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   818篇
  免费   46篇
  国内免费   2篇
电工技术   18篇
化学工业   245篇
金属工艺   2篇
机械仪表   23篇
建筑科学   36篇
矿业工程   2篇
能源动力   16篇
轻工业   153篇
水利工程   2篇
石油天然气   4篇
无线电   85篇
一般工业技术   103篇
冶金工业   99篇
自动化技术   78篇
  2024年   1篇
  2023年   9篇
  2022年   54篇
  2021年   54篇
  2020年   22篇
  2019年   12篇
  2018年   19篇
  2017年   21篇
  2016年   27篇
  2015年   16篇
  2014年   27篇
  2013年   43篇
  2012年   50篇
  2011年   51篇
  2010年   24篇
  2009年   34篇
  2008年   46篇
  2007年   33篇
  2006年   23篇
  2005年   17篇
  2004年   17篇
  2003年   22篇
  2002年   20篇
  2001年   11篇
  2000年   17篇
  1999年   19篇
  1998年   46篇
  1997年   28篇
  1996年   23篇
  1995年   16篇
  1994年   10篇
  1993年   8篇
  1992年   5篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1988年   3篇
  1987年   2篇
  1986年   2篇
  1984年   1篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1977年   2篇
  1976年   5篇
  1973年   1篇
  1972年   1篇
排序方式: 共有866条查询结果,搜索用时 31 毫秒
11.
This paper reports a study undertaken using techniques of static and dynamic light scattering to investigate the influence of sodium salicylate and methyl salicylate on droplet size of oil-in-water emulsions. The rates of changes were measured by determining the size and distribution of the oil droplet in the material. All emulsions showed a bimodal size distribution; the mean diameters and polydispersity were calculated from intensity. These data were analyzed with nonlinear regressions and bootstrap methodology. An amount of methyl salicylate component induced a decrease of mean diameter and standard deviation. On the contrary, sodium salicylate entailed the growth of all droplet populations and coalescence for the highest concentration.  相似文献   
12.
The experimental implementation of an adiabatic coupling technique for efficient coupling between photonic crystal single-line defect waveguides and coupled-cavity waveguides is reported. The samples were fabricated in a silicon-on-insulator substrate using 248-nm-deep ultraviolet lithography. Experimental results are compared with three-dimensional (3-D) finite-difference time-domain simulations. Furthermore, the discrepancies between two-dimensional and 3-D simulation results are analyzed.  相似文献   
13.
The mechanisms of carrier transfer from barrier regions (superlattices, side-wall and vertical quantum wells) into arrays of quantum wires are investigated by time-resolved photoluminescence. The wires are grown by different techniques on V-groove substrates. The transfer times range from 25 to 900 ps, depending on the details of the whole structure. The fast carrier transfer is modeled by a diffusion equation which allows one to estimate the quantum mechanical capture time from a two-dimensional vertical QW into a one-dimensional QWR to be <2 ps.  相似文献   
14.
15.
Atherothrombosis exposes vascular components to blood. Currently, new antithrombotic therapies are emerging. Herein we investigated thrombogenesis of human arteries with/without atherosclerosis, and the interaction of coagulation and vascular components, we and explored the anti-thrombogenic efficacy of blockade of the P2X purinoceptor 7 (P2X7). A confocal blood flow videomicroscopy system was performed on cryosections of internal mammary artery (IMA) or carotid plaque (CPL) determining/localizing platelets and fibrin. Blood from healthy donors elicited thrombi over arterial layers. Confocal microscopy associated thrombus with tissue presence of collagen type I, laminin, fibrin(ogen) and tissue factor (TF). The addition of antibodies blocking TF (aTF) or factor XI (aFXI) to blood significantly reduced fibrin deposition, variable platelet aggregation and aTF + aFXI almost abolished thrombus formation, showing synergy between coagulation pathways. A scarce effect of aTF over sub-endothelial regions, more abundant in tissue TF and bundles of laminin and collagen type I than deep intima, may suggest tissue thrombogenicity as molecular structure-related. Consistently with TF-related vascular function and expression of P2X7, the sections from CPL but not IMA tissue cultures pre-treated with the P2X7 antagonist A740003 demonstrated poor thrombogenesis in flow experiments. These data hint to local targeting studies on P2X7 modulation for atherothrombosis prevention/therapy.  相似文献   
16.
