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   241955篇
  免费   2946篇
  国内免费   424篇
电工技术   4351篇
综合类   258篇
化学工业   39553篇
金属工艺   9396篇
机械仪表   7418篇
建筑科学   5463篇
矿业工程   1396篇
能源动力   5172篇
轻工业   24872篇
水利工程   2472篇
石油天然气   5095篇
武器工业   32篇
无线电   25110篇
一般工业技术   44934篇
冶金工业   45662篇
原子能技术   5967篇
自动化技术   18174篇
  2021年   2104篇
  2019年   2022篇
  2018年   3496篇
  2017年   3434篇
  2016年   3695篇
  2015年   2243篇
  2014年   3912篇
  2013年   10236篇
  2012年   6160篇
  2011年   8332篇
  2010年   6578篇
  2009年   7284篇
  2008年   7611篇
  2007年   7743篇
  2006年   6913篇
  2005年   6069篇
  2004年   5838篇
  2003年   5629篇
  2002年   5697篇
  2001年   5584篇
  2000年   5405篇
  1999年   5336篇
  1998年   12697篇
  1997年   8983篇
  1996年   6909篇
  1995年   5358篇
  1994年   4767篇
  1993年   4657篇
  1992年   3683篇
  1991年   3399篇
  1990年   3604篇
  1989年   3481篇
  1988年   3311篇
  1987年   2912篇
  1986年   2941篇
  1985年   3387篇
  1984年   3231篇
  1983年   2900篇
  1982年   2755篇
  1981年   2832篇
  1980年   2725篇
  1979年   2634篇
  1978年   2690篇
  1977年   2956篇
  1976年   3826篇
  1975年   2373篇
  1974年   2247篇
  1973年   2378篇
  1972年   1973篇
  1971年   1858篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Neuramide (NMD), a substance found in crude preparations of porcine stomach extract, is a viral inhibitor that also has putative immunostimulatory effects. The effects of NMD on stress-hormone (ACTH and prolactin-PRL) release were assessed in in vivo and in vitro studies. In the former, blood levels of corticosterone and PRL were measured in NMD-treated male rats. In vitro experiments were performed to evaluate the effects of NMD and three of its fractions (obtained with high performance liquid chromatography) on ACTH and PRL release from perfused rat pituitary slices. NMD increased plasma corticosterone levels in vivo and produced dose-dependent increases in in vitro pituitary release of ACTH. No effects on PRL secretion were observed in vivo or in vitro. The stimulatory effects on ACTH release were caused by the NMD fraction with a molecular weight of > 5000 < 10000 Da.  相似文献   
993.
Replies to comments by H. W. Marsh and L. A. Roche (see record 1997-43129-003) on the author's article (Educational Policy Analysis Archives, 1997) on student evaluation and academic freedom. The author expresses his dismay that Marsh and Roche misrepresented (not misinterpreted) the article without documenting their misrepresentation. A documented response to this undocumented misrepresentation is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
B cell knockout mice are unable to clear a primary erythrocytic infection of Plasmodium chabaudi chabaudi. However, the early acute infection is controlled to some extent, giving rise to a chronic relapsing parasitemia that can be reduced either by drug treatment or by adoptive transfer of B cells. Similar to mice rendered B-cell deficient by lifelong treatment with anti-mu antibodies, B cell knockout mice (muMT) retain a predominant CD4+ Th1-like response to malarial antigens throughout a primary infection. This contrasts with the response seen in control C57BL/6 mice in which the CD4+ T-cell response has switched to that characteristic of Th2 cells at the later stages of infection, manifesting efficient help for specific antibodies in vitro and interleukin 4 production. Both chloroquine and adoptive transfer of immune B cells reduced parasite load. However, the adoptive transfer of B cells resulted in a Th2 response in recipient muMT mice, as indicated by a relative increase in the precursor frequency of helper cells for antibody production. These data support the idea that B cells play a role in the regulation of CD4+ T subset responses.  相似文献   
995.
996.
997.
BACKGROUND: In order to elaborate recommendations for the dietetic care of diabetic patients and other clinical disorders we have measured the concentration of carbohydrates and trace elements in a group of non alcoholic refreshments of current use in Spain. MATERIAL AND METHODS: Thirty refreshments were classified into 10 groups. Glucose and phosphate were measured by hexokinase and reduction of phospho-molybdate methods respectively in an autoanalyzer Dax-72. Glucose and fructose were analyzed by cellulose thin-layer chromatography; glucose, fructose and sucrose by gas chromatographys. Sodium and potassium by emission spectrophotometry and calcium, magnesium, iron, copper and zinc by atomic absorption spectrophotometry. RESULTS: Light refreshments and soft drinks have no carbohydrates. Isotonic beverages, fruit juices, cool tea and non alcoholic beers had less than 10 g/dl. Tonic waters, Fanta, different coles, non alcoholic bitter and others had more than 10 g/dl. Sodium levels between 15-20 mEq/l were found in the isotonic beverages and 7-Up and levels of 7 mEq/l in the others. Potassium values between 15-40 mEq/l were found in the fruit juices, 3-4 mEq/l in Gatorade and less than 1 mEq/l in the others. CONCLUSIONS: Light refreshments and soft drinks contain low concentrations of carbohydrates and sodium. Fruit juices have high potassium concentration. Such information can be especially useful for dietetic care of diabetic patients.  相似文献   
998.
The Norwegian Societies of Thoracic Medicine and Occupational Medicine established a working group to standardise diagnostic procedures and evaluation of work-related respiratory disorders. In cases of suspected work-related diseases the physician may be asked by the National Insurance Administration or an insurance company to make a statement which will be one of the documents used to decide the patient's right to compensation benefit. We discuss the role of the physician as an independent expert. This is different from his role as clinician. The statement should include a balanced presentation of information from different sources, including health and occupational history, and the employer's information about the work environment (quantitative and qualitative exposure data). The statement must also include the results of a clinical examination and an assessment of functional status based on objective tests. The paper contains recommendations for evaluation of permanent impairment in light of the present Norwegian laws and regulations.  相似文献   
999.
Novolac-type polycondensation of benzaldehyde (B) and pyrogallol (P) has been carried out at 60°C, 75°C and 90°C and at B/P mole ratios of 1.5 and 3.0 using phosphoric acid as catalyst. The reaction follows a 2nd order rate law. By using GC consumption data of benzaldehyde and pyrogallol, kinetic parameters such as the overall rate constants, activation energies (Ea) and logA values are investigated. The activation energies for 1.5 and 3.0 B/P mole ratios are found as 62.3 kJ mol?1 and 56.4 kJ mol?1, respectively. The molecular weights of the resins determined by measuring intrinsic viscosities (25°C, THF) are in the range of 0.03 to 0.07 dL g?1 at various temperatures and B/P mole ratios.  相似文献   
1000.
Reported is an attempt to attain orientation of macromolecules during extrusion of films of cellulose derivatives that led to the liquid-crystalline state of a polymer and resulted in enhanced film strength.  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