全文获取类型
收费全文 | 484篇 |
免费 | 9篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 5篇 |
综合类 | 14篇 |
化学工业 | 33篇 |
金属工艺 | 6篇 |
机械仪表 | 4篇 |
建筑科学 | 16篇 |
能源动力 | 6篇 |
轻工业 | 37篇 |
水利工程 | 6篇 |
武器工业 | 1篇 |
无线电 | 15篇 |
一般工业技术 | 41篇 |
冶金工业 | 238篇 |
原子能技术 | 21篇 |
自动化技术 | 56篇 |
出版年
2024年 | 1篇 |
2022年 | 12篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 32篇 |
2012年 | 14篇 |
2011年 | 17篇 |
2010年 | 8篇 |
2009年 | 20篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 12篇 |
2005年 | 6篇 |
2004年 | 15篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 72篇 |
1997年 | 45篇 |
1996年 | 36篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 15篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1970年 | 1篇 |
1955年 | 1篇 |
1946年 | 1篇 |
1945年 | 2篇 |
排序方式: 共有499条查询结果,搜索用时 15 毫秒
101.
Alexander Lazovik Marco Aiello Mike Papazoglou 《International Journal on Digital Libraries》2006,6(3):235-246
Interaction with web services enabled marketplaces would be greatly facilitated if users were given a high level service request
language to express their goals in complex business domains. This can be achieved by using a planning framework which monitors
the execution of planned goals against predefined standard business processes and interacts with the user to achieve goal
satisfaction.
We present a planning architecture that accepts high level requests, expressed in a service request language known as XSRL.
The planning framework is based on the principle of interleaving planning and execution. This is accomplished on the basis
of refinement and revision as new service-related information is gathered from service repositories such as UDDI and web services
instances, and as execution circumstances necessitate change. The planning system interacts with the user whenever confirmation
or verification is needed. 相似文献
102.
JH Aiello 《Canadian Metallurgical Quarterly》1998,23(2):12-3, 17-8, 23-4 passim; quiz 32-3
Diabetic nephropathy is the leading cause of end-stage renal disease in the United States and is associated with significant human and economic cost. It is recognized that care of the person with diabetes should be focused on the prevention of the many devastating long-term complications of the disease. The primary care provider is in a key position to implement good preventive care. Monitoring for microalbuminuria is the accepted method for identifying early nephropathy. Individual providers need to be aware of current guidelines for performing screening exams. Once early nephropathy is detected, prudent care with tight glycemic control, angiotension-converting enzyme therapy, control of hypertension, and lifestyle risk-factor modification are warranted. Currently, there is strong indication that the progression of renal disease can be slowed with appropriate early interventions. Positive outcomes are dependent on timely detection of microalbuminuria. 相似文献
103.
In Drosophila melanogaster, regulation of the sex determination genes throughout development occurs by sex-specific splicing of their products. The first gene is Sex-lethal(Sxl). The downstream target of Sxl is the gene transformer (tra): the Sxl protein controls the female-specific splicing of the Tra pre-mRNA. The downstream target of the gene tra is the gene double-sex (dsx): the Tra protein of females, controls the female-specific splicing of the Dsx pre-mRNA. We have identified a gene, female-lethal-2-d fl(2) d, whose function is required for the female-specific splicing of Sxl pre-mRNA. In this report we analyze whether the gene fl(2)d is also required for the sex-specific splicing of both Tra and Dsx pre-mRNAs. We found that the Sxl protein is not sufficient for the female-specific splicing of Tra pre-mRNA, the fl(2)d function also being necessary. This gene, however, is not required for the female-specific splicing of Dsx pre-mRNA. 相似文献
104.
LO Simpson 《Canadian Metallurgical Quarterly》1993,85(4):832-834
Red cells appear to change shape in response to alterations in their environment both in vitro and in vivo. To investigate the qualitative aspects of this phenomenon, five drops of a venous blood sample were fixed in buffered glutaraldehyde for baseline observations and 0.5 ml of blood added to 4 ml of four different saline solutions. Triplicated 10-drop samples from the suspensions were fixed in the glutaraldehyde solution after 2.5, 5, 10, 20 and 40 min and prepared for scanning electron microscopy. Red cell shape analysis of the resulting micrographs showed that the cells had changed shape, although no two patterns of change were the same. 相似文献
105.
