全文获取类型
收费全文 | 5932篇 |
免费 | 142篇 |
国内免费 | 20篇 |
学科分类
工业技术 | 6094篇 |
出版年
2023年 | 20篇 |
2022年 | 15篇 |
2021年 | 122篇 |
2020年 | 59篇 |
2019年 | 68篇 |
2018年 | 79篇 |
2017年 | 80篇 |
2016年 | 107篇 |
2015年 | 80篇 |
2014年 | 121篇 |
2013年 | 226篇 |
2012年 | 208篇 |
2011年 | 306篇 |
2010年 | 195篇 |
2009年 | 216篇 |
2008年 | 206篇 |
2007年 | 217篇 |
2006年 | 189篇 |
2005年 | 189篇 |
2004年 | 164篇 |
2003年 | 163篇 |
2002年 | 132篇 |
2001年 | 123篇 |
2000年 | 117篇 |
1999年 | 143篇 |
1998年 | 549篇 |
1997年 | 299篇 |
1996年 | 223篇 |
1995年 | 172篇 |
1994年 | 138篇 |
1993年 | 126篇 |
1992年 | 88篇 |
1991年 | 84篇 |
1990年 | 62篇 |
1989年 | 73篇 |
1988年 | 57篇 |
1987年 | 56篇 |
1986年 | 66篇 |
1985年 | 65篇 |
1984年 | 59篇 |
1983年 | 42篇 |
1982年 | 45篇 |
1981年 | 49篇 |
1980年 | 44篇 |
1979年 | 32篇 |
1978年 | 29篇 |
1977年 | 28篇 |
1976年 | 75篇 |
1975年 | 18篇 |
1973年 | 15篇 |
排序方式: 共有6094条查询结果,搜索用时 115 毫秒
61.
The effect of Zr on reduction of hardness and microstructure in an FS weld of equal channel angular-pressed Al alloy was investigated. Zr addition to Al suppressed dynamic recovery in the thermomechanically affected zone and enabled retention of the high hardness of the ECA-pressed material throughout the weld. 相似文献
62.
Frequency-shifted feedback (FSF) laser exhibits outstanding features in its oscillation spectrum. We analyze build-up dynamic properties of the FSF laser by means of rate equation and analyze steady-state dynamic properties of the FSF laser by means of Wigner-Ville distribution of intracavity electric field. Furthermore, we analyze instantaneous oscillation frequency at peak spectral intensity and oscillation bandwidth of its spectrum using the formula of instantaneous spectral intensity derived from Wigner-Ville distribution of intracavity electric field. These analytical results are in good agreement with the experimental ones which have been observed by a diode-pumped Nd:YVO4 FSF laser. It becomes clear that the FSF laser supports many frequency components simultaneously even though the gain medium is homogeneously broadened and has a continuously chirped frequency components of comb in which the creation of chirped frequency components are strongly correlated in phase because of a replica of the preceding components. Also, the instantaneous oscillation frequency is closely related to the detuning frequency which depends on the total net gain in the cavity and the gain bandwidth of atomic transition. The oscillation bandwidth is defined as the product of the saturation-broadened bandwidth and the total resonant modes contributing to FSF operation 相似文献
63.
An X-ray preionized XeCl laser with a wide aperture of 10×10 cm2 is described. The density for preionization electrons is estimated from an X-ray energy distribution to be greater than 6×109 cm-3 under operational gas conditions. In high pressure operation at 4500 torr, sufficient preionization has led to successful discharge-breakdown at a low E /N of 6.4×10-17 V-cm2, resulting in a high electrical efficiency of 3.1% with an output energy of 17.6 J. An output energy of 50 J in an 85-ns (FWHM) optical pulse has been extracted from an active volume of about 10:1 for a pulse-forming-line (PFL) voltage of 400 kV. The effects of impedance transformation of a pulse-transmission-line (PTL) following the PFL have been investigated using two types of PTL with output impedances of 0.26 and 0.48 Ω 相似文献
64.
The authors propose a method for measuring the group velocity dispersion, including the polarity, of optical fibre by using a single wavelength light source. The method is based on the interplay between phase modulation-amplitude modulation (PM-AM) conversion and self-phase modulation (SPM) 相似文献
65.
