全文获取类型
收费全文 | 5841篇 |
免费 | 182篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 75篇 |
综合类 | 8篇 |
化学工业 | 959篇 |
金属工艺 | 157篇 |
机械仪表 | 121篇 |
建筑科学 | 51篇 |
矿业工程 | 16篇 |
能源动力 | 307篇 |
轻工业 | 228篇 |
水利工程 | 36篇 |
石油天然气 | 21篇 |
无线电 | 652篇 |
一般工业技术 | 1157篇 |
冶金工业 | 1593篇 |
原子能技术 | 34篇 |
自动化技术 | 632篇 |
出版年
2023年 | 72篇 |
2022年 | 92篇 |
2021年 | 172篇 |
2020年 | 146篇 |
2019年 | 124篇 |
2018年 | 169篇 |
2017年 | 157篇 |
2016年 | 185篇 |
2015年 | 108篇 |
2014年 | 186篇 |
2013年 | 413篇 |
2012年 | 215篇 |
2011年 | 230篇 |
2010年 | 199篇 |
2009年 | 267篇 |
2008年 | 178篇 |
2007年 | 130篇 |
2006年 | 129篇 |
2005年 | 113篇 |
2004年 | 103篇 |
2003年 | 106篇 |
2002年 | 89篇 |
2001年 | 70篇 |
2000年 | 68篇 |
1999年 | 97篇 |
1998年 | 434篇 |
1997年 | 261篇 |
1996年 | 219篇 |
1995年 | 137篇 |
1994年 | 126篇 |
1993年 | 127篇 |
1992年 | 66篇 |
1991年 | 95篇 |
1990年 | 75篇 |
1989年 | 61篇 |
1988年 | 60篇 |
1987年 | 56篇 |
1986年 | 49篇 |
1985年 | 59篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 29篇 |
1981年 | 35篇 |
1980年 | 26篇 |
1979年 | 30篇 |
1978年 | 34篇 |
1977年 | 44篇 |
1976年 | 61篇 |
1975年 | 18篇 |
1973年 | 13篇 |
排序方式: 共有6047条查询结果,搜索用时 281 毫秒
91.
92.
The distal accessory flexor muscle (DAFM) in the lobster (Homarus americanus) walking leg consists of 5 muscle fiber bundles. All five bundles, one proximal, one distal, and 3 medial, are innervated by one excitatory and one inhibitory motor neuron. Both neurons release more transmitter on the distal bundle than on the proximal bundle. The aim of our studies was to investigate the structural basis of this differentiation. Thin sections cut at 50 microns intervals showed a similar number of excitatory synapses on the two bundles. Freeze-fracture views of excitatory synapses showed that synapse size, active zone number per synapse, and intramembrane particle density in the postsynaptic membrane are similar proximally and distally. Active zones at synapses on the distal bundle are larger and contain about 50% more large intramembrane particles, which are thought to include the voltage-gated Ca2+ channels that couple the action potential to transmitter release, than their counterparts on the most proximal bundle. This difference in channel number appears to produce a disproportionate increase in the probability of transmitter release sufficient to account for most of the proximal-distal disparity in the amplitude of the excitatory postsynaptic potential. In contrast, staining the inhibitor for antibodies to the inhibitory neurotransmitter, GABA, showed that it forms more varicosities on the distal bundle than on the proximal bundle. Because most of the synapses are located in the varicosities, differences in synapse number likely regulate the proximal-distal disparity in the amount of inhibitory transmitter released. Therefore, the regional differentiation in the amount of transmitter released in the DAFM appears to be based on two distinct mechanisms. In the inhibitor, transmitter release appears to be regulated differentially by differences in synapse number. In the excitor, transmitter release appears to be regulated differentially from a similar number of synapses by differences in active zone structure. 相似文献
93.
94.
Long-period fibre gratings in specially designed birefringent few-mode fibres are used to demonstrate spectrally flat polarisers with bandwidths of 10 nm and polarisation extinction levels of 20 dB. This is enabled by the special dispersive properties of few-mode fibres, yielding fibre polarisers with performance approaching that of bulk-optic devices. 相似文献
95.
We report a case of homozygous alpha-thalassaemia with hydrops fetalis presenting at 22 weeks of gestation. In utero exchange transfusion was performed with maternal blood at 23 weeks. 25 weeks and 29 weeks of gestation. The fetus was delivered at 29 weeks of gestation without significant neonatal complication. Post-transfusion haemoglobin pattern after transfusion suggested that a total haematocrit of 0.52 may be the desired post-exchange transfusion haematocrit to aim for and the total haematocrit of haemoglobin A and haemoglobin Portland dropped approximately one percent per day. 相似文献
96.
This study examines the role of ArginMax, a natural daily dietary supplement, on male sexual function. 25 subjects diagnosed with mild to moderate erectile dysfunction were evaluated over a 4-week period while on ArginMax. Of the 21 subjects that completed the study, 88.9% improved in ability to maintain erection during sexual intercourse and 75.0% improved in satisfaction with their overall sex life. No significant side effects were noted. 相似文献
97.
The classical stochastic analog of the deterministic linear system in engineering is the linear system driven by white noise. As the promise of artificial neural networks in modeling nonlinear systems continues to grow, the need for a stochastic analog with quantitative foundations for analysis and synthesis will increase. This paper presents recent work in this direction, examining recurrent neural nets (RNN driven by white noise. We examine the effect of noise on the typical continuous-time RNN model. First, we perform qualitative analysis establishing uniform boundedness of moments of the neuron states over time. To enable practical application, however, it is necessary to relate these properties to useful measures that can be estimated. We thus subsequently derive bias and variance measures for the noisy RNN with respect to the corresponding deterministic RNN. This has significant practical implications, since net design is nonminimal in the sense that several nets can solve the same problem. The results allow the user to evaluate given RNN for noise performance. The designer can use these results to constrain the design space so that the design satisfies performance specifications whenever possible. An example is provided using the measures derived in this paper to predetermine the best among several RNN designs for a given problem. 相似文献
98.
JK Kang SW Lee MW Baik BC Son YK Hong CK Jung KH Ryu 《Canadian Metallurgical Quarterly》1998,14(7):297-301
Accurate assessment and replacement of blood loss and fluid-electrolyte deficit during craniosynostosis repair is difficult owing to patient size and the diversity of surgical technique. Forty-three patients undergoing primary craniosynostosis repair over a 10-year period were studied retrospectively to determine blood loss and fluid deficit and to assess blood transfusion practices during both intraoperative and postoperative periods. Blood loss was calculated on the basis of estimated red cell mass (ERCM) and fluid-electrolyte imbalance was investigated with blood samplings. Blood transfusion was considered appropriate if the postoperative or posttransfusion ERCM was within 12% of the preoperative value. Estimated fluid requirement (EFR) was used in 4 ml kg(-1) h(-1) except for neonates. Intraoperatively, 80% of all patients were appropriately managed with respect to blood transfusion and EFR. Postoperatively only 20% of the patients receiving transfusions were transfused appropriately. In 23.3% of these patients (10/43) unexpected respiratory distress developed immediately after their recovery from the anesthesia. With the measurement of estimated blood volume and allowable blood loss, appropriate transfusion could be achieved for the successful treatment of the primary craniosynostosis. 相似文献
99.
100.
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