全文获取类型
收费全文 | 30413篇 |
免费 | 1074篇 |
国内免费 | 113篇 |
专业分类
电工技术 | 375篇 |
综合类 | 230篇 |
化学工业 | 5089篇 |
金属工艺 | 625篇 |
机械仪表 | 586篇 |
建筑科学 | 968篇 |
矿业工程 | 94篇 |
能源动力 | 930篇 |
轻工业 | 3855篇 |
水利工程 | 242篇 |
石油天然气 | 151篇 |
武器工业 | 7篇 |
无线电 | 2243篇 |
一般工业技术 | 4095篇 |
冶金工业 | 8122篇 |
原子能技术 | 247篇 |
自动化技术 | 3741篇 |
出版年
2024年 | 50篇 |
2023年 | 149篇 |
2022年 | 493篇 |
2021年 | 781篇 |
2020年 | 532篇 |
2019年 | 596篇 |
2018年 | 683篇 |
2017年 | 767篇 |
2016年 | 721篇 |
2015年 | 549篇 |
2014年 | 851篇 |
2013年 | 1412篇 |
2012年 | 1246篇 |
2011年 | 1579篇 |
2010年 | 1150篇 |
2009年 | 1206篇 |
2008年 | 1101篇 |
2007年 | 960篇 |
2006年 | 774篇 |
2005年 | 834篇 |
2004年 | 907篇 |
2003年 | 821篇 |
2002年 | 790篇 |
2001年 | 692篇 |
2000年 | 539篇 |
1999年 | 583篇 |
1998年 | 2650篇 |
1997年 | 1690篇 |
1996年 | 1122篇 |
1995年 | 708篇 |
1994年 | 577篇 |
1993年 | 660篇 |
1992年 | 230篇 |
1991年 | 307篇 |
1990年 | 250篇 |
1989年 | 215篇 |
1988年 | 228篇 |
1987年 | 182篇 |
1986年 | 176篇 |
1985年 | 200篇 |
1984年 | 131篇 |
1983年 | 92篇 |
1982年 | 123篇 |
1981年 | 131篇 |
1980年 | 127篇 |
1979年 | 90篇 |
1978年 | 79篇 |
1977年 | 184篇 |
1976年 | 297篇 |
1975年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
OD de Rada AC Villaro LM Montuenga A Martínez DR Springall JM Polak 《Canadian Metallurgical Quarterly》1993,162(1-2):121-124
The presence of nitric oxide synthase (NO-synthase), the enzyme responsible for the production of nitric oxide (NO) from L-arginine, is shown immunocytochemically in the intrinsic neurons of the human and porcine respiratory tract. NO-synthase immunoreactivity is demonstrated in a subpopulation of neurons of the microganglia present in the wall of the extra- and intrapulmonary bronchi as well as in the hilar region of the lung in relation to blood vessels. The immunostaining was also found in some nerve fibers of the respiratory nervous system. Human and porcine lung gave similar results. The possible involvement of NO in the nonadrenergic noncholinergic (NANC) nervous regulation of the lung is discussed. 相似文献
62.
R de Franchis 《Canadian Metallurgical Quarterly》1998,10(12):1041-1044
Bleeding oesophageal varices (BOV), resulting from portal hypertension, can prove fatal. Not only is it important to stop the initial bleeding, which may lead to hypovolaemic shock, but also to treat this condition in the longer term, and, consequently, the prevention of rebleeding needs to be addressed. This review highlights the current findings on the haemostatic drug, terlipressin, focusing particular attention on the potential for longer-term treatment strategies in the prevention of rebleeding. The efficacy of terlipressin in treating acute BOV, its low incidence of severe side-effects (comparable to those of somatostatin) and its favourable comparison with sclerotherapy in the prevention of early rebleeds, all indicate the potential for terlipressin administration to be extended to 5 days in the longer-term treatment of BOV. In addition, terlipressin administration, in conjunction with sclerotherapy, can significantly reduce the likelihood of rebleeding compared with sclerotherapy alone and further supports its potential use in the longer-term treatment of BOV. 相似文献
63.
J Gálvez R García-Domenech C de Gregorio Alapont JV de Julián-Ortiz L Popa 《Canadian Metallurgical Quarterly》1996,14(5):272-276
BACKGROUND: There is no empirical data available on attitudes concerning AIDS and habits towards HIV infected patients of physicians in general or private practice. In this study results of a self-evaluation are presented. METHODS: 178 physicians working with out-patients in different medical fields were randomly selected for a cross sectional study and interviewed using a standardised questionnaire. RESULTS: 89% think that they are sufficiently informed about AIDS (in the USA 20%). They regarded the risk of infection to be lower than the Anglo-American physicians. They believed there is a lack of interchange of information between colleagues regarding the degree of infectiousness of referred patients. A third of the physicians fear that other patients will go elsewhere if they find out that their physician is treating AIDS patients. 54% would hold special clinic sessions for HIV-patients outside the normal schedule for practice times. 89% believed that HIV patients were partly to blame for their illness. CONCLUSIONS: Although the physicians recognise the problem of HIV-infection, they partly deny the real necessities and facts. A reason for this could be the emotions underlying the general attitude to everything pertaining to HIV-disease. Attitudes to HIV-disease and the dealing with it in daily practice must be considered on the basis of individual emotional motives. 相似文献
64.
65.
66.