66.
67.
PURPOSE: Previous research has demonstrated that testosterone therapy causes a profound suppression of autoimmune disease in lacrimal glands of female mouse models of Sj?gren's syndrome. The aim of the present study was to determine whether other anabolic androgens, nonandrogenic steroids, or immunosuppressive agents might duplicate this hormonal effect. For comparative purposes, we also evaluated the influence of these various pharmacologic compounds on the tear volume, the magnitude of lymphocyte infiltration in the submandibular gland, and the extent of mucosal and peripheral lymphadenopathy. METHODS: Female MRL/MpJ-lpr/lpr mice were administered vehicle, steroids, or immunosuppressive compounds for 21 days after the onset of disease. Lacrimal glands and tears, as well as submandibular glands, spleens, and superior cervical and mesenteric lymph nodes were collected immediately before or after treatment and then processed for analysis. RESULTS: Our results showed that: (1) the immunosuppressive impact of testosterone on lymphocyte infiltration in lacrimal tissue was reproduced by the administration of 19-nortestosterone or cyclophosphamide, but not by therapy with 17 beta-estradiol, danazol, the experimental steroid Org 4094, cyclosporine A or dexamethasone; (2) treatment with testosterone, 19-nortestosterone, cyclophosphamide, or dexamethasone significantly reduced the extent of inflammation in salivary glands; (3) exposure to cyclophosphamide markedly diminished the size of lymphatic and splenic tissues, whereas glucocorticoid treatment only decreased the weight of superior cervical lymph nodes; and (4) administration of 17 beta-estradiol, Org 4094, or dexamethasone led to a significant decrease in tear volume. CONCLUSIONS: Overall, these results demonstrate that androgen or cyclophosphamide therapy may successfully ameliorate autoimmune expression in lacrimal and salivary glands of a female mouse model of Sj?gren's syndrome. 相似文献
68.
69.
Y Tanaka N Enomoto S Kojima L Tang M Goto F Marumo C Sato 《Canadian Metallurgical Quarterly》1993,13(4):203-208
To examine HCV infection histologically, we attempted non-radioactive in situ hybridization of HCV-RNA in the liver. We amplified cDNA probe (360 base pairs) by PCR using the primers deduced from the core region of the HCV genome. The probe was labelled with digoxigenin by PCR and used for in situ hybridization on paraformaldehyde-fixed frozen liver sections. The hybrids were visualized immunohistochemically with alkaline-phosphatase-conjugated anti-digoxigenin and alkaline-phosphatase substrates. HCV-RNA-cDNA hybrids were detected in 21 of 24 patients with positive serum HCV markers, whereas there were no positive signals in the liver of 12 cases without HCV infection. The signal intensity of HCV-RNA-cDNA hybrids was abolished after RNase treatment. Various other specificity experiments also verified specific hybridization of HCV-RNA-cDNA. HCV-RNA was visualized in liver cells and most of them were regarded as hepatocytes from their characteristic features. The infected hepatocytes were frequently associated with mononuclear cell infiltration. Hepatocytes positive for HCV-RNA were sometimes binuclear and distributed in various patterns among cases tested. The present in situ hybridization of HCV RNA is highly sensitive and specific and the results suggest the host immune response to HCV-infected cells. 相似文献
70.
Some work is so complicated and unsteady that it is not possible to use automatic robots, such as FA robots. In such a case, a teleoperated manipulation system is applied. In this research, the authors aim at a reduction in the operator's physical and mental burdens. An artificially intelligent manipulator system has been developed with nonsymmetric and redundant master-slave. This system has five features: (1) a polar coordinates master arm; (2) a highly operational articulated slave arm with 7 degrees of freedom; (3) a nonsymmetric configuration and different degrees of freedom master-slave control; (4) an expert system; and (5) a new master-slave control motion, which makes the operator's task easier with automatic force/position control. The system was experimentally produced and its performance tested and evaluated. A qualitative evaluation was carried out by conducting a comparative test on the conventional master-slave control and the new master-slave control. It was found to be effective in reducing operating time, as well as work-induced fatigue. 相似文献