全文获取类型
收费全文 | 5018篇 |
免费 | 34篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 127篇 |
金属工艺 | 10篇 |
机械仪表 | 19篇 |
建筑科学 | 64篇 |
能源动力 | 33篇 |
轻工业 | 119篇 |
水利工程 | 5篇 |
石油天然气 | 15篇 |
无线电 | 114篇 |
一般工业技术 | 128篇 |
冶金工业 | 4244篇 |
原子能技术 | 9篇 |
自动化技术 | 140篇 |
出版年
2022年 | 10篇 |
2021年 | 9篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 18篇 |
2012年 | 30篇 |
2011年 | 39篇 |
2010年 | 42篇 |
2009年 | 37篇 |
2008年 | 50篇 |
2007年 | 38篇 |
2006年 | 41篇 |
2005年 | 34篇 |
2004年 | 37篇 |
2003年 | 38篇 |
2002年 | 23篇 |
2001年 | 27篇 |
2000年 | 36篇 |
1999年 | 138篇 |
1998年 | 1283篇 |
1997年 | 775篇 |
1996年 | 497篇 |
1995年 | 251篇 |
1994年 | 256篇 |
1993年 | 245篇 |
1992年 | 33篇 |
1991年 | 57篇 |
1990年 | 53篇 |
1989年 | 51篇 |
1988年 | 50篇 |
1987年 | 47篇 |
1986年 | 57篇 |
1985年 | 43篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 31篇 |
1980年 | 54篇 |
1978年 | 12篇 |
1977年 | 121篇 |
1976年 | 271篇 |
1975年 | 9篇 |
1973年 | 5篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有5053条查询结果,搜索用时 15 毫秒
71.
Recent literature has shown that relative to baseline the renal resistive index remains unchanged in nonobstructed kidneys and increases in obstructed kidneys after administration of furosemide. To our knowledge the effect upon the renal resistive index of furosemide administered in conjunction with intravenous normal saline fluid load has not been reported. We evaluated the renal resistive index in 13 nonobstructed kidneys in 8 children 6 to 18 years old before and after furosemide and intravenous normal saline fluid load. The mean resistive index decreased from baseline (mean decrease was 0.06 +/- 0.06 standard deviation), with the observation of a resistive index decrease significant to p < 0.005). It appears likely that the combination of an intravenous normal saline fluid load and furosemide caused the resistive index decrease, since a decrease was not observed with furosemide alone; however, these results cannot exclude the possibility that the resistive index decrease was due to the intravenous normal saline fluid load alone. Nonetheless, these data are important since they may provide the foundation for the development of a pharmacologically challenged Doppler sonographic examination using furosemide and intravenous normal saline fluid load to evaluate better potentially obstructed kidneys. 相似文献
72.
F Espa?a M Martínez J Sánchez-Cuenca CD Vera A Estellés JF Jiménez-Cruz 《Canadian Metallurgical Quarterly》1996,30(4):512-518
OBJECTIVE: To improve the specificity and sensitivity of the prostate-specific-antigen (PSA) assay for the distinction between prostate cancer and benign prostate hyperplasia (BPH). METHODS: Two sensitive immunoassays, one that measures free PSA and PSA complexed to alpha 1-antichymotrypsin (alpha 1-ACT) with the same efficiency (PSAag assay) and another that specifically measures the complex between PSA and alpha 1-ACT, have been designed to measure the PSA forms in the plasma of 84 patients with prostate disease and in the seminal plasma from 60 healthy individuals. RESULTS: The proportion of plasma PSA in complex with alpha 1-ACT was significantly higher in the 34 patients with prostate cancer (89 +/- 12%, mean +/- SD; median, 91%) than in the 50 patients with BPH (71 +/- 12%; 73%) and did not correlate with the total amount of PSA. Normal seminal plasma (n = 60) had 2.1 +/- 0.6 mg/ml PSA, 175 +/- 62 microns/ml alpha 1-ACT and 9.6 +/- 3.4 micrograms/ml PSA: alpha 1-ACT complex. CONCLUSION: These results confirm that PSA: alpha 1-ACT may be a good marker for a differential diagnosis of carcinoma of the prostate and BPH. 相似文献
73.
