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   683篇
  免费   24篇
电工技术   12篇
综合类   1篇
化学工业   130篇
金属工艺   5篇
机械仪表   17篇
建筑科学   14篇
矿业工程   3篇
能源动力   17篇
轻工业   125篇
水利工程   1篇
石油天然气   3篇
无线电   36篇
一般工业技术   104篇
冶金工业   152篇
原子能技术   6篇
自动化技术   81篇
  2023年   12篇
  2022年   8篇
  2021年   16篇
  2020年   17篇
  2019年   15篇
  2018年   11篇
  2017年   12篇
  2016年   11篇
  2015年   12篇
  2014年   19篇
  2013年   31篇
  2012年   34篇
  2011年   35篇
  2010年   25篇
  2009年   37篇
  2008年   19篇
  2007年   27篇
  2006年   26篇
  2005年   25篇
  2004年   15篇
  2003年   8篇
  2002年   8篇
  1998年   38篇
  1997年   17篇
  1996年   17篇
  1995年   13篇
  1994年   6篇
  1993年   15篇
  1992年   4篇
  1991年   6篇
  1990年   5篇
  1987年   4篇
  1986年   7篇
  1985年   10篇
  1983年   10篇
  1981年   8篇
  1976年   9篇
  1975年   3篇
  1974年   8篇
  1973年   12篇
  1971年   4篇
  1970年   7篇
  1969年   7篇
  1968年   5篇
  1967年   7篇
  1966年   5篇
  1963年   3篇
  1961年   4篇
  1960年   5篇
  1958年   7篇
排序方式: 共有707条查询结果,搜索用时 31 毫秒
51.
This paper focuses on the design of an effective method that computes the measure of circularity of a part of a digital boundary. An existing circularity measure of a set of discrete points, which is used in computational metrology, is extended to the case of parts of digital boundaries. From a single digital boundary, two sets of points are extracted so that the circularity measure computed from these sets is representative of the circularity of the digital boundary. Therefore, the computation consists of two steps. First, the inner and outer sets of points are extracted from the input part of a digital boundary using digital geometry tools. Next, the circularity measure of these sets is computed using classical tools of computational geometry. It is proved that the algorithm is linear in time in the case of convex parts thanks to the specificity of digital data, and is in O(nlogn) otherwise. Experiments done on synthetic and real images illustrate the interest of the properties of the circularity measure.  相似文献   
52.
Ohne Zusammenfassung  相似文献   
53.
54.
Composition, shape factor, size, and fractal dimension of soot aerosol particles generated in a propane/O2, flame were determined as a function of the fuel equivalence ratio (φ). Soot particles were first size-selected by a differential mobility analyzer (DMA) and then analyzed by an Aerodyne aerosol mass spectrometer (AMS). The DMA provides particles of known mobility diameter (dm ). The AMS quantitatively measures the mass spectrum of the nonrefractory components of the particles and also provides the vacuum aerodynamic diam eter (dva ) corresponding to the particles of known mobility diameter. The measured dm, dva , and nonrefractory composition are used in a system of equations based on the formulation presented in the companion article to estimate the particle dynamic shape factor, total mass, and black carbon (BC) content. Fractal dimension was estimated based on the mass-mobility relationship. Two types of soot particles were observed depending on the fuel equivalence ratio. Type 1: for φ < 4 (lower propane/O2), dva ; was nearly constant and independent of dm . The value of dva increased with increasing φ. Analysis of the governing equations showed that these particles were highly irregular (likely fractal aggregates), with a dynamic shape factor that increased with dm and φ. The fractal dimension of these particles was approximately 1.7. These particles were composed mostly of BC, with the organic carbon content increasing as φ increased. At φ = 1.85, the particles were about 90% BC, 5% PAH, and 5% aliphatic hydrocarbon (particle density = 1.80 g/cm3). Type 2: for φ > 4 (high propane/O2), dva was linearly proportional to dm . Analysis of the governing equations showed that these particles were nearly spherical (likely compact aggregates), with a dynamic shape factor of 1.1 (versus 1 for a sphere) and a fr actal dimension of 2.95 (3 for a sphere). These particles were composed of about 50% PAH, 45% BC, and 5% aliphatic hydrocarbons (particle density = 1.50 g/cm3). These results help interpret some measurement s obtained in recent field studies.  相似文献   
55.
56.
