全文获取类型
收费全文 | 3455篇 |
免费 | 7篇 |
专业分类
电工技术 | 23篇 |
化学工业 | 142篇 |
金属工艺 | 14篇 |
机械仪表 | 19篇 |
建筑科学 | 54篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 97篇 |
水利工程 | 6篇 |
无线电 | 197篇 |
一般工业技术 | 208篇 |
冶金工业 | 2539篇 |
原子能技术 | 14篇 |
自动化技术 | 132篇 |
出版年
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 23篇 |
2013年 | 36篇 |
2012年 | 27篇 |
2011年 | 38篇 |
2010年 | 37篇 |
2009年 | 48篇 |
2008年 | 38篇 |
2007年 | 39篇 |
2006年 | 41篇 |
2005年 | 27篇 |
2004年 | 29篇 |
2003年 | 38篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 21篇 |
1999年 | 104篇 |
1998年 | 758篇 |
1997年 | 408篇 |
1996年 | 288篇 |
1995年 | 164篇 |
1994年 | 145篇 |
1993年 | 165篇 |
1992年 | 39篇 |
1991年 | 41篇 |
1990年 | 42篇 |
1989年 | 51篇 |
1988年 | 41篇 |
1987年 | 73篇 |
1986年 | 52篇 |
1985年 | 61篇 |
1984年 | 23篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 33篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 55篇 |
1976年 | 129篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1971年 | 11篇 |
排序方式: 共有3462条查询结果,搜索用时 0 毫秒
21.
Berries of Vaccinium meridionale Swartz native to Colombia were analysed for chemical composition, total phenolic content, anthocyanin content, and antioxidant activity. In addition, high-performance liquid chromatography with photodiode array detection (HPLC–DAD) and HPLC-electrospray ionisation tandem mass spectrometry (ESI–MS/MS) were used to determine anthocyanin and phenolic composition. Anthocyanin content was 329.0 ± 28.0 mg cyanidin 3-glucoside equivalents/100 g (fresh weight) FW and total phenolic content was 758.6 ± 62.3 mg gallic acid equivalent/100 g FW. Cyanidin 3-galactoside was the major anthocyanin while the most abundant non-anthocyanin phenolic was chlorogenic acid. 相似文献
22.
EP Lautenschlager GW Marshall KE Marks J Schwartz CL Nelson 《Canadian Metallurgical Quarterly》1976,10(6):837-845
Admixing of several antibiotic powders which were insoluble in methyl methacrylate did not decrease the compressive and diametral tensile strengths of two acrylic bone cements when tested after setting for 1 day and after leaching 40 days in water at 37 degrees C. When antibiotics were added as water solutions, the included water resulted in a significant decrease in these bulk mechanical properties. Storage in water for 40 days caused surface irregularities only on specimens of the set antibiotic admixtures. Approximately 0.5% of the admixed dosage of these water-soluble antibiotics could be leached from the set cements. The observed surface channels, presumably left by the loss of antibiotic, suggest further study of surface-sensitive mechanical properties may be needed. The bulk mechanical strengths presented here are conclusive only for the particular combinations of antibiotics and cements investigated, and should not be generalized at this time to any or all antibiotic admixtures or other mechanical properties. 相似文献
23.
RL Kincaid WJ Miller LS Jensen DL Hampton MW Neathery RP Gentry 《Canadian Metallurgical Quarterly》1976,55(5):1954-1957
Weight gains of younger broiler chicks were not reduced by up to 2400 p.p.m. added zinc fed to four weeks of age. Tissue zinc was not changed significantly by 600 or 1200 p.p.m. supplemental dietary zinc, but at 2400 p.p.m. added zinc, blood, kidney, and liver zinc were significantly elevated (P less than 0.05). In the heart, zinc was not affected by the added dietary zinc but increased over time with all diets. Unlike the calf and weanling pig, the metabolism of zinc in the young chick does not appear to change appreciably with increasing maturity. Thus, the homeostatic control mechanisms of the young chick are effective for up to 1200 p.p.m. dietary zinc, but are partially overcome by 2400 p.p.m. added dietary zinc. 相似文献
24.
Iodine-131, ruthenium-103, and neptunium-239 are present as contaminants in the eluate of 99Mo-99mTc generators loaded with 99Mo prepared by thermal-neutron irradiation of enriched 98Mo. The elution pattern of each of these contaminants is determined, together with the amounts found in the eluate of all generators tested over a 7-month period. 相似文献
25.
Cell-mediated immunity (CMI) to homologous spermatozoal antigens was studied in sixty-two males following vasectomy of a duration of 1-10 years. A group of twenty-two normal, fertile non-vasectomized males was also included in the study. The inhibition in the leucocyte migration test (LMT), in the presence of spermatozoal antigen, was taken as an index of CMI. Twenty of the sixty-two vasectomized males (32.2 percent) showed a positive LMT reaction. When the results were analysed with reference to the duration of vasectomy, it was noted that four cases each (22.2 percent), showed a positive LMT reaction in the groups 0-2 years, and 3.5 years. On the other hand twelve cases gave a positive reaction in the group 6-10 years (46.1 percent). It appears that the incidence of CMI to spermatozoa increases with the duration in vasectomy. 相似文献
26.