PJ Weston RB Panerai A McCullough PG McNally MA James JF Potter H Thurston JD Swales 《Canadian Metallurgical Quarterly》1996,39(11):1385-1391
Autonomic dysfunction in insulin-dependent diabetic (IDDM) patients has been associated with abnormalities of left ventricular function and an increased risk of sudden death. A group of 30 patients with IDDM and 30 age, sex and blood pressure matched control subjects underwent traditional tests of autonomic function. In addition, baroreceptor-cardiac reflex sensitivity (BRS) was assessed using time domain (sequence) analysis of systolic blood pressure and pulse interval data recorded non-invasively using the Finapres beat-to-beat blood pressure recording system. 'Up BRS' sequences-increases in systolic blood pressure associated with lengthening of R-R interval, and 'down BRS' sequences-decreases in systolic blood pressure associated with shortening of R-R interval were identified and BRS calculated from the regression of systolic blood pressure on R-R interval for all sequences. We also assessed heart rate variability using power spectral analysis and, after expressing components of the spectrum in normalised units, assessed sympathovagal balance from the ratio of low to high frequency powers. IDDM subjects underwent 2-D echocardiography to assess left ventricular mass index. Standard tests of autonomic function revealed no differences between IDDM patients and control subjects, but dramatic reductions in baroreceptor-cardiac reflex sensitivity were detected in IDDM patients. 'Up BRS' when supine was 11.2 +/- 1.5 ms/mmHg (mean +/- SEM) compared with 20.4 +/- 1.95 in control subjects (p < 0.003) and when standing was 4.1 +/- 1.9 vs 7.6 +/- 2.7 ms/mmHg (p < 0.001). Down BRS when supine was 11.5 +/- 1.2 vs 22 +/- 2.6 (p < 0.001) and standing was 4.4 +/- 1.9 vs 7.3 +/- 2.5 ms/mmHg (p < 0.003). There were significant relations between impairment of the baroreflex and duration of diabetes (p < 0.001) and poor glycaemic control (p < 0.001). From a fast Fourier transformation of supine heart rate data and using a band width of 0.05-0.15 Hz as low-frequency and 0.2-0.35 Hz as high frequency total spectral power of R-R interval variability was significantly reduced in the IDDM group for both low-frequency (473 +/- 62.8 vs 746.6 +/- 77.6 ms2 p = 0.002) and high frequency bands 125.2 +/- 12.9 vs 459.3 +/- 89.8 ms2 p < 0.0001. When the absolute powers were expressed in normalised units the ratio of low frequency to high frequency power (a measure of sympathovagal balance) was significantly increased in the IDDM group (2.9 +/- 0.53 vs 4.6 +/- 0.55, p < 0.002 supine: 3.8 +/- 0.49 vs 6.6 +/- 0.55, p < 0.001 standing). Thus, time domain analysis of baroreceptor-cardiac reflex sensitivity detects autonomic dysfunction more frequently in IDDM patients than conventional tests. Impaired BRS is associated with an increased left ventricular mass index and this abnormality may have a role in the increased incidence of sudden death seen in young IDDM patients. 相似文献
74.
75.
We employed an anatomically realistic three-dimensional finite-element model to explore several biomechanical variables involved in coring or bone-grafting of a segmentally necrotic femoral head. The mechanical efficacy of several variants of these procedures was indexed in terms of their alteration of the stress:strength ratio in at-risk necrotic cancellous bone. For coring alone, the associated structural compromise was generally modest, provided that the tract did not extend near the subchondral plate. Cortical bone-grafting was potentially of great structural benefit for femoral heads in which the graft penetrated deeply into the superocentral or lateral aspect of the lesion, ideally with abutment against the subchondral plate. By contrast, central or lateral grafts that stopped well short of the subchondral plate were contraindicated biomechanically because they caused marked elevations in stress on the necrotic cancellous bone. Calculated levels of stress were relatively insensitive to variations in the diameter of the graft. 相似文献
76.
77.
78.
79.
80.