全文获取类型
收费全文 | 5749篇 |
免费 | 184篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 44篇 |
综合类 | 15篇 |
化学工业 | 572篇 |
金属工艺 | 41篇 |
机械仪表 | 60篇 |
建筑科学 | 68篇 |
矿业工程 | 4篇 |
能源动力 | 127篇 |
轻工业 | 300篇 |
水利工程 | 17篇 |
石油天然气 | 48篇 |
武器工业 | 1篇 |
无线电 | 517篇 |
一般工业技术 | 438篇 |
冶金工业 | 3262篇 |
原子能技术 | 10篇 |
自动化技术 | 431篇 |
出版年
2023年 | 14篇 |
2022年 | 33篇 |
2021年 | 51篇 |
2020年 | 31篇 |
2019年 | 49篇 |
2018年 | 63篇 |
2017年 | 128篇 |
2016年 | 56篇 |
2015年 | 56篇 |
2014年 | 101篇 |
2013年 | 191篇 |
2012年 | 134篇 |
2011年 | 192篇 |
2010年 | 144篇 |
2009年 | 141篇 |
2008年 | 130篇 |
2007年 | 104篇 |
2006年 | 103篇 |
2005年 | 136篇 |
2004年 | 126篇 |
2003年 | 100篇 |
2002年 | 75篇 |
2001年 | 63篇 |
2000年 | 63篇 |
1999年 | 144篇 |
1998年 | 967篇 |
1997年 | 543篇 |
1996年 | 357篇 |
1995年 | 201篇 |
1994年 | 195篇 |
1993年 | 223篇 |
1992年 | 68篇 |
1991年 | 64篇 |
1990年 | 49篇 |
1989年 | 73篇 |
1988年 | 70篇 |
1987年 | 74篇 |
1986年 | 50篇 |
1985年 | 47篇 |
1984年 | 13篇 |
1983年 | 22篇 |
1982年 | 23篇 |
1981年 | 32篇 |
1980年 | 52篇 |
1979年 | 12篇 |
1978年 | 20篇 |
1977年 | 102篇 |
1976年 | 222篇 |
1975年 | 13篇 |
1970年 | 10篇 |
排序方式: 共有5955条查询结果,搜索用时 15 毫秒
11.
12.
H Lee KB Idler P Swanson JJ Aparicio KK Chin JP Lax M Nguyen T Mann G Leckie A Zanetti 《Canadian Metallurgical Quarterly》1993,196(1):57-69
Seven cardiac electrophysiology stimulators from four manufacturers (Biotronik, Bloom, Digitimer and Medtronic) in common current use are reviewed. The stimulators differ in the features provided and the design adopted to achieve these features. The number of output channels ranges from one to four, the number of extra-stimuli available ranges from two to six, and these can be delivered as a variety of sequences. Some of the stimulators (Digitimer and Bloom) are modular while others (Biotronik and Medtronic 532 series) are of an integrated design comprising a single physical unit. The design of the Medtronic EP-2 has both integrated and modular characteristics. The features of the stimulators associated with input, output, control and the user interface are specifically reviewed. The features are also compared against the published recommendations of the American Heart Association. In addition, a summary of stimulator user comments from a number of electrophysiology centres is presented. All of the stimulators fulfil, or are close to fulfilling, basic electrophysiological requirements, but some provide more complex facilities such as would be required by specialist centres. 相似文献
13.
The adult songbird forebrain undergoes neuronal production throughout adulthood, with the production of new neurons in discrete regions of the neostriatal ventricular zone. Upon mitogenesis, these new neurons migrate into the subjacent brain parenchyma along radially directed guide fibers. In long-term ventricular zone explant cultures, derived from the higher vocal center of the adult canary, newly migratory neurons were found to associate preferentially with a characteristic substrate cell type. These small, parvonuclear substrate cells formed tightly packed epithelioid sheets, in which ciliated ependymal cells were common, as recognized by both live observation and electron microscopy. A subpopulation of these cells was immunostained by monoclonal antibody 3A7, which preferentially stains the guide fiber network of the adult avian brain. These 3A7+ cells included ependymal cells and bipolar radial cells, as well as morphologically defined astrocytes. As they matured in vitro, the 3A7+ bipolar radial cells extended long, unbranching fibers, which ultimately traversed the culture substrate. Like ependymal cells, they supported neuronal migration. These cells were likely homologous to radial guide cells in vivo. Thus, neuronal migration in adult avian forebrain culture occurred upon guide cells of ependymal derivation. 相似文献
14.
The mode of interaction between muramyl dipeptide (MDP), a compound with immunopharmacological activities, and 5-hydroxtryptamine (5-HT, serotonin) was studied in isolated nerve-smooth muscle preparations of the carp stomach. Application of exogenous 5-HT evoked direct smooth muscle contractions; electric neurogenic stimulation evoked twitches due to release of 5-HT from nerve endings. Contractions evoked by a high concentration of 5-HT (3-30 microM) were resistant to atropine and potentiated in the presence of MDP. Isamoltan (5-HTID antagonist) decreased the amplitude of contractions, whereas ketanserin (5-HT2 antagonist) and MDL 72,222 (5-HT3 antagonist) had no effect. The addition of low concentrations (0.1-1.5 microM) of 5-HT did not contract the preparation but caused a decrease in the amplitude of neurogenic twitches, which might be due to the presynaptic inhibition of serotonin release. This effect of 5-HT was not changed by isamoltan or ketanserin, but it was largely reduced in the presence of 5-HT3 antagonists tropisetron and MDL 72,222. This inhibitory effect of 5-HT on twitch amplitude was potentiated by MDP. The interaction of MDP with the serotonergic system thus involved not only potentiation of the postsynaptic effect of higher 5-HT concentrations, which might have been mediated via the 5-HT1 subsystem, but also presynaptic inhibition. MDP enhancement of 5-HT's inhibitory effect, mediated via 5-HT3 receptors, might represent a new feature in mutual 5-HT-MDP interactions. 相似文献
15.
16.
17.
A method of positive identification of the specificity of polymerase chain reaction (PCR) product using internal oligonucleotide probe is introduced. The hybridization was done on the agarose gel which was dried after electrophoresis. Detection of the expression of T cell receptor a chain variable (TCR V alpha) genes on mRNA level was used as the experimental model. Twenty nine TCR V alpha gene subfamilies could be distinguished clearly in healthy human peripheral blood lymphocytes by this method. Positive identification of PCR product on dried agarose gel by internal oligonucleotide probe is relatively simple and less time consuming. 相似文献
18.
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
19.
20.
M Wisard A Bitton P Jichlinski JB Wasserfallen HJ Leisinger 《Canadian Metallurgical Quarterly》1997,86(44):1755-1757
Day surgery in urology is in full growth actually. The present report is based on our first 120 patients. Low post-operative complication rate, patients' satisfaction and economical savings are the main factors for the important increase in this type of surgery. 相似文献