J van Delft LO Uttenthal OG Hermida T Fontela M Ghiglione 《Canadian Metallurgical Quarterly》1997,70(2-3):191-198
This study has determined long-term continuation rates of clients who attended clinics of the New Zealand Association of Natural Family Planning and became autonomous users. It has also identified factors which might influence the continuation of NFP use. A total of 509 female subjects, 452 of them with their male partners, were enrolled in the study at the beginning of clinic teaching. Once autonomous they were sent questionnaires at 6-monthly intervals for a period of 24 months. Time out was allowed for pregnancy. The number of female subjects entering the 2-year follow-up phase of the study was 406 (79.8%). Of these 164 completed 2 years of use with 102 (20% of study entrants) using NFP and 62 (12.2%) using fertility awareness in combination with a barrier method. Subjects for whom NFP was their first family planning method, who were Catholic or who gave religion as their reason for choosing NFP were more likely to continue long-term use. The majority of subjects (> 90%) were highly satisfied with NFP use, with the most common reasons for satisfaction being self-awareness, freedom from drugs, naturalness and effectiveness. The difficulties reported related to abstinence and cycle interpretation. 相似文献
106.
Men assigned to the chlorohydrin unit of Union Carbide's South Charleston plant in the Kanawha Valley of West Virginia were followed up for mortality from 1940 to the end of 1988. This 10 year update was conducted to verify previous findings of excesses of cancer among the 278 men assigned to the chlorohydrin unit, which primarily produced ethylene chlorohydrin from 1925 to 1957. This process produced ethylene dichloride and bischloroethyl ether as byproducts. Mean duration of assignment was 5.9 years and mean duration of follow up was 36.5 years. Standardised mortality ratios (SMRs) were calculated based on comparisons with the United States white male population. Duration-response trends were assessed by internal comparisons with two different groups of unexposed chemical workers in the Kanawha Valley. The evidence that the earlier finding of an excess of pancreatic cancer was work related is strengthened by the occurrence of two additional cases (0.9 expected). The SMR for pancreatic cancer was 492 (95% CI 158-1140), based on eight observed v 1.6 expected deaths. There were no additional deaths due to leukaemia, but the three to four-fold excess risk for lymphopoietic cancers persisted due to new cases of non-Hodgkin's lymphoma and a death from multiple myeloma. The SMR for lymphatic and haematopoietic cancers was 294 (eight observed v 2.7 expected; 95% CI 127-580). Pronounced increases in risk were seen for total cancer, pancreatic cancer, all lymphatic and haematopoietic cancers, and leukaemia with increasing durations of assignment to the chlorohydrin unit. Most of the cases were first assigned to the unit in the 1930s when chemical manufacturing was in its infancy and exposures were less controlled. These data are insufficient to identify conclusively the causative agent or agents. The weight of evidence, however, based on probable exposure, known toxicity of the chemicals, and animal responses suggest that high exposures to ethylene dichloride, perhaps in combination with other chlorinated hydrocarbons, is the most likely explanation. 相似文献
107.
CJ Coté A Zaslavsky JJ Downes CD Kurth LG Welborn LO Warner SV Malviya 《Canadian Metallurgical Quarterly》1995,82(4):809-822
BACKGROUND: Controversy exists as to the risk for postoperative apnea in former preterm infants. The conclusions of published studies are limited by the small number of patients. METHODS: The original data from eight prospective studies were subject to a combined analysis. Only patients having inguinal herniorrhaphy under general anesthesia were included; patients receiving caffeine, regional anesthesia, or undergoing other surgical procedures were excluded. A uniform definition for apnea was used for all patients. Eleven risk factors were examined: gestational age, postconceptual age, birth weight, history of respiratory distress syndrome, bronchopulmonary dysplasia, neonatal apnea, necrotizing enterocolitis, ongoing apnea, anemia, and use of opioids or nondepolarizing muscle relaxants. RESULTS: Two hundred fifty-five of 384 patients from eight studies at four institutions fulfilled study criteria. There was significant variation in apnea rates and the location of apnea (recovery room and postrecovery room) between institutions (P < 0.001). There was considerable variation in the duration and type of monitoring, definitions of apnea, and availability of historical information. The incidence of detected apnea was greater when continuous recording devices were used compared to standard impedance pneumography with alarms or nursing observations. Despite these limitations, it was determined that: (1) apnea was strongly and inversely related to both gestational age (P = 0.0005) and postconceptual age (P < 0.0001); (2) an associated risk factor was continuing apnea at home; (3) small-for-gestational-age infants seemed to be somewhat protected from apnea compared to appropriate- and large-for-gestational-age infants; (4) anemia was a significant risk factor, particularly for patients > 43 weeks' postconceptual age; (5) a relationship to apnea with history of necrotizing enterocolitis, neonatal apnea, respiratory distress syndrome, bronchopulmonary dysplasia, or operative use of opioids and/or muscle relaxants could not be demonstrated. CONCLUSIONS: The analysis suggests that, if it is assumed that the statistical models used are equally valid over the full range of ages considered and that the average rate of apnea reported across the studies analyzed is accurate and representative of actual rates in all institutions, the probability of apnea in nonanemic infants free of recovery-room apnea is not less than 5%, with 95% statistical confidence until postconceptual age was 48 weeks with gestational age 35 weeks. This risk is not less than 1%, with 95% statistical confidence, for that same subset of infants, until postconceptual age was 56 weeks with gestational age 32 weeks or postconceptual age was 54 weeks and gestational age 35 weeks. Older infants with apnea in the recovery room or anemia also should be admitted and monitored. The data do not allow prediction with confidence up to what age this precaution should continue to be taken for infants with anemia. The data were insufficient to allow recommendations regarding how long infants should be observed in recovery. There is additional uncertainty in the results due to the dramatically different rates of detected apnea in different institutions, which appear to be related to the use of different monitoring devices. Given the limitations of this combined analysis, each physician and institution must decide what is an acceptable risk for postoperative apnea. 相似文献
108.
