全文获取类型
收费全文 | 1952篇 |
免费 | 33篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 65篇 |
综合类 | 1篇 |
化学工业 | 388篇 |
金属工艺 | 61篇 |
机械仪表 | 26篇 |
建筑科学 | 26篇 |
能源动力 | 34篇 |
轻工业 | 116篇 |
水利工程 | 4篇 |
无线电 | 192篇 |
一般工业技术 | 269篇 |
冶金工业 | 629篇 |
原子能技术 | 50篇 |
自动化技术 | 130篇 |
出版年
2023年 | 10篇 |
2022年 | 27篇 |
2021年 | 21篇 |
2020年 | 8篇 |
2019年 | 19篇 |
2018年 | 23篇 |
2017年 | 25篇 |
2016年 | 28篇 |
2015年 | 15篇 |
2014年 | 25篇 |
2013年 | 58篇 |
2012年 | 44篇 |
2011年 | 77篇 |
2010年 | 38篇 |
2009年 | 56篇 |
2008年 | 53篇 |
2007年 | 53篇 |
2006年 | 36篇 |
2005年 | 49篇 |
2004年 | 46篇 |
2003年 | 47篇 |
2002年 | 43篇 |
2001年 | 45篇 |
2000年 | 44篇 |
1999年 | 63篇 |
1998年 | 264篇 |
1997年 | 150篇 |
1996年 | 109篇 |
1995年 | 60篇 |
1994年 | 48篇 |
1993年 | 46篇 |
1992年 | 28篇 |
1991年 | 33篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 10篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 23篇 |
1976年 | 27篇 |
1974年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有1991条查询结果,搜索用时 15 毫秒
21.
R Ikeda T Nagao H Okabe Y Nakano H Matsunaga M Katano M Mori 《Canadian Metallurgical Quarterly》1998,46(5):875-878
The constituents in the fruit of Anthriscus sylvestris Hoffm. were investigated, and four lignans [deoxypodophyllotoxin, morelensin, (-)-deoxypodorhizone, and (-)-hinokinin], one phenylpropanoid [1-(3',4'-dimethoxyphenyl)-1 xi-hydroxy-2-propene], two phenylpropanoid esters [3',4'-dimethoxycinnamyl (Z)-2-angeloyloxymethyl-2-butenoate and 3',4'-dimethoxycinnamyl (Z)-2-tigloyloxymethyl-2-butenoate], and one polyacetylenic compound (falcarindiol) were isolated. Their antiproliferative activity against MK-1, HeLa and B16F10 cell lines is reported. 相似文献
22.
OBJECTIVE: The purpose of our study was to evaluate the effectiveness of MR imaging for showing the intrinsic anatomy of a peripheral nerve. Cadaver wrist specimens that included the median nerve were imaged with MR imaging at 3 T, then sectioned, stained, and inspected grossly and microscopically. The size, shape, and signal intensity of the sheath and axonal structures in the median nerve were identified in MR images by comparison with anatomic sections. CONCLUSION: This study suggests that MR imaging with sufficiently high-resolution techniques shows the internal structure of peripheral nerves. These results suggest that MR imaging may be a means to distinguish neuritis, tumor, degeneration, or fatty proliferation in a peripheral nerve and to evaluate the nerve before microsurgical anastomosis. 相似文献
23.
24.
Seshita T. Ikeda Y. Wakimoto H. Ishida K. Terada T. Matsunaga T. Suzuki T. Kitaura Y. Uchitomi N. 《Solid-State Circuits, IEEE Journal of》1994,29(12):1583-1588
An ultrahigh-speed 8 bit multiplexer (MUX) has been developed for future-generation optical-fiber communication systems having a data rate of 20 Gb/s. This IC was fabricated using a 0.5 μm WNx/W-gate GaAs MESFET process based on optical lithography, ion implantation, and furnace annealing for good reproducibility and high throughput. The WNx/W bilayer gate has a low sheet resistance, improving the circuit high frequency performance. To attain 20 GHz operation, advanced circuit techniques for the source-coupled FET logic (SCFL) were introduced. A cross coupled source-follower (CCSF) was developed mainly for the highest speed buffers to enhance the bandwidth. The first-stage T-type flip-flop was designed with optimization techniques and operated up to 21.1 GHz 相似文献
25.
