全文获取类型
收费全文 | 10683篇 |
免费 | 455篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 154篇 |
综合类 | 40篇 |
化学工业 | 2042篇 |
金属工艺 | 204篇 |
机械仪表 | 209篇 |
建筑科学 | 521篇 |
矿业工程 | 26篇 |
能源动力 | 239篇 |
轻工业 | 893篇 |
水利工程 | 112篇 |
石油天然气 | 7篇 |
无线电 | 935篇 |
一般工业技术 | 1756篇 |
冶金工业 | 2252篇 |
原子能技术 | 92篇 |
自动化技术 | 1671篇 |
出版年
2023年 | 80篇 |
2022年 | 118篇 |
2021年 | 261篇 |
2020年 | 172篇 |
2019年 | 207篇 |
2018年 | 246篇 |
2017年 | 227篇 |
2016年 | 281篇 |
2015年 | 217篇 |
2014年 | 355篇 |
2013年 | 510篇 |
2012年 | 504篇 |
2011年 | 638篇 |
2010年 | 445篇 |
2009年 | 424篇 |
2008年 | 461篇 |
2007年 | 465篇 |
2006年 | 339篇 |
2005年 | 320篇 |
2004年 | 265篇 |
2003年 | 242篇 |
2002年 | 230篇 |
2001年 | 144篇 |
2000年 | 164篇 |
1999年 | 209篇 |
1998年 | 744篇 |
1997年 | 486篇 |
1996年 | 340篇 |
1995年 | 220篇 |
1994年 | 205篇 |
1993年 | 211篇 |
1992年 | 100篇 |
1991年 | 89篇 |
1990年 | 98篇 |
1989年 | 87篇 |
1988年 | 101篇 |
1987年 | 64篇 |
1986年 | 61篇 |
1985年 | 88篇 |
1984年 | 57篇 |
1983年 | 44篇 |
1982年 | 51篇 |
1981年 | 52篇 |
1980年 | 46篇 |
1979年 | 53篇 |
1978年 | 44篇 |
1977年 | 52篇 |
1976年 | 83篇 |
1975年 | 38篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
J Langhorne C Cross E Seixas C Li T von der Weid 《Canadian Metallurgical Quarterly》1998,95(4):1730-1734
B cell knockout mice are unable to clear a primary erythrocytic infection of Plasmodium chabaudi chabaudi. However, the early acute infection is controlled to some extent, giving rise to a chronic relapsing parasitemia that can be reduced either by drug treatment or by adoptive transfer of B cells. Similar to mice rendered B-cell deficient by lifelong treatment with anti-mu antibodies, B cell knockout mice (muMT) retain a predominant CD4+ Th1-like response to malarial antigens throughout a primary infection. This contrasts with the response seen in control C57BL/6 mice in which the CD4+ T-cell response has switched to that characteristic of Th2 cells at the later stages of infection, manifesting efficient help for specific antibodies in vitro and interleukin 4 production. Both chloroquine and adoptive transfer of immune B cells reduced parasite load. However, the adoptive transfer of B cells resulted in a Th2 response in recipient muMT mice, as indicated by a relative increase in the precursor frequency of helper cells for antibody production. These data support the idea that B cells play a role in the regulation of CD4+ T subset responses. 相似文献
42.