LO Essen O Perisic M Katan Y Wu MF Roberts RL Williams 《Canadian Metallurgical Quarterly》1997,36(7):1704-1718
The crystal structures of various ternary complexes of phosphoinositide-specific phospholipase C-delta 1 from rat with calcium and inositol phosphates have been determined at 2.30-2.95 A resolution. The inositol phosphates used in this study mimic the binding of substrates and the reaction intermediate and include D-myo-inositol-1,4,5-trisphosphate, D-myo-inositol-2,4, 5-trisphosphate. D-myo-inositol-4,5-bisphosphate, and D,1-myo-inositol-2-methylene-1,2-cycli?monophosphonate. The complexes exhibit an almost invariant mode of binding in the active site, each fitting edge-on into the active site and interacting with both the enzyme and the catalytic calcium at the bottom of the active site. Most of the active site residues do not undergo conformational changes upon binding either calcium or inositol phosphates. The structures are consistent with bidentate liganding of the catalytic calcium to the inositol phosphate intermediate and transition state. The complexes suggest explanations for substrate preference, pH optima, and ratio of cyclic to acyclic reaction products. A reaction mechanism is derived that supports general acid/base catalysis in a sequential mechanism involving a cyclic phosphate intermediate and rules out a parallel mechanism where acyclic and cyclic products are simultaneously generated. 相似文献
109.
Phosphoinositide-specific phospholipases C (PI-PLCs) are ubiquitous enzymes that catalyse the hydrolysis of phosphoinositides to inositol phosphates and diacylglycerol (DAG). Whereas the eukaryotic PI-PLCs play a central role in most signal transduction cascades by producing two second messengers, inositol-1,4,5-trisphosphate and DAG, prokaryotic PI-PLCs are of interest because they act as virulence factors in some pathogenic bacteria. Bacterial PI-PLCs consist of a single domain of 30 to 35 kDa, while the much larger eukaryotic enzymes (85 to 150 kDa) are organized in several distinct domains. The catalytic domain of eukaryotic PI-PLCs is assembled from two highly conserved polypeptide stretches, called regions X and Y, that are separated by a divergent linker sequence. There is only marginal sequence similarity between the catalytic domain of eukaryotic and prokaryotic PI-PLCs. Recently the crystal structures of a bacterial and a eukaryotic PI-PLC have been determined, both in complexes with substrate analogues thus enabling a comparison of these enzymes in structural and mechanistic terms. Eukaryotic and prokaryotic PI-PLCs contain a distorted (beta alpha)8-barrel as a structural motif with a surprisingly large structural similarity for the first half of the (beta alpha)8-barrel and a much weaker similarity for the second half. The higher degree of structure conservation in the first half of the barrel correlates with the presence of all catalytic residues, in particular two catalytic histidine residues, in this portion of the enzyme. The second half contributes mainly to the features of the substrate binding pocket that result in the distinct substrate preferences exhibited by the prokaryotic and eukaryotic enzymes. A striking difference between the enzymes is the utilization of a catalytic calcium ion that electrostatically stabilizes the transition state in eukaryotic enzymes, whereas this role is filled by an analogously positioned arginine in bacterial PI-PLCs. The catalytic domains of all PI-PLCs may share not only a common fold but also a similar catalytic mechanism utilizing general base/acid catalysis. The conservation of the topology and parts of the active site suggests a divergent evolution from a common ancestral protein. 相似文献
110.
F. GEOTTI-BIANCHINI P. POLATO S. LO RUSSO P. MAZZOLDI 《Journal of the American Ceramic Society》1984,67(1):39-42
The results of optical and chemical investigations on the anti-reflective layers obtained by Ar+ implantation on a soda-lime fiat glass are presented and discussed. The antireflective effect is ascribed to the appearance of an interferential layer with a perturbed refractive index and a lower Na content than the bulk glass and can be optimized by choosing a suitable range of implantation energies and doses. Sodium depth profiles were measured with the 23 Na( p, α )20 Ne nuclear resonance reaction and the results compared with the information provided by the specular reflectance curves. 相似文献