全文获取类型
收费全文 | 104058篇 |
免费 | 1415篇 |
国内免费 | 1232篇 |
专业分类
电工技术 | 1977篇 |
综合类 | 139篇 |
化学工业 | 10723篇 |
金属工艺 | 5501篇 |
机械仪表 | 3227篇 |
建筑科学 | 2067篇 |
矿业工程 | 159篇 |
能源动力 | 2988篇 |
轻工业 | 6138篇 |
水利工程 | 714篇 |
石油天然气 | 668篇 |
武器工业 | 15篇 |
无线电 | 16084篇 |
一般工业技术 | 21976篇 |
冶金工业 | 25513篇 |
原子能技术 | 1418篇 |
自动化技术 | 7398篇 |
出版年
2022年 | 460篇 |
2021年 | 711篇 |
2020年 | 529篇 |
2019年 | 692篇 |
2018年 | 1155篇 |
2017年 | 1112篇 |
2016年 | 1199篇 |
2015年 | 938篇 |
2014年 | 1508篇 |
2013年 | 4714篇 |
2012年 | 2613篇 |
2011年 | 3893篇 |
2010年 | 3139篇 |
2009年 | 3768篇 |
2008年 | 3941篇 |
2007年 | 4135篇 |
2006年 | 3730篇 |
2005年 | 3354篇 |
2004年 | 3208篇 |
2003年 | 3055篇 |
2002年 | 2709篇 |
2001年 | 2987篇 |
2000年 | 2735篇 |
1999年 | 3097篇 |
1998年 | 9536篇 |
1997年 | 6233篇 |
1996年 | 4806篇 |
1995年 | 3191篇 |
1994年 | 2813篇 |
1993年 | 2760篇 |
1992年 | 1642篇 |
1991年 | 1614篇 |
1990年 | 1522篇 |
1989年 | 1333篇 |
1988年 | 1183篇 |
1987年 | 870篇 |
1986年 | 899篇 |
1985年 | 935篇 |
1984年 | 818篇 |
1983年 | 705篇 |
1982年 | 714篇 |
1981年 | 693篇 |
1980年 | 577篇 |
1979年 | 480篇 |
1978年 | 424篇 |
1977年 | 538篇 |
1976年 | 971篇 |
1975年 | 302篇 |
1974年 | 279篇 |
1973年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
Nonaka Y. Nakane H. Maeda T. Hasuike K. 《IEEE transactions on instrumentation and measurement》1995,44(3):679-682
A method is proposed for a simultaneous measurement of the resistivity and permeability of a film inserted between two coils facing each other. Connecting in series, the total impedance of the coils was measured in two ways, i.e., 1) the current passes through the coils in the same direction, and 2) the current passes through each coil in opposite directions to each other. The resistivity and permeability of the film were simultaneously obtained from the difference in the impedance for the two cases. It was theoretically found that the optimum frequency for high accuracy in the measurement was proportional to the resistivity and inversely proportional to a thickness of a sample film. The results of the simultaneous measurements of the resistivity and permeability of nickel films of a thickness ranging from 0.01-0.08 mm at a frequency range of 1-100 kHz are shown in this paper. The measured values of the resistivity and permeability with this method agreed with the values obtained by conventional methods, i.e., the dc four-probe method for the resistivity measurement and the toroidal coil method for the permeability measurement 相似文献
992.
993.
The effect of a permanent transection on myelin gene expression in a regenerating sciatic nerve and in an adult sciatic nerve was compared to establish the degree of axonal control exerted upon Schwann cells in each population. First, the adult sciatic nerve was crushed, and the distal segment allowed to regenerate. At 12 days post-crush, the sciatic nerve was transected distal to the site of crush to disrupt the Schwann cell-axonal contacts that had reformed. Messenger RNA (mRNA) levels coding for five myelin proteins were assayed in the distal segment of the crush-transected nerve after 9 days and were compared to corresponding levels in the distal segments of sciatic nerves at 21 days post-crush and 21 days post-transection using Northern blot and slot-blot analysis. Levels of mRNAs found in the distal segment of the transected and crush-transected nerve suggested that Schwann cells in the regenerating nerve and in the mature adult nerve are equally responsive to axonal influences. The crush-transected model allowed the genes that were studied to be classified according to their response to Schwann cell-axonal contact. The levels of mRNAs were 1) down-regulated to basal levels (P0 and MBP mRNAs), 2) down-regulated to undetectable levels (myelin-associated glycoprotein mRNAs), 3) upregulated (mRNAs encoding 2'3'-cyclic nucleotide phosphodiesterase and beta-actin), or 4) not stringently controlled by the removal of Schwann cell-axonal contact (proteolipid protein mRNAs). This novel experimental model has thus provided evidence that the expression of some of the important myelin genes during peripheral nerve regeneration is dependent on continuous signals from the ingrowing axons. 相似文献
994.
