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   729篇
  免费   11篇
  国内免费   1篇
电工技术   6篇
化学工业   165篇
金属工艺   3篇
机械仪表   16篇
建筑科学   22篇
矿业工程   1篇
能源动力   13篇
轻工业   61篇
水利工程   5篇
无线电   95篇
一般工业技术   117篇
冶金工业   171篇
原子能技术   5篇
自动化技术   61篇
  2023年   6篇
  2022年   18篇
  2021年   21篇
  2020年   10篇
  2018年   7篇
  2017年   8篇
  2016年   9篇
  2015年   11篇
  2014年   10篇
  2013年   37篇
  2012年   19篇
  2011年   26篇
  2010年   21篇
  2009年   22篇
  2008年   37篇
  2007年   21篇
  2006年   24篇
  2005年   15篇
  2004年   23篇
  2003年   13篇
  2002年   9篇
  2001年   10篇
  2000年   22篇
  1999年   17篇
  1998年   69篇
  1997年   36篇
  1996年   22篇
  1995年   29篇
  1994年   9篇
  1993年   18篇
  1992年   14篇
  1991年   4篇
  1990年   4篇
  1988年   5篇
  1987年   5篇
  1986年   6篇
  1985年   5篇
  1984年   7篇
  1983年   6篇
  1982年   6篇
  1981年   9篇
  1980年   3篇
  1979年   12篇
  1978年   6篇
  1977年   3篇
  1976年   10篇
  1975年   3篇
  1974年   5篇
  1965年   4篇
  1957年   2篇
排序方式: 共有741条查询结果,搜索用时 15 毫秒
1.
2.
The short contact time dissolution of vitrinite and inertinite concentrates of an Australian bituminous coal was studied under isothermal conditions with tetralin as solvent. The reactivity of the two maceral types and the yields and nature of the products were determined for a range of reaction temperatures (400, 420 and 440 °C) and reaction times (2–20 min). The dissolution of vitrinite proceeded at a significantly greater rate than for inertinite and was associated with greater selectivity to soluble non-gaseous products. At very short reaction times (2 min), the vitrinite underwent solubilizing reactions to yield products of higher molecular weight and greater oxygen functionality than was the case for inertinite, for which changes in the chemical nature of the products were negligible over the range of conditions studied. At longer reaction times (5 min), the composition of the vitrinite-derived products was similar to that of the inertinite-derived products.  相似文献   
3.
We report systematic measurements of the response of a Vibrating Wire Resonator (VWR) in normal and superfluid liquid 3He. Special attention has been paid to the hydrodynamic regime of the superfluid B-phase, where the response parameters of the VWR do not follow a simple law. We show that a simple interpolation between the region where first order slip-corrections can be applied and the ballistic regime is insufficient. Measuring an empirical effective viscosity, we propose a temperature calibration method which allows the use of VWRs as a secondary thermometer at intermediate and high pressures in the temperature range 0.2 T c < T < 50 mK.  相似文献   
4.
Solidification of aluminum oxide from undercooled melts was investigated in containerless experiments. Specimens were levitated in a gas jet, stabilized with an acoustic positioning device, and melted with cw CO2 laser beams. Cooling curves were obtained by optical pyrometry when the laser intensity was reduced. The materials examined were high-purity Verneuil sapphire, 99.5% polycrystalline alumina, and oxide materials recovered from the effluent of an aluminum-fueled rocket motor. The degree of undercooling, the apparent temperature behavior during the thermal arrest on solidification, and the structure of the materials formed were different in argon and oxygen atmospheres. Undercooling of the sapphire and alumina materials was 360 ± 10 K in an oxygen atmosphere and approximately 450 K in argon. Melting and solidification of high-purity sapphire resulted in a dendritic and porous polycrystalline material in oxygen. Dense, larger crystals were obtained in argon. Products formed from 99.5% alumina were discolored and the cores were white, indicating impurity segregation effects. More reproducible behavior was observed for the sapphire and 99.5% alumina than for the tungstencontaminated rocket motor effluent materials.  相似文献   
5.