EM Van der Aa IJ Meuwsen AC Boersen AC Wouterse JH Copius Peereboom-Stegeman FG Russel 《Canadian Metallurgical Quarterly》1994,15(3):279-289
The mechanism of uptake of p-aminohippurate (PAH) by syncytial microvillous membrane vesicles of human term placenta was investigated. Initial PAH uptake and efflux were increased in the presence of a pH-gradient and a Cl(-)-gradient, respectively. Forced negative and positive membrane potentials did not influence the uptake, which indicated that the transport is not electrogenic. The pH-dependent increase is probably the result of a higher rate of diffusion due to a lower degree of dissociation of PAH. Because several organic anions failed to transstimulate PAH uptake and FCCP did not decrease the uptake in the presence of an inwardly directed H(+)-gradient, ruling out a PAH/OH- antiport, an anion exchange system does not appear to be present in these membranes. Since electrogenicity and anion exchange seem not to be involved in the Cl(-)-dependent increase, an allosteric effect of Cl- on the transporter might be possible. Various organic anions were able to inhibit pH-stimulated PAH uptake significantly. Kinetic analysis of the probenecid sensitive part of uptake provided further evidence for mediated transport of PAH (Km = 7.4 +/- 2.6 mM and Vmax = 2.0 +/- 0.4 nmol/mg/15 s). Non-inhibitable diffusion accounted for the main part of total transport. Concentration dependent inhibition of PAH transport by probenecid showed a Ki of 2.5 +/- 0.9 mM. It is concluded that human placental syncytial microvillous membrane vesicles possess a low affinity transport mechanism for PAH with low specificity. The importance of this system, for placental excretion of anionic drugs, will depend on the intrasyncytial concentration of these drugs, caused by the transport across the basal membrane. 相似文献
43.
Gorgievski-Duijvesteijn Marjan J.; Bakker Arnold B.; Schaufeli Wilmar B.; van der Heijden Peter G. M. 《Canadian Metallurgical Quarterly》2005,10(3):210
This study of 513 Dutch farmers tested a dynamic equilibrium model of resources (an extension of the conservation of resources theory; S. E. Hobfoll, 1989, 1998, 2001). With structural equation modeling, the advantages of a 3-wave longitudinal design were comprehensively used, such as addressing bidirectional causal effects and within-individual vs. between-individual change. This allowed for a careful analysis of the management function of resources in the stress process. Results showed that well-being had stronger within-person stability than finances. Increased levels of financial problems temporarily increased psychological distress but not self-reported illness. Conversely, farmers with higher stable baselines of psychological distress also had higher baselines of self-reported illness and experienced more negative changes in their financial situation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
44.
45.
N. C. W. Kuijpers W. H. Kool P. T. G. Koenis K. E. Nilsen I. Todd S. van der Zwaag 《Materials Characterization》2002,49(5)
During homogenisation of AA 6xxx aluminium alloys, the platelike β-AlFeSi intermetallic phase will transform to a less Si-rich and more spheroidised α-Al(FeMn)Si phase which is more favourable for extrusion. In this study, several quantitative methods, which determine the relative volume fraction of α-Al(FeMn)Si and β-AlFeSi, are compared and an assessment of each method is made. The methods used are optical microscopy, scanning electron microscopy (SEM) in combination with electron dispersive X-ray (EDX) using polished samples, and X-ray diffraction (XRD) on intermetallics, extracted through selective dissolution of the Al matrix. The highest accuracy is obtained by using SEM/EDX analysis and applying two criteria. 相似文献
46.
Biosynthesis and assembly of alcohol oxidase, a peroxisomal matrix protein in methylotrophic yeasts: a review 总被引:8,自引:0,他引:8
Alcohol oxidase (AO) catalyses the first step of methanol metabolism in yeasts. In vivo the enzyme is compartmentalized in special cell compartments, called peroxisomes. The enzyme along with the organelles are induced during growth of methylotrophic yeasts on methanol as the sole carbon source. Like all other peroxisomal matrix proteins, AO is encoded by a nuclear gene. Expression of the protein is regulated by a repression/derepression mechanism, but also by induction. Inactive monomeric precursor protein is synthesized in the cytosol and subsequently imported post-translationally into peroxisomes without further processing. Assembly into the active homo-octameric enzyme and binding of the prosthetic group flavin adenine dinucleotide occurs inside the organelle. When enhanced concentration of octameric alcohol oxidase are present in the organelles, the enzyme may form a crystalloid. Oligomerization is not dependent on translocation of AO precursors into their target organelle since octameric, active AO is detected in the cytosol and nucleus of peroxisome-deficient mutants of Hansenula polymorpha: at high expression rates large cytosolic AO crystalloids are formed, which occasionally are also encountered inside the nucleus of such mutants. This paper summarizes recent findings and views on the mechanisms involved in synthesis, import, assembly and crystallization of this important peroxisomal enzyme. 相似文献
47.
