首页 | 官方网站   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   19587篇
  免费   1362篇
  国内免费   13篇
工业技术   20962篇
  2024年   35篇
  2023年   156篇
  2022年   193篇
  2021年   475篇
  2020年   445篇
  2019年   500篇
  2018年   845篇
  2017年   803篇
  2016年   797篇
  2015年   642篇
  2014年   807篇
  2013年   1546篇
  2012年   1241篇
  2011年   1101篇
  2010年   905篇
  2009年   828篇
  2008年   828篇
  2007年   796篇
  2006年   524篇
  2005年   395篇
  2004年   408篇
  2003年   354篇
  2002年   337篇
  2001年   235篇
  2000年   208篇
  1999年   286篇
  1998年   1497篇
  1997年   968篇
  1996年   602篇
  1995年   319篇
  1994年   257篇
  1993年   292篇
  1992年   95篇
  1991年   84篇
  1990年   77篇
  1989年   81篇
  1988年   79篇
  1987年   63篇
  1986年   69篇
  1985年   86篇
  1984年   50篇
  1983年   39篇
  1982年   56篇
  1981年   66篇
  1980年   53篇
  1979年   26篇
  1978年   26篇
  1977年   99篇
  1976年   194篇
  1974年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Indices of fluid balance were evaluated during and after aortic surgery in 16 consecutive patients. Thoracic electrical impedance (TI), heart rate (HR), central venous (CVP), pulmonary artery mean (PAMP), pulmonary wedge (PWP) and mean arterial (MAP) pressures as well as fourteen arterial and venous blood gas variables were followed. Consistent with a reduction of TI during the operation, fluid balance was in excess, and it remained elevated on the first postoperative morning. The HR, MAP and PWP remained stable, while CVP and PAMP decreased. Of the determined variables only TI revealed a meaningful correlation to fluid balance (rho = -0.41; p < 0.01). The results indicate that while central venous and pulmonary artery mean pressures gave the impression of a volume deficit, the positive fluid balance was mirrored by thoracic electrical impedance.  相似文献   
62.
63.
Several in vivo and in vitro methods for monitoring immunological properties of two allergoids obtained by formaldehyde treatment of ovalbumin (OA) were developed. The calculated molecular weight of allergoids was 80 kD (OA-F1) and 165 kD (OA-F2), respectively. The allergenic activity in vitro of allergoids in mast-cell histamine release assay was 1000 times lower than of OA. Both allergoids showed reduced ability to induce passive cutaneous anaphylaxis in the Sprague-Dawley rats or systemic anaphylaxis in Dunkin-Harley guinea-pigs. The ability of OA and allergoids to bind to the OA-specific IgE antibodies was measured in vivo by the inhibition of passive cutaneous anaphylaxis (PCA-inhibition). Allergoid binding to IgE was 51-66% lower than the native allergen. Moreover, the avidity of OA-specific IgG antibodies, measured by ELISA-inhibition, for allergoids and allergen was of the same order. Allergoids induced a different pattern of humoral immune response from that, induced by the native allergen. Thus, after immunization of BALB/c mouse, both allergoids induced a higher production of IgG and a lower production of IgE than OA, only OA-F2 induced a lower production of IgG1. The differences in the IgA response to the immunogens was not significant. Delayed hypersensitivity studies in the BALB/c mouse showed that allergoids were 5- to 12-times less effective in inducing a cell-mediated immune response than OA. The present study provides a battery of immunological methods for preclinical testing of modified allergens.  相似文献   
64.
65.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
66.
A three-dimensional (3D) finite-difference time-domain (FDTD) scheme is introduced to model the scattering from objects in continuous random media. FDTD techniques have been previously applied to scattering from random rough surfaces and randomly placed objects in a homogeneous background, but little has been done to simulate continuous random media with embedded objects where volumetric scattering effects are important. In this work, Monte Carlo analysis is used in conjunction with FDTD to study the scattering from perfectly electrically conducting (PEC) objects embedded in continuous random media. The random medium models under consideration are chosen to be inhomogeneous soils with a spatially fluctuating random permittivities and prescribed correlation functions. The ability of frequency averaging techniques to discriminate objects in this scenarion is also briefly investigated. The simulation scheme described in this work can be adapted and used to help in interpreting the scattered field data from targets in random environments such as geophysical media, biological media, or atmospheric turbulence  相似文献   
67.
Generation of Technology-Independent Retargetable Analog Blocks   总被引:1,自引:0,他引:1  
This paper introduces a complete methodology for retargeting of analog cells to different sets of specifications. This methodology is technology-independent, thus allowing the migration, from one technology to another, of the circuit under retargeting. Careful integration of the device sizing and layout generation tasks via the incorporation of layout constraints during the sizing process allows to generate fully functional designs in a few minutes. The methodology is illustrated via the retargeting of a fully-differential Miller-compensated two-stage operational amplifier for a new set of specifications and two different technological processes.An erratum to this article can be found at  相似文献   
68.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene.  相似文献   
69.
Conducted a study of client expectations of psychological services in Yucatán, Mexico, under the sponsorship of a grant from the Organization of American States. The Expectations about Counseling–Brief form (EAC-B) questionnaire was translated and administered to 488 subjects across age, sex, and experience with psychological services. Subsequent analyses supported the reliability and robustness of the Spanish EAC-B, with factor structure similar to the EAC-B in English. Some relation was found among age, sex, prior counseling experience, and expectations about counseling. Implications of these data for future research and comparison with U.S. subjects are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
70.
We present a new iterative alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method. By recognizing the ADI-FDTD method as a special case of a more general iterative approach to solve the Crank-Nicolson (CN) FDTD scheme, the splitting error in ADI-FDTD can be reduced systematically. Numerical examples are used to illustrate the improved accuracy of this method.  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-23

京公网安备 11010802026262号