全文获取类型
收费全文 | 3858篇 |
免费 | 2篇 |
专业分类
化学工业 | 15篇 |
机械仪表 | 1篇 |
轻工业 | 25篇 |
水利工程 | 1篇 |
无线电 | 2篇 |
一般工业技术 | 6篇 |
冶金工业 | 3800篇 |
自动化技术 | 10篇 |
出版年
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2015年 | 1篇 |
2013年 | 2篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2009年 | 2篇 |
2008年 | 3篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 6篇 |
2003年 | 13篇 |
2002年 | 1篇 |
2000年 | 2篇 |
1999年 | 137篇 |
1998年 | 1252篇 |
1997年 | 779篇 |
1996年 | 477篇 |
1995年 | 232篇 |
1994年 | 215篇 |
1993年 | 219篇 |
1992年 | 20篇 |
1991年 | 31篇 |
1990年 | 35篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 23篇 |
1980年 | 28篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 57篇 |
1976年 | 133篇 |
1975年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有3860条查询结果,搜索用时 0 毫秒
91.
92.
93.
EK Kemsley RR Swinhoe AC Smith MC McCann TL Wang 《Journal of the science of food and agriculture》2004,84(9):966-976
Mechanical tests have been used to assess the engineering properties of pea (Pisum sativum L) stems. Measurements were made on plants of three different genotypes at four different stages of development and at five defined locations along the stem. The force–displacement curves obtained were used to estimate values of the engineering properties of toughness and flexural modulus, from cutting and flexure mechanical tests respectively. Specimens of all genotypes showed an increase in toughness with age and generally also with stem height. However, there were marked differences in flexural modulus between genotypes. One genotype, known to exhibit a ‘stiff straw’ characteristic, showed a consistent increase in modulus with age and stem height, and at and beyond fruiting had substantially the greatest flexural modulus. The remaining genotypes showed decreasing flexural modulus with age. Chemometric methods were used to analyse sets of complete force–displacement curves, following suitable pre‐processing to allow the application of linear algebra methods. Whereas univariate consideration of the engineering quantities allowed trends to be observed, multivariate analysis of force–distance curves was able to model empirically the genotype differences so that individual specimens could be largely correctly classified. Examination of some of the model coefficients suggested that the ability to discriminate between genotypes is related to structural features of the specimens and that cutting tests in particular are sensitive to the anatomy of the specimen. This is the first time that chemometric methods have been applied to such data and suggests the potential of mechanical tests combined with multivariate analysis to form the basis of a screening system for phenotypic properties of new lines and varieties. Copyright © 2004 Society of Chemical Industry 相似文献
94.
Most lipid extraction procedures [Folch, J., Lees, M., and Sloane-Stanley, G.H., (1957) A Simple Method for the Isolation
and Purification of Total Lipids from Animal Tissues, J. Biol. Chem. 226, 497–509; Bligh, E.G., and Dyer, W.J. (1959) A Rapid Method of Total Lipid Extraction and Purification, Can. J. Biochem. Physiol. 37, 911–917] employ biphasic solvent mixtures designed to dissolve the lipids in an organic phase and remove impurities in an
aqueous phase. However, when applying these protocols to biological matrices such as that of the ocular lens, the formation
of an emulsion layer between the organic and aqueous phases causes poor reproducibility in extraction yields and gives only
a small amount of the lipid-containing chloroform phase. In this study, we quantified phospholipids at each step of the Folch
et al. extraction protocol and compared the yield of human and bovine lens phospholipids obtained by the Folch-based approach and
a novel monophasic methanol extraction method designed to circumvent the problems associated with biphasic extraction protocols.
A monophasic methanol extraction coupled with 31P NMR spectroscopy was found to be the simplest, quickest, and most effective method for quantifying the phospholipid content
of the lens. 相似文献
95.
Q Yang T de Beer L Woods JD Meyer MC Manning M Overduin CE Catalano 《Canadian Metallurgical Quarterly》1999,38(1):465-477
Terminase is an enzyme from bacteriophage lambda that is required for insertion of the viral genome into an empty pro-capsid. This enzyme is composed of the viral proteins gpNu1 (20.4 kDa) and gpA (73.3 kDa) in a holoenzyme complex. Current models for terminase assembly onto DNA suggest that gpNu1 binds to three repeating elements within a region of the lambda genome known as cosB which, in turn, stimulates the assembly of a gpA dimer at the cosN subsite. This prenicking complex is the first of several stable nucleoprotein intermediates required for DNA packaging. We have noted a hydrophobic region within the primary amino acid sequence of the terminase gpNu1 subunit and hypothesized that this region constitutes a protein-protein interaction domain required for cooperative assembly at cosB and that is also responsible for the observed aggregation behavior of the isolated protein. We therefore constructed a mutant of gpNu1 in which this hydrophobic "domain" has been deleted in order to test these hypotheses. The deletion mutant protein, gpNu1DeltaK, is fully soluble and, unlike full-length protein, shows no tendency toward aggregation; However, the protein is a dimer under all experimental conditions examined as determined by gel permeation and sedimentation equilibrium analysis. The truncated protein is folded with evidence of secondary and tertiary structural elements by circular dichroism and NMR spectroscopy. While physical and biological assays demonstrate that gpNu1DeltaK does not interact with the terminase gpA subunit, the deletion mutant binds with specificity to cos-containing DNA. We have thus constructed a deletion mutant of the phage lambda terminase gpNu1 subunit which constitutes a highly soluble DNA binding domain of the protein. We further propose that the hydrophobic amino acids found between Lys100 and Pro141 define a self-association domain that is required for the assembly of stable nucleoprotein packaging complexes and that the C-terminal tail of the protein defines a distinct gpA-binding site that is responsible for terminase holoenzyme formation. 相似文献
96.