Cerebral ischemic events associated with prolapsing mitral valve 总被引:1,自引:0,他引:1
Twelve patients who had no evidence of arteriosclerotic cerebral vascular disease, lacked hypertension or coagulation defect, and had not been receiving contraceptive therapy had recurrent transient cerebral ischemic attacks (TIAs) and partial nonprogressive strokes. All had prolapsing mitral valve proved by angiocardiography. The average age was 38 years, compared with 62 years in a larger series of patients with TIA associated with arteriosclerosis. We propose that the ischemic events are related to emboli emanating from the abnormal mitral valve with or without an associated paroxysmal cardiac arrhythmia. 相似文献
27.
S Duca A Suiu I Szantay C Duca R Lezeu M Schwartz H Szilagyi 《Canadian Metallurgical Quarterly》1976,26(5):858-862
Accumulation of radioactive material in the isolated rat liver was noted when 125I-fibrinogen was added to the perfusing medium. Owing to an enhanced production of fibrinogen and to a diminished fibrinolysis, fibrin deposits were found to occur in the capillaries of fhe isolated liver. This would cause a decrease of hepatic flow and an impairment of the nutrition of this organ which leads to subsequent necrosis. Administration of streptase removed the fibrin deposits and restored the perfusive flow in the isolated liver. 相似文献
28.
Two cases of juvenile gastrointestinal polyposis are described and the literature is reviewed. Despite the benign nature of the individual polyps, the disease has a poor prognosis. Of 13 reported patients, 4 had macrocephaly, and one of the authors' 2 patients had large peripheral intracranial cysts. This appears to be the first reported documentation of the etiology of macrocephaly associated with juvenile polyposis. Major clinical problems are related to severe loss of blood and protein from the gastrointestinal tract. 相似文献
29.
GL Johnson RA Meyer DC Schwartz J Korfhagen S Kaplan 《Canadian Metallurgical Quarterly》1976,38(5):611-619
Left ventricular function was evaluated echocardiographically within 24 hours of cardiac catheterization in 45 children with fixed aortic stenosis. Left ventricular systolic time intervals, mean velocity of circumferential fiber shortening, left ventricular end-diastolic volume and shortening fraction were evaluated. Some patients with severe aortic stenosis had a shortened preejection period, prolonged ejection time and increased mean velocity of circumferential fiber shortening in comparison with normal subjects, but these findings were not consistent within the group with severe aortic stenosis or apparent in patients with mild or moderate aortic stenosis. Left ventricular end-diastolic volume was smaller in children with severe obstruction than in normal children. Evaluation of the shortening fraction provided good separation of patients with significant obstruction from those with mild disease. Further, there was a linear correlation between the shortening fraction and the left ventricular-aortic gradient demonstrated at cardiac catheterization. This correlation was also of use in evaluating the response of patients to surgical relief of obstruction. Pre- and postoperative echocardiographic evaluation of the shortening fraction appears to provide a readily available noninvasive method of assessing the course and severity of obstruction in fixed aortic stenosis in children. 相似文献
30.
Microvillar membrane (Vm) and transmural (Vt) potential differences were measured in proximal colon taken from pigs at birth and up to 10 days of age. 2. Vm remained independent of the age of the animal provided it was measured in the absence of methionine. The over-all mean was -43-3 mV. Adding methionine to fluid bathing the mucosal surface of new-born pig colon caused a 9-8 mV depolarization of Vm and a 6-7 mV increase in Vt. These effects, which were Na+-dependent, were not seen in the 10-day-old animal. 3. Substituting SO4(2-) for Cl- in methionine-free medium caused a hyperpolarization in Vm. Increasing the concentration of K+ caused corresponding depolarization. Substituting choline for Na+ had no effect on VmCl- and K+ movement across the microvillar membrane together account for the bulk of the measured membrane potential. These results apply to all stages of development. 4. Na+ uptake across the microvillar membrane of the new-born pig colon was increased in the presence of methionine. This effect disappeared in older animals. Na+ uptake in the absence of methionine doubled during the first 24 h of post-natal life. This increase was maintained using colons taken from older animals. 5. Methionine depolarization of Vm in the new-born pig colon is probably caused by the electrogenic influx of Na+. The ability of the colon to actively concentrate methionine within tis mucosa disappears at the same time as methionine ceases to affect Vm and Vt. It is suggested that methionine and Na+ form a ternary complex with a carrier in the brush border of the new-born pig colon and that this carrier is lost or modified during early post-natal development. 相似文献