首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4095篇
  免费   10篇
  国内免费   7篇
电工技术   10篇
综合类   2篇
化学工业   85篇
金属工艺   18篇
机械仪表   16篇
建筑科学   15篇
矿业工程   2篇
能源动力   10篇
轻工业   41篇
水利工程   3篇
石油天然气   2篇
无线电   54篇
一般工业技术   105篇
冶金工业   3658篇
原子能技术   6篇
自动化技术   85篇
  2022年   4篇
  2021年   4篇
  2020年   5篇
  2019年   5篇
  2017年   6篇
  2016年   4篇
  2015年   6篇
  2014年   5篇
  2013年   19篇
  2012年   18篇
  2011年   26篇
  2010年   12篇
  2009年   16篇
  2008年   21篇
  2007年   17篇
  2006年   24篇
  2005年   20篇
  2004年   23篇
  2003年   25篇
  2002年   14篇
  2001年   19篇
  2000年   10篇
  1999年   115篇
  1998年   1126篇
  1997年   598篇
  1996年   461篇
  1995年   238篇
  1994年   231篇
  1993年   227篇
  1992年   33篇
  1991年   43篇
  1990年   50篇
  1989年   55篇
  1988年   52篇
  1987年   55篇
  1986年   50篇
  1985年   35篇
  1984年   8篇
  1983年   15篇
  1982年   24篇
  1981年   21篇
  1980年   33篇
  1979年   8篇
  1978年   10篇
  1977年   83篇
  1976年   188篇
  1975年   9篇
  1974年   6篇
  1973年   4篇
  1972年   4篇
排序方式: 共有4112条查询结果,搜索用时 10 毫秒
41.
Carriers for chronic granulomatous disease (CGD) and patients with lupus erythematosus (LE) share several characteristics: They are mostly females, they reduce nitroblue tetrazolium (NBT) poorly in their neutrophils, and, in some cases, they have similar skin lesions. We thus investigated 19 female LE patients for the presence of laboratory findings characteristic of the carrier state for CGD. None of these patients turned out to have the combined abnormality of neutrophil bactericidal activity and neutrophil NBT-reduction that is diagnostic of CGD carrier state in the X-linked form. An increased frequency of CGD carriers among female LE patients thus appear to be unlikely. Why some CGD carriers develop skin lesions typical of LE remains unexplained.  相似文献   
42.
43.
44.
The Australian lungfish (Neoceratodus forsteri) responds to intravenous injections of 0.63 ng/kg or more of arginine vasotocin with increased dorsal aortic blood pressure, inulin clearance, urine flow, and tubular rejection of Na+. Single injections of 1 ng/kg or more of angiotensin II or norepinephrine also increase dorsal aortic pressure but do not cause consistent diuresis and natriuresis, Continuous infusions of angiotensin II or repeated injections of norepinephrine produce sustained hypertension and more modest diuresis and natriuresis than are seen after injections of arginine vasotocin that cause less hypertension. Infusions of isosmolar or hyposmolar NaCl solutions increase blood pressure, inulin clearance, urine flow, and tubular Na+ rejection in a manner resembling the response to argininge vasotocoin injections. These data are consistent with the hypothesis that arginine vasotocin is released in response to volume expansion in lungfishes and that it may act on the kidney as a diuretic and natriuretic hormone. They do not rule out a more direct action of expansion on renal functions.  相似文献   
45.
A model is developed to describe the decay of seven insecticides on stored paddy rice, maize, sunflowers and peas, and is shown to be more precise than each of six literature models on pesticide decay. It relates residues (R), as a ratio of applied concentration (R(0)), to time after insecticide application (t), modifying the usual first-order kinetics equation lnR=lnR(0)-kt by assuming that the rate constant k has a mixture of values according to a gamma distribution with mean K. The resulting equation is lnR=lnR(0)-Kcln(1+t/c), where c is a constant determined empirically. For large c, this model reduces to the first-order model with K=k. The parameter K is further modelled as linear in temperature for maize and rice. The rate of loss of protectants was found not to be seriously affected by co-application with other insecticides, and this is a useful finding for future studies on rates of loss of grain protectants. The apparent rate of loss was also not seriously affected by the method of analysis, whether by gas chromatography or high-performance liquid chromatography, and this finding supports previous validation of the methods.  相似文献   
46.
Potential step chronocoulometric methods were used to measure kinetic parameters for the oxidation of ferrocene at platinum vitreous carbon electrodes in acetonitrile. The formal rate constants observed, kof ~ 0.02 cm s?1, were independent of electrode material and of the supporting electrolyte chosen (LiClO4, TEAP or TEABF4). After correcting for the effects of double layer structure, the experimental activation energy for electron transfer was found to be ΔG≠ (exp) = 0.03 ±0.01 eV molecule?1 which agreed within 20% with a theoretical value ΔG≠ (theor) = 0.26 eV molecule?1 calculated for activation by solvent repolarization alone from the Born equation.  相似文献   
47.
Abstract: Phenolic compounds and anthocyanins in muscadines have attracted much attention due to their diverse biological activities. With bioassays of antioxidant activities in terms of total phenolic content (TPC), total anthocyanin content (TAC), total procyanidin content (TPA), oxygen radical absorbance capacity (ORAC), and ferric reducing antioxidant power (FRAP) of different parts of the Noble muscadine, the butanol (BuOH) extract of the muscadine skin showed the highest TPC (317.91 ± 1.83 mg GAE/100 g FW), which might be ascribed to its high TAC of 227.06 ± 1.29 mg/100 g fresh weight (FW). The ethyl acetate (EtOAc) extract of the muscadine seed contained the highest TPA (55.30 ± 0.63 mg CE/100 g FW). Correlation analyses demonstrated a significant linear relationship of TPC and TAC compared to their ORAC and FRAP values within the range of R2 from 0.9283 to 0.9936, which suggested that phenolics and anthocyanins in the extracts contributed significantly to their antioxidant potential. Nineteen individual phenolics and 5 anthocyanins were identified by HPLC‐MS, which indicated different chemical profiles of anthocyanins and other phenolics in the muscadine extracts. Practical Application: The paper has provided rich information of bioactive phytochemical profiles in different solvent extracts and their correlation with the antioxidant activity in the muscadine that is a very special regional fruit in U.S. Its high content of phenolic compounds demonstrates that muscadine could be beneficial to human health.  相似文献   
48.
49.
50.
Previous NMR microimaging studies at 360 MHz have demonstrated a clear differentiation between the nucleus and cytoplasm in isolated single neurons. In particular, theT 2 of the cell nucleus is 2.5 times larger than that of the cytoplasm. In order to determine the magnitude of possibleT 2 * influences on these observations, images of single cells have been obtained at 500 MHz using spin-echo and line-narrowing sequences. Comparison of the images acquired by the two sequences, and of the spin-echo images at 360 and 500 MHz, imply that anyT 2 * contributions are relatively small. Consequently, the measuredT 2 differences in spin-echo imaging represent a true difference in theT 2 relaxation in the two cellular compartments.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号