Linking service climate and customer perceptions of service quality: test of a causal model 总被引:2,自引:0,他引:2
A set of foundation issues that support employee work and service quality is conceptualized as a necessary but not sufficient cause of a climate for service, which in turn is proposed to be reflected in customer experiences. Climate for service rests on the foundation issues, but in addition it requires policies and practices that focus attention directly on service quality. Data were collected at multiple points in time from employees and customers of 134 branches of a bank and analyzed via structural equation modeling. Results indicated that the model in which the foundation issues yielded a climate for service, and climate for service in turn led to customer perceptions of service quality, fit the data well. However, subsequent cross-lagged analyses revealed the presence of a reciprocal effect for climate and customer perceptions. Implications of these results for theory and research are offered. 相似文献
97.
MC Vantyghem J Kerr-Conte F Pattou MH Gevaert C Hober A Defossez JC Beauvillain M Mazzuca 《Canadian Metallurgical Quarterly》1998,30(2):571-573
Life-threatening, recurrent ventricular tachycardia developed in a 54-year-old heart transplant candidate with ischemic cardiomyopathy. The episodes of ventricular tachycardia were refractory to aggressive medical management and implantable cardiac defibrillator placement. A Heartmate left ventricular assist device was implanted, in combination with isolated right coronary artery bypass grafting, which abolished any further episode of ventricular tachycardia. The patient successfully underwent cardiac transplantation 79 days later. 相似文献
98.
N Nicoli Aldini P Caliceti S Lora MC Maltarello M Fini M Rocca L Martini G Giavaresi FM Veronese R Giardino 《Canadian Metallurgical Quarterly》1996,67(6):843-848
Biodegradable polymers gives interesting perspectives of use in making artificial conduits for peripheral nerve reconstruction. Poliphosphazenes are materials highly biocompatible and have a controllable reabsorption rate. According to the substitutes that are introduced in the molecule, they can also be used as a framework for drug release. Conduits obtained with poli [bis(etilalanate) phosphazene] were evaluated as guides for nerve regeneration in an experimental animal model. In six Wistar rats, under general anesthesia and with microsurgical technique, the ischiatic nerve was isolated. On the right side a segment of the nerve was removed in order to create a 10 mm gap. The defect was then repaired using the conduit. On the controlateral limb the nerve continuity was restored using as an autograft the segment removed from the right. Control were performed at 30, 90, 180 days and consisted in histological and electron microscopy investigations. They showed the gradual degradation of the conduit without signs of local and general toxicity. The regeneration of the nerve fibers in the lumen of the conduit was not significantly different from the one obtained with the autologous grafts. So poliphosphazene conduits may be considered effective as a guide for nerve regeneration, above all for the possibility of use the polymer as a carrier for neurite-promoting factors. 相似文献
99.
JD Meyer RF Falk RM Kelly JE Shively SJ Withrow WS Dernell DJ Kroll TW Randolph MC Manning 《Canadian Metallurgical Quarterly》1998,87(9):1149-1154
A new method for preparing poly(L-lactide) (PLA) biodegradable beads impregnated with an ionic aminoglycoside, gentamycin, is described. The process employs hydrophobic ion pairing to solubilize gentamycin in a solvent compatible with PLA, followed by precipitation with a compressed antisolvent (supercritical carbon dioxide). The resulting precipitate is a homogeneous dispersion of the ion-paired drug in PLA microspheres. The microspheres are approximately 1 microm in diameter and can be compressed into beads (3-6 mm in diameter) strung on surgical sutures for implantation. The bead strings exhibit no significant change in release kinetics upon sterilization with a hydrogen peroxide plasma (Ster-Rad). The kinetics of gentamycin release from the PLA beads are consistent with a matrix-controlled diffusion mechanism. While nonbiodegradable poly(methyl methacrylate) (PMMA) beads initially release gentamycin in a similar manner, the drug release from PMMA ceases after 8 or 9 weeks, while the PLA beads continue to release drug for over 4 months. Moreover, only 10% of the gentamycin is released from the PMMA beads, while PLA beads release more than 60% of their load, if serum is present in the release medium. The PLA system displays improved release kinetics relative to PMMA, is biodegradable, is unaltered by gas sterilization, can be used for a range of antibiotics, and can be manipulated without disintegration. These are all desirable properties for an implantable drug delivery system for the prevention or treatment of osteomyelitis. 相似文献
100.