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   12551篇
  免费   508篇
  国内免费   294篇
电工技术   532篇
综合类   355篇
化学工业   1276篇
金属工艺   490篇
机械仪表   425篇
建筑科学   411篇
矿业工程   185篇
能源动力   174篇
轻工业   1090篇
水利工程   133篇
石油天然气   132篇
武器工业   83篇
无线电   1064篇
一般工业技术   1248篇
冶金工业   4391篇
原子能技术   184篇
自动化技术   1180篇
  2023年   76篇
  2022年   165篇
  2021年   232篇
  2020年   167篇
  2019年   153篇
  2018年   138篇
  2017年   171篇
  2016年   174篇
  2015年   192篇
  2014年   270篇
  2013年   443篇
  2012年   515篇
  2011年   562篇
  2010年   503篇
  2009年   480篇
  2008年   511篇
  2007年   530篇
  2006年   436篇
  2005年   370篇
  2004年   309篇
  2003年   245篇
  2002年   198篇
  2001年   205篇
  2000年   210篇
  1999年   256篇
  1998年   1077篇
  1997年   667篇
  1996年   511篇
  1995年   313篇
  1994年   286篇
  1993年   320篇
  1992年   154篇
  1991年   156篇
  1990年   149篇
  1989年   168篇
  1988年   150篇
  1987年   118篇
  1986年   139篇
  1985年   124篇
  1984年   88篇
  1983年   90篇
  1982年   84篇
  1981年   71篇
  1980年   71篇
  1979年   79篇
  1978年   80篇
  1977年   157篇
  1976年   262篇
  1975年   61篇
  1974年   56篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
以双酚A型环氧树脂为主要成膜物质,以氮化硼为功能填料,以丁醇醚化脲醛树脂为固化剂,并添加己二酸聚酯弹性体树脂改善其柔韧性、提高涂膜的机械性能,最终得到附着力强、耐热性好、隔热作用明显的飞机发动机叶片用防护涂料.  相似文献   
32.
The reaction of dimethyl maleate and some related dienophiles with vegetable oils under pressure has been studied successfully. When safflower oil reacts with 100% excess maleate, sulfur dioxide catalyst, and hydroquinone inhibitor at 290° for 1hr., 80 to 90% yields of adduct fraction, based on linoleate, are obtained. Under the same conditions almost equally good yields result with either linseed or soybean oils. With safflower oil, dimethyl fumarate gave slightly lower yields. Di-n-butyl maleate gave even poorer yields, and much residue was formed. Paper II in a series entitled, “Reactions of Dienophiles with Vegetable Oils”. Presented at annual meeting, American Oil Chemists' Society, St. Louis, Mo., May 1–3, 1961. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.  相似文献   
33.
Protein, total phospholipid, phosphatidyl cholines and phosphatidyl choline fractions from liver mitochondria and microsomes of female rats were analyzed after treatment with CCl4 (0.3 ml of CCl4 suspended in corn oil) or ethionine (50 mg in 0.9% saline) or after feeding a choline deficient, low protein diet for seven days. Phosphatidyl cholines were separated into four fractions differing in the degree of fatty acid unsaturation. Over 50% of total phosphatidyl choline phosphorus was present in fraction 3 of liver mitochondria and microsomes. The major fatty acid in fraction 1 was docosahexaenoic acid. Fraction 4 contains oleic and linoleic acids. Arachidonic acid occurs in fraction 2 and 3. Ethionine decreased the amount of microsomal protein and phosphatidyl choline fraction 1 of mitochondria. Microsomal protein was decreased by CCl4. The choline deficient, low protein diet caused a decrease in mitochondrial and microsomal phospholipids. The amount of the mitochondrial phosphatidyl choline decreased. Corn oil increased the level of phosphatidyl choline fraction 3. Choline deficiency decreased the amount of phosphatidyl choline fraction 3, increased fraction 4 of mitochondria and microsomes and increased fraction 1 of microsomes.  相似文献   
34.