RM Bionta G Blewitt CB Bratton D Casper A Ciocio R Claus M Crouch ST Dye S Errede GW Foster W Gajewski KS Ganezer M Goldhaber TJ Haines TW Jones D Kielczewska WR Kropp JG Learned JM LoSecco J Matthews HS Park LR Price F Reines J Schulz S Seidel E Shumard D Sinclair HW Sobel JL Stone L Sulak R Svoboda G Thornton van der Velde JC C Wuest 《Canadian Metallurgical Quarterly》1987,36(1):30-36
48.
J H J Hulskotte H A C Denier van der Gon A J H Visschedijk M Schaap 《Water science and technology》2007,56(1):223-231
In this article we show that brake wear from road traffic vehicles is an important source of atmospheric (particulate) copper concentrations in Europe. Consequently, brake wear also contributes significantly to deposition fluxes of copper to surface waters. We estimated the copper emission due to brake wear to be 2.4 kiloton per year. For comparison, the official database for Europe (without brake wear) totals 2.6 kiloton per year. In Western Europe the brake wear emissions dominate the total emission of copper. Using the spatially resolved emission data, copper distributions over Europe were calculated with the LOTOS-EUROS model. Without brake wear the model underestimates observed copper concentrations by a factor of 3, which is in accordance with other studies. Including the brake wear emissions largely removes the bias. We find that 75% of the atmospheric copper input in the North Sea may be due to brake wear. We estimate that about 25% of the total copper input in the Dutch part of the North Sea stems from brake wear. Although the estimated brake wear copper emission is associated with a large uncertainty, it significantly improves our understanding of the copper cycle in the environment. 相似文献
49.
Carballo V.M.B. Chefdeville M. Fransen M. van der Graaf H. Melai J. Salm C. Schmitz J. Timmermans J. 《Electron Device Letters, IEEE》2008,29(6):585-587
An unpackaged microchip is used as the sensing element in a miniaturized gaseous proportional chamber. This letter reports on the fabrication and performance of a complete radiation imaging detector based on this principle. Our fabrication schemes are based on wafer-scale and chip-scale postprocessing. Compared to hybrid-assembled gaseous detectors, our microsystem shows superior alignment precision and energy resolution, and offers the capability to unambiguously reconstruct 3D radiation tracks on the spot. 相似文献
50.
Véronique Baroghel-Bouny Patrick Belin Matthias Maultzsch Dominique Henry 《Materials and Structures》2007,40(8):759-781
Within the framework of the evaluation and the prediction of chloride-induced corrosion risks, simple and rapid AgNO3 spray tests can be proposed for various issues. This paper forms the first part of a series. In this first part, the Maultzsch
procedure (spraying of 0.1-N AgNO3 solution + K2CrO4) as well as the procedure based on the use of a sole AgNO3 solution have been investigated on a broad range of concretes. These procedures have also been compared to the Collepardi
procedure (spraying of 0.1-N AgNO3 + fluoresceine). The feasibility of these colorimetric techniques on saturated specimens cast in laboratory, after non-steady-state
diffusion tests carried out in various conditions, is discussed. In addition, the results obtained from applying such spray
tests in field conditions on cores drilled out from various RC test specimens exposed to a marine environment (tidal zone)
and to a road and cold environment (freezing-thawing cycles and spraying of deicing salts) are presented. Colorimetric methods
have in particular been applied here to the assessment of the average chloride penetration depth and of its evolution versus
time (kinetics). Moreover, the detection threshold of these techniques has been investigated in various environments. The
possible sources of discrepancy on the results have been analysed. 相似文献