全文获取类型
收费全文 | 5544篇 |
免费 | 81篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 40篇 |
综合类 | 4篇 |
化学工业 | 824篇 |
金属工艺 | 89篇 |
机械仪表 | 81篇 |
建筑科学 | 154篇 |
矿业工程 | 12篇 |
能源动力 | 88篇 |
轻工业 | 310篇 |
水利工程 | 27篇 |
石油天然气 | 12篇 |
武器工业 | 2篇 |
无线电 | 344篇 |
一般工业技术 | 598篇 |
冶金工业 | 2418篇 |
原子能技术 | 41篇 |
自动化技术 | 584篇 |
出版年
2021年 | 40篇 |
2020年 | 32篇 |
2019年 | 38篇 |
2018年 | 63篇 |
2017年 | 46篇 |
2016年 | 57篇 |
2015年 | 45篇 |
2014年 | 98篇 |
2013年 | 217篇 |
2012年 | 133篇 |
2011年 | 188篇 |
2010年 | 120篇 |
2009年 | 134篇 |
2008年 | 178篇 |
2007年 | 141篇 |
2006年 | 141篇 |
2005年 | 132篇 |
2004年 | 105篇 |
2003年 | 102篇 |
2002年 | 105篇 |
2001年 | 64篇 |
2000年 | 71篇 |
1999年 | 137篇 |
1998年 | 748篇 |
1997年 | 385篇 |
1996年 | 282篇 |
1995年 | 186篇 |
1994年 | 156篇 |
1993年 | 166篇 |
1992年 | 43篇 |
1991年 | 68篇 |
1990年 | 71篇 |
1989年 | 47篇 |
1988年 | 59篇 |
1987年 | 49篇 |
1986年 | 75篇 |
1985年 | 58篇 |
1984年 | 46篇 |
1983年 | 48篇 |
1982年 | 49篇 |
1981年 | 62篇 |
1980年 | 51篇 |
1979年 | 43篇 |
1978年 | 44篇 |
1977年 | 83篇 |
1976年 | 118篇 |
1975年 | 37篇 |
1973年 | 24篇 |
1972年 | 24篇 |
1971年 | 24篇 |
排序方式: 共有5628条查询结果,搜索用时 341 毫秒
41.
Urinary tract infections (UTIs) are common conditions in clinical practice. For uncomplicated UTIs, the causative organisms and their antimicrobial susceptibility profiles are generally predictable, and empiric short course (3 day) antibiotic therapy after an abbreviated laboratory workup is advocated. Acute pyelonephritis requires a 2 week antibiotic course, often with initial parenteral therapy. Women with frequent recurrences of UTIs may require intermittent self-treatment or continuous or postcoital antibiotic prophylaxis. Catheter-associated UTIs generally only require treatment if the patient shows signs of systemic infection. Treatment of asymptomatic bacteriuria is only recommended in certain circumstances. Careful consideration of the clinical circumstances, the patient's known or predicted urinary tract anatomy, and the antibiotic susceptibility of the bacterial pathogen(s) are critical factors in the choice of appropriate therapy for urinary tract infections. 相似文献
42.
TM Drabkina DP Matyushkin VK Radzjukevich Romanovsky DYu 《Canadian Metallurgical Quarterly》1995,14(2):153-170
The effect of frog skeletal muscle incubate on fatigue was studied in frog sciatic nerve, sartorius muscle preparation. Fatigue was produced by prolonged repetitive (1 s-1) stimulation of motor nerve or of curarized muscle. The incubate partially restored isometric contraction amplitudes of muscle fatigued by nerve stimulation. This effect of partial recovery from fatigue (PRF effect) was exerted mainly by a relatively low-molecular fraction (LMF; < 10 kDa) of the incubate. The incubate and its fractions failed to produce the PRF effect in experiments with directly stimulated muscle. The action of LMF on synaptic transmission in unfatigued cutaneous-pectoris muscle was examined using binomial analysis of quantal transmitter release. LMF produced an increase in the end-plate potential quantal content (m) at synapses with low initial m values. In contrast, it produced a decrease i n m at synapses with higher m values. Both effects were due to respective changes in binomial parameter n. It is assumed that the stimulatory presynaptic action of the incubate on synapses the effectiveness of which was lowered during fatigue, could account for the PRF effect. A possible contribution of low- and high-molecular components of the incubate is discussed. 相似文献
43.
