全文获取类型
收费全文 | 378966篇 |
免费 | 3647篇 |
国内免费 | 599篇 |
专业分类
电工技术 | 6401篇 |
综合类 | 371篇 |
化学工业 | 60873篇 |
金属工艺 | 16861篇 |
机械仪表 | 11898篇 |
建筑科学 | 7982篇 |
矿业工程 | 2946篇 |
能源动力 | 7450篇 |
轻工业 | 31849篇 |
水利工程 | 4754篇 |
石油天然气 | 11930篇 |
武器工业 | 42篇 |
无线电 | 36614篇 |
一般工业技术 | 76235篇 |
冶金工业 | 68744篇 |
原子能技术 | 11280篇 |
自动化技术 | 26982篇 |
出版年
2021年 | 3256篇 |
2019年 | 3189篇 |
2018年 | 5683篇 |
2017年 | 5752篇 |
2016年 | 6152篇 |
2015年 | 3554篇 |
2014年 | 6174篇 |
2013年 | 15325篇 |
2012年 | 9487篇 |
2011年 | 12516篇 |
2010年 | 10041篇 |
2009年 | 11118篇 |
2008年 | 11528篇 |
2007年 | 11645篇 |
2006年 | 10163篇 |
2005年 | 9120篇 |
2004年 | 8688篇 |
2003年 | 8462篇 |
2002年 | 8517篇 |
2001年 | 8421篇 |
2000年 | 8128篇 |
1999年 | 7956篇 |
1998年 | 18567篇 |
1997年 | 13268篇 |
1996年 | 10146篇 |
1995年 | 7847篇 |
1994年 | 7003篇 |
1993年 | 6981篇 |
1992年 | 5521篇 |
1991年 | 5299篇 |
1990年 | 5604篇 |
1989年 | 5398篇 |
1988年 | 5221篇 |
1987年 | 4716篇 |
1986年 | 4826篇 |
1985年 | 5295篇 |
1984年 | 5049篇 |
1983年 | 4693篇 |
1982年 | 4414篇 |
1981年 | 4626篇 |
1980年 | 4418篇 |
1979年 | 4520篇 |
1978年 | 4671篇 |
1977年 | 4957篇 |
1976年 | 6433篇 |
1975年 | 4225篇 |
1974年 | 4161篇 |
1973年 | 4292篇 |
1972年 | 3772篇 |
1971年 | 3439篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The effects of adenosine and sodium nitroprusside (SNP) on central hemodynamics and myocardial blood flow and metabolism were investigated postoperatively after elective coronary artery bypass (CABG) surgery in ten sedated and mechanically ventilated patients in the intensive care unit. During three consecutive 15-min periods, SNP (0.8 +/- 0.1 micrograms.kg-1 x min-1), adenosine (88.9 +/- 13.3 micrograms.kg-1 x min-1), and then again SNP (0.7 +/- 0.1 micrograms.kg-1 x min-1) were infused to control postoperative hypertension at a mean arterial pressure of approximately 80 mm Hg. Systemic and pulmonary hemodynamics and global (coronary sinus flow, CSF) as well as regional (great cardiac vein flow, GCVF) myocardial blood flow and metabolic variables were measured. During adenosine infusion, in comparison to SNP, heart rate was unchanged, stroke volume index and cardiac index increased (24% and 32%, respectively), and the systemic vascular resistance index decreased (-26%). Mean pulmonary arterial pressure (24%) as well as pulmonary capillary wedge pressure (27%) and central venous pressure (18%) were higher with adenosine compared to SNP. Adenosine also increased CSF and GCVF (108% and 103%, respectively) without altering the CSF/GCVF flow ratio compared to SNP. Furthermore, adenosine increased the coronary oxygen content (51%) and decreased the arterio-great cardiac vein oxygen content difference (-48%) without changing regional myocardial oxygen consumption, indicating a more pronounced hyperkinetic myocardial circulation compared to SNP. In addition, adenosine infusion decreased arterial PO2 (-11%) and increased the intrapulmonary shunt fraction (57%). The PR interval time of the electrocardiogram was prolonged (12%) and the ST segment was more depressed during adenosine infusion compared to SNP.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
142.
