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   4435篇
  免费   31篇
  国内免费   3篇
电工技术   20篇
综合类   3篇
化学工业   194篇
金属工艺   43篇
机械仪表   34篇
建筑科学   28篇
矿业工程   1篇
能源动力   113篇
轻工业   85篇
水利工程   21篇
石油天然气   1篇
无线电   136篇
一般工业技术   330篇
冶金工业   3305篇
原子能技术   11篇
自动化技术   144篇
  2021年   23篇
  2020年   9篇
  2019年   9篇
  2018年   25篇
  2017年   25篇
  2016年   31篇
  2015年   16篇
  2014年   27篇
  2013年   68篇
  2012年   50篇
  2011年   50篇
  2010年   42篇
  2009年   42篇
  2008年   31篇
  2007年   37篇
  2006年   43篇
  2005年   29篇
  2004年   28篇
  2003年   21篇
  2002年   22篇
  2001年   21篇
  2000年   24篇
  1999年   148篇
  1998年   1090篇
  1997年   674篇
  1996年   408篇
  1995年   249篇
  1994年   180篇
  1993年   226篇
  1992年   42篇
  1991年   52篇
  1990年   35篇
  1989年   40篇
  1988年   40篇
  1987年   40篇
  1986年   37篇
  1985年   44篇
  1984年   22篇
  1983年   32篇
  1982年   34篇
  1981年   33篇
  1980年   36篇
  1979年   15篇
  1978年   20篇
  1977年   81篇
  1976年   143篇
  1975年   9篇
  1974年   15篇
  1973年   8篇
  1955年   6篇
排序方式: 共有4469条查询结果,搜索用时 0 毫秒
31.
It is widely believed that hyper elliptic curve cryptosystems (HECCs) are not attractive for wireless sensor network because of their complexity compared with systems based on lower genera, especially elliptic curves. Our contribution shows that for low cost security applications HECs cryptosystems can outperform elliptic curve cryptosystems. The aim of this paper is to propose a discrete logarithm problem‐based lightweight secure communication system using HEC. We propose this for different genus curves over varied prime fields performing a full scale study of their adaptability to various types of constrained networks. Also, we propose to evaluate the performance of the protocol for computational times with respect to different genus for main operations like Jacobian, Divisor identifications, key generation, signature generation/verification, message encryption, and decryption by changing the size of the field. A formal security model was established based on the hardness of HEC‐Decision Diffie‐Hellman (HEC‐DDH). Finally, a comparative analysis with ECC‐based cryptosystems was made, and satisfactory results were obtained.  相似文献   
32.
Indian borage (Plectranthus amboinicus) was investigated for antifungal activity through agar well diffusion assay. Indian borage oil (IBO) was found to be effective against various fungi tested, as it inhibited the radial growth of mycelia and exhibited broad fungitoxic properties against Aspergillus flavus, Aspergillus niger, Aspergillus ochraceus CFR 221, Aspergillus oryzae, Candida versatilis, Fusarium sp. GF-1019, Penicillium sp., and Saccharomyces cerevisiae. The effective concentration of IBO on the growth of A. ochraceus in yeast extract sucrose medium was determined. IBO completely inhibited ochratoxin (OTA) production by the toxigenic strain A. ochraceus at 500 ppm. Also, the application of IBO at 100 mg/g in food samples resulted in inhibition of the growth of A. ochraceus in food systems such as groundnut, maize and poultry feed and no detectable amount of OTA was found at a high moisture level of 30%, even after seven days. IBO has the potential for use as a botanical fungitoxicant against fungal attack in stored food commodities.  相似文献   
33.
Eleven substituted 4-biphenylylalkyl carboxylic acids and three methyl esters were synthesized and assayed for inhibition of rat liver beta-hydroxy-beta-methylglutaryl coenzyme A reductase. Five of the acids were analogs, resulting from various isosteric replacements of the carbonyl and ether oxygens of the previously described reversible inhibitor 1-(4-biphenylyl)pentyl hydrogen succinate. No significant change in activity was noted, except upon introduction of an amide linkage where a decrease in inhibition was found. Six carboxylic acids and three methyl esters, all containing the 4-biphenylyl radical but lacking the n-butyl side chain found in 1-(4-biphenylyl)pentyl hydrogen succinate, also were inhibitors of the reductase.  相似文献   
34.