Y. FARES M. CHAUSSUMIER A. DAIDIE J. GUILLOT 《Fatigue & Fracture of Engineering Materials & Structures》2006,29(8):588-596
The fatigue behaviour of bolts under axial load has always been considered from the component point of view for which fatigue limit is usually taken equal to 50 MPa, and few results are available to designers for limited lifetimes. Here, we take up this problem from a material point of view using a local approach. For each case of fatigue testing, using finite‐element (FE) model of the bolt, we determine the stabilized local stress at the root of the first thread in contact with the nut. To characterize bolt behaviour with these numerical results, we use Dang Van multiaxial fatigue criterion for which we extend application to the medium fatigue life. These results can be correlated with the experimental numbers of cycles to failure to determine material parameters of the generalized criterion. Using statistical Gauss method, we can make lifetime predictions for any level of risk of failure. In addition, we propose an analytical model to rapidly determine the local stress condition from nominal loading data (mean stress and alternating stress). This model dispenses us from a new modelling if the bolt is stressed in the same manner as the bolts used for behaviour characterization. Using this model and the generalized criterion, it is extremely easy to make lifetime predictions whatever the risk considered. 相似文献
995.
Gashinova M.S. Goubina M.N. Guoyong Zhang Kolmakov I.A. Kolmakov Y.A. Vendik I.B. 《Microwave Theory and Techniques》2003,51(3):792-795
This paper presents design and measurement results of a high-T/sub c/ superconducting planar filter based on a pair of coupled modified hairpin resonators considered to be a key constituent of the filter structure. This provides the filter characteristics, which are very close to the Chebyshev prototype of the same order. 相似文献
996.
S.Y. Cheng K.S. Chiang H.P. Chan 《Photonics Technology Letters, IEEE》2003,15(5):700-702
We report the fabrication of benzocyclobutene strip optical waveguides and the measurement of their birefringence properties. To take into account the stress-induced birefringence in the waveguide, we generalize the formulas reported previously for the analysis of strip waveguides. Our experimental results are shown to agree closely with the theoretical calculation. The condition for achieving zero modal birefringence by control of the aspect ratio of the strip of the waveguide is highlighted. The dependence of the birefringence in the waveguides on the temperature is also measured and discussed. 相似文献
997.
A comprehensive, GIS‐based modelling approach is developed to estimate runoff and phosphorus transport within a watershed at a daily time step. The approach relies on the use of GIS data for deriving major critical model parameters that exhibit distinct spatial variability over the catchment. Surface runoff is calculated by a modified rational method, which depends upon rainfall intensity, soil moisture status, slope, land‐use and soil characteristics. Phosphorus loading is estimated as a function of the runoff volume and the event mean concentration for different land use categories. A diffusive approximation method is used to trace runoff and phosphorus transport to the basin outlet. The modelling approach is tested in the Margecany catchment, Hornad River basin, Slovakia, to simulate runoff, phosphorus loading, and its transport on a daily time scale using data observed between 1995 and 2000. Satisfactory results of the hydrographs and phosphorus concentration at the basin outlet are obtained, though more efforts regarding the phosphorus cycling and its biochemical reactions need to be clarified by further research. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
998.
L. X. Che R. Q. Yang Y. Gu T. K. Xia 《The International Journal of Advanced Manufacturing Technology》2006,31(5-6):614-620
This paper presents a method of calculating the insulating safety distances for hot-line working robots at high voltage when dielectric is adulterated with conducts. Also, finite element method is adopted to calculate the electric field strength to find whether it is beyond the critical. The above methods have been applied to analyze the insulating safety of the robot for hot-line sweeping post insulators in a 220 KV substation. They have also been testified by experimentations. 相似文献
999.
Coal is potentially a very inexpensive source of clean hydrogen fuel for use in fuel cells, turbines, and various process applications. To realize its potential however, efficient low-cost gas separation systems are needed to provide high purity oxygen that will enhance the coal gasification reaction and to extract hydrogen from the resulting gas product stream. Several types of inorganic membranes are being developed for hydrogen or oxygen separation, including porous alumina, transition metal oxide perovskites, and zirconia. Because they form the heart of the working device, numerous advances have been made in the fabrication and performance of these membrane materials. However, less emphasis has been placed on the materials that will be used in the balance of the device; in particular, the seals that bond the functional ceramic to the metallic structural component. In an effort to begin addressing this issue, we have examined ceramic-to-metal brazing as a method of sealing a model set of gas separation component materials: yttria-stabilized zirconia and stainless steel. In comparative high-temperature exposure testing of joints prepared using commercial brazes and a newly conceived braze alloy, the commercial material proved to be unsuitable due to excessive oxidation. On the other hand, the new material not only displayed superior oxidation resistance, but also excellent hermeticity in prototypic membrane testing. 相似文献
1000.