Sulfate-reducing reactive walls installed in situ in the path of acid mine drainage contaminated groundwater, present a promising passive treatment technology. However, a rigorous and methodical selection of the most appropriate reactive mixture composition still needs to be investigated. The aim of this study was the selection of the most reactive medium using a multiple factor design and the modeling of the sulfate-reduction rate. Reactivity of 17 mixtures was assessed in batch reactors (in duplicates) using a synthetic AMD. Results indicate that within 41 days, sulfate concentrations decreased from initial concentrations of 2,000-3,200 mg/l to final concentrations of <90 mg/l. Metal removal efficiencies ranged between 51-84% for Ni and 73-93% for Zn. Generated sulfate-reduction rate predictive models which had very satisfactory parameters (R2 = 0.86, F = 62.38 (p-level < 10(-13)) and R2 = 0.90. F = 62.30 (p-level < 10(-13))) identified poultry manure and two other carbon sources as the critical variables for sulfate-reduction rate. 相似文献
44.
Bernard Williams 《Metal Powder Report》2003,58(10):27-28
With commercially available PIM feedstock reportedly unable to fulfill the requirements for the microPIM components under investigation, researchers at the Institute for Materials Research III (IMR) in Karlsruhe, Germany, have developed new binder systems for feedstock based on both nanoceramic and ultrafine metallic powders. In the case of ceramics (zirconia) the powders can be as fine as 300 nm, and for metals in the 3μm-5μm particle size range. The powders are used to develop PIM gearwheels (Figure 1) and other components for a demonstrator micro annular gear pump design (Figure 2); however, the technology is also said to be applicable to micro gears used in watches. 相似文献
45.
Bernard Chazelle 《Acta Informatica》1987,24(5):565-582
Summary There are many efficient ways of searching a set when all its elements can be represented in memory. Often, however, the domain of the search is too large to have each element stored separately, and some implicit representation must be used. Whether it is still possible to search efficiently in these conditions is the underlying theme of this paper. We look at several occurrences of this problem in computational geometry and we propose various lines of attack. In the course of doing so, we improve the solutions of several specific problems; for example, computing order statistics, performing polygonal range searching, testing algebraic predicates, etc. 相似文献
46.
Effects of dietary trielaidin upon the alkenyl chain profile of plasmalogens were studied using heart mitochondria of rats
fed a semi-purified diet containing 10% of fat supplement in which elaidic acid accounted for 69% of total fatty acids. Alkyl
substituted dioxane (ASD) derivatives of the alkenyl groups of plasmalogens were prepared and analyzed by silver nitrate TLC
and by GLC on different phases (BDS and OV-275). After two months of feeding the experimental diet, 40% of the ASD contained
atrans-octadecenyl chain, suggesting that dietary elaidic acid was reduced in vivo to the corresponding alcohol and incorporated
into plasmalogens. There was a simultaneous decrease in the percentage of ASD containing saturated chains, but the percentage
of ASD substituted withcis-octadecenyl chains was not significantly affected. These observations suggested that elaidic acid may compete with saturated
fatty acids, but not withcis-octadecenoic acids during the plasmalogen biosynthesis. Feeding trielaidin did not seem to have any significant influence
on the relative proportions of plasmalogens, which accounted for 11–12%, on a phosphorus basis, of total heart mitochondria
phospholipids. 相似文献
47.