Bone marrow transplantation (BMT) using HLA-partially matched family donors has produced disappointing results (25-30% of long-term survivors) in patients with severe aplastic anemia. We describe two children affected by severe aplastic anemia, not responsive to immunosuppressive therapy, who underwent allogeneic bone marrow transplantation using a HLA-partially matched family donor. Both cases presented 2 first class HLA-antigens (A and B) disparity between donor and recipient. The pretransplant conditioning regimen consisted of cyclophosphamide, thoracoabdominal irradiation, cytosine-arabinoside, and antilymphocyte globulin. As graft versus host disease (GVHD) prophylaxis, Cyclosporine-A was administered at usual dosages for 6 months. A full marrow engraftment was observed in both cases. Only grade I acute GVHD, promptly responsive to corticosteroid therapy, developed with no chronic GVHD. Five months after transplant, both children progressively developed hypertension, renal function impairment, thrombocytopenia, and severe normochromic anemia, with erythropoietin serum levels lower than expected for the haematocrit. After antihypertension treatment and supportive therapy, the clinical picture progressively improved, while treatment with recombinant human erythropoietin completely corrected the long-lasting anemia. The two children are alive and well 28 months after the transplant, with a Karnofsky score of 100% and a normal peripheral blood count. The authors suggest that, once immunosuppressive therapy has failed, BMT from donors other than HLA-identical sibling is a feasible approach in children affected by severe aplastic anemia, not having an HLA-identical donor.  相似文献   
6.
7.
A processing algorithm for automatically detecting a specific type of ion distribution (called the ion conic distribution) in data obtained from a space-based mass spectrometer has been devised. Automation of this task is necessary due to the sparseness of conic events within the very large databases typical of space plasma instruments. The algorithm used to perform this automated analysis and the methods used to verify the algorithm are described. Initial results on the characterization of the near-Earth space plasma are summarized  相似文献   
8.
The double or even triple dividend hypothesis of green tax reforms has beena major issue of dispute in both the scientific community and the politicalarena during the last decade. Theoretical analysis has provided a number ofimportant qualitative insights to the debate but lacks of actual policyrelevance due to very restrictive assumptions. Applied research that takes thestep from stylized analytical to complex numerical models usually comes as ablackbox to non-expert modelers. This paper aims at bridging the gap betweenstylized theoretical work and numerical analysis. We develop a flexible,interactive simulation model which is accessible underhttp://brw.zew.de. Users can specify their own green tax reforms andevaluate the induced economic and environmental effects. Based on illustrativesimulations, we demonstrate the usefulness of our do-it-yourself approach fora better understanding of the double (triple) dividend hypothesis.  相似文献   
9.
In life testing, the failure-time distributions are often specified by choosing an appropriate hazard-rate function. The class of life-time distribution characterized by a linear hazard-rate includes the one-parameter exponential and Rayleigh distributions. Usually the parameters of the linear hazard-rate model are estimated by the method of least squares. This work is concerned with Bayes estimation of the two-parameters from a type-2 censored sample. Monte Carlo simulation is used to compare the Bayes risk of the regression estimator with the minimum Bayes risk. Discrete mixtures of decreasing failure rate distributions are known to have decreasing failure rates. The authors prove that the result holds for continuous mixtures as well  相似文献   
10.
Tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and IL-1 have been shown to stimulate the synthesis of acute-phase proteins; however, few studies have examined the effect of these cytokines on gluconeogenesis. We investigated the effects of these cytokines on gluconeogenesis in primary cultures of rat hepatocytes. Incubation of hepatocytes for 24 hours with TNF-alpha or IL-1 alpha did not affect gluconeogenesis. Hepatocytes incubated with 100 pmol/L and 1 nmol/L IL-6 had a dose-dependent increase (P < .05) in gluconeogenesis (2.6 +/- 0.1 and 3.2 +/- 0.1 pmol/10(6) cells/min, respectively) as compared with controls (2.0 +/- 0.1).  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