全文获取类型
收费全文 | 25103篇 |
免费 | 561篇 |
国内免费 | 783篇 |
专业分类
电工技术 | 534篇 |
综合类 | 111篇 |
化学工业 | 2828篇 |
金属工艺 | 2432篇 |
机械仪表 | 1048篇 |
建筑科学 | 604篇 |
矿业工程 | 108篇 |
能源动力 | 918篇 |
轻工业 | 1223篇 |
水利工程 | 168篇 |
石油天然气 | 442篇 |
武器工业 | 16篇 |
无线电 | 2903篇 |
一般工业技术 | 6841篇 |
冶金工业 | 4002篇 |
原子能技术 | 317篇 |
自动化技术 | 1952篇 |
出版年
2024年 | 15篇 |
2023年 | 78篇 |
2022年 | 163篇 |
2021年 | 260篇 |
2020年 | 178篇 |
2019年 | 307篇 |
2018年 | 464篇 |
2017年 | 438篇 |
2016年 | 506篇 |
2015年 | 428篇 |
2014年 | 638篇 |
2013年 | 1623篇 |
2012年 | 1021篇 |
2011年 | 1500篇 |
2010年 | 1185篇 |
2009年 | 1372篇 |
2008年 | 1389篇 |
2007年 | 1361篇 |
2006年 | 1205篇 |
2005年 | 1104篇 |
2004年 | 907篇 |
2003年 | 835篇 |
2002年 | 800篇 |
2001年 | 768篇 |
2000年 | 741篇 |
1999年 | 764篇 |
1998年 | 1506篇 |
1997年 | 1070篇 |
1996年 | 930篇 |
1995年 | 584篇 |
1994年 | 470篇 |
1993年 | 382篇 |
1992年 | 251篇 |
1991年 | 256篇 |
1990年 | 161篇 |
1989年 | 176篇 |
1988年 | 126篇 |
1987年 | 89篇 |
1986年 | 63篇 |
1985年 | 68篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 29篇 |
1981年 | 33篇 |
1980年 | 17篇 |
1978年 | 9篇 |
1976年 | 19篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Clinical manifestations and peripheral blood lymphocyte subset changes were studied in patients with myasthenia gravis (MG) to elucidate the mechanism of clinical improvement following treatment, with thymectomy (Tx) or glucocorticoid (GC) therapy. The changes found were: 1. There was a significant increase in percentages of CD3+, CD29+ CD4+ cells and CD4/CD8 ratio and a significant decrease in percentages of CD8+ and CD16,56+ cells in patients who had never been treated with any immune therapy. 2. After Tx or GC therapy, CD3+ and CD4+, CD29+ cells were decreased, but the number CD19+ and CD16, CD56 cells did not change. 3. Tx had a special effect on CD8+ cells. In most of the patients who showed clinical improvement after Tx, CD8+ cells were increased and CD4/CD8 ratio wad decreased. 4. Anti-acetylcholine receptor (AChRAb) titers were markedly decreased after GC therapy. These results indicate that there were obvious abnormalities in cell-mediated immunity in addition to those in humoral immunity in myasthenia gravis. These abnormalities tended to be normalized after Tx or GC therapy. 相似文献
32.
The influence of the specimen thickness B and the ligament length b on the J
R
-curves is numerically investigated for CT specimens. The thickness effect is taken into account with 2-D analyses by dividing a plain sided specimen into a plane stress part and a plane strain part. The fracture process is controlled by experimentally determined critical values of the crack tip opening displacement for crack growth initiation (CTODi) and the crack tip opening angle for stable crack growth (CTOAC). It is shown that for the global behaviour of a plain sided specimen, the B/b ratio is essential. The difference between the geometry dependence of the initiation value of the J-integral and the geometry dependence of the slope of the J
R
-curves is also shown. 相似文献
33.
34.
X. Ruiz 《Microgravity science and technology》2006,18(3-4):51-56
The binomial single g-pulses — dopant segregation in a generic virtual µg Bridgman growth arrangement is discussed here with the help of a time dependent two-dimensional scheme. To attain this objective, the so-called solid composition drop distribution has been previously defined enabling a global two-dimensional information of the segregation impact in each virtually grown crystal. Based on this parameter it has been concluded that, at equal g-dose, solid segregation is independent on the shape of the single external pulse and that, for single g-pulses of equal g-dose, compositional variations are practically independent on the activity time but depend on the crystal growth rate. Finally, taking into account all these set of results, the pertinence of the g-dose as the only self-consistent parameter to describe the segregation impact has been discussed. 相似文献
35.
36.
37.
High spatial order finite element method to solve Maxwell's equations in time domain 总被引:2,自引:0,他引:2
Pernet S. Ferrieres X. Cohen G. 《Antennas and Propagation, IEEE Transactions on》2005,53(9):2889-2899
This paper presents a finite element method with high spatial order for solving the Maxwell equations in the time domain. In the first part, we provide the mathematical background of the method. Then, we discuss the advantages of the new scheme compared to a classical finite-difference time-domain (FDTD) method. Several examples show the advantages of using the new method for different kinds of problems. Comparisons in terms of accuracy and CPU time between this method, the FDTD and the finite-volume time-domain methods are given as well. 相似文献
38.
An improved coupled-mode equation for nonlinear directional couplers (NLDC) with Kerr-like nonlinear media is proposed. The method is based on the generalized reciprocity relation in which two sets of field solutions satisfying Maxwell's equations are for the NLDC and for the isolated nonlinear waveguide. That leads to a reasonable result that all the coefficients in the coupled-mode equations, including the coupling coefficient, become power dependent. For the NLDC with a self-focusing or self-defocusing nonlinear material, the authors examine how the coupling coefficient, the coupling length, and the guided power depend on the input power in the range of coupling stronger than in previous reports. It is found that the critical power at which the coupling length becomes infinity does not increase as much with the two guides for the case of self-focusing media 相似文献
39.
It is demonstrated for the first time that long nanowires with radii as small as 30 nm can be manufactured with a conventional coupler fabrication rig. The temporal deterioration of nanowire optical properties has been studied and correlated with its mechanical behaviour. The original transmission properties have been restored by a post-fabrication treatment. 相似文献
40.
Transformations in machining. Part 1. enhancement of wavelet transformation neural network (WT-NN) combination with a preprocessor 总被引:2,自引:0,他引:2
X. Wang P. Chen I.N. Tansel Yenilmez A 《International Journal of Machine Tools and Manufacture》2006,46(1):36-42
Properly selected transformation methods obtain the most significant characteristics of metal cutting data efficiently and simplify the classification. Wavelet Transformation (WT) and Neural Networks (NN) combination was used to classify the experimental cutting force data of milling operations previously. Preprocessing (PreP) of the approximation coefficients of the WT is proposed just before the classification by using the Adaptive Resonance Theory (ART2) type NNs. Genetic Algorithm (GA) was used to estimate the weights of each coefficient of the PreP. The WT-PreP-NN (ART2) combination worked at lower vigilances by creating only a few meaningful categories without any errors. The WT-NN (ART2) combination could obtain the same error rate only if very high vigilances are used and many categories are allowed. 相似文献