全文获取类型
收费全文 | 28914篇 |
免费 | 803篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 346篇 |
综合类 | 14篇 |
化学工业 | 6152篇 |
金属工艺 | 564篇 |
机械仪表 | 500篇 |
建筑科学 | 1279篇 |
矿业工程 | 339篇 |
能源动力 | 712篇 |
轻工业 | 1921篇 |
水利工程 | 239篇 |
石油天然气 | 254篇 |
无线电 | 1879篇 |
一般工业技术 | 4437篇 |
冶金工业 | 6908篇 |
原子能技术 | 276篇 |
自动化技术 | 3931篇 |
出版年
2022年 | 257篇 |
2021年 | 421篇 |
2020年 | 274篇 |
2019年 | 363篇 |
2018年 | 434篇 |
2017年 | 387篇 |
2016年 | 496篇 |
2015年 | 410篇 |
2014年 | 638篇 |
2013年 | 1766篇 |
2012年 | 987篇 |
2011年 | 1280篇 |
2010年 | 989篇 |
2009年 | 1029篇 |
2008年 | 1217篇 |
2007年 | 1139篇 |
2006年 | 1038篇 |
2005年 | 948篇 |
2004年 | 805篇 |
2003年 | 765篇 |
2002年 | 746篇 |
2001年 | 534篇 |
2000年 | 435篇 |
1999年 | 498篇 |
1998年 | 655篇 |
1997年 | 546篇 |
1996年 | 554篇 |
1995年 | 515篇 |
1994年 | 526篇 |
1993年 | 499篇 |
1992年 | 467篇 |
1991年 | 293篇 |
1990年 | 430篇 |
1989年 | 406篇 |
1988年 | 357篇 |
1987年 | 424篇 |
1986年 | 370篇 |
1985年 | 463篇 |
1984年 | 484篇 |
1983年 | 412篇 |
1982年 | 400篇 |
1981年 | 321篇 |
1980年 | 316篇 |
1979年 | 381篇 |
1978年 | 322篇 |
1977年 | 274篇 |
1976年 | 277篇 |
1975年 | 259篇 |
1974年 | 230篇 |
1973年 | 242篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
To enhance the understanding of the behavior and effects of the precipitation of MnO2 particles in the subsurface generated during in situ chemical oxidation (ISCO) using permanganate, laboratory batch experiments were completed to examine the influence that varied reaction matrix conditions have on the generation and properties of manganese oxides. The conditions examined include organic material type and concentration, permanganate concentration, pH, and the presence of calcium (as a representative divalent cation) in solution. Experimental studies included: (1) spectrophotometric examination of permanganate depletion and manganese oxides generation over time during reactions with trichloroethene; (2) scanning electron microscopy analyses of manganese particle morphology; (3) particle size distribution (filtration) characterization studies; and (4) optical particle sizing and numeration studies. Bench-scale, batch experiments were conducted to focus on fundamental chemical properties affecting particle development under varied potential environmental conditions. The amount of manganese oxides particles that develop, grow, and potentially settle as a result of permanganate ISCO of organic contaminants is a function of the particle size and concentration, the time allowed for particle development, and the impact of matrix conditions on the ability of particles to agglomerate. 相似文献
22.
The perceived locations of paired auditory images, simulating direct sounds and their echoes, have been recently studied in budgerigars (Melopsittacus undulatus; M. L. Dent & R. J. Dooling, 2003a, 2003b). In this article, the authors extend those experiments to include measurements of the precedence effect using a discrimination paradigm in two additional bird species: canaries (Serinus canaria) and zebra finches (Taeniopygia guttata). Although time courses of summing localization, localization dominance, and echo thresholds were similar across all species, budgerigars had slightly higher overall levels of discrimination. The results from these experiments add further support that the precedence effect in birds is similar to that found in other animals and that the ability to suppress echoes that might degrade localization and auditory object perception may be a general property of the vertebrate auditory system. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
23.
Dual command travel times and miniload system throughput with turnover-based storage 总被引:2,自引:0,他引:2
Byung Chun Park Robert D. Foley John A. White Edward H. Frazelle 《IIE Transactions》2003,35(4):343-355
We analyze travel times for automated storage/retrieval systems. In particular, we apply our travel time model to turnover-based storage systems and determine the mean and variance of dual command travel times. We present detailed numerical results for selected rack shape factors and ABC inventory profiles. We then investigate the effect of alternative rack configurations on travel time performance measures. We also show how to determine the throughput of miniload systems with turnover-based storage and exponentially distributed pick times. 相似文献
24.
Resilient optical networks are predominately designed to protect against single failures of fiber links. But in larger networks, operators also see dual failures. As the capacity was planned for single failures, disconnections can occur by dual failures even if enough topological connectivity is provided. In our approach the design of the network minimizes the average loss caused by dual failures, while single failures are still fully survived. High dual failure restorability is the primary aim, capacity is optimized in a second step. For WDM networks with full wavelength conversion, we formulate mixed integer linear programming models for dedicated path protection, shared (backup) path protection, and path rerouting with and without stub-release. For larger problem instances in path rerouting, we propose two heuristics. Computational results indicate that the connectivity is of much more importance for high restorability values than the overall protection capacity. Shared protection has similar restorability levels as dedicated protection while the capacity is comparable to rerouting. Rerouting surpasses the protection mechanisms in restorability and comes close to 100% dual failure survivability. Compared to single failure planning, both shared path protection and rerouting need significantly more capacity in dual failure planning. 相似文献
25.
