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   206122篇
  免费   2339篇
  国内免费   565篇
电工技术   3517篇
综合类   141篇
化学工业   31845篇
金属工艺   10274篇
机械仪表   7015篇
建筑科学   3994篇
矿业工程   2161篇
能源动力   4642篇
轻工业   12882篇
水利工程   2923篇
石油天然气   7726篇
武器工业   22篇
无线电   21512篇
一般工业技术   45183篇
冶金工业   34444篇
原子能技术   6621篇
自动化技术   14124篇
  2021年   2052篇
  2019年   1999篇
  2018年   3678篇
  2017年   3719篇
  2016年   3998篇
  2015年   2232篇
  2014年   3784篇
  2013年   8744篇
  2012年   5681篇
  2011年   7218篇
  2010年   5859篇
  2009年   6492篇
  2008年   6618篇
  2007年   6495篇
  2006年   5574篇
  2005年   5118篇
  2004年   4630篇
  2003年   4555篇
  2002年   4366篇
  2001年   4474篇
  2000年   4188篇
  1999年   4204篇
  1998年   10213篇
  1997年   7194篇
  1996年   5510篇
  1995年   4134篇
  1994年   3600篇
  1993年   3842篇
  1992年   2983篇
  1991年   2998篇
  1990年   2891篇
  1989年   2852篇
  1988年   2867篇
  1987年   2511篇
  1986年   2572篇
  1985年   2855篇
  1984年   2688篇
  1983年   2555篇
  1982年   2300篇
  1981年   2270篇
  1980年   2345篇
  1979年   2359篇
  1978年   2383篇
  1977年   2488篇
  1976年   2881篇
  1975年   2188篇
  1974年   2068篇
  1973年   2167篇
  1972年   1941篇
  1971年   1755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
To determine whether a 3-week hepatitis B (HB) vaccination could achieve protective immunity, 89 healthy non-immunized young adults received three doses of 20 micrograms each of HBs antigen (GenHevac B, Pasteur) and were randomly assigned to schedule A (n = 44): two doses at day 0, one dose at day 21; or schedule B (n = 45): one dose at days 0, 10 and 21. Seroprotection rates (anti-HBs > or = 10 mIU ml-1) for groups A and B respectively were: 23 and 40% at day 21; and 77 and 91% at day 82 (not significant). Anti-HBs geometric mean titres were higher in group B than in group A (p < 0.05) at days 21 (6.4 versus 3.8) and 82 (77.6 versus 33.5). One year after primary vaccination, the seroprotection rate remained as high as 90% in the vaccinees of group B; after boosting all vaccinees had protective levels of anti-HBs antibodies. Thus 3-week HB vaccination with GenHevac B allowed early and durable protective immunity.  相似文献   
992.
Insulin solution (25 U/ml/kg, pH 8.0) was administered with 50 mM of various C8-Cl8 fatty acid and derivative absorption enhancers to the duodenum, colon and rectum of fasted normal rats under sodium pentobarbital anesthesia. Solutions were administered directly into ligated or sealed intestinal segments. Blood was sampled periodically from the jugular vein and blood glucose levels determined. The maximum decrease in blood glucose level and area under the depression curve were used to estimate bioavailability. Enhancing effects rectally were further investigated in streptozotocin-induced diabetic rats in both the fasted and non-fasted states. Blood glucose levels and serum insulin concentrations were determined.  相似文献   
993.
1. We characterized the endothelial cell-derived growth factors of SHRSP and Wistar Kyoto rats (WKY), respectively and found that platelet-derived growth factor (PDGF)-B chain related growth factor constituted a major portion of the mitogenic activity of the conditioned media of endothelial cells from both animals. There were no remarkable qualitative differences between the endothelial cell-derived growth factors of SHRSP and WKY. 2. Northern analysis revealed that the expression of PDGF-B chain was 2-4-fold enhanced in cultured aortic endothelial cells of SHRSP. This enhanced expression of PDGF-B chain, which may be induced under chronic hypertensive conditions, is suggested to contribute to the increase in endothelial cell-derived growth factors reported in this animal.  相似文献   
994.
995.
Gastroesophageal reflux disease (GERD) is a disease with serious consequences that may result in significant impairment in quality of life and disease morbidity. Across all grades of severity of symptoms and severity of underlying esophageal disease, proton pump inhibitors (PPIs) provide therapeutic gains over prokinetics (PKs) or H2 receptor antagonists (H2RAs). The potential cost effectiveness of using medications with higher acquisition costs that may lower health care costs overall is often disregarded when conducting cost comparisons with medications having lower 'up-front' costs. Limiting therapy to less effective agents condemns many patients to protracted suffering, repeated physician visits and needless reinvestigation of symptoms that could have been resolved by appropriate initial therapy. Based on current data, use of any classification of symptom severity as a basis for selecting one class of therapeutic agents over another for first line therapy (i.e. PKs, H2RAs for 'mild' GERD, versus a PPI for 'severe' disease) is unwarranted.  相似文献   
996.
997.
The properties of glasses of the lithium-aluminoborosilicate system were investigated, namely, the density, spreadability, thermal expansion, and nature of crystallized phases at various temperatures. A crystal-optical analysis was conducted. The glasses were used to prepare abrasive compositions. Their strength properties were studied as a function of the composition of the glass binder and the regime of heat treatment.Translated from Steklo i Keramika, No. 3, pp. 27–30, March, 1996.  相似文献   
998.
The results of a thermal engineering analysis of a bath furnace heated by natural gas with the surface area of the melting part equal to 303.3 m2 and equipped with six pairs of burners are presented. Practical recommendations are given for increasing the efficiency of the furnace. The data can be used for developing a mathematical model of heat transfer in a glass furnace.Translated from Steklo i Keramika, No. 3, pp. 9–11, March, 1996.  相似文献   
999.
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 71–86, May–June, 1995.  相似文献   
1000.
A series of vanadium-tin mixed oxide catalysts have been prepared by the solid-state reaction of V2O5 and SnO2 at 1250°C. The fresh and the used catalysts have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). High temperature oxygen chemisorption (HTOC) has been employed to titrate the coordinatively unsaturated vanadia sites. Ammoxidation of mesitylene has been carried out on these catalysts and an optimum composition of vanadium is arrived at. Better yields of tricyanobenzene (TCB) compared to literature values are obtained. A good correlation between the oxygen uptake and the TCB yield extends the applicability of HTOC to the fused oxide system.IICT Communication No. 3507.  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