Comparative studies of cefamandole and cephalothin were carried out in 32 cancer patients. After rapid intravenous injection of 1 gm cefamandole or cephalothin, the peak mean serum concentrations in 11 patients achieved at 0.25 hr were 103.4 mcg/ml and 56.7 mcg/ml, respectively. Except at 6 hr, the serum concentration of cefamandole was higher (p less than 0.05) at all times. The terminal half-lives (t 1/2) were similar, being 1.2 hr for cefamandole and 1.0 hr for cephalothin. Cefamandole, 1 gm intramuscularly, induced a peak mean serum concentration of 26.6 mcg/ml at 1 hr, with a slow decay. Intermittent cefamandole (2 gm intravenously every 6 hr) induced very high mean serum concentrations (7 patients), but at 4 hr the concentrations were similar to those after 1 gm intravenously. Per cent of urinary excretion was similar for both drugs regardless of dose and mode of administration. Continuous-infusion cefamandole or cephalothin (2 gm loading followed by 2 gm every 6 hr) in 14 patients showed consistently higher serum concentrations for cefamandole (p less than 0.05) over a 5-day period. There was no evidence of drug accumulation in the multiple-dose studies. Both the single- and multiple-dose schedules were well tolerated.  相似文献   
35.
A review of 22,971 pregnancies from 1969-74 reveals that the reasons for requesting excretory urography were renal colic of pregnancy 11, pyelonephritis 8, renal contusion 2, threatened abortion 1, and suspected degeneration of fibroid 1. The final diagnoses were similar except that two patients with torsion of ovarian cysts and a renal calculus were discovered. The only intravenous pyelographic examination that was decisive for diagnosis was in a patient with a ureteric calculus. Careful clinical correlation should reduce excretory urography during pregnancy.  相似文献   
36.
An infant with a typical Edwards syndrome and a modal chromosome number of 46 is reported. In all cells analyzed one chromosome G was missing and an additional chromosome similar to a pair No. 16 was present. The phenotype of the child indicates that the extra element is a translocation between G and 18 chromosomes as in one case described previously.  相似文献   
37.
Change in pulmonary venous admixture with varying inspired oxygen   总被引:1,自引:0,他引:1  
Pulmonary venous admixture (Qsp/Qt) was analyzed as a function of fractional concentration of inspired O2 (FIO2) in 30 patients who required postoperative mechanical ventilation. Pulmonary and radial artery blood-gas tensions and pH were measured and Qsp/Qt was calculated with FIO2 ranging from 0.21 to 1. In all patients, Qsp/Qt decreased when FIO2 was increased from 0.21 to 0.4 and then stabilized to an FIO2 of approximately 0.6. As the FIO2 was increased to 1, Qsp/Qt increased. Since the inhalation of gas mixture with FIO2 greater than or equal to 0.6 increased right-to-left intrapulmonary shunting of blood, we recommend respiratory function be evaluated during inhalation of a clinically useful concentration of O2 rather than at an FIO2 of 1.  相似文献   
38.
Phagocytic cells were obtained from children at ages comparable to those at which the disease is most commonly seen during pregnancy. The effect of P-HCl on the phagocytic action of these cells on opsonized red blood cells was studied in vitro.  相似文献   
39.
To study the mechanism of action by which droperidol exerts a negative chronotropic effect, 3 series of experiments were performed: a) on isolated right atria of rabbits, b) on the isolated vas deferens of guinea-pigs and c) by injecting the drug directly into the sinus node artery of anesthetized dogs. Isolated tissue results include: lack of cholinergic action or beta-adrenergic antagonism: a calcium ion flux interference could not be demonstrated. Alpha adrenergic antagonism of the drug (pA2) was ascertained in the vas deferens. Injections of droperidol in the sinus node artery caused a negative chrontropic effect proportional to the dose and arrest ensued with the largest dose followed by His escape rhythm. Droperidol could not inhibit isoproterenol or dopamine-induced tachycardia and showed similar negative chronotropism in vagotomized and atropinized dogs. Negative chronotropic effects of the drug appear to be caused by an exit blockade of sinus impulses.  相似文献   
40.
From measurements of maximum and minimum motor nerve propagation velocity and neuronal excitability we conclude that there is a functional loss of motor units and distal nerve "dying back" in persons affected with unilateral acute cerebral vascular lesions. The study also suggests that transynaptic degeneration affects the lower motor neurone function on both sides.  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