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   28148篇
  免费   1029篇
  国内免费   34篇
电工技术   378篇
综合类   46篇
化学工业   6251篇
金属工艺   525篇
机械仪表   554篇
建筑科学   1465篇
矿业工程   100篇
能源动力   682篇
轻工业   2170篇
水利工程   241篇
石油天然气   78篇
无线电   2147篇
一般工业技术   5046篇
冶金工业   5405篇
原子能技术   268篇
自动化技术   3855篇
  2023年   237篇
  2022年   384篇
  2021年   606篇
  2020年   367篇
  2019年   468篇
  2018年   583篇
  2017年   505篇
  2016年   692篇
  2015年   603篇
  2014年   815篇
  2013年   1539篇
  2012年   1259篇
  2011年   1631篇
  2010年   1167篇
  2009年   1105篇
  2008年   1234篇
  2007年   1185篇
  2006年   1049篇
  2005年   841篇
  2004年   835篇
  2003年   739篇
  2002年   644篇
  2001年   487篇
  2000年   453篇
  1999年   502篇
  1998年   980篇
  1997年   709篇
  1996年   578篇
  1995年   489篇
  1994年   444篇
  1993年   432篇
  1992年   310篇
  1991年   240篇
  1990年   305篇
  1989年   304篇
  1988年   255篇
  1987年   270篇
  1986年   256篇
  1985年   294篇
  1984年   260篇
  1983年   257篇
  1982年   234篇
  1981年   217篇
  1980年   206篇
  1979年   225篇
  1978年   200篇
  1977年   243篇
  1976年   316篇
  1975年   188篇
  1974年   158篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
This paper highlights the role of the faculty member in recruiting students currently enrolled in B.S. programs in engineering and the sciences into full-time pursuit of a graduate-level engineering degree. The faculty member is demonstrated to be in a unique position to influence such students, providing strong counterforces to a confluence of attitudes and pressures experienced during the B.S. experience which effectively create a barrier to full-time engineering graduate study. We analyze this barrier via the method of force field analysis, and demonstrate that effective recruitment into full-time graduate study must be based on a four-fold strategy of education, expectations, improved B.S. experience and better control of the B.S. environment. Approaches to implement these strategies are discussed.  相似文献   
52.
A statistical study of the particle shape and size of pure V2O5 and TiO2, and samples of coprecipitated V2O5---TiO2 catalysts with different V/Ti ratios, has been performed. They were also characterized by XRD, EDAX, SEM and XPS. The results showed that pure vanadium pentoxide is compose by large square or needle-shaped particles, while pure titanium dioxide has small and rounded ones. VTiO samples presented an area and shape, depending on the V/Ti ratio.

These results and the spectroscopical characterization conducted to a particle model of the catalysts. Those VOTi samples with high V/Ti ratio would have large V2O5 crystals acting as support of a V/TiO2 solid solution. In contrast, those samples with a low V/Ti ratio, would have the solid solution supporting vanadium pentoxide crystals.  相似文献   

53.
54.
55.
56.
Studied Minnesota Multiphasic Personality Inventory (MMPI) profiles of 362 patients with acute and chronic low back pain (LBP) for replicable homogeneous subgroups using 3 cluster-analysis procedures. Two normal and 3 clinically elevated profile subgroups were identified. The 2 normal subgroups were characterized by relatively normal musculoskeletal condition and were least disabled but differed from each other in duration of pain, presence of physical abnormalities, and daily functioning. The most pathologic profile subgroup consisted largely of acute-pain patients whose musculoskeletal condition and daily functioning were similar to those of the normal subgroups. Patients in the 3 abnormal MMPI subgroups were exposed to more LBP physical-risk factors in the workplace. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
57.
The automation of the design of electronics has advanced greatly since the middle 1970s. The state of this development is such that additional considerations are now being incorporated into the automation process. One of the essential elements of a successful electronics design is reaching the reliability and maintainability (R&M) potential that should be achieved in any design effort. The automation of portions of the design process to address R&M must be based upon design rules that are basic to producing a reliable and maintainable system. This paper discusses a framework for considering these R&M design rules and points the developers of computer-aided engineering systems in the direction that is necessary if electronics designs are to realize their potential.  相似文献   
58.
Four sites in the Detroit River/Lake Erie western basin were evaluated for their toxicity. The evaluation was based on 1) bulk chemical characterization of the sediments, 2) chemical composition of the sediment elutriates, and 3) toxicity of the elutriates to ultraplankton and microplankton/net plankton. A sequence of decreasing contamination was determined from the chemical composition of the elutriates based on the elutriation release of metals such as Zn, Mn, Cd, Ni, and Co. Bioassessment of elutriate toxicity was determined by carbon-14 Algal Fractionation Bioassays (AFB's) which were conducted with various dilutions of standard and Chelex-100 treated elutriates. Site A (near Windsor, Ontario) and Site D (western Lake Erie) were found to be toxic to ultraplankton. The observed toxicity was attributed to the bioavailability and synergistic impact of elutriated metals on ultraplankton production. A direct relationship between the water soluble metal fraction and toxicity was observed. These results confirmed that sediment toxicity should not be evaluated solely on bulk chemical composition of the sediments. The AFB's have been proven useful in the bioassessment of sediments due to their rapidity/sensitivity and hence could be routinely used for the screening and early detection of contaminants affecting fast growing organisms which form the basis of the aquatic food chain.  相似文献   
59.
Buchbesprechung     
Ohne Zusammenfassung  相似文献   
60.
Thrombocytopenia is a major cause of morbidity following intensive chemotherapy for acute leukemia. Over recent years, there has been an increasing use of platelet transfusions which, although generally efficacious to prevent severe hemorrhage, have associated risks of transmitting blood-borne disease and of alloimmunization. Therefore, there is a clinical requirement for a drug that will reliably alleviate the thrombocytopenia associated with leukemia therapy. The c-mpl ligand thrombopoietin is the most interesting factor for the treatment of thrombocytopenia because of its lineage specificity. Phase I and II studies confirm its biological efficacy to induce rise in platelet count in patients with solid tumors and acute leukemia. Several other pleiotropic hematopoietic growth factors are also currently in clinical trials. These include interleukin-6, interleukin-3, interleukin-11, PIXY321 and stem cell factor. The effects of these cytokines appear to be modest at most and, with the exception of interleukin-11, their side effects are likely to limit their clinical application. Combinations of factors may prove more efficacious approaches to enhance platelet recovery.  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