Despite the universal and understandable distress associated with the death of a child from pediatric illness, do psychologists help surviving families in ways that match their need for assistance? Many families do not seek psychological help and cope adaptively with their loss. Indications for psychotherapy with bereaved families are based largely on experience with families who engage in treatment and who have greater distress. Other families may not receive sufficient services but are at risk for ongoing difficulties and unlikely to engage in treatment. Suggestions for intervention are made, with attention to the fit of therapeutic approaches with family needs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
Albrecht Jason E.; O'Brien Edward J.; Mason Robert A.; Myers Jerome L. 《Canadian Metallurgical Quarterly》1995,21(2):364
An implicit assumption of several causal reasoning models is that readers adopt the goals of a narrative's protagonist during text comprehension. In apparent violation of this assumption, readers participating in Experiment 1 of the present study drew inferences relevant to a protagonist's goal even when that goal was already satisfied from the perspective of the protagonist. In Experiments 2 and 3, participants were explicitly asked to view the text situation from the point of view of the protagonist. In this case, the goals of the reader and the protagonist should be the same. In these experiments, participants focused on the goals of the protagonist only when those goals had not been satisfied from the perspective of the protagonist. These results are discussed in terms of reader- and character-based perspectives and in terms of text characteristics that cue perspective taking. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
The thermal decomposition products of pyridinium sulfate differ from those of pyridinium sulfate supported on zirconia which in turn differs from that of pyridine adsorbed on a sulfated zirconia. Unsupported pyridinium sulfate decomposes to produce pyridine and sulfuric acid, and these subsequently react to produce oxides of carbon and sulfur. Zirconia that is sulfated and then exposed to pyridine does not release detectable amount of pyridine during heating in an inert gas; rather the pyridine undergoes oxidation reduction reactions simultaneously to release CO2 and sulfur compounds. Pyridinium sulfate supported on zirconia decomposes upon heating to release pyridine and sulfuric acid, which reacts with the zirconia. The desorption of pyridine in one case and only CO2/SOx in the other case suggests that sulfated zirconia does not contain Brønsted acidity that can form pyridinium sulfate. 相似文献
28.
P de Lonlay JC Fournet J Rahier MS Gross-Morand F Poggi-Travert V Foussier JP Bonnefont MC Brusset F Brunelle JJ Robert C Nihoul-Fékété JM Saudubray C Junien 《Canadian Metallurgical Quarterly》1997,100(4):802-807
Sporadic persistent hyperinsulinemic hypoglycemia of infancy (PHHI) or nesidioblastosis is a heterogeneous disorder characterized by profound hypoglycemia due to inappropriate hypersecretion of insulin. An important diagnostic goal is to distinguish patients with a focal hyperplasia of islet cells of the pancreas (FoPHHI) from those with a diffuse abnormality of islets (DiPHHI) because management strategies differ significantly. 16 infants with sporadic PHHI resistant to diazoxide and who underwent pancreatectomy were investigated. Selective pancreatic venous sampling coupled with peroperative surgical examination and analysis of extemporaneous frozen sections allowed us to identify 10 cases with FoPHHI and 6 cases with DiPHHI. We show here that in cases of FoPHHI, but not those of DiPHHI, there was specific loss of maternal alleles of the imprinted chromosome region 11p15 in cells of the hyperplastic area of the pancreas but not in normal pancreatic cells. This somatic event is consistent with a proliferative monoclonal lesion. It involves disruption of the balance between monoallelic expression of several maternally and paternally expressed genes. Thus, we provide the first molecular explanation of the heterogeneity of sporadic forms of PHHI such that it is possible to perform only partial pancreatectomy, limited to the focal somatic lesion, so as to avoid iatrogenic diabetes in patients with focal adenomatous hyperplasia. 相似文献
29.
Andreas Pierratos Michaelene Ouwendyk Robert Franceur 《Hemodialysis international. International Symposium on Home Hemodialysis》1997,1(1):32-35
In order to provide a highly efficient, long-duration form of hemodialysis, we developed nocturnal hemodialysis. Patients were dialyzed nightly at home for 8 – 10 hours, 6 – 7 nights/week. We kept the dialysate flow at 100 mL/min and the blood flow at 250 – 300 mL/min. Patients were monitored remotely from the hospital through a computer connection. An internal jugular line was used as an access. We have trained 12 patients over 30 months and have accumulated 160 patient-months worth of data. The patients tolerated the dialysis very well and slept through the night. There was a significant improvement in their sense of well-being. Nightly Kt/V was 0.99. Weekly removal of phosphate was two times as high and β 2 -microglobulin four times as high as conventional hemodialysis. All patients have discontinued their phosphate binders and have increased their dietary phosphate and protein intake. Hypertension was controlled with fewer medications, and erythropoietin dosages decreased. Complications were infrequent and included catheter occlusion and infections. Reusing the dialyzers decreased the cost of the treatment to levels similar to continuous ambulatory peritoneal dialysis. Nocturnal hemodialysis represents a viable dialysis modality that combines high quality, low cost, and excellent tolerance. 相似文献
30.