PURPOSE: To compare outcomes of bone marrow transplants for leukemia from HLA-identical siblings, haploidentical HLA-mismatched relatives, and HLA-matched and mismatched unrelated donors. PATIENTS: A total of 2,055 recipients of allogeneic bone marrow transplants for chronic myelogenous leukemia (CML), acute myelogenous leukemia (AML), and acute lymphoblastic leukemia (ALL) were entered onto the study. Transplants were performed between 1985 and 1991 and reported to the International Bone Marrow Transplant Registry (IBMTR). Donors were HLA-identical siblings (n = 1,224); haploidentical relatives mismatched for one (n = 238) or two (n = 102) HLA-A, -B, or -DR antigens; or unrelated persons who were HLA-matched (n = 383) or mismatched for one HLA-A, -B, or -DR antigen (n = 108). HLA typing was performed using serologic techniques. RESULTS: Transplant-related mortality was significantly higher after alternative donor transplants than after HLA-identical sibling transplants. Among patients with early leukemia (CML in chronic phase or acute leukemia in first remission), 3-year transplant-related mortality (+/-SE) was 21% +/- 2% after HLA-identical sibling transplants and greater than 50% after all types of alternative donor transplants studied. Among patients with early leukemia, relative risks of treatment failure (inverse of leukemia-free survival), using HLA-identical sibling transplants as the reference group, were 2.43 (P < .0001) with 1-HLA-antigen-mismatched related donors, 3.79 (P < .0001) with 2-HLA-antigen-mismatched related donors, 2.11 (P < .0001) with HLA-matched unrelated donors, and 3.33 (P < .0001) with 1-HLA-antigen-mismatched unrelated donors. For patients with more advanced leukemia, differences in treatment failure were less striking: 1-HLA-antigen-mismatched relatives, 1.22 (P = not significant [NS]); 2-HLA-antigen-mismatched relatives, 1.81 (P < .0001); HLA-matched unrelated donors, 1.39 (P = .002); and 1-HLA-antigen-mismatched unrelated donors, 1.63 (P = .002). CONCLUSION: Although transplants from alternative donors are effective in some patients with leukemia, treatment failure is higher than after HLA-identical sibling transplants. Outcome depends on leukemia state, donor-recipient relationship, and degree of HLA matching. In early leukemia, alternative donor transplants have a more than twofold increased risk of treatment failure compared with HLA-identical sibling transplants. This difference is less in advanced leukemia.  相似文献   
57.
Infection with Helicobacter pylori is associated with the development of gastric cancer. To study whether the infection with H. pylori strains expressing the vacuolating cytotoxin (VacA) and/or the cytotoxin-associated protein (CagA) is associated with an increased risk of developing gastric adenocarcinoma, sera of 90 patients with gastric cancer and 90 matched controls with cardiovascular diseases were investigated for the presence of antibodies to VacA and CagA by immunoblot. Although no significant difference in the overall H. pylori seropositivity was found between cancer patients and controls, antibodies against VacA or CagA were significantly more frequent in cancer patients than in control subjects. Seventy-five (97.4%) of 77 H. pylori-positive patients in the cancer group, but only 60 (84.5%) of 71 H pylori-positive control patients had antibodies against either VacA or CagA (chi 2 = 6.63; relative risk, 2.00; 95% confidence interval, 1.18-3.39; P = 0.01). The presence of antibodies against VacA or CagA alone was also associated with an increased cancer risk (92.2% vs 80.3%; chi 2 = 5.30; relative risk, 1.74; 95% confidence interval, 1.08-2.78; P = 0.021, for VacA; and 87.0% vs 74.6%; chi 2 = 4.90; relative risk, 1.61; 95% confidence interval, 1.06-2.45; P = 0.037, for CagA). The relative risk for gastric cancer was mainly elevated in patients under 65 years, but not in patients at or over 65 years. There is evidence that infection with VacA- or CagA-producing H. pylori strains increases the risk of developing gastric cancer, especially in younger patients.  相似文献   
58.
We describe a new high voltage power supply, developed for the leadglass calorimeter of the WA98 experiment at CERN. The high voltage is produced for each of the 10 080 photomultiplier tubes of the detector individually, by the same number of active bases with on-board Greinacher voltage multipliers. The full VME-based HV controller system, which addresses each base via bus cables once per second, is miniaturized and fits into a single VME crate. The main advantages of this approach are the low heat dissipation, the considerably reduced amount of cabling and cost, as well as the high stability and low noise of the system.  相似文献   
59.
Pulsed power is a technology that is suited to drive electrical loads requiring very large power pulses in short bursts (high-peak power). Certain applications require technology that can be deployed in small spaces under stressful environments, e.g., on a ship, vehicle, or aircraft. In 2001, the U.S. Department of Defense (DoD) launched a long-range (five-year) Multidisciplinary University Research Initiative (MURI) to study fundamental issues for compact pulsed power. This research program is endeavoring to: 1) introduce new materials for use in pulsed power systems; 2) examine alternative topologies for compact pulse generation; 3) study pulsed power switches, including pseudospark switches; and 4) investigate the basic physics related to the generation of pulsed power, such as the behavior of liquid dielectrics under intense electric field conditions. Furthermore, the integration of all of these building blocks is impacted by system architecture (how things are put together). This paper reviews the advances put forth to date by the researchers in this program and will assess the potential impact for future development of compact pulsed power systems.  相似文献   
60.
Lithium containing silicon carbonitride ceramics (SiCN:Li) were synthesized via precursor-to-ceramic-transformation of Li-containing (poly)silazanes. The precursors were obtained by lithiation of the model compound 2,4,6-trimethyl-2,4,6-trivinylcyclotrisilazane and of a commercial poly(organosilazane) VL20® with n-butyllithium in different molar ratios. According to Raman spectroscopic measurements, lithiation takes place at the NH groups of the molecular organosilazane structure. If the amount of n-BuLi exceeds the stoichiometric amount of NH groups, addition of n-BuLi at the vinyl groups (attached as substituents at the Si atoms of the silazane) occurs. Thermal analysis coupled with in situ mass spectrometry evidenced the loss of methane and hydrogen as the main gaseous by-products formed during the precursor-to-ceramic-transformation. The ceramization process is completed at 1100 °C in argon and yielded Li-containing silicon carbonitride, SiCN:Li. X-ray powder diffraction revealed that the resulting SiCN:Li ceramics were basically amorphous and contained LiSi2N3 as a crystalline phase with increasing amount of Li. Possible applications of the new SiCN:Li ceramics are seen in the field of Li-ion batteries as alternative anode or solid electrolyte material.  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