全文获取类型
收费全文 | 1872篇 |
免费 | 24篇 |
专业分类
电工技术 | 23篇 |
综合类 | 2篇 |
化学工业 | 120篇 |
金属工艺 | 6篇 |
机械仪表 | 14篇 |
建筑科学 | 24篇 |
能源动力 | 24篇 |
轻工业 | 86篇 |
水利工程 | 5篇 |
石油天然气 | 2篇 |
无线电 | 211篇 |
一般工业技术 | 97篇 |
冶金工业 | 1197篇 |
原子能技术 | 3篇 |
自动化技术 | 82篇 |
出版年
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2017年 | 11篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 27篇 |
2012年 | 14篇 |
2011年 | 25篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 25篇 |
2007年 | 39篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 19篇 |
2003年 | 19篇 |
2002年 | 23篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 44篇 |
1998年 | 348篇 |
1997年 | 224篇 |
1996年 | 146篇 |
1995年 | 85篇 |
1994年 | 84篇 |
1993年 | 92篇 |
1992年 | 27篇 |
1991年 | 21篇 |
1990年 | 49篇 |
1989年 | 36篇 |
1988年 | 36篇 |
1987年 | 33篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 31篇 |
1976年 | 64篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1969年 | 5篇 |
排序方式: 共有1896条查询结果,搜索用时 15 毫秒
131.
This paper describes a postal survey of palliative care services and teams which were identified in the 1992 Directory of Hospice Services in the UK and Ireland. Its aims were to investigate how units assess the need for bereavement follow-up, and to determine the nature and extent of services provided for bereaved adults. We sent out 397 questionnaires, of which 187 were returned, a response rate of 47%. Results indicate that 156 respondents (84%) provided follow-up and a further 13 (7%) were planning bereavement services. Only 48 (25%) units undertook formal standardized risk assessment procedures to allocate appropriate services; in 41 units (85%) this was done by a nurse. Of the remaining 125 units, 58 (46%) reported basing their decisions on clinical impressions. Content analysis of the formal assessment instruments revealed 39 subcategories, which were broadly grouped into three areas: circumstantial factors at or near to the time of death, personal factors and social factors. Recommendations are made for further study. 相似文献
132.
Lyle H. Lanier was at the core an experimental psychologist who exerted influence on psychology at large by both his research and his administrative endeavors. Lanier passed away at his retirement home, in Phoenix, Arizona, on December 30, 1988. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
133.
A co‐polyester liquid crystalline polymer (LCP) was melt blended with an acrylonitrile–butadiene–styrene copolymer (ABS). LCP fibrils are formed and a distinct skin/core morphology is observed in the injection moulded samples. At higher LCP concentration (50 wt%), phase inversion occurs, where the dispersed LCP phase becomes a co‐continuous phase. While the tensile strength and Young's modulus remain unchanged with increasing LCP content up to 30 wt% LCP, a significant enhancement of the modulus at 50 wt% LCP is observed due to the formation of co‐continuous morphology. The blend modulus is lower than the values predicted by the rule of mixtures, suggesting a poor interface between the LCP droplets and ABS matrix. A copolymer of styrene and maleic anhydride (SMA) was added in the LCP/ABS blends during melt blending. It is observed that SMA has a compatibilizing effect on the blend system and an optimum SMA content exists for mechanical properties enhancement. SMA improves the interfacial adhesion, whereas excess of SMA reduces the LCP fibrillation. Copyright © 2003 Society of Chemical Industry 相似文献
134.
Myxococcus xanthus is a gram-negative bacterium which has a complex life cycle. Autochemotaxis, a process whereby cells release a self-generated signaling molecule, may be the principal mechanism facilitating directed motility in both the vegetative swarming and developmental aggregation stages of this life cycle. The process requires the Frz signal transduction system, including FrzZ, a protein which is composed of two domains, both showing homology to the enteric chemotaxis response regulator CheY. The first domain of FrzZ (FrzZ1), when expressed as bait in the yeast two-hybrid system and screened against a library, was shown to potentially interact with the C-terminal portion of a protein encoding an ATP-binding cassette (AbcA). The activation domain-AbcA fusion protein did not interact with the second domain of FrzZ (FrzZ2) or with two other M. xanthus response regulator-containing proteins presented as bait, suggesting that the FrzZ1-AbcA interaction may be specific. Cloning and sequencing of the upstream region of the abcA gene showed the ATP-binding cassette to be linked to a large hydrophobic, potentially membrane-spanning domain. This domain organization is characteristic of a subgroup of ABC transporters which perform export functions. Cloning and sequencing downstream of abcA indicated that the ABC transporter is at the start of an operon containing three open reading frames. An insertion mutation in the abcA gene resulted in cells displaying the frizzy aggregation phenotype, providing additional evidence that FrzZ and AbcA may be part of the same signal transduction pathway. Cells with mutations in genes downstream of abcA showed no developmental defects. Analysis of the proposed exporter role of AbcA in cell mixing experiments showed that the ABC transporter mutant could be rescued by extracellular complementation. We speculate that the AbcA protein may be involved in the export of a molecule required for the autochemotactic process. 相似文献
135.
