全文获取类型
收费全文 | 7302篇 |
免费 | 356篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 86篇 |
综合类 | 10篇 |
化学工业 | 1292篇 |
金属工艺 | 184篇 |
机械仪表 | 316篇 |
建筑科学 | 123篇 |
矿业工程 | 2篇 |
能源动力 | 309篇 |
轻工业 | 577篇 |
水利工程 | 20篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 1069篇 |
一般工业技术 | 1273篇 |
冶金工业 | 1535篇 |
原子能技术 | 57篇 |
自动化技术 | 808篇 |
出版年
2024年 | 10篇 |
2023年 | 83篇 |
2022年 | 117篇 |
2021年 | 207篇 |
2020年 | 158篇 |
2019年 | 150篇 |
2018年 | 180篇 |
2017年 | 179篇 |
2016年 | 211篇 |
2015年 | 189篇 |
2014年 | 295篇 |
2013年 | 409篇 |
2012年 | 429篇 |
2011年 | 465篇 |
2010年 | 346篇 |
2009年 | 335篇 |
2008年 | 367篇 |
2007年 | 277篇 |
2006年 | 220篇 |
2005年 | 217篇 |
2004年 | 183篇 |
2003年 | 158篇 |
2002年 | 148篇 |
2001年 | 116篇 |
2000年 | 112篇 |
1999年 | 132篇 |
1998年 | 494篇 |
1997年 | 305篇 |
1996年 | 230篇 |
1995年 | 131篇 |
1994年 | 110篇 |
1993年 | 117篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 29篇 |
1989年 | 42篇 |
1988年 | 45篇 |
1987年 | 44篇 |
1986年 | 27篇 |
1985年 | 42篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 28篇 |
1978年 | 16篇 |
1977年 | 49篇 |
1976年 | 100篇 |
1974年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有7670条查询结果,搜索用时 31 毫秒
91.
A micellar electrokinetic capillary chromatographic (MECC) method has been developed and optimised for the separation of 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG). The running buffer consisted of a mixture of 20 mM sodium phosphate and 20 mM sodium borate containing 50 mM sodium dodecyl sulphate (SDS) adjusted to pH 9.5 with 1 M NaOH. The running voltage and temperature were 20-25 kV and 30 degrees C, respectively. The MECC method for the analysis of PBG is fast and simple and is useful for the screening of PBG in the urine of patients suspected to have acute intermittent porphyria (AIP), and for the confirmation of lead exposure by measuring red-cell ALA-dehydratase (ALA-D) activity with ALA as the enzyme substrate. 相似文献
92.
R Nau C Lassek M Kinzig-Schippers A Thiel HW Prange F S?rgel 《Canadian Metallurgical Quarterly》1998,42(8):2012-2016
The broad antibacterial spectrum and the low incidence of seizures in meropenem-treated patients qualifies meropenem for therapy of bacterial meningitis. The present study evaluates concentrations in ventricular cerebrospinal fluid (CSF) in the absence of pronounced meningeal inflammation. Patients with occlusive hydrocephalus caused by cerebrovascular diseases, who had undergone external ventriculostomy (n = 10, age range 48 to 75 years), received 2 g of meropenem intravenously over 30 min. Serum and CSF were drawn repeatedly and analyzed by liquid chromatography-mass spectroscopy. Pharmacokinetics were determined by noncompartmental analysis. Maximum concentrations in serum were 84.7 +/- 23.7 microg/ml. A CSF maximum (CmaxCSF) of 0.63 +/- 0.50 microg/ml (mean +/- standard deviation) was observed 4.1 +/- 2.6 h after the end of the infusion. CmaxCSF and the area under the curve for CSF (AUCCSF) depended on the AUC for serum (AUCS), the CSF-to-serum albumin ratio, and the CSF leukocyte count. Elimination from CSF was considerably slower than from serum (half-life at beta phase [t1/2beta] of 7.36 +/- 2.89 h in CSF versus t1/2beta of 1.69 +/- 0.60 h in serum). The AUCCSF/AUCS ratio for meropenem, as a measure of overall CSF penetration, was 0.047 +/- 0.022. The AUCCSF/AUCS ratio for meropenem was similar to that for other beta-lactam antibiotics with a low binding to serum proteins. The concentration maxima of meropenem in ventricular CSF observed in this study are high enough to kill fully susceptible pathogens. They may not be sufficient to kill bacteria with a reduced sensitivity to carbapenems, although clinical success has been reported for patients with meningitis caused by penicillin-resistant pneumococci and Pseudomonas aeruginosa. 相似文献
93.
94.