Saturated fluorocarbon elastomers are very resistant to chemical reactions, including those of a crosslinking nature. In order to study proper methods of preparing these materials, Viton GLT was mixed with various levels of trimethylol propane trimethacrylate, TMPTM, and triallyl isocyanurate, Diak #7. After molding, the materials were subjected to electron beam irradiation. The glass transition, rubbery modulus, viscoelastic behavior, and equilibrium swelling were used to characterize the materials as a function of crosslinker and irradiation level. In general, the modulus and gel fraction increased with both crosslinker content and irradiation level. Mixtures of both crosslinking monomers produced an unexpected synergism, yielding higher tensile strength, and earlier onset of gelation.  相似文献   
35.
Moderate or intense low oxygen dilution(MILD)combustion plays a significant role in the mitigation of combustion-generated pollutants and greenhouse gases whilst meeting thermal efficiency needs.However,due to the lack of the fundamental knowledge on this combustion,there is a misconception that MILD combustion should be established by high preheating of the air,which has limited its application.Our research and development on this combustion has been performed for several years. We have found that the requ...  相似文献   
36.
窄带滤光片是应用于光谱学、激光、天文物理学、通信等各个领域的光学组件,精确控制每一层膜厚是制备滤光片的困难所在.采用光学极值法直接监控工件,可以同时制备多件滤光片.设计了监控光路和信号获得电路,通过探测到的测试信号,监控薄膜膜厚,实现了直接监控.  相似文献   
37.
An experimental study of the gas-dynamic aspects of the high-velocity oxyfuel (HVOF) thermal spray process has been performed using commercially available HVOF equipment (Hobart-Tafa JP-5000, Ho-bart-Tafa Technologies, Inc., Concord, NH). Optical diagnostic techniques, including microsecond-expo-sure schlieren and shadowgraph imaging, were applied to visualize the hot supersonic jet produced by this equipment without particle injection. Rapid turbulent mixing of the jet with the surrounding atmos-phere was observed, which is an issue of concern in coating quality due to the possibility of oxidation of sprayed particles. This mixing appears to be a function of the ratio of densities of the hot jet and the cold atmosphere as well as a function of the velocity of the jet, rather than one of combustion-chamber pres-sure or barrel length. The supersonic core of the HVOF jet dissipates rapidly due to the mixing, so that the jet is no longer supersonic when it impinges on the target surface being sprayed. Secondary issues also observed in this study include strong jet-noise radiation from the HVOF plume and the entrainment and induced bulk motion of the surrounding air.  相似文献   
38.
Academic librarians have shared their experiences with tablet computers, but few examine how librarians use tablets in their instruction design. While the education literature provides technology integration models, the nature of library instruction requires adapting these models to the library classroom. After reviewing literature related to tablets in library instruction and a number of technology integration frameworks, this article demonstrates an application of the Substitution, Augmentation, Modification, Redefinition framework to analyze observations of an iPad-equipped classroom at a university library. Demonstrating this use of a framework provides an approach to technology integration and continues the discussion about tablets’ potential to promote innovative pedagogy.  相似文献   
39.
Although Hodgkin's disease is considered one of the "curable" cancers, the high cure rates associated with this disease are not accomplished without risk of potentially severe, immediate, and late side effects. Because the predominant histologic subtype of Hodgkin's disease found in the United States generally affects the 15- to 25-year-old age group, the disease, its treatment, and the side effects of treatment will affect many women of childbearing age. The treatment and its effects on the patient and offspring, including posttreatment fertility, are key issues for perinatal nurses.  相似文献   
40.
Intravenous infusion of mice with viable allogeneic lymphocytes can produce donor-specific enhancement of skin graft survival, but only if the injected lymphocytes can persist in the host's recirculating lymphocyte pool for at least 3 days. We have investigated the relative roles of class I and class II MHC for C57BL/6 mice infused with lymphoid cells from co-isogenic strains mutated at class I MHC (bm1) or class II MHC (bm12), and for A.TH lymphoid cells infused into C3H (class I different, class II identical) or A.TH (class II different, class I identical). Injected cells differing from the host at class I MHC, but not at class II MHC, can be rapidly removed by host natural immune mechanisms (probably NK cells). Persistence is favored if the injected cells also carry host class I MHC, i.e., tolerance is more readily induced by injecting F1 (A x B) into A rather than B into A, consistent with the "missing self" hypothesis of NK recognition, with class I MHC being the relevant self-marker. Injected cells differing from the host at class II MHC but not at class I MHC always persist for at least 3 days, even when class I-different cells are being actively removed.  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