic drive mode with slip control of the driving tracks is essential. Based on experimental studies at IKS, University of Siegen, slip control for the NIOT-IKS mining machine has been developed and implemented. The experimental setup for the development of the slip control along with the logic of the automatic driving mode is described. The system is critically discussed and the test results and future work are briefly outlined. Note to Practitioners-The work is carried out as part of the polymetallic nodule mining program of the Government of India. The technique of slip control is a specific requirement for a tracked vehicle used in the deep sea. Slip is common in many vehicles-tracked and otherwise. Examples are steam engines in the early days and ordinary cars while negotiating slush or snow/ice and dozers working in soft soil. While these are manually controlled by drivers who have firsthand knowledge of the environmental conditions, in the case of a mining machine in deep sea, it has to be completely automatic and, hence, is challenging. The knowledge generated in this work could be effectively used by practitioners in other related areas of automobile engineering for updating their expertise. Also, similar techniques may be used for maneuvering vehicles sent to other planets 相似文献
4.
Dietmar Schulze 《化学,工程师,技术》1995,67(1):60-68
Flowability of Bulk Solids – Definition and Measuring Principles . The flowability of bulk solids has to be known for many practical applications. The present paper describes how the flowability is defined and on which physical properties it depends. Experimental determination of the flowability using a shear test is demonstrated. Conditions influencing measuremed results are described. Finally an overview of various methods used for characterization of the flowability of bulk solids is given. 相似文献
5.
Cell suspensions of Escherichia coli as a model for bacterial populations in wastewaters were treated with ozone as a disinfectant in a continuously operated pilot plant with a plug flow reactor. Suspensions with an initial number of CFU (colony forming units) of 108 mL?1 were ozonized with ozone concentrations up to 12 mg/L. Metabolic activities and membrane functions break down with increasing ozone concentrations. The fluorochromization using 3′,6′-diacetylfluorescein (FDA) proved to be a suitable method for the detection of an alteration in permeability of the cell membranes and an inactivation of metabolic activity. By fluorescence microscopic and photometric investigations it could be clearly demonstrated that, in the case of disinfection with ozone, inactivation of the cells includes first of all a damage of the cell membranes. In contrast to the determination of the number of CFU, fluorochromization allows the detection of alteration in metabolic activities. 相似文献
6.
U. H. Pi D. H. Kim Z. G. Khim U. Kaiser M. Liebmann A. Schwarz R. Wiesendanger 《Journal of Low Temperature Physics》2003,131(5-6):993-1002
We have studied vortex dynamics in Bi2Sr2CaCu2O8 single crystal with low density columnar defects by using a magnetic force microscope. Single crystal Bi2Sr2CaCu2O8 sample was irradiated by 1.3 GeV uranium ion to form artificial pinning centers along the crystalline c-axis. The irradiation dose corresponded to a matching field of 20 gauss. The radius of an individual vortex is approximately 140 nm, which is close to the penetration depth of this material. Magnetic force microscope (MFM) images show that intrinsic crystalline defects such as stacking fault dislocations are very effective pinning centers for vortices in addition to the pinning centers due to ion bombardment. By counting the number of vortex, we found that the flux trapped at each pinning center is a single flux quantum. At higher magnetic field, the vortex structure showed an Abrikosov lattice disturbed only by immobile vortices located at pinning centers. When increasing or decreasing the external magnetic field, the spatial distribution of vortices showed a Bean model like behavior. 相似文献
7.
8.
R Germann M Haisjackl B Schwarz N Salak E Deusch W Pajk HJ Wolf B Riedmann W Hasibeder 《Canadian Metallurgical Quarterly》1997,79(3):357-362
Haemorrhage is associated with intestinal mucosal hypoxia and impaired gut barrier function. Dopamine increases oxygen delivery to the intestinal mucosa and may thus counteract haemorrhage-induced mucosal hypoxia. Jejunal mucosal tissue oxygen tension (mucosal PO2) and jejunal oxygen saturation of mucosal microvascular haemoglobin (mucosal HbO2) were measured in 14 anaesthetized pigs. Seven animals served as controls (group C) and seven received continuous infusion of dopamine 16 micrograms kg-1 min-1 (group D) while 45% of blood volume was removed in three equal increments. Resuscitation was performed using shed blood and fluid. Mean arterial pressure and systemic oxygen delivery decreasing significantly during haemorrhage and returned to baseline after resuscitation in both groups. Mucosal PO2 decreased from 4.4 to 1.7 kPa after haemorrhage (P < 0.01) and further to 1.5 kPa after resuscitation (P < 0.01) in group C whereas group D showed an increase from 3.9 to 5.9 kPa after the start of the dopamine infusion (P < 0.05), but no significant difference from baseline after haemorrhage (2.3 kPa) (ns) or resuscitation (3.1 kPa) (ns). Mucosal HbO2 decreased from 52 to 32% after haemorrhage (P < 0.05) and increased to near baseline (37%) (ns) after resuscitation in group C whereas group D showed no significant changes from baseline (54%) throughout the experiment. Comparison between groups showed higher mucosal PO2 and HbO2 values for group D animals after the start of the dopamine infusion (P < 0.05 each), after the first two steps of haemorrhage (P < 0.01 each) and after resuscitation (P < 0.05 each). We conclude that i.v. dopamine 16 micrograms kg-1 min-1 improved tissue oxygenation of the small intestinal mucosa during moderate haemorrhage and subsequent resuscitation. 相似文献
9.
We have used a resonant ultrasound spectroscopy technique to measure the bulk and shear modulus of fully dense, polycrystalline MgB2 between 4 and 300 K. Both moduli show good agreement with published first principle calculations. The internal friction shows a broad maximum around 40 K. 相似文献
10.
J.A. Schwarz 《Catalysis Today》1992,15(3-4):395-405
Three intrinsically connected phenomena occur during adsorption/impregnation of aqueous electrolytes onto oxide carriers. They are: pH-dependent development of surface charge carriers on the oxide; pH-dependent aqueous speciation of catalytic precursors; surface adsorption by complexation and coordination. Modeling of these processes yields basic thermodynamic properties of the adsorbed phase, which could provide useful information of the catalytic properties of the metal, support, and reveal metal-support interactions, thus contributing to design criteria for supported-metal catalysts.
The spectrum of catalytic systems that can be studied using the above approach is greatly extended when both pure and composite oxide carriers are considered. This presentation will focus on three metal/support systems, each of which provides results of both practical and fundamental importance. 相似文献