K. Nakano S. Tomiya M. Ukita H. Yoshida S. Itoh E. Morita M. Ikeda A. Ishibashi 《Journal of Electronic Materials》1996,25(2):213-216
Using electroluminescence (EL) topography and transmission electron microscopy (TEM), we investigated the nonluminescent regions
which form while current is being injected into ZnMgSSe/ZnSSe/ZnCdSe-based blue light emitters. Small dark spots were observed
just after turn-on and spread out forming rough nonluminescent triangles in the <100> directions in the EL image of the active
region. TEM studies showed that the small dark spots are pre-existing stacking faults originating at the substrate/epitaxial
layer interface. The nonluminescent triangles were found to be a dense region of dislocation dipoles and dislocation loops.
Each dipole was aligned along two <110> directions in the {111} planes. The Burgers vectors were of the type a/2<011> inclined
at 45° to the (001) junction plane. 相似文献
26.
27.
28.
T Akema A Chiba T Ikeda Y Nagami F Kimura J Toyoda 《Canadian Metallurgical Quarterly》1997,9(11):849-857
The present study aimed to examine the effect of melatonin on naloxone-induced luteinizing hormone (LH) secretion in ovariectomized estrogen-primed rats. A single intracerebroventricular (i.c.v.) injection of naloxone (mu opioid receptor blocker, 15 micrograms) or an intravenous (i.v.) injection of LH-releasing hormone (LHRH, 50 ng/kg) elicited a transient and significant increase in the serum LH concentration within 10 min. While an i.c.v. injection of 100 ng melatonin by itself did not change the basal LH release, it almost completely inhibited the naloxone-induced LH release. Melatonin (10 ng) also significantly reduced the effect of naloxone. However, an i.c.v. injection of 100 ng melatonin did not affect the LHRH-induced LH release. In separate experiments, the effect of melatonin on naloxone-induced pulsatile LH secretion was studied in estrogen-treated rats. A continuous i.v. infusion of naloxone (20 mg/kg/h) induced LH pulses in rats treated i.c.v. with saline. An i.c.v. administration of 100 ng melatonin, which by itself did not affect basal LH secretion, significantly reduced the frequency, but not the amplitude, of LH pulses induced by the naloxone infusion. These results show that melatonin has a suprapituitary site of action to inhibit naloxone-induced LH release, and suggest that melatonin has an effect in inhibiting the activity of the hypothalamic LHRH pulse generator, either directly or indirectly, in female rats. 相似文献
29.
OBJECTIVES: To determine the prevalence of thyroid dysfunction in institutionalised elderly people in Cape Town and to assess the usefulness of an abnormal thyroid-stimulating hormone (TSH) concentration as a screening test in this group. DESIGN: Cross-sectional survey. SETTING: Four old-age homes in Cape Town. SUBJECTS: Old-age home residents aged 60 years and over. OUTCOME MEASURES: Serum concentrations of TSH, free thyroxine and free tri-iodothyronine. RESULTS: Serum TSH estimations were performed on 658 participants, and were abnormal in 103 (15.6%)-41 (6.2%) being elevated (> 5.0 microU/ml) and 62 (9.4%) being low (> 0.4 microU/ml). There were 3 newly diagnosed cases of hyperthyroidism and 7 of hypothyroidism. Subclinical disease was diagnosed in 40 subjects. The overall prevalence of thyroid dysfunction in this population was 11.2%. In 22 (3.4%) this had previously been recognised, while in 50 (7.8%) the dysfunction was newly diagnosed by the current survey. The positive predictive value of a TSH concentration > 20 microU/ml in predicting hypothyroidism is 67%, while it will predict 100% of cases of subclinical hypothyroidism. A TSH concentration < 0.1 microU/ml will predict 23% of cases of hyperthyroidism, but 81% of cases of subclinical disease. CONCLUSIONS: The prevalence of thyroid dysfunction in institutionalised elderly people in Cape Town is similar to that reported for elderly people in other centres. Thyroid dysfunction had not previously been recognised in approximately two-thirds of the subjects in this study. The serum TSH concentration is a reliable screening test for thyroid dysfunction in the elderly, but is less useful if used to identify biochemical thyroid disease. An elevated TSH concentration is a better predictor of thyroid dysfunction in the elderly than a depressed TSH concentration. 相似文献
30.
The authors propose an adaptive modulation with dynamic channel assignment (AMDCA) to achieve high capacity voice transmission in microcellular systems. The proposed system measures the received carrier-to-noise plus interference power ratio (C/(N+I)) of each time division multiple access (TDMA) slot to search for available slots and to discover the optimum modulation parameters for each slot, thereby effectively combining the buffeting effect of spatially distributed electric field strength by slow adaptive modulation, and that of spatially and temporally distributed traffic by dynamic channel assignment (DCA). Computer simulation confirms that the proposed AMDCA system can achieve ~7.5 times higher system capacity than the conventional QPSR with a fixed channel assignment (FCA) 相似文献