The p-tert-butylcalix[6]arene hexamide 2 and syn-1,3,5–trimethoxy-2,4,6-triamide 4 were synthesized by reaction of α-chloro-N,N-diethylacetamide and the corresponding calix[6]arenes 1 and 3 , respectively. 1H NMR spectroscopy shows that 2 is a mixture of different conformations whereas 4 is fixed in a cone conformation. Extraction experiments, (S-L) and (H2O–CDCl3) with picrate salts, indicate that 2 complexes both alkali metal (1:2 complex) and guanidinium salts (1:1 complex) but 4 complexes only guanidinium (1:1 complex). Incorporated in supported liquid membranes (Accurel® / o-nitrophenyl n-octyl ether) the calixarenes 2 and 4 transport guanidinium salts. The hexamide 2 is a more efficient carrier of guanidinium but the syn-1,3,5-trimethoxy-2,4,6-triamide 4 is much more selective. Both 2 and 4 are sufficiently lipophilic to give membranes that are stable over longer periods (weeks).  相似文献   
17.
We report on the absence of the so-called fishtail or peak effect in the magnetisation curves of properly oxygenated high purity (5N) single crystals of YBa2Cu3O7–. As we recently reported [1] high pressure oxygenation procedures are suitable to produce a monotonous dependence of the critical current density with the magnetic field. In this article we report furthermore how to reversibly produce or remove this effect on the same crystal by proper oxygenation methods. Along with the high purity of the samples, — due to crystal growth in non reactive BaZrO3 crucibles —, this proves that at least in pure samples the fishtail effect is due to different oxygenation states and/or oxygen distributions. In less pure samples, however, other sources for this anomaly like metallic impurities can act as an additional source for the fishtail anomaly.  相似文献   
18.
19.
Evidence for immunologic processes taking part in the pathogenesis of what until now has been called the "essential" form of EPH gestosis is cited. The name of immunogestosis (IG) is introduced. The data of this preliminary study suggest that regular "inoculation" of the female genital tract with allogeneic spermatozoal histocompatibility antigens reduces the incidence of IG. Information about preconceptional sexual habits and contraceptive measures was obtained from 83 selected primigravid patients. Twenty-eight women had mild to moderate IG (Group B);55 did not (Group A). Women in Group B had had less contact with spermatozoa of partners than did women in Group A. Oral contraceptive consumption was less in Group B than in Group A. Women in Group B were younger than women in Group A. All these differences were statistically significant. A new immunoetiologic hypothesis referring to IG, as well as the theoretic and clinical implications arising from it, are discussed. This hypothesis is based on the assumption that spermatozoal histocompatibility antigens can either induce immunologic tolerance or be responsible for the phenomenon of immunologic enhancement in the maternal immunosystem. As the fetus inherits paternal histocompatibility antigens, it is concluded that pre-existing tolerance (or enhancement) exerts an IG-preventive function in a subsequent pregnancy.  相似文献   
20.
Yield stresses, allowable stresses, moment capacities (plastic moments), external loadings, manufacturing errors, etc., are not fixed quantities in practice, but must be modelled as random variables with a certain joint probability distribution. In reliability-oriented structural optimization the violation of the random behavioural constraints are evaluated by means of the corresponding probabilityp s of survival. Hence, the approximative computation ofp s and its sensitivities is of utmost importance. After the consideration of lower bounds ofp s based on a selection of certain redundants in the vector of internal forces/bending moments, and the consideration of upper bounds ofp s based on an optimizational representation of the yield or safety constraints by a pair of dual linear programs, a conical representation ofp s is introduced based on a coneY o of admissible pairs of external loads/strength increaments. Approximations ofp s can be constructed then by replacing the (finitely generated) coneY o by more simple ones, e.g. spherical or ellipsoidal cones. For the direct numerical computation of sensitivities ofp s and its bounds or approximations by using e.g. sampling methods or asymptotic expansion techniques based on Laplace integral representation of multiple integrals, exact differentiation formulae — of arbitrary order — forp s and its bounds or approximations with respect to deterministic input or design variables are obtained by applying the transformation method/stochastic completion techniques; the derivatives ofp s are represented again by certain expectations or multiple integrals.  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