Surendra P. Verma Jean R. Philippot Bernard Bonnet Josette Sainte-Marie Yves Moschetto Donald F. H. Wallach 《Lipids》1985,20(12):890-896
Raman and resonance Raman spectra of plasma lipoproteins ± malondialdehyde were studied at concentrations which block the
normal receptor-mediated uptake by cells. The strong resonance Raman bands at about 1010, 1162 and 1530 cm−1, due to the presence of carotenoids in the lipoproteins, are envisaged as structural probes. High resolution resonance Raman
spectra of the 1500–1600 cm−1 region reveal multiple features suggesting the coexistence of several structural populations of β-carotene whose precise
assignment is complex. When plasma lipoproteins are reacted with malondialdehyde, a complex change occurs in the resonance
Raman banding of β-carotene in the 1500–1600 cm−1 region. Malonaldehyde (MDA) also modifies the acoustical region (70–200 cm−1 of low density lipoprotein (LDL) lipids. We suggest that malondialdehyde association with plasma lipoproteins alters the
lipid structure via apoprotein or apoprotein/lipid associations. 相似文献
48.
TM Munger DL Packer SC Hammill BJ Feldman KR Bailey DJ Ballard DR Holmes BJ Gersh 《Canadian Metallurgical Quarterly》1993,87(3):866-873
BACKGROUND: Virtually all natural history studies of Wolff-Parkinson-White (WPW) syndrome have been case series and, as such, have been constrained by referral biases, skewed age and sex distributions, or brief follow-up periods. The purpose of our study was to examine the natural history, the development of arrhythmias, and the incidence of sudden death in an entire cohort of pediatric and adult WPW patients from a community-based local population. METHODS AND RESULTS: We identified 113 residents of Olmsted County, Minnesota, during the period 1953-1989 using the centralized records-linkage system provided by the Mayo Clinic and the Rochester Epidemiology Program Project. Medical records and ECGs were reviewed to confirm the diagnosis and to establish pathway location by ECG criteria. Follow-up, via record review and telephone interview, was complete in 95% of subjects through 1990. The incidence of newly diagnosed cases was approximately four per 100,000 per year. Preexcitation was not present on the initial ECG of 22% of the cohort. Approximately 50% of the population was asymptomatic at diagnosis, with 30% subsequently having symptoms related to arrhythmia at follow-up. Two sudden cardiac deaths (SCD) occurred over 1,338 patient-years of follow-up, yielding an overall SCD rate of 0.0015 (95% confidence interval, 0.0002-0.0054) per patient-year. No SCD occurred in patients asymptomatic at diagnosis. CONCLUSIONS: The incidence of sudden death in a local community-based population is low and suggests that electrophysiological testing should not be performed routinely in asymptomatic patients with WPW syndrome. Nevertheless, young, asymptomatic patients, particularly those < 40 years old, should return for medical follow-up should symptoms develop. 相似文献
49.
50.
Witold Brostow Bernard Bujard Patrick E. Cassidy Haley E. Hagg Pablo E. Montemartini 《Materials Research Innovations》2002,6(1):7-12
Samples were prepared by addition of a fluorinated poly(aryl ether ketone) (12F-PEK) to a commercial epoxy resin and curing
at either 24 °C or 70 °C. The concentrations of fluoropolymer in the samples were 0, 5, 10, 20, 30, 40, and 50%. Phase inversion
facilitates the formation of more and more smooth surfaces for scratch testing with increasing fluoropolymer concentration.
A progressively increasing load from 0.03 N to 12 N was administered with a diamond tip to the surfaces of the samples; depths
were determined within ±7.5 nm. The original scratch depth is a function of the fluoropolymer concentration. Scratch recovery
(healing) reaches values up to 95%. Plots of the residual depth versus concentration of the fluoropolymer at 4, 6, 8, and
10 N reveal minima for all forces and both temperatures. Addition of only 5% or 10% 12F-PEK improves the scratch recovery
significantly. The results are explained by changes of material morphology with the fluoropolymer concentration.
Electronic Publication 相似文献