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   2852篇
  免费   62篇
  国内免费   12篇
电工技术   177篇
综合类   5篇
化学工业   618篇
金属工艺   77篇
机械仪表   53篇
建筑科学   47篇
矿业工程   1篇
能源动力   137篇
轻工业   194篇
水利工程   12篇
石油天然气   7篇
无线电   294篇
一般工业技术   515篇
冶金工业   477篇
原子能技术   97篇
自动化技术   215篇
  2023年   10篇
  2022年   11篇
  2021年   31篇
  2020年   16篇
  2019年   24篇
  2018年   31篇
  2017年   26篇
  2016年   51篇
  2015年   28篇
  2014年   48篇
  2013年   106篇
  2012年   102篇
  2011年   111篇
  2010年   100篇
  2009年   117篇
  2008年   116篇
  2007年   113篇
  2006年   113篇
  2005年   86篇
  2004年   87篇
  2003年   87篇
  2002年   76篇
  2001年   73篇
  2000年   85篇
  1999年   65篇
  1998年   263篇
  1997年   135篇
  1996年   112篇
  1995年   63篇
  1994年   60篇
  1993年   77篇
  1992年   36篇
  1991年   32篇
  1990年   38篇
  1989年   29篇
  1988年   25篇
  1987年   26篇
  1986年   23篇
  1985年   30篇
  1984年   31篇
  1983年   30篇
  1982年   31篇
  1981年   33篇
  1980年   20篇
  1979年   27篇
  1978年   22篇
  1977年   18篇
  1976年   13篇
  1975年   10篇
  1973年   10篇
排序方式: 共有2926条查询结果,搜索用时 312 毫秒
71.
A theory for the high temperature superconductors is proposed. The dispersion of carriers in the 2D t-J model is calculated using numerical and analytical techniques, and compared with recent photoemission experimental results that reported a flat dispersion near the X and Y points. Good agreement is observed between theory and experiments. The density of states (DOS) of these dressed quasiparticles has a van Hove singularity. From the two carriers problem in an antiferromagnet, an effective Hamiltonian for holes is proposed. This effective model has superconductivity in the dx 2–y2 channel, a critical temperature Tc 100Kat the optimal hole density, x = 0.15, and a quasiparticle lifetime linearly dependent with energy. The appearance of an optimal concentration is a consequence of the van Hove singularity in the DOS. Other experimental results are also quantitatively reproduced by the theory. The present contribution is based on two recent papers by the authors (Phys. Rev. Lett.73, 728 (1994) and NHMFL preprint, July 1994).  相似文献   
72.
The authors report two cases of multicentric osteolytic lesions in the occipital bone without any history of head trauma. The excisional biopsy of the first case revealed that the lesion was multicentric but a continuous cavity with the subarachnoid space through various sizes of dural defect, and the cavities were covered by arachnoid lining. Together with the previously reported similar 5 cases, the characteristic common feature is multicentric osteolytic lesions in the occipital bone at advanced age without marginal sclerosis. "The cluster of arachnoid diverticula in the occipital bone (CADOB)" is probably the most appropriate term for these non-traumatic lesions with the following characteristics: elderly patients, occipital bone, midline, multiple, intact outer table, nonsclerotic margin and without history of trauma. Operation may not be indicated because of its non-progressive and benign nature.  相似文献   
73.
Anisotropie properties of the single crystal Pb2Sr2Ho0.5Ca0.5Cu3O8 have been investigated by measuring the electrical resistivity in theab-planeρ ab (H, θ,T), which depends on the angleθ between theab-plane and the magnetic-field direction, in various constant fieldsH perpendicular to the current direction. All the angle-dependent values ofρ ab (H, θ,T) at a constant temperature are scaled to be on one curve as a function of reduced field. The anisotropic parameter γ≡(m c * /m ab * )1/2 is estimated as 12–13, which is larger than that of YBa2Cu3O7 and much smaller than that of Bi2Sr2CaCu2O8. It has been concluded that the anisotropy does not always depend on the thickness of the blocking layer but seems to depend on the overlap of the electronic wave functions along thec-axis. Anisotropy in the pinning potential has also been discussed from the resistive tail in the temperature dependence ofρ ab (H,θ,T).  相似文献   
74.