MH Davidson KC Maki J Kalkowski EJ Schaefer SA Torri KB Drennan 《Canadian Metallurgical Quarterly》1997,16(3):236-243
OBJECTIVE: The objective of this study was to evaluate the effects of daily dietary supplementation with 1.25 g or 2.5 g of docosahexaenoic (DHA), in the absence of eicosapentaenoic acid (EPA), on serum lipids and lipoproteins in persons with combined hyperlipidemia (CHL) [serum low-density lipoprotein cholesterol (LDL-C) 130 to 220 mg/dL and triglycerides 150 to 400 mg/dL]. METHODS: After a 6-week dietary stabilization period, subjects entered a 4-week single-blind placebo (vegetable oil) run-in phase. Those with adequate compliance during the the run-in were randomized into one of three parallel groups (placebo, 1.25, or 2.5 g/day DHA) for 6 weeks of treatment. Supplements were administered in a triglyceride form contained in gelatin capsules. Primary outcome measurements were plasma phospholipid DHA content, serum triglycerides, high-density lipoprotein cholesterol (HDL-C). LDL-C and non-HDL-C. RESULTS: The DHA content of plasma phospholipids increased dramatically (2 to 3 fold) in a dose-dependent manner. Significant (p < 0.05) changes were observed in serum triglycerides (17 to 21% reduction) and HDL-C (6% increase) which were of similar magnitude in both DHA groups. Non-HDL-C [+1.6 (NS) and +5.7% (p < 0.04)] and LDL-C [+9.3% (NS) and +13.6% (p < 0.001)] increased in the DHA treatment groups. All lipid effects reached an apparent steady state within the first 3 weeks of treatment. CONCLUSION: Dietary DHA, in the absence of EPA, can affect lipoprotein cholesterol and triglyceride levels in patients with combined hyperlipidemia. The desirable triglyceride and HDL-C changes were present at a dose which did not significantly increased non-HDL-C or LDL-C. These preliminary findings suggest that dietary supplementation with 1.25 g DHA/day, provided in a triglyceride form, may be an effective tool to aid in the management of hypertriglyceridemia. 相似文献
136.
S. M. Salom G. Birgersson T. L. Payne C. W. Berisford 《Journal of chemical ecology》1992,18(3):527-528
137.
115-W Tm:YAG diode-pumped solid-state laser 总被引:12,自引:0,他引:12
Honea E.C. Beach R.J. Sutton S.B. Speth J.A. Mitchell S.C. Skidmore J.A. Emanuel M.A. Payne S.A. 《Quantum Electronics, IEEE Journal of》1997,33(9):1592-1600
A compact diode-pumped Tm:YAG laser capable of generating greater than 100 W of CW power at 2 μm has been demonstrated. A scalable diode end-pumping architecture is used in which 805-nm radiation, coupled to the wing of the Tm3+3H6-3H 4 absorption feature, is delivered to the end of the laser rod via a lens duct. To facilitate thermal management, undoped YAG end caps are diffusion bonded to the central doped portion of the laser rod. For 2% and 4% Tm-doped rods of the same length, the lower doping level results in higher power, indicating that cross relaxation is still efficient while offering lower thermal stress and reduced absorption at the laser wavelength. Output powers for various output coupler reflectivities are compared to the predictions of a quasi-three-level model. Thermal lensing, cavity stability, and stress-induced birefringence measurements are described. The beam quality was analyzed with the 2% Tm-doped rod and a flat output coupler, yielding M2 values of 14-23 相似文献
138.
XB Qiu YL Lin KC Thome P Pian BP Schlegel S Weremowicz JD Parvin A Dutta 《Canadian Metallurgical Quarterly》1998,273(43):27786-27793
A human protein (RUVBL1), consisting of 456 amino acids (50 kDa) and highly homologous to RuvB, was identified by using the 14-kDa subunit of replication protein A (hsRPA3) as bait in a yeast two-hybrid system. RuvB is a bacterial protein involved in genetic recombination that bears structural similarity to subunits of the RF-C clamp loader family of proteins. Fluorescence in situ hybridization analysis demonstrated that the RUVBL1 gene is located at 3q21, a region with frequent rearrangements in different types of leukemia and solid tumors. RUVBL1 co-immunoprecipitated with at least three other unidentified cellular proteins and was detected in the RNA polymerase II holoenzyme complex purified over multiple chromatographic steps. In addition, two yeast homologs, scRUVBL1 and scRUVBL2 with 70 and 42% identity to RUVBL1, respectively, were revealed by screening the complete Saccharomyces cerevisiae genome sequence. Yeast with a null mutation in scRUVBL1 was nonviable. Thus RUVBL1 is an eukaryotic member of the RuvB/clamp loader family of structurally related proteins from bacteria and eukaryotes that is essential for viability of yeast. 相似文献
139.
140.
Vasoprotective drugs decrease the vulnerability of blood vessels to cardiovascular risk factors such as hypertension and hypercholesterolemia. Mechanistic treatment end-points of hypertension (normalization of endovascular pressure) may not correct nonhypertensive components of the pathobiology of hypertension. Estrogen replacement therapy, antihypertensive treatment with angiotensin-converting enzyme inhibitors, and manipulations of nitric oxide metabolism may have beneficial effects on vessels in the absence of blood pressure normalization. Estrogens and L-arginine, the precursor of nitric oxide, can partly correct impaired endothelium-dependent vasodilation, a pathophysiologic hallmark of hypertensive states. Angiotensin-converting enzyme inhibitors preserve endothelium-dependent vasodilation and protect arteries against the atherogenic effects of hypercholesterolemia by a non-hypolipidemic, non-hypotensive mechanism. 相似文献