Gonzalez A. Valero-Garcia M. Diaz de Cerio L. 《Parallel and Distributed Systems, IEEE Transactions on》1995,6(8):803-814
Many parallel algorithms use hypercubes as the communication topology among their processes. When such algorithms are executed on hypercube multicomputers the communication cost is kept minimum since processes can be allocated to processors in such a way that only communication between neighbor processors is required. However, the scalability of hypercube multicomputers is constrained by the fact that the interconnection cost-per-node increases with the total number of nodes. From scalability point of view, meshes and toruses are more interesting classes of interconnection topologies. This paper focuses on the execution of algorithms with hypercube communication topology on multicomputers with mesh or torus interconnection topologies. The proposed approach is based on looking at different embeddings of hypercube graphs onto mesh or torus graphs. The paper concentrates on toruses since an already known embedding, which is called standard embedding, is optimal for meshes. In this paper, an embedding of hypercubes onto toruses of any given dimension is proposed. This novel embedding is called xor embedding. The paper presents a set of performance figures for both the standard and the xor embeddings and shows that the latter outperforms the former for any torus. In addition, it is proven that for a one-dimensional torus (a ring) the xor embedding is optimal in the sense that it minimizes the execution time of a class of parallel algorithms with hypercube topology. This class of algorithms is frequently found in real applications, such as FFT and some class of sorting algorithms 相似文献
67.
Using high-NA step index optical fibers, we show, theoretically, that large-bandwidth second-harmonic generation and sum frequency generation can be achieved at conversion frequencies in the visible region of the spectrum 相似文献
68.
F van Rhee RM Szydlo J Hermans A Devergie F Frassoni W Arcese T de Witte HJ Kolb D Niederwiser N Jacobsen G Gahrton G Bandini E Carreras A Bacigalupo M Michallet T Ruutu J Reiffers JM Goldman J Apperley A Gratwohl 《Canadian Metallurgical Quarterly》1997,20(7):553-560
The purpose of this study was to determine the long-term results of allogeneic bone marrow transplantation for chronic myeloid leukemia. A retrospective analysis was carried out of the outcome of 373 consecutive transplants performed at 38 European institutions between 1980 and 1988 and reported to the registry of the European Group for Blood and Marrow Transplantation. All transplants were carried out for first chronic phase of chronic myelogenous leukemia using unmanipulated marow cells from HLA-identical sibling donors. The probability of survival and leukemia-free survival at 8 years were 54% (95% CI: 49-59) and 47% (95% CI: 41-52) respectively. The probabilities of developing acute GVHD (II-IV) at 100 days and chronic GVHD at 4 years after transplant were 47% (95% CI: 41-53) and 52% (95% CI: 46-58) respectively. The probabilities of transplant-related mortality and leukemic relapse 8 years after BMT were 41% (95% CI: 36-48) and 19% (95% CI: 14-25), respectively. Transplant within 12 months of diagnosis was associated with reduced transplant-related mortality (34 vs 45%, P = 0.013) and resulted in improved leukemia-free survival (52 vs 44%, P = 0.03). The probability of relapse was significantly reduced in patients who developed chronic GVHD (RR = 0.33, P = 0.004). The probability of relapse occurring more than 2 years after transplant was increased more than five-fold in patients transplanted from a male donor (RR = 5.5, P = 0.006). Sixty-seven patients in hematologic remission were studied for residual disease by two-step RT/PCR for BCR-ABL mRNA and 61 (91%) tested negative. We conclude that bone marrow transplantation can induce long-term survival in approximately one-half of CML patients; the majority of survivors have no evidence of residual leukemia cells when studied by molecular techniques. The probability of late relapse is increased with use of a male donor. 相似文献
69.
This paper focus on some characteristics of the qualitative methodology. Some of these methods are explored such as: participatory research, phenomenology, grounded theory and ethnography critical theory Perspectives of their utilization in nursing research are examined. 相似文献
70.
AO Güre NK Altorki E Stockert MJ Scanlan LJ Old YT Chen 《Canadian Metallurgical Quarterly》1998,58(5):1034-1041
Supplementation with high doses of alpha-tocopherol has increased the oxidation resistance of LDL in many clinical trials. There have been only a few placebo-controlled trials in healthy persons of alpha-tocopherol doses usually contained in dietary supplements. We carried out a single-blind, placebo-controlled, randomized trial to examine the effect of 200 mg RRR-alpha-tocopheryl acetate/d on the oxidation resistance of atherogenic lipoproteins (VLDL+LDL including intermediate-density lipoproteins) in 40 smoking men. VLDL+LDL oxidation resistance was assessed as conjugated dienes after copper induction and hemin degradation after hydrogen peroxide induction. Also, the LDL total peroxyl-radical trapping antioxidant parameter (LDL TRAP) and plasma malondialdehyde were measured at baseline and after 2 mo of supplementation. Plasma RRR-alpha-tocopherol concentrations were measured at 2-h intervals for 12 h at baseline and after 2 mo of supplementation. Compared with placebo, 200-mg RRR-alpha-tocopheryl acetate supplementation elevated plasma and VLDL+LDL alpha-tocopherol concentrations, LDL TRAP, and oxidation resistance of VLDL+LDL. Plasma alpha-tocopherol increased by 88% (P < 0.0001), VLDL+LDL alpha-tocopherol increased by 90% (P < 0.0001), and LDL TRAP by 58% (P < 0.0001). The time to the start of oxidation (lag time) was prolonged by 34% when assessed with a copper-induced method and by 109% when assessed with a hemin + hydrogen peroxide-induced method; the time to maximal oxidation was prolonged by 21% (copper-induced method) in the vitamin E-supplemented group. Changes in plasma alpha-tocopherol, lipid-standardized alpha-tocopherol, and VLDL+LDL alpha-tocopherol correlated significantly with changes in LDL TRAP, lag time, and time to maximal oxidation. Differences in changes between groups in the area under the curve for plasma alpha-tocopherol were significant (P < 0.009). Our results suggest that 200 mg oral RRR-alpha-tocopheryl acetate/d had a clear effect on the in vitro oxidation of VLDL+LDL in smoking men. 相似文献