75.
We have produced diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. These diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Therefore, we decided to use the X-rays lithography technique that used synchrotron radiation of the directivity for a manufacture process. The accuracy of the completed structure depends largely on the accuracy of the X-ray mask. In our group, a resin material is conventionally used for the membrane of large X-ray masks. However, X-ray masks comprising a resin membrane have the disadvantage that, after several cycles of X-ray exposure, they crease and sag due to X-ray-derived heat. As a substitute for the conventional resin membrane, we experimentally fabricated a new X-ray mask using a carbon wafer membrane. The newly fabricated X-ray mask was subjected to X-ray exposure experiment. We succeeded in making the structure body which was almost shape. And the experimental results verified that the new mask did not deteriorate even when used repeatedly, demonstrating that it was highly durable.  相似文献   
76.
The nickel electroforming method using a high-concentration nickel sulfamate bath is commonly used to fabricate micro metal molds in the LIGA process; however, this method does not produce micro metal molds of sufficient hardness. One means of improving the hardness of micro metal molds made using the nickel electroforming method is to include additives in the nickel plating solution. Another method is nickel alloy plating or a similar technique. In this research, we used a nickel–boron (Ni–B) electroless alloy plating method to obtain a hard nickel plated film having hardness of 832 Hv. It was also ascertained that Ni–B electroless alloy plated film retains its high hardness even during heat treatment in conditions of 250°C for 1 h. To deal with the high stresses developed in high-hardness plated films, we proposed double-layer nickel electroforming. This method is covered and used on conventional nickel electroforming layer by high hardness micro mold. High hardness micro metal mold using double-layer was fabricated by nickel electroforming and Ni–B electroless alloy plating method.  相似文献   
77.
Thermocapillary deformations of an ultra-thin liquid film caused by temperature distribution were three-dimensionally analyzed using the unsteady and linearized long wave equation considering the temperature and film thickness dependence of surface tension. The temperature and film thickness dependence equation for the surface tension of a liquid was firstly established. The temperature dependence of the surface tension was obtained experimentally using a surface tensiometer and the film thickness dependence was obtained theoretically from the corrected van der Waals pressure equation for a symmetric multilayer system. Time evolutions of depression and groove of the ultra-thin liquid film caused by local heating were obtained quantitatively.  相似文献   
78.
79.
Purpose : We aimed to identify novel chemotherapy responsiveness biomarkers for osteosarcoma (OS) by investigating the global protein expression profile of 12 biopsy samples from OS patients. Experimental design : Six patients were classified as good responders and six as poor responders, according to the Huvos grading system. The protein expression profiles obtained by 2‐D DIGE consisted of 2250 protein spots. Results : Among them, we identified 55 protein spots whose intensity was significantly different (Bonferroni adjusted p‐value<0.01) between the two patient groups. Mass spectrometric protein identification demonstrated that the 55 spots corresponded to 38 distinct gene products including peroxiredoxin 2 (PRDX 2). Use of a specific antibody against PRDX 2 confirmed the differential expression of PRDX 2 between good and poor responders, while PRDX 2 levels as measured by Western blotting correlated highly with their corresponding 2‐D DIGE values. The predictive value of PRDX 2 expression was further confirmed by examining an additional four OS cases using Western blotting. Conclusions and clinical relevance : These results establish PRDX 2 as a candidate for chemotherapy responsiveness marker in OS. Measuring PRDX 2 in biopsy samples before treatment may contribute to more effective management of OS.  相似文献   
80.
Animations of characters with flexible bodies such as jellyfish, snails, and, hearts are difficult to design using traditional skeleton‐based approaches. A standard approach is keyframing, but adjusting the shape of the flexible body for each key frame is tedious. In addition, the character cannot dynamically adjust its motion to respond to the environment or user input. This paper introduces a new procedural deformation framework (ProcDef) for designing and driving animations of such flexible objects. Our approach is to synthesize global motions procedurally by integrating local deformations. ProcDef provides an efficient design scheme for local deformation patterns; the user can control the orientation and magnitude of local deformations as well as the propagation of deformation signals by specifying line charts and volumetric fields. We also present a fast and robust deformation algorithm based on shape‐matching dynamics and show some example animations to illustrate the feasibility of our framework.  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