95.
Current applications of electronic performance monitoring based on job design theories that consider worker performance rather than stress issues are likely to generate unsatisfying and stressful jobs (Smith et al, 1986). This study examines critical job design elements that could influence worker stress responses in an electronic monitoring context. A questionnaire survey of employees in telecommunications companies representative of each region in the United States examined job stress in directory assistance, service representative and clerical jobs with specific emphasis on the influence of electronic monitoring of job performance, satisfaction and employee health. Useable surveys were received from 745 employees representing seven operating companies and AT & T; a response rate of about 25%. The results of this survey indicated that employees who had their performance electronically monitored perceived their working conditions as more stressful, and reported higher levels of job boredom, psychological tension, anxiety, depression, anger, health complaints and fatigue. It is postulated that these effects may be related to changes in job design due to electronic performance monitoring. 相似文献
96.
97.
Yeonsil Moon Changmok Lim Yeahoon Kim Won-Jin Moon 《International journal of molecular sciences》2021,22(6)
The role of the blood–brain barrier (BBB) breakdown has been recognized as being important in Alzheimer’s disease pathogenesis. We aimed to evaluate whether regional BBB integrity differed according to sex and whether differences in BBB integrity changed as a consequence of aging or cognitive decline, using dynamic contrast-enhanced (DCE)-magnetic resonance imaging (MRI). In total, 75 participants with normal cognition (NC) or mild cognitive impairment (MCI) underwent cognitive assessments and MRI examination including DCE-MRI. Regional Ktrans was calculated in cortical regions and the Patlak permeability model was used to calculate BBB permeability (Ktrans, min−1). Females had a lower median Ktrans in the cingulate and occipital cortices. In the “older old” group, sex differences in Ktrans were only observed in the occipital cortex. In the MCI group, sex differences in Ktrans were only observed in the occipital cortex. Age was the only predictor of cognitive assessment scores in the male MCI group; however, educational years and Ktrans in the occipital cortex could predict cognitive scores in the female MCI group. Our study revealed that females may have better BBB integrity in cingulate and occipital cortices. We also found that sex-related differences in BBB integrity are attenuated with aging or cognitive decline. 相似文献
98.
Kin Kit Fong Inn Shi Tan Henry Chee Yew Foo Man Kee Lam Adrian Chiong Yuh Tiong Steven Lim 《中国化学工程学报》2021,33(5):297-305
The rising production of produced water from oilfields had been proven to bring detrimental environmental effects. In this study, an efficient, recyclable, and environmental-friendly reduced graphene oxide immobilized κ-Carrageenan hydrogel composite(κCa GO) was fabricated as an alternative sorbent for crude oil-in-water demulsification. Polyethyleneimine(PEI) was employed to form a stable hydrogel composite. The conditions for the immobilization of graphene oxide(GO) on PEI-modified κ-Carrageenan(κC) beads were optimized appropriately. An immobilization yield of 77% was attained at 2% PEI, 2 h immobilization activation time, and p H6.5. Moreover, the synthesized κCa GO is capable of demulsification with an average demulsification efficiency of 70%. It was found that the demulsification efficiency increases with salinity and κCa GO dosage, and it deteriorates under alkaline condition. These phenomena can be attributed to the interfacial interactions between κCa GO and the emulsion. Furthermore, the κCa GO can be recycled to use for up to six cycles without significant leaching and degradation. As such, the synthesized κCa GO could be further developed as a potential sorbent substitute for the separation of crude oil from produced water. 相似文献
99.
100.
Jeung -Soo Huh Jae -Chang Kim Jeong -Ok Lim K. F. Jensen 《Metals and Materials International》1997,3(2):103-107
The growth of high quality ZnSe by organometallic vapor phase epitaxy (OMVPE) has been investigated fortertiary-butyl allyl selenide (tBASe), combined with dimethylzinc-triethylamine (DMZn : NEt3). Single crystalline ZnSe films were grown on GaAs at temperature as low as 350°C with a reasonable growth rate (~1 µm/h). Secondary ion mass spectrometry (SIMS) spectra show a negligible carbon incorporation in ZnSe films from tBASe even at high VI/II ratio, in contrast the carbon concentration of 1021 cm-3 in ZnSe films grown from diallyl selenide (DASe)and methylallylselenide (MASe). Good surface morphology, crystalline and interface quality of ZnSe on (001) GaAs are confirmed by scanning electron microscopy, double crystal diffractometry (DCD) and Rutherford backscattering spectrometry (RBS). Photoluminescence at 10K shows sharp near-band-edge excitonic spectra. 相似文献