全文获取类型
收费全文 | 3150篇 |
免费 | 42篇 |
专业分类
电工技术 | 22篇 |
综合类 | 1篇 |
化学工业 | 260篇 |
金属工艺 | 35篇 |
机械仪表 | 38篇 |
建筑科学 | 94篇 |
矿业工程 | 113篇 |
能源动力 | 15篇 |
轻工业 | 162篇 |
水利工程 | 16篇 |
石油天然气 | 5篇 |
无线电 | 159篇 |
一般工业技术 | 278篇 |
冶金工业 | 1744篇 |
原子能技术 | 22篇 |
自动化技术 | 228篇 |
出版年
2021年 | 13篇 |
2020年 | 19篇 |
2019年 | 29篇 |
2018年 | 32篇 |
2017年 | 30篇 |
2016年 | 33篇 |
2015年 | 23篇 |
2014年 | 45篇 |
2013年 | 110篇 |
2012年 | 47篇 |
2011年 | 78篇 |
2010年 | 49篇 |
2009年 | 53篇 |
2008年 | 56篇 |
2007年 | 59篇 |
2006年 | 61篇 |
2005年 | 40篇 |
2004年 | 56篇 |
2003年 | 47篇 |
2002年 | 55篇 |
2001年 | 42篇 |
2000年 | 36篇 |
1999年 | 73篇 |
1998年 | 508篇 |
1997年 | 287篇 |
1996年 | 210篇 |
1995年 | 109篇 |
1994年 | 119篇 |
1993年 | 122篇 |
1992年 | 32篇 |
1991年 | 38篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 35篇 |
1985年 | 38篇 |
1984年 | 21篇 |
1983年 | 20篇 |
1982年 | 33篇 |
1981年 | 38篇 |
1980年 | 39篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 62篇 |
1976年 | 111篇 |
1975年 | 12篇 |
1974年 | 11篇 |
1972年 | 14篇 |
1970年 | 6篇 |
排序方式: 共有3192条查询结果,搜索用时 15 毫秒
61.
Denaturing gradient gel electrophoresis revealed changes in the bacterial species obtained from enrichment cultures with different inoculum dilutions. This inoculum dilution enrichment approach may facilitate the detection and isolation of a greater number of bacterial species than traditional enrichment techniques. 相似文献
62.
TE Cawston VA Curry CA Summers IM Clark GP Riley PF Life JR Spaull MB Goldring PJ Koshy AD Rowan WD Shingleton 《Canadian Metallurgical Quarterly》1998,41(10):1760-1771
OBJECTIVE: To study the interaction of interleukin-1alpha (IL-1alpha) and oncostatin M (OSM) in promoting cartilage collagen destruction. METHODS: Bovine, porcine, and human cartilage and human chondrocytes were studied in culture. The levels of collagenase (matrix metalloproteinase 1 [MMP-1]) and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by bioassay and enzyme-linked immunosorbent assay (ELISA). The levels of OSM in rheumatoid synovial fluid were measured by ELISA. RESULTS: When combined with OSM, IL-1alpha, IL-1beta, and tumor necrosis factor alpha released proteoglycan and collagen from cartilage. OSM was the only member of the IL-6 family to have this effect. Human tendon also responded to IL-1alpha and OSM. OSM increased the production of MMP-1 and TIMP-1 but when combined with IL-1alpha, synergistically promoted MMP-1 production in human chondrocytes and synovial fibroblasts. High levels of OSM were found in human rheumatoid synovial fluids, and confocal microscopy showed that OSM was produced by macrophages in rheumatoid synovial tissue. CONCLUSION: These results highlight an important new mechanism by which there is irreversible loss of collagen from cartilage. 相似文献
63.
PF Eire D Vallejo JL Sastre MA Rodriguez M Garrido 《Canadian Metallurgical Quarterly》1998,33(12):1820-1821
Mesenteric venous thrombosis (MVT) after appendicectomy has not been reported in the pediatric literature. This complication is associated with significant morbidity and mortality rates in adults. The report of this case attempts to analyze the features found in an appendicectomized child documented by radiological examination and surgery before and after starting heparin therapy. Anticoagulation treatment should be started as soon as possible and continued for a long time to decrease the risk of relapse. 相似文献
64.
Recombinant human granulocyte colony-stimulating factor (G-CSF) at a dose of 1 to 300 micrograms/kg/day was administered intravenously to rats daily for 13 weeks. Serum alkaline phosphatase (ALP) activity increased dose-dependently with leukocytosis. Most of the increased leukocytes were segmented neutrophils, and neutrophil alkaline phosphatase (NAP) scores were elevated markedly. Serum ALP activity correlated very well with the segmented neutrophil counts, and the coefficient of correlation was more than 0.97 in both sexes. Pathological examinations revealed splenomegaly and a marked increase in neutrophils in the red pulp of the spleen. In the spleen, phagocytosis of neutrophils by macrophages was observed. These data indicate that the increased ALP was of neutrophil origin. Serum ALP activity may be increased by the direct release of ALP from the high number of neutrophils into the blood, or by the leakage of ALP into the blood mainly from the spleen where many neutrophils are pooled and destroyed by the macrophage system. 相似文献
65.
This paper reports on a preliminary study of parenting quality, parental stress and child behaviour in families with twins conceived by in-vitro fertilization (IVF) in comparison with families with naturally conceived twins. No differences were found between the types of family in parenting quality or child behaviour. However, parents whose children were conceived by IVF reported greater stress associated with parenting than parents with naturally conceived twins. 相似文献
66.
