全文获取类型
收费全文 | 26027篇 |
免费 | 690篇 |
国内免费 | 772篇 |
专业分类
电工技术 | 494篇 |
综合类 | 55篇 |
化学工业 | 3048篇 |
金属工艺 | 2284篇 |
机械仪表 | 983篇 |
建筑科学 | 584篇 |
矿业工程 | 46篇 |
能源动力 | 917篇 |
轻工业 | 1298篇 |
水利工程 | 157篇 |
石油天然气 | 371篇 |
武器工业 | 7篇 |
无线电 | 3330篇 |
一般工业技术 | 7225篇 |
冶金工业 | 4167篇 |
原子能技术 | 327篇 |
自动化技术 | 2196篇 |
出版年
2023年 | 67篇 |
2022年 | 142篇 |
2021年 | 238篇 |
2020年 | 179篇 |
2019年 | 329篇 |
2018年 | 515篇 |
2017年 | 464篇 |
2016年 | 529篇 |
2015年 | 437篇 |
2014年 | 670篇 |
2013年 | 1772篇 |
2012年 | 1013篇 |
2011年 | 1531篇 |
2010年 | 1204篇 |
2009年 | 1400篇 |
2008年 | 1408篇 |
2007年 | 1416篇 |
2006年 | 1233篇 |
2005年 | 1117篇 |
2004年 | 944篇 |
2003年 | 887篇 |
2002年 | 825篇 |
2001年 | 782篇 |
2000年 | 755篇 |
1999年 | 804篇 |
1998年 | 1569篇 |
1997年 | 1111篇 |
1996年 | 963篇 |
1995年 | 617篇 |
1994年 | 500篇 |
1993年 | 404篇 |
1992年 | 269篇 |
1991年 | 285篇 |
1990年 | 194篇 |
1989年 | 193篇 |
1988年 | 136篇 |
1987年 | 112篇 |
1986年 | 76篇 |
1985年 | 76篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 23篇 |
1975年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
MRI techniques were developed and employed for non-destructive and noninvasive study of seedcoat cracking in low moisture soybean kernels during heated air drying. Proton density image and transient moisture distribution profile of a single soybean kernel can be obtained using MRI. These MRI techniques proved to be particularly useful for the continuous observation of initiation and propagation of seedcoat cracking during the entire period of drying process without interruption.
The proton density images of soybean kernels showed that seedcoat cracking was initiated perpendicular to the long axis of the kernel near the hilum. The transient moisture distribution profiles in soybean kernels during drying indicate that moisture gradient developed during drying was higher in the seedcoat than in the cotyledon. Drying temperature and initial average moisture content were positively correlated with the soyhean seedcoat crackig. The location of the 相似文献
The proton density images of soybean kernels showed that seedcoat cracking was initiated perpendicular to the long axis of the kernel near the hilum. The transient moisture distribution profiles in soybean kernels during drying indicate that moisture gradient developed during drying was higher in the seedcoat than in the cotyledon. Drying temperature and initial average moisture content were positively correlated with the soyhean seedcoat crackig. The location of the 相似文献
73.
We report the first demonstration of proton-exchanged optical planar waveguides in x-cut and z-cut LiNbO3 doped with 6 mol% ZnO using adipic acid as proton source. These waveguides exhibit a graded index profile which can be modeled by a linear step function with a surface index increase of 0.135 and 0.14 for x-cut and z-cut waveguides, respectively. The diffusion constant Do and the activation energy Q are characterized optically to be 1.64×109 μm2/h and 88.8 KJ/mol for x-cut waveguides, and 1.478×109 μm2/h and 91.25 KJ/mol for z-cut waveguides, respectively. The diffusion rate along the z-axis is slower than that along the x-axis, whereas the surface index increase on z-cut waveguides is larger than that on x-cut waveguides. 相似文献
74.
In this study, 16 cases of unilateral alveolar cleft with cleft lip and palate were repaired with autografts of cancellous bone (13 cases) or hydroxyapatite (3 cases). The grafts were covered by reflected mucoperiosteal flaps and a mucosal flap from the upper lip. Twelve of the thirteen cases were followed up for 1-5 years. Nine of whom using cancellous bone had bony continuity of the maxilla and 7 cases erupted permanent maxillary canines within the area of autografts. None of the 3 cases using hydroxyapatite erupted a canine tooth. The results showed that autograft was better than hydroxyapatite in terms of maxillary canine eruption. 相似文献
75.
The represention of circuit variables in frequency-domain complex matrix and nonlinearities by power series gives rise to a nonlinear distortion prediction technique, the intermodulation-balance method. This operates entirely in the frequency domain. The technique is verified by a single-amplifier filter with a two-tone input signal 相似文献
76.
Epidemiological studies have linked dietary fiber to the prevention of human colorectal cancer and suggest that short chain fatty acids such as butyric acid, which is produced by fermentation of dietary fiber in the large intestine, may be an important mediator of the protective effects of fiber. We investigated the role of Bcl-2 deregulation on the sensitivity of colorectal carcinoma cells to undergo butyrate-induced apoptosis. Here we report an inverse relationship between the levels of Bcl-2 and the sensitivity of colorectal carcinoma cell lines to undergo apoptosis in response to butyrate. Overexpression of Bcl-2 in colorectal carcinoma DiFi cells resulted in suppression of butyrate-induced apoptosis and enhanced cell survival in response to butyrate. Butyrate-induced apoptosis was accompanied by inhibition of expression of a 30 kDa protein (p30, immunorecognized by anti-Bcl-2 mAb) and this cellular effect of butyrate was inhibited by Bcl-2 overexpression. These findings suggest that deregulation of Bcl-2 in human colorectal carcinoma cells confers resistance to induction of apoptosis by butyrate, a dietary micronutrient. 相似文献
77.
InAs channel field-effect transistors of 1-μm gate length were grown by molecular beam epitaxy and observed to operate at channel electric fields (20 kV/cm) higher than previously demonstrated and several times greater than the threshold for impact ionization in bulk InAs. Voltage gains on the order of 10 were observed with transconductances as high as 414 mS/mm and output conductances as low as 33 mS/mm. These voltage gains are comparable to those of GaAs-based devices and are the highest observed for InAs channel devices. The results demonstrate the potential for practical room-temperature operation of InAs FETs 相似文献
78.
79.
80.
To investigate the prognostic factors of primary liver cancer (PLC) and improve the long-term results, 1,248 cases of PLC were analysed. Univariate analysis demonstrated that discovery approach, staging of PLC, original gamma-GPT, resection, radical resection, original AFP, tumor size, tumor number, and tumor capsule have very significant effects on prognosis of PLC (all P < 0.001); cirrhosis, HBsAg, local resection, and tumor embolus in portal vein were also significant difference (all P < 0.05); age, sex, original AFP, hepatitis, and differentiation of PLC cells were no significant difference (all P > 0.05). Multivariate analysis demonstrated that original gamma-GPT, radical resection, tumor size, and tumor number were the most significant prognostic factors (all P < 0.001). Some aspects improving long-term survival were discussed. 相似文献