全文获取类型
收费全文 | 358772篇 |
免费 | 3966篇 |
国内免费 | 1703篇 |
专业分类
电工技术 | 5533篇 |
综合类 | 2830篇 |
化学工业 | 51167篇 |
金属工艺 | 15732篇 |
机械仪表 | 11375篇 |
建筑科学 | 8494篇 |
矿业工程 | 2122篇 |
能源动力 | 8041篇 |
轻工业 | 25886篇 |
水利工程 | 4232篇 |
石油天然气 | 6119篇 |
武器工业 | 43篇 |
无线电 | 42432篇 |
一般工业技术 | 71841篇 |
冶金工业 | 53322篇 |
原子能技术 | 7728篇 |
自动化技术 | 47544篇 |
出版年
2021年 | 2153篇 |
2019年 | 2063篇 |
2018年 | 17629篇 |
2017年 | 16608篇 |
2016年 | 13582篇 |
2015年 | 3067篇 |
2014年 | 4552篇 |
2013年 | 12121篇 |
2012年 | 10069篇 |
2011年 | 18792篇 |
2010年 | 15489篇 |
2009年 | 14068篇 |
2008年 | 15626篇 |
2007年 | 16613篇 |
2006年 | 7902篇 |
2005年 | 8383篇 |
2004年 | 8250篇 |
2003年 | 8086篇 |
2002年 | 7211篇 |
2001年 | 6923篇 |
2000年 | 6645篇 |
1999年 | 6807篇 |
1998年 | 16338篇 |
1997年 | 11602篇 |
1996年 | 8955篇 |
1995年 | 6851篇 |
1994年 | 6023篇 |
1993年 | 6059篇 |
1992年 | 4406篇 |
1991年 | 4202篇 |
1990年 | 4073篇 |
1989年 | 4055篇 |
1988年 | 3759篇 |
1987年 | 3387篇 |
1986年 | 3392篇 |
1985年 | 3739篇 |
1984年 | 3460篇 |
1983年 | 3217篇 |
1982年 | 3024篇 |
1981年 | 3038篇 |
1980年 | 3030篇 |
1979年 | 2829篇 |
1978年 | 2869篇 |
1977年 | 3141篇 |
1976年 | 4098篇 |
1975年 | 2416篇 |
1974年 | 2379篇 |
1973年 | 2396篇 |
1972年 | 2018篇 |
1971年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
901.
R Nani P Novello M Decastello A Cavarzerani M Sarpellon 《Canadian Metallurgical Quarterly》1997,63(6):209-212
A clinical case of a patient in whom a right atrial thrombosis was casually discovered by transthoracic echocardiography is described. The hypothesis that also the central venous catheter (CVC) could be seat of thrombosis was done, and was confirmed by chest X-ray with dye injection in the CVC. A thrombolytic therapy with plasminogen tissular activator and with heparin infusion was started. After 24 hours from the beginning of therapy instrumental control were performed (transesophageal echocardiography ECOTEE, chest X-ray with dye injection in CVC), showing the completely dissolution of the thrombus. It is observed that, when in a patient with CVC high degree of thrombogenic factors (age over 60 years, presence of cardiac arrhythmias with ventricular hypokinesis, polyglobulia due to chronic obstructive pulmonary disease, CVC, low levels of antithrombin III) are present, the usual prophylactic measures (subcutaneous heparin, hydrophylic catheter) couldn't be sufficient to avoid superior caval vein thrombosis. The conclusion is drawn that these patient should be studied with ECOTEE and eco Doppler. Chest tomography and superior caval venography are also useful its early diagnosis of superior caval thrombosis. 相似文献
902.
Apoptosis in the failing human heart 总被引:1,自引:0,他引:1
G Olivetti R Abbi F Quaini J Kajstura W Cheng JA Nitahara E Quaini C Di Loreto CA Beltrami S Krajewski JC Reed P Anversa 《Canadian Metallurgical Quarterly》1997,336(16):1131-1141
BACKGROUND: Loss of myocytes is an important mechanism in the development of cardiac failure of either ischemic or nonischemic origin. However, whether programmed cell death (apoptosis) is implicated in the terminal stages of heart failure is not known. We therefore studied the magnitude of myocyte apoptosis in patients with intractable congestive heart failure. METHODS: Myocardial samples were obtained from the hearts of 36 patients who underwent cardiac transplantation and from the hearts of 3 patients who died soon after myocardial infarction. Samples from 11 normal hearts were used as controls. Apoptosis was evaluated histochemically, biochemically, and by a combination of histochemical analysis and confocal microscopy. The expression of two proto-oncogenes that influence apoptosis, BCL2 and BAX, was also determined. RESULTS: Heart failure was characterized morphologically by a 232-fold increase in myocyte apoptosis and biochemically by DNA laddering (an indicator of apoptosis). The histochemical demonstration of DNA-strand breaks in myocyte nuclei was coupled with the documentation of chromatin condensation and fragmentation by confocal microscopy. All these findings reflect apoptosis of myocytes. The percentage of myocytes labeled with BCL2 (which protects cells against apoptosis) was 1.8 times as high in the hearts of patients with cardiac failure as in the normal hearts, whereas labeling with BAX (which promotes apoptosis) remained constant. The near doubling of the expression of BCL2 in the cardiac tissue of patients with heart failure was confirmed by Western blotting. CONCLUSIONS: Programmed death of myocytes occurs in the decompensated human heart in spite of the enhanced expression of BCL2; this phenomenon may contribute to the progression of cardiac dysfunction. 相似文献
903.