67.
Chandrasekharam N. Nagineni Sarwat Naz Rajani Choudhuri Gadisetti V. R. Chandramouli Murali C. Krishna Jeffrey R. Brender John A. Cook James B. Mitchell 《International journal of molecular sciences》2021,22(9)
Understanding the global metabolic changes during the senescence of tumor cells can have implications for developing effective anti-cancer treatment strategies. Ionizing radiation (IR) was used to induce senescence in a human colon cancer cell line HCT-116 to examine secretome and metabolome profiles. Control proliferating and senescent cancer cells (SCC) exhibited distinct morphological differences and expression of senescent markers. Enhanced secretion of pro-inflammatory chemokines and IL-1, anti-inflammatory IL-27, and TGF-β1 was observed in SCC. Significantly reduced levels of VEGF-A indicated anti-angiogenic activities of SCC. Elevated levels of tissue inhibitors of matrix metalloproteinases from SCC support the maintenance of the extracellular matrix. Adenylate and guanylate energy charge levels and redox components NAD and NADP and glutathione were maintained at near optimal levels indicating the viability of SCC. Significant accumulation of pyruvate, lactate, and suppression of the TCA cycle in SCC indicated aerobic glycolysis as the predominant energy source for SCC. Levels of several key amino acids decreased significantly, suggesting augmented utilization for protein synthesis and for use as intermediates for energy metabolism in SCC. These observations may provide a better understanding of cellular senescence basic mechanisms in tumor tissues and provide opportunities to improve cancer treatment. 相似文献
68.
Calculated hardenability for improved consistency of properties in heat treatable engineering steels
W. T. Cook P. F. Morris L Woollard 《Journal of Materials Engineering and Performance》1997,6(4):443-448
Hardenability is one of the most important parameters controlling the heat treated properties of engineering steels. It affects
the consistency of response for microstructure, hardness, strength, toughness, and dimensional change (distortion). This study
illustrates that a major benefit of controlling hardenability is improving the consistency of dimensional distortion resulting
from heat treatment. To facilitate the supply of steels to hardenability limits, especially restricted hardenability, a new
technique was developed for the prediction of Jominy hardenability from chemical composition. The technique, termed the “Database
Method,” uses measured Jominy hardenability and chemical composition data, contained in a database, to calculate the hardenability
for a query composition. Using up to ten known steels, selected from the database with compositions closely matching that
of the query steel, a small adjustment is made to the measured hardenability of each known steel allowing for the small difference
in composition between the query and chosen steel. The final calculated result for the query steel is taken as the average
of the various estimates. The basis of the Database Method is explained, and the advantages are illustrated for selecting
engineering grades. 相似文献
69.
Robert F. Cook 《Journal of the American Ceramic Society》2005,88(10):2798-2808
An indentation fracture mechanics analysis is developed to characterize the toughening effects of a compressive surface layer in brittle materials. The analysis is used to describe the enhanced toughness of cordierite glass–ceramic laminate composites, in which thermal-expansion mismatch effects induced uniform stress in the exterior layers of the symmetric exterior:interior:exterior structures. Interpretation of indentation crack length and inert strength tests via the analysis shows that cracks can be viewed as experiencing discrete regions of decreasing stabilization on propagation from small cracks and complete containment within the compressive layer to large cracks and partial extension into the compensating tensile interior. The observations are described using a stress-intensity factor for circular cracks in linear stress fields that includes different base and surface values for extended cracks. Deconvolution of inert strength data for the model cordierite system studied suggested an increase in toughness from 1.4 MPa·m1/2 for the base material to a peak of about 5 MPa·m1/2 for a 1:18:1 composite structure, with attendant increases in strength and flaw tolerance. 相似文献
70.
Campbell CA Cook FJ Pickett JA Pope TW Wadhams LJ Woodcock CM 《Journal of chemical ecology》2003,29(10):2225-2234
Gynoparous female and male damson-hop aphids, Phorodon humuli (Schrank), were caught in the field by water traps that were releasing the sex pheromone of this species, (1RS,4aR,7S,7aS)-nepetalactol. No behavioral activity was elicited by (4aS,7S,7aR)-nepetalactone, the major sex pheromone component of other aphid species such as Megoura viciae Buckton, even though olfactory cells were found in the secondary rhinaria on the third antennal segment of P. humuli that responded strongly to this compound. Gynoparous female P. humuli in the field responded less strongly to (1R,4aS,7S,7aR)-nepetalactol, the sex pheromone of the bird cherry-oat aphid, Rhopalosiphum padi (L.), than they did to the (4aR,7S,7aS)-nepetalactols, but males responded only to the latter. The (4aR,7S,7aS)-nepetalactone showed no electrophysiological activity so was not used in field trials. Releasing either the (4aS,7S,7aR)-nepetalactone or the (1R,4aS,7S,7aR)-nepetalactol with the (4aR,7S,7aS)-nepetalactols did not inhibit the response of P. humuli gynoparous females and males to the latter. Males of R. padi responded as strongly to the (4aR,7S,7aS)-nepetalactols as they did to (1R,4aS,7S,7aR)-nepetalactol. Males of P. humuli and R. padi responded positively to an increased concentration of the (4aR,7S,7aS)-nepetalactols released from two vials compared with that from a single vial, as did P. humuli (in one of two experiments) and R. padi to the (1RS,4aR,7S,7aS)- and (1R,4aS,7S,7aR)-nepetalactols when released together. 相似文献