F. Cioffi E. M. Cohen Richard Badick 《Drug development and industrial pharmacy》1993,19(14):1741-1746
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well. 相似文献
143.
Translated from Izmeritel'naya Tekhnika, No. 3, pp. 40–42, March, 1993. 相似文献
144.
145.
Sh. V. Gedevanishvili V. I. Yukhvid G. Sh. Oniashvili 《Journal of Engineering Physics and Thermophysics》1993,65(5):1134-1137
Use of inexpensive ore concentrates as initial components in SHS metallurgy [1–3] brings about some specific features in the process and the properties of the materials obtained. Ore reagents contain a considerable amount of impurities (Al2O3, SiO2, Fe2O3) that decrease the energetics of SHS systems and the temperature and the rate of combustion and create the limits of combustion and phase separation. In addition, the impurities participate in chemical reactions and enter the desired product. In many cases the presence of silicon, iron, and aluminum in a cast product does not prevent use of this product for practical purposes.Institute of Metallurgy, Academy of Sciences of the Republic of Georgia, Tbilisi. Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 613–616, November, 1993. 相似文献
146.
147.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period 相似文献
148.
E. Smith 《Journal of Materials Science》1993,28(4):880-884
The criterion for crack growth instability in an elastic-softening material that is subjected to displacement control loading conditions is examined. A theoretical analysis of the model of a solid containing two symmetrically situated deep cracks and with tensile loading of the remaining ligament, defines the criterion for crack growth instability. The criterion is expressed in terms of the material's softening characteristics and the solid's geometrical parameters. The analysis covers the complete spectrum of material behaviour from the case where the softening zone is very small to the case where instability does not occur until the softening zone traverses the ligament between the crack tips. 相似文献
149.
E Vernon-Roberts 《Canadian Metallurgical Quarterly》1993,14(3):208-211
A perinatal death presenting as a possible homicide is reported. An infant was born with a cleft palate, but without other apparent abnormality, to a mother who experienced postpartum depression. The infant apparently died during feeding. A death certificate, giving cot death and congenital malformations as the causes of death, was rejected by the registering authority. The possibility of homicide was considered. Exhumation and autopsy showed multiple abnormalities, including congenital heart disease and the karyotype of DiGeorge's anomaly. The case highlights the value of the autopsy in such cases, and emphasizes the role of cytogenetics, even after considerable postmortem delay. 相似文献
150.
N Pasetto V Petrozza C Ticconi A Zicari F Carpino E Piccione M Melis 《Canadian Metallurgical Quarterly》1993,35(2):99-102
Ten patients with biopsy verified chronic hepatitis C virus (HCV) infection were treated with oral ribavirin at a dose of 1,000-1,200 mg per day in two divided doses for 12 weeks. Serum alanine aminotransferase (ALT) levels and hepatitis C viral ribonucleic acid (RNA) levels in serum were followed prior to, during, and 12 weeks posttreatment. ALT levels decreased significantly in all patients during therapy from a mean level of 3.21 mukat/l (range 1.22 to 7.79) before, to 1.25 mukat/l (range 0.78 to 2.04) at the end of treatment (P < 0.005). Hereafter, relapse to pretreatment levels was seen within 12 weeks after treatment stop. The hepatitis C viral RNA levels decreased from a mean 10 log titer of 4.1 (range 1-6) before treatment to 3.4 (range 1-5) at treatment stop. Five patients did not change their HCV RNA titers during treatment. Twelve weeks posttreatment only 3 patients had lower titers than prior to treatment. We conclude that oral ribavirin seems to reduce the viral load, at least temporarily, in some patients with chronic viremic HCV infection. Further studies are needed to evaluate fully the effect of oral ribavirin on chronic HCV infection. 相似文献