Bondyopadhyay P.K. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1998,86(1):63-77
The junction transistor, technologically the most important solid-state device, invented theoretically by W.B. Shockley on January 23, 1948, brought about the semiconductor revolution. That invention was triggered by the experimental discovery of the point-contact transistor by W. Brattain and J. Bardeen 38 days earlier. Bardeen's notebook entries at Bell Telephone Laboratories for the crucial 100-day period November 21, 1947-February 29, 1948 have been examined to ascertain why this winner of two Nobel Prizes in physics could not invent the junction transistor. It was found that the boundary between the thin p-type inversion layer and the n-type bulk germanium semiconductor in their original point-contact transistor discovery was characterized as a “high resistance boundary” in macroscopic electrical engineering terms by Bardeen, the electrical engineer turned mathematical physicist. Pages from Shockley's notebook are reproduced in full to show what exactly he was thinking on December 16, 1947, the day the point-contact transistor was experimentally discovered by Brattain and Bardeen. The origin of U.S. Patent 2524035 has been traced to the Bell Telephone Laboratories notebook pages of its inventors and examined. It is shown that this patent could not be considered as the first patent describing Shockley's revolutionary theoretical invention of the minority carrier injection concept underlying bipolar transistor action 相似文献
904.
905.
906.
The first VLSI digital signal processor that performs both high-precision image backprojection and spatial histogram calculations at raster-scan rates as high as 30 MHz is described. Realized in 1 μm CMOS technology, this 13.3 mm×13.3 mm chip is designed to handle images as large as 1024×1024 12 b pixels. Loadable coefficients and a unified architecture allow this IC to be used with a variety of computed-tomography scanners for image reconstructions, including fan- and parallel-beam reconstruction. This chip also computes the forward Radon transform, which is a spatial histogram, permitting it to be used for iterative reconstruction algorithms. The bit lengths in the fixed-point architecture assure 12 b reconstruction accuracy 相似文献
907.
AC Fluckiger P Garrone I Durand JP Galizzi J Banchereau 《Canadian Metallurgical Quarterly》1993,178(5):1473-1481
Interleukin 10 (IL-10) has recently been shown to induce normal human B lymphocytes to proliferate and differentiate into immunoglobulin (Ig)-secreting cells. Herein, we show that IL-10 also promotes DNA synthesis and IgM production by anti-CD40 activated B cell chronic lymphocytic leukemia (B-CLL). Most strikingly, IL-2 and IL-10 were found to synergize to induce the proliferation and differentiation of B-CLL cells. This synergy between IL-2 and IL-10 was also observed with normal B cells which proliferated strongly and secreted large amounts of IgM, IgG, and IgA. The observed synergy is likely to be due to the IL-10-induced increase of high affinity IL-2 receptors on both normal and leukemic B cells. This increase of high affinity receptor is associated to an increase of Tac/CD25 expression that can be detected by flow cytometric analysis. Taken together, these results indicate that IL-10 permits anti-CD40 activated B cells to respond to IL-2 through an induction of high affinity IL-2 receptors. This effect of IL-10 may partly explain how T cells, which activate B cells in a CD40-dependent fashion, induce B cell proliferation and differentiation mostly through IL-2. 相似文献
908.
Discusses the use of personality as a predictor in personnel selection. Recent data has suggested that personality measures (PRMs) are related to performance criteria that are unrelated to cognitive ability when the traits measured are conceptually related to these criteria. It seems that PRMs may predict job performance dimensions that cannot be predicted by cognitive ability measures. The use of PRMs in personnel selection may be warranted when a careful job analysis is undertaken to determine which performance dimensions may be related to personality traits. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
909.
910.