全文获取类型
收费全文 | 1845篇 |
免费 | 96篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 29篇 |
综合类 | 1篇 |
化学工业 | 189篇 |
金属工艺 | 29篇 |
机械仪表 | 51篇 |
建筑科学 | 36篇 |
能源动力 | 24篇 |
轻工业 | 43篇 |
水利工程 | 19篇 |
石油天然气 | 2篇 |
无线电 | 193篇 |
一般工业技术 | 197篇 |
冶金工业 | 967篇 |
原子能技术 | 7篇 |
自动化技术 | 163篇 |
出版年
2023年 | 17篇 |
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 35篇 |
2018年 | 34篇 |
2017年 | 36篇 |
2016年 | 38篇 |
2015年 | 24篇 |
2014年 | 30篇 |
2013年 | 73篇 |
2012年 | 42篇 |
2011年 | 64篇 |
2010年 | 50篇 |
2009年 | 56篇 |
2008年 | 30篇 |
2007年 | 47篇 |
2006年 | 44篇 |
2005年 | 48篇 |
2004年 | 35篇 |
2003年 | 24篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 12篇 |
1999年 | 44篇 |
1998年 | 322篇 |
1997年 | 176篇 |
1996年 | 125篇 |
1995年 | 63篇 |
1994年 | 49篇 |
1993年 | 63篇 |
1992年 | 13篇 |
1991年 | 37篇 |
1990年 | 9篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1978年 | 6篇 |
1977年 | 21篇 |
1976年 | 31篇 |
1975年 | 5篇 |
1969年 | 5篇 |
1966年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有1950条查询结果,搜索用时 15 毫秒
21.
The present study in conscious rabbits with intracisternal (i.c.) catheters sought to determine the relative contribution of the I1 subtype of imidazoline receptors (IR) and alpha 2 adrenoceptors to the hypotensive effects of rilmenidine, clonidine and moxonidine with an I1-IR/alpha 2 adrenoceptor antagonist efaroxan and a specific alpha 2 adrenoceptor antagonist 2-methoxyidazoxan (2-MI). The alpha 2 adrenoceptor antagonist effect of efaroxan was compared with 2-MI by performing cumulative dose-response curves in the presence of alpha-methyldopa (400 micrograms/kg i.c.). 2-MI was 5.6 times more potent than efaroxan at reversing 75% of the hypotension elicited by alpha-methyldopa (P < .025). This dose ratio was used to match doses of efaroxan and 2-MI for similar alpha 2 adrenoceptor blockade. The effects of efaroxan (4.1, 13, 41 micrograms/kg i.c.) and 2-MI (0.74, 2.3, 7.4 micrograms/kg i.c.) were investigated on a single i.c. dose of rilmenidine (12 micrograms/kg), clonidine (0.75 microgram/kg) and moxonidine (0.51 microgram/kg). These doses of the antihypertensive agents, which were determined from cumulative dose-response curves, produce 90% of the maximum hypotension. Efaroxan was more effective at reversing the hypotension induced by moxonidine and rilmenidine than was 2-MI (P < .01). These findings suggest that rilmenidine and moxonidine act predominantly via IR. By contrast, 2-MI was more effective at reversing the clonidine-induced hypotension than was efaroxan (P < .001), suggesting that clonidine acts mainly via alpha 2 adrenoceptors in conscious normotensive rabbits. Thus, a higher selectivity of the second generation agents moxonidine and rilmenidine for I1-IR over alpha 2 adrenoceptors, compared with the first generation agent clonidine, appears to be necessary for this effect to be manifested in their hypotensive actions. 相似文献
22.
23.
24.
25.
PURPOSE: To assess the efficacy and safety of percutaneous catheter drainage combined with alcohol sclerosis in the treatment of postoperative lymphoceles. PATIENTS AND METHODS: Thirteen patients with 14 postoperative symptomatic lymphoceles were treated. Drainage catheters were inserted under ultrasound (n = 13) or computed tomographic (n = 1) guidance. Lymphocele sclerosis was performed by instilling 10-100 mL of absolute alcohol into the lymphocele cavity and aspirating the alcohol after 30 minutes. Sclerosis sessions were carried out one to three times per day, usually three times per week. Catheter sinograms were obtained and prophylactic antibiotics administered. Imaging was repeated if symptoms or signs of recurrence developed. RESULTS: Successful drainage and sclerosis were achieved in all 13 patients. One patient with a recurrence was successfully treated with repeated drainage and alcohol ablation. No adverse effects of alcohol instillation were seen. The mean duration of catheterization was 36 days (range, 17-65 days; median, 30 days). CONCLUSION: Percutaneous drainage combined with alcohol ablation is a safe and effective treatment of postoperative lymphoceles. 相似文献
26.
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
27.
28.
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
29.
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
30.